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OUTLINES

OF

COMPARATIVE ANATOMY,

PRESENTING A SKETCH OF THE PRESENT STATE OF KNOWLEDGE,

AND OF THE PROGRESS OF DISCOVERY, IN THAT SCIENCE ; AND

DESIGNED TO SERVE AS AN INTRODUCTION TO ANIMAL PHYSIOLOGY,

AND TO THE PRINCIPLES OF CLASSIFICATION IN ZOOLOGY.

BV

ROBERT E. ^RANT, M.D.

F.R.S. L. & ED. F.L.S. F.G.S. F.Z.S. M.W.S. &c.

FELLOW OF THE ROYAL COLLEGE OF PHYSICIANS OF EDINBURGH, LATE PROFESSOR OF

PHYSIOLOGY IN THE ROYAL INSTITUTION OF GREAT BRITAIN, AND PROFESSOR OF

COMPARATIVE ANATOMY AND ZOOLOGY, IK UNIVERSITY COLLEGE, LONDON.

CONTAINING

PART FIRST,

Organs of Relation or of Animal Life,

AND

PART SECOND,

Organs of Vegetative or Organic Life.

LONDON: a

HIPPOLYTE BAILLIERE,

dFordgn ftoofcgdUr to t&e &ogal College of j&urgcons,
219, REGENT STREET.

PARIS : J. B. BAILLIERE, RUE DE L'ECOLE DE MEDECINE.

LEIPSIC : T. O. WEIGEL.

1841.

LONDON' :
PRINTED BT SCIUaZE AND CO. 13, ,OLAXD

STREET.

OUTLINES

OF

COMPARATIVE ANATOMY.

CHAPTER FIRST.

ORGANS OF SUPPORT, OR OSSEOUS SYSTEM.

FIRST SECTION.

General Observations on the Osseous System of Animals.

As animals are organized to select and obtain foreign
matter for their subsistence, and to convey it into their
digestive organs, to be transported with them from place
to place, they- generally require some solid means of support
for the attachment of their active organs of motion. These
denser parts of the body serve as a solid frame-work to give
form and solidity to the whole fabric, and to protect the more
delicate organs. They consist for the most part of earthy
materials separated from the food by the vital processes of
the animal, and may be placed on the exterior or in the in-
terior of the soft parts. These inert materials, or passive
organs of locomotion receive their forms from those of the
soft parts, and are liable to change with the varying condi-
tions of the contiguous living parts. When placed on the
exterior of the body, they may, without being organized,

PART 1. B

2 ORGANS OF SUPPORT,

keep pace with the progress of growth in the living parts,
by being periodically cast off and renewed ; or they may in-
crease by the addition of more extended layers to their
surface ; or their dimensions may be continually influenced
by the contact of the parts which formed them. But when
this solid frame-work is internal, and is everywhere sur-
rounded by the soft parts, giving attachment to muscles, or
enveloping and protecting delicate organs, it cannot be con-
veniently removed from the system in a mass, nor preserve its
proportions by the mechanical addition of layers to its sur-
face, and is generally organized or permeated in every point
by the soft parts which absorb the decayed materials and re-
new them particle by particle. The earthy materials thus
formed by animals for the support of their soft parts are
various, and their particles are generally united together by
means of a condensed albuminous or gelatinous matter,
which gives firmness and tenacity to the mass. Silica is
found in the lowest forms of radiated animals ; carbonate of
lime in the molluscous classes ; carbonate and phosphate
of lime in the articulated animals, and phosphate of lime
in the organized skeletons of the vertebrata. These earths, in
consolidating, assume forms by the influence of laws which are
in accordance with their ordinary physical properties, this we
observe most obviously in the lowest animals, and least in the
highest classes where the crystalline arrangement of the par-
ticles is most equivocal ; but under every condition they alike
form a normal part of the structure, a solid frame-work
more or less complete, constant in its form and structure
in the same species, and varying in its form with the speci-
fic differences of animals. This solid framework forms the
osseous system of animals, or the skeleton, as it has been
termed from the dry and earthy nature of the materials
which compose it. The osseous system, though not the
most important nor the most universal system of animal or-
ganization, is met with under some form in every class of the
animal kingdom, though not in all the animals of each class.

OR OSSEOUS SYSTEM.

SECOND SECTION.

Organs of Support in the Radiated, or Cycto-neurose Classes.

THE skeletons are as various as the forms of the animals
in this lowest division of the animal kingdom, and scarcely
indicate in their composition or structure a determinate plan
common to the whole. They are sometimes external, most
frequently internal, often composed of minute pieces sym-
metrically arranged, or of one solid mass, often of a thin
flexible diaphanous horny consistence, or composed of dense
silicious or calcareous spicula, or of masses of carbonate
with a little phosphorate of lime. The osseous parts in
these classes appear to be extravascular, and to grow by the
juxtaposition of new portions, and from the simplicity of the
general structure and functions of these animals, and the in-
ternal situation of their solid parts, they are not exuvi-
able.

I. Polyyastrica. — Many of the minute and soft polygastric
animalcules possess an exterior firm, elastic covering,
which protects the more delicate internal parts. This
covering sometimes consists only of a more condensed form
of the common integument, enveloping every part of the
body, in others it forms a distinct thin pellucid sheath into
which the animal can withdraw its soft parts for protection.
The exterior surface, even of the softest and most naked
animalcules, supports the organs of motion — the minute vi-
bratile cilia by which they are carried to and fro, and consists
apparently of a thin film of the general cellular tissue of
their body, rendered more firm in its texture by the con-
tinued action of the surrounding element. This condensa-
tion of the exterior integument is the origin of most of the
skeletons of invertebrated animals, which have generally
the organs of support thrown over the surface of their body
to afford them at the same time protection. We have an
example of one of these loricated animalcules in the volvox
globator, (Fig. 1. A) so common in stagnant pools of fresh
water, and which often owe their green colour to the abun-
dance of this animalcule. This sperical transparent green

B 2

ORGANS OF SUPPORT,

FIG. I.

coloured, tuberculated animalcule exhibits in its interior nu-
merous smaller, round, spotted, and similarly formed beings
moving to and fro, as seen at A, and the entire volvox does not
change or vary its external form while it is seen swimming
about slowly with the enclosed young. When the exterior
capsule, or the parent animalcule bursts, as is represented at
B, and the young have escaped, we observe its fragments to
retain their original form with some degree of elasticity when
they are tossed about in the fluid by the motions of other
animalcules. We see the same transparent elastic integument
giving form, and support to the volvox morum, (Fig. 1 . C.)
which contains a much greater number of young in its interior,
and the same is seen also enveloping the separate globules
which compose the body of the gonium pectorals. (Fig. I. D.)
But the most distinct form .of the skeleton met with in
this class, is that which envelopes the body as a sheath, into
which the animalcule can withdraw its soft parts when
alarmed, and from which it can extend its ciliated anterior
portion for the purposes of nourishment, respiration, or
progressive motion. This vaginiform, exterior, thin, pellucid,
elastic covering is seen in the vaginicola innata, common in
sea water. This animalcule, formed like a vorticella, is seen
in Fig. 1. E, extending its ciliated anterior margin from the
opening in its sheath, and swimming by the action of its
cilia. The same animalcule is represented at Fig. 1. F with-
drawn into its transparent covering and fixed by its candiform
projecting posterior part. This form of the skeleton seen in
the vaginicola leads to the vaginiform horny coverings of
campanularue, and other forms of keratophytes. There are

OR OSSEOUS SYSTEM. 5

about thirty known genera of polygastric animalcules which
possess a firm elastic exterior covering, more or less envelop-
ing the body, and analogous to the more solid skeletons of
higher classes.

II. Poriphera. — The skeleton of poripherous animals con-
sists of separate minute, earthy, crystalline spicula, connected
together by a condensed, elastic, cellular substance j or of
tubular elastic filaments of a horny consistence. These hard
parts are developed internally throughout the whole cellular
tissue of the body, and are often protruded externally through
the surface, to protect the pores, or the large vents. The
earthy spicula in most of these animals are silicious,
in many they are calcareous, and, like the horny filaments of
other species, they appear to be tubular like many natural
crystals, and to have no aperture leading into their internal
cavity. The spicula are generally united into fasciculi by an
enveloping glutinous, or condensed cellular substance, and by
the junction of these fasciculi in various modes, fibres are
formed which traverse every part of the body, forming the
boundaries of canals and orifices, and giving form and sup-
port to the whole of the gelatinous or soft cellular substance
of the animal. The forms of these hard parts are different
in every distinct species of these animals, and they are con-
stant in the same, so that they present useful characters for
the distinction of species in this polymorphous class. They
are formed from materials due to the vital energies of the
animal, and they form normal and necessary parts of its
structure, like the solid skeletons of higher animals. In
Fig 2 is represented at A the haliclona occulata ; one of these
soft animals, with a silicious skeleton. It is represented as
alive, suspended from a rock by its spreading branched base
of attachment (c,) the currents of water are seen at (a) rush-
ing in through the pores, and issuing from the internal
canals by the large orifices or vents at (b). The pores, canals,
and orifices are seen exposed in the longitudinal section of
the same poripherous animal at B. Fibres composed of
bundles of spicula generally extend in a longitudinal direc-
tion in these animals from the base of attachment to the
remotest points of the surface. Smaller transverse fibres of
the same composition connect those which are disposed
longitudinally, and form the frame-work of the internal

ORGANS OF SUPPORT,

FIG. II.

canals. The form of the spicula which belong to several
distinct species of poripherous animals are shewn in Fig. 2.
at C. D. E. F. G. H. I. K. L. M., each of these forms belong-
ing to a distinct animal, and serving to characterize it. The
pores are surrounded with groups of spicula disposed in such
a manner as to strengthen and protect the parietes of these
minute orifices, and to form a delicate net-work over the whole
surface of the body, as shewn on a magnified scale at O,
and a single pore is shewn at N still more magnified, with its
bounding and defending spicula, and a delicate gelatinous
net- work, which protects it from the entrance of small foreign
particles floating in the water. The silicious spicula are
found in some of these animals while they are yet floating
gemmules newly detached from the parent mass, and seeking
a suitable place to fix and develope. One of these gem-
mules is figured at P, highly magnified, and broken to show
the spicula already developed in the cellular substance of this
minute embryo. Similar silicious spicula occur abundantly

OR OSSEOUS SYSTEM.

in plants with which these poripherous animals are the most
nearly allied.

Several of the animals of this class have the skeleton
composed of calcareous spicula which have generally more
complex forms than the silicious. They are disposed in the
same manner and for the same object through the in-
terior cellular substance of the body. They impart a white
colour to the whole body of the animals in which they occur.
They do not appear to occur along with silicious spicula in
the same animal. The skeleton is generally more loose and
friable in the calcareous poriphera, and the connecting gluti-
nous and cellular matter is less abundant. One of these
white friable calcareous poriphera, the leuconia compressa,
very common in our seas, is represented in Fig. 3 at 4 in
form of a compressed FIG- IIT-

lengthened sac suspend-
ed by its peduncle from
any submarine substance

The pores through
which the currents are
conveyed into this sack
are seen all over the ex-
terior surface, as at a a ;
the canals are contained
within the thickness of
its parietes, and the large
vents or fecal orifices here
open into the interior, as
seen where it is broken
open at b. The sac being
open only at its pendent
extremity d, the whole of the inhaled water rushes incessantly
out through that general aperture. In the silicious skeletons
of this class we find but one form of spiculum for each ani-
mal ; but in the calcareous generally two, and one of these
has a triradiate form, as represented in Fig. 3 at 1. This
triradiate form of calcareous spiculum is accompanied by one
of some other form, as by that clavate form of spiculum be-
longing to the leuconia compressa, shewn in Fig. 3 at 2 ; the
small spicula in Fig. 3 at 3, found in the same animal ap-

8

ORGANS OF SUPPORT,

pear to be only fragments of triradiate spicula. The tri-
radiate spicula chiefly bound the pores, canals, and orifices,
while the curved ends of the clavate spicula hang over the
exterior entrance of the pores to protect them. The cal-
careous spicula do not appear to occur in any of these animals
along with silicious forms, and the true horny tubular filaments
appear also to occur alone in the more tropical species, with-
out either silicious or calcareous spicula. The calcareous
forms of these animals appear to be much more rare, and
generally much smaller than the silicious or the horny species.
In the horny species of poriphera the skeleton consists
of thin elastic tubular translucent filaments united together
and distributed around the pores, canals, and vents.
These horny, tough, flexible threads have a close analogy in
their mode of distribution through the whole interior of the
body to the tough connecting matterof the spicula in the earthy
species, and they give form and support to the whole fabric.
Sometimes the internal canal which extends through these
tubular horny filaments is filled with an opaque matter which
gives a greater friability to the threads ; but most frequently
they contain only a transparent colourless fluid, as we see in
the fibres of the common
officinal sponge, which is
a poripherous animal be-
longing to this horny
group. The skeleton of
all the poripherous ani-
mals is so soft and flexible
in the living state, that
none of the lengthened
forms appear to be capable
of growing in an upright
position from their base
of attachment. They hang
down from the under sur-
face of submarine bodies,
as represented in these
figures. A specimen of
the common officinal
sponge with a horny fi-
brous skeleton, is repre-

FIG. IV.

OR OSSEOUS SYSTEM. 1)

sented in fig. 4 at 2, as alive and cut from its point of attach-
ment, c. The circular minute pores by which the streams of
water enter the internal tortuous canals are seen all over the
surface, as at a #, and the large vents by which the currents
issue from the body are seen on the most prominent
parts, as at bb. The manner in which the horny filaments
are united to each other throughout the whole mass of the
body is seen at fig. 4, 1 , where the broken ends of the fibres
show their tubular character, and this is still more magnified
at fig. 4.* The meshes formed by these horny fibres, though
apparently without order or regularity when the soft parts
are removed, have the closest relation to the pores and the
tortuous canals which wind through every part of the body.
Now we see in these simple skeletons of poripherous ani-
mals, as in many vegetables still more remote from human
organization, that nature begins the formation of an internal
framework for the support and protection of the soft parts,
by the deposition of detached earthy spicula throughout the
cellular substance of the body, as we see in the human em-
bryo the deposition of minute spicula of phosphate of lime
in various parts of the soft gelatinous bones begins the con-
solidation of the skeleton. The abundance of silicious
needles in the skeletons of the lowest poriphera assists in
their conversion into flint, when their remains have been ex-
posed for ages in chalk or other strata traversed by silicifying
percolations.

III. Polypiphera. — The skeletons of zoophytes present a
great variety of forms and characters, being branched or
globular, or filiform, free or fixed, solid, massive, and calca-
reous, or soft, flexible, and horny, external or internal. The
animals of this class obtaining their food by polypi, or highly
organized sacs developed from the fleshy substance of the
body, we generally find the skeletons, whether external or
internal, to present cavities or cells for the reception and
protection of these delicate organs ; and the various forms
of these cells constitute a principal distinction among the
skeletons of this class. The simplest forms of the skeleton
are presented by the horny zoophytes, or keratophytes,
where it sometimes consists of tough, soft, flexible filaments
which surround the cells of the polypi throughout the whole
mass of the body, as in the alcyonium and lobularia. These
form a transition from the horny species of poriphera to

10

ORGANS OF SUPPORT,

the more distinct forms of keratophytes. In the horny
species of zoophytes the skeleton sometimes forms a tubular
external sheath enveloping the fleshy substance throughout
all the ramifications of the body, as in all the sertularia,
plumularice, antennular'uR* and many other soft, flexible, and
ramified forms. The horny skeleton is sometimes formed
by the deposition of successive layers within the fleshy
substance of the animal, as in the gorgonia and antipathes.
We have an example of an
external, tubular, horny
skeleton in the common
campanularia dichotoma,
Fig. 5, where we observe it
enveloping as a sheath the
fleshy substance which
occupies the centre of all
the divisions of the root,
the stem, and the branch-
es. The exterior horny
sheath which is exuded
upon the surface of the
flesh is seen at a, and this
sheath expands at the
extremities of all the
branches to form cells, b,
for the lodgment of polypi
e, i. The base of attach-
ment, spread out and ram-
ified like a root, exhibits
the same fleshy interior,
and the horny covering
extended over all its divisions at c. A magnified view of a
small portion of a branch is represented at Fig. 5. 2, which
shows the fleshy granular or cellular substance f in the centre,
surrounded by the tough, elastic, amber coloured skeleton
exuded upon its surface *. In the axillae of many of the
branches we observe large vesicles, 1 1, for the protection and
development of the embryo. These vesicles in the vagini-
form keratophytes are composed of the same firm pellucid
substance as the rest of the skeleton ; and from^the con-
stancy of their forms in the same animal, and their differ-

OR OSSEOUS SYSTEM. 1 1

ences according to the species, they afford useful characters
for the distinction of these animals. They are deciduous
parts of the skeleton as they fall off after the matured gem-
mules have escaped from their interior. These gemmules
are seen in little ciliated capsules at m m, and the polypi are
seen in the same figure extended in various attitudes from
the cells, in search of animalcules as food. The skeleton of
these vaginiform zoophytes often presents a jointed appear-
ance on the stem or branches, as seen in the campanularia
at/"; these consist of circular indentations of the surface
which do not pass through the interior of the body where
they would interrupt the circulation of the nutritious fluid
which passes through the fleshy substance in all parts of the
body. They allow of a certain degree of flexibility at the
most suitable parts of the skeleton, and in some of the horny
cellar'KB they are connected with the deciduous character of
the branches. In the gorgonia, and some other cortical
zoophytes, there is an exterior fleshy substance in the living
state which covers all parts of the horny skeleton. This
fleshy exterior crust is indeed the animal, which forms by
the deposition of successive layers the whole of the flexible
branched, horny, and solid internal skeleton. If we make a
transverse section of a thick portion of the gorgonia, or
antipathes, we can easily perceive the concentric layers of
which it is composed ; and by peeling off the cortical fleshy
mass from the exterior, and placing this living flesh in the
sea, we find it to secret a new internal horny axis for itself.
The polypi, which are always and necessarily continuations
of the fleshy substance of zoophytes, are developed from this
thick fleshy crust in the cortical kinds, and hence we do not
see any appearance of cells on the central horny axis in
these animals, after the flesh has been removed.

In the calcareous zoophytes the solid mass forming the
skeleton is composed chiefly of the carbonate of lime, with a
little of the phosphate, and the same condensed glutinous
matter which forms the entire skeleton in the keratophytes,
is diffused through the whole of the calcareous mass in the
more solid lithophytes, where it serves to aglutinate the
earthy particles, and to give solidity and tenacity to the en-
tire mass. The calcareous skeletons of lithophytes are for
the most part internal, massive, and consisting of a single
piece. In madrepores, and many similar forms, the thin

[•2 ORGANS OF SUPPORT,

fleshy crust penetrates to a considerable extent the loose,
porous surface of the calcareous mass, from which it is
capable of receiving some protection, and consequently we
perceive distinct indications of the positions of the polypi
on the surface of the skeleton in these animals. These cells,
for the protection of the polypi, have generally a radiated
lamellar structure, and vary remarkably in their size and
also in their form in different lithophytes. They are very
minute in the porites, larger in the madrepores, still larger in
the caryophyllia, and the fungia agariciformis forms but
one enormous cell for the lodgment of a polypus like an
actinia.

In some of the lithophytes the fleshy crust, as in the cortical
kinds of keratophytes, is of great thickness, and the polypi
developed from this fleshy exterior mass leave no indications
of their position on the surface of the internal calcareous
axis. This is seen in the common red coral, which is a solid
internal calcareous skeleton, striated with superficial lon-
gitudinal grooves, but presenting no calcareous cells for the
polypi, which are protected solely by the fleshy thick
covering of which they form parts. In the agaricm, mean-
drinte, and many others, we observe a laminated general sur-
face of the skeleton for the protection of the fleshy mass,
but no distinct cells for the polypi. In the virgularm the
skeleton consists of a straight internal calcareous solid
cylindrical pillar, occupying the longitudinal axis of the body,
and protruding from the lower part of the animal. In the
pennatula the internal calcareous axis is soft and flexible at
its extremities, from the abundant proportion of glutinous
matter in its composition, and to allow of the necessary con-
tractions and extensions of the animal's body in a longitudi-
nal direction. In the isis the internal solid calcareous
skeleton is jointed at regular and short distances throughout
the whole body, and there are no external cells for the
polypi, which are entirely confined to the thick fleshy crust
which covers the entire animal in the living state. The
joints here consist of the same glutinous tough matter which
pervades the whole calcareous axis, and are only uncalcified
portions of the general solid axis. They are formed by con-
centric layers, like the calcified solid portions of the skeleton,
and they allow of considerable flexion in the branches and
stem of this delicate ramified, and highly organized animal.

OR OSSEOUS SYSTEM. 13

As in most other classes of invertebrata, we find many
zoophytes which are destitute of an external or internal
skeleton, as the common fresh water polype, or hydra. Be-
sides the solid internal skeleton in the corticiferous zoophytes
we commonly find in the fleshy crust itself minute calcareous
spicula. These small spicula compose the hard crust which
is seen covering the horny axis of the gorgonia, as it is com-
monly preserved dried in cabinets ; and in their occurring thus
spread through the general fleshy mass in gorgonue, lobularia,
and many other zoophytes we observe a lingering analogy
with the spicular form of the skeleton in the class of pori-
pherous animals, especially in the calcareous group. The
skeleton in the keratophytes is exuded from the fleshy sub-
stance in a soft and semi-fluid state, and quickly hardens after its
separation from the living parts upon which it is moulded.

As the skeletons of zoophytes are not permeated by vessels,
or organized as it is termed, their materials do not expand by
growth, but encrease in dimensions by the mechanical addi-
tion of new matter. Hence in the vaginiform keratophytes, as
plumularia and campanularice, we find the base or lower part
of the stem, which was formed in the younger state of the
animal, to be smaller than the upper part of the stem, which
was formed of larger dimensions when the animal, or the
contained fleshy substance, had encreased in bulk and de-
velopment. The large globular masses ofmeandrince, astr&ce,
and similar solid lithophytes encrease in bulk by the constant
addition of new superficial layers of calcareous matter upon
the same primitive plan by the polypherous fleshy covering
of the mass. From the origin, and the mode of growth of
these calcareous masses, it is obvious that when torn from
their primitive seat, they may re-attach themselves, or con-
tinue to grow, by the deposition or exudation of new matter,
as long as the secreting fleshy crust retains its vitality.
These extra-vascular skeletons appear to be very little modi-
fied by the contact of the living fleshy parts after they have
been once deposited in a soft state, portion by portion, and
fully consolidated by the hardening of the glutinous matter
in the keratophytes, or by the deposition of earthy matter
in the more solid lithophytes.

It is by the contact of living membranes, in the form of
capillary vessels, containing fluids, that the decayed earthy

14 ORGANS OF SUPPORT,

particles of organized skeletons are removed, and have new
particles exuded in their place. There are some skeletons
of this class which retain an intermediate degree of conso-
lidation between the solid lithophytes and the horny flexible
keratophytes, as we see in theflustra and calcareous cetlaria,
where the proportion of earthy matter is very small com-
pared with the quantity of tough glutinous substance in their
flexible skeletons, and we observe them to be thin, soft,
transparent, and gelatinous all around their free and growing
margins. When these skeletons, whether horny or calcareous,
have once been consolidated, they are, like the shells of
articulata and mollusca, or like the antlers of the deer, no
longer susceptible of growth, and they enlarge or extend by
the successive additions of new matter, or of new parts.
The carbonate of lime is the common consolidating earth of
zoophytes, as silica is that of poriphera ; and these are two
of the most abundant materials of the mineral kingdom.
By the abundance of these calcareous lithophytes on the
shallow shores of the tropical seas, they prepare a rich soil
for new islands and continents to be raised by volcanic action
from the deep, while they at the same time tend to purify
the mass of the ocean for the maintenance of higher animals
by thus precipitating, in an insoluble state, the corrosive
materials conveyed incessantly into its bed by rivers that
wash the surface of continents. The deep purple colours of
the corrallium, the tubipora, the corallina, and many others,
the azure blue of the pocillopora, the bright yellow of the
melitaa, and all the other lively colours seen in these calca-
reous skeletons are removed by the action of heat, and do
not appear to depend on any peculiar mineral ingredient ;
and we observe the same animal nature of the colouring
matter in the shells of articulata and mollusca, and in the
coloured bones of many vertebrated animals.

These skeletons of zoophytes are not exudations from the
surface of polypi ; the cell always precedes the existence of
the polypus which is developed within it. They are de-
veloped from the gelatinous substance of the reproductive
gemmules before any polypi begin to be formed, and they
continue to be developed and extended by the fleshy mass
of the zoophyte whether polypi are developed in the cells
or not. There is but one life, and one plan of development

OR OSSEOUS SYSTEM. 15

in the whole mass ; and these depend not on the polypi
which are but secondary, and often deciduous parts, but on
the general fleshy substance of the body.

IV. Acalepha. — Although there are no solid skeletons in
any of the soft, gelatinous, free, and floating animals of this
class, we generally perceive some firmer cartilaginous por-
tions of the body which afford support to the organs of pro-
gressive motion or of prehension. There are crescentic car-
tilaginous lamine around the inferior central part of the
body in the medusae which give support to the contracting
fleshy overhanging mantle, and to the absorbent tubes pro-
longed from that part. There are firm superficial longitudi-
nal bands in most of the ciliograde acalepha for the support
of those minute vibratile fins by the motions of which they
are carried through the sea. From the feebleness of their
muscular system, and from their swimming habits, it is
obvious that the acalepha can only support the lightest forms
of the skeleton.

In the velella limbosa, Fig. 6,
which floats on the surface of the
sea there is a thin flexible per-
pendicular crest, (Fig. 6. 2. a,)
which is covered with a thin
layer of the deep blue coloured
mantle, and which rests obliquely
on a horizontal stronger transpa-
rent flexible plate, (Fig. 6, 2 b.)
The thin perpendicular crest,
which rises above the water and serves as a sail, appears to
be composed of the same condensed glutinous or horny
substance which composes the skeletons of the keratophytes.
The horizontal plate is thicker, concave below, marked with
concentric lines of growth, and gives support to the deep
blue mantle above, to the delicate marginal tentacula, (seen
at b b, in both views of the velella,) to the numerous tubular
suckers, and to the stomach placed beneath this concave
horizontal plate.

The porpita, which is another of these floating acalepha,
presents a similar thin plate, to this horizontal lamina
of the velella, for the support of the same parts, but of a
round form, of a white colour, and of a porous texture.

ORGANS OF SUPPORT,

These two simple genera of acalepha present examples of
the thin, light, and delicate forms of the skeletons which
we find in almost all the floating marine invertebrata.

V. Echinoderma. — The skeletons of the animals of this
class are generally in the form of external crusts or shells,
covered with projecting spines. They are composed of the
carbonate, mixed with a small but variable proportion of the
phosphate of lime, and are hardened by animal matter. The
phosphate is always in a small quantity compared with the
carbonate of lime, but is more abundant in the solid shells of
the echinida than in the softer coriaceous and tuberculated
coverings of the stellerida. The skeleton of all these animals
consists of numerous detached or separate pieces, which protect
the interior viscera, give attachment to the organs of motion,
and generally give form to the whole body. The solid pieces
which compose the skeleton are for the most part in form of
calcareous plates, symmetrical in their shape and in their
arrangement, and which present considerable uniformity of
plan in their disposition throughout the diversified forms of
this class. The body most frequently presents a radiated
form in the animals of this class, the parts projecting in a
stellular manner from around a longitudinal axis, as is seen
in the various crinoid animals fixed by a jointed peduncle
and ramified above, and in the various forms of existing
stellerida, as the asterias, the ophinra, the euryale, and the
comatula, which are not fixed by a peduncle ; and we can
easily observe the same plan of structure in the more con-
centrated and globular forms of the echinida, as the scutellae,
the clypeasters, the spatangi, and the echini.

The radiating portions of these animals are composed of
numerous rings or segments, like the trunk and members
of articulated animals, and each of these component seg-
ments is surrounded by numerous calcareous plates. One
of these radiated or stellular forms of echinoderma is seen in
the common asterias aurantiaca, (Fig. 7- A.) where there are
five rays or divisions of the body, the number most frequent
in this class. On examining the sides of these rays from
above,, as the animal is placed in the figure, we observe the
ends of large lateral plates (Fig. 7, A. a a a) which bound
the margins of all the rays. These plates are connected
with others which surround chiefly the sides and lower surface

18 ORGANS OF SUPPORT,

above, and presents an exterior surface marked by numerous
tortuous grooves, like the surface of a meandrina. In its
concave interior surface it protects a small membranous sac,
which contains a thick grumous matter chiefly composed of
carbonate of lime with a little phosphate, and was supposed
by Tiedemann to be the organ which separates from the fluids
of the body the calcareous matter of the exterior covering.
The arrangement of the plates enveloping the segments is
very similar to this in all the other forms of asterias, how-
ever they may vary in the number of the rays, and in the
ophiurce where the rays do not contain prolongations of the
digestive and generative organs,, and in the other forms of
stellerida.

In the more compact forms of the echinida, the skeleton
is more solid, contains more phosphate of lime, and the
component plates are arranged with more obvious symmetry.
The plates are arranged in perpendicular or longitudinal
columns extending from around the mouth to the anus, as is
seen in the figure of the common echinus esculentus, (Fig. 75
B.) which represents the entire shell, as seen from above,
and deprived of its exterior spines. Some of these vertical
columns are seen to be perforated with the same kind of
small round oblique ambulacral holes as in the asterias.
These perforated ambulacral columns, (Fig. 7? B, «,«,«,) are ten
in number, disposed two and two together, so as to form five
pairs. The letters a, a, a, point to the middle line of separation
between each pair of ambulacral columns. Between these
five pairs of small perforated columns are placed alternately five
pairs of columns of. larger tuberculated plates which are not
perforated for the feet. These tuberculated columns in pairs
interposed between the successive pairs .of ambulacral
columns are seen in Fig. 75 B at b ; and the line of separa-
tion between the tuberculated and the ambulacral columns
is represented at c, c. The whole exterior of the shell being
covered in the recent state with moveable spines attached to
the tubercles we cannot perceive the arrangement of these
vertical columns of separate plates till the spines are re-
moved, or the shell is broken and viewed on the inner sur-
face.

A small portion of the shell of the echinus esculentus,
magnified and viewed from the inner surface, where the ar-

OR OSSEOUS SYSTEM. 17

FIG. 7.

of the rays, and form the ambulacral grooves below for the
tubular fleshy feet. Besides the tuberculated coriaceous
irritable skin covering the upper or dorsal part of each
small segment of each ray, we can generally distinguish eight
calcareous plates placed transversely on each segment, and
surrounding its sides and lower surface. In the sea-star
represented in the figure there are eighty of these transverse
divisions or segments in each of the five rays of the animal.
In all the segments of a single ray there are about seven
hundred plates, and about three thousand five hundred cal-
careous pieces in the segments of the whole animal. The
concave lower surface of each ray is perforated by numerous
pairs of small oblique holes placed on each side of a longitu-
dinal median line, which are the ambulacral perforations for
the tubular fleshy suckers, by which these animals drag
themselves along the bottom of the sea, or up the perpendi-
cular sides of rocks. The lateral and dorsal parts of the
segments often support fixed or moveable spines which grow
like the plates themselves by the successive addition of
calcareous layers from the thin fleshy secreting membrane
which covers every part of the calcareous skeletons ofechino-
derma.

On the back of these animals, and a little to one side of
the centre, between the commencement of two of the rays,
there is a small, round, solid, calcareous body, represented
at by in Fig. 7? A. This round calcareous plate is convex

PART I. C

OR OSSEOUS SYSTEM.

rangement of the plates is best seen, is represented in Fig.
8, 1 , where a, a, represents the smooth inner surface of the
large tuberculated plates, and FIG. 8.

b, by the inner surface of the a ^j_y-^-^^^-^-~~^^^M
perforated ambulacral plates.
There are ten vertical co-
lumns of tubercular and ten
of ambulacral plates which
vary in the number of pieces
they contain, according to the
<age of the animal. The
larger plates are the tuber-
cular a, a, which have a pen-
tagonal form, and are length-
ened transversely. There are
about thirty-two of these tubercular plates in the adult ani-
mal, in each of the vertical columns, making three hundred
and twenty plates of this form in the ten columns. The
columns of tubercular plates meet each other by obtuse,
salient and re-entrant angles, as seen at d in Fig. 8, 1, form-
ing thus a regular zig-zag line by the contiguous columns of
these plates, and the shell is much strengthened by the al-
ternate manner in which the sutures are arranged. The am-
bulacral plates form also five pairs of columns (Fig. 8, 1, b,b,)
each column containing about eighty pieces. The tubercular
columns are united to the ambulacral by minutely serrated
edges, and the ambulacral columns are united to each other by
the same form of zig-zag suture as that between the tubercular
plates. The ambulacral plates however (Fig. 8, 1, b,b,) appear
to have their perforated portions detached by small sutures
which traverse all the foramina, (Fig. 8, 1, c, c.) There are thus
ten columns of these minute perforated pieces, each column
having one hundred and sixty pieces. The contiguous portions
of the ambulacral pieces, (Fig. 8, 1, b9 by) are covered externaUy
with tubercles like the larger tuberculated pieces. (Fig. 8, 1, a,a.)
When we examine the fractured edges of these shells, we
observe the colouring matter of the surface to pass under the
superficial tubercles, which appear not to be continuous por-
tions of the plates to which they adhere by a broad spreading
circular base. The tubercles are few on the small terminal
plates, but numerous on the large pieces in the middle of

c 2

20 ORGANS OF SUPPORT,

the columns. There are at an average at least ten tubercles
for each tubercular plate, and three tubercles for each of the
tuberculated portions (Fig. 8, 1, b, b,) of the ambulacra! plates.
Every tubercle of the shell supports an external, moveable,
calcareous spine ; so that there are more than ten thousand
pieces in the shell of the echinus esculentus, without counting
the complicated dental apparatus of the mouth, or the respira-
tory and ovarial plates, or the very minute calcareous pieces
disposed irregularly on the coriaceous membrane around the
oral and the anal orifices. There are five large heart-shaped
plates disposed around the anal aperture, as seen in the central
part of Fig. 7- B, each of which is perforated by a large round
hole for the termination of one of the five oviducts. Between
the tapering exterior ends of these five ovarial plates there are
five smaller heart-shaped plates, each of which is likewise per-
forated with a small round hole. Around the lower orifice of
the shell the last pairs of tubercular plates send in arched
processes which meet each other over the ambulacral plates,
nud u;ive a fixed and extensive surface for the muscles of the
dental apparatus. The five teeth and their alveoli are repre-
sented as seen laterally at Fig. 8, 2, and as seen from above at
Fig. 8. 3. There are five teeth, (Fig. 8, 2, 0, a,) of a compact
and dense texture where they project downwards from the
alveoli, and of a loose and fibrous structure at their upper
part, where they are enclosed in their complicated alveoli.
The alveoli (Fig. 8, 2, b, b,) are long, slightly curved, hollow,
tapering from above downwards, moveable individually and
collectively, and held in connection by several distinct move-
able pieces, (Fig. 8, 3, b, by) at their proximal extremities. This
dental apparatus, which exists also in the cidaris, is wanting
in the spatangus, and several other genera.

The exterior surface of the shell is covered, in the echinida,
with solid calcareous spines, which rest and move upon
the round tubercles. These spines are very large in the
cidaris, where the shell is small ; and they are small in
the echinus and spatangus where the shell is large. They
grow like the other parts of the shell, by successive
deposition from the enveloping fleshy substance. Sec-
tions of these spines, and of the tubercles on which
they rest, are represented in Fig. 9, where 1, represents the
entire spine of the common echinus esculentus, and 2, a

OR OSSEOUS SYSTEM.

transverse section of the
same spine. In Fig. 9, 1, #, is
the round tubercle on which
the spine moves ; b represents
the muscular fibres which
descend from the margin of
the spine to the circumfer-
ence of the base of the tuber-
cle ; c, d, is a distinct part of
the base of the spine formed
within the capsule of the joint ; and /, f represents the soft
secreting fleshy layer which envelopes the whole exterior
of the skeleton. The concentric layers by which this spine
is enlarged are seen in the transverse section, Fig. 9, 2. These
superimposed layers of growth are represented in the lon-
gitudinal section of a large spine of echinus mammillatus
(Fig. 9, 3,) where a represents the muscular fibres by which
it is moved and attached, and b is the compact portion of
the spine formed within the capsule of the joint.

In some of these external spines of echinida the growth
appears to be effected by the addition of calcareous matter
only to the proximal extremity, or fixed ends of the spines.
The lines of growth do not then converge and meet in the
longitudinal sections, but diverge and terminate at the sides
of the spines. This structure is seen in the spines of the
cidaris pistillaris, represented in Fig. 9, 4, 5, 6, where a is the
tubercle with a cavity at its summit, as we commonly find
in the animals of this genus ; b is the concave base of the
spine, with a cavity in its centre, as in the tubercle on which
it moves. The compact portion of the spine formed within
the capsule is seen occupying the middle of its whole extent,
and the successive layers of growth are observed extending
from this central portion to the sides along the whole spine.
A view of the base of this spine is given at Fig. 9, 5, and a
transverse section of its middle is represented at Fig. 9, 6',
where we see the concentric layers of growth around the
middle compact portion. Interspersed among the spines of
the echini we find small, fleshy, cylindrical organs which ter-
minate in three moveable calcareous spines. Many of the
echinoderma have no external skeleton, and are covered only
with a coriaceous irritable skin.

22 ORGANS OF SUPPORT,

In the holothuria, which are animals of this kind, there
are only five pairs of small calcareous pieces disposed around
the mouth like the dental apparatus of the echini. These
pieces give support to the ramified tentacula, and afford a
firm attachment to the strong longitudinal muscular bands
which encompass the body.

THIRD SECTION.

On the Organs of Support in the Diplo-neurose, or
Articulated Classes.

The animals of this great division have the trunk of the
body for the most part long and cylindrical, divided trans-
versely into segments, and provided with numerous pairs
of organs of motion symmetrically disposed along the sides.
From their activity, their skeleton is generally in form of a
light, thin, exterior, enveloping, condensed integument, to
the inner surface of which the muscles are attached through
the medium of the cutis, and which is periodically cast
and renewed, to allow of the growth and increase of the en-
closed soft parts. The articulated appearance of the skele-
tons in these animals is generally proportioned to the density
of its texture. Where the whole skeleton is soft and flexi-
ble, there are few or no traces of articulations, and where its
texture is dense and unyielding, the articulations are most
distinct and complete ; hence in the helmithoid classes, and
in the young state of the entomoid animals, the articulated
appearance of the skeleton is less distinct than in the adult
forms of the articulated animals with articulated members.
The tubular form of the hard enveloping parts of the arti-
culated animals, and their unorganized nature require them
to be exuviable, and as they are thus the result of a single
effort of formation, they are always thin and light coverings.
They are not reinforced by successive deposits added to the
surface, through the whole of life, as in the molluscous
classes, and consequently we find but little of that softer
material, the carbonate of lime, employed in their consolida-
tion. The more dense material of the phosphate of lime

OR OSSEOUS SYSTEM.

is almost always substituted for that earth, as we see also in
the vertebrated classes. In some of the more solid and massive
coverings, however, of these animals we meet with the
carbonate of lime, as in the serpula, the cirrhopods, and the
Crustacea.

VI. Entozoa. — The intestinal worms have for the most
part a tough exterior, transparent and almost hermogenous
covering spread over their whole body, to which they owe
their peculiar stiffness and elasticity, and to the inner surface
of which their cutaneous muscles are attached. This part
is composed of the true skin, and that epidermic covering
which becomes consolidated into a dense exterior skeleton
in higher classes. It is here soft and elastic, to allow them
with more ease and safety to move through the tough and

constantly moving parts of the
living animals in which they
reside. The long cylindrical bodies
of these parasitic worms would be
impeded in their motions by any
,hard, inflexible shelly covering?
which likewise could not be cast
off and renewed in such a medium;
hence their smooth, glistening,and
unctuous covering has only that
degree of density and toughness,
which is adapted to protect them
from tearing and compression
during the movements of the living
parts around them. This trans-
parent elastic tunic is especially
thick and firm in the long cylin-
drical, filiform, or trematoid en-
tozoa,as thejilaria,ihe strongylus,
the echinorhynchus, and the as-
caris. Intheascaris lumbricoides,
which is represented in Fig. 10, A,
this covering is thick and tough ;
but so transparent as to allow the
white layers of muscular fibres to
be perceived through it. The
three moveable oral lobes are

FIG. 10.

24 ORGANS OF SUPPORT,

seen at 0, the abdominal nerves are seen as a single line
running along the middle of the ventral surface, and separat-
ing to encompass the vulva at b, and the anal opening is
seen near the posterior termination of the body at d. In
the jointed teenies and bothriocephali, this covering is soft
and thin, these being almost aggregates of simpler animals,
and it is still more thin and dilatible in the hydatids and
caenuri. This exterior covering often presents an irregular
transversely-corrugated appearance during the contracted
state of the long filiform antozoa, which arises from the still
irregular attachment of the interior interrupted longitudinal
muscular fibres ; and these irregular transverse corrugations
present us with the first condition of those joints and rings
which become so regular and distinct in higher articulated
classes. This exterior soft covering of the entozoa presents
us also with the lowest form of that cyclo-vertebral element,
which forms by its consolidation and repetition, a series of
calcified rings or segments around the exterior of the trunk
in higher entomoid articulata, and the solid bodies of the
vertebrae in the red-blooded classes.

In most of the inferior orders of entozoa there are numer-
rous dense conical recurved hollow, and sharp pointed spines
which are sometimes disposed as teeth around the mouth,
and sometimes are found covering a great portion of the
anterior part of the body, giving it the appearance of a file
to abrade the surface on which they are to feed, or through
which they have to force their way. These hollow spines
are thus organs of progressive motion, like the cirrhi and
setse of annelides. They are strongest and most numerous
in the acanthocephalous species, where they cover the whole
of the retractile proboscis, and sometimes, as in the echino-
rhynchus hystrix, nearly the whole of the anterior surface
of the body. There is thus a transition from these teeth-like
organs in the interior of the mouth, and those covering the
surface of the body in these soft worms which move through
a fleshy resisting medium everywhere in contact with them,
to the lateral spines of the annelides which can be moved
with more freedom and more precision through a thin aquatic or
aerial medium, as in the aquatic annelides and the earth-worms.

The exterior covering is more dense in its texture, and
consequently more articulated in its appearance in those

OR OSSEOUS SYSTEM. 25

parasitic worms, which are found attached to the exterior
surface of the gills, the lips, the eyes, and other soft parts
of fishes, and which have thence been called epizoa. We
already find in many of these animals, as in the lerncea
and chondrocanthi, not only the head forming a distinct
segment of the body, and the trunk partially divided by
transverse depressions, but numerous appendices already
developed from the sides of these segments, and some of
these appendices, especially on the head, provided with move-
able articulation. This dense covering is still so transparent
and hermogenous, that we can distinctly perceive through it,
the longitudinal muscular fibres which produce the numerous
corrugations of the skin, and also the contained viscera.
The transition is quite imperceptible from these epizoa, as
the tracheliastes and the achtheres to the fixed parasitic
entomostracous crustaceous animals, as the ergasilus and the
lamproglena, where the exterior covering has the same
texture and properties, and where the articulated appearance
of the trunk and its appendices is nearly in the same simple
condition. One of these lowest of the entomoid tribes
almost inseparable from the epizoa, the lamproglena pulchella,
is represented in Fig, 10, B. where we already observe the
head and three principal divisions of the thorax distinctly
marked, as in insects. We perceive in this little animal,
found attached to the gills of the cyprinus jeses, two pairs of
maxillae, a, a, b, b, formed like curved pointed feet, and two
pairs of antennae c, c, d, d, as in higher Crustacea. Above the
mouth e, are seen the two eyes united on the median plain as
in higher monoculi, and the intestinal canal /*, is observed
surrounded by the follicles of the liver, and passing straight
through the middle of the whole body, as in most parasitic and
carniverous articulata. Pairs of feet, ^, q, r, are seen extending
from the sides of the segments, and transverse fasciculi of
muscular fibres i, h, k. The unimpregnated ovaries /, closed
above and filled with imperfectly developed ova which after-
wards descend to external sacs, open on each side of the
last distinct segment by a trilobate orifice m. All the ex-
ternal parts of this very minute animal are developed nearly
to the same extent, and articulated to as great a degree in
the achtheres and several of the higher of the acknowledged
epizoa ; so that we have already developed in the lowest of

ORGANS OP SUPPORT,

FIG. 11.

the helminthoid classes, the rudiments of all those character-
istic parts of the complicated skeletons of insects, and of all
the higher entomoid articulata.

VII. Rotifera. — The wheel animalcules are more closely
allied to the helminthoid articulata than to any of the inferior
radiated classes, especially in their supra and infra-sesopha-
geal ganlia, their abdominal longitudinal nerves, their dorsal
vessel for circulation, their lateral maxillae, their highly deve-
loped genetal system, and their muscular activity. Their
exterior covering, though generally thin and transparent as
crystal, appears to possess
considerable firmness from the
numerous powerful muscles
inserted into it, and from the
transverse corrugations it
presents when the body is
drawn backwards to their
fixed caudal extremity. Some-
times it is in form of a sheath
enveloping the middle of the
body,and open both before and
behind, to allow the head and
tail to be retracted and pro-
tected. This firm tough
elastic covering of the roti-
fera has some resemblance in
its hermogenous texture to
that of the entozoa, and pro-
bably is persistent and en-
larges with the body. There
are no earthy deposits formed
in any part of the body of
these minute and active
animals. The densest parts of
their body appear to be the
two jaws which move trans-
versely by powerful muscles,
and are generally provided
with numerous sharp teeth.
One of these wheel- animal-
cules, termed hydatina senta, common in our ponds of fresh

OR OSSEOUS SYSTEM. 2/

water, is represented in Fig. 1 1, where we perceive seventeen
muscular lobes, a, a, for the movement of the vibratile cilia,/;
disposed around the mouth. The muscular apparatus b, of
the maxillae and the mouth are retracted by longitudinal
muscles c, which pass obliquely backwards, and the whole
body is forcibly retracted towards the fixed caudal extremity
by several longitudinal bands d, of muscular fibres which
extend the whole length of the body. The large central or
supra-eesophageal ganglion o, is accompanied by four other
ganglia, disposed around the oesophagus, and abdominal
nervous filaments p, are perceptible, extending longitudinally
on the inferior surface, as in other articulated classes. The
muscular apparatus of the jaws may almost be regarded as
analogous to the muscular stomach armed with teeth com-
mon in Crustacea. The narrow part of the intestine considered
as the oesophagus g, leads to a long and capacious digestive
cavity, which in many of the genera of rotifera developes nu-
merous caecal appendices, like the biliary follicles of annelides.
In this capacious intestine, extending from ^, considered as the
oesophagus to near the anus, i, on the dorsal part, we observe
small animalcules, naviculce, h, which have been swallowed
entire. The longitudinal dorsal vessel e, more like an
abdominal nerve, as in other articulata, follows the median
line, and gives off numerous lateral branches in its course.
Two glandular sacs /, appear to pour their secretions into
the muscular cavity of the mouth, as the liver into the
muscular stomach of Crustacea, or the salivary sacs into
the oesophagus of mollusca. The two ovaria m, form large
lobed organs extending upwards on each side of the intestine,
and open by one orifice into the cloaca, behind the rectum £,
and two long narrow glandular sacs k, k, considered as testes,
pour their secretions into a large membranous vesicle
situate behind the cloaca. The jaws of this FIG.
animal are represented apart from the body,
along with their enveloping muscular apparatus,
in Fig. 12, where 1, «, shows the serrated edges
of the numerous teeth on each side of the open-
ing of the mouth, 1, #, the muscular apparatus
of the jaws, and 1, c, the general muscular sac
of the mouth. One of the jaws is represented
at 2, Fig. 12, separated from the muscular sac

28 ORGANS OF SUPPORT,

of the mouth,, where the parallel teeth composing the jaw, so
variable in number in the rotiferous animals, are seen at a,
and the insertions of the muscles at b. Sometimes only a
single tooth on each side is seen to compose the jaws, and
they have been observed to vary in the number of component
teeth in the jaws of different animals from one to six in each
jaw. Thus their most solid parts relate solely to digestion,
and the lightness of their exterior covering corresponds with
the constant and rapid movements of these rotifera through
their watery element.

VIII. Cirrhopoda. — The cirrhopods, like the entomostra-
cous Crustacea, are articulated animals enclosed in shells
like those of mollusca, so that they present both forms of
the skeleton. They have six pairs of curled jointed mem-
bers extending from each side of the body, from which
this class has received its name. Each pair arises from a
short thick fleshy peduncle, and the peduncle or haunch
of the anterior shortest pair, those 011 each side of the
mouth, support a pair of short, pyramidal, laminated, branchiae,
like those attached to the haunches of the legs in most of
the Crustacea. The feet are covered externally with a trans-
parent, firm, elastic integument, are regularly and closely
jointed to their finest extremity, and are furnished with
minute jointed cirrhi disposed along each side of their inner
concave surface. The trunk of the body between the feet
is also partially jointed ; it presents the usual nervous
columns and ganglia disposed along the ventral surface, as in
other articulated classes ; and, as in them, the intestine
passes straight from the mouth to the anus, which opens into
a long thin flexible conical tube. The mouth of these ani-
mals is furnished with an upper and a lower lip, with a pair
of mandibles and a pair of maxillae. The maxillae are fur-
nished with small fleshy palpi, and the lower lip is formed
by the union of the exterior maxillae. The cirrhopods are
almost always inclosed in multivalve shells secreted from the
outer surface of a fleshy, thin enveloping mantle, and which
are attached to submarine bodies either directly by their
base, or by means of a fleshy tubular peduncle. These
exterior shells are generally thin, laminated, dense, composed
of carbonate of lime with animal matter, and grow by the
successive addition of layers to their inner surface. The

OR OSSEOUS SYSTEM,

testaceous coverings are most developed in the balani, where
the articulated members of the contained animal are least,
and these exterior shells are least in the anatifa, and other
pedunculated genera where the feet are largest. The acorn-
shells, or balani, form a hollow cone composed of six pyra-
midal pieces, ribbed longitudinally with tubular cavities,
and overlopping each other in an imbricated manner by their
thin margins. These strong pyramidal plates, striated in-
ternally, both transversely and longitudinally, rest their broad
bases on the margin of a circular fixed calcareous disk,
striated in a radiated manner with small hollow tubes which
open into those of the pyramidal plates. Between the su-
perior separated apices of these larger plates, are interposed
six smaller pyramidal pieces with their points directed
downwards, so that their bases complete the upper free
and smaller margin of this truncated hollow cone. The smaller
inverted plates appear to be anchylosed to the larger inferior
pieces. Within this fixed cone, which has the means
of continued increase by its subdivision into numerous
pieces, there are four moveable triangular plates, two larger
and two smaller, which form an operculum to open and
close at the will of the animal. In the anatifa or pentalasmis,
represented in Fig. 13, we have an example of the ordinary
form of the skeleton in the barnacles, or lepades, suspended
by a fleshy peduncle. The shells here are thin and diapha-
nous, and by their striated outer surface, they mark the limits
of the successive layers of growth, and the opposite direc-
tions in which these lay- FIG. 13.
ers are extended in the
two lateral pieces of the
shell. Fig. 13,1, represents
the entire shell with the
jointed members of the
animal projectingfrom the
aperture, and a portion
of the contracted pedun-
cle. The jointed mem-
bers «, with their jointed
cilia are here very long, and are seen partially extended
from the open anterior aperture b, of the shell. The pedun-
cle/, is composed of a tough exterior coriaceous tunic, and

30 ORGANS OF SUPPORT,

an inner muscular coat, so that it is capable of rapidly
contracting when alarmed. The dorsal shell e, is the only
piece placed on the median plain, and grows by layers added
to its inner surface and increasing successively from the
proximal to the distal extremity. The larger lateral pieces,
c, c, to which the animal is fixed by a strong transverse
muscle of attachment, as in bivalved mollusca, grow likewise
by layers extended from the whole of the distal margin, the
centre of ossification being at the proximal point. The two
distal smaller opercular pieces d, grow from their distal to-
wards their proximal ends. From their greater extent of
motion by means of their long fleshy peduncle, these le-
pades do not require to possess external shells so strong as
the fixed sessile balani. A dorsal view of the same shell on
a more reduced scale is given in Fig. 1 3, 2, which represents
the direction of the successive layers of growth of the dorsal
plate «, which is analogous to the whole complex cone of the
balani, the four lateral moveable pieces representing the four
valvular small pieces in the sessile species. In Fig. 13, 3,
the tubular peduncle is divided to show its outer coriaceous
covering k, and the inner muscular coat /, with the inter-
posed skin i, and the right side of the shell is removed to
show the inverted and curved position of the animal in its
cavity. In some of the pedunculated cirrhopods, as the
poUicipes, there are several small supplementary calcareous
pieces placed at the junction of the peduncle with the base
of the shell, and some, as the cineras, have only a cartilage-
nous or membranous covering unconsolidated by calcareous
pieces. The anterior part of the body (Fig. 13, 3, «,) of this
enclosed animal, as in most other articulata, has less of the
articulated appearance, less distinct segments than the pos-
terior portion of the trunk, and the skin of that anterior part
is here thin and membranous. The abdominal, or posterior
portion of the body (Fig. 13, 3, b, c,) is that tapering articu-
lated, and free part, from the sides of which the articulated
cirrhated and pedunculated members project. The muscles
by which the anterior bulbous part of the trunk is attached
to the valves of the shell are seen at y, and the strong
adductor muscle passing across from the right to the left
valve, and by which they are firmly closed when the animal
is alarmed, is seen at/. The six thick muscular peduncles

OR OSSEOUS SYSTEM. 31

for supporting and moving the six pairs of long articulated
members on each side are seen at b, c, and the branchiae at-
tached to the anterior or smallest pair of these haunches are
seen at h, h. The membranous conical long tube continued
from the anus is seen extending from the shell at e. These
articulated organs of the cirrhopods attached to the sides
of the abdominal portion of the trunk are in constant move-
ment during life, extending and retracting, like the branchial
organs of the post-abdomen in the branchiopodous crus-
tacea.

IX. Annelida. — The red-blooded worms lead us a stage
higher in the development of the articulated skeleton, and
especially in the organs of locomotion. Some, as the pleione
and the halithea, have the exterior covering of the body
still so soft and membranous, as scarcely to present an arti-
culated appearance. Some, as the leech, have only the trunk
of the body developed, and from the want of lateral setae
and cirrhi for progressive motion, have the segments sur-
rounding the body very short and numerous, and thereby
possess great flexibility of the trunk. In the earth-worm, the
segments of the trunk are larger and firmer, and each ring is
provided with eight very small curved, conical, hollow, sharp
pointed spines or setae, which are disposed on the sides of
the segments in two upper and two lower pairs. These
setse are surrounded each with a muscular sheath for their
advancement and retraction, and they serve as organs of
locomotion. In some annelides the setee are hooked at their
points, in others they are compressed, or spatulate, and in
others subulate. In the simplest forms of annelides we
sometimes find, as in the nais, but one long filament or seta
developed from each side of each segment, which however
still materially assists them in moving over a solid surface,
or through narrow passages, or in their serpentine motions
through the water. The softness of the skin in most of the
annelides compensates for the want of articulated feet, by
allowing greater flexibility to the trunk, and the delicate
sensibility of the whole skin compensates for the imperfect
development of their organs of sense. This delicate and
unprotected condition of their outer surface requires many
of them to shield their whole body in external solid adven-
titious tubes, often most artfully constructed, and some, as

32

ORGANS OF SUPPORT^

the serpuke exude a calcareous conical tube from the surface
of their skin, which enlarges like the conical shell of a gas-
teropod, by the successive addition of new and wider cones
to its interior surface. But the true skeleton of these arti-
culated worms, as in the higher entomoid classes, is their
exterior skin and epidermic covering, to which the muscles
of locomotion are attached, whether this part be hard or
soft. The upper lateral setae of the annelides appear to be
the analogues of the wings of insects, and other corresponding
parts extending from the sides of the segments in higher
classes. When the setae of the annelides are hollow and
jointed, or sub-articulate, they are commoiily called cirrhi,
as we see in the long jointed cirrhi accompanying the tufts
of setae on the sides of the nereides. One of the most
articulated forms of the body and members presented by
this class is seen in the sea-centiped, the nereis nuntia, re-
presented in Fig. 14, where a dorsal view of the entire ani-
mal is given at 1, a transverse section of a single segment at
2, and a magnified view of one of the lateral organs of mo-
tion at 3. We already find in this worm FIG. 14.
the head (Fig. 14. l,a, b) distinct from the
trunk, and consisting of several separate and
moveable segments. The head is provided
with sharp, curved pointed maxillae, with ser-
rated inner edges. There are numerous se-
parate small simple eyes, or ocelli, disposed
chiefly in transverse rows, and there are se-
veral lateral tentacular filaments having the
character of antennae. There is an enlarged
anterior part of the trunk (Fig. 14, 1, b, e,)
corresponding with the thorax of insects,
and the segments are nearly equally develop-
ed from this point to the posterior end of
the trunk. All the segments of the head
and trunk are still moveable on each other ;
they are almost equally developed and equally
provided with lateral appendices. In the
transverse view of one of the segments (Fig.
14, 2,) of this nereis, we observe the lateral
appendices to consist, on each side, of a long
jointed slender tubular cirrhus (Fig. 14, c, d,) and a fasciculus

OR OSSEOUS SYSTKM. 33

of shorter setse placed below. This lateral organ of motion
is seen on a more magnified scale in Fig. 14.3, where a re-
presents the jointed cirrhus, and b,c the tuft of setae. These
segments and their appendices vary much in their degree of
consolidation, in some being soft and transparent, and in others
opaque dense and covered with pearly or metaUic lustre. The
tubicolous annelides which form the densest exterior tubes
have generally the segments less marked, and covered with a
softer skin than those which are found in soft tubes, or are en-
tirely without such protection. We have thus already developed
in the annelides, the segments of the body and their jointed
tubular appendices for progressive mo- FIG. 15.

tion, and all the essential parts of the
skeleton which present themselves
under various forms throughout the
entomoid classes.

X. Myriapoda. — In the myriapods
the skeleton is more dense, the articula-
tions are more distinct, and the jointed
tubular appendices, for progressive mo-
tion, are more developed from the sides
of the segments than in the helminthoid
classes. Their muscles having firmer
points of attachment, act with more
energy and effect, and their movements
effected in the thinner medium of the air
are more lively than those of the hel-
minthoid animals which mostly inhabit
a more dense aquatic medium. The seg-
ments of the body are here more numer-
ous thanin the higher articulated classes,
and they are still, as in the annelides,
nearly equally developed throughout the
whole trunk. In some, as the iuli, the
segments are calcareous, hard, and cylin-
drical, and the lateral appendices or feet
are short, and for the most part double
on each side of each segment. In other
myriapods, as the scolopendra, repre-
sented in Fig. 15, the segments are de-
pressed, coriaceous, composed simply

PART I.

.* I ORGANS OF SUPPORT,

of an upper and a lower arched plate, attached by a softer
flexible portion of the skin upon the two sides, and generally
each segment presents but one pair of extremities more
lengthened than in the iuli. The first pair of feet are here
in form of simple curved perforated hooks placed at the
sides of the mouth, and the succeeding feet along the whole
sides of the trunk terminate in a single sharp conical claw
less curved, with a very minute oppo sable spine extending
from the interior of each terminal joint. The antennae (Fig.
1 5, c, c) are two in number, as in insects, and for the most
part long, filiform, and multi-articulate, and the organs of
vision generally consist of numerous simple eyes placed in a
group behind the bases of the antennae.

In the cylindrical vermiform chilognatha, the mandibles
appear to be still destitute of palpi, which are developed on the
mandibles of the larger chilopoda. The segments of the head,
thorax, and abdomen are scarcely yet distinguishable from each
other. The stigmata for respiration open on the sides of the
alternate rings of the trunk, as if these were equivalent to only a
half of the ordinary rings or segments of insects. The two last
pairs of feet (Fig J 5.e, e) generally extend backwards in form of
a bifid tail: they are for the most part longer than the other feet,
and sometimes form foliated expansions at their free extremi-
ties, as we likewise often see in the Crustacea. The segments
of the trunk lie over each other in an imbricated manner at
their line of junction, so as to defend the internal soft parts
during the bending serpentine motions of the body. These
animals do not undergo metamorphoses like insects, nor ac-
quire wings, but the number of their segments varies with
their period of growth ; and from the density of their exter-
nal coverings, their unorganized nature, and their enveloping
tubular forms, they are exuviable, like the dense skeletons
of all the articulated tribes with articulated members.

XI. Insect a. — The skeleton of insects, from its super-
ficial position, and from the lightness and density of its
materials, is well adapted for intevertebrated animals
destined for an aerial life. It is composed, in its densest
parts, of a thin epidermic layer, a colouring matter often
presenting the most lively hues, and a brilliant metallic
lustre, and a thicker internal layer much resembling the
woody fibres of plants, but composed of peculiar animal

OR OSSEOUS SYSTEM. 35

substances, termed chitine and coccine, and consolidated
by small proportions of the phosphates of lime, magnesia,
and iron. As in other entomoid classes, the trunk is
surrounded with hollow rings or segments, which on the
anterior parts of the body support lateral appendices ap-
propriated to sensation, mastication, or progressive mo-
tion ; and consequently, on these anterior portions of the
body, the segments are more consolidated and more firmly
united together than in the flexible and capacious pos-
terior part. There are generally thirteen segments dis-
tinguishable in the trunk of insects, of which the anterior
forms the head, the next three the thorax, and the posterior
nine the abdomen. The annexed diagram from Carus shows the
form and position of these parts of the skeleton viewed from be-
hind in the calosoma sycophanta, (Fig. 16.) a coleopterous in-
sect. The body of insects generally tapers more or less at both
ends, and the terminal segments before and behind are
those least developed ; those composing the head indeed

FIG. 16.

-6 ORGANS OF SUPPORT,

are so small, indistinct, and anchylosed together, that
entomologists are not agreed as to their number, some
considering this part as composed of one segment, some of
three, and others of seven segments consolidated together.
The head, (Fig. 1 6. g,) supports the organs of mastication and
of the senses, and contains internally the parts of the mouth,
the pharynx, the commencement of the oesophagus, and
the two first pairs of ganglia. We observe attached to the
head an inferior lip, or labium, with its jointed pal^n
(Fig. 16. «,) and a superior lip or labrum, both of which
extend transversely across the axis of the body, a pair
of mandibles without palpi, and a pair of maxillae pro-
vided with these jointed organs of sense. The head
supports also a single pair of articulated antenna (Fig. 1 6.
e,) most variable in form, a lingua, and a pair of eyes
(Fig. 16. /,) generally compound, with three simple
ocelli.

The thorax supports the legs arid the wings, and is
composed of three segments, the anterior of which (Fig.
16. h}) is termed prothorax, the second mesothorax (Fig.
16, m,) and the third metathorax (Fig. 16. o.) The pro-
thorax supports the first pair of legs, the mesothorax
the second pair of legs, and the first pair of wings,
and the metathorax has attached to it the third pair of
legs, and the second pair of wings. These segments of
the thorax, like vertebrae, are composed of several ele-
ments which send processes inwards for the attachment
of muscles, and the protection of the contained organs,
and each of the segments exhibits a development pro-
portioned to that of the parts it supports or contains.
The parts of the legs have received names taken from
those of the locomotive organs of vertebrata. Each leg
is attached to its corresponding segment by a short,
round, moveable articulation, called the coxa, or haunch
(Fig. 16. m ; ) to this succeeds the trochanter (Fig. 16, i,)
which is likewise a very short joint, and less moveable.
The femur (Fig. 16. &,) is a strong and lengthened ar-
ticulation, commonly extended horizontally, and the tibia
(/,) which succeeds it is generally the most lengthened
and slender joint of the leg, and directed vertically. The
little joints of the tarsus (Fig. 16. A, B, C,) which follow,

OR OSSKOrs SYSTEM. 37

compose the foot which commonly terminates with simple
crooked ungues or opposeable chili.

The segments of the abdomen, commonly divided into
an upper and a lower piece connected together at the
sides by an unconsolidated portion of the integument,
encompass the digestive and the generative organs, which
for the most part terminate in the last segment. Each
of the abdominal and thoracic segments is perforated on
each side by a small spiracle or stigma which leads into
the respiratory tracheae ramified through every part of the
body. The wings and the legs are the parts most subject
to variations of form and magnitude, and their variations
are accompanied with corresponding differences in the
relative development of the thoracic segments which lodge
the muscles and nerves of these locomotive organs. In
insects where the exterior or first pair of wings are
little used in progression, as in most of the coleoptera,
the mesothorax is small, and the other two segments,
the anterior and posterior, are large ; but in dipterous
insects, where the anterior or first pair of wings are
alone developed, the mesothorax has assumed a pro-
portionally great development, and the pro- and meta-
thorax are very small. In the hymenoptera, the meso-
thorax is large, in the hemiptera and orthoptera, the
anterior segment is most developed, and in the neurop-
terous insects, the meso- and the meta-thorax are large
compared with the anterior thoracic segment. The meso-
thorax is commonly the most important segment of this
region of the body, and that which best shows its com-
ponent elementary pieces. We observe four elements
on its tergum or dorsal surface, arranged in a single lon-
gitudinal series, the anterior of which is the prse-scutum ;
then follow the scutum, the scutellum, and the post-
scutellum. On the anterior aspect, or pectus, of the same
segment^ are seen the sternum single on the median plain,
and arranged in pairs on its sides, the paraptera, the epis-
ternum, and the epimera. These tegumentary parts, form-
ing the skeleton of insects, are thrown off about five
times during the larva state, and once from the chry-
salis before the animals assume their perfect adult
form.

ORGANS OF SUPPORT,

XII. Arachnida. — In those air-breathing entomoid ani-
mals, without metamorphosis, without wings, without an-
tennae, and with generally more than three pairs of legs,
which compose the class of aracknida, we observe a more
concentrated form of the segments, and a more consolid-
ated condition of the skeleton on the anterior portion of
the trunk than in the lower articulated classes. The seg-
ments of the head are anchylosed to those of the thorax,
so as to form a single division^ the cephalo-thorax, which
supports the organs of the senses, those of mastication,
and those of locomotion. The posterior division of the
trunk is the abdomen. In place of the long jointed antennee
on the anterior part of the head which we see in other
entomoid classes, there are generally a pair of lateral
pincers, or cheli, or a pair of flat and sharp-pointed piercing in-
struments at the sides of the head more suited to their
retired, cunning, watchful and carniverous habits. Their
mouth is provided with a labrum, a labium, a pair of man-
dibles, a pair of maxillae, and a pair of jointed palpi, often
extended like short feet. The general disposition and
form of the external parts in the animals of this class
are seen in this outline of the lycosa tarentula, (Fig. 17-)
where a represents
the cephalothorax,
and b the abdominal
portion of the trunk.
The eyes are simple
small isolated ocelli,
placed on the upper
and anterior portion
of the cephalotho-
rax, and varying in
number from two to
twelve ; they are of
very different sizes
in the same animal,
and variously dis-
posed in the differ-
ent species. Four
large eyes are seen at d, placed as at the angles of a square,
and four smaller eyes are seen behind them at d*, arranged

FIG

OR OSSEOUS SYSTEM. ',W

in a single transverse row. The long jointed palpi, at-
tached to the maxillae are seen at c, c, extended like
feet. In the four pairs of legs attached to the sides of
the cephalothorax, we observe the long femur /, extending
as in insects, from the trochanter e ; but we commonly
lind a smaller articulation or protibia interposed between
the femur and the tibial joint. In some there are only
six legs, as in insects. On the lower and anterior por-
tion of the abdomen, or sometimes on the posterior and
lower part of the cephalothorax, are placed the open-
ings into the; respiratory organs, which spiracula are
found to vary in number from two to eight, they
sometimes lead to pectinated simple air-sacs, and some-
times they open into extended and ramified tracheae.
Although these animals retain the form with which
they escaped from the ovum, they throw off periodically
their exterior covering, like the larvae of insects ; and like
the Crustacea, they reproduce entire legs when they have
been removed from the body. The last abdominal seg-
ment of the scorpion is in form of a sting, or ossified
tubular poison-duct, as we frequently see that segment in
insects.

XIII. Crustacea. — The crustaceous animals possess the
most solid form of the skeleton met with in the arti-
culated classes. It is found in the larger decapods to
contain nearly half its weight of carbonate of lime, and
there is also a considerable proportion of phosphate of
lime, with traces of magnesia, iron, and soda. These sub-
stances are exuded from the surface of the true skin,
along with a tough coagulable animal gluten, which con-
nects all their particles, and forms a thin varnish on the
surface. The colouring matter is generally beneath this
varnish, and on the exterior surface of the calcareous de-
posit, but sometimes it pervades the whole substance of
the shell. This extravascular crust forms hollow rings
to envelope the trunk, and tubular sheaths to cover ah* its
appendices, and these are periodically cast off and renewed
on the whole exterior of the body, to allow of the necessary
growth of the soft parts. The head and thorax are here
commonly united to form, as in arachnida, a cephalo-
thorax, which is covered above by a large continuous

40

ORGANS OF SUPPORT.

FIG. 18.

arched plate, or carapace, and supports the usual appen-
dices for mastication, sensation, and locomotion. There
are two strong mandibles, with their palpi attached to
them, at the sides of the mouth ; two pairs of slender
maxilke, also provided with palpi ; and exterior to these
there are three pairs of larger convertible maxillae, or feet-
jaws, with their attached jointed palpi, as seen in the
larger decapods, as in the astacus fluviatilis, represented in
Fig. 18. There are two pairs of antennae, the inner pair
(«, a,) of which are commonly divided at their free ex-
tremities, and the exterior larger pair (b, b,) have at their
proximal extremity, in their
broad expanded basilar joint,
the small circular prominent
opening of the vestibule or
ear, on each side, directed
downwards, sometimes co-
vered with a membrane, and
sometimes with a calcined
plate. The eyes (c, c,) are
compound, generally pedun-
culated and moveable, some-
times fixed or sessile. The
upper and anterior part of the
cephalo-thorax is occupied by
the stomach ( e, ) with its
strong muscular and osseous
apparatus, and containing
five teeth. In the middle of
the posterior part of the ce-
phalothorax is seen the pro-
jecting portion which covers
the heart (/). Towards the
sides are seen the two curved longitudinal lines on the
carapace, which mark the internal attachment of the mem-
branous diaphragm, which separates the respiratory cavities
on the sides from the abdominal viscera contained in the
middle portion of the cephalothorax. The anchylosed
segments of the cephalothorax send inwards and upwards
numerous vertical thin calcified plates, which give attach-
ment to the muscles of the haunches, and by meeting

OR OSSEOUS SYSTEM. 41

above, they form an inferior median canal to protect the
nerves and ganglia of this part of the trunk. There are
most frequently five pairs of legs, which like the exte-
rior pairs of jaws, have branchiae attached to their bases.
In the female of the decapods, we observe the round
opening of the vulva in each haunch of the middle or
third pair of legs ; and in the male the open sheath of
the penis is seen in each haunch of the fifth or posterior
pair of legs. The front pair of legs are generally the most
powerful, and have the last tarsal joint (/, /,) inserted high,
and opposable to the penultimate articulation (k, k). The
segments of the post-abdomen (m, n,) are moveable, and
sometimes extend backwards in a line with the cephalo-
thorax, or are short, and fold in beneath that part. Below
the middle of the last small segment, is the opening of
the anus, and the two last segments of the post abdo-
men have their lateral appendices (p, o,) in form of flat
expanded caudal plates for swimming and for protecting,
when folded inwards, the delicate inferior parts of the
trunk, or the ova in the female. On the lower surface
of the post-abdominal segments are attached the false
feet, to which the ova are affixed after their discharge
from the two ovaries, and from which the branchiae are
commonly suspended in the inferior orders of Crustacea.
The chief differences in the skeletons of this class arise
from the size, and the forms assumed by the convertible
lateral appendices of the segments, and the extent to
which the segments are developed or anchylosed. This
solid crust, forming the skeleton of Crustacea, is thrown off
periodically from every part of the trunk and even its most
delicate appendices. This is done by the animal first de-
taching the cutis and muscles from the inner surface of
the old shell, then excreting from the surface of the cutis
a new layer of epidermis, then a deposit of colouring
matter, and within this the calcareous materials of the new
shell, the old having been broken off in detached pieces
in succession from all parts of the body.

ORGANS OF SUPPORT

FOURTH SECTION.

Organs of Support in the Cyclo-Gangliated, or Molluscous

Classes.

THE external skeletons of the molluscous animals are
consolidated by the carbonate of lime, without the phos-
phate which is common in the other great divisions of
the animal kingdom. This earthy matter is secreted from
the skin in successive layers mixed Avith a glutinous co-
agulable animal matter, which gives firmness and tenacity
to the whole mass, and the skeletons are not exuviable,
as in the other articulated classes. From the low condi-
tion of all the organs of relation in the molluscous ani-
mals, they are less able to perceive, or avert, or escape
from danger than the free and active articulata, and they
accumulate and preserve ah1 the successive layers of their
rocky covering permanently in contact with their surface.
The sheUs of these animals are remarkable for their want
of symmetry on the two sides of the body, the want of
unity in their plan of formation, and their inconstancy in
animals of similar structure.

XIV. Tunicata. — The tunicated animals have no external
shell nor internal solid parts, but are covered with a tough
elastic homogeneous tunic, in form of an enveloping sac,
with a respiratory and an anal orifice. This exterior sac
is the analogue of the valves of conchifera, and has the
muscular fibres of the lining mantle inserted into its
inner surface, as in the shells of bivalvia. It presents
every variety of colour and consistence in the different
species, and has often a coating of extraneous particles
of shells or gravel adhering to its outer surface. Some-
times it extends at its lower part into numerous short
processes, or into a long peduncle to attach the body to
rock or other hard substances. This exterior cartilaginous

OR OSSEOUS SYSTEM. 43

skeleton is most dense, thick, and opaque in the larger
isolated forms of ascidise, and is most soft, delicate and
transparent in the aggregated or compound forms of tuni-
cata. Two very dissimilar kinds of tunicated animals are
represented in Fig. 19, where 1, is the cynthia papillata,
and 2, the pyrosoma gigantium ; the first is permanently
fixed, like most of the animals of this class, FIG. 19.
and the second is an aggregate mass of nu-
merous individuals which floats by their com-
bined movements freely through the sea. In
the cynthia we observe the transparent tough
cartilaginous tunic forming a sac, which is
entirely closed except at the respiratory orifice
(«,) which admits the currents of water brought
by the vibratile cilia of the gills, and the
vent (£,) by which the currents escape from
the respiratory cavity. The lining muscular
tunic of the mantle is most firmly united to the
sac around these two orifices, where there are
also distinct sphincter muscles. At the bottom of the sac
is seen the stomach (c,) the great branchial vein (d,) which
dilates below the stomach to form a heart, the convoluted
intestine (e,) the ovary (fy) and the liver (#,) enveloping the
pyloric end of the stomach. The pyrosoma, Fig. 19. 2, is
a long tube closed at the upper end (a,) open at the lower
extremity (#,) and composed of innumerable distinct in-
dividuals (c, €,) which are similarly organized internally to
the cynthia, but have their respiratory orifices on the
sides of the long projecting external papillae (c, c,) and the
vents or anal orifices of all the separate individuals open-
ing into the interior of the tube ; so that by the act of
respiration alone, this transparent and luminous tube is
carried up through the still seas. The exterior tunics of
these component animals are thin, soft, transparent, and
of a bluish white colour, and are the only parts by which
they appear to be united together. In some of the com-
pound forms of these tunicata, however, the enveloping
tunic has a third opening, which admits the currents of
respiration or circulation to extend from one individual to
another.

XV. Conchifera. — The shells of these animals consist

44 ORGANS OF^ SUPPORT,

generally of two moveable pieces or valves placed on the
exterior of the body, and connected together by ligaments
and muscles. These valves are composed of carbonate
of lime mixed with an albuminous coagulable matter,
which is secreted chiefly by the glandular pores on the
exterior surface of the lining mantle. The valves grow
by the successive addition of larger layers to their inner
surface, and the limits of these superadded laminae are
commonly marked by distinct striae on the outer surface
of the shells. As the calcareous laminae are cast upon
the surface of the mantle which envelopes all the soft
parts of the body, the shells vary in their form ac-
cording to the shape of the enclosed animal, and es-
pecially of the secreting glandular portion of their lining
membrane. The exterior surface of the valves is covered
with a thin layer of the same albuminous matter which
unites the particles of the shell : this forms a dense and
tough varnish or epidermis, which protects the colouring
matter immediately beneath it, and the whole texture
of the solid layers. Although most of the conchifera
are bivalved, some, as the pholades, possess small sup-
plementary pieces at the hinge of the valves, and are
thence called multivalves. The relations of these cal-
careous shells to the parts of the enclosed animal will be
perceived by the annexed sketch of the common muscle,
mytilus edulis, Fig. 20, where the soft parts are repre-
sented as attached to the right valve (0,) and the left
valve (by) is opened and folded upwards. The ligament (c,)
connects the two valves to- FIG 20.

gether, and tends by its
elasticity to open them to
a limited extent. The liga-
ment of bivalvia grows like
the shell by successive in-
ternal layers, and is placed
at the hinge, where there
are generally processes
of the shell termed teeth,
which lock into each other when the valves are closed.
The position of the stomach (d,) with the short oesophagus,
and the two pairs of long labial tentacula (e9) mark the

OR OSSEOUS SYSTEM. 45

anterior part of the shell. The muscular foot (f}) extends
from the ventral surface of the body, where we see also
the byssus (g,) by which the delicate mytiloid shells are
fixed to solid bodies. The respiratory orifice (^,) is placed
at the most open part of the shell, and near this is the
vent (i,) by which the respired water and the excretions
are discharged. The rectum (/<:,) opens near to the vent
after perforating the ventricle of the heart. The large lobes
of the liver (/,) envelope the turns of the intestine, and the
pyloric portion of the stomach . On the ventral or inferior
surface of the abdomen, is the respiratory cavity in which
are seen the four long pectinated laminae of the gills (m,)
and towards the posterior part of the shell is the strong
adductor muscle (n,) by which the valves are drawn forcibly
together when the animal is alarmed. The ovary (o,)
fills a great portion of the posterior and upper part of
the shell. From this position of the soft parts within the
valves, we perceive the anterior part (d9) of the shell to
be that next the mouth (e,) and the posterior part (b,)
to be that next to the anus (&,) and the vent. The
dorsal margin (a,) of the valves is that next to the liver
and ovary, and the ventral part is that which encloses
the respiratory gills (m) ; we also observe from these
parts the reason for designating the one valve («,) the
right, and the other (b,) the left, as we term the lateral
parts of the skeleton in higher animals. As these shells
of conchifera are extravascular exudations from the surface
of the mantle, they are incapable of growth but by su-
perposition of new parts, and the various spines and
lamince, which are so often developed on their exterior
surface are mere depositions from the edge of the mantle,
and indicate former positions of the margin of the valves.
The ordinary direction in which these processes of the
shells are formed is seen in the long narrow projecting
laminae of the spondylus gcederopus, (Fig. 21. 1 .) where
they are arranged, with great symmetry, in rows which
are regular both in the longitudinal and transverse direc-
tions, and indicate the positions of the processes of the
mantle which excreted them. The adductor muscle of the
valves leaves a depression on the inner surface of each,
which marks its place of insertion and its form, and which

ORGANS OF SUPPORT,

FIG. 21.

is termed the muscular
impression. When the
shells have a short and
round form, as the spon-
dylus, (Fig. 21. 1.) the
anomia, (Fig. 21. 2.) the
ostrea, there is commonly
but one adductor muscle,
and one muscular im-
pression, and these are
monomyaria ; when the valves have a more lengthened form, as
the area, (Fig. 21. 3.) the tellina, and many others, there are at
least two muscles and two muscular impressions, and these
form the dimyaria. The hinge of the valves is supported
by the ligament, and formed by the teeth which afford
the most obvious, regular and constant characters for the
discrimination of these shells. The teeth are seen in the
figure of the area barbata, (Fig. 21. 3. #,) projecting from
the whole extent of the hinge, and the two muscular im-
pressions are seen in the interior towards the ends of
the valves. The epidermic filaments which give a barbed
appearance to the surface of this and many other shells,
are merely uncalcified marginal projections of the albumi-
nous matter which pervades all the successive layers of
the valves. In the anomia, (Fig. 2 1 . 2, and 2*,) there is a
circular perforation (a,) in the flat valve, through which the
central portion of the adductor muscle passes to be inserted
into a third small circular calcareous piece, which is perma-
nently fixed to some extraneous solid body. The pe-
riphery of the adductor muscle is inserted into the flat
valve around the margin of the hole ; so that the muscle
here secretes the calcareous matter of the small fixed
opercular piece into which it is inserted, as the muscular
foot of a gasteropod secretes the calcareous operculum
which covers the orifice of its shell. There is a great
difference in the extent to which the right and left valves
resemble or differ from each other. Some are equivalve,
or have their two valves alike in form, as the cardium,
the mactra, the solen, the pholas ; some, as the tridacna,
are sub-equivalve, or have them nearly alike ; and others
as the anomia, the terebratula, the gryphcea, are inequivalve,

OR OSSEOUS SYSTEM. 47

or have the valves very unlike each other. The waved
disposition of the calcareous particles in the layers of
these shells, often gives them a beautiful nacreous lustre,
especially in the more pellucid internal layers, which
constitutes the mother-of-pearl; and when spherical glo-
bules of this matter, composed of concentric layers en-
veloping some extraneous particle, are secreted by the
mantle and unconnected with the shell, they form the rich
pearls of commerce. The edge of the mantle sometimes
extends itself beyond the margin of the valves, so as to
touch some extraneous body, and by their exuding the
usual calcareous and albuminous matter, it causes the con-
tiguous surfaces to become cemented together ; in this
manner the oyster glues its shell immovably to the rocks at
the bottom of the sea.

XVI. Gasteropoda. — The shells of the gasteropods are
composed, like other molluscous shells, of carbonate of lime
with animal matter. They are extravascular, and generally ex-
creted from the outer surface of the skin in the form of hol-
low unilocular laminated cones, which envelope the exterior
of the animal, and they grow by the addition of successive
layers to their inner surface. They take the form of the exterior
of the body, especially of the mantle, and they are perma-
nently connected with the muscular system. The laminae
which compose these shells have generally a fibrous struc-
ture, and the parallel fibres which form them have a zig-
zag direction nearly vertical to the surfaces of the layers.
They are generally covered with a thin epidermic varnish,
which protects the colouring matter of the surface ; their
outer layers are commonly more loose, opaque and porous
than the dense, pellucid, glassy layers of the interior, and
they are often provided with an operculum which is some-
times horny, sometimes calcareous, and is permanently
attached to the muscular foot which secretes it. Many
gasteropods have no shell, as the scyllaea, the tritonia, and
the doris ; some have a thin calcareous lamina within the
skin of the back, as the aplysia, and some have an ex-
ternal shell so small as to cover only a portion of the
animal's surface, as the testacella, the cryptostoma and the
carinaria. The shell is perforated in the haliotis the fissu-
rella and the emarginula, and it is composed of eight trans-

48 ORGANS OF SUPPORT,

verse parallel imbricated pieces in the chiton. It is however
most generally in form of a hollow cone, wide and open at
the base, closed at the apex, and more or less convoluted
or spiral. This cone has been considered as analogous to
the two valves of the conchifera united together. It is
short, wide, and nearly straight in the patella, more length-
ened, narrow, and slightly bent in the dentalium, a little
twisted in the crepidula, the haliotis, and the capulus, and
it revolves round its apex in a single plane in the planorbis
and some of the helices, forming a flat disk like an ammonite.
In most of the gasteropodous shells, the plane of revolution is
constantly changing during growth, so as to cause the cone
to turn to the right side, and to revolve in a spiral manner
round an axis or pillar called the columella of the shell. This
spiral twist appears to be the result of the descent of the
foot over the columella, and the influence of the great
centres of the circulating and respiratory systems on the
left side of the body ; so that the apex of the spire is on the
right side of the animal, and the canal of the shell for
respiration is on its left side. In a few reverse shells, where
the spire lies to the left side of the aperture, the circulating
and respiratory organs are found transposed to the right side
of the animal. The general disposition of the soft parts in
the cavity of a spiral unilocular univalve shell will be seen
by this diagram of the common buccinum undatwn, Fig. 22,
where the animal is represented as creeping upon its ex-
panded foot. The upper and back part of the foot supports
the operculum (m,) which

closes up the aperture of FIG- 2~-

the shell when the ani-
mal is retracted. The
adductor muscle (b,) is at-
tached to the columella,
and is the only part of
the body adhering to the
shell. The mantle (i, g, «,
ky e, /,) is open in front,
lines the aperture of the shell, secretes the calcareous layers,
and covers the respiratory organs (g.) The muscular funnel
(i,) extends through the canal on the left side of the aper-
ture of the shell, and leads the currents to the two branchiae

OR OSSEOUS SYSTEM. 4J>

(g,) at the base of which are the auricle and the ventricle (h.)
On the right side, within the mantle, is seen the anal orifice
(£,) and the male organ (/.) The head (e?,)- provided with
two fleshy tentacula, with little black eyes at their base, is
extended from a short muscular neck, and projects from
the mouth a long powerful proboscis, furnished at its ex-
tremity with sharp recurved conical horny teeth (e.) The
closed and tapering part of the shell is occupied by the
turns of the liver and testicle in the male, or the liver
and ovary of the female, which organs accompany each
other to the apex of the spine. When the animal creeps
forwards, covered with its shell, it extends its foot, its head
and its neck from the aperture in such a mariner that
the upper lip of the shell lies over the free edge of the
mantle above the head, and the foot extends over the
lower lip, or the columella. The columella, or pillar, is the
axis of revolution, and is sometimes perforated through
its interior with a cavity called the umbilicus, which has
no communication with the cavity of the cone contain-
ing the animal, but tends to lighten massive shells,
where the wide revolutions are at a distance from each
other.

As the calcareous layers of the shell are chiefly secreted
and formed by the anterior glandular portion of the
mantle, which is a part most liable to vary in its form
according to the age and the season, the chief differences
in gasteropodous shells are those produced by the diver-
sified forms of the upper lip. In the young animals
the upper lip of the shell is generally quite even and
smooth, and corresponds with the simple condition of
the margin of the mantle, but at maturity this upper
secreting portion of the mantle often assumes a highly deve-
loped, folded, or fimbriated edge, and the upper lip of
the shell takes a similar form. In the young strombus
gigas, the upper lip is quite even and uniform with the
ordinary turns of the cone, but at maturity it expands,
thickens, folds backwards, and becomes eifuse. The shell
of the pterocera scorpio, in its young state, (Fig. 23. 3,)
has the ordinary simple thin, incurvated margin of other
growing shells ; the canal, (Fig. 23. 3. &,) appears short
and truncated, and the apex of the spire (Fig. 23. 3. «,) pro-

PART I. E

50 ORGANS OF SUPPORT,

jects, naked and acute,
from the opposite end of
the shell. But as it ap-
proaches maturity, (Fig.
23. 4,) the upper lip ex-
pands, becomes effuse,
extends to the right and
to the left side, so as to conceal the apex of the spire, (Fig.
23. 4. a,) and lengthen the canal (Fig. 23. 4. £,) and it
shoots upwards several processes which are at first thin
and hollow open canals, (Fig. 23. U c,) and are gradually
filled up with successive layers, and converted into solid
spines, which entirely change the appearance of the shell.
These changes of the upper lip take place periodically,
and at regular intervals during the development of many
shells, as in the murices, thus producing transverse rows
of variously formed processes from the outer surface of all
the turns of the cone. The young and the adult shells
of the cypraa are scarcely recognisable as belonging
to the same individual, from the changes of form they
experience at maturity. The form of the young shell of
the cypraa exanthema is represented in Fig. 23. 2, where
the aperture is wide, the upper lip thin and even, the
canal (b) projecting, and the apex (a) of the spire extended
and free. But in the adult form (Fig. 23. 1,) of the same
shell the aperture is contracted, narrow and serrated, the
upper lip is thickened and rounded backwards, the canal is
converted into a groove, and the whole of the spire is
covered and concealed. These adult changes in the cypraea
are produced by the extension of the sides of the mantle
over the upper and lower lips of the shell, and now
the new layers are added to the exterior surface, as if
it were an internal shell, and the line of junction of the
two enveloping folds of the mantle is marked by a trans-
verse discoloration or groove on the exterior of the shell
along the whole of its convex dorsal part. By this ad-
dition of new layers to its whole exterior surface, the
adult cyprsea has a smooth, glistening, naked and variously
coloured exterior, like the interior surface of most other
shells, and can present no rough epidemic covering when
arrived at that state. In the cypraea, the dolium, the

OR OSSEOUS SYSTEM. 51

and many others, the interior surface of the shell has
experienced no change by being long in contact with the
living soft parts of the contained animal ; the grooves,
the striae, the prominences, and even the colouring mat-
ters which were upon the outer exposed surface in the
young condition of the shell, still preserve in the adult
state, their primitive appearance and integrity throughout
the whole interior of the revolutions. These have grown
by the revolution of the upper lip around the columella ;
but many others add new layers also to the inferior or
columellar lip during their growth, thus covering over
the superficial external* layers on the left side of the
revolutions, and generally presenting strong parietes and
a thick and solid columella, as in the strombus gig as. In
many forms, however, as in the cones and olives, where the
widely expanded upper lip sufficiently covers and protects
the smaller revolutions, the total weight of the shell is
diminished without weakening its exposed part by carrying
forward the calcareous matter from the inner first formed
concealed revolutions, and depositing it upon the exterior
surface of the last or outer turn of the shell which alone
is exposed to danger from external causes. The vertical,
zig-zag, parallel fibres composing the thick parietes of
these shells is distinctly preserved in their fossilized re-
mains. The hybernating gasteropods, as the snails, which
want an operculum, close up the aperture of their shell,
when they retire to their winter slumber, with a thick
deposit of calcareous matter, called an cpiphragma, which
is not connected with the muscular foot, like the true
operculum of other shells, but only with the aperture of
the cone. The operculum is a permanent part attached
to the contained animal, and the epiphragrna is a de-
ciduous part attached only to the orifice of the shell.

XVII. Pteropoda. — As the pteropodous animals are not
provided with a muscular foot to creep upon a solid sur-
face, but are all organized to swim freely through the
sea by means of muscular expansions like fins, they are
never encumbered with a massive or heavy skeleton.
Their skeleton, when present, is generally external, extra-
vascular, thin, pellucid, horny, or vitreous ; it is univalve,
unilocular. of various forms, generally without a spiral twist,

K 2

52 ORGANS OF SUPPORT,

capable of enveloping the whole body, and it is destitute
of an operculum, as in most of the light shelled floating
gasteropods, and the swimming testaceous cephalopods.
The annexed figure of the cymbulia of Peron (Fig. 24,)
represents a typical form of a testaceous pteropod from
the Mediterranean, as swimming FIG 94

with its expanded fins ( #, a. )
which support the branchiae, and
covered below with its thin,
lengthened, fusiform, carinated
and serrated shell (b.) The up-
per part of its body (c) between
its muscular and highly vascular
fins (a, a,) appears to present two
tentacula, two eyes, and an ex-
tended proboscis. The thin dia-
phanous, conical shell of the
spiratella is twisted spirally on itself, and with its apex
on the left side, like a turrilite ; the delicate pellucid
shell of the hyalea enveloping the round body of the
animal is tricuspid below ; in the shell of the cuvieria
columnella there is a partially formed chamber at the
lower closed extremity ; and in the creseis virgula the
shell has a long, straight, conical form, common to the
belemnites, baculites, orthoceratites, and many other extinct
cephalopods.

XVIII. Cephalopoda. — In this highest of the mollus-
cous, and of all the invertebrated classes, we trace the
gradual disappearance of the external unorganized shells
of the hivrertebrated tribes, and the commencement of
the internal organized bones of the vertebrata. The shells
are sometimes external, as in the nautilus, and sometimes
internal, as in the sepia, and they are consolidated by the
carbonate of lime, as in the lower molluscous classes.
They are almost always polythalamous, and without an
operculum. Many of the extinct shells have the form of
straight cones, as belemnites, baculites, and orthoceratites ;
some are curved, as hamites and scaphites, some are con-
voluted and orbicular, as the spirula, the nautilus, and
the ammonites, and some, as the turrulites, are spirally
twisted, like the lurbinated shells of gasteropods. The

OR OSSEOUS SYSTEM.

53

FIG. 25.

several chambers of these polythalamous cones communi-
cate with each other, sometimes by means of a prolonged
calcareous syphon, as in the spirula and nautilus, some-
times by one or more simple foramina in the partitions.
As the cephalopods do not creep upon a muscular foot,
like the slow-moving gasteropods, but for the most part
swim freely through the sea, their shells are thin and
light, and sometimes xconsist of simple straight laminae
unconsolidated by calcareous matter. The form and struc-
ture of the external polythalamous shells of the cepha-
lopods is seen in the section of the nautilus pompilius,
represented in Fig. 25. 2, where (0,) shows the interior of
the last formed chamber, in which the animal is fixed
by two muscles of attachment. The syphons (£,) by which
all the posterior chambers (c,) communicate with each
other, are seen to extend for a short
distance, tapering from before back-
wards, into each of the succeeding
chambers. These separated partitions
and chambers of this convoluted cone
have nearly the same relations to
each other and to the contained ani-
mal, as the successive contiguous
layers of the convoluted shell of a
gasteropod, and they are formed in
the same manner by periodical exuda-
tions of calcareous matter from the
exterior surface of the mantle. In
the spirula., the long calcareous syphon
of each septum extends through the
whole of the chamber, and into the commencement of
the next succeeding syphon ; so that there is a continuous
calcareous tube passing through the whole shell on the
inner concave side of its convolutions. The shell of the
sepia, (Fig. 25. 1. 0,) affords an example of an internal
shell belonging to this class. It is contained within the
substance of the dorsal part of the mantle, and consists
of numerous nearly flat layers, placed within each other,
the first formed being at the outer part and posterior termi-
nation of the shell, and the succeeding new layers ex-
tending always more forwards than the edges of the old.

54

ORGANS OF SUPPORT,

These compressed layers are connected together by in-
numerable, very mimits tubular fibres ; so that there is
a great analogy between the structure of this internal
laminated shell, and the external polythalamous shells,
where the successive laminae are more detached. In the
figure of the sepia (Fig. 25. 1,) the mantle has been cut
open at («,) to show the position and the successive lay-
ers of the shell. The lateral muscular fins (#,) by which
the animal swims, extend along the whole sides of the
abdomen, the funnel (c,) for the passage of all the ex-
cretions, extends from the anterior part of the open
sac. In the centre of the arms or feet, radiating from
the head, is placed the mouth (d,) provided with two
dense and sharp mandibles, and the two long muscular
tentacula (e,) extend from the fore part of the head (/,)
between the first and second pairs of feet* In many of
the naked cephalopods the dorsal shell contained within
the substance of the mantle is destitute of calcareous
matter, and reduced to a mere thin, flexible, transpa-
rent, cartilagenous lamina, as we find in the loligo, the
sepiola, the loligopsis, and others. These uncalcified shells
are contained in a dorsal sac of the mantle, like the cal-
careous laminated shell of the sepia. The position of
the thin, stiliform, cartilaginous lamina in the lack of the
sepiola vulgaris, is seen in (Fig. 26. 1. «,) where the co-
loured covering and skin have been removed to show
the situation of the hard

parts and the superficial FIG« 2e-

muscles. The dorsal la-
mina («,) is here very
small, flexible and short
from the great mobility
of the muscular part,
which forms its sheath.
In the loligopsis guttata,
the dorsal lamina (Fig.

26. 2,) extends the whole length of the back of the man-
tle to the point of the tail, being spear-shaped, with very
thin flexible edges, especially at its broadest middle part.
That of the loligo sagittata, (Fig. 26. 3,) is more broad
and leaf-shaped, and extends, as most of the other soft,

OR OSSEOUS SYSTEM. 55

cartilaginous, internal shells, from the upper edge of the
mantle to the point of the tail, being contained loose in
a closed dorsal sac of the mantle. In the octopus, the
dorsal lamina is wanting, but there are two small lateral
stiliform, loose, cartilaginous pieces contained in the sub-
stance of the mantle, as the median shell in other
species.

In this highly complicated class of molluscous ani-
mals, which approach so near to the cartilaginous fishes
in the structure of many of their internal parts, we already
find several internal rudimentary pieces of an organized
cartilaginous skeleton. The brain encompassing the eeso-
phagus is enclosed in a large curved cranical .bone, which
forms also part of the orbits on each side, contains the
cavities of the ears, and has numerous muscles inserted
into it. Other cartilaginous, organized pieces are seen
extending downwards from the back part the skull, like
the rudiment of a vertebral column. Two clavicular
pieces in front unite to the first rudiments of a sternum,
and attach the sides of the mantle to the trunk, and
there are generally two scapular pieces, more or less firm,
extending along the sides to which the muscles of the
lateral fins are attached. These two scapular pieces are
seen in the sepiola vulgaris, (Fig. 26. 1.) b, where they
support the arms (c, c}) and are freely moveable on the
back, like the scapulae of vertebrata. We also perceive
muscles inserted into the strong upper and lower man-
dibles (Fig. 26. 5. 0, b,) of these animals, formed like the
bills of a parrot. The suckers of the arms, (Fig. 26. 4.
b, c,) whether sessile (c,) or pedunculated (b}) have their
inner circular margins supported, each by a firm cartila-
ginous circular plate («,) with minute sharp teeth extend-
ing inwards from one of its sides, by which the action of
these prehensile organs is aided. In the onychia, there
are dense, sharp, curved, conical spines placed in these
suckers, like the conical teeth disposed on the oral disk
of lampreys, among the lowest of the cartilaginous
fishes.

5(> ORGANS OF SUPPORT,

FIFTH SECTION.

Organs of Support in the Spini- Cerebrated or Vertebrated

Classes.

In the lowest vertebrated animals we still find traces
of the external unorganized shells of inferior classes, in
the form of calcareous scales in fishes, and of horny
plates in many reptiles ; but these are generally reduced
to small detached pieces, and do not serve as organs of
support. The organs of support in the vertebrated classes
are placed within the soft parts, so that these animals
are more intimately related to the properties of surround-
ing objects and outward nature, by the sensibility and
delicacy of their surface. Their skeleton being internal,
it is not exuviable in a mass, and as it cannot grow
and preserve its proportions by the simple addition of
layers to its surface, it is organized or permeated in all
directions by vessels which take "away and replace its
materials atom by atom. The phosphate of lime, which
forms the chief consolidating earth, increases in its pro-
portion to the gelatin as we ascend through the verte-
brated classes ; so that the bones of the lowest fishes
are soft, flexible, and cartilaginous ; those of hot-blooded
classes are of great density and strength, and those of
reptiles possess intermediate properties. The bones have
a fibrous structure, which is the best adapted for the
transmission of minute vessels through their texture.
They form solid levers for the motions of the body,
and cavities to protect its viscera. The most constant
and the first formed part of the skeleton is the verte-
bral column, which is composed of moveable vertebrae,
each of which consists of several elements that are found
most isolated and distinct in the lowest classes, and in
the embryo state of the highest. The elements which

OR OSSEOUS SYSTEM. 57

appear most constant and distinct in the composition of
a vertebra are the round central body, or cyclo-vertebral
element, the two superior laminae or peri-vertebral ele-
ments which encompass the spinal chords, the two por-
tions of the superior spinous process, or the epi-vertebral
elements, the two inferior laminae, or para vertebral ele-
ments, which form a cavity for the blood-vessels, and
the two portions of the inferior spinous process, or the
cata-vertebral elements. The most frequent position of
these nine component elements of a perfect vertebra is
shown in the annexed diagram, (Fig. 27.) where (a,) repre-
sents the spinal cord protected by the two peri-vertebral

FIG. 27.

-vertebral
elements.

pieces ; (b,) is the common position of the artery, and
(c}) of the vein beneath the bodies of the vertebrae in
most parts of the column, and these are embraced by
the two para- vertebral elements. The cyclo-vertebral ele-
ments are tubular in the articulated classes of animals
where they envelope the whole trunk as hollow seg-
ments, they are nearly solid to their centre, and present
two concave surfaces in fishes ; they are convexo-concave
in reptiles, and have flat surfaces in mammalia. They
are the most constant and typical parts of the vertebral
column. The other vertebral elements vary their forms
and positions chiefly according to the dimensions of the
organs they embrace, and the extent of surface required
for muscular attachment ; consequently they vary much
in different parts of the same column, and in the ske-
letons of different classes. Three very different positions
of the same vertebral elements are represented in this

58

ORGANS OF SUPPORT,

diagram (Fig. 28,) where A shows their most common
positions with relation to each other in the caudal por-
tion of the skeleton of an osseous fish where they are de-
signed to give great extension for the attachment of the
powerful lateral muscles which move the tail. The body
of the vertebra, or cyclo-vertebral element (a,) supports
the two superior laminae or peri- vertebral elements (b, b,)
which early unite above to form the small foramer for
the spiral cord (e) ; and beyond their termination we
observe the interspinous bone (c,) and the ray (d,) of the

FIG. 28.

external fin, which are the two epi-vertebral elements
placed in a vertical line. The analogous elements are
seen on the lower part of the vertebra, where the two
inferior laminae (/,/,) or para-vertebral elements, form a
larger foramen for the lodgment of the great continua-
tion of the aorta (i,) above, and the vena cava (&,) below.
The inferior interspinous bone (g,) and the ray (h,) of
the external fin, are the two cata-vertebral elements placed
in a vertical line, like the epi-vertebrals above. These
vertebral elements often assume, in the region of the
abdomen in fishes, the position marked in the diagram
B, of Fig. 28, where the superior elements remain as in
Fig. A, but the inferior laminae (/,/,) or para-vertebrals,
are stretched out in a horizontal direction, and have the
two cata-vertebrals (g,y,) extended from their ends in

OR OSSEOUS SYSTEM. 59

form of a pair of ribs to encompass the organs of this
part of the trunk. The vertebral elements situate above
the body of the bone expand in the region of the head
in the same manner as we here see those below the
cyclo-vertebral element in the region of the abdomen ;
and this they do in order to encompass the soft parts
contained in the cavity of the skull, and in the face.
Another position of these vertebral pieces, which is
common in the caudal region of the column in higher
classes, especially among the long-tailed reptiles, and in
cetaceous mammalia, is represented in the diagram C of
Fig. 28, where we observe the large foramen for the
nervous columns (/,) above the cyclo-vertebral element (a,)
requiring the whole extent of the two peri-vertebrals (b, b,)
for its formation, and the strong superior spinous pro-
cess is composed of the two epi-vertebrals placed side
by side. In the lower part of the same vertebra the
inferior laminae extend outwards to form strong trans-
verse processes (/,/,) and an inferior spinous process,
and an inferior foramen for the aorta (i,) and the vena
cava (#,) are formed by the approximation of the two
cata-vertebrals ( g, gj) which show their displacement by
being generally thrust backwards between two cyclo-ver-
tebral elements. When the two cata- vertebral elements are
extended outwards to form ribs in fishes, we very often
find them bifurcated, as represented in Fig. 28. B, g, g<
The general form of the vertebral elements is very much
modified and varied in different parts of the column by
the shape and magnitude of the parts these elements
embrace, and the extent of surface for muscular attach-
ments which they require to present. The epi- and peri-
vertebrals are most expanded in the skull and the sacrum,
and the para- and cata-vertebrals, where they embrace
the viscera of the trunk. The appearance of the entire
skeleton of vertebrated animals is greatly varied by the
difference in the position of the ribs, or of that part of
the column where the para- and cata-vertebral elements
are extended over the great viscera of the trunk. In
fishes, as shown in the annexed figure, (Fig. 29. 3,) and
in cetaceous mammalia, the fixed, ribbed, and thoracic
part of the column («,) is placed near its anterior extre-

GO

ORGANS OF SUPPORT.

mity, and all the posterior portion is freely moveable, to
give impulse to the tail in swimming. In birds, (Fig. 29. 2,)
where the head and neck are used as a hand and arm,
for all prehensile pur-
poses, the fixed thora-
cic portion (a,) of the
column is placed near to
its posterior extremity,
and the anterior portion
is free for extensive mo-
tion. Most quadrupeds
(Fig. 29. 1,) and reptiles,
balanced on two pairs of
extremities, hold an in-
termediate place, and have the ribbed and solid portion
( a, ) of their trunk placed near the middle of the
column.

XIX. Pisces. — The bones of fishes contain less gelatine,
and a larger proportion of water than those of higher
classes, and are less dense and compact in their texture.
The soft bones of cartilaginous fishes yield more water
than those of osseous fishes, and they contain the soluble
salts of soda, the chloruret, the sub-carbonate, and the
sulphate, while the more dense bones of osseous fishes
are strengthened, like those of higher classes, with the
more insoluble phosphates. The bones of fishes resemble
those of the embryos of higher animals, not only in their
soft, gelatinous, or cartilaginous character, but also in
the isolated condition of all the elements, or centres of
ossification, of the more complicated bones, especially of
the head. The skeleton of fishes consists almost entirely
of the vertebral column, from the extremity of the face
to the end of the tail, like that of the embryos of mam-
malia at a corresponding stage of their development. The
bodies of the vertebrae are composed of concentric layers,
as represented in Fig. 30. 0, which are broadest at the
circumference, and become narrower as they approach the
centre, where there is commonly a small hole (Fig. 30. b, b.)
These bodies are therefore concave both on their anterior
and posterior surfaces, and when applied to each other,
they leave large intevertebral spaces between them, which

OR OSSEOUS SYSTEM. 6'1

are filled up each with a short sac of a gelatinous thin
fluid, as seen in Fig. 30. C. c, so that these vertebrae
play freely over the surface of so many
elastic interposed balls. The bodies of the
vertebrae are the elements first developed
in the animal kingdom. They are the
most important, as means of support ;
they are the parts most developed in the
vertebrae of fishes, and the skeletons of
the lowest cartilaginous species, are com-
posed almost solely of these elements.
Even in the sharks, the other elements
are remarkably small and are not ajichy-
losed to the bodies of the vertebrae ; so that by macera-
tion they fall off, and leave deep depressions ( Fig. 30.
B, c.) in the sides of the cyclo-vertebral elements where
they were attached. By the great size of the central
passage in the bodies of the vertebrae of many cartila-
ginous fishes, the inter-vertebral substances communicate
with each other, and form a continuous elastic beaded
chord passing through the whole vertebral column, as in
the lampreys. The component elements of the vertebrae
of fishes are disposed in such a manner as to give great
vertical extension to the trunk, and thus to form a broad
lateral surface to strike the water in their horizontal mode
of progression. As the spinal chord is small, the upper
vertebral foramen is also small in fishes, and the two
superior laminae therefore soon meet to form a spinous
process by their junction, as seen in the skeleton of the
perch, (Fig. 31. c,c, c.) Along the greater portion of the
back, we observe the two epi-vertebral elements (Fig. 3 1 .
74, 75,) placed end to end in a vertical direction, the
short inferior portion forming the interspinous bone. (74,)
and the more slender superior portion extending from the
trunk and covered with a prolonged fold of the skin,
forms a ray (75,) of the dorsal fin, and thus are con-
structed all the dorsal fins placed along the middle of
the back from the head to the tail. The same two ele-
ments in several of the last cocygeal vertebrae, pass back-
wards in a very oblique manner, and constitute the cau-
dal fin (70, 78.) The corresponding elements below the

ORGANS OF SUPPORT,

FIG. 31.

bodies of the vertebrae occupy the same relative position
wherever there are anal fins developed between the tail
and the anus, as at a, J2. The inferior foramen of the
vertebrae, for the blood vessel is larger than that above
for the spinal chord, and it widens much in the pelvic
region (83,) in order to embrace the posterior parts of
the urinary and genital organs. The elements of the
cocygeal vertebras of fishes being thus extended upwards
and downwards, they present no transverse processes in
that region to impede the lateral motions of the tail, and
their nervous and vascular systems are here protected
from injury during the violent actions of that part of the body.
In the region of the abdomen the inferior interspinous
bones and the rays are placed at the ends of the trans-
verse processes, and extended more or less round the
viscera, as ribs (72,) which often present a bifurcated ap-
pearance by their sending a long process (73,) outwards
and backwards. The ribs are often merely minute epiphyses
at the ends of the transverse processes, as in the rays
and sharks, and they are continued forwards along the
vertebral column to the atlas ; so that there are no dis-
tinct free cervical vertebras. The bodies of the cranical
vertebrae continue along the floor of the cranium through
the basilar part of the occipital bone, the body of the
sphenoid, the ethmoid, and the vomer ; and these parts
are here extended forward in the same straight line with
the rest of the vertebral column. The ordinary concave

OR OSSEOUS SYSTEM. 63

ends of the bodies of the vertebrae can be traced for-
ward to a variable extent through those of the cranium,
as at both ends of the basilar portion of the occipital,
and of the body of the spenoid. The bones of the cranium
in osseous fishes are generally thin, diaphanous, elastic,
united by squamous sutures ; they present a large exterior
surface for the attachment of the powerful muscles of the
trunk, and they continue to grow and to preserve the
same proportions to the rest of the skeleton through
life. The interior of the large cranical cavity is filled
chiefly by the soft cellular tissue of the arachnoid coat,
the brain occupying but a small portion of the base of
the skull. The number of distinct osseous pieces in the
composition of the skull is greatest in fishes, and they
correspond nearly with the theory of this part of the ske-
leton, being composed of seven vertebrae, each consisting
as usual, of a body with four elements above, and four
elements below. The number of separate pieces diminishes
as we ascend through the vertebrated classes, by the early
and permanent anchylosis of a variable number of these
elements common to all forms of crania.

The spine of the occipital bone, or the superior oc-
cipital (8,) is here large for muscular attachments, like
that of the vertebrae of the trunk ; and this ridge is often
continued forward over the whole skull to the nose.
From the horizontal position of the head on the trunk,
the occipitals and the frontals generally meet and force
the parietals (7,) to assume a lateral position, as we see
in the skulls of cetacea, for the same reason. The ele-
ments of the temporal bone are large^ detached, and
mostly moveable. The petrous portion is exterior to the
organ of hearing in the osseous fishes, and surrounds
that organ, imbedding it in its substance in the cartila-
ginous species,, as in higher classes. The principal frontal
bones (I,) are long and bounded before and laterally by
the anterior frontals (2,) and on the posterior and lateral
part by the posterior frontals (4,) as in other oviparous
vertebrata. The jugal (19,) is generally long, curved, and
slender, as in the blowing cetacea, and composed of a
series of separate pieces, which bound the inferior margin
of the orbit, they form the suborbital bones of Cuvier.

(>'l ORGANS OF SUPPORT,

The detached condition of the bones of the head is most
remarkable in those of the anterior part of the face,
where the palatine bones ( 22, ) extending longitudinally
on the sides of the mouth, and often covered with teeth,
as in serpents, are freely moveable. The superior maxilla-
ries (18,) extending downwards laterally behind the inter-
maxillaries (17,) on each side of the face, are loosely ar-
ticulated to the vomer (16',) and to the palatine bones,
and are freely moveable in the osseous fishes, as are
also the intennaxillaries ( 1 7,) which bound the fore part
of the upper jaw. The lower jaw is generally composed
of at least two pieces on each side, the dental portion
(34,) in front containing the teeth, and the articular portion
(35,) behind connected with the head by a tympanic bone,
(below 27,) considered by Cuvier as the jugal. Fishes
have teeth implanted in almost every bone around the
interior of the mouth, in the intermaxillary, superior and
inferior maxillary bones, on the branchial arches, pharyn-
geal bones, palatine bones, os hyoides, and on the tongue
itself. The teeth are almost entirely osseous, without
fangs, and without alveoli ; irregular in size and position,
generally recurved spines placed in numerous rows, and
they often become anchylosed to the bones which sup-
port them. Their soft osseous texture, their thin cover-
ing of enamel, and their feeble attachment, correspond
with the soft condition and the imperfect union of the
bones which support these prehensile teeth, as we see
also in amphibia and serpents. Where the bones of the
head, which support them, are strong, and firmly united,
as in crocodilian reptiles and mammalia, the teeth are more
dense, covered with a thicker layer of enamel, provided
with fangs, and lodged in deep alveoli. Behind the
lower jaw is placed the operculum, consisting of a large
opercular bone (28,) a sub-opercular bone (32,) an inter-
opercular bone (33,) and often an additional small piece
below the sub-opercular. As fishes have no tympanic
cavity of the ear to confine their ossicula auditus, the
opercular bone is considered as an enlarged stapes, the
sub-opercular bone as the os orbiculare, the inter-oper-
cular as the malleus,, and the fourth small bone as the
iocus. These are placed behind the pre-opercular bone, (30,)

OR OSSEOUS SYSTEM. 65

and have been also regarded by some as elements of the
lower jaw.

The arches, which hang down from the sides of the
vertebral column, are more like ribs in fishes than in
higher classes, as the lower jaw, the os hyoides, the sca-
pular arch, and that of the pelvis. The os hyoides is very
large here, as in all water-breathing vertebrata, from its
supporting the branchial arches ; it consists of five pairs
of pieces besides the body or lingual bone ; it is suspended
from the temporal bones, and it is chiefly by its motions
backwards and forwards that respiration is effected, not only
in fishes, but in amphibia and chelonia. It forms the
second arch below the head, between the arch formed by
the lower jaw, and that formed by the scapular and coracoid
bones. Its sides support the four pairs of branchial arches,
the analogues of tracheal rings, and its exterior gives at-
tachment to the branchiostegous rays of the opercular
membrane.

The arms of fishes, or their pectoral fins are almost
always more developed than their legs, or ventral fins, and
they are generally attached to the back part of the skull,
by means of an osseous arch composed behind of the
two scapulse, and before of the two coracoid bones. In the
perch (Fig. 31.) the two highest or first portions of this
arch on each side (46, and 47,) are regarded as the scapulae,
the long angular bone (48, 48.) attached to these, as the
humerus, the two succeeding bones (51,52,) as the ulna
and the radius. To these succeed the bones of the carpus
(53,) and this member is terminated by the long and nu-
merous phalanges of the fingers. The small styliform ter-
mination (50,) of the scapular arch, composed sometimes
of one, and sometimes, as in the perch, of two pieces (49,
50,) is considered as the coracoid bone, and they occasion-
ally meet in front, as in higher oviparous classes, though
without the intervention of a sternum. The relative mag-
nitude of the arms of fishes, and their constancy, compared
with the posterior members, corresponds with their great
size in the embryo of higher classes, and their preceding
the legs in their development from the trunk. The posterior
members, the legs, or the ventral fins of fishes (80, 81, 82,)
are unconnected with the vertebral column, suspended from

PART I. F

ORGANS OF SUPPORT,

two rib-like iliac bones, and placed on the lower part of the
trunk, sometimes near the anus, sometimes near the head,
or between these two parts. The iliac bones not being
here attached to the vertebral column, there is no portion
of that column fixed to form a sacrum, and the same is
observed in the cetacea, and the perennibranchiate am-
phibia, where there is no sacrum, and the whole column
behind the head is thus free for the extensive motion re-
quired in swimming. These two pelvic bones (80,) are
sometimes closely applied to each other, extend along
the middle of the abdominal surface, like two pubic bones,
and are attached to the scapular arch, or to the humeri (48,)
as in the perch. In the apodal fishes, as the eels, the pelvic
bones (80,) are wanting, as well as the legs ; and in the
abdominal fishes, the pelvic bones are quite unconnected
with the skeleton. From this freedom of the posterior
members in fishes, they are most frequently placed forward,
near the head, where they afford least impediment to the
lateral motions of the vertebral column. The long pha-
langes of the feet (81, 82,) are attached directly to the
pelvic bones, there being seldom a trace of the intermediate
bones of the legs developed in this class, where they are
not required either to give support to the trunk, or mobility
to the feet.

In the plagiostome cartilaginous fishes, the highest ani-
mals of this class, the ribs and the spinous processes of
the vertebrae of the trunk, are as little developed as in am-
phibia, many of the anterior vertebrae (e9) of the trunk,
are often anchylosed, and the whole bones of the cranium
are united into a single
piece, as seen in the
skeleton of the common
skate, raia betis, ( Fig.
32.) The skull («,) is of
great size, with tough,
thick, cartilaginous pa-
rietes ; it is filled chiefly
with the soft, glary,
arachnoid tissue, and
contains within the thick-
ness of the temporal bone

FIG. 32.

OR OSSEOUS SYSTEM. 6'/

the whole of the internal ear. From each side of the head
there passes down a short, round, moveable piece (£,) in the
situation of the tympanic bone, which supports the lower
jaw (d,) and the moveable, free upper jaw (c,) both covered
closely with small teeth, like mosaic work. The scapular
arch (/,) is fixed to the anterior, thick, anchylosed portion
(e,) of the vertebral column, and the bones of the arms
are also anchylosed together, and to this scapular arch.
This fish lies at the bottom without an air-bag ; its motions
therefore in swimming being chiefly vertical, its hands (g, g,)
are very large, and extended nearly round the whole trunk,
from the point of the nose to the pelvic arch (h.} In the
large hands of the rays and sharks, there are not only very
numerous fingers or rays, but each finger (g,) is divided into
a variable number of short, cylindrical phalanges, slightly
dilated at their points of contact. The pelvic arch (h,) is
generally very perfect in the plagiostome chondropterygii,
and presents the rudiments of the three ordinary con-
stituent bones, the ilium, the ischium, and the pubis, on
each side ; the two pubic bones united form a band passing
transversely before the anus, the iliac bones ascend taper-
ing to near the sides of the column, and the ischium on
each side passes backwards. The feet are less than the
hands, and consist of toes (i, i,) which are shorter, less
numerous, and less divided than the fingers, ( g. ) The
great size of the hand is the more required in the rays,
from the smallness of the tail (&,) rendering it almost use-
less as an organ of motion. In the sword-fish, and in the
saw-fish, the upper jaw bones, the vomer, and the nasal
bones form a long projecting weapon of offence extending
from the face above the free intermaxillaries, which bound
the upper part of the mouth. The orbits are prolonged
laterally to a great distance in the zycena, or hammer-headed
shark, so as to give a pedunculated appearance to the eyes.
From the softness of the skeleton in the cartilaginous fishes,
the mouth, and especially the lower jaw, is very short, and
often extended much transversely ; and for the same reason,
these animals have numerous rows o'f teeth prepared to
supply the places of those which are successively lost, as
in the sharks, or have their jaws covered, as in the rays, with
a continuous compact layer of small permanent teeth.

F 2

68 ORGANS OF SUPPORT,

XX. Amphibia. — The amphibious or batrachian animals
commence their career as fishes, with one auricle and one
ventricle, and breathing by means of gills which in many
are retained through life, but in their adult state they ac-
quire a pulmonic respiration, arid a pulmonic auricle of
the heart, and this early aquatic life and subsequent meta-
morphosis affect the whole condition of the skeleton, and
the forms of the several bones. The skeletons of the am-
phibia come nearest to those of fishes in the imperfect
ossification, and the thin, diaphanous, elastic character
of the bones, in the loose condition of the bones of the
face, and in the imperfect development of the ribs. The
perennibranchiate amphibia, and the tadpoles of the
caducibranchiate species, present the softest and the most
detached condition of the bones, and the most fish-like form
of the whole skeleton. Their vertebral column is prolonged
backwards to a great extent, as an organ of motion ; their
arms and legs are wanting, or are very imperfectly developed,
and their os hyoides, like that of a fish, supports a variable
number of branchial arches, as seen in the annexed figure
of the skeleton of the proteus anguinus (Fig. 33.) The ver-

FIG. 33.

tebrse here have the bodies terminated before and behind by
concave surfaces, as in fishes, and all the processes of these
vertebrae are short, to allow of extensive motion, especially in
a lateral direction. There is no sacrum, and the pelvic (&,) and
scapular (#,) arches are as free as in fishes. A few small de-
tached points of bone at the ends of the transverse processes
of some of the anterior dorsal vertebrae are the only ribs here
developed ; and in this, as in many other characters, the pro-
teus and the siren resemble the sharks. The parietal (e,) and
the frontal bones are long and separate, the tympanic bone is
long and moveable. The wide inferior jaws, the long in-
termaxillaries, and the loose upper jaw-bones are provided
with sharp, recurved, conical teeth. The body (£,) and

OR OSSEOUS SYSTEM. 69

cornua (a,) of the os hyoides are proportionally large, and
support the three branchial arches (c,) on each side to
which the permanent gills (d,) are attached. The flat dorsal
portion of the scapula (^,) is thin and cartilaginous, and the
coracoid pieces (/,) meet in front by broad extended edges.
There are only three toes (h,) developed on the fore feet,
the two inner consisting of three phalanges, and the outer
of two ; and on the hind feet there are only two toes (i,)
each consisting of three bones. The expanded, cartilaginous,
iliac bones (&,) extend upwards to the sides of the vertebral
column, as in the plagiostome fishes, without being attached
to a sacrum, and the pubic bones unite with each other
and with the ischia, to form a transverse anterior band for
the support of the small legs. The condition of all parts
of the skeleton is nearly the same in the siren lacertina,
where the prolonged fish-like vertebral column has still
greater freedom of motion from the entire want of legs
and a pelvic arch ; the spinous processes of the verteBse are
more elevated, the coracoid bones meet by a longer sur-
face, the hands have four toes, there are four branchial
arches on each side : the body and cornua of the os hyoides
are very large, and the tympanic and intermaxillary bones
are as moveable as in a fish. The ribs are developed to a
greater extent in the land salamander, where they have the
form of straight tapering spines extending from the trans-
verse processes of all the vertebrae of the trunk. The arms
and legs which here support the trunk in a lighter me-
dium than in the former animals, have all their bones larger
and stronger, and have four toes before and behind. The
whole bones of the skull and face are more fixed in their
articulations, and the pelvic arch is more connected with the
sides of the vertebral column, but without forming a
sacrum.

It is however in the anurous amphibia, as the common
frog, (Fig. 34.) that we find the most solid and fixed con-
dition of all the bones, and the nearest approach to rep-
tiles and higher classes in the structure of the different
parts of the skeleton. The vertebra of the tadpole are
formed like those of a fish, with two cup-like cavities, but
by the ossification and anchylosis of the intervertebral soft
substance, it becomes fixed to the posterior end of the

70

ORGANS OF SUPPORT,

FIG. 34.

body of each vertebra, so as to change their forms almost
to those of reptiles. A great portion of their vertebral
column, and of their os hyoides, and their branchial arches
become absorbed, their legs and arms become developed,
and many of the coccygeal vertebrae unite to form a single
piece ; so that these anurous highest kinds of amphibia
pass through the inferior forms of their class before arriving
at their perfect state. There are nine vertebrae in the frog
(Fig. 34.) the first of which (b,) has a double articular sur-
face, like two condy-
loid depressions for
the two prominent
condyles formed by the
body of the occipital
bone (a,) and this atlas
is without transverse
processes. The bodies
of the succeeding ver-
tebrae terminate pos-
teriorly by slightly con-
vex surfaces, and an-
teriorly by correspond-
ing depressions, and
the transverse pro-
cesses are long, but irregular in their forms and magnitude.
There are no ribs, and the pelvic arch is moveably connected
with the ends of the transverse processes of the last or
ninth vertebra (c, c.) This single vertebra forms, therefore,
a true sacrum, and the succeeding coccygeal vertebrae (d,)
are anchylosed into a single unperforated bone, slightly
grooved at its commencement, running along the dorsal
part of the pelvis, and entirely concealed within this part
of the trunk. The two iliac bones (e, e,) long, cylindrical,
and slightly curved, extend backwards from the sides of the
sacrum (c, c,) to the ossa ischii (f,) behind, and the small
pubic bones in front ; and these three bones, united by
sutures, form on each side of this compressed terminal
part (/,) of the pelvis, the cotyloid cavity for the reception
of the. head of the femur. The legs are here very large,
both for leaping and swimming. The long femur (/,) is suc-
ceeded by another long single bone (w, m,) the grooved

OB OSSEOUS SYSTEM. ]\

surface of which shows it to be formed of the tibia and
fibula anchylosed together. To this succeeds a lengthened
astragulus and calcaneum (n,) then three very minute cunei-
form bones of the tarsus, and then the lengthened bones of
the meta- tarsus and the phalanges of the five toes (o.) The
humeri (A, A,) are comparatively short, strong, and slightly
bent ; the radius and the ulna (i, i,) are anchylosed like the
tibia and fibula, and the six small carpal bones (k, k,) are
succeeded by four long meta-carpal bones, the phalanges of
four fingers, and a small rudiment internally of a fifth. The
scapular apparatus (Fig. 35,) for the support of the arms
is here very complete, and also the sternum, although there

are no ribs to reach it. The posterior

,. ,\ f ., FIG. 35.

curved portions («, t,) of the scapulae,

are thin and cartilaginous, as in many
fishes and reptiles, and the anterior
parts (f)fy) which chiefly contribute
to the formation of the glenoid cavity
(k, k,) for the head of the humerus is
strong, and ossified. From the gle-
noid cavity, on each side, proceeds inwards the coracoid
bone (e, e,) which expands as it reaches the sternum (d.)
Above the two coracoid bones, (e, e9) are the two slender cla-
vicles (c, c,) which also proceed from the glenoid cavities to
the sternum, and leave a considerable vacant space between
them and the coracoid bones. The anterior (a,) and the
posterior (h,) portions of the sternum are thin, flexible, car-
tilaginous laminae, and the intermediate parts are ossified
and strong, for the insertion of muscles, the support of the
scapular arch, and the protection of the fore part of the
trunk. The upper thin portion («,) appears to consist of
the two epi-sternal pieces, the next part (b,) of the two hyo-
sternal elements, the next (d}) the single ento-sternal, to
which both the clavicles and coracoid bones are attached ;
the next (t/9) the two hypo-sternal elements, and the inferior,
thin, cartilaginous, terminal piece (h,) the two united xiphi-
sternal elements which usually terminate this bone.

The bones of the head, even in the highest of the caduci-
branchiate amphibia, are still as loosely united together as
in most of the osseous fishes, as is seen in the skull of the
common frog, rana esculenta, (Fig. 36.) The occipital bone

7^ ORGANS OF SUPPORT,

has its basilar part divided by a vertical suture, and is se-
curely united to the atlas by two prominent condyles (b, b,)
belonging to that portion

vi r- *3ft

of the bone. The parietals
(c9 c9) are long, narrow, near-
ly separated by a sagittal
suture, arid extend forward
over a large portion of this
lengthened narrow cranium,
as we see also in ophidian
and saurian reptiles. The
sphenoid bone has also a
very lengthened form along
the base of the skull, as in
fishes. On the fore part of
the skull are the two posterior frontals (a,) separate in the
young frogs, but united into a single bone extended between
the parietals (c, c,) and the two anterior frontals (h, h,) which
extend laterally to the two pterygoid, and the two upper
jaw-bones (&, k.) The two intermaxillary bones (/,/,) the
two upper jaws (k, k,) and two bones behind these, regarded
as divisions of the vomer, are provided with small, sharp,
recurved conical teeth, although none are found opposed to
them in the lower jaw. The slender jugal bone (o,) is ex-
tended from the upper jaw bone backwards and downwards
to the lower end of the long tympanic (»,) which is here
moveable, as in most oviparous vertebrata. The tympanic
bone (n,) here, as in most of the lower vertebrata, sends
down a condyloid process to be articulated with a glenoid
cavity (/,) on the back part of the lower jaw. The lower jaw
is divided at the symphisis, and each lateral portion consists
of an anterior (s,) a middle (r,) and a posterior (/,) piece,
which extend to a great distance transversely, and are en-
tirely destitute of teeth, although there are teeth in the
lower jaw of the salamander and the proteus. As we pro-
ceed upwards through the vertebrated classes, the teeth
become more circumscribed in their number and in their
distribution over the parietes of the mouth, till we find them
confined to a single row disposed along the upper and lower
jaws. We thus observe in the adult anurous amphibia a
greater consolidation of the whole texture of the bones,

OR OSSEOUS SYSTEM. 73

and of the different parts of the skeleton than we find in
fishes ; and many elements originally separate have become
anchylosed together, which conditions prepare the solid
frame-work to support and carry the whole fabric through a
much rarer medium than the dense water in which they
commenced their career, and in which the fishes perma-
nently reside.

XXI. Reptilia. — The bones of serpents are more com-
pact, white, dense, and elastic than those of the other
orders of reptiles ; but their skeleton is the most deficient
in its parts, consisting almost solely of the vertebral column
without legs or arms, or a pelvic or scapular arch, or even
a sternum to connect the ribs, as seen in the skeleton of the
boa constrictor, (Fig. 3J-) With this simple skeleton they
are able to creep quickly on the ground, to combat with

FIG. 37.

their prey, to climb trees, to spring into the air, and to swim
rivers and lakes. The ribs are developed from the sides of
the vertebral column from the atlas to the anus, and the
transverse processes continue to extend to a considerable
length from the sides of many of the anterior coccygeal
vertebrae. From the absence of a sternum in front, and the
free articulation of the ribs with the ends of the transverse
processes of the vertebrae, the ribs possess the means of
extensive motion, and cause the transverse scuta on the
lower surface of the abdomen to move like so many feet.
The ribs of serpents are tubular, with thin compact parietes,
and containing a soft cancellated structure in their interior,
by which they possess great elasticity and strength. They
are narrow, and compressed from before backwards, strong
and broad at their head and neck, and taper regularly to
their free ventral extremity, where they generally terminate

74 ORGANS OF SUPPORT,

with a thin, flexible, cartilaginous prolongation. Their head
presents a broad, arched, concave surface, to form a secure
and free articulation with the rounded, prominent, transverse
processes of the vertebrae. The broad and long transverse
processes in the coccygeal region of the column, cover a long
pelvic cavity in the male, in which the two divisions of the
penis are lodged in their retracted state. As the ribs ex-
tend along the whole sides of the trunk, from the head to
the anus, there are no cervical nor lumbar vertebrae ; and as
there are no legs nor pelvis, there is no sacrum.

The vertebrae are here more numerous than in any other
class of animals, so that there is great flexibility of the
whole body, and their articulations are remarkably secure
from the extent and the number of the articular surfaces
between each pair of vertebras. All the processes of these
vertebrae are short, to admit of greater freedom of motion, ex-
cepting the four articular processes, which are very broad, to
give a greater security of attachment ; and hence the quadran-
gular or cubical form presented by the vertebrae of serpents,as
seen in the front view of those of the boa constrictor) (Fig. 38.)
The lower part of the body of each vertebra terminates in
a large, oblique, hemispherical convexity (a,) smooth on the
surface, and covered with a thin layer -0

of cartilage. This prominent end of
the vertebra is received into a corres-
ponding deep, cup-like cavity (b9) with
sharp margins, and lined with carti-
lage, at the anterior end of the next
succeeding vertebra, and this regular
ball-and-socket form of articulation is
continued through the whole vertebral
column. These articulations are se-
cured by strong capsular ligaments,
and lubricated by a copious secretion

of synovia. The two anterior, and the two posterior arti-
cular processes present broad flat surfaces, extended trans-
versely, those of the anterior vertebra passing over those of
the next succeeding vertebra, as in other classes. The
shortness of the transverse processes (Fig. 38. c, c, c,c,)
allows of a greater extent of lateral motion in the column,
and, for the same reason, the vertebral foramina for the

OB OSSEOUS SYSTEM. *J 5

spinal chord are most dilated before and behind in that
direction. These very short, strong, transverse processes
have each a large, convex, prominent, articular surface, ex-
tending downwards, inwards, and a little forwards, which is
received into the articular concavity of the head of the
rib. From the four articular processes of the vertebrae
extending to a great distance laterally in a straight and
horizontal direction, they give great extent and safety to
those lateral motions which are chiefly required in the trunk
of serpents. The bodies of the dorsal vertebras are cari-
nated below, and have a narrow contracted neck at the base
of the posterior, hemispherical, articular tubercle. The
laminae are here very strong, and evasated before and behind,
to enlarge the two ends of each vertebral foramen, that
the spinal chord may not be pressed upon during the mo-
tions of the vertebrae. The spmous processes are short,
strong, and broad, from before backwards, so as to afford a
strong attachment to the muscles, without interfering with
the motions of the vertebrae.

In the skulls of reptiles, as in fishes and amphibia, we
still find the cranial vertebrae disposed in the same straight
line as those of the rest of the column, and most of the
elements of the cranial bones still remain separate through
life. The serpents and lizards present the most detached
condition of all these cranial bones met with in the class
of reptiles ; the crocodilian animals, and the chelonia have
them the most firmly united by sutures. This loose state
of the bones of the head is the more necessary in serpents,
which, from the want of arms and legs to hold down their
prey, and assist in its subdivision, are compelled to swallow
it entire. The annexed figure of the skull of the python
(Fig. 39.) shows the most common disposition and form of
the bones of the head of serpents. The basilar portion (a,)
of the occipital bone remains distinctly isolated from the
two lateral condyloid pieces («*,) and these three elements
form the large, transversely elongated, occipital condyle, the
basilar element forming the greater portion of it. The
superior or median occipital (£,) is here small and detached^
as in the saurian reptiles. The parietal bones (c, c,) are
long, and anchylosed together along the median line, to
afford a solid unyielding covering to the lengthened brain

ORGANS OF SUPPORT,

FIG. 39.

beneath them. These two bones are thus early united in
most other reptiles, in all birds, and in the greater number
even of the mammalia, although they are separate in the
normal form of the human skull.
This condition of the two pari-
etals is the more required in
serpents, from the loose state of
most of the other bones of the
head, and the exposure of these
animals to the trampling of qua-
drupeds, and other dangers while
they lie concealed in their natu-
ral haunts. The anchylosis of
the two parietal s gives greater
security to the strong temporal
muscles of these animals, as in
other classes, where this solidity
of attachment is required. From
the length, and the loose attach-
ment of the squamous portion (e})
of the temporal bone to the parietals, the tympanic bone (/,)
and consequently the lower jaw (#,) has much greater ex-
tent of motion in a lateral direction. The two anterior (i, i,)
the two middle (h, h,) and the two posterior (k, k,) frontals
remain detached, and form, as in other reptiles, the greater
portion of the front of the skull. The great breadth of
the two lachrymal (/, /,) and of the two nasal (p9p9) bones
corresponds with the general flat and broad form of the
head of serpents. The two upper jaw-bones (m, m,) and
the two intermaxillaries (q,) are separate and quite moveable
on the surrounding bones ; and the two palatines are also
moveable and long, and support the most permanent teeth
of these animals. The two sides of the lower jaw are quite
detached from each other, and freely moveable at the sym-
phesis, and the pieces of which it is composed are also
moveable. This freedom of motion of the lower jaw (g, t/9)
extends through the long tympanic (/,/,) and squamous
(e, <?,) elements of the temporal bone to its more fixed
petrous portion (</,) so that the mouth is here capable of
extraordinary dilation, to transmit through its cavity entire
prey, which the serpents have not the means of dividing.

OR OSSEOUS SYSTEM. 77

Their teeth are organs of prehension, and not of mastica-
tion ; they are conical, slender, sharp, recurved, osseous
spines, covered with enamel, with very shallow alveoli,
placed along the upper and lower jaws, the intermaxillaries,
and the palatine bones. The upper jaw bones in the poi-
sonous snakes terminate abruptly in a round peduncle below
and before the orbits, which supports the tubular poison-
fang, and the small teeth which usually accompany it upon
each side of the head.

The saurian reptiles have the skeleton more complete than
the serpents, as they possess a complex sternum, and
scapular apparatus, a fixed pelvis, together with atlantal and
sacral extremities ; but the transition from the one form is
very gradual from the serpents with the rudiments of pelvic
and scapular bones, to the bimanous and the biped lizards ;
and from these to the regular saurians with fore feet, and to
the more solid and complete forms of the skeleton presented
by the crocodilian reptiles. By the increased development
of all the processes of the vertebral column, we perceive
the preparation for more solidity in the articulations, and
more limited motions in that part of the skeleton, the loco-
motion is now to be effected by the arms and legs, and not
by the vertebral column, as in most of the lower vertebrata.
The large bones of the sauria present a coarse fibrous struc-
ture, contain a large proportion of animal matter, and have
a cancellated loose texture internally, where we find tubular
cavities in the birds and mammalia. The bodies of the ver-
tebrae, in the lacertine sauria, preserve the ball-and-socket
joint throughout the column ; but these parts of the verte-
brae are more compressed, and the articulations are more
oblique than in the serpents. From the necessity for sup-
porting the trunk upon the legs, the pelvis is united firmly
to a sacrum, consisting generally of only two enlarged ver-
tebrae. The bodies of the vertebrae are generally more
lengthened, and the articular processes more extended in
a longitudinal direction than in the serpents. There are two
concave surfaces of the bodies of the vertebrae, of the
gecko, as in fishes and tadpoles, and in the ichthyosaurus.
In the coccygeal vertebrae, besides the lengthened superior
spinous process, and the two transverse processes, there
are inferior spinous processes, which are interposed between

78 ORGANS OF SUPPORT,

the bodies of the vertebrae, and by forming a small arch
they give protection to the large blood-vessels of the tail,
which is generally a thick muscular continuation of the
trunk. There are false ribs in front of the true, as well as
behind them, as we see also in birds, and in some mam-
malia ; and there are generally about seven cervical vertebrae,
as in quadrupeds. The head is extended forwards in the
same straight line with the vertebral column, as in the
inferior vertebrated classes. As in these inferior classes
also we observe the bones of the head of the lacertine rep-
tiles remarkably loose and moveable in their articulations,
as seen in this figure of the skull of the lacerta nilotica,
Cuv. (Fig. 40.) The occipital bone, as in the serpents, has
its transversely elongated condyle composed chiefly of the
basilar portion of that bone. Exterior to the two condyloid

pieces, (g, a,) of the oc-

. ., i ^11 i FIG. 40.

cipital are the long slen-
der, curved, squamous
(/,) and mastoid (m}) ele-
ments of the temporal
bone, almost as loose as
in serpents, and giving
support to the short and
moveable tympanic por-
tion (r,) of that bone to which the articular portion of the
lower jaw is attached. The two parietals (n,) are anchylosed
together, as in serpents, and support the posterior edges of
the two middle frontals (c, c.) The anterior (e, e,) and the
posterior (i, i,) frontals form the upper boundary of the
large bird-like orbits. The petrous portion (p9p9) of the
temporal bone is here the largest and strongest element,
extending forwards to the sphenoid (ss) and backwards to
the very long and slender squamous (/,) and mastoid (m,)
portions. The two lachrymal bones (/,/,) extend less over
the face than in serpents, and between them and the an-
terior frontals (e, e9) are the superciliary bones (h, h}) as in
birds. The upper jaw bones (d, d,) and the intermaxillaries
(a,) are more fixed than in the former order of reptiles, and
these intermaxillaries are often anchylosed together, as are
also the two narrow lengthened nasal bones (b.) The large
inferior turbinated bones are here exposed, from the small-

OR OSSEOUS SYSTEM. 79

ness of the anchylosed nasal bone ; the palatine bones are
more fixed than in serpents, and are destitute of teeth, and
the two pterygoid bones (v,) extend, as in serpents, back-
wards and outwards to the tympanic (r.) The lower jaw is
divided at the symphysis, and consists on each side of six
pieces, of which the anterior or dental portion is the largest,
and the prehensile teeth are here as loosely attached by
their expanded base to the alveolar flat surface of the jaw,
as in serpents, protected at their bases by an outer, and
sometimes an interior ridge of the dental bone, but not
lodged in separate alveoli. The osseous bases of these
teeth in the lizards often anchylose to the surface of the
jaws, as in fishes, and the new teeth generally rise up on
the inner side of the base of the old or of the lost, and not
in the interior of their cavity, as they do in the croco-
diles.

The ribs of lizards are for the most part rounded and
slender, and without the tubercle so much developed in
quadrupeds and birds. The scapula is thin, broad, and
curved ; the coracoid also terminates in front by a very
broad curved margin by which it unites to the large ento-
sternal piece. The acromion is a distinct bone of very
variable size and form, and the clavicles are anchylosed and
extended in form of a cross along the fore part of the ster-
num. The sternal elements are thin, soft, and extended
transversely, and have chiefly the ento-sternal enlarged
and strong, as in birds. The humerus, also as in birds, is
much expanded at its upper and lower extremities, the ulna
is much stronger than the radius, and distant from it, espe-
cially at the carpus. There are nine bones in the carpus,
as in tortoises. The three pelvic bones contribute to the
formation of the cotyloid cavity for the head of the femur.
The expanded edges of the ossa pubis, and ossa ischii meet
and form a lengthened symphysis on the median line in
front, and the spine of the iliac bones is extended, not for-
wards, as in higher classes, but backwards along each side
of the sacrum towards the coccygeal vertebrse. The head
of the femur is compressed, and bent forward, and the great
trochanter is also compressed and turned towards the tibia.
The patella is always small, the tibia short, strong, thick at
its ends, and much curved at its fibular margin. The fibula

80 ORGANS OF SUPPORT,

is always slender in its middle, apart from the tibia, and
thickened at its ends. There are four bones of the tarsus, as
in the crocodiles, and the bones of the meta-tarsus like
those of the meta-carpus, and the phalanges of the toes and
fingers are lengthened to form prehensile flexible mem-
bers for climbing in these land forms of saurian rep-
tiles.

The skeleton of the nilotic crocodiles (Fig. 41.) like that
of the gavials and alligators, belongs to reptiles destined to
swim through the water by the lateral movements of a

FIG. 41.

powerful muscular vertical tail, and also by the impulse of
long webbed feet. Their long bones are coarse in texture,
and filled internally with a loose osseous structure contain-
ing a thin oily marrow. The whole bones of the head are
firmly united together by sutures, so as to admit of no
motion on each other. The parietals are anchylosed to-
gether, the tympanic bone is fixed by sutures to the other
parts of the temporal, and forms a prominent condyle for
the lower jaw ; the median frontals are anchylosed together,
but the two anterior and the two posterior frontals are
detached. The large malar bones, continued from the
lachrymal to the temporals, form the outer boundary of the
orbits. The nasal bones extend between the upper jaw
bones to the intermaxillaries in the crocodiles and alligators ;
but in the gavials they extend only to a short distance
along the muzzle, so that that lengthened part of the face
is not weakened by so many sutures. The whole of the
rounded termination of the upper jaw is formed by the in-
termaxillaries which surround the nasal aperture. The teeth
of these crocodilian sauria are hollow striated cones, which
contain within their cavity the new teeth which are to

OR OSSEOUS SYSTEM. cS 1

succeed them, and they are firmly lodged in deep alveoli.
The vertebrae of the crocodilian animals have for the most
part a lengthened narrow body, concave before and convex
behind, as in other reptiles. The transverse processes of the
cervical vertebrae are very broad and long, and detached like
ribs, and impede the lateral movements while they encrease the
muscular power of the neck, for carrying off and struggling
with their large prey. There are two pairs of false ribs before,
and two pairs behind the true ribs. The true ribs have a
strong attachment, by fheir lengthened head and prominent
tubercle, to the sides of the bodies of the vertebras, and the
extremities of their transverse processes. The sternal ribs
(Fig. 41. q,) are ossified, and similar ossified ribs are con-
tinued along the fore part of the abdomen to the pubis. The
scapula and the coracoid bone are separate, more lengthened
and narrow than in the lizards, and more thick and solid.
The clavicular bone of the lizards is here extended forward
below the neck, and the ento- and xiphi-sternal portions
are most developed in the sternum. The three pelvic bones
are more loose than in other saurians. The short expanded
iliac bones (gj) are attached to two broad sacral vertebrae. The
ossa ischii (A,) meet in front, and form an expanded symphysis,
like most pubic bones ; the pubic bones (i}) are the most
slender, and extend forward from the cotyloid cavity, converg-
ing, but without meeting to form a symphysis. The humerus
(by) and the femur (#,) are both curved in the direction best
calculated to give effect to their movements in the water.
The radius (c,) and the ulna (d,) as well as the tibia (/,)
and the fibula (m,) are here strong and separate to their
extremities, leaving a large interosseous space, and forming
a broad and highly moveable articulation at the carpus (e,)
and the tarsus (n.) The bones of the meta-carpus, (/,)
and meta-tarsus (o,) and the phalanges of the fingers and
toes, are long and securely articulated at both ends for their
double use in the water and on land.

The chelonian reptiles differ from the sauria in having the
ribs immoveable, and from the serpents in having arms and
legs ; but their skeleton retains the ordinary conditions of
that of the class in the coarse fibrous texture of the bones,
in the want of continuous cavities in the long bones, and
in the permanent separation of the cranial and other osseous

PART I. G

ORGANS OF SUPPORT,

elements. The cervical and the coccygeal vertebrae are those
which alone are moveable, and nearly throughout the
whole column their bodies present the usual concavity at
their anterior end, and convex termination behind. The
vertebrae of the trunk have a lengthened form, as seen in
the caretta caouana (Fig. 42,) and their bodies, their laminae,
and their spinous processes are connected only by sutures.
There are eight pairs of ribs united to each other by sutures,
and attached between the bodies of the vertebrae. By their
union with each other, and with the expanded spinous pro-
cesses of the dorsal vertebrae, they form the upper shield
or carapace. The lower shield, or plastron, is formed by
the nine elements of the sternum, and these two parts are
attached to each other, by the sternal appendices (&,) which
admit of motion in the
turtles. The scapulae
(a,) are generally cylin-
drical bones more or less
lengthened, extending
from the sides of the
first pair of dorsal ver-
tebrae to the glenoid ca-
vity for the head of the
humerus, and they are
anchylosed to the cora-
coid bones (£,) which
converge and have their

free ends attached to the interior of the ento-sternal bone.
The two clavicles (c,) are separated by suture from the
scapulae, and are generally flat and expanded at their free
extremities, which extend backward and inwards. The ver-
tebrae composing the sacrum are anchylosed to each other,
and from their sides extend downwards and outwards two
short, cylindrical, iliac bones (/,) which enter into the forma-
tion of the cotyloid cavity, like the two other pelvic bones,
the ossa ischii, which meet in front, as in other reptiles, and
the two broad expanded pubic bones (i,) which generally
send upwards obliquely a large process like the marsupial
bones of mammalia. In the sternum of the land tortoise
(Fig. 43. 1.) the nine elements are firmly united to each
other by sutures, and also in the same manner to the sternal

OR OSSEOUS SYSTEM. 83

ribs. The two epi-sternal pieces (a, «,) form the anterior
margin, and unite behind with the ento-ster- FIG
nal piece (£,) which is single on the median
plane, and with the two hyo-sternal pieces
(e, c,) which extend laterally to unite with the
sternal ribs. The two hyposternal elements
(d, d,) are large and broad, like the hyo-ster-
nal, and also like them unite laterally
with the sternal ribs. The two xiphi-sternal
pieces (e, e,) are united to each other, and to
the hypo-sternals by serrated sutures, and form
the whole posterior termination of the plastron
or lower shield. In the sternum of the tur-
tles (Fig. 43, 2.) nearly all these elements are moveable on
each other, and at their points of contact with the sternal
ribs. The two epi-sternals («, #,) taper laterally to a point,
and are not united by sutures ; the ento-sternal (#,) has its
whole posterior portion free, and although the hyo- (c, c,)
and hypo- (d, d,) sternals on each side are united together
by firm sutures, they have moveable articulations on their
lateral margins. The xiphi-sternals (e, e,) are here freely
moveable, and taper to a point posteriorly, like the two
epi-sternals. So that there is great solidity in the whole
plastron, as in the whole carapace of the land animals to
resist pressure, to which they are much exposed, and they
form a dense frame-work for their muscular movements on
the land, while there is great mobility in the sternal apparatus
of the aquatic species, for the extensive respiration which
they require in that dense element.

The bones of the head in the chelonia, like those of the
crocodiles, are immoveably united by sutures, and in place
of teeth there are strong cutting, horny plates covering the
alveolar surface of the jaws, as in birds. The occipital
condyle is composed of three distinct facets, formed by the
basilar and the two condyloid portions of that bone. The
superior median portion of the occipital extends backwards
in form of a long spinous process, as in most osseous
fishes, for the attachment of the powerful muscles of the
neck. The two parietal bones are separate, and form in
the tortoises of the land an elevated longitudinal ridge,
which is continued forwards over the cranium to the frontal

84 ORGANS OF SUPPORT,

bone. In the marine turtles, and in the fresh -water emydes,
as seen in the skull of the emys expansa (Fig. 44. h, h,)
the parietal bones rise upwards on the median line of the
head, and extend laterally over the temporal fossa. The
tympanic bones are large, fixed by suture as in the croco-
diles, and extend downwards to form a condyle for the
articular cavity of the lower jaw. The two posterior (g, g,)
and the two middle

frontals bound the orbits
above, and the two malar
bones (i, i,) behind. The
two anterior frontals (a,
a,) bound the orbits in
front, and expand over
the nasal aperture, like
nasal bones. The inter-
maxillaries are narrow,
vertical, with an extensive palatine surface, and like the
superior maxillaries, they present a sharp alveolar edge,
which is covered with the cutting, horny, superior mandible.
Behind the two jugal bones (i, i,) are the expanded squamous
portions (k, k,) of the temporals, and behind these the two
long, descending, mastoid bones (m, m.) Anterior to the
mastoid bones (m* m,) are the upper portions of the tym-
panic bones (r, r.) Two portions (o, o,) detached from the
condyloid elements (q, q,) of the occipitals, are termed ex-
terior occipitals by Cuvier. The ossicula auditus are an-
chylosed together, as in many of the lower vertebrata. The
symphysis of the lower jaw is anchylosed at a very early
period of growth, as in birds. From the importance of the
os hyoides in the motions of respiration in these animals,
where the ribs are fixed,, its body and cornua are very large
and strong.

The arms of the tortoise are fixed in a state of pronation,
to' strengthen them for the support of the heavy trunk ;
and, like those of the legs, all their bones are short and
massive in their proportions. The humerus is much bent,
the radius and ulna short, strong, and with a very broad
articular surface at the carpus, and the succeeding bones of
the hands are short and almost cubical, for support and for
digging, like those of the mole. The same proportions are

OR OSSEOUS SYSTEM. 85

observed in the bones of the posterior extremities, but the
outer toe is generally quite rudimentary, while the five
fingers are more equally developed on the hands. In the
aquatic chelonia the bones of the extremities have a more
lengthened, straight, and slender form, and especially of the
anterior extremities (Fig. 42,) which are much more developed
than the posterior. They are also more flat and compressed,
and less moveable on each other ; so that they form a near
approach to the condition of these bones in the arms of a
cetaceous animal, or in the arms and legs of an ichthyo-
saurus and a plesiosaurus. The humerus (Fig. 42. d,) the
radius (e,) and the ulna (/,) the bones of the carpus (ff}) and
even those of the meta-carpus, and the phalanges of the
fingers (h,) partake of this lengthened and flattened form,
the best adapted for progressive motion through the water.
And we observe the same character, though to a less extent,
in the femur (m,) the tibia (n,) and the fibula (o,) and in the
bones of the tarsus (p,) the meta-tarsus, and the phalanges
of the toes (q,) where all the parts are shorter than the
corresponding bones of the anterior extremities.

XXII. Aves. — The bones of birds are more compact,
white, dense, and brittle than those of any other class ;
they have thinner parietes, their internal cavities are pro-
portionally larger, and for the most part they contain air
in place of marrow. From the great extent of their res-
piration, and the consequent encreased energy of all their
functions, ossification proceeds in birds to the greatest ex-
tent, not only in the consolidation of the several pieces of
the skeleton, but in the anchylosis of the separate elements
and separate bones with each other, throughout the skeleton,
and in the consolidation, by phosphate of lime, of cartilagi-
nous and tendinous parts, not ossified in other classes.
In the young state the bones of birds are filled with a thin
serous marrow, like those of reptiles, and this is displaced
by the admission of air during growth, to a very variable
extent, in the different orders of this class, the air being
admitted most extensively in the high flying rapacious birds,
and least in the heavy swimming palmipeds. There is greater
uniformity in the skeleton of this, than of the other ver-
tebrated classes. The arms are here adapted solely for flight,
the legs for support, and the head and neck are long and

86

ORGANS OF SUPPORT,

FIG. 45.

extensively moveable, as organs of prehension ; hence the
peculiar forms presented by these regions of the skeleton in
birds, as seen in the skeleton of the griffon vulture, vultur
fulvus, (Fig. 45.) As the body is supported wholly on the
legs, the toes extend to a great length, to afford a broad
base, the legs are placed
forwards upon the sides of
the pelvis, the trunk is in-
clined backwards upon these
organs of support ; the neck
and head are proportionally
elongated, to reach the food
upon the ground, and the arms
and hands are folded longitu-
dinally along the sides of the
trunk, as in the bats. The trunk
of birds is almost as fixed
as that of a tortoise, to give
strength to the muscles em-
ployed in flight, and the ver-
tebrae of the neck and tail
are almost alone moveable.
The rapid ossification and

anchylosis here affects not only the bones of the skull, but
the whole bones of the pelvis, the lower jaw, the scapular
arch, the clavicles, and the sternum. This tendency to
ossification affects the sterno-costal cartilages, the tendons
of the muscles of the legs, the sclerotic coat of the eye, the
rings of the trachea, and the inferior larynx.

The vertebrae of the neck are always more numerous than
in the mammalia, and are sometimes more than three times
the number common to that class. They have their articu-
lar surfaces so directed that the neck is naturally concave in
front at the upper part, and convex in front at the lower
part, presenting more or less of that sigmoid curviture,
which is so conspicuous in the long-necked 'birds. The
oblique processes, as seen in those of the swan, (Fig. 46.
h9 hj) are generally long, narrow, and diverging, admitting
with safety of very extensive motion. The spinous pro-
cesses (i, i,) are very short, to offer no obstruction to the
movements of the neck. The transverse processes (/,/,)

OR OSSEOUS SYSTEM.

FIG. 46.

are short, and strong, and give passage to a large foramen
(c, c,) on each side, for the vertebral arteries and nerves.
The foramen for the spinal chord is dilated at its anterior
and posterior extremity, in the direction of the greatest
motion of the vertebrae, in order to protect from compres-
sion the spinal chord, and the nerves which enter it laterally.
The posterior ends of the bodies
of the vertebrae (#, «,) are nar-
row, convex, arched transversely,
and received into a corresponding
transverse groove on the anterior
part of the body of the next
succeeding vertebrae. The trans-
verse processes are prolonged so
far backwards (g, y,) as almost
to form a continuous canal along
the sides of the neck, for the
protection of the enclosed large
vertebral arteries, and the cervi-
cal portion of the sympathetic
nerves. The forms of the pro-
cesses, and of the articulations
of the dorsal vertebrae are calcu-
lated by every means but by anchylosis to impede motion
and to give solidity to that part of the trunk. The spinous
processes of these vertebrae are developed forwards and
backwards to such an extent that they come almost into
contact with each other before and behind. The free ends
of the transverse processes extend so much forwards and
backwards that they commonly pass over each other in an
imbricated manner, and prevent ah1 lateral motion. And
the anterior or sternal surface of the bodies of these verte-
brae are often compressed, carinated, and extended down-
wards, like inferior spinous processes, which further impede
motion. The dorsal vertebrae are often anchylosed toge-
ther, like all the lumbar and sacral, to give greater solidity
to the trunk, for the movements of flying. The lumbar
vertebrae are most free in the ostrich ; in other birds they
are anchylosed to each other and to the sacral, as the sacral
are to each other and to the iliac bones ; so that the
different kinds of vertebrae in this region of the trunk are

ORGANS OF SUPPORT,

almost indistinguishable from each other, and the sacral
vertebrae are more numerous than in all other forms of ver-
tebrata. The canal for the spinal chord in the middle of
the sacrum, between the two cotyloid cavities, where the
nerves of the posterior extremities commence, is very wide,
and corresponds with the great inferior enlargement of the
spinal chord at that place. In the intervals between the
transverse processes of the sacral vertebrae are contained
internally on each side the several unequal lobes of the
kidneys. The coccygeal vertebrae are moveable and strong
in birds, to support the plumage and muscles of this great
and flexible organ of motion. They have long transverse
processes, and spinous processes both above and below the
bodies, and the last of the vertebrae (Fig. 45. g.} has a
lengthened, compressed, crescentic form, to increase the ex-
tent of its lateral surfaces.

The lengthened form of the head in birds depends chiefly
on the elongation of the jaws, and corresponds with the
lengthened form of the neck, and the various manipulations
and prehensile uses to which this part is applied. The
cranium is short 'and broad, like that of most cetacea ; it is
bounded before by very large orbits, separated from each
other only by a thin membranous partition, or by a thin
plate of the sphenoid bone, and the bones which form it are
anchylosed together, so that all traces of the coronal, sagittal,

lamdoidal, squamous, and other su-
tures have here disappeared, as seen
in the skull of the golden eagle, falco
fulvus (Fig. 47.) The occipital (a,) the
parietal (b}) the frontal (e,) and the
temporal bones are for the most part
thin, diaphanous, smooth externally and
internally, like the surface of the cere-
bral hemisphere, and embrace a large
lobed cerebellum, large optic lobes, and
smooth hemispheres of the brain,
which taper forwards to the ethmoid
bone. The nasal (/,) and the superior
maxillary bones (g9) are moveable on
the frontals, sometimes by a distinct
articulation, as in the parrots and

FIG. 47.

OR OSSEOUS SYSTEM. 89

cockatoos, but most generally by means of the thin flexible
condition of these bones at their line of junction 5 and by
this the gape of birds is widened, to take in or seize bulky
objects, which their toothless jaws and the form of their
hands do not enable them to subdivide. The basilar part of
the occipital bone is short, from the shortness of the cranical
cavity, as in reptiles, amphibia, and cetacea, and it extends
backwards in the form of a single, round, prominent con-
dyle, by which greater extent of rotation is afforded to the
head on the neck. The body of the sphenoid is lengthened,
as in the inferior vertebrata, and the two pterygoid bones
still remain permanently detached, extending laterally to the
loose tympanic bones (/.) The tympanic element of the
temporal bone, or the os quadratum (/,) is here freely move-
able, as in fishes, amphibia, and most sauria ; it sends
downwards a convex, prominent, articular surface, for the
attachment of the lower jaw, and is likewise attached to the
long, slender, malar bone (n,) which forms the inferior boun-
dary of the orbit, by which attachment it is enabled to push
forwards and upwards the superior maxiUary, and thus
widen the mouth. The palatine bones are long, large, and
detached, leaving a wide fissure between them ; but the in-
termaxillaries are anchylosed to each other, and to the
superior jaw bones, which are also united to each other.
On the anterior part of the orbits, the large lachrymal
bones (e9) and the small superciliary bones (d,) are detached,
especially in the rapacious birds ; and, notwithstanding the
wide openings of the nostrils externally, the turbinated la-
minee are small, soft, and cartilaginous ; the olfactory nerves
are transmitted through the back part of the large orbits to
the nose, there being no perforation for these nerves in the
thin cancellated structure of the ethmoid and sphenoid
bones separating the orbits, and here filled with air. The
diploe of the cranium, which is largely developed in noc-
turnal birds, as owls, is filled with air, like the bones of the
trunk and of the extremities, which is admitted through the
Eustachean tube, and the cavity of the tympanum ; so that
it encreases the intensity of sounds and the dimensions of
the organs of hearing. No parts of the skeleton vary so
much in birds, as the upper and lower jaws, according to
the kind of food on which the different species subsist and

90 ORGANS OF SUPPORT,

their modifications are therefore intimately connected with
the general forms of the skeleton, and the living habits of
the species. The tipper bill is long and hooked in fishing
birds, shorter in vultures, and still shorter in eagles and
hawks. The jaws are long, straight, tapering, and pointed
in herons and storks, shorter and slender in wood-peckers,
and still more slender and pointed in insectivorous singing
birds. They are long and curved in the ibises, and curlews,
and humming birds, short, conical and strong in the gallin-
aceous and granivorous birds, and still shorter and stronger
in the parrots and cockatoos, to break the hard nuts on which
they feed. They are flat and depressed, and generally with
serrated margins in the mallards, and ducks, and swans,
flatter in the spoon-bills, and still broader in the pelicans.
With these forms of the bills and jaws, correspond especially
the forms of the digestive organs, and the claws of the
feet, as the analogous parts correspond with the forms of the
teeth in quadrupeds.

From the length and varied uses of the tongue in birds,
the elements of the os hyoides are much extended longitu-
dinally, especially its cornua, or cerato-hyal portions, which
are often extended so far backwards that they rise upwards
behind the occipital bone, and arch forwards over the skull.
The lingual portions of the os hyoides, the basi-hyal, and
the glosso-hyal elements are also lengthened, like the tongue
and the whole face of these animals. There are in birds,
as in the inferior vertebrated classes, and as in some of the
mammalia, false ribs, anterior as well as posterior to the
true ribs. The ribs are here broad and compressed, securely
articulated to the vertebrae by their long head arid long
tubercle, and they have generaUy a process extending up-
wards and backwards from their posterior margin, especially
those placed towards the middle of the trunk. At their
vertebral extremity the ribs are compressed from before
backwards, so as to present their sharp edge to the cavity
of the trunk ; and at their sternal end they are compressed
in the opposite direction, so as to present their broad con-
cave surface to the interior of the body. The sternal ex-
tremities of the true ribs are united by cartilage to the ends
of the sternal ribs, or ossified sterno-costal cartilages ; and
it is at this articulation that ' the most extensive motions

OR OSSEOUS SYSTEM. J)l

take place during respiration. The broad and thick anterior
ends of the sternal ribs are received into deep articular
cavities on the sides of the sternum, and principally of the
hyo-sternal portions of that bone, and they move freely
and securely in these sternal cavities. The sternum in birds,
as in chelonia, covers the greater part of the anterior surface
of the trunk, and presents, excepting in the strutheous
birds, an elevated, median, longitudinal, external crest,
which greatly extends the surface for the attachment of the
pectoral muscles. Its elements are anchylosed together,
like those of the cranium and pelvis in the adult ; but at an
early period the rudiments of nine elements can be detected
in its composition, which are generally disposed as repre-
sented in that of the peacock, pavo cristatus, (Fig. 48,)
although they vary much in their relative development in
different species. The two epi- sternal pieces (/,) are small,
compressed, anchylosed portions, which rise FIG
upwards between the two coracoid bones
(cy) behind the united clavicles (/*,) and are
ossified to the upper edge of the large and
long ento-sternal element (o,) which is the
largest element of the sternum, and that
which has to sustain almost the entire force
of the pectoral muscles during flight. The
ento-sternal piece (o,) forms the crest of the
sternum, which is hollow and open above in
many aquatic birds, to admit a turn of the
trachea, and is thick and solid in the strong-
est rapacious birds ; it admits air into its interior by aper-
tures on its inner and upper part, and it receives the arti-
cular surfaces of the two coracoid bones (cy) at its upper
edge. The two lateral portions (m,) which give attachment
to the sternal ribs (s, s,) are the hyo-sternal elements, which
are very large in the ostrich. Extending downwards and
backwards from the posterior margin of the hyo-sternal
element (m,) is a long narrow bone, generally bifurcated in
the gallinaceous birds (n,) which is analogous to the hypo-
sternal portion of this bone in the chelonian reptiles ; it is
more extensively developed in the water birds, and most of
all in the raptorial species, where it forms a continuous
piece with the lower end of the ento-sternal. The small

92 ORGANS OF SUPPORT,

tapering terminal cartilage of the sternum, continued from
the posterior end of the ento-sternal portion (o,) is com-
posed of the two xiphi-sternal elements (q,) analagous to
the xiphoid cartilage of the human sternum. The scapular
arch is very strong in birds, to form a solid resisting fulcrum
for the powerful movements of the humerus ; and the -mag-
nitude and strength of these bones corresponds in the dif-
ferent species with the power of flight, or the resistance
they have to oppose to the pectoral muscles on the one side,
and the branchial on the other. The scapulae (Fig. 49. a, a,)
are long, curved, compressed bones, extending along the
back, on each side of the dorsal vertebrae ; they become
more narrow and rounded as they approach the glenoid
cavity, where they suddenly expand to enlarge that cavity
(b^ and they are partially

anchylosed at that place to 'IG* 49*

the large and strong cora-
coid bones (c, k.) The two
coracoid bones (k, ky) extend
from the articular cavity (c,)
for the head of the humerus
downwards and inwards, to
rest their broad expanded
base (i,) in a deep groove on

each side of the anterior margin of the ento-sternal bone.
These coracoid bones almost alone resist the approximation
of the humeri on the median plane, and their descent in the
direction of the pectoralis major on each side, and they have
generally more than double the thickness and strength of
the scapulae. The two clavicles (d, d,) descend converging
from the upper or humeral ends of the coracoid bones (c,)
and they are anchylosed together at their lower ends (e,)
where they commonly present a flat compressed prominence
(/,) connected by cartilage, by tendinous expansions, or
sometimes by anchylosis, with the anterior projecting point
of the crest of the sternum (g.) The clavicles are very
thick and strong, and meet at an obtuse rounded angle in
the most powerful of the rapacious birds, and are long, thin,
and slender, and meet at an acute angle in the gallinaceous
and other birds of feeble flight. In the ostrich the clavicles
are very small and short, and disunited on the median

OR OSSEOUS SYSTEM. 93

plane, as in mammalia. In the arm of the bird there is a
great development of the proximate bones, which by their
magnitude and strength are best able to withstand the re-
sistance to which they are so frequently opposed, while the
more delicate and the more distant bones of the hand are
few and less perfectly developed. The humerus (Fig. 45. e,)
has a broad, compressed, and curved head, the large articular
surface of which plays freely in the shallow glenoid cavity
formed by the scapular and coracoid bones. In the con-
cavity at the back part of the head of the humerus, are the
large apertures by which the air from the axillary cells gains
admission into the capacious interior cavity of this bone.
The distal extremity of the humerus is curved forwards, and
presents a broad articular surface with a double condyle, on
which chiefly rotates the large ulna (Fig. 45. h,) the radius
being a more slender bone. The radius and the ulna are
so articulated as to resist pronation and supination of the
hand, these motions being partially admitted at the head of
the humerus. The arm of the bird is fixed in a state of
pronation, the position best suited to strike the air with
effect, and the hand moves upon the arm, not in the
common mode of flexion and extension, but
by abduction and adduction. At the ex-
tremity of the radius (Fig. 50. «,) and the
ulna (b,) there are two carpal bones (c, «?,)
which are succeeded by a single long meta-
carpal bone (y,} composed of three pieces an-
chylosed together. One of these pieces (e,) on
the radial side of the hand is very short, and
supports the single small phalanx of the radial
or fore finger (h.) The middle meta-carpal
piece (/*,) is by much the largest, and supports
at its extremity generally three phalanges of
the middle finger (k, I, m,) the last of which is
very short and slender. The first phalanx (k,)
of the middle finger has a flat compressed
form, like the meta-carpal bone. At the ulnar
side of the distal termination of the meta-car-
pal bone is a small single phalanx of the outer
or little finger (i,) which is more immediately
connected with the exterior slender portion (g,)

FIG. 50.

*M ORGANS OF SUPPORT,

of the meta-carpal bone. When in a state of rest the hand
of the bird is folded along the exterior edge of the ulna, and
the large primary feathers are thus extended along the sides
of the trunk to the tail. These fingers appear to be the
analogues of the three middle fingers of the human hand,
and there is sometimes a single phalanx covered with a spur
on the radial side of these three fingers of the hand of the
bird.

The bones of the pelvis, though anchylosed into a single
piece, consist of the ordinary three elements on each side,
as seen in that of the wild swan, (Fig. 51.) The two iliac
bones (a,) still extend forwards and backwards from the
cotyloid cavity along the sides of the sacrum, as in the
saurian reptiles ; and, as they are anchylosed to that bone,
the sacro-iliac articulation is here of great extent and secu-
rity. The iliac bones anchylose behind with the two ischia
(b,) and the sacro-sciatic
notch of mammalia is FIG-

converted into a fora-
men (/«,) but in the os-
trich it is a notch open
behind, as in most quad-
rupeds. The ossa ischii
are anchylosed at the
cotyloid cavity (/,) with the pubic bones (c,) and the three
pelvic bones enter into the composition of that cavity for
the head of the femur, as in other classes. The pelvic
bones are lengthened backwards, and taper downwards thin
and elastic to the anterior part of the pubis, where the two
pubic bones (d, d,) are separate and free at the symphysis,
excepting in the ostrich, where they are united by sychon-
drosis, as in mammalia. The obturator foramen (i,) has
here a long and narrow form, corresponding with the length-
ened form of all the bones of the pelvis. The pubic bones
are here free and elastic at their anterior terminations (d, d,)
that they may be susceptible of the necessary dilation, when
the large, brittle, and inflexible eggs are passing out through
the cloaca, and also to afford the necessary support to the
contents of the pelvis. The cotyloid cavities (Fig. 51./5)
are generally complete foramina, without an interior osseous
septum, and they are placed far forwards upon the pelvis,

OR OSSEOUS SYSTEM.

in order to be more under the centre of gravity, to poise
alone the entire trunk. The posterior extremities having more
of the ordinary use of these members in other animals than
the anterior, have their osseous elements constructed more
according to the normal character and number of these parts
in other vertebrated classes. The head of the femur is small,
short, and rounded,, with a very short cervix, and projects
at a right angle a little lower than the trochanter major,
which here forms an extensive arch from before backwards.
The femur (Fig. 45. v,) in birds is generally very short and
strong compared with the succeeding bones of the leg, even
in the long-legged grallatores, and the running birds. The
air is admitted into this hollow bone, by a large aperture on
the fore part of the trochanter major. Between the two
prominent sharp condyles of the femur and the upper end
of the long tibia is placed the patella, as in quadrupeds. At
the upper and outer part of this long and strong tibia (Fig.
45. w,) is a small, imperfectly formed fibula, thin, tapering,
and anchylosed to the tibia at its lower part, and separate
above ; sometimes it is separate throughout. The lower
part of the tibia presents a broad, expanded, articular sur-
face for the succeeding long bone of the meta-tarsus, which
is single, like the meta-carpal bone of the hand. There is a

small tarsal bone in the ostrich, which
thus leads to the structure of this part in
the lowest ruminantia. The tibia and the
meta-tarsal bone are long in most birds, but
especially in the wading birds, as cranes and
storks. The meta-tarsal bone (Fig. 52. «,)
has two articular depressions at its upper
part, for the two inferior condyles of the
tibia, and at its lower end it commonly pre-
sents three pulley-like articular prominences
(b,) for the attachment of the three toes,
which are directed forwards. It resembles
that of the jerboa among the rodentia.
There is generally at the inner and back
part of this bone another very small meta-
tarsal bone (€,) for the attachment of the
toe which is directed backwards. The
outer toe of birds has five phalanges (1 . d,)

FIG. 52.

96 ORGANS OF SUPPORT,

the second has four phalanges (2. e,) the third has three
(3 /,) the inner toe directed backwards has two phalanges
(4. ff9) and the spur seen in the male of many gallinaceous
birds is supported by a single osseous phalanx (5.) Where
there are only three toes, as in the rhea, and emu, and cas-
sowary, the inner toe has three phalanges, and the outer
still five ; and in the ostrich, where there are only two toes,
the inner toe has four phalanges, and the outer five, as in
other birds ; so that the toes are here deficient on the inner,
and not on the outer side of the foot where the number of
the phalanges remains uniformly the same. In wood-peckers,
parrots, cockatoos, and other zygodactylous birds, the outer
and the inner toes are both directed backwards, the better
to assist in climbing, and consequently one of these has
five phalanges, and the other only two.

XXIII. Mammalia. — The bones of mammalia are inter-
mediate in density and compactness of texture, and in the
extent of their anchylosis between those of birds and those
of reptiles. They have generally thick and solid parietes
traversed by numerous sutures, which have disappeared
in birds, and in the interior of the long bones are large
cavities filled with marrow, which in birds are filled with
air, and in reptiles with a cancellated structure. The most
imperfect forms of the skeleton are presented by the ceta-
ceous mammalia, where the vertebral column, as in fishes,
is the chief organ of progressive motion, and almost alone
developed. They have no sacrum, nor pelvic extremities,
and their cervical vertebrae are more or less anchylosed to-
gether. Their long bones are almost in the condition of
those of reptiles, filled with a loose, internal, cancellated
structure, containing a thin, serous, or oily marrow, and all
their bones have a coarse, fibrous structure compared with
those of land mammalia. The head is still extended in a
straight line with the vertebral column, the arms are con-
structed for swimming, and the tail is expanded horizon-
tally, for the vertical movements of the body, required by
their aerial respiration, as seen in the skeleton of the por-
poise (Fig. 53.) The bodies of the vertebrae terminate in
flat surfaces, united to each other by an elastic, fibro-cartila-
ginous, interposed substance, which admits of the necessary
movements by means of its compressibility. The terminal

OR OSSEOUS SYSTEM.

FIG. 53.

flat portions of the bodies of the vertebra remain long, se-
parate, as detached pieces, in these animals. The cervical
vertebrae are sometimes all anchylosed together, and in the
herbivorous cetacea, where the neck is longer and more
moveable, ah1 the cervical vertebrse are larger, and detached
from each other. In the preserved skeletons of the laman-
tine there are but six cervical vertebrse. The spinous pro-
cesses extending upwards from the dorsal and coccygeal
vertebrae (h, h, h}) are here long and strong, and often sup-
port a cartilaginous hunch upon the back, in form of a ver-
tical fin (i}) and inferior spinous processes are developed
below the coccygeal vertebrae, for the protection of the great
blood-vessels. The transverse processes are also long, for
the attachment of powerful muscles, and they limit the ex-
tent of lateral motion in the column. Many of the last
coccygeal vertebrae (uy) have only their round bodies developed,
and admit of free and extensive motion in every direction.
The anterior part of the thorax is the most fixed, to give at-
tachment to the powerful muscles of the neck and of the arms,
and the ribs are there attached both to the bodies and to
the transverse processes of the vertebrae ; but on the pos-
terior part of the thorax, where there is greater freedom of
motion, the ribs are attached only to the ends of the long
transverse processes. There are no bones extending into
the fin-like cartilaginous hunch (i,) upon the back, nor into
the lateral cartilaginous expansions of the tail (v,) as we find
in these parts in fishes. The sternum is very short, and
confined to the anterior ribs, and the sternal ribs are gene-
rally ossified, as in many other quadrupeds, and in birds, and
in many reptiles. Although there are no legs, we always

PART I. H

98 ORGANS OF SUPPORT,

find here two lengthened slender pelvic bones, unconnected
with the rest of the skeleton, and having the rib-like form of
the iliac bones of fishes and amphibia.

The head is most lengthened, straight, and fish-like in the
piscivorous cetacea, as the porpoise (Fig. 53,) where the
face is chiefly composed of the long maxillary and inter-
maxillary bones, («,) and the vomer, which is extended
between them. The small nasal bones are placed far back-
wards upon the forehead, behind the nasal apertures, and
behind them is the narrow band of the frontal bone, which
is in contact with the occipital, from the parietals being
confined to the temporal region of the head. From the
great extent and the vertical position of the occipital bone,
and the extension of the maxillary bones upon the forehead,
the cranium is here generally small, compared with the face,
and is much extended transversely ; great extent of surface
for muscular attachment is thus given to the back part of the
head, and great development to the jaws in front, for pre-
hension. The teeth, like those of fishes and reptiles, are
adapted for prehension, and not for mastication ; they are
similar in form, conical, bent, and placed alternately in the
opposite jaws. In the cachalots, they are present only in
the lower jaws, which are very narrow, and in contact with
each other throughout the greater part of their course, and
thus are opposed only to the middle part of the roof of the
mouth. In the foetus of the balsena there are teeth in the
lower jaws, which soon entirely disappear, and the alveolar
margin of the upper jaws are occupied with vertical, long,
thin, horny laminae, which are fimbriated on their inner
edges, and by straining the water, they collect the small
floating animals on which the whales feed. The malar bone
forms the lower boundary of their very small orbit (f,) and
is here a remarkably thin, slender, and curved bone, com-
pared with the massive malar bone of the herbivorous spe-
cies, which require a more powerful masseter for mastication.
The petrous and tympanic portions of the temporal bone,
though anchylosed together, are connected only by cartilage
to the other bones of the skull, the ethmoid bone presents
no cribriform plate, and the infraorbitary foramen is divided
into a series of small apertures extending forwards along the
upper jaw-bones. The right side of the head is generally

OR OSSEOUS SYSTEM. 99

more developed than the other, and the nostrils are inclined
thus to the left side. The arms of these cetacea are moved
in a piece, as fins, and the articulations of the several bones,
especially of the hand, are very imperfectly formed. There
is no clavicle, but the great expansion of the scapula (Fig.
53. n,) presents a large surface for the powerful muscles of
the humerus, by which the arm is chiefly moved, the suc-
ceeding bones being scarcely moveable on each other in the
living state. The humerus (o,) has a large round head, but
is compressed at its lower end, like that of a turtle, and
the same compressed form is seen in the radius (p,) and the
ulna (q,) and in the detached round bones of the carpus (r,)
the meta-carpus, and the phalanges of the five fingers
(*, t.)

In the herbivorous cetacea, as in the dugong (Fig. 54,) we
find a much nearer approach, in many parts of the skeleton,

FIG. 54.

to the ordinary condition of these parts in the land quad-
rupeds, than in the piscivorous tribes, especially in the forms
of the jaws and teeth, in the cervical vertebra, and in the
whole bones of the arms. The cervical vertebrae (a,) are
here detached and moveable on each other, and the neck is
thus longer and more flexible. The occipital bone (#,)
rises to a much less extent upon the cranium and its ele-
ments, like those of most of the other bones, remain long
disunited. The cranical cavity is smaller considerably than
in the former group. All the sutures of the cranium re-
main very loose, and the petrous and tympanic portions of
the temporal bone are permanently detached from the squa-
mous, as in the other cetacea. The frontals are divided by
a continuation of the sagittal suture ; the malar or jugal

H 2

100 ORGANS OF SUPPORT,

bones (/,) are here of great size and strength, the jaws are
of great depth, for the long molares, with flat crowns adapted
to their vegetable food, and the intermaxillary bones ( g,) are
of great size, for the long and large incisors (h,) which they
contain. The lachrymal bone forms a small portion of the
margin of the orbit, and is interposed between the anterior
end of the jugal bone and the malar process of the frontal.
The muzzle is straight in the predaceous tribes (Fig. 53. #,#,)
and thus directed to the prey, which floats or swims in the
water ; but in the herbivorous cetacea it is bent down to the
fuci, which are attached to the bottom of the sea. As the neck
is here more lengthened and moveable, the trunk is more fixed
in its condition by the development of the sternum and of more
numerous and larger ribs, the pelvic arch is more complete,
and the inferior spinous processes of the coccygeal vertebrae
are larger and stronger. The whole bones of the arms are
constructed more according to their normal forms in the
land mammalia, and these animals are able to clamber upon
rocks on the sea shore, like seals and walruses, and to ma-
nipulate their young while suckling at their pectoral mammae.
The scapula (o,) is more narrow and lengthened, the hu-
merus (q,) is longer and more cylindrical than in the blow-
ing cetacea, and the radius (/?,) and ulna (r,) have a more
lengthened and rounded form, and admit of more extensive
motion at both extremities. The forms and articulations
are more complete, and admit of freer motion in all the
bones of the carpus (s}) and meta-carpus, and in the pha-
langes of the fingers (u) ; so that the hands possess much
more prehensile power in the herbivorous than in the pisci-
vorous cetacea.

The skeletons of ruminating quadrupeds still present
many marks of an inferior grade of development, when
compared with carnivorous and higher orders of mammalia,
especially in the small size of the cranial cavity, compared
with the face, in the deficiency of teeth in the jaws, in the
want of clavicles, and in the imperfect condition of the arms
and legs, and of the hands and feet, as seen in the skeleton
of the fossil elk (Fig. 55.) Their frontal bone, which ge-
nerally develops horns from its tuberosities, is divided by a
longitudinal suture, and the parietals are anchylosed toge-
ther, to consolidate the skull behind. The tuberosities of

OR OSSEOUS SYSTEM,

101

FIG. 55.

the frontal bones in the males of most genera of this order,
extend upwards into permanent processes, of a loose can-
cellated structure, which are covered with permanent, horny,
and extravascular sheaths, as in antelopes, sheep, goats and
oxen. In the deers the antlers are deciduous, organized
osseous processes, continued from the same tuberosities of
the frontal bones, with thick, dense, and very compact pa-
rieties, and a softer internal core passing through all the
branches. These deciduous horns, which are diverticula of
the blood at stated seasons, and intimately connected in
their development with the condition of the genital system,
are annually cast and renewed, each successive pair being
larger and more complex in form than the preceding. There
are permanent rudimentary osseous horns in the giraffe,
together with a median frontal eminence, like that on the
frontal bone of the two-horned rhinoceros ; but there are
no horns in the camels, dromedaries, lamas, pacas, and

102 ORGANS OF SUPPORT^

musk-deers, where there are canine teeth, and they are
wanting in the females of most ruminantia. The orbits are
thrown to the sides of the head by the great development
of the frontal bones, which are chiefly occupied with air ;
from the large sinuses, they communicate with the tem-
poral fosse, but have a complete osseous margin by the
extension downwards of the malar process of the frontal to
the jugal bone. The lachrymal bone extends downwards
over the face, to assist in lengthening the head, the alveolar
portions of the jaws are deep, for the long malar teeth, and
the broad nasal bones cover a large and long nasal cavity.
The turbinated bones are of great size, the malar bone is
prolonged over the face, the zygomatic arch is very small,
and has the coracoid process of the lower jaw extended to a
great height through it, which limits the lateral motion of
the lower jaw during mastication. The long slender inter-
maxillary bones are generally destitute of teeth, the malar
teeth with oblique crowns have the layers of enamel directed
longitudinally, the motion of the lower jaw being from side
to side. The lower jaw being much narrower than the
upper, the lateral motion is required to bring the teeth into
apposition for mastication, and the glenoid and condyloid
surfaces are therefore flat, to admit of this extensive motion.
The cervical vertebrae (Fig. 55. c,) are of a lengthened form,
with short processes, to give length and mobility to the
neck, and the spinous processes of the dorsal vertebrae (c?,)
are long, for the attachment and support of the long neck
and often weighty head. The ribs extend over a great part
of the trunk (z9) and the transverse processes of the lumbar
vertebrae are of great length, to assist in the support of the
heavy abdominal viscera. The pelvis (p,) is lengthened
backwards, the sacro-iliac articulation (n,) is more or less
oblique, to give greater elasticity to the movements of the
legs, and the coccygeal vertebrae (o,) are numerous and
highly moveable, the tail being generally employed as a
hand, to brush away insects from the surface of the body. The
anterior part of the thorax, destitute of clavicles, is so com-
pressed that several of the first pairs of ribs are almost straight,
by which the arms are approximated and brought more nearly
under the centre of gravity of the heavy trunk, from which
they would have been thrown out and endangered by the

OR OSSEOUS SYSTEM. 103

interposition of clavicles. The elements of the sternum (y,)
placed in a line, are extended longitudinally, like the ribbed
part of the trunk, and are generally narrow and compressed
laterally. The long narrow scapulae (e,) have scarcely the
rudiments of the acromion and coracoid processes developed.
The humerus (/,) and the femur (q,) are generally short and
strong bones, much inclined from the vertical position, es-
pecially in the lighter and nimbler forms of this order. The
secure articulations of the long radius (h,) and tibia (s,)
admit of free flexion and extension, but are fixed in a state
of pronation. The imperfect ulna is anchylosed below to
the back part of the radius, and consists chiefly of an elon-
gated olecranon (g,) to secure the elbow joint and afford a
strong attachment to the extensor muscles of the arm. At the
lower end of the radius are found the four usual small carpal
bones of the first row separate, and the four of the second
row are here generally anchylosed into two pieces (i,) which
form the articulation with the long single meta-carpal bone (k.)
This broad meta-carpal, like the compressed meta-tarsal bone,
consisted in the foetus of two separate bones, and it retains, in
the adult state, longitudinal median grooves before and
behind, which mark the line of original separation. There
are often likewise the slender rudiments of two other meta-
carpal and two meta-tarsal bones seen, one on each side of
these long anchylosed bones of the meta-carpus (k,) and
metatarsus (t?,) and the rudiments of two corresponding
toes are found at the sides of all the feet. There are two
long pulley-like articular condyles at the lower end of the
meta-carpal bone, and there are three phalanges on each
of the two toes prolonged to the ground. The trochanter
major is large, and elevated on the strong and short femur
(q) ; the long and strong tibia (s,) forms the whole articulation
with the femur and with the astragulus (u,) and fibula forms
only a small splint. The calcaneum (/,) extends upwards
in the elevated heel, like the olcranon ( ^,) at the elbow.
Besides the astragulus and calcaneum, there are generally
two cuneiform bones, and a compound cubo-scaphoid bone
in the tarsus of ruminantia ; but there is one more bone in
the camel, as in the tarsus of the solidungulous pachyderma.
The long, anchylosed, compound meta-tarsal bone (v,) is more
compressed and narrow than the corresponding broad and

104 ORGANS OF SUPPORT,

flattened meta-carpal (&,) of the hand, and has attached to its
inferior pulley-like articular processes two toes (l,m}) prolonged
to the ground, which like the fingers of the hands, have three
phalanges in each. Great elasticity is given to the extremities
in the ruminating quadrupeds by the alternately inclined
direction of most of the bones, and great security is given to
the articulations by the pulley-like form of nearly all the joints.

The skeletons of the pachyderma, like those of rumi-
nating quadrupeds, have no clavicles, and have the jaws and
teeth adapted for vegetable food ; the articulations are con-
structed generally for limited, slow, and secure movements,
and the bones are more strong and massive in their pro-
portions. The nearest approach to the ruminating form of
the skeleton is that of the solidungulous quadrupeds, where
we observe, as in the camels, three kinds of teeth in the
jaws. The jaws and face are there lengthened to reach the
turf, and the upper and lower maxillary bones are of great
depth, to lodge the long prismatic, quadrangular molar teeth.
The cranial cavity is small, as in all the pachyderma, and
the orbits are surrounded with an osseous ring, as in the
ruminantia. The transverse ridge of the occipital bone is
much elevated, for the attachment of the strong muscles
and ligaments of the neck. By the great development of
the interposed bones, the orbits are thrown to the extreme
lateral points of the head, and directed to the sides. The
ethmoid bone presents internally two large and deep fossae
for the olfactory tubercles, and the turbinated bones pre-
sent a very extensive surface, for the distribution of the first
pair of nerves. In their long neck, their long spinous pro-
cesses of the dorsal vertebrae, the compressed form of the tho-
rax, the lengthened form of the bones of the scapular and pelvic
arches and of their extremities, they more approach to the
ruminantia than to the ordinary short and massive forms of
the pachyderma, and the anchylosis which extends in the
ruminating quadrupeds only through the inferior row of the
carpal and tarsal, and through the meta-carpal and meta-
tarsal bones, is here continued downwards through the pha-
langes of the two middle fingers and toes to the extremity
of the hands and feet.

In most of the ordinary pachyderma, as the pecari, the
babyrussa, the tapir, the hippopotamus, and the rhinoceros the

OR OSSEOUS SYSTEM. 105

back part of the skull presents an elevated transverse ridge,
and a broad surface of attachment for the muscles and liga-
ments of their heavy head and strong neck, the head being
sometimes employed in digging, as in the hog tribe, or to
support a strong instrument of defence, as in the rhino-
ceros, or being proportionally large and weighty, as in the
hippopotamus. The air is admitted from the frontal sinuses
over a large portion of the diploe in the babyrussae and
other animals of the hog tribe, to extend the external sur-
face without adding to the weight of the head, as we see to
a much greater extent in the huge head of the elephant.
All the processes of the cervical vertebrse are here more
strongly developed than in the long flexible neck of the ru-
minantia, and the spinous processes of the dorsal vertebrse
are lengthened and strong, and generally terminated by
round tubercles. The scapula is generally broader at its
vertebral margin, and the strong pelvic arch is more vertical
in its direction. The extremities are generally shorter and
more massive, and the separate bones more completely
formed than in the former groups of quadrupeds, the ulna
and the fibula being developed throughout, and four toes,
at least, generally reaching the ground on all the extremities.
As the kind of vegetable food varies much more here than
in the ruminating quadrupeds, there is a greater diversity
in the forms of the teeth, and of the jaws, and of many
other parts of the skeleton.

The general forms and proportions of the bones
most common in the ordinary pachyderma are seen
in the massive skeleton of the rhinoceros ( Fig. 56, )
where the head and neck are more lengthened than
in the proboscidian tribe, and the trunk is almost en-

106 ORGANS OF SUPPORT,

tirely encompassed by large and broad ribs. The fore part
of the head presents an arched appearance from the eleva-
tion of the anchylosed nasal bones (a,) for the support of
the horn, and the intermaxillaries (#,) are very slender and
short, and contain each a single incisor tooth. The orbits
(e,) are quite continuous with the temporal fosse, as in the
tapir, but in the hippopotamus they are surrounded with a
bony margin, as in the solidungula. The inferior molar
teeth are here remarkably narrow, when compared with the
broad cubical crowns of those of the upper jaws, and the
two long conical inferior incisors (c,) project forwards, like
those of a hippopotamus. The great elevation of the oc-
cipital bone (d,) the great size of all the processes of the
cervical vertebrae (g,) and the magnitude of the spinous
processes of the dorsal vertebrae (/,) indicate the force with
which the head is moved, and the powerful offensive instru-
ments which it supports. In the two-horned species the
anterior part of the frontal bone is raised, like the nasal
bones, into an arch for the support of the posterior horn.
The infra-orbitary foramen is of great size, for the nerves
of the large expanded upper lip, like that of the elephant,
for the nerves of the proboscis. The spinous processes
continue large and strong on the lumbar, and even the
sacral vertebrae, and the sacro-iliac articulation (<?,) is nearly
vertical to that of the femur with the cotyloid cavity,
as in many of the other ponderous skeletons of pachy-
derma. The spine of the scapula (i,) arches backwards
over the infra-spinati muscles, as in the elephant. The ulna
and the fibula are developed and distinct throughout their
whole extent, and the olecranon of the arm, like the patella
of the leg, is of great size, as are the muscular processes of
all the bones of the extremities. The iliac bones (q,) are
expanded transversely, the tuberosities of the ischia ex-
tend outwards, and the cotyloid cavities are directed down-
wards. Three toes are continued to the ground before and
behind, consisting each of three phalanges, the two first of
these phalanges have a broad cubical form, and the last is
remarkable for its rough irregular form, and its extension
transversely. The terminal phalanx of the middle toe on
all the feet is elongated transversely on both sides, but in
the other toes it is elongated only on one side, that most
remote from the middle toe ; so that ample support is

OR OSSEOUS SYSTEM. 107

afforded to the broad hoofs, and a broad base for the pon-
derous carcase of this powerful quadruped. The carcase
being still more ponderous in the elephants, the scapular
and pelvic arches, and the whole extremities, are more
vertical in their direction, and the scapular and iliac bones
are of great breadth. The heavy molar teeth, and the large
tusks, and the large proboscis give so much weight to the
head, that the neck in these proboscidian animals is very
short, and the external surface of the cranium is greatly
extended for muscular and ligamentous attachments, with-
out adding to the weight of the head, by the vertical cells
of the diploe being filled with air admitted through the
Eustachian tubes. From the strong attrition to which the
molar teeth of the elephants are subjected, they are com-
posed of numerous thick transverse plates of enamel en-
closing the osseous portions and united together by an en-
veloping crusta petrosa, and they are successively worn
down to their base, and replaced by new teeth from behind,
for eight or nine times during the life of the animals, while
the long tusks are renewed but once. The base of the
lower jaw projects more than the human.

In the monotrematous animals the skull is thin, smooth,
and diaphanous, and with a lengthened toothless muzzle, as in
birds, as we see in the skeleton of the ornithorhyncus (Fig.
57 ,) where there are only two horny thin crowns of molar
teeth (A,) at the back part, and on each side of the two jaws.

FIG. 57.

Their intermaxillary bones converge at their free anterior
extremities ; there is a median longitudinal osseous crest in
the ornithorhynchus, extending along the interior of the occi-
pital and parietal bones, and the occipital foramen (d,) is
prolonged upwards, narrow in a vertical direction. The
scapula (/,) especially in the ornithorhyncus, is lengthened

108 ORGANS OF SUPPORT,

and curved backwards, like that of a bird ; and, as also in
that oviparous class, the large coracoid bones reach and
unite with the sternum, the clavicles (m,) meet and are
anchylosed together in front, and the sternal appendices are
ossified. The ribs encompass a large proportion of the
trunk, and long marsupial bones (1,) are extended forwards
from the margin of the pubic bones. The long arms and
legs, and the extended feet of the ornithorhyncus suit it for
its aquatic life, while the stronger extremities and short feet
of the echidna are suited for digging in the ground. In
many of the edentata the upper and lower jaws are long,
narrow, curved, and toothless, as in birds, and the trunk, as
in the armadillos, is surrounded with very broad ribs. The
pubic bones also are often lengthened backwards, and meet
at a very narrow symphesis, and there is generally a sacro-
sciatic foramen, as we find in birds, in place of the ordinary
sacro-sciatic notch of quadrupeds. In the sloths there are
false ribs anterior to the true ribs, as well as behind them,
as we observe in most of the oviparous vertebrata, and the
zygomatic arch is open in some of the ant-eaters, as the
myrmecophaga jubata. From the longitudinal movement of
the lower jaw in the rodentia, its condyles are extended
longitudinally, and the layers of enamel are disposed trans-
versely in the molar teeth. Their two chisel-shaped incisors
above and below are kept sharp by means of the thin layer
of very dense enamel which coats their anterior surface, and
the broad crowns of their molares are kept rough by the
unequal densities of the layers of enamel and of osseous
substance which compose them. As the cerebral hemis-
pheres are destitute of convolutions, the surfaces of the
skull are thin, smooth, and often diaphanous, as in birds,
and the squamous portion of the temporal bone generally
remains long separate from the other elements of that bone.
The mastoid bone generally forms a large bulla communi-
cating with the tympanum, as in the carnivorous quadrupeds,
and the orbit is here also continuous with the temporal
fossa. The intermaxillary and the nasal bones are of great
size, the zygomatic arch has its convexity directed down-
wards, and the palatine holes are of great size, as in birds.
The clavicle is sometimes complete and strong, and in many
it is developed only in its central part ; the sacrum and the
iliac bones are long, and the pelvis is extended backwards,

OR OSSEOUS SYSTEM.

10!)

as in many edentulous quadrupeds and birds. Although the
radius and the ulna are free on the arms, the fibula is very
imperfect, and is anchylosed to the tibia on the posterior
extremities. Notwithstanding the differences observed in
the skeletons of the different kinds of marsupial quadrupeds,
they agree in the possession of two triangular, lengthened,
marsupial bones articulated moveably to the anterior margin
of the pubes, and extending forwards behind the pouch and
the mammary glands, and in contact with the recti muscles
of the abdomen.

The skeletons of carnivorous quadrupeds have gene-
rally the bones of a more compact and dense texture,
combining lightness with strength in their forms, and
secure, yet freely moveable in their articulations, which
corresponds with their great muscular development, with the
extent of their respiratory system, with the increased energy
of all their functions, and with their living wants and in-
stincts. From their great cerebral and intellectual develop-
ment, their cranial cavity is comparatively large, and to give
strength to their jaws their face is generally short and broad,
as seen in these skulls of the Bengal tiger, felis tigris (Fig.
58. A. B.) The transverse occipital ridge («,) is re-
markably high and prominent, for the strong muscles of
the neck, as also the longitudinal ridge (b, b,) extending
forwards along the occipital and parietal bones, which

FIG. 58.

HO ORGANS OF SUPPORT,

alone separates the the two large temporal muscles
from each other. The sides of the cranium often assume
a compressed form, especially where the temporal muscles
are of great force as in the hyaena and in old carnivora, where
many of the cranial sutures also disappear. The mastoid
process (A. r,) forms a large cavity or bulla communicating
with the tympanum, and enlarging the organ of hearing in these
as in other nocturnal animals. The zygomatic arch (e, e,) is
of great magnitude and strength, and is convex above. The
temporal fossse are continuous with the orbits from the de-
ficiency of the frontal, (B. #,) and the malar bone (B. A,)
behind the orbits, and the zygomatic process (B. c, d,)
extends laterally at a right angle from the squamous por-
tion (A. c,) of the temporal, in order to form a long trans-
verse glenoid cavity for the transverse articular condyle (A. #,)
of the lower jaw. The parietal bones (b, b,) early anchylose
in the animals of this order, so as to resist the tearing action
of the temporal muscles, which have a great surface for inser-
tion on the large coronoid process (A. t,) which forms the
entire ramus of the lower jaw. There is a strong ossified
tentorium extending inwards between the brain and cerebel-
lum, to protect these delicate organs from the effects of their
leaping and bounding movements. The infra-orbitary fora-
men (/, /,) is large for the nerves of the upper part of the face,
and the upper part of the nasal cavity is enlarged for the
ethmoid and turbinated bones, by the great breadth of the nasal
process (k, k,) of the superior maxillary bone and of the nasal
bones, (z, i.) The intermaxillaries (o, o,) contain each three
teeth, the outer of which are the largest, and the canine teeth
(w, »,*) above and below are large, conical, curved, and insert-
ed in very deep alveoli, (m, m.) The large transverse condyle
(A. #,) of the lower jaw is little raised above the base, and is
secured in a very deep glenoid cavity of the temporal bone
that the jaws and teeth may meet with great precision,
especially the molar teeth which have sharp cutting crowns
(A. u, v, w,) directed longitudinally, and entirely covered with
a very dense and thick layer of enamel. The anterior small
detached molar teeth (w,) behind the canine (ny) are the false
molar es ; the larger prominent cutting molar tooth, with a
tubercle at the interior of its base, is the carnivorous tooth ;
(A. u,} ; and the flat broad-crowned tuberculated teeth, which
are more or less developed behind these are the tuberculated

OR OSSEOUS SYSTEM.

Ill

molares, (A. a.*) of which there is only a very small one in the
feline carnivora. The lachrymal bone is here almost confined
to the orbit. By the zygomatic arch being carried forwards
beneath the orbit and the condyle of the lower jaw being
extended backward, the masseter muscles act with great force
and advantage on the lower jaw, their place of insertion being,
like that also of the temporal, considerably anterior to the
point of resistance and of rotation. The transverse processes
of the atlas and the spinous process of the axis are of great
length, and the processes generally of the cervical vertebrae
for the strong muscles of the neck, by which they have to
tear their food to pieces, or to carry their victims to a place
of retreat. There is great strength with flexibility in all parts
of the vertebral column, and hence their slender ribs encom-
pass a smaller portion of the trunk than in the ponderous
bodies of the pachyderma, but their thoracic cavity is wide
and capaceous. The lumbar region is extensive, and the trans-
verse processes of the vertebrae are there directed forwards.
The sacro-iliac articulation is very oblique, giving greater
elasticity to the attachment of the legs to the trunk, and the
coccygeal vertebras are generally very numerous and moveable.
The scapula is broad and strong, the clavicles imperfect or
wanting, and the muscular processes of the bones of the arm
and fore-arm are strongly marked. Above the inner condyle
of the humerus (fig. 59, C. «,) is a large oblique foramen,
through which the ulnar artery passes forwards, protected
from external pressure, as we see also in some of the climbing
quadrumana. In the soft and flexible hand of the carnivora,
as in that of the tiger (fig. 59, A.), the carpal bones are
generally reduced to seven
by the anchylosis of the
scaphoid and lunar bones
(a), and the succeeding
bones of the metacarpus (c)
and the phalanges of the
fingers (d, e,) present strong
and secure articulations, the
last phalanx on the hands
(e, e,) as on the feet (B. e, e,)
being directed upwards to d
preserve the sharp claws

FIG. 59.

112 ORGANS OF SUPPORT,

from abrasion. The inner toe of the anterior and posterior
extremities (A. d, B. £,) so imperfectly developed in most of
the digitigrade carnivora is generally longer in the plantigrade
and the aquatic species.

In the true insectivorous quadrupeds without wings, as the
hedge-hogs shrews and moles, the jaws are more lengthened,
the canine teeth are often small, the molar teeth have broad
crowns with an outer and inner row. of sharp-pointed tuber-
cles to seize and bruise the insect food, the scapular arch
is strengthened by clavicles, the radius and ulna are separate
and moveable on each other, the rudimentary fibula is anchy-
losed to the tibia, all the feet are plantigrade and pentadacty-
lous and the toes and claws are strong for scraping and digging.
The orbit is continuous with the temporal fossa, the zygoma-
tic arch is very slender and straight, the infra-orbitary foramen
large, and the articulation of the lower jaw flat. There is
great mobility in the articulations of the hedge-hogs, as in
other spiny and scaly quadrupeds, to allow of their coiling
their body into the form of a ball for protection. The ante-
rior portion of the skeleton is more developed than the pos-
terior in the moles, to enable them more easily to burrow,
and in the cheiroptera to favour their flight through the air.
The cranial bones, the occipital, the parietal, and the frontal,
are remarkably extended forwards in the mole, compared with
the extent of the anterior bones of the face. The coronoid
process of the lower jaw rises high through the zygomatic arch,
and the angle of the jaw is prolonged backwards and a little
inwards over the mastoid portion of the temporal bone.
The fore part of the septum of the nose is ossified in this
animal as in the hogs, to support the nose in digging.
The spinous process of the axis is large and extended back-
wards, but the succeeding cervical vertebrae are like narrow
distant rings, almost destitute of spinous and transverse pro-
cesses, to allow the freest motion in this part with safety to
the enclosed spinal chord. The sternum is extended for-
wards to a great distance before the first pair of ribs, and is
carinated like that of a bird, to afford an extensive surface of
attachment to the large pectoral muscles ; and for the same
reason,, as well as to lodge large respiratory organs, the ribs
encompass a widely expanded thoracic cavity. The clavicles
are very short and strong, the scapulae long and narrow, the

OP OSSEOUS SYSTEM. 1 1 .'J

humerus short and widely expanded at both ends, the ole-
cranon of great magnitude and extent, the bones of the hand
short, fixed, and strong for rapidly excavating the ground, and
one of the carpal bones is lengthened and curved forwards
to increase the inner surface of this digging instrument.
The pelvis and the posterior extremities are very small, the
pelvic bones are anchylosed to the sacrum, the pubics are
separate in front, and the fibula is reduced to a small process
of the tibia as in most other digging and burrowing qua-
drupeds.

The skeletons of the cheiroptera are constructed for flight
and present, as in the moles, the anterior portion much more
developed than the posterior. The jaws are lengthened for
the reception of numerous broad-crowned sharp- tuberculated
insectivorous molar teeth. The canine teeth are generally
long and pointed, the intermaxillary bones small and imper-
fectly ossified, the palatine bones separate, the zygomatic
arch is very feeble, and the orbits, for their very small eyes,
are continuous with the temporal fossse, as in carnivora.
The bones of bats are generally light and compact in their
texture and some of their ordinary sutures, as the sagittal,
early disappear in the cranium. The orbit is surrounded
with a complete osseous margin in the pier opus. In the
rhinolophus the intermaxillaries are small, soft, and cartilagi-
nous, and contain each but one incisor tooth; and in the
nycteris these bones are united by a moveable articulation to
the upper jaw-bones, like the moveable upper bill of parrots
and cockatoos. The cervical and lumbar regions of the
skeleton admit of free motion, and the long iliac bones are
often anchylosed to the sacrum as in the feathered tribes.
The coccygeal vertebrae are often prolonged to support an in-
ter femoral membrane, as in the pteropus and rhinolophus.
The long pubic bones scarcely meet at the symphesis, and
the cotyloid cavities are directed obliquely backwards which
assists in the retroversion of the feet. The scapulae have a
broad expanded form, the clavicles are long and strong, the
coracoid process is lengthened and curved downwards and
inwards, and the fore part of the sternum is often deeply
carinated like that of a bird. The long cylindrical humerus
is succeeded solely by the radius in the fore-arm, the ulna
being reduced to its olecranon, which often forms a separate

PART I. 1

114 ORGANS OF SUPPORT,

moveable patella at the elbow, like that of the knee-joint.
The carpal bones occupy a very small space in the hand, and
the long fingers are here fixed in a state of extension, as they
are in the hand of the bird, the thumb alone admitting of free
flexion and extension. The hand of the bats rotates on the
carpal end of the radius by a motion of abduction and adduc-
tion, as the wing of the bird, so that, when folded, the little
finger lies along the outside of the radius. The thumb is not
enclosed in the interdigital membrane, but is extended for-
wards free as a prehensile organ for progressive motion, or
for suspending its body. The long slender meta-carpal
bones and phalanges of the four succeeding fingers support
the interdigital membrane, and there are often claws on the
fore and on the middle finger. The small legs are twisted
outwards from their commencement in the oblique cotyloid
cavities of the open pelvis. The femur is of a cylindrical
form, slender, and with a large articular head, and a large
trochanter minor directed forwards, the trochanter major
being here turned backwards. The fibula is broad at its
tarsal extremity, but is almost lost before it reaches the
upper end of the long slender tibia. From the retroverted
direction of the cotyloid cavities and of the whole legs the
tibia is" placed externally, and the fibula internally. The
short bent calcaneum directed inwards has often extending
from its tuberosity, along the margin of the interfemoral
membrane, a slender elastic bone, which supports that
membrane. The slender parallel toes directed backwards
terminate in long, curved, sharp prehensile claws, by which
they most frequently suspend their body in an inverted posi-
tion, the best suited for their launching instantaneously into
the air with outspread wings, when called by hunger or
alarm.

In the lowest of the quadrumanous animals, as the lemurs
of Madagascar, the jaws are still lengthened for numerous
insectivorous molar teeth, and the skeleton generally is
adapted for the horizontal position of the trunk. The oc-
cipital foramen is placed near the posterior margin of the
skull, the mastoid cells are as large as in carnivorous quad-
rupeds, and although the orbit is here surrounded with an
osseous margin, it is still continuous behind with the tem-
poral fossa. The cranial cavity, however, is here capacious,

OR OSSEOUS SYSTEM. 115

and the ordinary sutures of the human cranium continue
permanent, as in the higher forms of quadrumana. The
sagittal suture often traverses the frontal bone, and the an-
terior frontals are sometimes seen separate. The temporal
fossa is small, the zygomatic arch feeble, the condyles of the
lower jaw and their glenoid cavities flat, the lachrymal bones
extend downwards from the orbits, and are perforated on
their facial surface, and the nasal bones, unlike those of
higher quadrumana, are broad, long, straight longitudinally,
and form an expanded arch in their transverse direction, as
in carnivora and other inferior tribes. The ramus of the
lower jaw is still very short, its condyles are nearly as low
as the alveoli of the teeth, and the coronoid processes rise
high through the zygomatic arches. The inferior incisor
teeth, four in number, as in the simise and in man, project
straight from the lower jaw, as those of a kangaroo, and
this direction is seen also in the stenops, the galago, and the
lichanotus. The face and entire head become shorter as
we ascend through these genera to the true simiae of the old
and new continents. In the simiee the lamdoidal, the sagit-
tal, the squamous, and the coronal sutures advance forwards
on the cranium more and more as the cerebral centres and
the cranial cavity enlarge, and the face becomes proportion-
ally small. As the muzzle shortens, the facial angle en-
creases by the elevation and expansion of the frontal bone,
and by this shortening of the jaws less space is afforded
for numerous molar teeth. The orbits approximate, assume
an anterior and parallel direction, separated only by a narrow
ethmoid, and their communication with the temporal fossae
is cut off by an osseous partition formed by the extension
of the frontal and malar bones. The temporal fossa be-
comes reduced in size, the zygomatic arch short and straight,
the condyloid articulation of the lower jaw flat and free,
the lachrymal bone confined to the orbit, and the nasal
bones flat, narrow, short, and often anchylosed together.
The intermaxillaries continue permanently separate up to the
orangs, and the incisors, four above and below, as in man,
continue more inclined forwards than in the human jaws.
The canine teeth, as instruments of prehension and of de-
fence, continue large and projecting, and the sharp tuber-
cles of the molar teeth of the insectivorous and nocturnal

i 2

116

ORGANS OF SUPPORT,

FIG. 60.

makis, become more short and rounded in the higher quad-
rumana, correspond with the softer quality of their succu-
lent and juicy food. The ramus of the lower jaw ascends
higher and more abruptly, and the coronoid process is re-
duced in length and strength. The occipital foramen ad-
vances forwards on the base of the skull by the expansion
of the posterior region, and the occipital bone becomes con-
fined to the basilar aspect of the cranium. The supra-or-
bitary foramen is generally absent, or a mere notch, and
the infra-orbitary hole is commonly divided into several
small apertures. In the orangs the intermaxillaries anchy-
lose to the upper jaw-bones, and to each other in the
adult, as in the human
jaws. The general forms
of the bones and articu-
lations of the rest of the
skeleton are adapted for
the semi-erect or climb-
ing position of the trunk,
as seen in the skeleton
of the mona monkey,
cercopithecus mona, (Fig.
60.) The cervical, and
lumbar, and coccygeal
regions of the column
generally admit of free
and extensive motion.
The cervical vertebrae
have their spinous pro-
cesses simple and point-
ed, the dorsal vertebrae
nearly of the same num-
ber as in man, and the
lumbar vertebrae encreas-
ed in number at the ex-
pense of the sacrum.
The transverse processes
more directed for-

are

wards towards the head
than the human in these
free and moveable lumbar vertebra;.

In the prehensile tails

Oil OSSKOrs SYSTEM. 117

of most of the American quadrumana the coccygeal verte-
brae are en creased in number and mobility, and in the
strength of their articulations ; they are generally more
lengthened and cylindrical in the long- tailed quadrumana
of the old continent. The scapulae are still lengthened and
narrow, but with an elevated spine, the clavicles are strong,
and curved like the human, the coracoid and acromion
processes are of considerable size, and the glenoid cavity
comparatively deep. The humerus is more curved than
the human, and the radius and ulna are more lengthened and
slender, and admit of very free pronation and supination.
There are often nine bones in the carpus by the division of
one in the second row, to give greater mobility and prehen-
sile power to the whole hand, and for the same object all
the bones of the meta-carpus, and the phalanges of the
fingers, which have the same number of bones as in the
human hand, are much lengthened. The thumb is shorter
and less opposeable to the other fingers than in man. The pos-
terior members have the same long, slender, and prehensile
character as the anterior. The sacrum generally consists
of three anchylosed vertebree, the iliac bones are long and
narrow, and directed longitudinally, and the tuberosity of
the ischium expands, outwards, covered with the callosities
on which these animals generally rest. The femur is much
curved, its neck short, and the trochanter major much ele-
vated. The long, slender, and separate tibia and fibula admit of
free motion in the foot, as a prehensile organ, and which is in-
creased by the shortness of the tuberosity of the calcaneum.The
astragalus is twisted obliquely outwards, and this inclination,
increased by the form of the calcaneum, is communicated
through the scaphoid and cuboid, and the three cuneiform
bones to the meta-tarsus and the whole foot, which is thus
made to rest obliquely on its outer margin, and the inner
toes are raised from the ground, and left free for prehension.
The inner toe of the foot is here attached in a very oblique
manner to the internal cuneiform bone, which is placed
much below the others, and it is thus opposed slightly to
the other more lengthened toes of the foot, and that organ
is converted into a prehensile hand. In the highest of the
quadrumana, the chimpanze of Africa, the nasal bones are
more raised from the face, the incisors more vertical, and

118

ORGANS OF SUPPORT,

FIG-

the facial angle greater than in the inferior forms, the scapulae
and the iliac bones are more expanded, the calcaneum extends
more backwards, and the forms and proportions of all the
bones of the skeleton approach most closely to the human.

The forms of the bones and of the articulations of
the human skeleton are adapted to support the trunk
in a vertical position upon the feet, by which the organs
of the senses are directed forwards, and the arms are left
free, for various employments. By the great develop-
ment of his cerebral
organs, and the su-
perior elements of his
cranial vertebrae (Fig.
61,) the skull is large,
and its cavity capa-
cious. The organs of
the senses being con-
fined to a narrow
space the face is small,
and it is nearly straight
from the frontal hour
to the chin, from the
slight projection of
the muzzle, excepting
in the negro, where
the projection of the
jaws and teeth, and
the receding of the
frontal bone, reduce
the facial angle more
near to that of the
orangs. The occipital
foramen, and the two
occipital condyles are
advanced further for-
wards on the base of
the skull than in any

of the quadrumana ; so that the head is more nearly poised
by the centre of its base on the atlas, and on the vertical
column of the trunk. The forehead, and nasal bones, and
the chin project more than in the nearest quadrumana, the

OR OSSEOUS SYSTEM. 119

incisors are more nearly perpendicular, the canini shorter,
and the tubercles of the molares more rounded, correspond-
ing with the softer condition of his food. The squamous
portion of the temporal bone, the great ala of the sphenoid,
and the superior portion of the occipital, are here more
largely expanded ; the temporal fossa, the zygoma, and the
coronoid process of the lower jaw are small. The ramus of
the lower jaw is larger, and forms a more acute angle with
the base, the condyle is more elevated and convex, and the
glenoid cavity for its reception is deeper than in the quadru-
mana. The nasal process of the superior maxillary and the
lachrymal bone pass more into the orbit, and the orbits are
more parallel in their direction, which gives greater preci-
sion to all visual impressions. The vertebral column in the
direction of the median plane has a greater sigmoid curva-
ture ; the cervical vertebrae have their spinous processes
more broad, short, and bifurcated ; the transverse processes
of the lumbar vertebrae extend more at a right angle from
the bodies -, the sacrum is longer, broader, and more arched,
and the coccyx is comparatively small. The ribs are more
convex, the sternum shorter and broader, the clavicles are
more curved and strong, and the scapula is shorter and more
expanded at its vertebral margin. The glenoid cavity of the
scapula is more lateral in its direction, the humerus, with a
large articular rounded head, is more straight ; the olecranon
of the ulna is comparatively short, and the bones of the
thumb are more lengthened and more opposeable to the
other fingers. The pelvis is shorter and broader than
in the inclined bodies of the quadrumana ; the iliac bones
are more expanded and convex, more extended over the
acetabulum, and with a longer crest ; the tuberosity of the
ischium is less prominent, and the symphesis pubis is
shorter. From the greater breadth of the pelvis, the femora are
more distant from each other, their head has a less extensive
articular surface, and is marked by the ligamentum teres
which is absent in the orangs ; the cervix femoris is longer,
and directed more obliquely downwards, and the trochanter
major is less elevated. The bones of the legs, stronger and
more distant from each other, afford a brOad and secure base
of support for the erect and weighty trunk, and the strength

120 ORGANS OF SUPPORT, &C.

of this base is encreased by the plantigrade position of the
whole foot, the parallelism and magnitude of the inner toe,
the advanced position of the astragalus, the extension back-
wards of the tuberosity of the calcaneum, the fixed condi-
tion of the tarsus, and the strength of the meta-tarsal bones,
and the phalanges of the toes.

-

CHAPTER SECOND.

ORGANS OP ATTACHMENT, OR LIGAMENTS.

THE solid parts of the skeleton, whether external or in-
ternal, are held in connexion and are allowed to move on each
other with more or less freedom, by means of soft parts,
which are almost as inert in their vital properties as the
bones themselves, and this low degree of vitality better
enables them to sustain the stretching and compression to
which they are continually subjected. Even in the highest
animals the ligaments which connect the bones, and
the cartilages which bound their contiguous sufaces, are
scantily supplied with blood-vessels and nerves, and have a
corresponding low degree of sensibility, great slowness of
growth and reproduction, and great tenacity of life. In the
lowest tribes the component pieces of the skeleton are held
together by the simplest mode of union, they have not their
points of contact protected by a layer of soft cartilage,
lubricated with synovia, and connected by capsular ligaments
and external ligamentous bands, they are partially or entirely
imbedded in a common tough connecting matter, which, by
its elasticity, admits of the few required motions. No
articulations nor ligaments appear in the soft, gelatinous,

122 ORGANS OF ATTACHMENT,

transparent bodies of the animalcules, but in the poriphe-
rous animals the dense silicious and calcareous spicula which
compose their solid frame-work are supported and maintained
in their positions by a more tough, elastic and firm portion
of the general cellular tissue of the body, perhaps stimu-
lated to condensation by the presence of these earthy crys-
talline bodies. By the motions of the body, produced by
external bodies, the points of these sharp spicula are made
to project from this tough connecting matter in various
directions from the gelatinous surface of the body, from the
margins of the pores, or into the internal canals. The tubu-
lar filaments in the horny species anastomose with each
other freely throughout the whole body, like the continuous
connecting matter in the earthy species. The jointed ap-
pearance seen in most flexible tubular keratophytes, as ser-
tularia, plumnlaria, campanularia, is confined to the exterior
covering, and does not interrupt the course of the fluids
circulating through the enclosed fleshy part. These thinner
portions and annular strictures of the horny covering allow
of the more ready development of new branches, cells, or
vesicles, and of the incessant movements of all their parts
produced by the ever-restless sea. The branches of the
cellaria thuya drop off regularly from below upwards along
the stem, at these apparent joints. The minute calcareous
spicula of many corticiferous and fleshy zoophytes, as gor-
gonia and lobularia, are connected by the general cellular
substance of the body. The black, flexible, elastic matter
deposited in concentric layers between the calcareous inter-
nal solid pieces of the isis hippuris, are merely uncalcified
portions of the common animal matter which pervades the
whole skeleton, and connects all its earthy particles ; they are
like the uncalcified portions of corallines, but are secreted,
as the calcareous matter of the skeleton, by the enveloping
fleshy crust. The exterior sharp spines of pennatulte are
connected and moved by the coriaceous irritable skin of the
body. The skeletons of zoophytes, as those of higher tes-
taceous animals, are insinuated into the minutest inequalities
of the surface of rocks, and thus adhere firmly, by being
exuded in a soft semi-fluid state, and then condensing. The
cartilaginous, internal, reticulate filaments of many alcyonia
are continuous, like those of horny poriphera, throughout

OR LIGAMENTS. 123

the whole body. Broken fragments of the solid skeletons
of zoophytes are readily re-united by the exudations from
the fleshy substance, of similar ossific matter around the
broken extremities, as we see in the testaceous extravascular
coverings of higher classes. The delicate vertical, crescentic
lamina of the velella is continuous with the more thick
horizontal plate on which it rests, and is not detached by
maceration. The moveable, lateral, solid plates of the stel-
lerida are connected both by irritable and ligamentous bands,
as are also the solid jointed moveable spines frequently
developed on their upper surface. The plates composing
the shells of the echinida are united by harmonic sutures,
and the spines are united to the tubercles by the enarthroid
form of articulation, where there are marginal muscles, an
exterior capsule, and generally a round central ligament,
like the ligamentum teres of the femur, as in the cidaris and
spatangus. The unconsolidated portions of the general
cuticular exudation form the means of connection between
the dense external parts of the trunk and its appendices in
the helminthoid and in the entomoid classes of diplo-neura.
This we already find in the segments of the trunk and of
the rudimentary antennse of some of the higher epizoa, in
the tough epidermic membrane connecting the pieces of
pedunculated cirrhopodous shells, and in the segments and
cirrhi of the same animals, and of many of the higher an-
nelides. In the more solid skeletons of the entomoid
classes, the calcified coverings of the segments of the trunk
and of the antennse and palpi are partially retracted within
each other, and are connected by numerous muscles, and by
the true skin, and its continuous thin epidermis. The other
appendices developed from the sides of the body present
chiefly the ginglimoid forms of articulation without the aid
of ligaments, where one portion of the skeleton is locked
into another, and where the motions of the joints are very
secure, but limited in extent ; these forms of the articula-
tions wre see especially in the strong members of the larger
Crustacea and coleopterous insects. The valves of con-
chifera are connected together both by the teeth of the
hinge, which are often locked into each other, as in spondy-
lus, and by the tough extra-vascular ligament, which gro\vs
by successive layers of epidermic matter, and constantly

124 ORGANS OF ATTACHMENT,

tends by its elasticity to separate the two valves between
which it is placed. The eight transverse plates composing
the shell of the chitons have generally a strong coriaceous
ligamentous band connecting their margins, and secreted
like the ligaments of conchifera, by the surface of the skin.
The byssus of conchifera consists of horny filaments se-
creted in a fluid state by a gland behind the base of the foot;
they are conveyed along a median groove of the foot, to be
attached to external solid bodies, to anchor the more delicate
shells, as pinna and other mytilacious bivalves. The horny
operculum of most of the testaceous turbinated gasteropods
is of a condensed albuminous nature, secreted in successive
superimposed layers added to the attached surface by the
muscular foot, to which it adheres in the same manner as
the retractor muscle adheres to the columella of the shell.
From the ginglimoid hinge of the shells of conchiferous
mollusca admitting only of flexion and extension in one
direction, few, though powerful, muscles are required to
effect their motions ; but the joints of the articulated classes
of animals being generally formed by a segment of one
sphere being enclosed within another, and consequently ad-
mitting of rotation in every direction, numerous muscles are
required to effect their varied movements. The ginglimoid
crural joints of the entomoid classes being formed by hollow,
cutaneous, solid tubes, have generally one very strong and
broad flexor tendon, and a more narrow and feeble extensor
tendon, into which all the muscles of the joint are inserted,
and they are deeply excavated and covered only by the
unconsolidated, thin, tough epidermis and skin on the side
to which the joints are inflected. There are no opercula, or
moveable pieces of the shells in the pteropoda or cephalo-
poda, and the soft cartilaginous, organized, internal bones of
the cephalopods are connected only by muscles, and by thin
unconsolidated portions of their own soft matter.

In the soft, flexible, cartilaginous skeletons of the lowest
cyclostome fishes, there are scarcely any traces of articula-
tions or ligaments, and in the higher chondropterygii they
are almost confined to the most moveable parts connected
with mastication, and the fins for progressive motion. In
fishes, as in the inferior classes, where the skeleton becomes
more consolidated by earthy depositions, the articulations

OR LIGAMENTS. 125

and ligaments become more developed and distinct. The
vertebral ligaments of osseous fishes are white, fibrous, and
dense in their texture, and by their elasticity they bring
back forcibly the vertebral column to the straight position
when it has been drawn to either side by the lateral strata
of muscles. The moveable intermaxillary, palatine, and
superior jaw bones are connected by a tough fibro-cartilagi-
nous membrane, as well as by muscular attachments. The
moveable articulations of fishes are mostly effected by a
tough interposed cartilage, which envelopes the contiguous
ends of the bones. This substance is much softer than the
corresponding fibro-cartilaginous parts of higher classes, and
is more readily dissolved by boiling water. In place of the
interposed elastic sacs between the cup-like cavities of the
vertebrae of fishes, or the firm connecting layer of fibro-
cartilage between the vertebrae of mammalia, we find the
bodies of the vertebrae of reptiles united by distinct move-
able articulations, or enarthroses, with strong capsular liga-
ments and synovial secretion, and many of the vertebrae of
birds, especially of the neck, are united by the same free
and secure articulations. In the amphibia and in the rep-
tiles, most of the articulations are constructed on a simpler
plan than in the warm-blooded classes ; there is yet no in-
ter-articular cartilage between the condyle of the lower jaw
and the temporal bone, nor a ligarnentum teres between the
femur and the cotyloid cavity ; but the articular surfaces
of the long bones are covered with smooth and firm carti-
lage, are lubricated with synovia, and are enclosed in strong
capsular ligaments. The articular processes of the vertebrae
have here their synovial capsules, and the spinous processes
their inter-spinal ligaments. The articular cavities of the
joints are less deepened by cartilaginous margins, the inter-
nal loose cartilages of the joints are more rare, the exterior
ligamentous bands are more simple in their arrangements,
and there are fewer immoveable synarthroses than in birds
and mammalia. The capsular ligaments are thinner, and of
a more dense texture in birds than even in mammalia, and
more synovia is poured into the joints, especially of the
neck and extremities, on account of the extent and rapidity
of their movements and the high temperature of their body.
Each end of the tympanic bone is here enveloped in its

ORGANS OF ATTACHMENT,

synovial capsule, although most of the cranial bones have
lost even their connecting sutures, and most of the vertebrae
have their bodies united by free and secure synarthroses.
Less pressure being exerted on the joints in the light bodies
of birds than in the heavy bodies of mammalia, there is a
much thinner layer of elastic cartilage on the contiguous
ends of their bones than in quadrupeds, and from the light-
ness of their head, as in other oviparous vertebrata, com-
pared with that of most quadrupeds, they have no necessity
for a ligamentum nuchae to support it. The thick, firm,
elastic layer of fibro-cartilage interposed between the flat
bodies of the vertebrae of quadrupeds is the mode of arti-
culation which best corresponds with the strength and the
slow and limited motions required in that region of their
skeleton. The synovial capsules of the articular processes
of the vertebrae are more developed in the active trunks of
carnivorous and of climbing mammalia than in the more
weighty and motionless bodies of pachyderma and rumi-
nantia. The long anterior and posterior vertebral ligaments
are of great strength and elasticity along the pliant columns
of cetacea without and within the spinal canal, and in the
long and pliant tails of many quadrupeds we find the highly
moveable bodies of the coccygeal vertebrae united by syno-
vial capsules, to facilitate their motions. The heavy-headed
herbivorous quadrupeds have the ligamentum nuchee of
great size and strength, extending from the occipital
protuberance along the spinous processes of the dorsal,
and often of all the succeeding vertebrae to the coccygeal,
sending a pair of laminae downwards to be attached to each
spinous process. In the light-headed and muscular car-
nivorous species this ligament is very small, and generally
extends forwards only to the large spinous process of the
axis, and in many of the most active rodent and quadruma-
nous mammalia, no trace of this cervical ligament is per-
ceptible. In the strong extremities of heavy herbivorous
quadrupeds, where limited motions and secure articulations
are required, the capsular ligaments are less loose and
elastic than in the carnivora, where greater freedom and
extent of motion are necessary, and greater force of action.
Strong transverse ligaments pass in the elastic feet of rumi-
nating quadrupeds from the one penultimate phalanx to the

OR LIGAMENTS. 127

other, to prevent the tearing of the two toes asunder during
their rapid and bounding movements, which are not com-
patible with the extensive movements of the toes of carni-
vorous species. In the slow-moving extremities of the ele-
phant, the rhinoceros, and the hippopotamus, there is no
° ligamentum teres to fix the head of the femur to the cotyloid
cavity, nor do we find it in the kangaroo^ the sloths, or the
monotrema, nor in the sedate orangs, which so much ap-
proach the human species.

CHAPTER THIRD.

ON THE MUSCULAR SYSTEM, OR ACTIVE ORGANS OF
MOTION.

FIRST SECTION.

General Observations on the Muscular System.

THE movements of animals are effected by the muscular
system, the most remarkable and essential property of
which is the power of contracting with rapidity and force
on the application of stimuli. The fibrous structure is not
a constant character, nor essential to the irritability of this
system, although that vital property is greatest in all the
higher classes, where this structure prevails. These irri-
table fibres appear to consist of lineal aggregates of fibri-
iious globules, the union of which is most intimate where
the contractile power is greatest. The cohesion of these
globules is least where all lineal arrangement is lost, in the
lowest tribes of animals, in which the slowly irritable fleshy
substance appears as a soft, homogeneous, cellular tissue.
The muscular system effects all the locomotions of animals,
and all the movements of their organs of relation, and forms

MUSCULAR SYSTEM. 129

a constituent part of all the active organs of vegetative life 5
so that the consideration of many parts of this system is
inseparable from the history of particular organs. The
contractity of the muscular fibre is intimately connected
with the extent of respiration in animals, being feeble in the
radiated and molluscous tribes, where the respiration is
small, and more energetic in the articulated classes, where
the respiration is greater, and generally aerial, and for the
same reason it is less powerful in the imperfectly aerated
reptiles than in the feathered tribes where the air permeates
every region of the body. It is by means of this system
that animals are enabled to move to and fro, to seize and
masticate their food, or to convey it through their alimen-
tary cavity, to circulate their fluids through the body, to
force all discharges from their system, to bring the surround-
ing element into contact with their blood, to produce various
sounds for mutual intercourse, and to vary to infinity the
outward form and expression of their body ; the different
parts of this great and complicated system can therefore be
classified and arranged according to the functions to which
they are most subservient. The movements of voluntary
muscles appear to be accompanied with a distinct perception
of their active state, and to become associated with feelings
of the mind ; so that they chiefly belong to the organs of
relation, or the functions of animal life, while those of the
involuntary muscles, unaccompanied by sensations, and more
independent of the rest of the body, are chiefly connected
with the organs and functions of vegetative life. In most
muscles the component fibres run parallel to each other, with
numerous minute nervous fibrils and capillary blood-vessels
running in the same longitudinal direction between them,
and freely anastomosing to produce a complicated net-work
throughout the whole texture. Although the muscular fibres
are organs distinct in their whole course, they are united
into fasciculi, and these into entire muscles by means of cellu-
lar tissue, and they are generally inserted into strong, tough,
fibrous tendons, which are less supplied with nerves and
blood-vessels than the muscles themselves, and are destitute
of irritability. The muscles of the highest classes of red-
blooded animals, during their development, pass through
the soft, colourless, homogeneous, and gelatinous condition

PART I. K

130 MUSCULAR SYSTEM.

of those of the lowest animals, before they assume the red
colour, the dense fibrous structure, and the highly irritable
and contractile property, which they possess in their mature
form.

-

SECOND SECTION.

Organs of Motion in the Cyclo-Neurose, or Radiated
Classes.

Although the aid of the microscope has not enabled us to
detect muscular fibres in the transparent and active bodies
of the polygastric animalcules, most of them exhibit distinct
signs of lively irritability in contracting bending and stretch-
ing their whole body, or its anterior prehensile part ; and they
are carried rapidly to and fro in their dense element by the
rapid vibration of minute cilia generally disposed in regular
series on their external surface. The cilia are the organs of
respiration, as well as of locomotion in these animalcules,
and they are generally longest and largest on the anterior
part of the body, especially around the mouth, and in the flat
forms, as the cyclidium, the long cilia form a vibratile zone
around the inferior margin of the body. Where the ante-
rior part of the body is obliquely truncated, as in many of
the kolpoda, the vibration of the cilia gives a revolving mo-
tion to the whole body in its progression. In most of the
trichodae and paramtecia the cilia are disposed in regular
close longitudinal series extending over the whole outer
surface of the body, and of the greatest length around the
oblique mouth. The vorticella have two rows of cilia dis-
posed around their anterior circular extremity. The cilia
have been observed in almost every class of animals from
the polygastrica to the mammalia, and both on the surface
and in the interior of the body ; but the means by which
they are moved have not been detected. No cilia have been
seen in the spermatic animalcules, which are extremely
minute and are moved by the lateral motions of their slender
tail, like tadpoles, which implies greater irritability and
muscular development than in the ordinary polygastrica.

MUSCULAR SYSTEM. 131

The action of vibratile cilia is always so much independent
of the will, or connection with the rest of the body, that it
continues for some time after the part to which they are
attached has been severed from the animal ; and this is
observed even in those of adult birds and quadrupeds. Jaws
containing sixteen teeth have been detected in the loxodes
cuculluluSy which necessitate great muscular development in
this minute polygastric animalcule.

The soft cellular tissue which pervades the whole fibrous
texture of poripherous animals, and lines their pores, canals,
and vents, does not exhibit distinct signs of irritability or
contractility when acted on by the strongest stimulants, and
the currents continue to be impelled rapidly through these
passages even in thin portions cut from the body. It is
probable, therefore, that the currents are produced solely by
means of cilia which are numerous and large over the sur-
face of these animals, when in the state of gemmules newly
detached from the parent. The ciliated free gemmules of
poriphera do not exhibit signs of irritability by contracting
their body, and changing their form like those of zoophytes.
The cellular substance of the poripherous animals, being
still of a soft and semi-fluid consistence, is incapable of
effecting any perceptible movements in the fibrous skeleton
which it permeates. The general fleshy mass of the body
possesses distinct though languid irritability in almost all
forms of zoophytes, although the fibrous structure is seldom
developed in any part. This property is manifested in the
lobidaria by the spontaneous slow contraction and dilation
of its body at different periods of the day by the influence
of temperature and light, or by the slow contraction of a
part of the body which has been touched or irritated. This
fleshy contractile part is the same which secretes the solid
matter of the skeleton in this class, and developes the po-
lypi from different parts of its surface. The relation of this
irritable and secreting part to the internal axis in the corti-
ciferous zoophytes is seen in the section of the isis hippuris,
(Fig. 62. B.) where the calcareous solid portions (#,) and the
flexible, elastic, ligamentous parts (b,) occupy the centre of
the fleshy substance (c,) and the cells of the polypi (d, d9)
are seen to be here confined entirely to this irritable crust,
and to leave no impression on the axis. The polypi are the

K 2

132

MUSCULAR SYSTEM,

FIG. 62.

most irritable and contractile parts of the body in all zoo-
phytes, and the most exquisitely sensitive to external im-
pressions. The polypi are prehensile sacs or mouths deve-
loped from and continuous with the fleshy substance of
zoophytes, their margin is surrounded with delicate fleshy
arms or tentacula, which vary in different species from six
to more than thirty. The polypi are seen extended from
the fleshy substance of the isis in Fig. 62. A., d, d, the
fleshy part covers the branch at (c,) and is removed
from the jointed skeleton at (0, a, b, b.) The fleshy part of
the isis appears to be incapable of bending the joints of the
skeleton, and it has as little effect on the skeleton in the
other corticiferous zoophytes. Where it forms thin laminae
consolidated with calcareous matter, and disposed around
the parietes of cells, as flustrce, eschara, and cellarice, it
is as little capable of moving the axis. In the cellaria
loriculata (Fig. 62. C,) where the cells of the polypi (a, a,)
are disposed in regular consecutive pairs with their apertures
opposite, and with contracted articulations (c, c,) at the
bases of the cells, neither the enclosed polypi, nor the
fleshy part of the entire animal are capable of bending the
articulations. The slow contraction of the pennatula phos-
phorca coils up the thin flexible extremities of its calcareous

MUSCULAR SYSTEM. 133

axis, and moves the retroverted spines of its exterior surface
so as to push the animal slowly along a rough surface. In
the vaginiform zoophytes the internal currents of the body are
not produced by the contractions of the internal fleshy parietes,
though compared by Cavolini to a heart, but by the action
of vibratile cilia, and the open base of the polypi often con-
tracts, as if by a movement of deglutition. The polypi
being the organs by which the food is attracted, seized, and
digested, and the surface of the body aerated, they possess
the most complicated structure and the highest vitality. The
tentacula surrounding the mouth, as in the flustra carbesia
(Fig. 63. d}) have generally minute vibratile cilia disposed
along their sides, by the action of which currents of water
conveying animalcules and other food, are directed towards
these prehensile and digestive cavities. In these compli-
cated and highly irritable polypi of the flustra, we perceive
numerous muscular bands (Fig. 63. c,) connecting the lower
part of the polypus with the aperture of the cell, and others
passing from the same part of the polypus downwards, to
connect it with the bottom of the cell (e.) The vibratile
cilia move the currents outwards along one side of each
tentaculum (d,) and inwards along the
other side, and they are generally vi-
sible only while they move in the di-
rection of the currents which they
produce, that is in their forward stroke.
When in full activity the cilia are in-
visible in their backward movement,
from the velocity with which they
resume their position, to commence a
new stroke forward. And as vibratile
cilia are thus generally perceptible only
in their slow forward impelling move-
ment, they have some resemblance to
a stream of globules flowing always in one direction. There
are about fifty cilia on each side of a tentaculum in the
flustra carbesia, and nearly forty millions on a moderate
specimen of the entire animal. In many zoophytes they
are much more numerous ; so that these fixed and plant-like
animals, though possessing a very low degeee of irritability
in their general mass, are well provided with active organs

134 MUSCULAR SYSTEM.

to bring their food towards them, and to renew the stratum
of water in contact with their surface, for the purpose of
respiration. The vibratile cilia are generally disposed around
the mouth of the polypus where the cilia of the tentacula
themselves are not vibratile, but merely lateral extensions of
these prehensile organs. The naked hydrae are irritable and
contractile in every part of the body, and their texture ap-
pears cellular throughout, without any distinct muscular
fibres. The fibrous structure is partially developed in the
irritable parts of some of the larger and more complicated
polypi, as those of the pennatula, virgularia, and lobulariay
and they form distinct longitudinal and sphincter bands in
the actinia and in the polypi of some of the larger litho-
phytes, as fungiae, explanaria, and car yophy Ilia, which so
much resemble fixed actiniae.

Many of the acalepha swim, like animalcules, by the
movement of external, longitudinally-disposed, vibratile
cilia. These cilia are large, and generally visible by the
naked eye, and are distinctly supported by parallel rays,
like the fins of a fish ; but the muscular apparatus by which
they are so rapidly vibrated is not perceptible. From the
development of the nervous system, and even of eyes con-
taining a crystalline lens, seen in some of the animals of
this class, it is probable that the parallel fibrous striae per-
ceptible in the highly contractile mantle of medusae are of a
muscular nature. The long tentacular filaments which we
so frequently find developed from the periphery of the man-
tle possess a high degree of irritability, and are exquisitely
sensitive. The muscular development is less required in the
hydrostatic or physograde species, which are supported at
the surface of the sea by an air-bag, or a sac filled with a
gaseous secretion due to its own parietes. The large pecti-
nated cilia of the ciliograde acalepha have the same
kind of rapid vibratile motion as the minuter forms of these
organs seen in zoophytes and animalcules, and they continue
in the same manner their movements independent of the
rest of the animal in parts severed from the body.

The fixed crinoid echinoderma appear to move their
numerous calcareous articulations by the exterior irritable
and secreting fleshy covering which envelopes all parts of
their body. In the free stellerida the nervous and the mus-

MUSCULAR SYSTEM. 135

cular systems "are already obviously developed, and eyes are
observed on the asterias. The segments of many of the
stellerida are connected together and moved by muscular
bands, which are distinctly fibrous, and both longitudinal
and circular fibres are seen on the highly irritable and con-
tractile feet, which extend from the ambulacra. The same
muscular structure is seen in the long tubular prehensile feet
of the echinida, where the segments of the trunk are im-
moveably united by harmonic sutures. Strong adductor
and abductor muscles are seen attached to the moveable
pieces of the jaws in many of these species, and strong
muscular fasciculi pass from around the base of the external
spines to the periphery of the tubercles on which they move.
In the naked holothurige, the tough, exterior, coriaceous
covering is . highly irritable and contractile ; these animals
are provided with five crowded longitudinal rows of the
usual tubular, muscular, prehensile feet extended like those
of other echinoderma by the injection of water into their
median cylindrical cavity ; their dental apparatus is provided
with its muscular bands, and the five larger of these osseous
plates around the mouth give attachment to five strong lon-
gitudinal muscular bands which extend beneath the skin to
the posterior extremity of the body.

THIRD SECTION.

Muscular System of the Diplo-Neurose, or Articulated
Classes.

The development and energy of the muscular system are
greater in the articulated than in the radiated, or even the
molluscous classes, which corresponds with the greater ex-
tent of their respiration, and with the higher condition of all
their other organs of relation. In the subcutaneous mus-
cular tunic of the nematoid entozoa, we already perceive the
longitudinal and transverse short interrupted filements, which
are more symmetrically arranged into bands and muscles,
where the segments of the trunk are more consolidated and

136' MUSCULAR SYSTEM.

distinct in higher classes. In the outer layer of this mus-
cular coat, the short interrupted and interlacing fibres have
a transverse direction, and those of the same kind forming
the inner layer have a longitudinal direction, and are generally
grouped to form four lengthened contractile bands ; the
longitudinal fibres compose distinct muscles, especially at
the anterior part of the body where they are attached
to the moveable parts of the mouth. The muscular fibres
are not perceptible and the irritability is most feeble in
the cystoid and cestoid forms of this class. The long
pliant organs of attachment by which the entomoid forms
of these entozoa adhere to the surface of aquatic animals,
present generally distinct longitudinal muscular bands, as we
see in lern&a, and they are also developed for the movement
of the maxillae and other dense, and articulated parts of
their body.

The muscular apparatus is most distinct and complicated
in most of the rotiferous or wheel animalcules, and cor-
responds with the high development of their nervous and
other important sytems. There are numerous fasciculi at
the anterior part of the body, for the movement of the long
vibratile cilia which surround the mouth ; the maxillae are
enveloped and moved by a strong muscular apparatus, which
can be deeply retracted within the body by longitudinal
bands, and similar longitudinal bands extend along the
whole internal parietes of their body for the retraction
and bending movements of the trunk. The muscles of
these animals, though most distinct, are almost as colourless
and transparent as the crystalline parietes of their body.
They are carried through the water by a slow and gliding
movement, produced by the rapid vibration of the long cilia
which surround the anterior parts of their body, and these
cilia while in action, appear like a revolving wheel from their
forward, slower and more forcible movement being alone
perceptible by the eye. The currents of water and the
surrounding particles move in the same direction in which
the circles appear to revolve.

In the cirrhopods we find united in the same animals,
both the articulated and the molluscous forms of the mus-
cular system, and these are accompanied with a fixed con-
dition of the exterior shell, and a high activity of the enclosed

MUSCULAR SYSTEM. 13;

animal. The peduncle and the mantle present distinct
musclar fibres, the dorsal part of the abdominal cavity near
the head, is attached by several muscular fasciculi to the
mantle and the shell, and a strong adductor muscle, as
in bivalves, passes straight across from one moveable piece
to the opposite. The fleshy parietes of the abdominal cavity,
the conical tubular funnel prolonged from that cavity, and
the haunches and innumerable tubular articulations of the
cirrhi present distinct muscular fasiculi. In the pedun-
culated forms, as in the pentalasmis, the whole of the con-
vex dorsal part of the enclosed animal, is covered with
crossing muscular fibres, which pass off in numerous sepa-
rate fasciculi to be attached to the inside of the proximal,
or closed part of the enveloping multivalve shell ; these
draw the animal forcibly and quickly back into the shell
after its body has been protruded for respiration or for
food. The haunches of the jointed members, and the base
of the funnel-shaped tube, also receive distinct muscles from
this fleshy dorsal part of the cirrhopod for their varied
movements.

The annelides generally present a distinct muscular tunic
of a complicated structure immediately beneath the outer
tough and annulated integument, and intimately united
to it, besides the muscular fasciculi appropriated to the
motions of the lateral setae and cirrhi which extend from
muscular sheaths. This subcutaneous muscular tunic is
resolvable into distinct layers, and each of these into in-
numerable separate fasciculi ; the most exterior of which
have generally a transverse or an oblique direction, and
the most interior a longitudinal course, as seen in the
same part of the entozoa. These longitudinal muscles are
more or less "distinctly divided into longitudinal bands, as
those of the nematoid entozoa, and as we see even in
the holothuria, the actinia and many other of the radiated
animals. This muscular tunic of the annelides appears
to act on the interior viscera, as well as on the external
imperfectly developed segments. Its exterior layer is some-
times double, the one portion consisting of oblique fasciculi
and the other of tranverse, and both of these exterior
to the usual internal layer of longitudinal fasciculi. The
several muscles are disposed similarly in the different seg-

138 MUSCULAR SYSTEM.

ments of the same: worm, and even in different worms,
in the larvae of insects, in myriapods, and in the segments
of the trunk of most of the articulated classes of animals.
In the common earth-worm, as in many others, the mus-
cular sheaths for the extention and retraction of the short
conical curved and pointed feet consist chiefly of radiating
fibres which extend from around the base of these hollow
spines. The fleshy lips of this animal are provided with
several longitudinal and circular muscles appropriated to
their varied movements, and the anus is distinctly furnished
with levator and spincter muscles.

From the aerial respiration and the higher general de-
velopment of most of the entomoid articulata their mus-
cular fibres are more dense and irritable, and from the
greater consolidation and distinctness of their segments,
their muscular fasciculi are more isolated and more me-
thodically disposed, than in the softer trunks of the aquatic
helminthoid tribes. The myriapods, like the worms, having
their segments and their lateral appendices equally developed
from the one extremity of the trunk to the other, without
distinction of thorax and abdomen, present the greatest
similarity in the muscular system throughout all their seg-
ments, and the greatest resemblance to the disposition of
that system in annelides and in the larvae of insects. More
than four thousand distinct muscles are found in the larva of
the common cossus ligniperda, and these are disposed in con-
centric strata, the fasciculi of which are directed, some longi-
tudinally some transversely, and others with various degrees
of obliquity, passing, as in the trunk of most adult entomoid
animals, from the concave inner surface of one segment, to
the anterior enclosed margin of the next succeeding. As the
extremities and wings for progressive motion become deve-
loped from the thorax, the muscular apparatus of that por-
tion of the trunk becomes more developed than in any other
segments. In the annexed figure from Straus, representing
the principal muscles of the trunk of the male cock-chaffer,
melolontha vulgaris (Fig. 6*4,) we observe that the interior
layer of muscles of the segments of the abdomen (/,) run in
a longitudinal direction, like those of the helminthoid
classes. The muscles of the abdominal segments consist
generally of parallel short fasciculi, which retain the same

MUSCULAR SYSTEM. 139

FIG. 64.

breadth and form from their origin to their insertion ; but in
the anterior part of the trunk, where the movements are
more powerful, the muscles have generally a conical form,
being broad at their origin, and tapering towards their point
of insertion ; so that more muscles can be inserted into a
limited point, to strengthen and vary its movements. This
form is seen in the depressor muscle (a,) of the head, and in
the lateral flexor (6,) of the same part. The fasciculi of the
rotator (d}) of the head are more parallel, but they converge
to a point in the two portions of the levator capitis (e, y,)
and in the inferior (c,) and the superior (f,) retractor of the
corselet, the levator (a?,) of the corselet, and the levator
obliquus (h,) of the jugular piece. The fasciculi are more
parallel in the large and powerful depressor muscle (i,) of the
wing, on which the flight of the insect so much depends,
and also in the several portions of its broad levator muscles
(k.) The same tapering and pointed form is seen in most
of the muscles in the region of the pelvis, or attached to
the moveable pieces of the anus, as in the strong levator (n,)
of the inferior anal piece, the retractor preputii (y,) the
posterior retractor (/?,) of the inferior anal piece, and the
retractor of the cloaca (o.) There is also great uniformity
observed in the disposition of the flexor and extensor
muscles in the ginglimoid articulations of the legs in all the
entomoid classes, and in the more moveable rotating articu-
lations of the antennee and palpi of these animals. The
muscles of the trunk in these highest articulated classes,
like those of the helminthoid forms, are still divided into
bands, which occupy chiefly the dorsal and the ventral
aspects of the body, and these are again partially divided

140 MUSCULAR SYSTEM.

on the median plain by the dorsal vessel above, and the
nervous columns below ; and here, as in the vertebrated
classes, we observe that these symmetrical and voluntary
muscles do not cross the median plain of the body. They
are connected through the medium of the skin to the solid
coverings of the segments ; so that the exuviable skeleton
is cast off in all these entomoid classes without affecting the
insertions of the muscles into the true skin. In the air-
breathing, pulmonated and tracheated arachnida we find the
same dense, irritable, and serrated character of the muscular
fibres as in the perfect insects, a similar structure of the
muscles and their tendons, and the same general disposition
of these organs where the articulations resemble. Their
capaceous cephalo-thorax is occupied chiefly with the large
and strong muscles of the haunches of their numerous long
legs, and with those of their masticating and poisonous appa-
ratus. The long cylindrical segments of the post-abdomen
of the scorpions are chiefly occupied with the powerful
muscles appropriated to the movement of the poisonous sting
formed by the last segment of the trunk. The tendons of
the muscles here, as in insects and Crustacea, are only calcified
prolongations from the exterior skeleton. The muscular
system of the Crustacea forms a larger proportion of their
body than in the air-breathing articulata, and their move-
ments are more rapid and powerful than in almost any other
branchiated invertebrata ; their individual fibres, however,
are softer, more white and pellucid, less compact in their
texture, and less irritable and strong, than in the pulmo-
nated or tracheated classes ; and they require less muscular
force on account of the support which they receive from the
density of the element through which they move. The
muscular apparatus of their external organs of mastication
and of locomotion closely resembles that of insects, but their
stomach is covered with powerful muscles for the movement
of the internal teeth with which it is provided ; the ventral
portion of their post-abdomen is furnished with numerous
and strong muscles for the movements of that part of the
trunk in swimming, or for its retraction when alarmed ; and
the muscles of the prehensile terminal parts of their legs,
especially of the anterior pair, are proportionally large and
strong for the contests in which they are continually en-
gaged.

MUSCULAR SYSTEM. Ml

FOURTH SECTION.

Muscular System of the Cyclo-Ganliated, or Molluscous
Classes.

The limited extent and the aquatic nature of the respira-
tion in most of the molluscous classes, and their fixed con-
dition, or imperfect means of locomotion, are accompanied
with a corresponding low degree of vitality and imperfect
development of their muscular system. The forms also of
this system, as of the whole body, vary much more in this
than in the articulated or vertebrated divisions of the
animal kingdom. Within the exterior cartilaginous covering
of the tunicated animals is placed their muscular coat by which
they are able to contract their whole body, and forcibly
to expel the contents of their respiratory or thoracic cavity.
This muscular enveloping tunic, as seen in that of the cyn-
thia pupa (Fig. 65,) consists chiefly of long diverging fasciculi
which originate from around the two orifices of the sac (a. b,)
and extend round the whole body of the animal. These
muscular fasciculi are attached to various points of the
exterior tunic, but most intimately around the respiratory
(#,) and the anal ( b, )

orifices, which we ob- FIG- 65>

serve also to be provided
with distinct and strong
sphincter muscles (d, e,)
passing in a circular man-
ner around them. By
the contraction of the
whole of this muscular
tunic, the orifices are

142 MUSCULAR SYSTEM.

retracted, the trunk of the animal is compressed, the
respirat< j emptied, and the whole body is

retracted ^ the fixed point to which the animal is

attached *e respiratory currents are produced by the
vibratile cilia, disposed on the branchiee, and on the
thoracic cavity, as in other acephalous mollusca, and
the swimming of some of the aggregate forms, as of
the pyrosoma, is effected by the same respiratory cur-
rents produced by vibratile cilia. The muscular coat of
the tunicata is analogous to the mantle of bivalves, as
their cartilaginous covering is the analogue of the
shell.

The conchiferous animals are much more generally free
than the tunicata, and some of them possess considerable
power of locomotion. The movements are chiefly performed
by the foot, which is commonly a lengthened tongue-
shaped, muscular organ, capable of being protruded to some
distance from the cavity of the mantle, and capable of as-
suming a great variety of forms. By this organ the con-
chifera attach their byssus, swim at the surface of the
water, creep on a solid surface, burrow in sand, or
other soft material, and extricate themselves when
covered. The foot is composed of muscular fasciculi,
which decussate each other in various directions to give
it great variety of movements, and water is often ad-
mitted into its interior cavity. It is sometimes wanting where
the shell is permanently fixed to a spot, as in the oyster.
It is generally more or less connected with the dorsal
part of the valves, and the fibres of its expanded base
embrace almost the whole of the abdominal cavity.
The adductor muscles are the active organs by which
the valves are closed against the elastic property of
the ligament, and they generally consist of one or two
thick, short, and strong muscles, which pass straight
across the ventral surface of the abdomen, to be at-
tached ta the inner surface of both valves. The pecten
is enabled to swim backwards by the powerful and
repeated action of its adductor muscle on the valves.

The adductor muscle is large and single in most of the
round forms of conchifera, as the pecten, ostrea, anomia,
spondylus, but in the more lengthened forms there are

MUSCULAR SYS 143

generally at least two. This mi^H tlie

pierced valve of anomia to be I nal

body. Between the two musci he di-

myaria, there is commonly a rough t halves

running near the ventral margin, and se^u 3 corres-

ponding situation in the monomyaria, which makates the
place of attachment of the fibres of the palleal muscle,
by which the projecting free margins of the mantle are
retracted into the shell. This marginal muscle consists
of numerous small fasciculi attached along this groove in
both valves, and spreading chiefly on the loose ventral
margins of the mantle. By forcibly retracting this part
of the mantle, these palleal muscles contract the respiratory
sac, so as to assist in a forced expiration of the contained
water, and they protect the most sensitive marginal part
of the mantle from being compressed and injured during
the closing of the valves. The currents of water which
are conveyed into the cavity of the mantle through the
respiratory orifice, and outwards through the vent, for the
purposes both of respiration and nourishment, are entirely
produced by the rapid action of vibratile cilia, which are
disposed in the closest arrangement around all the minutest
meshes of the branchiae, and cover all the fringed edges
of the respiratory orifice and nearly the whole inner surface
of the respiratory cavity of the mantle. As all other vibra-
tile cilia, these continue in lively activity on portions of
the gill or mantle which have been long cut from the
body of the animal. The respiratory cavity of the mantle,
with highly contractile muscular parietes, is often prolonged
to a great distance beyond the margin of the valves, es-
pecially in burrowing species, to reach with the respiratory
and anal orifices, the surface of the bed or rock in which
the animal is concealed. Besides the usual large adductor
muscles, there are frequently smaller supplementary trans-
verse muscular bands passing from the dorsal part of one
valve to the other.

The muscular foot of the gasteropods sometimes covers
the whole ventral surface of the body, and sometimes ex-
tends only from the under surface of the neck ; it is the
largest muscle of the body, and that by which progressive
motion is effected both in creeping and swimming. In the
inhabitants of turbinated shells or the trachelipodous gas-

M U SC U L A R S V S T K M .

teropods, the alar fibres of the foot extend upwards

along th( a strong fasciculus is prolonged back-

wards UIK to be attached to the columella of the

shell. This tractor muscle forms the only bond of con-
nection between the shell and the animal it contains, and it is
constantly advancing slowly along the pillar of the shell dur-
ing growth like the adductor muscles of conchifera. The open
mantle which secretes the calcareous matter of the shell is
also distinctly muscular and contractile, and the funnel for
respiration is an open canal prolonged from its left side.
The foot is often expanded by the introduction of water into
its interior cavity, and its dorsal surface secretes the calca-
reous or horny layers which compose the operculum of the
shell. The neck forms generally a thick muscular sheath
around the complex apparatus of the mouth and proboscis,
and supports on the right side the muscular exciting organ of
the male ; anteriorly it forms the lips or the sheath of the pro-
boscis, and the tentacula which have generally the eyes at the
exterior of their base. In the naked gasteropods found generally
adhering to floating plants in the ocean, as the scyll&a and
tritonia, the foot forms a long narrow groved organ for em-
bracing the tender stems to which they adhere, and on which
they feed. Most of the predaceous gasteropods possess a
long and powerful muscular proboscis capable of being ex-
tended to a distance from the mouth, and provided at its ex-
tremity with an exsertile bifid fleshy tongue armed with
sharp conical recurved teeth, as seen in that of the common

FIG 66.

whelk, buccinum undatum (Fig. 66.)
Both the proboscis (g, g.) and the en-
closed bilabiate spiny tongue (a, b.) are
provided with numerous powerful ex-
tensor and retractor muscles contained
in the neck. The two divisions (a.) of
the tongue to which the teeth are at-
tached are often supported internally by
two long cartilaginous laminae, large and
strong in the buccinum, which appear
to be the analogues of the gastric dart
of conchifera. The phytophagous gas-
teropods have generally jaws for com-
pressing their vegetable food, or a long spiny tongue for
filing it to pieces.

MUSCULAR SYSTEM.

The muscular system of the pteropods, like that of many
of the floating gasteropods, is generally soft, transparent, and
nearly colourless ; so that the disposition of the fibres in the
exterior closed mantle, and in the fin-like arms can be per-
ceived through the outward pellucid coverings of the body.
Having no muscular foot for creeping, their progressive mo-
tion depends on the movement of two muscular membranes,
unsupported by rays or by cartilage, and extending from the
sides of the body. These muscular fins are developed both
in the naked and the testaceous forms, they present the most
favourable situation for the branchiae which are generally
placed on their surface, and they sometimes serve as organs
of prehension, embracing the surface of plants, and other
objects floating through the sea. The muscular mantle,
closed above, forms a large abdominal cavity, and its con-
tractions assist in expelling the natural excretions of the vis-
cera, or in retracting the whole body within the shell. The
tentacula also, and the whole apparatus of the head, are re-
tracted and extended by their own muscular fibres, and the
oesophagus is sometimes provided with a distinct muscular
bulb, like many gasteropods. The annexed figure, (Fig. 6'7,)
represents two naked and two testaceous forms of pteropods,

FIG. 67-

PART II.

146 MUSCULAR SYSTEM.

with their muscular organs of motion extended laterally from
the sides of the trunk, and placed more anteriorly than those
of the naked cephalopods. In the clio australis, (Fig. 67, A)
the form approaches very closely to the cephalopodic in the
numerous conical, tubular,cephalic tentacula (A,a,a*,) the form
of the head (#,) the position of the eyes, and the lengthened
cylindrical form of the trunk, enveloped in a closed muscular
mantle (d.) The muscular fins (c,) support, on their pectinated
surface, the numerous ramifications of the branchial vessels ;
so that the motions of these organs promote the aeration of the
blood. In the pneumodermon, (Fig. 67. B,) the muscular pro-
boscis (0,) and the lateral tufts of tentacula (b9) terminated
each by a sucker, are retractile, the muscular arms (c,) are ex-
tended from the sides of an anterior division of the trunk,
and the branchiae (d,) are placed, as in the doris, on the pos-
terior part of the back, but at a distance from the anus, which
here opens on the anterior part of the right side, as in the
clio. The muscular arms are comparatively large in the
small testaceous cleodora, (Fig. 6'7- C. b,) as they are also in
the testaceous cymbulia, represented in Fig. 24. The fleshy
mantle of the cleodora extends laterally to a distance from
the sides of the head («,) and the slender pellucid, depressed,
tapering shell (c,) is also expanded transversely with deeply
grooved sides. The fins for progressive motion are more
lengthened and straight in their form in the minute testa-
ceous cuvieria (Fig. 6J . D. a,) where there are dentiform
masticating buccal organs, as in a cephalopod, and in which
the shell (c,) is straight, lengthened, conical, and pointed,
like a belemnite. The muscular organs of these and the
other known forms of pteropods, are constructed, like their
shells, on the plan of those of the cephalopods, especially of
the lower forms of that class.

The organs of motion in the cephalopods, as in the ptero-
pods, are generally in form of muscular fins extending from
the sides of the trunk, and unsupported by osseous rays ;
they move also by means of the muscular feet developed
from the fleshy disk surrounding the head. The nautilus,
like a gasteropod, is fixed by two lateral muscles to the bot-
tom of its shell, its muscular open mantle is thin and deli-
cate, the muscular funnel is open beneath throughout its
whole length, and the mouth, surrounded with strong mus-

MUSCULAR SYSTEM. 14J

cles for the calcified jaws, is provided with broad muscular
feet, like the expanded feet of an argonaute, and supporting
numerous sheathed tentacula. In the argonaut a, (Fig. 68. A,)
there are eight muscular long feet provided with large sessile
suckers, as in other octopods. The ventral, or anterior sur-
face of the body is directed towards the concave or spiral
side of the shell, as in the planorbis, and other mollusca with
orbicular shells, and the dorsal part of the animal with the
expanded pair of membranous feet (^,) are placed next to

FIG. 68.

B

the convex outer margin of the shell (a.) The mantle is
spotted externally, as in the naked cephalopods, and is des-
titute of muscular fins, as seen in Fig. 68. B, which repre-
sents the animal removed from the shell. The shell cover-
ing a part of the body has been observed by Poli in the
ovum, as represented in Fig. 68. C. a. The muscular por-
tion of the posterior pair of feet (Fig. 68. B. gj) and the
gradually diminishing sessile suckers are continued around
the margin of the expanded membranous part (Fig. 68. A. h,)
so that this pair of feet may be employed as organs of pre-
hension, or for creeping at the bottom, or for swimming

L 2

148 MUSCULAR SYSTEM.

beneath or above the surface of the water. Here, as in
the naked cephalopods, there is a thin panniculus carnosus
immediately beneath the coloured skin of the mantle, the
fibres of which interlace to form a thin recticulate tunic.
The parietes of the mantle are chiefly composed of longitu-
dinal muscular fibres, with a thin external and transverse
layer. The external and internal muscles of the abdominal
fins in the naked species, both those which connect these
organs with the trunk, and those which move their free mar-
gins, are inserted into two thin longitudinal cartilaginous
scapular plates. The palleal muscles are not inserted into
the shell of the argonaute, nor into the internal dorsal shells
of the naked cephalopods, as they are in the nautilus. The
upper margin of the mantle is attached behind to the cepha-
lic cartilage in the sepiola and the octopus, but is free in sepia,
loligo, and loligopsis. The cavity of the abdomen is partially
divided by two strong and broad muscular bands extending
downwards and forwards from the base of the funnel to be
attached to the anterior parietes of the sac. These two
strong longitudinal muscular columns, between which the
rectum passes forwards to the base of the syphon, serve to
contract longitudinally the cavity of the mantle, to limit the
extent of its dilatations, and to retract the funnel. There are
other muscular bands passing down from the back part of
the head to the base of the funnel at its posterior part. The
folds of peritoneum, which attach the branchiae to the sides
of the abdominal cavity, have distinct muscular fasciculi, for
raising and retracting these organs. The whole muscular
parietes of the abdominal sac are firm, white, arid remark-
ably compact, and besides their transverse and longitudinal
muscular layers, there are oblique and straight short fibres,
which pass through their thickness from one surface to the
other. Within the abdominal cavity a distinct muscular
tunic embraces the whole liver and oesophagus as far as the
gizzard, and connects them with the upper and back part of
the trunk. The strongest and the largest muscles of the
naked cephalopods are those which are attached around the
head, connecting that part with the trunk behind, and with
the arms before. Strong muscular bands pass upwards from
the back and fore parts of the trunk, and expand into radiat-
ing fasciculi, which enter into the bases of the feet The

MUSCULAR SYSTEM.

149

FIG. 69.

funnel consists chiefly of two strata of muscular fibres, the
inner of which is transverse, and the outer longitudinal. In
the annexed front view of the muscles of the argonaute,
(Fig. 69,) the funnel (e,) is folded down over the fore part of
the abdomen (/,) and
its strong posterior
muscular bands (d, d,)
are seen passing down-
wards from its base.
The anterior ascending
radiating fasciculi (a,)
cross each other at the
bases of the feet, so as
to interlace and mingle
their fibres before they
enter into the compo-
sition of these organs.
These muscular fibres
are more straight and
parallel as they advance
along the feet (b9) en-
veloping the trunks of
the vessels and nerves which are seen ramifying on the ex-
panded terminal membrane (c,) of the posterior pair of feet.
The suckers in two rows, as on the other feet, continue
around the margin of these expanded terminations of the
posterior pair. All the naked cephalopods are octopods, like
this testaceous argonaute, having only eight feet developed
from the muscular disk surrounding the mouth ; but many
of the genera, as sepia, loligo, and sepiola, have also two long
muscular tentacula, which have a deeper origin near the car-
tilaginous orbits, and from these superadded pediform tenta-
cula, such genera have been considered as decapods. The
rudimentary eye-lids of the naked cephalopods are already
surrounded with distinct orbicular muscles, and the eye-
balls are moved by four recti muscles, and sometimes by an
inferior oblique, arising from the base of the orbits around
the optic nerves. The tentacula have generally pedunculated
muscular suckers developed on their inferior surface, at their
free extremities, like those of the feet in the tentaculated
species of this class. The muscular suckers are sessile, large,

150 MUSCULAR SYSTEM.

and strong, on the long feet of the octopods, as the argonauts
and the octopus, they adhere to external objects by the close
application of their thick muscular margins, and by forming
a partial vacuum in their centre. By these organs the cepha-
lopods can creep upwards on a vertical surface, even when
out of the water. The octopus, destitute of any lateral fins,
is assisted in swimming by muscular membranes extended
between the bases of the feet ; this animal swims backwards
by impelling the water forwards, but the species which have
lateral fins extending from their trunk can swim with ease
either forwards or backwards, and they appear to spring up-
wards sometimes, to a distance from the surface of the sea.
These predacious animals have very powerful muscles con-
nected with the mastication of their food, as well as with its
prehension. Large sphincter muscles, with a fimbriated
fleshy lip, surround the entrance of the mouth, and strong
retractor muscles of the jaws are inserted around the reso-
phageal opening of the cranium. The bases of the jaws are
surrounded with superimposed strata of powerful compressor
muscles, and the short, thick, fleshy tongue, covered with
numerous rows of sharp, conical, horny spines, is moved by
strong muscles attached to a rudimentary os hyoides. The
maxillary apparatus is also provided with two lateral rotator
muscles, which pass forwards to be inserted into its anterior
part.

FIFTH SECTION.

Muscular System of the Spini-Cerebrated or Vertebrated

Classes.

The muscular system is placed on the exterior of the hard
parts in the vertebrated animals ; its fibrous structure is
here the most distinct and irritable, and its separate muscles
and fasciculi are most obvious and defined. The muscles
have generally a red colour, from the red blood sent through
them, and they are connected with the bones, for the most
part, by tendinous prolongations. They are most pale, soft,

MUSCULAR SYSTEM. 151

and pellucid, in fishes, where their feebleness is compensated
for by the great number which co-operate in the same move-
ment. The progression of fishes being effected chiefly by
the lateral motions of the tail and of the trunk, the vertebral
column is expanded vertically upwards and downwards, and
the great muscles of the trunk are disposed in transverse
strata along its sides, like those which move the segments of
a worm or an insect. The feeble irritability of the muscular
fibres in fishes, their softness, and their colourless transpa-
rency, correspond with their common conditions in the inver-
tebrata, and in the embryos of the higher vertebrated classes,
and they accord with the still soft condition of the bones into
which they are inserted. Aided in their ascent and descent
in the water by the compression and expansion of their air-
sac, and with very imperfectly developed arms and legs, the
active movements of fishes are but little varied, their mus-
cles seldom divide into fasciculi, or terminate in narrow ten-
dons to be attached to small points of their feeble skeleton.
The fibres which compose the great lateral muscles of the
trunk run in a longitudinal direction, are divided into nu-
merous transverse oblique strata by intervening tendinous
aponeuroses, and are disposed chiefly in four series of oblique
muscles, as seen in the perch, (Fig. /O. a, b, c, d.) The in-

FIG. 70.

tervening white tendinous bands which connect these strata
of muscles have a crescentic form, are disposed vertically
along the sides of the vertebrae and the ribs, and are attached
externally by their zig-zag margin to the inner surface of the
skin. The upper series («,) have their thin white tendons

152 MUSCULAR SYSTEM.

directed obliquely downwards and backwards, the second
(b}) downwards and forwards, the third (c9) like the first, and
the fourth («?,) like the second. The upper series of lateral
muscles (#,) attached anteriorly to the occipital bone, occupy
the deep cavity on each side of its projecting spine, and
extend backwards to the longitudinal diverging tendons and
muscles of the caudal fin, in which they terminate. The
oblique direction of all these lateral muscles increases the
velocity of their motions, as in the intercostals of quadru-
peds. These strata of muscles are arched backwards, having
all their convex surfaces directed forwards, and as their fibres
pass obliquely backwards and peripherad, they draw their
cutaneous attachments forwards and inwards when the ver-
tebrae are the fixed points. They are attached also to the
temporal bone and to the back part of the scapular arch, and
the inferior series (d,) extends forwards under the arms (n,)
to the os hyoides. The layers of these large lateral muscles
of the trunk are seen similarly disposed in the cylindrical
body of the cyclostome fishes, in the compressed trunk of
most of the osseous forms, and also in the broad depressed
body of the flat fishes. They correspond with the vertebrae
into which their aponeuroses are inserted, and they are at
once analogous to the muscles of the segments of articulata
and to the more lengthened and isolated muscles of the ver-
tebral column and trunk in higher vertebrated classes. The
flat surfaces of the interspinous bones (/,) are covered with
diverging muscular fibres, which pass downwards and move
them in every direction, and exterior to these are larger dis-
tinct muscular fasciculi which are inserted into the broad
bases of the rays of the median fins, for their varied move-
ments. The longitudinal straight muscles which extend
along the median line of the dorsal and the abdominal sur-
face of the trunk are interrupted by the dorsal and anal fins.
The longitudinal straight muscle of the back in fishes generally
commences from each side of the spine of the occipital bone,
and proceeds in two separate fasciculi to be inserted into the
base of the anterior ray of the first dorsal fin. When there
are more than one dorsal fin, it is extended in two fasciculi
from the last ray of each of these fins to the first ray of the
next, and it is continued in the same manner (#,) from the
last dorsal to the beginning of the caudal fin. On the ven-

MUSCULAR SYSTEM. 153

tral surface of the body, the first pair of straight muscles
generally pass from the scapular arch or the humeri to the
anterior part of the pelvis, the second pair (e,) commence
from the pelvis, and passing on each side of the anus, con-
tinue to the first ray of the anal fin (h.) They are developed
between the anal fins, as between the dorsal, when there are
more than one, and from the last ray of the posterior anal
fin they are continued backwards to the beginning of the
caudal fin. By these longitudinal straight muscles above
and below, the median fins are moved and supported, and
the trunk is moved in a vertical plane. The sides of the
head are occupied by two large and powerful muscles, (&, /,)
apparently analogous to the masseter and the temporal
muscles, and which pass forwards and downwards to be in-
serted into the lower jaw. The lower jaw is depressed both
by muscles passing backwards from it to the os hyoides, and
by those which extend from the os hyoides to the scapular
arch. The operculum is raised by two or more short and broad
muscles, placed at its upper part, and is depressed by short
round muscles placed on the inner surface of the same part.
The branchiostegal rays are moved by short oblique muscles,
which descend from the opercular bones to these rays, and
by others which are interposed obliquely between each pair
of rays, like intercostal muscles in higher classes. The
branchial arches, in the osseous fishes, are attached by dis-
tinct muscles to the back part of the skull, to the sides of
the vertebrae, and also to the scapular arch and the os
hyoides. In the cartilaginous fishes, where there is no oper-
culum over the branchiae, that apparatus is covered exter-
nally with a layer of short muscles, like intercostals, passing
between soft cartilaginous bands, like ribs. The pectoral
fins, or arms, have on each of their flat surfaces a band of
adductor and abductor muscles, (Fig. 71-/>) which extend
from the scapular arch to the commencement of the pha-
langes or rays. These muscles act also as flexors and exten-
sors of the arms, and correspond with the magnitude of these
organs ; they are greatest in the expanded pectoral fins of
the plagiostome fishes. The ventral fins or feet are also
moved by two similar muscles (Fig. 71- ^5) on each of their
flat surfaces, extending from the pelvic bones to the com-
mencement of the rays, and corresponding in size and
strength with the magnitude of the feet. The anguillifo rm

154

MUSCULAR SYSTEM.

fishes want the feet and their muscular
apparatus, and the cyclostome fishes
want also the arms and their muscles.
The muscular system is greatly relieved
in the vertical motions of most fishes
by the compression and expansion of
their air-sac ; but many of the fiat
fishes and the cyclostome species are
destitute of this aid, and lie generally
at the bottom of the water. The
movement of some fishes through the
water is aided by a muscular disk in
form of a sucker, placed on the back
part of the head in the remora, on the
fore part of the belly in the lump-suck-
er, and around the mouth in the lam-
preys, by which they adhere to other
animals or bodies moving through the

water. By the great development of the lateral muscles of the
trunk, the saw-fish and the sword-fish are enabled to use
their offensive weapons with effect ; the large muscles of
the anterior dorsal rays give powerful and varied movements
to these parts in the silurus, balistes, lophius, and many
other fishes, and the strength of those of the pectoral fins
enable the flying-fishes to escape from the water, and to
move some hundred times their own length through the
air.

The long compressed trunks of the perenni-branchiate
amphibia, as the proteus, the siren, and the axolotl, and of
the tadpoles of the higher anurous species, are moved
through the water chiefly by the lateral motions of the ver-
tebral column and of the tail, as in fishes^ and these motions
are effected in the same manner by numerous transverse
strata of longitudinal muscular fibres, occupying chiefly the
sides of the trunk. These great lateral muscles are still
comparatively pale, bloodless, and feeble, and the tendinous
intersections of their strata are thin, soft, and delicate. The
cellular substance interposed between the muscles of amphi-
bia is scanty, of little consistence, colourless, and almost in
a semifluid state ; there are yet few tendons connecting the
muscles to the soft bones of the skeleton, and there is gene-

MUSCULAR SYSTEM.

155

rally very little connexion between the skin and the sub-
jacent muscles of the body. The general disposition of the
superficial muscles in the urodelous amphibia is seen on re-
moving the skin from the common crested triton, triton cris-
tatus (Fig. 72.) In the back view of the trunk (Fig. 72. 1,)
short transverse strata of lateral muscles (b,) separated from
each other by thin, soft, tendinous aponeuroses, are seen

FIG. 72.

occupying the dorsal portion of
the body, from the occipital
bone to the posterior extremity
of the tail. The muscular strata
(c,) which descend from these in
a more oblique direction down-
wards and backwards, are united
together on the fore part of the
abdomen (Fig. 72. 2. b,) to form
a large continuous descending
oblique muscle. But behind the
anus (2. c,) the tendinous inter-
sections (2. d,) continue distinct
along the tail, below the vertebral
column as well as above it. In the
rigid state of these lateral muscles
in the tadpoles, as in that of
the rana paradoxa, the sides of the trunk are marked by trans-
verse vertical furrows, similar to those on the sides of fishes.
We perceive also in the tadpoles, as in fishes, a thin vertical
prolongation of the skin along the upper and lower surfaces
of the tail, like dorsal and anal fins, but unsupported by
rays. The recti abdominis of the tadpoles form a broad
muscular expansion covering the fore part of the trunk, di-
vided by several transverse tendinous intersections, and
tapering to the pelvis. These two muscles become more
contracted and narrow in the adult animal. In the salaman-
der strong muscular fasciculi descend from the free ends of
the short ribs of the trunk, and expanding as they pass over
the abdomen, they unite to form a continuous external
oblique. The muscles of the extremities are more developed
in these animals, to support them on land, than in the tritons
and other aquatic species, wrhere they are little used for pro-
gressive motion. In the anurous species, in their adult

156

MUSCULAR SYSTEM.

state, the muscular system is the most remote from that of
fishes in its general characters and in the disposition of its
parts, which arises from their greater extent of respiration,
their inhabiting a rarer medium, the great development of
their extremities, and the large portion of the trunk which
they lose by their metamorphosis. Their muscles are more
vascular, dense, red-coloured and strong, more distinct and
defined in their course and in their insertions, more ventri-
cose, seldom exhibiting parallel strata, and generally inserted
into distinct and often lengthened tendons. From the leap-
ing and swimming habits of many of these species, we per-
ceive their short trunk terminated by lengthened and strong
legs and provided generally with less perfectly developed
arms, and the greater development of the extensors than of
the flexors of the legs, gives an anthropoid character to these

extremities. In the back
view of the muscular system
of the common frog, rana
esculenta (Fig. 73,) the small
size of levatores scapulae, (1.
2,) corresponds with the
soft and feeble condition of
the dorsal portion of these
bones into which they are
inserted. The depressor of
the lower jaw (5,) the sca-
pular (6,) and the sub-sca-
pular muscles (8,) occupy
the anterior part of the back
immediately behind the head,
having before them the broad
temporal muscles, and be-
hind them the quadratus
lumborum, (19, 24,) the sa-
cro lumbalis, (23,) and the
dorsal portion of the obliquus
externus (22.) The ilio-coccy-
geus, (25, 26,) is of great
length, like the coccygeal
bone, and the ilium to which
it is attached, and the trans-

FIG. 73.

MUSCULAR SYSTEM. 157

versus abdominis (20,) extends over a large portion of the
trunk from the want of ribs in these anurous amphibia.
The inter-transversales (21.) are of considerable breadth,
from the length of the transverse processes of the vertebrae.
The pectoralis major, here of great size and strength, is
divided into several distinct parts, which extend forwards,
inwards, and backwards, as separate flat muscular bands,
covering a great portion of the anterior surface of the trunk.
The muscles of the os hyoides are of great size, as in fishes
and the lower amphibia, from the size of that bone, and its
importance in respiration where there are no ribs. The pec-
toralis minor is also divided into several detached and di-
verging muscular bands, like the external, arid both these
muscles acquire increased influence on the arm by their low
insertion on the short humerus. The deltoid (7,) the anco-
nei (9, 10,) and most of the proximal muscles of the arm are
strong ventricose masses, and even the flexors and extensors
of the wrist and fingers are short and fleshy, giving an an-
thropoid character to these members. The knees extend,
not forwards as in most vertebrata, but directly outwards
from the sides of the trunk, and the long webbed feet have
the same lateral direction, the best adapted for swimming
and leaping. The glutei muscles (27,) are here long and
narrow, from the lengthened and cylindrical form of the iliac
bones, and also the iliaci muscles (28, 37,) and the semi-
tendinosus (33,) the semi-membranosus (31,) and other ex-
tensors of the thigh. The recti (29,) and the vasti muscles
(40,) and the other extensors of the knee-joint, and also the
gastrocnemius (34,) the tibialis posticus (42,) the peronei (48,)
and other extensor muscles of the heel are here of great size,
and of great importance in the progressive motions of these
animals both on land and in the water, and by their great
development they give a rotundity to the thighs and to the
calfs, unusual in the cold-blooded vertebrata. The plantar
aponeurosis is here continued from the tendo achilles, which
has a moveable sesamoid bone where it plays over the heel ;
so that the great extensors of the heel-joint contribute like-
wise to the flexion of the toes, and the general support of
the long webbed feet in swimming through the water, or in
leaping on the ground.

The higher classes of air-breathing vertebrata, by respiring

158 MUSCULAR SYSTEM.

a purer element and by possessing organs more extensive,
and more complicated, for the aeration of their blood, have
their muscular system encreased in energy and strength be-
yond that of the fishes and amphibia, which, for the most
part, are organized to move by means of their vertebral
column, through an element nearly of the same specific
gravity as themselves. The rarity of the medium through
which most of the reptiles and higher animals move, neces-
sitates this increased muscular strength, and their bones
have an increased solidity proportioned to the greater force
of the muscles which are to act upon them. The progres-
sive motion of serpents, like that of fishes, depends upon
the movements of their trunk, and their muscles are disposed
so as to act with most effect on the sides of the vertebrae
and on the ribs. The deep grooves along the back, between
the spinous and the transverse processes on each side,
are occupied chiefly with the multifidus spina, the spi-
nales, and the semi-spinales dorsi, which inflect powerfully
the column to either side. Short as the distance is from one
spinous process to another, and between the short transverse
processes which support the ribs, those parts are moved se-
parately by strong interspinales and intertransversales mus-
cles. The ribs being free at their distal extremities, they
admit of extensive motion, and are furnished with large in-
tercostal muscles which partly represent the oblique and
transverse muscles of the abdomen in higher animals. The
recti muscles are divided in front by the soft cartilaginous
tapering extremities of the ribs, as they are by tendinous in-
tersections in most of the higher animals. These intercostal
muscles, of various lengths, some passing directly from one
rib to the next, and others passing over one or more ribs, to
have a more distant insertion, are strongest on the anterior
portion of the trunk, where their action is important in res-
piration, by compressing and expanding the respiratory sacs.
The large imbricated abdominal scuta, so important in the
progression of serpents, are moved and supported by dis-
tinct muscular fibres, which pass down to their fixed ex-
tremities. Many of the ordinary muscles of the head, as
seen in that of the rattle- snake (Fig. 74,) have a lengthened
and divided form in serpents, from the elongated form and
the great mobility of most of the bones of that part. An-

MUSCULAR SYSTEM. 159

terior to the external pterygoid (&,) and the digastric (h,)
muscles are seen three separate parts of the temporal muscle
(d, e,f.) A portion of this muscle (e,) extending forwards
like a buccinator, embraces the posterior part of the poison-
gland (a,) and forces the secretion into the duct (#*,) and
thence into the perforated fang (b.) The strong muscles of
the lower jaw (/, w,) extend upwards to the vertebrae and
backwards to the ribs, and unite into a single band on their
fore part. The row of salivary glands (b, c,) extend back-
wards beneath the poison gland («,) and forwards before the
masseter muscle (a.) The great length of all the muscles of
the head and trunk of serpents contributes to the velocity of
their movements, and their numerous subdivisions contribute
to the variety of their motions. Their muscles, for the most
part, terminate in narrow, shining, tendinous bands, which
allows of a greater number of muscles being inserted into a
limited space, and consequently a greater variety in the
movements of the articulations. These elongated forms,
and tendinous terminations are most conspicuous in the ex-
ternal and internal muscles of the ribs, which are the legs
of these animals. The cloaca has its distinct muscles for
opening and closing that cavity ; the pelvic bones and rudi-
mentary feet, sometimes developed, are provided with mus-
cles analogous to those of the ventral fins and pelvic bones
of fishes ; the scapular arch, developed in the most per-

160 MUSCULAR SYSTEM.

feet species, is attached by muscles to the trunk, though not
yet destined to support atlantal extremities, and the internal
lateral muscles passing from the vertebras to the ribs, form
the rudiment of a diaphragm.

The muscles of saurian reptiles are more numerous and
complicated than in ophidia, because they possess members
for progressive motion, adapted sometimes for swimming
and sometimes for running or climbing, and sometimes these
animals are organized for moving through the air. The
stratified disposition of the great lateral muscles of the
trunk, so conspicuous in the fishes, the urodelous amphibia,
and even in the serpents, is less marked in the comparatively
motionless bodies of the saurian reptiles, excepting in those
which have scarcely yet the members developed. This ar-
rangement of the muscles, in regular series around the ver-
tebrae, is still continued in the coccygeal region of the co-
lumn, which, together with the neck, is more flexible than
in the ophidia. Several muscles of the face are wanting on
the rough and hard head of the crocodilian reptiles, their
temporal and masseter muscles are protected externally by
the temporal, frontal, and malar bones, and their insertions
are on the inner surface of the lower jaw, the muscles of the
os hyoides, and those which connect the head with the trunk
are distinct and powerful, as in most reptiles, and those of
the tail, which is nearly as thick as the trunk, are of great
strength, for the lateral motions of that part in swimming.
The short muscular legs of these animals, diverging out-
wards, scarcely raise the trunk oif the ground, on which the
saurians, and most other reptiles rest the body, when not
in actual progression. The legs, in these aquatic sauria, are
compressed in form, to facilitate their advancement in the
water, as in web-footed birds, and they have strong extensor
muscles, to give impulse to their webbed feet. More nimble
movements, and more light and pliant forms of the locomotive
organs and of the wholebody are seen in most of the terrestrial,
climbing, long-toed,and long-tailed lacertine sauria. The direc-
tion outwards of the humerus and femur weakens the limbs,
and adapts them better for climbing and prehension than for
support or for running. The long fingers and toes, with
their powerful flexors in the lacertine sauria, adapt them for
climbing on trees in pursuit of their prey. The opposed

MUSCULAR SYSTEM. 161

fingers and toes, and the muscular prehensile tail of the
chamoelion enable it to creep with security on the agitated
branches ; the muscles of its eyes are not synchronous in
their movements, by which it commands an extensive field
of vision without moving its head, and the muscular, clavate,
prehensile tongue is moved writh velocity, like a sheath to
and fro, from the long body of the os hyoides. The power-
ful intercostals of the flying dragon expand its ribs with
their connecting skin, and move them like wings, to enable
it to pursue its insect prey through the air. The saurian
reptiles, possessing a more distinct cervical region than any
of the inferior vertebrata, and often carrying bulky prey to a
distance in their jaws, require a great development of the
muscles which suspend and move their heavy head and neck,
as the recti and obliqui muscles of the head, the splenii, sca-
leniy complexus and serratus posticus, the inter- and semi-spi-
nales colli, the transversalis, trapezius, and rhomboideus.
The fibres of ihepanniculus carnosus are intimately connected
with the large osseous, external plates of the loricated croco-
dilian reptiles, but the skin is more free in the lacertine spe-
cies. The external and internal obliqui abdominis and the
transversalis are distinct in the crocodiles, and also a rudi-
ment of the diaphragm. The posterior portion of the
diaphragm is likewise perceived in the dragons and geckos,
where it consists of muscular bands ascending from the bo-
dies of the vertebree to be attached to the ribs before
them.

Many of the ordinary muscles of the trunk are wanting
in the chelonian reptiles, from the immobility of the skeleton
in that part of the body, especially in the land species. Se-
veral muscles of the face are deficient from the immoveable
horny covering of the jaws and lips, and from the close ap-
plication of the horny scales to the periosteum in that part.
The muscles on the dorsal part of the spine, and all the in-
tercostals, are likewise deficient. Those of the cervical, sa-
cral, and coccygeal regions, and those of the scapular and
pelvic arches, together with the muscles of the arms and
legs, are the most distinct and powerful in this order, and
correspond with the mobility of these parts, or the weight
they have to sustain. The temporal muscles are covered
over by the parietal bones in the turtles, but in the tortoises,

PART II. M

MUSCULAR SYSTEM.

where the whole head is easily withdrawn within the strong
arched and capaceous carapace, these muscles are exposed
on the sides of the cranium (Fig. 75. A.) as in warm-blooded
animals. The orbicularis palpebrarum, (Fig. 75. A, a,) is

here thin and feeble, and chiefly appropriated to the large
moveable lower eye-lid. The oblique muscles of the eye-ball
are also very small, while the recti and the suspensorius oculi,
(Fig. 75. B. a) are more distinct and strong. The mylo-hyoideus
(Fig. 75. A. by) and the latissimus colli (75. A. c,) here form
a large panniculus carnosus, covering the whole of the lower
part of the sides of the neck. The spinalis cervicis, (A. d,)
here forms numerous strong detached bands, which prin-
cipally support the head, and retract it, when alarmed, within
the cavity of the trunk. Behind this muscle lies the inser-
tion of the longus colli, (A. /,) which has a similar action on
the neck. Between these extends downwards the latissimus
dorsi, (A. e,) tapering to the humerus, before which is the
extended latissimus colli, and the imperfect diaphragm, (A.#,)
extending over the peritoneal covering of the lungs. The

MUSCULAR SYSTEM. J G3

obliqui, (A. /,) and the transversales abdominis, (A. £,) are
here of considerable extent, passing forwards around the
abdominal cavity, beneath the sternum and the ribs, and
assisting in respiration and in the discharge of all the natural
excretions. Behind the diaphragmatic bands (B. /, m,) are
the posterior insertions of the large retrahentes capitis et colli
(B. k,) which extend forwards along the back part of the
neck (B.,/,) to retract the head and neck under the ribs. As
the ribs are immoveable, the motions of inspiration are ef-
fected chiefly by the os hyoides, as in amphibia where the
ribs are almost or completely wanting, and most of the mus-
cles connected with that bone are large and distinct, like the
parts of the os hyoides itself. The genio-hyoideus (B./.)
forms a broad muscle extending forwards to the lower jaw,
and the omo-hyoideus, (B. iy) continues backwards as a broad
muscular expansion, covering the lower part of the neck.
The hyo-glossus, hyo-maxillaris, genio-glossus, are also here
distinct, and the stemo-mastoideus, the digrasticus maxilla,
trachelo-mastoideus, (B. /*,) and most of the muscles which
move the head, are well marked in these long-necked ani-
mals. The large pectoral muscles have an extensive attach-
ment to the interior of the sternum. Two broad muscles
proceeding, in different directions, from the sternum to the
pubic bones, and constituting the attrahens and retrahens
pelvim on each side, appear to be the analogues of the recti
abdominis. The serratus magnus, deltoides, sub- and super -
scapularis, triceps, (A. <?,) and biceps (B. y}) brachii, and most
of the succeeding muscles of the arm and hand are powerful,
especially in the land tortoises, where the arms are fixed in
a state of pronation, the best suited to support the weight of
the body. The flexor sublimis (A. r}) forms a strong mus-
cular band on the outside of the fore-arm. The broad ten-
dons of the extensor communis digitorum manus, (A. s,) cover
the back part of the carpus, and on the upper part of the
fingers are the five strong extensores breves digitorum manus,
(A. /.) The brachialis internus (B. #,) the palmaris, (B. z.)
the flexor profundus, (B. 2,) and most of the flexor muscles
of these extremities are strong, both for support and for
digging. In the long, fin-like arms of the turtles, the mus-
cles of the shoulders are those chiefly developed, while the
muscles of the fore-arm and hand are very feeble, as in ceta-

M2

16'4 MUSCULAR SYSTEM.

ceous animals. The ylutei (A. 0,) the iliacus internus,
and the psoas, are strong muscles in the land species, as are
almost all the extensors and flexors of the thigh-bone. The
biceps cruris, (A.v,) and the semitendinosus, (A. w,) form long
muscular bands behind the femur, and the rectus femoris,
(A. #,) in front, which unites below with the vastus externus,
(A. y,) the vastus internus, and the crureus, to be inserted
into the tuberosity of the tibia, below the knee, by a common
tendon. The sartorius (A. z,) semimembranosus, obturator,
and graciliSy have here their usual position and action. The
extensor communis digitorum pedis, (A. 1,) and the short ex-
tensors of the four toes, (A. 5,) resemble the corresponding
muscles of the hand. The peroneus, (A. 4,) the gastrocnemii
(A. 3,) and the other extensors, are strong on the posterior as
those on the anterior extremities in the tortoises, to support
and move their heavy body on the land, but they are scarcely
perceptible in the long flat fin-like feet of the turtles. The
cloaca has its dilating and its sphincter muscles, and the
highly moveable tail has its numerous flexors and its exten-
sor muscles in the reptiles of this order, and even the glottis,
the penis, and the clitoris, have already their accompanying
muscles developed, as in higher animals.

The muscles of birds are more red and vascular, more
irritable and dense than in the cold-blooded vertebrata be-
neath them, and they possess these properties in the greatest
degree in the rapaceous tribes, where the respiration is great-
est, and where all the functions are most energetic. This
condition of the muscular system is required in birds, from
the lightness of the medium through which they move, and
from their quick and long continued movements through that
element. The muscles are more feeble, pale, soft, and pala-
table in the heavy, slow-moving, phytophagous tribes, where
the condition of the bones and most of the other systems,
mark an inferior or reptile state of development. The fleshy
parts of the muscles are generally short and thick, especially
in the arms and legs of birds, and their tendons are generally
long, slender, dense, and often ossified, like many cartilagi-
nous parts of the skeleton. The active, heavy, fleshy parts
of the muscles being situate, for the most part, on or near
the solid trunk of the bird, the extreme parts, so important
for progression, are lightened by receiving and supporting

MUSCULAR SYSTEM. 165

only the long narrow tendons ; hence the long slender legs
and the lightness of the arms in this class. As birds have
nearly all the same general form and movements, there is
remarkable uniformity in the muscular system throughout
this class. Their trunk being almost as fixed as in the che-
lonia, the muscles destined to move that part are here also
very imperfectly developed, but its fixed condition affords
the most advantageous attachment for the powerful muscles
of the extremities, which have generally a very high origin.
The arms and hands being entirely appropriated to flight,
and the legs and feet being constructed chiefly for support,
their long flexible neck and highly moveable head supply the
place of anterior extremities for all ordinary purposes of
prehension, and the cervical region is therefore strong, move-
able, and muscular, like the trunk of a serpent. The face of
the birds, from the imrnoveable horny sheaths which cover
the exterior of the jaws, is like that of the crocodilian and
chelonian reptiles, destitute of many muscles destined to
move the fleshy lips in other classes. The temporal, (Fig.
76. «,) the masseter, and the pterygoid muscles are powerful
in birds, and correspond with the great length and the mo-
bility of their lower jaw ; they are stronger in the rapacious
birds, from the resistance they have to overcome, and they
are most unequally developed on the two sides of the head
in the crossbills, which habitually draw the lower jaw to one
side of the head. The large eyes in this class are moved by
four recti muscles, as in mammalia, and have their middle
portion surrounded, compressed, and rotated by two obliqui.
The orbicularis palpebrarum, expanded over their large orbit,
acts most on the lower eye-lid, as in inferior classes ; the
lower eye-lid has also its small depressor, as the upper has
its levator muscle, and the membrana nictitaus, with its long
inferior tendon passing behind and over the ball, is moved
with great velocity by its pyramidalis and quadratus muscles.
The fixed condition of the dorsal vertebrae affords a more
solid attachment to the muscles of the long neck, and in
rapaceous birds, which frequently carry their prey suspended
from their jaws, to a distance through the air, the neck is
comparatively short and strong, and the muscles of great
power which move these vertebrae, as seen in the annexed
figure from Carus, representing the muscles of the falco

166

MUSCULAR SYSTEM.

FIG.

/i

y (Fig. 76-) The recti postici and antici, the obliqui ca~
pitis, the splenii capitis et colli, and the strong complexi (Fig.
76. c,) rotate the head on its single occipital condyle, and
bend the neck to either side. The inter-transversales, inter-
spinales, transversalis colli, spi-
nales dorsi et colli, trapezius, cu-
cullaris, biventur cervicis, rhom-
boideus, trachelo-mastoideus, and
scaleni muscles are also well
marked in the flexible neck of
birds, and important in the move-
ments of this part of the skele-
ton. The longus colli passes up-
wards from the spinous processes
of the lower cervical and ante-
rior dorsal vertebra, to be in-
serted into the transverse pro-
cesses of most of the vertebrae of
the neck. The external inter-
costals are divided each into an
anterior and a posterior, half by
the osseous appendices extend-
ing backwards from the margins
of the ribs, and the internal in-
tercostals extend backwards no
farther than these appendices.
The serrati, the latissimus dorsi,
the obliquus externus, and inter-
nus abdominis, the transversalis
and most of the muscles con-
fined to the trunk are feeble in
this class. The broad thin recti
abdominis, connected together by
a broad linea alba, and destitute
of tendinous intersections, diverge at their posterior or lower
part, to be inserted into the detached and feeble pubic bones.
The muscular parietes of the abdomen are here thin and
feeble, and very short, from the greater portion of that ca-
vity being covered and supported by the large sternum, and
the muscular bands forming the rudimentary diaphragm ex-
tend upwards and inwards from the margins of the sternal

MTSCULAll SYSTEM. l(»7

ribs, spreading like a thin aponeurosis over the peritoneum
covering the abdominal surface of the lungs, as in many of
the cold-blooded vertebrata. The iliacus is here a small
muscle within the pelvis, and the psoas appears to be want-
ing, but the glutei muscles are of great strength, having to
support the whole weight of the trunk upon the posterior
extremities alone, as in the human body. The tail is moved,
and its feathers are expanded, by several lateral muscles
both above and below the coccygeal vertebrae, extending
from the sacrum to the spinous, and to the transverse pro-
cesses, and extending to the bases of the large quill-feathers
themselves. The anterior extremities, like the posterior,
have the proximate muscles of great magnitude and strength,
while the more distant muscles of these parts are compara-
tively small and feeble, and those are especially strong which
are placed on the fore part of the sternum, and effect the
depression of the humerus, the most powerful and important
movement in the flight of birds. The pectoralis major, (Fig.
76. d,)' covers nearly the whole surface of the sternum and
its crest, and continues its origin along the edge of the cla-
vicle, and the surface of the broad ligament which unites the
clavicle to the upper margin of the sternum. The insertion
of this muscle is extended along a great portion of the hu-
meruSj and its magnitude corresponds most generally with
the power of flight, and the rapaceous character of the spe-
cies. The subclavius, the serrati, the subscapularis, and
most of the muscles connected with the scapula, on the
upper part of the shoulder, are small in birds as in reptiles,
and correspond with the limited extent of surface of that
bone. Beneath the extended pectoralis major are the long
narrow pectoralis minor, and the coraco-brachialis, which,
from its position, looks like a third pectoral muscle. The
integuments on the fore part of the wing are expanded like a
web, in the bent position of the arms, by two long elastic
tendons which originate from a strong cutaneous muscle like a
deltoid, extending from the scapula over the head of the hume-
rus, (Fig. 76» d, e.) One of these tendons is short, and ex-
tends only to a small distance beyond the lower end of the
humerus, while the other extends to the wrist, as seen in the
annexed figure of the wingof the common buzzard,/a/co£«teo,
(Fig.77. e,e,e.*} In this back view of the muscles of the arm in a

168 MUSCULAR SYSTEM,

rapaceous bird, the small thin cucullaris, (a, a,) Is seen ex-
tending outwards from the vertebral column, and above it
the two divisions of the latitsimus dorsi, (c, d,) which cover
also the infra spinatus, (b.} The short fleshy mass of the
deltoid muscle (/",) extends to the middle of the humerus,
and behind it is the long triceps extensor cubiti (g, h.) On
the fore-arm are seen the fleshy parts of the extensor carpi
radialis (i}) with its long tendon passing over the end of the
radius, the supinator radii brevis (k,) the strong extensor digi-
torum communis (/,) and beneath this the extensor metacarpi
ulnaris (m, n,) which has its long tendon inserted into the
middle strong element of the single metacarpal bone in birds.
Beneath the thumb (<?,) is the very small flexor pollicis, and
on the ulnar side of the long middle finger (/*,) is the tendon
of the abductor indicis which passes down fleshy between the
long anchylosed metacarpal bone, and has its tendon inserted
into the base of the last phalanx. The flexor indicis has its
tendon inserted into the distal extremity of that phalanx (r.)
The flexor carpi ulnaris (p,) passes fleshy along the ulnar
side of the outer metacarpal bone, and the outer finger, con-
sisting of a single minute phalanx, has its own flexor digiti
minimi (s.) The muscles and articulations of the wing are
chiefly adapted for adduction and abduction, and they admit
of little flexion and extension, or promotion and supination,
excepting at the head of the humerus ; so that the whole
arm moves with greater solidity and effect as an organ of
flight, and is more easily folded along the side of the trunk
when in a state of repose. On the posterior extremities the
extensor muscles are more developed than the flexors from

MtJSCULAR SYSTEM. 169

the trunk being supported by these members alone in walk-
ing. From the extent, and the fixed condition of the dorsal
part of the pelvis, the extensors of the femur have a high
origin and a lengthened form, and the glutens maximus, me-
dius, and minimus are developed in this region, as in qua-
drupeds. The glutens majcimus here reaches along the femur,
as low as the fibula, passing below and behind the knee-joint.
The only distinct abductor of the femur is the gemellus supe-
rior^ which rotates the thigh outwards, and this muscle is
deficient in many aquatic birds. The pyriformis, quadratus
femoris, and obturator externus extend the femur, and are
aided by a muscle analogous to the pectineus. The peroncus
longus and the tibialis posticus, arising from the back part of
pelvis, are connected below with the extensor tendon of the
heel. The rectus femoris arising from the upper part of the
pubis, continues its long tendon over the extensor tendon of
the knee, and unites below with the common perforated flexor
of the toes. The gracilis arises very low from the femur, and
acts as an extensor of the knee, and the popliteus, directed
transversely, is situated high on the tibia. The foot is raised
by the tibialis anticus, which passes from the tibia to the
metatarsal bone, and rotates the foot inwards in the climb-
ing movements of the zygodactylous birds ; these birds have
likewise the peroneus brevis of considerable size, which arises
from the exterior of the tibia and fibula, and rotates the foot
outwards. The gastrocnemius, (Fig. 76. u,) arises from the
condyles of the femur, and passes down thick and fleshy to
the broad aponeurotic tendon of the heel, which forms a
groove for the passage of the flexor tendon of the toes, and
is inserted below into the long metatarsal bone. Behind the
tibialis anticus (Fig. 76. r,) arises the fleshy head of the ex-
tensor longus digit orum, (Fig. 76- £,) the tendon of which,
bound down by strong ligaments in its course, divides at the
lower end of the metatarsal bone, into three separate ten-
dons, which proceed along the upper part of the toes to be
inserted into the base of each terminal phalanx. The pos-
terior toe has a distinct extensor muscle which descends from
the upper part of the metatarsal bone, and is inserted into
both phalanges. The long flexor of the toes descending from
the upper part of tibia exterior to the gastrocnemius, is con-
nected with two cartilages at the heel-joint, which represent

170 MUSCULAR SYSTEM.

the astragalus and the calcaneum, and which I have found in
the ostrich, in the condition of a large, solid, sesamoid
bone.

The muscular system of the mammalia is greatly diversi-
fied by the variety of forms and habits of the animals which
compose this class, some of which are organized to move
like fishes through the ocean, some to burrow in the earth or
to walk on its surface, or to climb on trees, and others to fly like
birds through the air. The differences here presented by the
muscular system relate therefore chiefly to the organs of motion,
which vary according to the nature and situation of the food.
The fleshy parts of the muscles in mammalia are generally large
and strong, and proportioned to the more massive bones of the
skeleton, and the encreased weight of the whole trunk. The
respiration being less extensive here than in birds, the tem-
perature is inferior, the tendons are less inclined to ossify,
the circulation is slower, the muscular fibres are less dense,
and their contractions are less energetic, and the muscles
compensate for their defective energy by their increase of
bulk, which gives a rotundity to the exterior form of the
body, and more massive proportions to all the parts of these
animals. As the cetaceous animals breathe by lungs, and
not by gills, like fishes, the muscles of their vertebral column
are disposed chiefly for movements in a vertical plane, and
not for horizontal motions, like those of the water-breathing
fishes. The great elevation and breadth of the occipital
region of the cranium afford an extensive surface of
attachment, as in fishes, for the powerful muscles of their
short fixed neck, and extended moveable trunk. From the
great length of the transverse and spinous processes of nearly
all the vertebrae of the trunk, there is a large angular space
on each side of the column, for the numerous long and pow-
erful muscles which move the caudal vertebrae, and the tail,
and the fleshy bodies of these muscles are very indistinctly
separated from each other, from the general similarity of
their direction and uses. The splenii muscles of the head
and neck, the longlssimus dorsi, the sacro-lumbalis, the tra-
chelo-mastoideus, the spinalis dorsi, and the complexus, are
here especially distinct on the dorsal region of the column,
and important in its backward movements. On the lower
part of the column is the large quadratics lumborum, and two

MUSCULAR SYSTEM. 11

muscles analogous to the psoas and the iliacus, which power-
fully assist in the downward movements of the coccygeal
vertebrae. The oblique, the transverse, and the recti mus-
cles of the abdomen are lengthened and feeble on the long
trunk of the cetacea, and the abdominal ring is wanting,
as in other mammalia, where the testes remain permanently
in the abdominal cavity. The proximate muscles of the an-
terior extremities, the subscapular, the infra-spinati, the pec-
toral and the deltoid muscles, are those principally employed
in the movements of these fin-like organs. The more distant
muscles of these extremities, however, especially the flexors
of the fore-arm and hand, are much more developed in the
herbivorous cetacea, which are able to seize and to climb
upon rocks. The muscles of the pharynx, of the os hyoides,
and of the exterior nares, are numerous and distinct in these
animals, and correspond with the magnitude and the mobi-
lity of these parts. The compressor muscles, embracing the
expanded nostrils of many of the blowing cetacea, enable
them forcibly to expel columns of water taken in by the
mouth, and the extension of these muscular cavities allows
them to breathe freely while the rest of their body is beneath
the surface of the water. The cetacea, like fishes, amphibia,
and serpents, consisting almost solely of the trunk, are
moved and supported by its muscles in the dense element
they inhabit ; but the land quadrupeds require strong mem-
bers and strong muscular apparatus to support and move
their heavy trunk in the light and unresisting element they
breathe. In the herbivorous quadrupeds, the muscular
energy and development are generally less than in the car-
nivorous species, which corresponds with the inferior deve-
lopment of their respiratory and nervous systems, and the
diminished activity of all their functions. The ruminantia,
like the pachyderma, having no clavicles, the humeri are ap-
proximated under the thorax, and the anterior part of the
trunk is suspended between the long vertical scapulae by the
strong serrati muscles, as by a band passing across beneath
the chest. From the weight and the horizontal position of
the trunk, the extensor muscles of the extremities are more
developed than the flexors, and to render these extremities
more light and nimble, the distal bones and tendons are
lengthened, and the heavy fleshy parts of the muscles, as in

17* MUSCULAR SYSTEM.

birds, have a high origin. The number, the divisions, and
the tendons of these muscles, are fewer than in the more
muscular and powerful carnivorous quadrupeds, from the
reduced number of the toes. From the weight of the horns,
and the use made of these defensive organs in many of the
larger ruminantia, as the buffalo, the bull, the gnu, and the
bison, the neck is short, and the muscles which support and
move the heavy head are large and powerful, and the same
is observed in many of the larger pachyderma, from the
weight of the teeth, or tusks, or proboscis, or horns. From
the great size and mobility of the exterior concha of the ear,
in most of the herbivorous quadrupeds, they present a great
development of the attollens aurem, and of the anterior and
posterior auris, and from the lengthened form of their face
and jaws, all the muscles of their lips and nostrils are gene-
rally lengthened and strong. The muscles of the nose are
particularly strong in the hog-tribe, to enable them to dig up
their food with that organ of smell, as they are also in the long
flexible nostrils of the tapirs. In the face of the elephant^

FIG. 78.

(Fig. 78,) so remarkable for the extent and flexibility of the
nostrils, and for their sensibility and prehensile power, the
levator and zygomatic muscles (a, s,) of the upper lip are in-

MUSCULAR SYSTEM. 17-*

•corporated with those of the prolonged nostrils. These
levator muscles of the heavy proboscis have a strong tendi-
nous attachment laterally (s,) to the zygojnatic bone, and the
anterior fasciculi (a,) are attached to the malar, the nasal and
the frontal bones. The upper portion of the orbicular is oris
(b,) is extended on each side along the base of the proboscis.
Below the levator muscles (s,) are seen the large branches of
the trifacial nerve proceeding forwards to the muscles of the
face and proboscis. Extending downwards and backwards
from the angle of the mouth, are several terminal fasciculi of
the platisma myoides or panniculus carnosus (c, d, q,) and be-
hind the ramus of the jaw is the large parotid gland, with
its duct passing forwards beneath the facial nerve. Above
the parotid is the attrahens aurem (o,) passing forwards to
the malar bone, and behind the outer margin of the ex-
panded orbicularis palpebrartim (a,) is the opening of the
short duct from the temporal gland. Beneath this gland
descends the powerful temporal muscle (k,) above which are
the detached portions of the large att aliens aurem, (m, n,)
destined to move in different directions the great expanded
concha of this animal. Detached muscular fasciculi (h, i,)
descend from the frontal to raise the skin in the region of the
eye-brows. The depressor labii inferioris (r,) is seen extend-
ing downwards from the margin of the lip, and the levator
anguli oris rising obliquely upwards and outwards from the
angle of the mouth. The panniculus carnosus, which is
scarcely perceptible over the trunk in the larger thick-skinned
pachyderma, is a strong, fleshy, subcutaneous layer in the
softer skinned ruminantia, where it extends from the trunk
over the neck to the head, and is attached both to the hu-
merus and to the femur. In the mammalia, covered with
spines, as the echidna, hedge-hog, porcupine, and in those
covered with imbricated scales, as the manis and the arma-
dillo, this muscle is also important in erecting or moving
these epidermic organs, and in coiling or uncoiling the body.
The neck is generally short, thick, and muscular in these ant-
eaters, or loricated insectivorous quadrupeds, to assist in exca-
vating the ground with their head in quest of food. In the ro-
dentia, as in birds, the pterygoid and the temporal muscles are
strong, and the pteryoid processes of the sphenoid bone have a
corresponding magnitude; their masseter muscle is also of great

174 MUSCULAR SYSTEM.

breadth, and by sending its fibres both forwards and back--
wards from the depressed zygomatic arch, it assists in the
longitudinal movement of the lower jaw in both these direc-
tions. The whiteness, or pale colour, and the velocity of
movement of the muscles of rodent quadrupeds, present
further affinities to the class of birds, especially to the heavy
inactive vegetable-eating gallinaceous kinds, where the blood
is less rapidly and less extensively distributed through their
muscular system than in the more powerful rapaceous tribes.
The flexor muscles of the arms are generally much deve-
loped and much exerted in this order of quadrupeds, either
for scraping the ground for food, or for burrowing in the
earth, or for climbing upon trees and cliffs. In the
marsupial quadrupeds, the abdominal pouch is em-
braced externally by the panniculus carnosus, the fibres of
which serve, by their extension over the pouch to the sym-
phisis pubis, to contract that cavity so as closely to embrace
the newly-received young, and to protect them during the
first period of their extra-uterine life. Within this pouch
are the mammary glands, which are embraced by distinct
muscular fasciculi destined to compress them and to aid the
escape of their secretion, and other delicate fasciculi force
the milk from the ducts and the nipples into the mouth of
these abortive foetuses, and thus to extend the nipples from
their ordinary retracted condition. The muscular system
of carnivorous quadrupeds corresponds, in its high develop-
ment with the solid texture of their bones, and the great
extent of their respiration, the nutritious character of their
food, and the living habits and wants of the species. By
the magnitude and the extension forwards of the zygomatic
arch their large temporal and masseter muscles have an ad-
vanced insertion on the lower jaw, most favourable to their
action, which is aided by the short truncated or rounded
form of the head, especially in the feline animals. The leva-
tor muscles of the lips and nose serve, by their magnitude,
to uncover the large tusks, to prevent injury of the lips in
seizing the prey, and to add ferocity to the aspect to in-
timidate and overcome that prey. The muscles of their short
and thick neck are strong, to enable them to carry off their
prey entire, or to tear it to pieces, as those of their shoulder
and arm are powerful, to enable them to grasp or hold down

MUSCULAR SYSTEM. I/-")

their prey, or to strike it to the ground, and they assist in
bending forwards the trunk in striking, by their large recti
abdominis, which here extend forwards to the anterior end of
the sternum. The great extent of the fleshy part of their
diaphragm aids their rapid and extensive respiration. The
central tendinous portion of the diaphragm is much more ex-
tensive, and consequently the muscular part less, in the ru-
minating and other herbivorous quadrupeds. The muscles
of the lower jaw in the cheiroptera and the levators of the
upper lip are generally strong, as in the carnivora, and most
of them are nocturnal predaceous animals, but as they pursue
their prey through the air, the muscles proceeding from their
scapula, their clavicle, and their sternum, to the humerus are
of great size and strength, and the flexors of their carpus
and fingers send down very long and thin tendons to the
lengthened phalanges of the fingers, so as to lighten the dis-
tal extremities of the hands, and to adapt them for progres-
sion through so rare a medium. The quadrumanous animals
being organized for a semi-erect position, and climbing move-
ments, have the flexor muscles strongly developed on all
their extremities, and the lengthened form and feebleness of
the extensors of their posterior extremities, as the glutei
muscles, the recti femor is ^ the vasti, the gastrocnemii, and
other extensors, so large in the human body, produce that
smallness of the nates, the thighs, and the calfs, so charac-
teristic of this climbing frugivorous order. The muscles of
the jaws and of the neck are strongest in the baboons,
where the trunk is most adapted for the horizontal posture,
and the ferocity and general strength are almost those of
carnivora. The flexors of the coccygeal vertebrae are most
powerful in the long prehensile tail of the aides, or spider-
monkeys of America, in which the long recti abdominis are
still destitute of tendinous intersections, as in many of the
inferior mammalia. From the vertical position of the human
trunk on the posterior extremities, and the freedom and
flexibility of the arms the extensor muscles are most deve-
loped on the legs, and the flexors on the arms. The muscles
also which support and move the spine, and those which
embrace the visceral cavities, are proportionally strong in
man, (Fig. 79.) The numerous flexors of the toes are here
powerful, to enable the foot to sustain the weight of the

176

MUSCULAR SYSTEM.

whole body in progression, and this organ is strengthened by
its shortness, and by the fixed condition of its solid parts. The
gastrocnemii, (79. B. k, I,) are large, and the tendo achilles,

FIG. 79.

(,

(79. B. m,) is thick and strong, to raise the heel and the
whole trunk in walking, and to preserve the tibia in a vertical
position on the astragalus in standing. For the same reason
the rectus femoris (79. A. n,) and the vastus exturnus (J9. A.
nf) and interims (79. A. w,f) are large and fleshy, to preserve
the femur erect upon the tibia, and the glutei muscles (79. B.
/,) are of great magnitude, to preserve the pelvis and trunk
vertical upon the femur. Hence the magnitude and rotun-
dity of the calfs, the thighs, and the nates, so characteristic

MUSCULAR SYSTEM. 177

of the human form. The trapezius (79. B. «,) the latissimus
dorsi (79. B. c,) the rhomboidei, serrati, sacro-lumbalis, multi-
fidus spin&y and most of the muscles of the back or extensors
of the spine are proportioned to the great weight which they
have to sustain in the movements of the trunk. The flexor
muscles of the ankle-joint, and those of the knee and of the
thigh are generally thin, lengthened, and feeble, compared
with the extensors of these joints, or when compared with
their development in many of the inferior mammalia. The
obliqui and the transversalis abdominis, here form strong
muscular parietes for the support of the heavy abdominal
viscera, the recti abdominis, are unusually short and thick in
man, and divided by distinct, transverse, tendinous intersec-
tions, and the small pyramidales are more constant than in
quadrupeds. The articulation -of the head of the humerus is
adapted for free and varied, rather than for powerful, move-
ments, and the pectorales (79. A. b,) the deltoid (79. A. e.)
and the scapular muscles, are short, broad, and of moderate
strength,, but the biceps brachii (79. A..f9) the flexor carpi
radialis (79. A. £,) and ulnaris, the supinator radii longus
(79. A. h}) the pronator radii teres (79, A. i,) and almost all
the other flexors of the fore-arm and those of the fingers,
are much more developed than the extensors of the same
joint ; so that while these extremities are unfit for supporting
the trunk in a horizontal position, they have the form and
movements best adapted for seizing or feeling outward ob-
jects, for manipulating the young, and for the various uses
to which they are applied in social intercourse and in the
arts. The great weight of the head, and its vertical position,
unsupported by a ligamentum nuchee, require the recti and
obliqui capitis, the splenius, complexus, and trachelo-mastoi-
deuSy the platisma myoides (79. A. c,) the sterno-cleido-mas-
toideuSy and nearly all the other muscles of the neck, to be
proportionally strong for the support and movement of that
heavy part. The teeth having little resistance to overcome,
by the general softness of the food, the temporal and mas-
seter muscles are of moderate size, and by the shortness of
the jaws the ordinary muscles of the face are confined to a
smaller extent of surface than in other mammalia, and their
actions consequently produce impressions more numerous
and diversified, and which are more visible from the nakedness,

PART II. N

178 MUSCULAR SYSTEM.

the softness, and the generally light colour of the human skin.
The moveable parts of the face into which the muscles are
chiefly inserted, are the lips and the eye-Brows, from the re-
lation of these parts to food, to speech, and to visual impres-
sions ; and as the motions of those parts are regulated by
present sensations, and are associated with corresponding
conditions of the mind, they are the chief seats of human
expression, in which we read the transient feelings of the
moment, or the habitual tendency of the passions, or the in-
ward workings of the soul.

NERVOUS SYSTEM.

CHAPTER FOURTH.

NERVOUS SYSTEM, OR ORGANS OF SENSIBILITY AND
MOTILITY.

FIRST SECTION.

General Observations on the Nervous System.

THE nervous system communicates to the muscles their
energy of action, and to all the sentient parts of the body
their power of feeling. By the rapidity of its action, and its
extensive distribution through the body, it establishes an in-
stantaneous communication between the most distant parts.
It is chiefly by this system that animals are connected with
surrounding nature, and there is no part of their economy
which is more indicative than this of the condition of the
whole organization, or of the grade which an animal occupies
in the scale. The nervous system has been detected in every
division of the animal kingdom, and almost in every class,
and it is everywhere connected with sensation and motion.
Its general form corresponds with that of the body, being short
and disposed in a circular manner in the short round bodies
of most of the radiated and molluscous animals, and having a

N 2

180

NERVOUS SYRTEM,

narrow and extended form in the more lengthened trunks of
the articulated animals, and the vertebrata. The great cen-
tral portion of the nervous system is perforated by the ali-
mentary canal in the invertebrated classes, either in its mid-
dle, as in the radiata and the mollusca, or at its anterior ex-
tremity, as in the articulata ; but in the vertebrata the spi-
no-cerebral axis lies wholly above the digestive cavity, by
which it is nowhere pierced. The nerves of sensation and
motion closely accompany each other, forming, by their
union, chords or columns, or a spino-cerebral axis ; but the
sympathetic nerves, appropriated to the more slow and re-
gular movements of organic life, form a more isolated sys-
tem, and these three systems are developed together, almost
from the lowest animals. The nervous system consists
of very fine tubular filaments, generally containing white-
coloured opaque particles, much smaller than the globules
of the blood ; these minute fibres do not ramify like blood-
vessels, but continue uninterrupted from their peripheral ex-
tremity in the textures of the organs, to their proximal end
in the cineritious substance of ganglia, or of the brain. The
cineritious, or cortical matter is composed of a vascular
plexus, in the meshes of which is an irregular granular
pulp, and the fibrous arrangement becomes more obvious
and regular at its junction with the white medullary portion.
In the white portion of the brain, and in the nerves of the prin-
cipal senses the ultimate component tubular filaments have
a knotted or beaded appearance, from their numerous small
dilations, and they appear to be empty, or to contain only a
transparent homogenous fluid, as seen in the annexed figure
of Ehrenberg (Fig. 80,) where (a) is a magnified view of the

NERVOUS SYSTEM. 181

knotted fibres composing the white matter of the hu-
man brain, (b) represents the coarser beaded fibres composing
the human auditory nerve, and (c) exhibits those of the hu-
man optic nerve. This structure is observed on pressing
fine sections of these parts between plates of mica or of
glass, and viewing them through the microscope. This
knotted structure of the minute filaments is seen also in the
olfactory nerve, and in the sympathetic. The ordinary sym-
metrical nerves of sensation and of motion, throughout
the body, are composed of tubular filaments of more equal
calibre throughout their course, and which are filled with
minute white globular particles, as seen in those of the hu-
man facial nerve (Fig. 80. d}) where the globular minute par-
ticles filling the neurilematous tubes are seen escaping from
the cut ends of the filaments. This knotted appearance of
the cerebral and sensitive filaments has been considered by
some as resulting from the external aggregation of clusters
of minute particles along the surface of chains of similar
globules composing the ultimate nervous fibrils. These ex-
tremely minute fibrils, variously aggregated together by en-
veloping sheaths of condensed cellular tissue, but without
anywhere anastomosing, constitute the nerves of sensation
and of motion throughout the animal kingdom, and the
spino-cerebral axis of the vertebrata. The nervous system is
developed, like other organs of the body, from the periphery
to the centre, and it presents great uniformity of plan in its
adult conditions in the inferior classes, and in its transient
embryo-forms throughout all the higher orders of animals.

SECOND SECTION.

Nervous System of the Cyclo-Neurose, or Radiated Classes.

Many of the poly gastric animalcules, as the cercarite, are
distinctly sensitive to light, and organs of vision, in form of
minute red points, are seen in almost every genus. They
appear also to possess an acute sense of taste, they distin-
guish, pursue, and seize their prey, they avoid impinging on
each other while swimming, crowded in myriads, in a drop of

182 NERVOUS SYSTEM.

water; they contract and bend their body in every direction, and
they increase or retard, or cease at pleasure, their progressive
motion and the vibration of their cilia, like the muscular and
gangliated rotiferous animalcules, yet nervous filaments have
not been distinctly detected in the minute transparent bodies
of the polygastrica. The numerous straight parallel jaws,
seen in many of the genera, are opened and closed, advanced
and retracted, with great quickness and precision, and all the
movements of these minute animals appear to be as regular,
methodical, spontaneous, and well-directed as those of many
higher animals with obvious nerves. The transparency of
the nervous filaments in all the minute forms of animals
probably prevents our detecting in the polygastrica the rudi-
ment of that form of the nervous system which is seen in
the wheel-animalcules, and in the higher articulated classes.
In the poriphera, the component particles of the nervous
and muscular systems are probably diffused through every
part of the soft cellular tissue of the body, which possesses
the same living properties in every part, and is almost inde-
finitely divisible without destroying its vitality. The repro-
ductive gemmules of these animals vibrate their cilia with
great regularity and force ; they appear to be conscious of
each other's approach, and can accelerate, retard, or cease
their motions at pleasure ; they are sensitive to light, and
appear to be guided by its influence in selecting the place of
attachment most suited for the growth of each species : yet
they exhibit no nervous or muscular filament in the gela-
tinous texture of their body. Many polypipherous animals,
even of the simplest forms, are obviously sensitive to light,
as hydra, lobularite, actiniae, and muscular fibres are distinctly
perceptible in the polypi and other parts of most of the
higher genera. The nervous system has been long known in
the actinia, which is a large isolated naked polypus, closely
resembling, in external form and internal structure, the po-
lypi of caryophillice, pavonite, and many of the larger litho-
phytes. Nervous filaments surround the muscular foot of
the actinia, beneath the stomach, and present minute gan-
glia in their course, from which nerves pass out to the cir-
cumference, and to the muscular folds which here possess
great power of contraction. The same system probably ex-
ists in many other closely allied forms of polypi. The lowest

NERVOUS SYSTEM.

183

ciliograde acalepha possess great activity, are provided with
numerous long tentacula exquisitely sensitive and contractile,
exhibit distinct internal organs for digestion, circulation, and
generation, and are found to be provided with nervous fila-
ments and even ganglia around the oesophagus. In the beroe
pileus (Fig. 81. A,) the nervous system is disposed around
the mouth, at the lower extremity of the body, in form of a
double filament (a,) with eight small white ganglia (b,) inter-
posed between the eight longitudinal
bands of cilia. From each of these gang-
lia a small filament proceeds upwards in
a longitudinal direction (c,) towards the
anal extremity of the body, and others
pass out laterally and downwards to
the projecting irritable lips surround-
ing the mouth. In the medusos a ner-
vous band, accompanying the marginal
circular continuation of the alimentary
cavity, is disposed around the irritable
border of the mantle, with minute gan-
glia placed near the bases of the marginal
tentacula. From each of these ganglia
nervous filaments proceed to the near-
est tentacula, along the bases of which they can be traced.
Eight optic ganglia are perceived at the bases of the eight
ocular peduncles, from which nerves proceed to the small
red coloured marginal eyes, which they are observed to en-
ter. Other ganglia are also perceived, near the ovaries,
around the entrance to the stomach, from which nervous
filaments, are seen passing downwards to the central groups
of tentacula. From each optic ganglion two nerves proceed,
which unite by a kind of decussation before they enter the
eye ; the eye is provided with a distinct crystalline lens, and
the pigment is red-coloured, like that of most of the simplest
forms of this organ. From the active movements of most
acalepha in swimming through the sea, from their gregareous
habits, the exquisite sensibility and contractility of their ten-
tacula, the distinct development of their muscular fibres, and
their perception of light, it is not likely that many are desti-
tute of some form of this system, so general in its occurrence
and so influential in the economy.

184 NERVOUS SYSTEM.

The echinoderma, like the acalepha, are all inhabitants of
the sea, and, as in other aquatic animals, they present a de-
velopment of the muscular and nervous systems, and of all
the other organs of relation, inferior to that of animals of a
corresponding grade, inhabiting the land ; their nervous fila-
ments are also less white and opaque, less firm in texture,
and less obvious than in the land animals. , The distribution
of the nervous system has been long known in several ge-
nera of this class, and it presents the same circular disposi-
tion as in the acalepha and other cyclo-neurose animals. In
the asterias (Fig. 81. B,) which has but one opening of the
alimentary cavity (e,) there is a small white opaque nervous
chord («,) passing round the mouth. From this circular
chord a nerve (c, c,) is given off to each of the radiating di-
visions of the body, which passes along the middle of the
lower parietes between the ambulacra, and gives filaments
to the muscular suckers and other parts of the rays. Mi-
nute ganglia (b,) are observed at the points where these ra-
diating nerves originate, and from each of these ganglia
two nerves (d,) extend obliquely upwards along the sides of
the stomach, and are confined in their distribution chiefly to
the parts contained within the central disk of the body. A
similar nervous chord is seen around the oesophagus of the
echinus, which sends delicate white filaments to the compli-
cated muscular and sensitive apparatus of the mouth ; other
nerves are seen extending upwards from the same oesophageal
ring, along the course of the vessels in the interior of the ab-
dominal cavity. In the holothuria, where the axis of the
body is greatly lengthened, and the animal reclines and
moves on one side of the trunk, like the higher classes,
where the calcareous shell is wanting, and the muscular sys-
tem is most distinct and powerful, the nervous system is
extensively distributed, and begins to manifest an approach
to the helminthoid type. Interior to the osseous apparatus
of the mouth is a white nervous ring around the oesophagus,
from which nerves pass outwards to the large ramified ten-
tacula around the mouth, and others extend upwards along
the course of the eight strong longitudinal muscular bands.
Fine white filaments are likewise seen passing inwards to the
stomach and alimentary apparatus. In the siponculus, which
is closely allied to the holothuria in internal structure and living

NERVOUS SYSTEM. 185

habits, but is much more lengthened and vermiform in out-
ward shape, two of the minute longitudinal nervous filaments
extending backwards from the cesophageal ring are developed
only on one side of the body, like the abdominal nerves in
the helminthoid articulata. Thus, in all the typical forms of
this extensive class the nervous columns of motion and sen-
sation are seen to form a collar around the entrance of the
alimentary canal, which corresponds with the inverted posi-
tion of the mouth, and the expanded, globular, or radiated
form of the body around a short vertical axis. The length-
ening of the axis in the soft naked apodal vermiform species
of echinoderma necessitates a horizontal position of the
trunk, and the nerves, yet unprotected by an osseous sheath,
are, for safety, continued only along the inferior surface of
the body. This introduces the distinction of dorsal and
ventral surface of the trunk, unknown in the inferior tribes
of radiata, where the parts are equally developed around a
central axis, and where the nervous system presents the
same peripheral development.

THIRD SECTION.

Nervous System of the Diplo-Neurose or Articulated
Classes.

In the long cylindrical trunks of the helminthoid and en-
tomoid classes, the nervous system partakes of the same
lengthened form, and its motor and sensitive columns are ex-
tended for protection along the ventral or under surface of
the body. This system is still contained in the same rings
or segments which envelop the other viscera of the trunk in
all the vermiform articulata, where the articulated members
are scarcely developed from the sides ; but in the highest
entomoid animals of this great division the nervous columns
are inclosed in a distinct thoracic osseous canal, separate from
that which contains the other organs. And in all these classes
the motor and sensitive columns appear to me to occupy the
same inverted position, with relation to the spino-cerebral

186

NERVOUS SYSTEM.

axis of vertebrata, as that first shown by Lyonet in insects ;
the motor columns always lie above and in contact with the gan-
glionic, as shown by him in the cossus (Fig. 84. A. b, c.) All
the other viscera of the trunk present the same inverted po-
sition ; the heart-forming portion of the sanguiferous system
occupies the dorsal surface, and the great nervous columns,
the ventral surface of the alimentary canal, in the articulated
classes. The position of these organs and of the whole trunk,
and consequently the nervous columns, is reversed in the spini-
cerebrata, where the great centres of the nervous system are
inclosed in a distinct osseous sheath.

In the lowest of the helminthoid classes, the entozoa,
where the animals remain, for the most part, permanently im-
bedded in the source of their nutrition, the nervous system
is very imperfectly developed, and is little required. The
more elevated forms of nematoid intestinal worms, as the
ascaris, (Fig. 82. A,) present a slender double, white, nervous

FIG. 82.

filament, occupying the median line of the abdomen, and
placed immediately within the inner longitudinal muscular
tunic. This abdominal nervous chord in the long cylindrical
body of the nematoid worms appears, from the close approx-
imation and the smallness of its component parts, to consist

NERVOUS SYSTEM. 187

of a single filament, but it unravels its compound structure
chiefly in two places of its course — where it meets with the
vulva of the female, and separates its columns to embrace
that orifice (Fig. 82. A. #,) and where it separates at. the an-
terior extremity of the trunk to encompass the resophagus
(Fig. 82. A. a.) These nervous columns are more obvious on
the large strongyli and echinorhynchi, where they present a
similar form and distribution. Their anterior extremities
generally ascend on each side of the resophagus, so as to em-
brace that canal more or less completely with a nervous
collar. The surface of the body, along which the nervous
columns run in these animals, and in all the other articu-
lated classes, is termed the ventral surface, from its being
the inferior in the ordinary position of the body, and from
the anus and other excretory orifices opening on that aspect
of the trunk ; the anus, the valva, and the penis are placed
on this surface in the entozoa. This simple form of the ner-
vous system presented by the lowest articulated class, re-
sembles the embryo form of this system in the higher classes
of this division, and corresponds remarkably with the first
perceptible form of the spino-cerebral axis in ah1 the verte-
brated animals, where it appears a double white streak on the
outer layer of the germinal portion of the cicatricula. These
simple worms, consisting solely of the trunk, present also the
embryo-form of the whole body of the highest articulated
classes. In the higher animals of this class, the epizoa,
which adhere to some part of the external surface of aquatic
animals, as in the achtheres and many others, the nervous
system is more developed, and these animals generally
possess rudimentary antennae, and even eyes ; they have the
two longitudinal nervous chords running separately and at
some distance from each other, separated by the whole
breadth of the alimentary canal. From the want of organs
of sense on the anterior extremity of the body in most of
the entozoa, the nervous system is very imperfectly deve-
loped in that direction, and although it often forms a ring
around the ossophagus, it seldom forms a perceptible supra-
cesophageal ganglion where these filaments meet.

In the rotiferous animals, where there is a complex mus-
cular apparatus at the anterior extremity of the trunk, for
the motion of the numerous large cilia, and another muscular
apparatus for the movements of the strong lateral maxillae,

188 NERVOUS SYSTEM.

the nervous system is most developed in that part of the
body. There is generally in these wheel-animalcules, as in
the hydatina (Fig. 82. B,) a distinct supra-oesophageal gan-
glion (a,) with smaller lateral ganglia (b, c9) surrounding the
entrance of the alimentary canal (e) ; and from the anterior
or inferior ganglia (c, c,) proceed the nervous columns back-
wards along the ventral surface of the trunk (d.) These ab-
dominal nervous columns, as in the entozoa, are sometimes
approximated to each other, and without perceptible ganglia
in their course, and in others they are separated to a greater
or less distance from each other, and have numerous ganglia
developed along their sensitive columns. In the hydatina,
the longitudinal nervous columns are united (82. B. d9) and
without apparent ganglia below the alimentary canal. In the
diglena lacustris the nervous columns are a little separated
from each other, and present only one pair of ganglia imme-
diately below the oesophagus, and another pair below the
pyloric extremity of the stomach. The longitudinal ventral
columns are much more separated from each other, in their
whole course, in the notommata clavulata, and each of these
lateral chords presents nine perceptible ganglia, in its course
backwards to the posterior extremity of the trunk. These
abdominal ganglia are symmetrically disposed in pairs,
though removed laterally to a distance from each other on the
inferior part of the trunk.

The nervous system of the cirrhopods (Fig. 82. C,) is
symmetrically disposed in approximated columns (b, c9)
along the abdominal surface of the trunk, with parallel pairs
of ganglia regularly developed along their course, as in all
the higher articulated classes. In the anitifa (Fig. 82. C,)
we perceive a slender white nervous ring surrounding the
oesophagus (a,) and sending out small filaments to the neigh-
bouring parts, but scarcely forming a perceptible supra-
ossophageal ganglion, from the imperfect development of the
sensitive and masticating apparatus in these fixed and in-
verted testaceous or entomostracous animals. As the long,
jointed and ciliated feet, with their thick muscular haunches,
and supporting the branchiee at their base, are developed
from the sides of the posterior part of the trunk, the ganglia,
like the nervous columns which connect them, are large in
that part of the body, and correspond in position with the
origin of the several pairs of legs (b, c, d, e, /.) So that

NERVOUS SYSTEM. 189

these animals, notwithstanding their molluscous exterior,
fixed in a multivalve shell lined by a fleshy mantle, are con-
nected with the articulated classes by the diplo-neurose cha-
racter of their nervous system, and by all their other organs
of relation.

The annelida present as great diversities in the extent of
development of their nervous system, as in their exterior
forms and their whole internal organization. In the minute
transparent bodies of the planaria, and in many of the
simplest forms of aquatic worms, scarcely a trace of nervous
columns can be perceived, although their organs of vision are
often numerous and obvious, and even in the naids and some
of the nereids the nervous chord along the middle of the ven-
tral surface of the trunk appears as uniform and simple, as in
the nematoid entozoa. The columns in the simpler anne-
lides, as in the first larva state of the higher entomoid
classes, scarcely present ganglionic enlargements in their
course along the abdomen, or supra-cesophageal ganglia at
their anterior extremity, from the general inferiority of their
organization, and from the still imperfect development of
their lateral appendices for progressive motion, and of their
cephalic appendices for sensation or mastication. In the
long cylindrical and muscular bodies of the air-breathing
earth-worms (Fig. 82. D,) with their myriad of short and
highly moveable segments, their exquisitely sensitive skin,
and their minute rudimentary feet, we can perceive innumer-
able mixed nerves (Fig. 82. D. b, £,) proceeding laterally
from the closely approximated nervous columns, but scarcely
a ganglionic enlargement is developed in their long and
equal course along the ventral surface of the trunk. In this
highest of the helminthoid classes the nervous columns are
still entirely enclosed in the cyclo-vertebral elements along
with all the other viscera of the abdominal cavity. The
abdominal chords of the earth-worm embrace the oesophagus
at their anterior extremity, and form two distinct cephalic or
supra-aesophageal ganglia (Fig. 82. D. a,) which supply
nerves to the large muscular apparatus of the mouth, and to
the long dorsal sympathetic. These two cephalic ganglia lie
in contact with each other, are lengthened transversely, like
those of insects, appear grey-coloured on the surface, and more
white internally, and seem to be composed of minute globules

UK) NERVOUS SYSTEM.

when examined under the microscope. The sympathetics are
distinct along the aorta in the nereides, and the globular par-
ticles are seen in their neurilema. The ventral columns are
separate from each other in the sabelke. Where the body of
the annelides is much developed transversely, as in the leech,
the sea-mouse, the pectinaria, and many others, the ganglia
along the columns, and the columns themselves are much more
developed and distinct, and are visible at a much earlier period
in the embryo. The abdominal ganglia of the leech, as shown by
Weber, are quite obvious in the embryo of that worm while it is
yet in the ovum. Where the setae for progressive motion are
large, numerous, and moved by strong extensor and retractor
muscles, as in the pleione and many of the tubicolous anne-
lides, the nervous columns and their ganglia are also large
and distinct. The motor and sensitive nerves come generally
from the same parts of the columns. The distribution of the
minutest filaments are seen without dissection through the
transparent and colourless body of the common pectinaria,
and in most annelides the abdominal columns and ganglia, of
a white colour and firm consistence, are obvious to the naked
eye through the thin parietes beneath them. In some of the
broad naked apodal annelides, where the segments of the
body are very numerous and short, to facilitate their ser-
pentine movements, as in the leech, the abdominal ganglia
could not be safely accommodated in every ring of the trunk,
and we find but one ganglion, of considerable size, for every
three or four segments. These abdominal ganglia, about twen-
ty-five in the leech, are more closely approximated to each
other at the two ends of the nervous columns than in the
middle, which already indicates the commencement of that
longitudinal concentration of the ganglia so remarkable in the
higher articulata, as the almost constant approximation of
the lateral columns themselves on the median plain of the
abdomen indicates development in a transverse direction, and
a higher grade of this system than the detached condition
of the columns seen in the lowest helminthoid animals.

The nervous system of the entomoid classes presents only
a more developed condition of the same plan of structure
presented by this system in the worms, and that of the most
elevated insect or crab begins its development with the
simplest helminthoid form, as the nervous system of man

NERVOUS SYSTEM. 191

passes through the simplest grades of that system presented
by the lowest fishes. The larva of the insect, like the red-
blooded worm, is almost a simple cylinder, soft, flexible,
smooth, and equal throughout, and the nervous columns
then manifest the same equal development from one extre-
tremity of the body to the other. The most helminthoid
adult form of the whole body presented by the entomoid
classes is that of the long equally developed myriapods, and
the simplicity of their outward form is accompanied with a
corresponding inferiority in the type of their nervous system,
and of all their internal organs. Their nervous system is
nearly that of the annelida and the larva ; but as their con-
solidated segments develop stronger muscular members to
support them on the land, their nervous columns and gan-
glia are encreased in size, to afford additional nerves to those
enlarged extremities. On looking through the abdominal
nervous columns of the scolopendra, we can distinctly per-
ceive, notwithstanding the transverse approximation of all
the parts, a distinct transparent line marking the original sepa-
ration of most of the united ganglia. The globular cineritious
particles, composing the ganglia, appear often united to form
a round isolated mass in the centre of the ganglia, and the
same opaque particles, when coagulated, are seen to occupy,
in an interrupted manner, the interior of the sensitive
columns. The motor columns I have found here of great
size, as those shown by Treviranus and by Muller in the
equally muscular body of the scorpion. The ganglia, like
the segments, are nearly equally developed, and equidistant
from one extremity of the chord to the other, excepting the
first pair or supra-cesophageal, which give nerves to the long
antennae and to the large eyes, and the remarkably small round
terminal ganglion below the anus. The intermediate trans-
verse motor nerves, pointed out as respiratory nerves by Lyonet
in the columns of insects, and by Morren in the annelides, do
not here come off, as they do in the earth-worm, midway be-
tween the ganglia, but very close behind the ganglionic nerves.
Four great nervous trunks originate from the columns on each
side at each ganglion, and the second anterior of these
branches, which is the largest, proceeds to the muscles of the
legs, where I have traced it as far as the tarsal joint. Only
two branches on each side proceed from the ganglionic space

192 NERVOUS SYSTEM.

of the columns in the earth-worm, and one branch from each
side in the middle of the inter-ganglionic space. The sympa-
thetic and its ganglia are here extremely minute, as in the anne-
lides from the lengthened, straight, and narrow form of all the
nutritive organs. The second ganglion, or first sub-eesophageal
pair, has a very lengthened form, and its nerves proceed back-
wards at a very acute angle, to escape from the large and long
cephalic segment of the scolopendra. The nerves from the
ganglia I have observed more yellow and opaque than the trans-
parent and colourless filaments from the motor columns, as if
some of the cineritious globules of the ganglia were continued
into the sensitive portions of the mixed nerves. The great
toughness and density of the neurilema, which envelopes
the nerves of the myriapods and insects which breathe
atmospheric air, is seen by the stiffness with which the
most delicate and lengthened filaments project right out-
wards in a radiating manner from around all the ganglia ; the
nervous filaments are much softer in the Crustacea, mollusca,
and other aquatic animals, and the same difference is ob-
served in the density of their muscular fibres. From the
great size of the motor columns in the scolopendra, there is
a distinct lateral longitudinal groove of separation between
them and the inferior or sensitive chords, and on seizing the
fourth or last pair of nerves from each ganglionic space, and
raising them upwards, the large motor columns I have found
to be nearly as easily separable from the sensitive beneath
them, as those which I have demonstrated, for many years
past, as the motor columns of the scorpion (Fig. 84. B. a, G,)
and which have more recently been imagined to be res-
piratory nerves in the muscular tail of that pulmonated
animal.

The abdominal nervous columns of insects have been cor-
rectly regarded by Lyonet, Straus, Dufour, Chiaje, and most
others, as analogous to the spino-cerebral axis of vertebrata,
and the first of these writers has described them seventy years
ago, as similar in anatomical structure and physiological proper-
ties to the spinal chord of the highest animals. There are gene-
rally at first thirteen pairs of approximated ganglia correspond-
ing with the original segments,and extended along the middle
of the ventral surface of the body, as shown by Lyonet in the
caterpillar of the cossus, and the oesophagus pas'ses downwards

NERVOUS SYSTEM. 193

to perforate the connecting nervous columns, between the
first and second pairs of ganglia, as in other articulated clas-
ses ; so that the first pair only are supra-oesophageal or ce-
phalic, and all the succeeding ganglia of the columns are be-
neath the alimentary canal. Those ganglia are at first, like
those of the worm and the centiped, nearly at equal distances
and of equal size, as the segments themselves of the young
caterpillar. The columns and the ganglia originally separate
on the two sides, early approximate transversely and unite,
and a slow movement of the ganglionic matter is at length
observed in a longitudinal direction to the parts of the columns
where it is most required in the adult condition of the spe-
cies. These transverse and longitudinal movements of the
nervous matter so accurately described by HEROL.D in the
spinal columns of insects, proceed to a very variable extent,
according to the degree of metamorphosis from the larva
state to which the whole body is subjected in the different
adult forms of this class. As in the myriapods, the first and
second pairs of ganglia are here contained within the head,
and the succeeding pairs are generally placed near the ante-
rior limit of the segments to which they belong. The osso-
phageal ring thus formed by the columns between the two
first or anterior pairs of ganglia is much wider during the
voracious larva state of the insects than in their adult con-
dition, (see Fig. 83. A, B, C.) The third pair of ganglia,
placed in the prothorax, appear to be generally smaller than
the fourth, and the fifth, in the metathorax, smaller than the
sixth, as in the cossus. The ganglia contained in the abdo-
men of the entomoid classes, like the segments of that part
of the trunk, are generally the least altered by develop-
ment, from their primitive condition ; but these are most
changed in insects, and are often obliterated by the process
of development, as shown by Straus in the coleopterous in-
sects, (see Fig. 83. D,) and by Dufour in many of the hemip-
tera. The last pair of ganglia are generally the first to ad-
vance forward to unite with the penultimate pair in the larva
state. In the annexed figures (Fig. 83. A, B, C,) are seen
the common conditions of the nervous system in the larva,
the pupa, and the imago state, and the changes produced in
that system by the metamorphosis to the perfect state, as
observed and .described by Herold, twenty years ago, in the

PART II. O

i ;> i-

XERVOUS SYSTEM.

papilio brassicas. In the larva of that lepidopterous insect
(Fig. 83. A,) the columns are lengthened, the ganglia widely
separated, and nearly equal, with a large ring between the ce-
phalic (1,) and the first infra-oesophageal (2,) ganglia. The first
or cephalic ganglia (A. 1,) were observed by Lyonet to give
off eight pairs of nerves, which pass chiefly to the organs of
the senses, besides the two columns which connect them

FIG. 83.

with the second pair of ganglia (A. 2.) They give off, like-
wise,, filaments to the small lateral ganglia (A. b,) of the
head, and to the commencement of the sympathetic series of
ganglia (A. «,) as shown by Lyonet in the cossus. Between
all the succeeding pairs of ganglia a solitary branch is seen
coming off from each side of the motor column, which inter-
ganglionic nerves were shown bv Lyonet to be distributed

NERVOUS SYSTEM. 195

on the muscles and the minutest ramifications of tracheae
for respiration. These inter-ganglionic nerves come off ge-
nerally at a greater distance from the ganglia in insects and
Crustacea, and in worms, than in the myriapods and the
arachnida. The last pair (A. 13,) of ganglia are already ap-
proached to those which precede them (A. 12.) In the pupa
state of this moth (Fig. 83. B,) the approximation of the
segments has not only shortened the total length of the co-
lumns, but has caused them to assume a puckered or curved
appearance, where they lie free between the ganglia ; the
shortening of the whole trunk during the metamorphosis
thus obviously takes place more quickly than the correspond-
ing changes of the nervous system. The oesophageal ring is
diminished, the cephalic ganglia are enlarging and extend-
ing transversely for the myriad of developing eyes, and the
thoracic pairs of ganglia are approaching to each other, pre-
paratory to their uniting together at the part best suited
to send nerves to the yet undeveloped thoracic members.
The third pair of ganglia often advance to unite closely with
the second pair, the fifth to unite with the fourth pair, and
the seventh pair to unite with the sixth, during the passage
to the imago state, and several, or the whole, of the ganglia
which succeed these in the cavity of the abdomen, entirely
disappear, while the motor and sensitive nerves still con-
tinue to come off from the same parts of the columns, as
seen in the nerves of the perfect insect (Fig. 83. C. 7, 8.) In
the imago, or perfect state of the insect, (Fig. 83. C,) the
loose inter-ganglionic portions of the columns, which were
zig-zag in the pupa, have assumed a straight and shorter
form, the two last pairs (12, 13,) have coalesced into one
ganglion, and advanced from their original position, the cine-
ritious matter has disappeared from two pairs of the abdo-
minal ganglia (7, 8,) without affecting the original origins of
their nerves ; four pairs of ganglia (6, 5, 4, 3,) have coalesced
at two points of the thorax, to supply nerves to the muscles
of the legs and wings ; the second and first pairs of ganglia
(2, 1,) have approached in the head, and diminished the dia-
meter of the oesophageal ring, the cephalic ganglia (C. 1,)
have enlarged and extended transversely, to form the ex-
panded optic lobe in each orbit, and the accessary nerves
j(C. b, b,) and the great sympathetic (C. a,) running back-

o 2

196 NERVOUS SYSTEM.

ward? in the median plain above the alimentary canal, have
assumed an encreased development, as shown by Lyonet
and Straus, and thus more intimately united all the seg-
ments and parts of the body by encreasing these bonds of
connexion between all the organs and functions of vegetative
or organic life. The same kind of change in the whole
condition of the nervous system, effected by the metamor-
phosis of the insect, is seen in Straus' figure of the adult or
imago state of that system in themelolontha vulgaris (Fig. 83.
D,) where the usual concentration of the nervous matter in
the head and thorax has proceeded to a greater extent than
in the papilio. The ganglia of the abdomen are most fre-
quently preserved through all the stages of life in the lepid-
opterous and the hymenopterous insects, and in those which
have the segments of the abdomen the least altered from
their larva condition by the process of metamorphosis. But
in this coleopterous insect (Fig. 83. D,) where the adult form
of the whole body is very remote from that of a caterpillar
or of an annelide, all the ganglia have disappeared from the
short round abdomen, and have accumulated in three con-
tiguous masses in the middle of the thorax, from which the
nerves radiate to the organs of motion, and extend back-
wards into all the segments of the abdomen. The cephalic
ganglia (1, 2,) have also encreased above and below the oeso-
phagus, the cerebral lobes (1,) passing laterally into the
large compound eyes, and the great sympathetic longitudinal
series of supra-cesophageal ganglia («,) with their accessary
lateral filaments and ganglia (b}) have advanced still more in
their development. The greatest change of the nervous
system, however, from its original larva condition, effected
by the metamorphosis in insects, is that presented by the
pentatoma, the cicada, and some others where all the ganglia
of the columns have accumulated in two points, above and
below the oesophagus, in the head and in the middle of
the thorax ; thus nearly approaching to the highest condi-
tion presented by this symmetrical nervous system in the
most elevated tribes of Crustacea, and to the cyclo-gangliated
character so general in the molluscous classes. Although
during this rapid series of changes the last and the penulti-
mate pairs of ganglia are generally the earliest to ap-
proach and unite, they are at first distinct pairs like those

NERVOUS SYSTEM.

197

before them on the columns, as seen in the annexed figure
by Lyonet, of the three last pairs of ganglia and of the nerves
which come from them, in the larva of the cossus ligniperda
(Fig. 84. A.) The upper portion (a,) of the columns is seen
to give off the inter-ganglionic nerves (d, c,) which Lyonet
showed to be distributed on the respiratory organs after
receiving a small connecting branch from the first pair of

FIG. 84.

the next succeeding ganglionic or mixed nerves (11. c} c.)
This arrangement of the motor and ganglionic nerves is
represented at each inter-ganglionic space along the columns.
It was likewise shown by Lyonet that these motor nerves
(13. 6,) proceeding to the lateral muscles and respiratory or-
gans, come from a tract occupying always the upper surface
of the columns, and distinctly passing over the upper surface
of at least the last pair of ganglia.

198 NERVOUS SYSTEM.

It was, however, in the class arachnida that Treviranus
first pointed out, more than twenty years ago, in the ner-
vous system of the scorpion (Fig. 84. B,) the continuity of
this motor tract (84. B. «, a,) over the upper surface of the
whole extent of the columns, and I have long shown the
same structure to pervade the articulated classes. The ner-
vous system, like most other parts of the arachnida, pre-
sents an intermediate condition of development betwixt that
of most insects and that of the higher Crustacea. While the
nervous columns of the scorpions, with their accompanying
series of ganglia, are lengthened in form, like those of lepi-
dopterous insects, the same parts in the spiders have the
concentrated form which they present in the highest crabs,
with their symmetrical ganglia concentrated in two points of
the body. The motor columns are large in the scorpion, as in
the scolopendra, and are here also easily separated from the
sensitive columns beneath them, excepting where they pass
over the surface of the ganglia, from which they cannot be
detached. The whole of the columns are less intimately
connected together, and the inter-ganglionic spaces are
larger in the cavity of the abdomen than in the round narrow
muscular tail, or caudal portion of the trunk. In this pos-
terior part of the body the motor columns are proportion-
ally more flat and more expanded over the ganglionic
chords, as they are likewise in Crustacea and other articulated
classes. Besides the cephalic, or supra-cesophageal ganglia
(Fig. 84. B. 1,) and the large infra-oesophageal mass of con-
centrated ganglia which radiates nerves to the five pairs of
legs, there are seven pairs of closely approximated ganglia
(84. B. 3 — 9,) of a lengthened form, disposed along the in-
ferior surface of the trunk. The motor or respiratory
nerves come off at the ganglia, as in the myriapods, and
not at a distance from the ganglia, as the inter-ganglionic
nerves of insects and Crustacea. Towards the caudal extre-
mity of the scorpion, the mixed nerves of the columns di-
verge suddenly in numerous minute fasciculi from the sides
of the ganglionic spaces (<84. B. g. 8.) But as we advance
in the trunk we find the whole of the mixed nerves coming
off in one large fasciculus from each side of each double
ganglion (84. B. 5, 4, 3.) The first and second pairs of ganglia
(84. B. 1, 2.) form a large, white, soft nervous mass occupy-

NERVOUS SYSTEM. 199

ing the anterior and lower part of the trunk, immediately be-
neath the eyes ; this lobed mass is perforated obliquely by a
small aperture through which the oesophagus passes to the
stomach. I have generally found the ganglionic spaces of
the columns of the scorpion, as in many insects, closely en-
crusted with small white lobes of adipose substance, in which
the oesophageal nervous collar is likewise imbedded. The in-
fra-oesophageal ganglia are much larger than the first pair which
have few and small parts to supply. This second pair of gan-
glia, composed of all the ganglia of the extremities (84. B. 2,)
is protected behind by a cartilaginous arch, through which the
columns pass to the third pair of ganglia, like the consolidated
internal arch for the nervous column in the thorax of Crustacea.
Numerous large nervous branches proceed backwards along the
inferior surface of the abdominal cavity from the infra-oesopha-
geal ganglia (84. B. 2,) beneath the motor and sensitive co-
lumns, as represented, many years ago, by Treviranus and
Muller, in their views of these columns in the scorpion. In
the short and rounded body of the spiders, the supra- and
infra-ossophageal ganglia form a large nervous collar around
the oesophagus, the inferior portion of which, as in the scor-
pions, forms a large lobed mass, from which all the nerves of
the extremities radiate. The supra-ossophageal ganglia are
small here also, from the imperfect development of the or-
gans of the senses and of mastication. The ganglia of the
abdomen, which are extended along the trunk separately
in the scorpions, are accumulated into a single mass in the
spiders, and placed near the anterior part of their short and
wide abdominal cavity. Thus the extent of concentration
of the nervous columns of arachnida, and the extent of dis-
tribution of their unsymmetrical or sympathetic system, cor-
respond with the high condition of the other systems in this
class, and while they vary in the different tribes, they ap-
proximate the more elevated forms to the highest insects and
Crustacea.

In the numerous and diversified class of Crustacea we meet
with every condition of the nervous system, from that of the
lowest annelide, or the earliest larva state, where scarcely a
filament is yet perceptible in the place of the nervous columns,
to that concentration of the nervous ganglia around the oeso-
phagus, which connects the highest articulata with the mol-

200

NERVOUS SYSTEM.

luscous classes. The motor and sensitive columns are seen
on a larger scale in the Crustacea, and they occupy the same
relative position as those long known in the other entomoid
classes. The supra-cesophageal ganglia are generally larger
than those of arachnida, and smaller than those of insects ; they
are, for the most part, united into a single cerebral ganglion de-
voted chiefly to the large organs of the senses, and their nerves
unite with the sympathetic, as in insects and mollusca. The ner-
vous ring of the oesophagus is here very wide, but the columns
are small which form it, and they give offlarge branches to the
stomach and the sympathetic while they pass along the sides
of the oesophagus. The ganglia of the cephalo-thorax vary
much in their number, their magnitude, and their degree of
approximation according to the form of that part of the trunk,
and the size of the several pairs of legs. The motor columns
are seen in the large macrourous decapods, as in the post
abdomen of the lobster, (Fig. 85. a,) passing over the upper sur-
face of the sensitive columns (#,) and their ganglia (c,) as a broad,
thin, white, fibrous layer, and giving off lateral branches
chiefly behind each pair of ganglia. The largest trunks and
mixed or moto-sensitive nerves of the
columns come off at their ganglionic
spaces (c, d.} These inter-ganglionic
motor nerves (e, e,) in the posterior
portion of the trunk come off at a great-
er distance behind the ganglia, as they
do in insects ; but as we advance to the
fore part of the body, their origins be-
come approximated to the ganglia. The
posterior terminal pair of ganglia have
generally a high position, and are of great size where the
caudal appendices of the trunk are much developed, as in the
long-tailed decapods. The same transverse and longitudinal
approximation of the nervous columns and their ganglia,seen in
the inferior articulata, is perceived in the development of the
Crustacea ; and the most concentrated form of the nervous
system met with in the highest brachyourous decapods, gra-
dually acquires this concentration of all its ganglia in two
points of the body, above and below the oesophagus (Fig. 86.
D,) by passing through all the inferior conditions which pre-
sent themselves as permanent or adult forms in this class.

NERVOUS SYSTEM. 201

Many of the lower amphipoda and isopoda have the segments
nearly equally developed from the anterior to the posterior
extremity of the trunk, and this equal development is seen
also in the nervous columns and ganglia of these segments,
as shewn in the annexed figure of those of the talitrus locust a,
or common sand-hopper (Fig. 86. A.) The slender longitudi-
nal columns and the minute ganglia along their course here
remain distinctly separated from each other by a small space
on the median plain ; the ganglia are nearly of the same
size from the first pair (1,) above the oesophagus (a,) to the
caudal pair (11,) and the pairs are almost equidistant along
the whole trunk, in a longitudinal direction. This simplest
adult form of the nervous system shown by Audouin and
Edwards in the talitrus, has been pointed out likewise by
Rathke in the idotea, and the same is seen through the trans-
parent bodies of many other minute isopods. The same
form of the nervous columns is seen in the highest Crustacea
while yet in their embryo condition in the ovum. In the
short and broad trunk of the cymothoa where the legs are still
equally developed along the whole sides of the body, the
nervous columns (Fig. 86. B,) have already approximated to

FIG. 86.

202 NERVOUS SYSTEM.

touch each other on the median plain, and the ganglia on the
two sides have coalesced to form a single chain along the
middle of the abdominal surface of the body. The ganglia
are still nearly equidistant, and equally developed along the
columns ; but where the minute posterior tapering segments
of this animal have advanced and united, their ganglionic
matter appears likewise to have been carried forwards to en-
large the ninth or terminal ganglion (Fig. 86. B.) The
transverse concentration of the columns and ganglia towards
the median plain, thus seen in the lowest Crustacea, is suc-
ceeded in higher species by a longitudinal movement of the
nervous matter directed, as we have seen in inferior classes of
articulata chiefly to two points of the body, the head and
the thorax, from which the largest and most important ap-
pendices of the body, whether for sensation, mastication, or
progressive motion are developed. In the long-tailed deca-
pods, as the lobster (Fig. 86. C,) and the cray-fish, not only
is the sympathetic system of nerves derived from the
lateral ganglia of the stomach, greatly developed, as shown
nearly twenty years since by Succow, and the ganglia
and columns have coalesced and met transversely along the
whole body ; but in the region of the thorax, from which
the five pairs of large extremities are developed, the ganglia
(Fig. 86. C. a. 6,) have both enlarged in size above those of
the post-abdomen (C. 6 — 12,) and considerably approximated
to each other in a longitudinal direction. In the higher enh
tomoid articulata the segments first coalesce on the anterior
and posterior portions of the trunk, and hence the enlarged
form presented by their cephalic and caudal ganglia, indepen-
dent of the great size often attained by the appendices deve-
loped from the terminal parts of the body. The ganglia and
columns of the post-abdomen in these macrourous decapods
(C. 6. 12,) as shown by Succow, retain much of their primi-
tive simple form, like the segments and appendices of that
portion of the trunk; but the last ganglion (C. 12,) advanced
to the penultimate segment, is here of great size, from the
magnitude of the swimming appendices developed from the
two caudal segments. The thoracic ganglia and columns are
excluded from the general cavity of the trunk, and are en-
closed in a distinct canal with solid calcified parietes prolong-
ed inwards from the exterior shell. The most concentrated
form of the nervous system met with in the Crustacea and its

NERVOUS SYSTEM. 203

highest condition presented by this articulated division of the
animal kingdom is that found in the short and broad trunks
of the brachyourous decapods (Fig. 86. D,) where all the
symmetrical ganglia of the columns are generally col-
lected into two masses, the one in the head, and the
other in the centre of the cephalo-thorax, and where the mo-
tor and sensitive columns are almost confined to a nervous
band around the wide oesophagus. The anterior of these, or
the supra-cesophageal ganglion (86. D. 1,) is comparatively
small in the brachyourous decapods, from the smalmess of
the cephalic appendices, which it supplies with nerves.
The infra-cesophageal nervous mass (86. D. 2,) is of great
size, consisting of the whole chain of ganglia, which was
originally extended along the body behind the oesophagus,
and is favourably situated between the haunches of the legs,
under a strong internal osseous arch, in the centre of the
trunk. It sends out numerous branches to the surrounding
viscera, and to the five pairs of legs which radiate from
around that point, and the columns are prolonged backwards
ramifying along the short slender post-abdomen, as a simple
nervous chord. There are many intermediate conditions of
these nervous columns and ganglia between those of the asta-
cus (Fig. 86. C,) and of the maia (Fig. 86. D,) some of
the macrourous decapods having the thoracic ganglia much
more approximated than in the former, and many of the bra-
chyourous species having them less concentrated into a mass
than in the latter, and similar links are observed to connect
together the typical forms of this system in the other orders
of Crustacea, and throughout all the articulated classes. Thus
the most elevated form of the nervous axis met with in
this division of the animal kingdom begins its development
with two simple abdominal filaments, like the lowest hel-
minthoid form of entozoa, and by a gradual process of con-
centration proceeding transversely and longitudinally from
the peripheral to the central parts, it arrives at the cyclo-gan-
gliated character of the molluscous classes, with its great
symmetrical ganglia confined to the resophageal ring.

204 NERVOUS SYSTEM.

FOURTH SECTION.

Nervous System of the Cyclo-gangliated or Molluscous
Classes.

The nervous system is distinctly developed and pro-
vided with several ganglionic centres, in all the molluscous
classes from the lowest compound forms of tunicata to
the highest of the cephalopods, and notwithstanding the
remarkable diversity of form which the animals of this
division present, we can trace a certain similarity of cha-
racter and unity of plan in the development of this system,
and in its typical forms, throughout all the cyclo-gangliated
classes. As all molluscous animals are aquatic, excepting
a few of the gasteropods, their nervous fibres present the
same soft and pellucid character observed in other aquatic
invertebrata, which often renders it less easy to trace
their ramifications and to detect their plan of distribution,
than to follow the denser opaque fibres of the air-breathing
tribes, and has repeatedly caused them to be mistaken for
sanguiferous or chyliferous vessels. In the short and broad
trunks of the animals of this division, as in the round bodies
of the radiata, the nervous system is characterised by a
tendency to accumulate around the entrance to the alimentary
canal, but from the high position of the molluscous classes
in the scale, their nervous oesophageal collar is provided
with distinct and often numerous ganglia. The same co-
lumnar arrangement of the great nervous centres, which I
have long observed and described in most of the articulated
classes, I have found to exist also in the molluscous, though
in a less extended or recti-lineal form. In the tunicated
and conchiferous animals the columns are chiefly disposed
beneath the alimentary canal; in the gasteropods and the
pteropods they are more equally distributed around the
entrance to the stomach; and in the more elevated forms of
cephalopods they at length mount to that supra-cesophageal
position which they preserve in all the vertebrata where

NERVOUS SYSTEM.

205

FIG. 88.

they cease to embrace the alimentary canal. In the lowest
compound tunicated animals as in the botryllus and the
pyrosoma, there is a small round white coloured opaque
ganglion, within the muscular tunic of each of the com-
ponent animals, placed near the entrance of the respiratory
sac, and between that orifice and the anal. When we com-
pare the position of the tho-
racic cavity (Fig. 87- /.) andits
apertures (a. b.) in the tuni-
cata with those of the conch-
ifera, we perceive that this
single median ganglion (e,) is
situate on the ventral side of
the body, though at some
distance from the entrance
(g.) to the stomach, (h.) This
ganglion is seen in the same
position in the minute com-
ponent animals of the poly-
clinum, the aplidium, the di-
demnum, the euccelium, the
synoicum, the diazona, and
the distoma. In the larger
forms of simple ascidia as in
the boltenia, phallusia, and
cynthia (Fig. 87,) this last
ganglion (e.) has generally a

more lengthened oval form, and I have sometimes found it bifid
both before and behind, where two nervous branches come off
from each of its extremities. The two anterior nervous branches
are larger than the two posterior which pass backwards
on each side of the anal opening (b.) of the muscular tunic.
The anterior pair encompasses the respiratory orifice (a),
sending off filaments to the fringed and highly sensitive
tentacula (c.) which guard this thoracic aperture ; these two
branches again meet behind the orifice (d.) and continue as
a broad chord along the dorsal part of the muscular coat
or mantle. Besides this ganglion, which is connected
with the muscular apparatus of the respiratory sac and
its openings, like the posterior pair of ganglia in the
conchifera which are also sometimes united into one, three

20() NERVOUS SYSTEM.

other ganglia are observed in the abdominal cavity, ex-
tended, as the ganglionic columns in the succeeding class,
between the alimentary and respiratory cavities.

The nervous columns of the conchifera are almost con-
fined to a sub-oesophageal position, and extend along the
inferior or ventral surface of the abdominal cavity, above
the respiratory sac; they are most detached from each
other at their anterior part, and often continue separate
through their whole course. The motor or simple co-
lums, which I have generally found more transpa-
rent and colourless than the ganglionic, keep in contact
with the sensitive chords, but sometimes they occupy a
lateral position, passing over the sides of the ganglia,
especially the last pair where the two kinds of nerves are
most obvious. On opening the respiratory sac of a conch-
iferous animal, as of the common muscle, mytilus edulis
(Fig. 8S) and throwing

aside the branchiae, the FIG< 8$?

foot, and the pectinated
lateral prolongations of
the lips, we perceive two
large white ganglia (88.
a.b.) placed on the lower
and lateral parts of the
mouth, resting on the
peritoneal covering of the
stomach or of the liver which envelopes it, and sending
upwards and forwards numerous large branches to the lips
and neighbouring parts, and to the sympathetics. Two
of these branches, after encompassing the short oesopha-
gus, often meet above that passage, and form a distinct
supra-cesophageal or cerebral ganglion, and two other branches
passing inwards from the same ganglia, beneath the
stomach, sometimes form another double ganglion on the
median plain, close to the first sub-oesophageal pair (88. a.b.)
The double nervous columns continue their course back-
wards, from these anterior lateral ganglia, running on the
same plain along the interior surface of the abdominal
cavity, to the broad expanded base of the muscular foot,
where the middle pair of ganglia are placed. These ab-
dominal or pedal ganglia (88. c. d.) , are the most variable in

NERVOUS SYSTEM. ^O/

size, and correspond in their development with the presence
or the magnitude of the foot which receives branches from
them. The columns which connect these two pairs of ganglia
are separated from each other on the median plain by
a space, which varies according to the lateral extension
of the trunk in the different species ; they are generally
parallel and near to each other in their course. The two
symmetrical columns of ganglionic and simple nerves,
continuing backwards beneath the ovary to the inferior
surface of the great adductor muscle of the valves,
meet with a third pair of infra-abdominal ganglia
(88. e.) which are the most approximated to each other,
and are often united into a single lobed ganglionic mass,
as in the pecten maximus. In this large pecten it is
easy to perceive that the motor portion of each of the
two converging columns passes laterally over the surface
of this large compound ganglion placed on the median
plain, under the middle of the large adductor muscle
of the valves. This pair of ganglia (e) appears to vary
in size with the magnitude of the adductor muscle, and
the extent of the palleal margins and branchke which receive
nervous branches from it. The columns which pass backwards
from the posterior ganglia, soon divide into numerous
branches which supply this part of the trunk, and the
largest nerves (/.), continued upwards along the adductor
muscle from the columns, are observed to extend, on each
side of the rectum, to the margins of the mantle, and to
supply the ciliated and fringed orifices of the abdominal
and thoracic cavities, and they send large branches to the
branchiae. The ganglia, which are most obvious on first
opening the valves of the conchifera, are the posterior pair
placed on the adductor muscle, and these have generally
bi'CMi described and figured by Poli as the centre of this
system, which he mistook for the chyliferous system of
these animals; the same pair has been uniformly designated
and represented by Chiaje as the brain of these acephalous
niollusca ; but both these authors have accurately represented
their forms and the distribution of their numerous diverging
branches. These two ganglia are connected by a trans-
verse band on the posterior adductor muscle of the broad
area noa, the nerves of which have been minutely traced

208 NERVOUS SYSTEM.

and represented by Poll, as extending over the branchiae and
the posterior portion of the mantle. These posterior ganglia,
situate on the great adductor muscle, and sending forwards
branches to the gills, are very remote from each other
in the avicula; they are separate in the mactra as in the
mytiluSy they are partially joined into a quadrilobate mass
in the cardium and the solen, they form a single gan-
glion in the spondylus as in the pecten, and they form
by their union a transverse thick nervous band on the
large abductor of the pinna. The first sub-cesophageal pair
of ganglia (88 a. b.) with their numerous anterior branches
and their two columns extending backwards to the pos-
terior ganglia (88. e) have been accurately traced and re-
presented by Poli in different species of solen. Small
ganglia are observed in the conchifera, as in the tunicata
and in the articulated classes, on other nerves besides the
two great sensitive columns. The visceral or sympathetic
nerves appear to receive their principal branches from the
nerves of the first sub-cesophageal pair of ganglia, as they
have been long known to receive their principal trunks
from those of the two corresponding lateral ganglia of the
stomach in the Crustacea.

From the great development of the organs of the senses and
of mastication at the entrance to the oesophagus in the gas-
teropods, their nervous axis is much more concentrated and
developed in that situation than it is in the conchifera ;
and from this general advancement of the great nervous cen-
tres to the head of these animals, we commonly observe a
proportional diminution in the extent of their two symme-
trical sub-ventral nervous columns. In the short and broad
bodies of the gasteropods, the symmetrical columns are still
generally separated from each other by a variable space along
the median plain, as in the conchiferous mollusca, but as the
general form and structure of the animals of this class vary
remarkably, we find a corresponding diversity in the form
and disposition of the great centres of nervous energy. In
the simple form of the nervous system presented by the
carinaria mediterranea (Fig. 89,) there is a close analogy
with the ordinary disposition of the symmetrical detached
nervous columns along the ventral surface of the abdomen in
the inhabitants of bivalve shells. Lobed ganglia (g. h,) are

NERVOUS SYSTEM. 1?09

observed in this animal at the sides of the oesophagus (*) and
a transverse nervous band («,) connecting them, and encom-
passing that passage. From this nervous oesophageal ring
(?,) the two optic nerves pass laterally to the eyes (/,/,) and

FIG. 89.

the tentacular branches pass upwards and forwards to the
long slender tentacula (89. e, e.) Numerous branches ex-
tend downwards and laterally, to ramify on the muscular
parietes of the abdomen, and two principal trunks (k, k,) ex-

PART II. p

210 NERVOUS SYSTEM.

tending backwards along the ventral surface of the abdomen,
like the great nervous axis of conchifera, meet with a large
compound quadrilobate ganglion (q,) behind the stomach (£,)
and above the diverging muscles of the compressed pinniform
foot (n, o.} These two sub-ventral, detached and converging
columns (k, k,) extending from the cesophageal collar to the
middle or pedal ganglia (#,) can be traced backwards from
these ganglia along the lower surface (q, m,) of the abdominal
cavity and beneath the intestine (c, d}) to near the caudal
extremity of the trunk. Another branch is described by
Chiaje as a sympathetic extending directly backwards from
the brain, or cesophageal collar, and spreading on the viscera
without passing to the quadrilobate ganglion (q.) Numerous
branches come off from the periphery of the pedal ganglia
(q,) to ramify on the muscles of the foot, and the surround-
ing parts. The pedal ganglia (q,) have been regarded as
sympathetic, but from their whole relations to the rest of
the nervous system, and from the form and position of the
great trunks (k, k, m,) connected with them, they appear
more analogous to the symmetrical sub-ventral ganglia of
conchifera, and of the articulated classes. The lateral ganglia
of the nervous cesophageal collar are generally the parts

NERVOUS SYSTEM. 211

from which the two principal nervous chords extend back-
wards beneath the abdominal viscera in the gasteropods as
in the bivalved mollusca, as seen in the annexed figure of 1 he
nervous system of the aplysia fasciata (Fig. 90.) In the
aplysia, as in many of the higher forms of gasteropods there
is a large median supra-cesophageal ganglion (a,) from which
the organs of the senses receive their nerves, and from this
single superior ganglion (a,) proceed downwards and laterally
two nervous bands to connect it with the usual pair of late-
ral cesophageal ganglia (b, c.) Two nervous branches (/,)
likewise proceed downwards and forwards from the" cerebral
ganglion («,) to form a small anterior collar around the oeso-
phagus (i9) and an inferior single ganglion (ff9) is seen be-
neath the muscular bulb of the oesophagus, where these
branches meet. The posterior large nervous collar is com-
pleted by an inferior transverse band passing between the
lateral ganglia (b, c,) and beneath the oesophagus (i.) From
the lateral cesophageal ganglia (b, c,) two nervous trunks (d9 d,)
extend backwards beneath the divisions of the stomach (k, I,
m, n9) and along the ventral surface of the abdomen to near
the bulb of the aorta (t9) where they meet with a single gan-
glion (e,) considered, from its position, its distribution and its
attachment to that arterial trunk, as a sympathetic ganglion.
The cerebral ganglion (#,) placed above the oesophagus, and
connected through the lateral ganglia (b, c,) with these two
longitudinal columns, has a quadrangular form, a reddish
brown colour, and is enclosed in a tough cranial membranous
capsule immediately above the posterior end of the bulb of
the oesophagus. The same reddish coloured nucleus and
granular structure are seen in all the ganglia of the aplysia,
and from the toughness of the neurilematous covering of the
ganglia and nerves they can be easily injected like vessels, as
in most other molluscous animals. The lateral ganglia (90.
b, c,} have each a trilobate form, and the nervous bands
which connect them with the brain have a distinct appear-
ance of separate component columns. There are two fila-
ments which proceed backwards from these lateral ganglia,
like the origins of the sympathetics of Crustacea, and which
here form by their union an arch around the trunk of the aorta.
The anterior bilobate sub-oesophageal ganglion (90. g9) gives
off eight nerves to the oesophagus, the salivary glands and

p 2

212 NERVOUS SYSTEM.

the muscles of the mouth. The two lateral ganglia are con-
nected together by a broad nervous band, which passes be-
low the oesophagus and completes the posterior ring around
that passage. The muscles of the head, the superior tenta-
cula, and the small eyes, receive their nerves from the cere-
bral ganglion (a.) The optic is a branch from the large ten-
tacular nerve on each side. The nerves from the lateral
ganglia are spread chiefly on the muscular parietes of the
trunk, and those from the aortic ganglion (e9) are observed
ramifying on the liver, the intestines, the branchiae, and the
generative organs. The aorta receives a minute branch
from the two anastomosing filaments of the lateral ganglia,
which embrace it, and a second ganglion almost impercepti-
ble, is found on one of the branches proceeding from the
great abdominal sympathetic ganglion. The sympathetic
ganglia are also distinct in the scylltea, the glaucus, and many
other small naked gasteropods. The nervous oesophageal
ring of the haliotis has two lateral ganglia which supply
nerves to the tentacula, the pedunculated eyes, and other
parts of the head, and presents below the oesophagus a large
median ganglion from which a series of long nerves extend
backwards along the inferior surface of the abdomen, as in
the carinaria, and the same plan of distribution is seen in
the nervous system of the patella and many similar forms.
In the bulla lignaria (Fig. 91,) there is a small lobed gan-
glion anterior to the usual cephalic ring (e,) and which is si-
tuate below the bulb (d9) of the oesophagus (a,) behind the
salivary glands (b, b9) and anterior to the insertions of the
diverging muscular bands (c9 c,) of the bulb of the oesopha-
gus. This ganglion is situate like the small anterior infra-
cesophageal ganglion of the aplysia. The cephalic ring (e, e,)
enveloping the oesophagus, behind this single ganglion, has
two large trilobate ganglia (/, /,) at its sides, which send
numerous branches to the surrounding muscular parts, and
two long branches (A, A,) extend backwards from them along
the sides of the abdomen to two symmetrical sub-ventral
ganglia (i9 i,) placed above the muscular foot. Behind these
are two sympathetic ganglia (k, &,) which send filaments to
the digestive organs, the ovary (o,) the oviduct (/?,) the uter-
ine sac (q,) the vulva (m,) and the urinary organs (n.) Two
anterior small sympathetic ganglia, which receive nerves

NERVOUS SYSTEM

FIG. in.

from the lateral ganglia (f,f,) of the brain (e, e}) are perceiv-
ed in this animal near the cardiac orifice of the strong, dense
muscular gizzard. So that, although the bulla is almost
acephalous, it has attained a considerable development both of
its symmetrical and sympathetic systems of nerves. Instead of
a simple nervous band passing over the oesophagus to connect
the lateral ganglia, as in the bulla, there are two pairs of gan-
glia around that passage in the jantkina, and in the limnea ;
the ganglia are approximated to form a collar around the
oesophagus. In the doris, the testacella, and many others,
these ganglia are confined to a supra-oesophageal position,
extending as a broad lobed nervous mass across the upper
part of that canal. In the chitons there is a broad supra-
cesophageal band and two closely approximated lateral gan-
glia below the oesophagus which send back large nerves to
the foot and sympathetic filaments to the abdominal viscera.

214

NERVOUS SYSTEM.

The vermetus has, like the aptysia, a small anterior infra-
oesophageal ganglion besides the ordinary supra-oesophageal
and two lateral ganglia ; the infra-oesophageal ganglion is
situate beneath the muscular bulb of the oesophagus, and a
small sympathetic ganglion, placed near the stomach, receives
filaments from the lateral ganglia, and sends nerves to the
abdominal viscera. In the long body of the dentalium the
brain forms a single lengthened quadrilateral ganglion ex-
tended longitudinally above the oesophagus, and sending
down small nerves on each side to complete the cesophageal
ring. In the pulmonated gasteropods the brain is generally
more equally divided between the upper and lower surfaces
of the cesophageal ring, the broad ganglia in these two situa-
tions having a bilobate form. The highest forms of the pec-
tinibranchiate gasteropods, as the buccinum and the harpa,

FIG. 92.

NERVOUS SYSTEM. 215

have the greatest portion of the ganglionic matter of the ceso-
phageal nervous ring accumulated in a cerebral position above
the entrance of the alimentary canal, as seen in the annexed
figure of the harpa elongata (Fig. 92,) from New Guinea,
where the mantle (0,) is opened to show the branchiae
(dy €}) and the syphon (c}) on the left, and the mucous
follicles the colon (n.) and the male organ (f.) on the
right side of the respiratory cavity. On opening the an-
terior part of the trunk the retracted proboscis (g) with
its muscles (h.) are seen extending backwards over the
brain (i.) which rests on the inferior turn of the oesophagus
where the two salivary glands (k. k.) are also placed.
From this cerebral mass (i.) large nerves are seen ex-
tending forwards to the head (#,) the tentacula, with the
eyes (s. s,) at their base, and to the broad fin-like ante-
rior fold (a,) of this long tapering inoperculate foot. Other
nervous chords extend downwards to the ventral surface
of the abdomen, and backwards to the sympathetics which
supply the abdominal viscera. This gradual concentration
of the ganglionic matter of the great cesophageal nervous ring
of the gasteropods into a cephalic position and form, on
the median plain above the alimentary canal, is a pre-
liminary to its enclosure in a distinct cranial covering,
which takes place in the cephalopods.

The nervous system of the pteropods presents the same
general plan and the same varieties of form in its ce-
phalic masses as seen in the gasteropods, especially
in the naked and swimming species. In the clio bo-
realis (Fig. 93, B.) one of the small naked swimming
pteropods, there is a double nervous collar around the
ossophagus, as in the aplysia and many other gasteropods.
Two small ganglia approximated to each other to form
a bilobate brain are placed above the oesophagus im-
mediately behind the lips (93, B «,) and indicate by their
diminutive size the imperfect development of the organs
of the senses in this animal which scarcely presents a
trace either of eyes or tentacula. Behind these central
ganglia are two larger lateral ganglia connected together
by a transverse band below the oesophagus, and which
supply the principal nerves to the muscular closed mantle
enveloping the trunk. Two nervous bands proceed from

216 NERVOUS SYSTEM.

each of this middle pair of ganglia, one of which con-
nects them with the cerebral, and another proceeding
backwards connects them with a posterior pair of ganglia,
which are united by a transverse chord above the oeso-
phagus. The ganglionic portion of this cerebral ring,
or perforated brain, is more developed below than above
the oesophagus in the pneumodermon, where there is only
a narrow transverse band above that passage, and three
pairs of ganglia disposed symmetrically below. Four of
these inferior ganglia are almost in contact on the me-
dian plain, and two are more lateral and separate. But
in the hyalea the nervous matter is chiefly concentrated
into a large supra-oesophageal broad ganglion of a quadran-
gular form, which gives off branches from its four angles.
Two of these nerves passing round the oesophagus enter
a double ganglion placed below that passage.

The nearest approach to the vertebrated form of the
nervous sytem is that presented by the cephalopods, the
highest of the mollusca and of all the invertebrata. The
oesophagus still perforates the brain, as in all the infe-
rior classes, but the greatest portion of that organ and
the symmetrical columns prolonged from it are here placed
above the alimentary canal. The brain is enclosed in a
distinct organized cranial cavity, numerous symmetrical
ganglia are developed on the great nervous axis both
before and behind that organ, and sympathetic ganglia
are observed in the abdominal cavity. The supra-oeso-
phageal portion of the brain in the nautilus forms a
thick transversely-elongated band, imperfectly surrounded
by the cranial cartilage, and enclosed in a tough mem-
brane, as in many of the gasteropods. It is extended
laterally into the small optic ganglia of this animal, and
is connected laterally with an anterior and a posterior
sub-oesophageal ganglionic ring, as in many of the inferior
mollusca. Each of the sub-oesophageal bands exhibits
two lateral ganglionic enlargements from which numerous
branches are ramified forwards and backwards, and the
two columns are prolonged backwards from the lateral
parts of the brain to the palleal ganglia, as in other
cephalopods. In the loligopsis (Fig. 93. A.) the brain is
enlarged both above and below the oesophagus, and its

NERVOUS SYSTEM. 217

superior portion, which forms an oval encephalic mass, is
more completely surrounded with a cartilaginous cranium.
From the lateral parts of this encephalic ring («,) come
off the optic nerves, and the two large longitudinal sym-
metrical columns (a. b. d.) which run parallel and near to
each other along the dorsal surface of the abdominal ca-
vity to the caudal extremity of the sac, having the pal-
leal ganglia (b,) in their course. The cerebral ganglion of
the octopus, (Fig. 93 C. «,) forms a more globular concentrated

mass enclosed in a thick cartilaginous cranium, covered with a
gelatinous cellular arachnoid and a dura mater giving off laterally
optic nerves (C. b.) to very large optic ganglia (C.c) contained
within the sclerotic coat of the eyes. The optic ganglia are sur-
rounded with lobed masses of adipose substance (e. e.) and
send out a large radiated pencil of detached optic fila-
ments (d,) to penetrate the choroid. The brain is sepa-
rated from the oesophagus (o,) and the aorta (n,) by the
membranous floor of the cranium, the whole periphery of
this perforated cerebral mass, encompassing the oesophagus,
not being yet surrounded with the consolidated portion
of the cranium. On each side of the cranium is a small
vestibular cavity occupied by a sac on which the audi-
tory nerve is distributed and containing a limpid fluid,
and a calcareous concretion. In the sepia the brain is
more distinctly bilobate, of a yellowish white colour, and
pulpy consistence, smooth on the surface and contained

218 NERVOUS SYSTEM.

in a thick cartilaginous cranium, which is perforated for
the passage of nerves, and gives attachment externally to
the muscles of the head and trunk. The cranium is
continued round the oesophagus though soft on its
interior part. Immediately anterior to the brain and the
cranium is a large heart-shaped supra-cesophageal ganglion,
of a yellowish colour, resting over the oesophagus, and
sending forwards numerous large nerves to the labial ap-
paratus enveloping the mandibles. On the lower part of
the muscular bulb of the mouth, are two small lateral
ganglia, which send in numerous large branches to the
strong muscles of the mandibles. Both the labial and
the mandibular ganglia are connected with the brain by
distinct nervous chords. Below the ossophagus, and an-
terior to the cranium, are two large lateral pedal ganglia,
which send forwards large nervous trunks to pass ramify-
ing through the tubular axis of all the feet. These two pedal
ganglia are likewise connected by nervous chords with
the sides of the brain. The two optic nerves pass through
the cranium, from the superior or dorsal lobes of the
brain, and enter two large crescentic optic ganglia within
the sclerotic, as in other naked cephalopods. The two
great longitudinal nervous columns are extended backwards
from the sides of the brain, separate from each other, and
along the dorsal aspect of the trunk, above the abdominal
cavity to the large palleal ganglia which distribute radiating
nervous chords chiefly to the interior muscular parts of the
mantle. The inner portion of each of these two symmetrical
columns (Fig. 93. A. b. d.) extending from the brain, along
the dorsal region of the cephalopods, does not enter the
palleal ganglion, but passing along the inner margin of
that ganglion, it penetrates the substance of the mantle
by a distinct foramen, and radiates into numerous rami-
fying chords, which are distributed chiefly on the exterior
parts of the trunk. The principal branches of these ex-
terior palleal nerves extend backwards in the direction of
the broad thin cartilaginous laminee which support the
branchial muscles, and two filaments extend inwards to
the abdominal sympathetic ganglia (93. A. e. e.) placed at
the base of the branchiae, near the lateral hearts. By means
of the two sub-cesophageal pedal ganglia anterior to the

NERVOUS SYSTEM.

219

brain, a second nervous ring is formed around the oesopha-
gus in the cephalopods, as in most of the gasteropods and
pteropods. On opening the skull of the argonauta from be-
hind, as in the annexed figure (Fig. 94,) by Chiaje, the brain
(fl,) of a round form above, separated from the inner parietes

FIG.

r"

of the skull by the gelatinous arachnoid, and extending
downwards to encompass the oesophagus (i,) is observed to
give off laterally the large optic nerves (^,) which perforate
the cranium to reach the pedunculated eyes, and from its
more anterior portion the separate great symmetrical columns
(94. b, b,) which extend backwards to the palleal ganglia (94.

220 NERVOUS SYSTEM.

c, cy) on each side of the crop (£,) the aorta (n, 0,) and the
salivary glands (ra,) and above the branchiae, and the genital
organs. By removing the anterior supra-cesophageal heart-
shaped labial ganglion, and the O3sophagus, the great lateral
sub-oesophageal pedal ganglia (/,) are perceived to send for-
ward large nervous trunks (d, d, d, e, e,) which extend rami-
fying through the central canal of each arm along with the
blood-vessels. A separate nervous tract, like that seen in
the dorsal columns of the cephalopods, is seen to pass back-
wards along the sides of the supra-cesophageal ganglion of
the buccinum and other gasteropoda, and having the same
pellucid appearance as the simple ungangliated nerves of
most invertebrata ; the same tract of simple nerves is seen in
the symmetrical columns of conchiferous mollusca especially,
as in the cephalopods, at the great posterior pair of symme-
trical ganglia. The dorsal columns prolonged from the brain
are more approximated, parallel, and lengthened in the loligop-
sis and loligo than in most of the naked cephalopods, which
corresponds with the lengthened and narrow form of the
trunk in these animals. The great nervous trunks, (94. d, d, d,)
proceeding from the inferior ganglia (f,fj) anterior to the
brain, and accompanying the artery and vein (p,p,pj q,q,g,)
through the axis of each arm, send out lateral ramifying
branches at regular, short, and decreasing distances from
both sides, corresponding with the position of the exterior
suckers, and these nervous trunks, diminishing in size as
they advance towards the apex of the arm, present through-
out their whole course a beaded or knotted appearance, like
the nervous axis of a worm. In the long cylindrical trunk
of the loligo the nervous columns are continued from the
two palleal ganglia, along the whole extent of the dorsal sur-
face of the body, and send out numerous lateral branches to
the caudal fins, which are seen radiating and ramifying to
their extreme margins. As the great trunks of the sympa-
thetic in the inverted bodies of the articulated animals occu-
py the dorsal region of the abdominal cavity, and the sym-
metrical columns the ventral, we find that in the cephalopods
where the columns extend along the back; as in the higher
classes of vertebrata, the branches of the great sympathetic
proceeding from the inferior surface of the brain, extend
along the ventral aspect of the abdomen, between the liver

NERVOUS SYSTEM. 221

and the ink-gland to the bottom of that cavity, where they
form a ganglion which sends nerves to the digestive, the
circulating, and the respiratory organs. So that, although
the brain of the cephalopods is still perforated by the oeso-
phagus, as in all the inferior classes, we find all the principal
parts of the nervous system of the vertebrata already deve-
loped in this class, and after undergoing a series of changes
of form and position in the inferior tribes of animals, regu-
lated by the general development and form of the body, they
have here acquired the form and situation which they pre-
serve throughout all the higher classes to man. This system
begins the development of its ganglionic axis in the lowest
acephalous mollusca, as in the lowest helminthoid articulata,
below the oesophagus, and extends along the ventral surface of
the abdomen ; but in the higher gasteropods, as in the highest
insects and Crustacea, we find it advanced in its position, ac-
cumulated around the entrance of the digestive canal, and
mounting to a dorsal position, which nearly the whole of the
lengthened spino-cerebral axis has attained in the cepha-
lopods.

FIFTH SECTION.

Nervous System of the Spini-cerebrated or Vertebrated
Classes.

The great axis of the nervous system occupies en-
tirely a dorsal position in the vertebrated classes: it is
enclosed in an osseous sheath, which is continued over
its posterior prolongation, and it is no where perforated
by the alimentary canal. The fibrous structure of the
encephalic portion which is perceptible in the cephalo-
pods, becomes more distinct and obvious as we ascend
through the vertebrated classes; and that anterior part
of the nervous axis becomes likewise proportionally larger,
leaving only slight traces, in the fourth ventricle, of its
original opening for the passage of the alimentary canal.
The spinal chord, the medulla oblongata, the optic lobes,

222 NERVOUS SYSTEM.

and the cerebral and cerebellic hemispheres,, form the most
constant elements of this axis, but their relative and actual
developments vary in the different classes. They are com-
posed of minute neurilematous tubular filaments which form
two posterior contiguous sensitive or ganglionic columns and
two anterior motor columns, the filaments and nerves of which
are not interrupted by ganglionic enlargements. Though
much varied in the extent of its development in the different
classes, there is great similarity in the successive stages of the
development of this system in the embryos of all the verte-
brated animals and great uniformity of plan in all its adult
forms. Beginning with the two columns of the axis, like the
two chords of a worm, it becomes reinforced by filaments
from every part of the periphery, and gradually receives its
ganglionic enlargements, as in all the inferior tribes, where
they are most required by the developing organs of the
body. The great sympathetic, or nervous system of
organic life, which is extended along the upper or dorsal
side of the symmetrical axis in the inverted bodies of
the articulata is here developed along the ventral or
under surface of the spino-cerebral axis, and like the sym-
pathetic system of the highest entomoid classes it is en-
closed with the viscera, in a cavity distinct from that
which envelopes the nervous axis of animal life.

In the long vermiform bodies of the lowest cyclo-
stome fishes, as the lamprey, the pride, and the gastro-
branchus, the two slender columns extended along the
back and scarcely protected by a cartilaginous sheath,
are nearly without cerebellum, and destitute of gangli-
onic enlargements in their course to the head, where
the minute cerebral elements are enclosed, like the
ganglia of a cephalopod, in a cartilaginous tube, con-
sisting of a single piece. This simple condition of the
axis presented by the lowest fishes, resembles the pri-
mitive embryo-state of this system in the highest ver-
tebrata before the extremities begin to shoot from the
sides of the trunk. In fishes, as in cephalopods, where
a large exterior surface of the skull is required for
muscular attachments, the minute brain does not fill
the cavity of the cranium, and the space between the
dvra mater which lines the skull and the pia mater

NERVOUS SYSTEM,

223

which invests the cerebral organs is occupied by the
soft transparent semifluid cellular tissue of the arach-
noid coat which passes down likewise through the ver-
tebral canal, enveloping the spinal chord. The spinal
chord is nearly equal in its development throughout
the vertebral column, even in many of the anguilliform
osseous fishes, from the smallness of the arms and legs
not requiring those enlargements which we observe in
most higher animals, where the nerves of larger and
more powerful extremities are given off. In species
which have the arms of great magnitude, as rays and
flying-fishes, there is a proportionate development of
the upper enlargements of the spinal chord. The num-
ber and the extent of these enlargements of the spinal
chord in fishes corresponds with that of the members
developed from the periphery of the trunk. In the
trigla (Fig. 95. C,) where the pectoral fins are of great
size, a series of ganglionic enlargements (95. C. b. £,)

FIG. 95.

of the spinal chord (a) are observed at its upper part,
which corresponds in number with the number of the
large detached rays of the pectoral fins presented by
the different species, trigla cuculus having five enlarge-
ments and five detached rays, and the trigla lyra (95, C.)

224 NERVOUS SYSTEM.

having six of each. The posterior extremity of the
chord is sometimes sensibly enlarged where nerves pro-
ceed to the muscles of a large caudal fin, and in abdo-
minal fishes an enlargement is observed, corresponding
with the ventral fins. In some fishes with a great de-
velopment of the head and anterior portion of the trunk,
as the frog-fish^ and the tetrodon, the spinal chord passes
but a short way through the vertebral canal, and a long
cauda equina extends backwards, as in the human body.
The symmetrical nerves arise by double roots from the
two grooves on each side of the spinal chord, the motor
nerves which commence more towards the tail than the
sensitive, originate from the anterior lateral groove, and
the sensitive nerves, provided each with a ganglion be-
yond the vertebral canal, originate from the posterior
groove. These unite, as in the invertebrated classes, to
form mixed, moto-sensitive nerves, they give sensibility
and motility to the organs of animal life, and they send
filaments to the sympathetics — each vertebra being analo-
gous to a segment of the trunk, and each pair of sym-
metrical nerves originating from the brain of that segment.
The nervous O3sophageal ring of the invertebrata is still
perceptible in the wide opening between the lateral halves of
the medulla oblongata of the lampreys. The great fasci-
culi composing the cerebral masses the corpora py-
ramidalia, olivaria and restiformia are already obvious
in the large medulla oblongata of fishes ; but the
crossing fasciculi of the corpora pyramidalia are slightly
marked, they become apparent and numerous as we ascend
through higher classes. The medulla oblongata, the apparent
origin of most of the cranial nerves, is here large and lobed,
and often nearly as broad as the cerebral organs before it in
the cranium ; it is deeply marked above by a calamus scrip-
torius, at the bottom of the fourth ventricle, which is situate
between it and the single median lobe composing the cere-
bellum.

Anterior to the medulla oblongata and cerebellum, there
are generally in osseous fishes three pairs of rounded lobes
placed in front of each other along the floor of the cranium,
and occupying but a small portion of that capacious cavity,
as seen in the brain of the conger-eel, muraena conger

NERVOUS SYSTEM. 225

(Fig. 95. A,) where these three pairs of lobes are nearly
equally developed and similar in form. The posterior pair,
(95. A. c,) immediately before the cerebellum (95. A. b,) are
the optic lobes or corpora quadrigemina, which are hollow in-
ternally, as in the human foetus, and give origin to the prin-
cipal fibres of the optic nerves. The second or middle pair
of lobes (95. A. e,) are the cerebral hemispheres, which are
here, as in the human embryo, destitute of internal ventricles
and without external convolutions. The anterior pair (95.
A. /,) are the olfactory tubercles, which are entirely appro-
priated to the olfactory nerves (95. A. g, a.) In the trigla
lyra, (Fig. 95. C,) where the medulla oblongata (b, b,) is
marked by ganglionic enlargements, and the cerebellum (d,)
is proportionally small, the optic lobes (e, e,) are much larger
than the cerebral hemispheres (/,) and the olfactory tuber-
cles (g,} are much inferior in size. In the perch, (Fig. 95.
B,) the medulla oblongata (a,) forms two broad lobes at its
anterior termination (b}) over which the elevated cerebellum
(e,) arches backwards. The optic lobes (95. B. d, d,) have
an elongated form, the cerebral hemispheres (e, e,) much
smaller than the optic lobes, are extended vertically, and the
olfactory tubercles (/,) form two slight spherical enlarge-
ments at the commencement of the olfactory nerves (g, g.)

In most fishes, as in the earliest condition of the human
brain, the optic lobes are larger than the hemispheres 5 they
are smooth and cineritious on the outer surface, and destitute
of the transverse sulcus which gives them a quadrigeminous
appearance in the adult mammalia ; they are hollow within
and have their inner parietes lined with white medullary
fibres. The ventricles of the optic lobes communicate freely
with each other, and they open behind, by a narrow aquiduct,
into the fourth ventricle beneath the cerebellum. The interior
white medully parietes of these two lateral cavities meet above
on the median line, and form an extended commissure like
the corpus callosum of the hemispheres ; they descend along
the median line to form a prominent ridge, but not a complete
septum, between the ventricles. The optic lobes of fishes,
like their medulla oblongata, are larger in proportion to the
cerebral hemispheres than in any of the higher vertebrata,
and they present the same great proportions the earlier we
observe them in the human embryo. Their development

PART in. Q

2-26 NERVOUS SYSTEM.

corresponds generally with that of the corpora olivaria, the
optic nerves, and the eyes, but is in the inverse ratio to that
of the cerebral and cerebellic hemispheres. The inner
medullary fibres of the optic lobes pass transversely and arch
upwards over the contained ventricles, but the exterior fas-
ciculi advance longitudinally to the optic nerves. The cine-
ritious portion predominates in these and other parts of the
brain, as in the human embryo ; and the wide canal extend-
ing through the middle of the spinal chord of fishes corres-
ponds also with the fretal condition of that part in mamma-
lia. These optic lobes, the first formed portions of the
brain anterior to the medulla oblongata, being analogous to
the supra-cesophageal ganglia which give origin to the optic
nerves in the invertebrata, are almost alone developed in the
cyclostome fishes ; they are large compared with the cerebral
hemispheres in most of the osseous fishes (95. C,) they are
comparatively small in the anguilliform fishes (95. A,) their
size is much reduced in the plagiostome chondropterygii (95.
D. d,) and they become proportionally smaller as we ascend
through the higher classes to man. They contain within
their cavity one or two pairs of tubercles and the large cor-
pora candicantia lie beneath them on the inferior surface of
the brain. The anterior and posterior commissures are al-
ready developed, and also a rudimentary fornix.

Anterior to the hollow optic lobes of fishes are the proper
cerebral hemispheres) (95 . A. e,) which are scarcely percep-
tible in the cyclostome fishes, are very small in most of the
osseous fishes, (95. B. e, e, — C. e, e,) equal the optic lobes in
the apodal fishes (95. A. e,) and have attained in the plagios-
tome species (95. D. e, e,) a much greater size than these
small optic lobes, (95. D, d.) In the osseous fishes, as in
the embryo condition of the human hemispheres, they are
destitute of internal ventricles^ smooth and cineritious on the
surface, without external convolutions, and they are com-
posed internally of radiating white fasciculi derived from the
corpora pyramidalia. In the rays and sharks (95. D. e, e,)
where the hemispheres attain a great size, they already pre-
sejit inequalities on the surface, they begin to extend back-
wards over the small optic lobes, (95. D. d,) and they already
manifest distinct ventricles in their interior, which continue
in almost all the higher animals to man. The cerebral or

NERVOUS SYSTEM. 227

lateral ventricles are continuous with the canals of the olfac-
tory nerves (95. D./,) as in all the higher classes. These
cerebral lobes, perhaps the analogues of the thalamic optici,
are developed in the direct ratio of the corpora pyramidalia
and crura cerebri, and their increased development in higher
animals corresponds also with the enlargement of the lateral
lobes or hemispheres of the cerebellum.

Before the cerebral hemispheres are placed the most an-
terior pair of lobes, which here, as in higher classes, are ap-
propriated to the olfactory nerves, and vary in their form,
size, and situation more than any of the other parts of the
brain. These olfactory tubercles are generally in the osseous
fishes, (95. B./, C. p}) in immediate contact with the cere-
bral hemispheres, and inferior to them in size ; in the an-
guilliform fishes (95. A. /,) they nearly equal the hemi-
spheres (95. A. e}) and in the plagiostome fishes (95. D. g,g,)
they are placed on the course of the olfactory nerves at a
greater or less distance from the hemispheres (95. D. e, e,)
and present a great transverse development, exceeding in
magnitude the hemispheres themselves. In these last fishes
the rays and sharks, the large cineritious olfactory lobes are
situated at the end of thick peduncles and lie immediately
above the cribriform plate of the ethmoid which the olfac-
tory nerves perforate to be distributed on the extensive
pituitary membrane covering the laminae of the nose.

The cerebellum forms only a minute transverse band on
the median plain in the cyclostome fishes, where it can be
perceived, and in the higher osseous fishes (95. B. c,) it still
consists merely of a simple median lobe, smooth on the sur-
face, destitute of lateral hemispheres, and analogous to the
vermiform median lobe first developed in the cerebellum of
the human embryo. It rises vertically in the osseous fishes
(Fig. 96. €,) compressed between the optic lobes (96, d,) and
the lobes of the medulla oblongata (96. b,) and generally ex-
tends backwards, tongue-shaped, over the fourth ventricle, but
is destitute of the laminated surface which it begins to present
in the plagiostome fishes. This median portion of the cere-
bellum, (95. D. e,) like the cerebral hemispheres, (e, e,) is
greatly developed in the muscular rays and sharks, extending
backwards over the medulla oblongata and forwards over the
small optic lobes (95. D. d,) and already presents not only a

Q2

228 NERVOUS SYSTEM.

transversely laminated structure, as in higher classes, but also
small hemispheres extending laterally like tubercles from its
base. Its magnitude here corresponds, as in higher classes,
with that of the corpora restiformia, which are conspicuous
in the plagiostome fishes, and it presents internally an ar-
borescent appearance of white diverging fasciculi, arising
from its laminated structure.

All these lobes contained within the capacious cranium of
fishes are covered with cineritious substance, and derive their
internal white fibrous parts distinctly from the great fasciculi
of the medulla oblongata, the corpora pyramidalia, olivaria,
and restiformia. From the great size of the olfactory and
the optic nerves in this class, as seen in the perch, (Fig. 96.

FIG. 96.

ff, q,) and also of the fifth pair (96. m,) and from the small-
ness of the three pairs of lobes from which these nerves ori-
ginate, the cerebral hemispheres (e,) the optic lobes (d,) and
the medulla oblongata (b,) appear only like small ganglia ap-
propriated to these nerves. The olfactory tubercles (96./,)
are generally contiguous to each other and to the hemi-
spheres, and the white fibres of the olfactory nerves (96. g,)
pass forwards on their lower surface from the cerebral lobes
(96. e.) Two commissures are generally perceptible in the
cerebral lobes, and beneath the small lobules in the optic
lobes a third ventricle is seen leading downwards to the in-

NERVOUS SYSTEM. '229

fundibulum and the large petuitary gland. The pineal gland
(95. A. c?,) with its small peduncles, is seen between the
optic lobes and the hemispheres, as in higher classes, and is
composed chiefly of cineritious substance.

From the great extent of the cranial cavity and the small-
ness of the brain, the cerebral nerves have a long free course
from their origin to their cranial foramina. In the osseous
fishes the optic nerves (96. q,} generally cross each other with-
out uniting or intermingling their fibres, but in the plagiostome
fishes they unite and decussate, as in mammalia. Fromthegreat
size of the organs of vision in this class, and of the muscles
which move them, not only the optic nerves are proportion-
ally large, but also the third, fourth and sixth pairs, or oculo-
motory, trochlear and abducent nerves, which are the motor
filaments of these muscles. The abducent nerves advance
forwards from the inferior surface of the medulla oblongata,
where they arise between the posterior fibres of the large
trigemini. This large fifth pair (Fig. 96. m,) arising from
the sides of the lobes of the medulla oblongata immediately
beneath the cerebellum (96. c,) gives off the ophthalmic (96.
p,) which passes forwards through the orbit above the eye
to be distributed on the upper part of the face ; — the supe-
rior maxillary (96. o,) which passes under the eye to ramify
on the sides of the face ; — and the inferior maxillary (96. n,)
which supplies chiefly the palate and lower jaw. The prin
cipal branches of the seventh or facial nerve (96. I,) are dis-
tributed on the posterior part of the face and neck. The
great pneumo-gastric nerves (96. &,) arising behind the trige-
mini, from the sides of the medulla oblongata present a large
ganglion, from which branches pass downwards to the
branchiae, and backwards along the oesophagus to the sto-
mach, and air sac or rudimentary lungs ; and before these is
a branch analagous to the glosso-pharyngeal, which supplies
the tongue and anterior branchial arch. This great ganglion
of the pneumo-gastric (96. k,) is sometimes close to the
origin of the nerve, and sometimes remote ; and a branch
from this nerve, like the accessary of Willis, extending lon-
gitudinally on the side of the whole body near the lateral line
sends filaments to the surface. The pneumo-gastric supplies
nerves also to the electrical organs of the torpedo. The
acoustic nerve, arising between the trigeminus and the great

230 NERVOUS SYSTEM.

pneumo-gastric, descends to the vestibule and long semi-cir-
cular canals.

The spinal nerves, like those of the cranium, have gene-
rally a long course before they pass out through the inter-
vertebral foramina, and the ganglia of their posterior roots
are often so small, especially in osseous fishes, as to be
scarcely perceptible, and slight enlargements of the spinal
chord can sometimes be distinguished at the origins of the
several pairs of symmetrical nerves. The great sympathetic
arising from cranial nerves as high as the trigeminus, is rein-
forced in its course backwards by branches from the spinal
nerves, and forms plexuses and ganglia, as in higher classes,
before being distributed on the organs of the trunk ; it is
more distinct in the plagiostome chondropterygii than in the
osseous fishes, and is least developed in the cyclostome spe-
cies. It forms small ganglia along the sides of the vertebral
column, where it receives filaments from the spinal nerves,
and its plexuses embrace the arterial trunks before ramifying
on the digestive, respiratory, and generative organs.

In the perennibranchiate amphibia, and in the larva state
of those which lose the gills, the spinal chord, the medulla
oblongata, and the cerebral parts contained within the cra-
nium present the same proportions and general conditions
which we observe as permanent characters in most of the
osseous fishes ; but the cerebellum is generally smaller in
amphibia and reptiles than in all the other vertebrata. As
in the lower fishes, the spinal chord in these inferior forms of
amphibia is prolonged, small and tapering, through the
greater part of the coccygeal vertebrae, without distinct en-
largements where the nerves usually come off to the arms
and to the legs. The medulla oblongata is yet broad and
lobed, the cerebellum in form of a very small median trans-
verse lobe without hemispheres, the optic lobes large, cine-
ritious, smooth without, hollow within, and quite exposed,
and the cerebral hemispheres, extended longitudinally,
smooth and cineritious externally, without internal ventricles,
and smaller than the optic lobes. The metamorphosis of the
caducibranchiate species changes the condition of their ner-
vous system from that of the lower fishes to nearly that of
the reptiles above them ; and these changes are effected so
rapidly that we can perceive a marked advancement in the

NERVOUS SYSTEM.

231

development of the nervous system of the tadpole produced
in one day. In the tadpole of the common frog, on the
fourth day, (Fig. 97. A.) the spinal chord is perceptibly en-

FIG. 97.

larged at its posterior part (a,) and also the medulla oblon-
gata. The cerebellum (b,) is scarcely visible, extended across
the median plain ; the optic lobes (c,) and the cerebral he-
mispheres (e,) are small, narrow, and so far separate longitu-
dinally as to expose entirely the intervening optic thalami
(d.) On the following or fifth day (Fig. 97. B,) besides the
general encrease of the spinal chord (B. #,) the cerebellum
(B. b^ is perceptibly enlarged, the optic lobes (B. e,) are
proportionately broader and shorter, and the cerebral hemi-
spheres (B. e,) encreased in every direction, begin to extend
backwards over the optic thalami (B. d.) As the tadpole
advances in its development, and the legs and arms are ex-
tended from the sides, the posterior and middle enlargements
of the spinal chord are proportionately encreased, the cere-
bral hemispheres enlarge, and their white fibrous internal

232 NERVOUS SYSTEM.

parts predominate over the cineritious covering, but they
present no convolutions nor ventricles. By the rapid growth
of the dorsal vertebrae, and the obliteration, anchylosis, and
absorption of the coccygeal vertebrae, the spinal chord ap-
pears to recede from behind forwards, within the vertebral
canal and the cauda equina to lengthen. The anterior extre-
mity of the chord is enlarged from the first, as it gives origin
to most of the cranial nerves, and the posterior end is en-
larged for the cauda equina, as is even perceptible in fishes
and serpents. Here, as in other classes, where the spinal
chord by the progress of development, is retracted within
its osseous sheath, and the cauda equina is thus length-
ened in the adult state, there is a greater distance ob-
served between the origins and the places of junction of
the motor and sensitive roots of the nerves which com-
pose it, and consequently between the intevertebral ganglia
and the spinal chord ; and this is most manifest at the pos-
terior end of the column, which has been most influenced by
the metamorphosis. The long narrow cerebral hemispheres
of the adult frogs taper to the olfactory nerves which com-
mence with cineritious tubercles, and the optic nerves are
observed distinctly to cross each other before the optic tuber-
cles. The changes effected in the nervous system by the
metamorphosis of the higher amphibia closely resemble those
produced by development in the human embryo. Their
sympathetic nerves and ganglia are more distinct than in
fishes.

In the class of reptiles the small cavity of the cranium
nearly corresponds with the dimensions of the enclosed
brain, as in some fishes, and the superficial cineritious sub-
stance still predominates over the internal white fibrous
matter, though to a less extent than in fishes and amphibia.
The cerebellum is remarkable for its proportionate smallness
in this class, and the cerebral hemispheres, containing each a
distinct ventricle, now always exceed the optic lobes. The
spinal chord of serpents, from their want of arms and legs, is
still destitute of enlargements, as in the apodal fishes, but the
medulla oblongata is of considerable size, and the fourth
ventricle, still uncovered by the small cerebellum, descends
into the spinal chord. From the smallness of the brain and
cranial cavity in the centre of the head of reptiles, the rela-

NERVOUS SYSTEM. 233

tive size of these parts does not influence that of the whole
head at different periods of life, and the head preserves the
same proportions to the rest of the body through life also in
amphibia and fishes. From the still imperfect development
of the cerebral parts in this class, the vital functions of rep-
tiles are less immediately dependent on them than in hot-
blooded animals, and they longer survive their mutilation.
In the saurian and chelonian reptiles the posterior and mid-
dle enlargements are obvious on the spinal chord at the ori-
gins of the nerves of the extremities. The wide medulla
oblongata within the cranium is marked longitudinally by the
limits of its three component fasciculi on each side, and the
decussating bands of its corpora pyramidalia are more dis-
tinct than in fishes. The nerves of the body bear a large
proportion to the size of the cerebral centres, and corres-
pond in their distribution to those of the higher air-breathing
classes. The great ganglia and plexuses of the sympathetics
now more closely accompany the arterial trunks, as we see to
become more exclusively their distribution from the articu-
lated and the moUuscous classes up to man. The twelve
pairs of cranial nerves are seen here as in birds and mamma-
lia, and they chiefly arise from the enlarged medulla oblon-
gata, as seen in the annexed figures of the brain of the tor-
toise, emys europaa, Fig. 97. C. D. Immediately before the
anterior roots of the first cervical nerves (97- D. «,) are seen
on the inferior surface of the medulla oblongata, the origins of
the hypo-glossal, or twelfth pair of cranial nerves, and on
the sides, the numerous branches of the spinal-accessory, or
eleventh pair. Before these are seen on the sides, two por-
tions of the pneumo-gastrics and the glosso-pharyngeal, or
ninth pair. Close together are the acoustic and the facial
nerves, and towards the median plain below are the sixth
pair, or abducentes oculorum, (97- D. b.) The small motor es
oculorum are seen anterior to these last, and on the sides the
large trunk of the trigeminus. The short and broad cere-
bellum (97. C. c,) not extending backwards to cover the
fourth ventricle, that cavity is found protected externally by
a highly vascular membrane (97. C. b.) The small trans-
versely developed cerebellum consists only of the median
lobe, without hemispheres, and consequently still is without
the corpus dentatum in its interior ; it is smooth and cineri-

234 NERVOUS SYSTEM.

tious without, and presents internally radiating fasciculi of
white nervous fibres extending peripherad from its base.
The great transverse commissure of the cerebellum, or the
pons Varolii is still wanting, like the cerebellic hemispheres.
The optic lobes (97- C. d, e,) reduced in their proportions,
and provided with internal ventricles (e,) are partially encom-
passed on their fore part by the large tapering hemispheres.
The cerebral hemispheres (97- D. d,) destitute of convolu-
tions, smooth and cineritious externally, hollow within, (97.
C. g,) present internally the thalami optici and corpora
striata (^,) and a distinct choroid plexus, (9J. C. h,) towards
the median side of their contained ventricles. These hemi-
spheres are broad and short in the crocodilian reptiles, and
more lengthened, narrow, and tapering forwards in the in-
ferior tribes, especially in the chelonia. Rudiments of cere-
bellic hemispheres are also seen in the crocodiles. The ol-
factory tubercles (97- D. g,) are much smaller than in fishes,
cineritious externally, and placed in contact with the cerebral
hemispheres. On the inferior surface of the brain in the
chelonia (97- D,) we observe an intimate union and decussa-
tion of the optic nerves (97. D./,) and behind these a long
tubular hypophysis (97. D. e,) or continuation of the third
ventricle into the infundibullum and petuitary gland. The
pineal gland (97- C./,) is still exposed on the upper part of
the brain between the optic lobes and the cerebral hemi-
spheres. All the parts of the brain are more compacted to-
gether in reptiles than in lower vertebrata ; the ganglia of the
posterior or sensitive roots of the spinal nerves are now more
conspicuous, like the lateral and splanchnic ganglia of the
sympathetics ; and the spinal nerves come off more nearly
opposite to the places of their respective destinations than in
the lower classes.

The nervous system of birds presents only a more elevated
condition of the same plan of structure already developed in
the crocodiles and inferior reptiles. The great centres of the
nervous system in the vertebrated animals like those of the
vascular, are at first developed in a lineal direction and ex-
tended longitudinally, as we see in the fishes, but at
length acquiring encreased lateral development, these parts,
in both systems become compacted together and accumulate
upon each other to form a more, short, circumscribed and

NERVOUS SYSTEM. 235

rounded mass, more easily accommodated and protected, as
we see in birds and mammalia. The spino-cerebral axis fills
the osseous cavities which protect it, and the form and size
of the upper part of the head now correspond with those of
the enclosed brain at every period of life. The spinal chord,
become more rounded in form, has an encreased proportion
of grey ganglionic matter in its interior, and the white
fibrous medullary portion is encreased in the brain. The
enlarged cerebral parts being now collected into a more
compact form, the hemispheres of the brain extend back-
wards to cover the optic lobes, and come into contact with
the greatly encreased cerebellum. The olfactory tubercles
have much diminished, but retain their tubular communica-
tion with the still small ventricles of the cerebral hemi-
spheres. The cerebral hemispheres still destitute of convo-
lutions and partially bilobate, and the median lobe of the ce-
rebellum deeply laminated and sulcated transversely, are the
parts here most developed in the cranium, and the white
fibres of the great cerebral commissure, the corpus callosum,
have begun to shoot across and unite the hemispheres. Not-
withstanding the great transverse extension of the cerebral
mass in adult birds, and its sudden tapering forwards to the
olfactory nerves, giving the whole brain a triangular appear-
ance, it presents the same lineal arrangement and longitudi-
nal extension of its parts in the embryo, which are preserved
as the permanent character of the nervous axis of fishes.
This is easiest observed by examining its development in the
transparent area of the cicatricula in the egg of the fowl,
where we perceive after two days5 incubation (Fig. 97. E,) the
two halves of the spinal chord (E. a,) united posteriorly, and
already forming the vesicular enlargement (97- E. £,) corres-
ponding to the caudaequina and pelvic dilatation, orrhomboidal
sinus of the adult. The cervical and dorsal vertebrae begin to
embrace the anterior portion (97. E./,) of the chord, and
three vesicular enlargements ar,e seen on the cephalic portion
of the nervous axis. The posterior (97- E. c,) of these en-
largements forms the rudimentary lobes of the medulla ob-
longata, the middle dilatation (97. E. d,) constitutes the out-
line of the optic lobes, the anterior (97- E. e,) and smallest
cephalic enlargement forms the embryo condition of the
cerebral hemispheres in the chick, and all these lobes are

XERVOVS SYSTEM.

still disposed on the same plain, and in a longitudinal direc-
tion, as we find them in the adult fishes and in the embryos
of mammalia. They incline forwards as they develope up-
wards and backwards and laterally, and in the adult condition
the optic lobes, reduced in their proportion and forced down-
wards and to the sides, are covered by the expanded cerebral
hemispheres, which reach and even partially overspread the
cerebellum. The spinal chord still extends into the coccy-
geal vertebrae, and the decussating bands of the corpora py-
ramidalia are more numerous and distinct than in the inferior
vertebrata, as seen in the medulla oblongata of the stork,
(Fig, 98. A. k.) The cylindrical spinal chord (98. A. «,) per-
forated by a small canal dilates on entering the cranium into

FIG. 98.

a wide and large medulla oblangata (98. A. b,) which is not
yet traversed by a cerebellic commissure, or pons Varolii.
The large cerebellum covers the fourth ventricle, which is
ext3nded into it, as seen in the cassowary, (Fig. 98. B. d,f,)
it consists of the vermiform or median lobe (98. B. d,) and a
small rudiment of the lateral lobes or hemispheres (98. A. /,)
and it is deeply sulcated transversely on the exterior, like the
cerebellic hemispheres of mammalia. The numerous me-

NERVOUS SYSTEM.

dullary bands which radiate outwards to the cineritious exte-
rior lamellae, from the white fibrous parietes of the fourth
ventricle (98. B../J) produce an arborescent appearance when
the cerebellum is divided vertically. The ordinary great
component fasciculi of the medulla oblongata are distinctly
marked externally, and the same nerves arise from this part
as in reptiles and mammalia. Where the lateral tubercles or
rudimentary hemispheres of the cerebellum are most distinct,
a small transverse commissure is already perceptible between
them, asin the human embryo, but there is no corpus dentatum.
The optic lobes (98. A. c,) reduced in size and separated
from each other to the sides of the medulla oblongata by
the encreasing cerebrum and cerebellum, are covered ex-
ternally, like the other lobes of the brain, with cineritious
matter, consist internally of white fibres, and present a small
ventricle (98. B. g,) in each, like the cerebral hemispheres.
They are proportionally small and round in the strutheous birds
(98. B. g, g,) more lengthened and oval in the inferior birds
(98. A. c, c,) and present between them transverse medullary
bands, (98. B. k}) forming a valvular commissure, on which
rests the pineal gland (98. B. i,) with its two peduncles ex-
tending forwards over the thalami optici. The optic thalami
covered by the cerebral hemispheres are connected by a cine-
ritious commissura mollis, the optic lobes are without trans-
verse exterior sulci, and the hemispheres are destitute of
convolutions though partially divided into two lobes, (98. A.
d, e,) by the fissura sylvii. The cerebral hemispheres, covered
externally with cineritious matter, smooth and undulated on
the surface, broad posteriorly, and tapering suddenly forwards
to the ethmoid bone, cover the thalami optici and the cor-
pora striata, and contain each a small ventricle which extends
forwards to the olfactory tubercles (98. A./.) The cerebral
hemispheres (98. B. i,) are composed chiefly of the ascending
and diverging fibres of the corpora pyramidalia and are con-
nected by an anterior commissure, and the crossing fibres of
a rudimentary corpus callosum. The olfactory tubercles
(98. A./,) commencing from two medullary tracts (98. A. h,
h,) on the inferior surface of the hemispheres, and containing
prolongations of the lateral ventricles, are still covered with
cineritious substance, and taper forwards to the olfactory
nerves, greatly reduced from their proportions in the inferior

238 NERVOUS SYSTEM.

vertebrata. The choroid plexus is obvious in each of the
lateral ventricles, which communicate below with the third
ventricle, and the corpora striata form lengthened transverse
eminences. The third ventricle communicates behind with
the fourth by the aqueductus Sylvii beneath the transverse
valve of Vieussenius, and is continued downwards in front
to the infundibulum and petuitary gland which here forms a
shorter hypophysis on the sella tursica than in reptiles. All
the lobes and cavities are immediately invested and lined by
the pia mater, and the dura mater lining the cranium forms
a distinct tentorium corebelli and a rudimentary falx ce-
rebri.

The sensitive spinal nerves of birds have their ganglia
larger, and approximated more nearly to their origins than in
reptiles, and from the retraction and high termination of the
spinal chord, as well as the comparative magnitude of the
legs in this class, the posterior ganglionic enlargement is re-
markable for its size, and at this place the motor and sensitive
roots pass out through separate foramina of the numerous
anchylosed sacral vertebrae. The twelve pairs of cranial nerves
are here distinct as in reptiles and mammalia. The olfactory
nerves still provided with distinct glandular tubercles (98. A.
/,) arise from two transverse medullary bands (98. A. h,) ex-
tending, as in mammalia, to the fissure of Sylvius, and pass
forward through the narrow tapering osseous canals formed
by the frontal and ethmoid bones. The optic nerves (98. A.
iy) corresponding in magnitude with the large eyes and the
optic lobes from which they originate, unite before the hypo-
physis, and partially decussate their numerous interwoven
component fasciculi before proceeding to the optic foramina.
The motores oculorum pass to the three innermost recti mus-
cles and the inferior obliquus of the eye, the trochlearis to
the superior obliquus, and the abducens to the rectus exterior
muscle, as in other classes. The large trigeminus sends its
ophthalmic branch to the upper parts of the face and nose,
the superior maxillary branch to the sides of the face and
upper mandible, and the inferior maxillary branch chiefly to
the lower jaw ; the two last branches exhibit a dental distri-
bution in the serrated mandibles of many aquatic birds, as in
the toothed jaws of quadrupeds. The smallness of the
facial nerve corresponds with the immobility and insensibility

NERVOUS SYSTEM. 239

of the superficial parts of the face, and the magnitude of the
acoustic nerve, with the great development of their internal
ear and their acute hearing, especially in nocturnal birds. The
glosso-pharyngeal passes as usual to the tongue and pharynx,
the hypo-glossal chiefly to the root of the tongue and upper
larynx, and the pneumo-gastric, communicating at the base of
the cranium with the accessory, descends with the jugular
vein along the neck to be distributed on the lungs, the in-
ferior larynx, the oesophagus and stomach, especially the
ventriculus succenturiatus. The spinal nerves are chiefly
cervical and sacral, from the number of vertebrae composing
these parts of the column, and the brachial and lumbar
plexuses are formed and distributed on the arms and legs,
nearly as in quadrupeds. The sympathetic, greatly encreased
in its development, presents distinct lateral ganglia from the
base of the skull to the end of the coccyx, it unites anteriorly
with the pneumo-gastric, the facial and the trigeminal nerves,
and at its posterior end the lateral ganglia become approxi-
mated and united on the median plain under the coccygeal
vertebra. It forms distinct ganglia and plexuses around the
great arteries, for the viscera of the trunk ; its cervical por-
tion is protected, along with the vertebral arteries, in the
foramina of the transverse processes ; and it is every where
connected by anastomosing filaments with the spinal nerves
along the sides of the vertebral column, as in other classes.

In the mammiferous animals a higher grade of the develop-
ment of this system is perceptible in the magnitude and ex-
tension of the spinal chord, and of the cerebral and cere-
bellic hemispheres, in the encreased number of internal
cineritious deposits in all parts of the white fibrous spino-
cerebral axis, in the more complete union of all the lateral
parts of this axis by means of decussating fasciculi and
various commissures of converging fibres, in the encreased
size and approximation of the ganglia on all the symmetrical
sensitive nerves, and in the more methodical and extensive
distribution of the great sympathetic, and its appropriation to
individual organs. The spinal chord, though encreased in its
proportion to the bulk of the body, is now less in proportion
to the cerebral mass than in the inferior classes ; its internal
longitudinal canal has almost become obliterated ; its lateral
halves are more intimately united together, and the crescentic

240 NERVOUS SYSTEM.

columns of cineritious matter have en creased in their interior.
The spinal chord is prolonged to a variable extent through
the column, being shortest in the tailless cheiroptera, qua-
drumana, and man, and longest in the cetacea, where it ex-
tends tapering through the coccygeal vertebrae, without pos-
terior enlargement, from the want of legs, as in apodal fishes,
and tadpoles, and serpents, and the human embryo. In the
long-tailed quadrupeds the spinal chord is extended to the
sacrum, and the detached nerves of the cauda equina are
prolonged through the coccygeal vertebrae. The ganglionic
enlargement of the spinal chord at the origin of each pair of
moto-sensitive nerves is now scarcely apparent, and the en-
largements corresponding to the atlantal and sacral extremi-
ties are of a more lengthened and fusiform shape. The
medulla oblongata is comparatively narrow, but it is more
deeply marked by the limits of the corpora pyramidalia,
olivaria, and restiformia. The decussations of the corpora
pyramidalia are more numerous and distinct, and the cine-
ritious matter of the corpus dentatum is generally percep-
tible in the corpora olivaria, which are themselves propor-
tionally small. The crura cerebri are traversed below by
the great commissure of the cerebellic hemispheres, the
tuber annulare, which is more or less provided internally
with transverse strata of cineritious matter.

The optic lobes, reduced in size, generally without ca-
vities, and traversed externally by sulci, which give them
a quadrigeminous appearance, are largest and most exposed
above in the lowest mammalia, as the rodentia and edentata,
they are larger in herbivorous than in carnivorous quadrupeds,
and are least in bulk, and most concealed in quadrumana
and man. The anterior lobes of the corpora quadrigemina
are larger than the posterior in herbivorous mammalia, the
posterior are the larger in carnivora, and these lobes are
nearly equal in the highest orders of this class. The ce-
rebral hemispheres follow a contrary ratio in their deve-
lopment, being smallest and destitute of convolutions in
the rodentia, and becoming larger in every dimension and
more marked with deep convolutions, as we advance up-
wards to man. The optic thalami and the corpora striata
encrease with the expanding hemispheres, while the olfactory
tubercles progressively dimmish. The olfactory tubercles

NERVOUS SYSTEM. 241

are greater in size, more cineritious externally, and contain
wider prolongations of the lateral ventricles in herbivorous
than in carnivorous quadrupeds. The lateral ventricles
always present the anterior and inferior cornua, the choroid
plexus, and the to3nia semicircularis between the thalami and
the corpora striata. The great transverse commissure of the
cerebral hemispheres, the corpus callosum, is here at its max-
imum of development, as are also the anterior and posterior
commissurse cerebri and the fornix, and we can always per-
ceive the hippocampus major, the septum lucidum between
the lateral ventricles, and the pineal gland with its two pe-
duncles. The cineritious matter is now less abundant on
the surface of the brain proportionally to the white fibrous
part within, and the external convolutions, which are still
wanting on the smooth bird-like brains of the montrema and
the rodentia, are very superficial in the cetacea, edentata,
ruminantia, and pachyderma. The convolutions penetrate
deeper in the large expanded hemispheres of carnivora, qua-
<lrumana and man, where we observe also the cerebrum to
pass more and more backwards over the cerebellum. The
symmetry of the convolutions on the two cerebral hemi-
spheres is most distinct where they are few and deep, as in
carnivora and quadrumana, and the laminae of the cerebellic
hemispheres encrease in number and depth as we ascend to
man. The brain of herbivorous quadrupeds is thus distin-
guished by several indications of inferior development from
that of carnivorous species, as seen in comparing the brain
of the pecari, Dicotyles torquatus, (Fig. 99. A,) with that of
the lion, Felis leo, (Fig. 99. B.) In the herbivora the spinal
chord and medulla oblongata (99. A. #, b,) are larger and
broader, compared with the cerebral parts which lie before
them, than in the carnivora (99. B. a, b,) and in the carnivora
the corpora pyramidalia (99. B. b}) the crura cerebri (99, B. d,)
the cerebral hemispheres (B. #, h,) the corpus callosum, the
cerebellic hemispheres (B./,/,) and the tuber annulare (B.c,)
are proportionally larger than the corresponding parts in the
vegetable-eating quadrupeds (99. A.) The convolutions are
more superficial on the narrow and short cerebral hemi-
spheres of the pecari, (99. A. g, h,) the hollow olfactory tu-
bercles or processus mammillares (99. A. 7c,) communicating
by wide canals with the lateral ventricles, are larger ; the in-

PART III. R

242 NERVOUS SYSTEM.

FIG. 99.

fundibulum (99. A. e,) like the hypophysis of a reptile, is
more broad and extended ; the corpora quadrigemina are
larger and less covered by the hemispheres, and the trans-
verse sulcus divides them more posteriorly than in the lion,
(99. B.) This transverse sulcus is wanting on the optic
lobes of the ornithorhyncus, where they are nearly as smooth
and undivided as those of a bird, and its cerebral hemi-
spheres are destitute of convolutions, like those of many
rodentia, edentata, and marsupialia. The broad cerebral he-
mispheres of the lion are surpassed in lateral extension by
those of the seals, and these parts in the dolphin surpass
those of all the other mammalia by their great breadth and
by the number of their superficial convolutions. But in none
of these animals are the cerebellic hemispheres entirely covered
by the extension backwards of the cerebral, till we ascend to
the higher quadrumana, where we find in the pithed, or
orangs, almost every other character of the human spino-cere-
bral axis already distinctly developed, as the hippocampus
minor and posterior cornu of the lateral ventricles, the deep
cerebral convolutions and numerous cerebellic laminae,
the cineritious substance of the corpora olivaria and the
large corpora dentata, or ganglionic nuclei of the cerebellic
hemispheres.

NERVOUS SYSTEM. 243

While the great nervous centres have thus arrived at their
maximum of development in mammalia, most of the cranial
nerves, like the spinal chord, when compared to them, are
proportionately small. The olfactory nerves and tubercles
are largest in the ruminantia and pachydernia (99. A. k})
smaller in the carnivora (99. B. i,) cheiroptera, and quadru-
mana, and are scarcely discoverable in several of the cetacea.
In the inferior orders and in the large eyed nocturnal qua-
drupeds the optic nerves are of greater size than in diurnal
and higher species, and in the blind subterranean moles not
only are the optic nerves extremely minute, but the motores
oculorum,. the trochleares, and the abducentes can scarcely
be detected. The optic nerves in this class unite before the
infundibulum, where they form a partial decussation of their
component fibres (99. B. #,). and the ophthalmic ganglion is
always perceptible in the orbit. The second and third
branches of the trigeminus have a great external distribution
in the long-muzzled, the proboscidian, and the large-lipped
quadrupeds, as the cetacea, ruminantia, pachyderma, and car-
nivora, and their internal dental distribution varies according
to the number and magnitude of the teeth and of the per-
forated fangs which they supply. Their development is also
influenced by the presence of horns on the frontal or nasal
bones, or of spines or bristles extending from the upper lip,
as in aquatic and terrestrial carnivora, or by other circum-
stances which influence the general form of the head or face ;
and the same causes influence the development of the facial
nerves and their branches, as in the inferior classes of verte-
brated animals. The bills of the ornithorhyncus, like those of
many aquatic birds, are supplied with large branches of the
superior and inferior maxillary nerves, and the pneumo-gas-
tric nerve in this animal is not united to the cervical portion
of the sympathetic, as it generally is in the neck of quadru-
peds. As the plan of development is most constant and ob-
vious in the great centres of animal and of vegetative life,
the spino-cerebral axis and the great sympathetic, it is chiefly
in those parts that we observe the highest condition arrived
at in the human body. The spinal chord of man (Fig. 100.
b9 i,) is smaller compared with the cerebral mass contained
within the cranium than in other mammalia, and short from the
want of caudal prolongation of the trunk ; its posterior and

B 2

244

NERVOUS SYSTEM.

middle enlargements (100. c. e?,) are conspicuous, and of a
lengthened form from the magnitude and number of the
nerves which proceed from them to the sacral and atlantal
extremities ; the cauda equina, ( 1 00. a, b,) is of great length
from the high and sudden FIG. 100.

termination of the spinal
chord; the motor roots (100.
I, /,) and anterior columns
are smaller than the sensi-
tive, as in other animals, and
the ganglia of the posterior
or sensitive roots (100. £,)
of the spinal nerves are here
larger than in other mam-
malia. The medulla oblon-
gata, though comparatively
small, has its component
fasciculi most deeply marked,
and the quantity of internal
ganglionic matter in the
course forwards of these
white fibrous fasciculi, cor-
responds with their great
development in the human
cerebral and cerebellic he-
mispheres, where the convo-
lutions (100. g,) and laminae,
(100. h, i,) surpass in num-
ber and depth those of al-
most all inferior animals,
but where the use or func-
tion of any filament has not
yet been determined. The
great systems of converging
fibres which cross the median
plain, which form the corpus
callosum, the tuber annu-
lare, and the various smaller
commissures, and which have
appeared to some as conti-
nuous with the diverging or

NERVOUS SYSTEM. 245

ascending fibres from the periphery of the cerebral mass, and
as forming the posterior or sensitive columns of the spinal
chord by their descent from the brain, are larger than in the
lower orders of quadrupeds. The periphery of the whole
body is now the most largely supplied with symmetrical
nerves of motion and sensation, whose roots are the most
imbedded and approximated ; the great central columns of
these nerves are the most intimately and compactly united
to each other in every part of the axis, and in passing from
the embryo state to this most complicated condition, the
great spino-cerebral axis of man presents successively the
various conditions exhibited as adult forms in the lower
classes of animals. The great sympathetic also presents its
highest condition of development in quadrupeds and man,
being here most intimately united with all the spinal and
cranial nerves from the caudal extremity of the trunk to the
trigemini, or fifth pair of cranial nerves. It forms numerous
distinct cineritious ganglia in the head, on both sides of the
neck, along the two sides of the vertebral column, and in
the three great cavities of the trunk, the thorax, the abdomen,
and the pelvis, embracing with its large anastomos-
ing plexuses and ganglia the great arteries proceeding
to the viscera, and; thus it establishes in the most com-
plicated of animal forms the greatest unity of action and
mutual dependence of all the organs of animal and of vege-
tative life.

246 ORGANS OF THE SENSES,

CHAPTER FIFTH

ORGANS OF THE SENSES.

FIRST SECTION.

General Observations on the Organs of the Senses.

THE power of locomotion enjoyed by animals, and their
mode of nutrition by the conveyance of foreign matter into
an internal sac, require them to possess the means of obtain-
ing cognizance of the properties of surrounding objects, that
they may direct their motions suitably to their ends, and
distinguish what is congenial from what is deliterious to
their nature. These means of establishing the most intimate
relation between external objects and the internal sentient
principle, are the organs of the senses, which are instruments
placed at the peripheral extremities of certain sensitive
nerves, generally those nearest the anterior extremity of the
trunk, or around the entrance of the alimentary canal, and
which vary in their structure according to the properties of
outward matter to which they relate. The organs of the senses
are thus necessarily placed in connexion with the external
surface of animals, and are not situate upon any of the insen-
sitive motor nerves which merely communicate activity to
the muscular fibres, nor upon the great ganglionic or sympa-
thetic system of unsymmetrical nerves by which the organs
of vegetative life throughout every point of the body are
kept in incessant activity without our consciousness, but

ORGANS OF THE SENSES. 247

only upon the distal terminations of the symmetrical sensi-
tive filaments of the great nervous axis of animal life. In
the vertebrated animals these optical, acoustic, and other in-
struments destined to modify the external impressions so as
to produce more distinct perceptions, are mostly placed at
the ends of the sensitive nerves which issue from the inter-
vertebral foramina of the cranium, and are supplied by other
nervous branches indispensible to their function. The cir-
cumstances which necessitate the existence of such organs
in animals, also require them to be more numerous and va-
ried in higher than in lower tribes, and to be most perfect
and delicate where the locomotive powers, and consequently
the dangers are greatest. Hence they are more developed
in the active insects and other entomoid articulata, than in
the slow and torpid mollusca, and are most numerous and
perfect in the vertebrated animals where they have to watch
over the most complicated and delicate forms of organisation.
The columns of nerves appropriated to sensation are greater
than those of motion throughout the animal kingdom, and
they are spread more extensively through every part of the
body, so that almost every point is sensitive to impressions
of the density or resistance of outward bodies, to the feel-
ings of heat and cold, and to that of pain when they are in-
jured. This general sensibility, which watches over the
well-being of every part of the body, is most acute in the
skin, the common covering of all the organs, and the sensa-
tions belonging to all the senses are but modifications of
this, as their organs also are mostly developments from the
cutaneous covering of the body. As the apparatus for diges-
tion are the most important to the maintenance of life, and,
next to the cutaneous covering, the most universal in the
animal kingdom, the general sense of touch is probably first
modified or speciallized at their entrance, to constitute that
of taste which most immediately relates to this function;
and so are successively developed the various other senses
of animals, as those of smelling, hearing and vision, of which
we are conscious, and which make known the physical or the
chemical properties of external objects at greater and greater
distances from the sentient body. The sentient nerves are
thus very differently modified at their peripheral expanded
terminations to adapt them for receiving impressions from

24S ORGANS OF THE SENSES.

bodies directly applied to the skin, or from sapid bodies dis-
solved in the secretions of the mouth, or from odorous ema-
nations diffused through the surrounding element, or from
simple undulations of that element reaching the surface of
the body, or from those finer vibrations which constitute the
phenomena of light. There may be many other kinds of
impressions derived from outward bodies, for which the
sensitive nerves of the lower animals are adapted, besides
those which affect us, and we cannot always be certain of
the identity of the feelings communicated to them by organs
which appear analogous to our own. Although we often
cannot detect distinct organs for the senses which we ascribe
to the lower animals, these organs are commonly enumerated
according to the supposed generality of their function in
the animal kingdom, from the most general feeling of the
nervous system, or the sense of touch to that of vision or of
hearing, but the most general organ of sense perceptible in
animals, as superadded to the nerves of feeling already de-
scribed, is that of vision which relates to light, so universally
diffused through nature, and so influential on both kingdoms
of organized beings and even on the constitution and proper-
ties of unorganized bodies.

SECOND SECTION.

Organs of Vision.

Many animals, like plants, are affected sensibly by light,
without their exhibiting either organs of vision or a single
filament of nervous matter. As plants, guided by light, open
and close their flowers and their leaves, or follow with their
expanded flowers the diurnal course of the sun, or seek his
light with their slow-moving branches and their leaves with-
out a perceptible nervous system, so we observe the nerve-
less gemmules of poriferous animals, and of zoophytes guided
by the same agent in selecting a proper place for fixing and
developing ; the hydra, without eyes or nerves, uniformly
moves to the light, the eyeless actinia shuns its influence,
and many zoophytes expand or contract their whole body

ORGANS OF THE SENSES. 249

or their polypi from the influence of this agent though desti-
tute of visual organs.

Distinct organs, however, appropriated to light, are already
perceptible in animals where no nervous filament has been
detected in any part of the body. Many polygastric animal-
cules, as the cercaria, are obviously sensible to light, and
move towards it like the hydrse, and they generally present
on the anterior part of their body one or more small round
opaque red coloured spots which have long been recognised,
figured, and described as the eyes of these minute animals.
Several, as the euglena longicanda and ophryoglena flavicans,
have but one eye, placed on the middle of the upper and
anterior part of their body, a monoculous character in which
they resemble the microscopic species of some higher classes
of animals. Eyes have been detected in most of the genera
of polygastrica, down to the monads which are mostly mono-
culous, and even the minute monad-like beings which unite
to form the volvox globator, the eudorina elegans, and some
other remarkable compound or aggregate animalcules, are
provided with single red-coloured organs of vision placed
near the part of their trunk from which the caudiform vibra-
tile appendix is prolonged. These minute red points of the
polygastrica are as obviously eyes, though of the simplest
structure, as are those of rotifera where we can perceive their
optic nerves and ganglia, and where they have the same red
colour and general disposition as in the polygastrica. This
superficial or cutaneous opaque spot, to absorb the rays of
light, without forming an image of external objects, is the
first form of the eye which we see also in annelides and in
the larvae of insects, and the young of higher classes, when
that organ is beginning to develop ; so that when the optic
nerve is superadded to this pigment, or choroid, or coloured
rete mucosum, it is first developed behind this opaque mat-
ter, as we frequently find it placed in the eyes of inverte-
brated animals, even when transparent parts are added to
collect light, or to form an image of external objects to be
transmitted through a hole in this choroidal pigment to the
subjacent nerve. The numerous vibratile organs of locomo-
tion, and the rapid movements and free condition of polygas-
trica require this general development of visual organs in
them, while the slow movements or the fixed condition of

250 ORGANS OF THE SENSES.

most other radiated animals render less necessary in them
the development of organs of this nature, and they have not
been detected in any of the poripherous or the polypipherous
animals, unless the bright coloured opaque points seen on
the disk of the locomotive actiniae, and of some other polypi
are organs destined to absorb and to communicate impres-
sions of light. In the acalepha, organs of vision have yet
been observed only in the medusa aurita, where they are mi-
nute round points on the dorsal side of eight brown globules,
placed on little peduncles, in the eight depressions around
the free edge of the mantle, and they have the same red co-
lour as those of many other transparent animals as polygas-
trica, rotifera, and entomostracous Crustacea. These eight
small, red, pedunculated eyes directed upwards, are provided
each with a crystalline lens, an optic ganglion, and two de-
cussating optic nerves derived from the exterior circle of
nerves which accompany the marginal canal of the mantle,
and they are placed near the bases of the marginal tentacula,
like the numerous marginal pedunculated shining eyes of a
spondylis or a pecten among the conchifera. The organs of
vision in the echinoderma, as well as those of the acalepha,
have been long figured by authors, though their nature has
been till lately overlooked. Beneath the distal extremity of
each radiating division of the body of the asterias violacea
and asterias militaris, a small, circumscribed, round, red
coloured, retractile point is observed, as represented by Vahl,
which rests upon a small optic ganglion at the end of each
of the five radiating nerves. These are analogous in their
position and characters to the common visual organs of ani-
mals thus low in the scale, and probably will be found on
holothurise and other active echinoderma, where the nervous
system is most developed. They yet present no transparent
parts besides the cornea which has sometimes a glistening or
shining appearance even in polygastrica.

The organs of vision, like the nervous and muscular sys-
tems and all the other organs of relation, present a high degree
of development in the lively and active articulated animals,
and they are common in almost every class of this division.
From the general structure and habits of the entozoa and the
density and opacity of the medium in which they commonly
reside, they little require the aid of eyes or of any other or-

ORGANS OF THE SENSES. 251

gans of sense, and none have been detected in the lowest cystic
forms of this class. In the scolex, however, among the ces-
toid entozoa, two minute red-coloured shining eyes have
been long observed, and two of a dark colour are found be-
hind the mouth in the polystoma, one of the flat trematoid
worms. But these organs are more commonly perceived on
those remarkable entomoid kinds of parasitic worms which
attach themselves to the surface of aquatic animals, and are
in that situation more exposed to the influence of light and
of the surrounding element, as various forms of lernsese.
The eyes are sessile in these epizoa, and most commonly
form a single organ on the median plain, as in many of the
entomostracous Crustacea which they at first so much re-
semble. In some the eyes are more numerous, and are
placed apart from each other, as in the gyrodactylus auricu-
latus, found attached to the gills of the bream, where there
are four minute red-coloured eyes, placed in two pairs be-
hind each other on the back part of the head. In the ach-
theres percarum, there is a single round prominent eye on
the fore part of the head, between the two short antennae,
which is very obvious through the coverings of the ovum,
and in the young animal in its free unattached condition, and
in this species the organ of vision remains through the whole of
life. But in the lernceocera cypinacea, where the little red
coloured circular eye, placed on the fore part of the head,
is also distinctly seen in the ovum, and continues through-
out the free and entomostracous state of this remarkable
animal, it is entirely lost after the metamorphosis and no
trace of it can be detected in the adult fixed condition of
this parasitic worm. The same disappearance of the eyes
has been observed in some of the rotifera. In nearly all the
rotiferous animalcules, however, eyes are distinctly observ-
able, of a round form, of a red colour, often two in number,
sometimes united to form a single organ, sometimes four as
in the meglotrocha, or a greater number as in the cydoglena,
and placed on the upper and fore part of the body. Their
constancy x their number, and their high development in the
wheel-animalcules corresponds with the general advanced
organization and the numerous active organs of locomotion
possessed by these minute transparent animals. From the
transparency of all their parts and the deep red colour of the

252 ORGANS OF THE SENSES.

choroidal pigment the eyes of the rotifera, like those of the
epizoa and those of most of the higher articulata and mol-
lusca, are very obvious in the embryos while yet within the
ovarium, or while the unhatched ova are yet suspended from
the exterior of the parent. They are commonly placed near
the large supra-oesophageal ganglion, and nervous filaments
are sometimes observed distinctly to pass into these organs.
They are protected by a smooth transparent and sometimes
glistening cornea, and when these little eyes are pressed be-
tween plates of mica or glass, the eye-ball is seen to burst,
and the deep red pigment, consisting of minute globules
united together by a transparent matter, is seen to escape
from the ruptured organ. A minute crystalline lens has
also been observed in some, behind the transparent cornea.
The fixed condition of the cirrhopods in their adult state,
inverted in their shell, and the opacity of their exterior
covering, afford little occasion for the employment of visual
organs in that condition of their life, and they have not been
observed in any of the mature animals of this class. Before
their metamorphosis, however, in their young and free con-
dition, the cirrhopods possess a distinct black coloured me-
dian organ of vision formed by the juxta-position of the two
lateral eyes as in many monoculous animals of other classes.
These two eyes, formed by the division of one primary organ,
appear to be covered with a smooth transparent cornea and
to enclose a small crystalline lens, and they are lost by the
metamorphosis like the eyes of many other articulated
animals.

In most of the free annelides there are numerous and very
distinct organs of vision, which commonly project shining or
glistening from the dorsal surface of the head, and contain a
minute transparent lens added to the variously coloured dark
pigment and the optic nerve. The eyes are here generally sim-
ple, sessile, slightly moveable, and placed apart from each in
transverse or longitudinal rows. In the little prostoma arma-
tum the head is covered with oculiform points of a dark colour,
in the minute prostoma clepsinoideum, a small planaria, there
are six of these organs, and in other species of prostoma four
are observed. Several of the planaria have two deep co-
loured eyes, in some as the planaria viganensis, there is a
single row of about forty eyes, passing round all the fore

ORGANS OF THE SENSES. 253

part of the body, and the same arrangement is seen in the
planaria nigra, which corresponds with the circular arrange-
ment of the same organs around the margin of the mantle
in some of the most active conchifera. The same transverse
arrangement is seen in the ten prominent eyes disposed
across the head of the medicinal leech. In the bdella nilotica
there are six eyes disposed transversely on the upper part of
the first segment, in the polynoe impatiens they are disposed
laterally in pairs. The optic nerves of some of the higher
annelides are observed to terminate in a broad circular pa-
pilla or retinal expansion. The choroid pigment behind the
crystalline lens in the medicinal leech is red in the young
animal and changes to black in the adult state, as observed
in many other animals. In the nereis nuntia (Fig. 14) there
are four large eyes disposed symmetrically in two pairs on
the upper part of the head, and nearly a hundred smaller
ocular points disposed in rows and groups on all the promi-
nent lobes around the mouth. In the syllis monilaris, there
are two pairs of eyes with prominent glistening cornese dis-
posed on the upper segment of the head. In some of the
higher forms of this class, however, as the euphrosine laureata
and the oenone lucida, the visual organs are reduced to two,
symmetrically disposed on the upper part of the first seg-
ment of the head, and thus approach to the normal character
of these organs in most of the higher classes of animals.

In the entomoid classes of articulata, the most active of all
the invertebrated animals, the organs of vision are very nume-
rous and commonly aggregated together to form two groups, or
two compound eyes symmetrically disposed on the upper or la-
teral parts of the head — a compound character which com-
mences as low as the rotifera by the approximation of the se-
parate ocular points. The eyes of the myriapods partake some-
times of the character of those of the inferior annelides and
sometimes of those of the higher forms of insects, and in
some species no organs of vision have been detected. Most
of these animals present numerous separate simple eyes
grouped together on the two sides of the head. The two
lateral eyes of the scolopendra consist each of a group of
about twenty-three small distinct eyes approximated and
placed in lineal rows, and the aggregate eyes of the iulus are
also composed of several rectilineal rows. The scuttgera has

254 ORGANS OF THE SENSES.

large eyes like those of an insect, where however the
several cornese are more round and larger than in
the compound organs of the true hexapodous insects.
The compound eyes of insects consist merely of a closer ag-
gregate of many of these more detached organs of the myria-
pods, forming hemispherical sessile masses of sometimes ten
or twenty thousand eyes on each side of the head, and these
are often accompanied by a few small separate simple eyes
placed more posteriorly. Lewenhoek calculated 1200 facetts
in the eye of a libellula. They are compound even in the
apterous lepisma, where they are accompanied by three simple
eyes, as in many of the higher winged insects, but the coleop-
terous insects, which approach nearest to the higher crus-
tacea in the concentrated forms of many of their organs,
possess only the two compound eyes. The larvae of the co-
leoptera and hymenoptera are often destitute of eyes. In the
compound eyes of insects the epidermis appears to continue,
as we see in serpents, over the exposed surface of the
globe, but colourless, and transparent. Beneath this ex-
terior covering are placed the numerous transparent prismatic
hexagonal facettes, or corneae of the several minute compo-
nent eyes, as seen in the annexed section of a part of the eye
of melolontha vulgaris, (Fig. 101. A. «.) Within this thick
continuous exterior layer of aggregated transparent hexagonal
corneas are placed the small conical transparent lenses, (101.
A. b, B. b9) of a regular tapering form and smooth rounded
surface, of a firm horny texture and colourless transparency.
The hexagonal corneas of the sphinx atropos are only the
sixtieth of a line in diameter. The flat bases of the lenses
directed outwards are applied to the inner surface of the

ORGANS OF THE SENSES. 255

corneee, and their pointed apex is turned inwards to the pe-
ripheral or retinal ends of the separate minute optic nerves
(101. A. c.) These small conical horny lenses are easily
scraped off from the inner surface of the cornea when their
regular form and smooth surface (101. B. b, b,) are best ex-
amined, and they acquire a whitish opaque colour by the ac-
tion of alcohol, like the fibrous lenses of the higher classes
of animals. They are surrounded by the choroid pigment,
and in some insects, as the libellula, this coloured choroid
forms a sort of iris or uvea between the flat base of the
lenses and inner surface of the cornese, and appear to leave
space for a small quantity of aqueous humour.

The lenses are very long in the eyes of the libellulse,
where they form lengthened slender nearly parallel cylinders
tapering very slightly to the retinal ends of the optic nerves.
They are generally shorter in proportion to their breadth in
other insects, like those of the melolontha (101. B. b, b.) The
separate slender optic nerves (101. A. c9) proceed backwards
from the apices of the lenses, though the semifluid pigment
or vitreous humour, consisting of variously coloured globules
to the great optic ganglion within the globe of the eye, which
is almost a prolongation of the cerebral or optic lobes them-
selves (Fig. 83. D. 1.) The undulations or rays of light
have thus an uninterrupted passage in the compound eyes of
insects through the outer transparent homogenous epidermic
covering, then through the transparent central axes of the
prismatic hexagonal cornese, and lastly through the pupilar
openings of the choroid and the axes of the conical hard
lenses behind them, where they reach the terminal or retinal
papillae of the several optic nerves, by which the impressions
are felt or transmitted to the brain.

Besides these compound eyes, insects in their mature state
often present at the back part of the head several simple de-
tached sessile eyes or ocelli, like those common in the infe-
rior articulated classes, and these are alone developed in the
larva-state of insects with perfect metamorphosis, as those
of orthoptera. In these ocelli of the larvae, as shown by
Lyonet in that of the cossus ligniperda, nearly the same
structure exists as in each of the component organs in the
compound eye of the perfect insect. There are six ocelli in
the cossus9 disposed in a circular order on the parietal lamina,

256 ORGANS OF THE SENSES.

they have a cup-like form, each is covered with its convex
cornea, having a transparent axis, and behind this is the
little hard spherical crystalline lens, together with the vitreous
humour, the chorid and its pigment, and the optic nerve.
Each ocellus receives a branch of a trachea along with its
nervous filament, and the tracheae have been traced also into
the compound eyes of perfect insects. Most generally there
are three ocelli, in perfect insects, behind each compound
eye, on the sides of the head. Some insects, as the claviger,
appear to possess neither simple nor compound eyes, nor any
other organ of vision, like many of the helminthoid animals
beneath them. The eyes of the higher forms of insects are
thus numerous, and varied in their directions, from the ses-
sile and immoveable character of these organs, and to suit
the rapid and varied movements of these animals \ and they
compensate for the want of the external protecting apparatus
of higher classes, by the density and insensibility of the out-
ward exposed parts of these organs, which they cleanse from
adhering matter by the brushes of hair developed on their
tarsi, or some other moveable parts. Hairs are often deve-
loped from the surface of the compound eyes, originating from
the depressions between the hexagonal cornese, and some-
times the margins of the corneae are themselves extended
outward like the hexagonal tubes of a honey-comb, as in the
sty fops. The eyes of the arachnida are the largest and most
perfect forms of the ocelli met with in the articulated classes ;
like those of the myriapods they are simple and sessile organs,
while those of Crustacea are compound, like those of insects,
and are generally pedunculated. From two to twelve of
these smooth eyes are found in the arachnida, and the largest
forms of the organs are presented by the scorpions where
their structure has consequently been most satisfactorily ex-
amined. They are commonly arranged symmetrically in one
or two transverse rows on the upper and fore part of the ce-
phalo-thorax, as we observe those, generally eight in number,
arranged on the back of the spiders. Beneath the prominent
convex cornea in the large ocelli of the scorpion there is a
spherical firm transparent lens, more like that of a molluscous
or of a vertebrated animal than that commonly found in the
entomoid articulata. There is a considerable vitreous humour
filling half of the eye-ball, placed behind the crystalline lens,

ORGANS OF THE SENSES.

and surrounded by the pigmentum and the choroid, excepting
on the fore part, where it bounds the pupil like an iris, and
on the back part, where it is penetrated by the optic nerve.
The optic nerve expands into a cup-like retina investing, with
the hyaloid membrane, all the convex posterior surface of the
vitreous humour. A disposition of the vitreous humour
with its retinal and hyaloid membranes, very similar to this,
has been observed even in the compound eyes of some noc-
turnal lepidopterous insects, which is perhaps more general
in that class. So that this optical instrument has already all the
essential parts presented by the highest forms of the organ, and
approaches the nearest to that of the vertebrata. The structure
of the simple eyes or ocelli of the mygaleand of the tarantulse
appears to be the same as that of the scorpion. The eyes of
crustaceous animals are compound, like those of insects ;
in the higher orders they are pedunculated, and moveable
by means of muscles inserted within their exterior hard
sclerotic covering ; they are commonly sessile and immove-
able, like those of insects, in the inferior Crustacea; and in
the lowest entomostracous forms the two sessile eyes are
frequently united on the median plain, to form a single
organ, a character approximating these parasitic Crustacea to
the epizoa and to many other inferior articulata. The
internal structure of these compound eyes is nearly the same
as those of insects, and was early illustrated by Lewenhoek,
who first observed the numerous small conical crystalline
lenses within the exterior layer of contiguous prismatic
transparent cornese in the astacus fluviatilis. The epidermis
in the compound eyes of Crustacea passes transparent and
homogeneous over the exterior surface of the thick layer of
prismatic cornese, which are here, as in insects, generally
hexagonal, but sometimes quadrangular, and to the internal
ends of the prismatic cornese are applied the broad bases of
the hard tapering transparent lenses which have their internal
truncated apices directed to the retinal expansions of the
numerous optic nerves. The whole sides of these transparent
conieal lenses, as well as the optic nerves extending back-
wards from their inner ends, are covered, as in insects,
with the dark choroid pigment, so that only a small pencil of
light gains admission through these long narrow darkened
tubes to the small aperture at the posterior truncated ends

PART III. S

258 ORGANS OF THE SENSES.

of these lenses, where the optic nerves terminate, as usual, in
their small soft retinal expansion. The optic nerves through-
out their course in the eye-ball are enveloped in the same
dark pigment which coats the lenses. The lenses in the
cray-fish and in the palcemon sulcatus, are not round in their
outline, but four-sided truncated pyramids ; most generally,
however, they are regular smooth cones truncated at their
interior apex, and they are seen of this form even under the
smooth and undivided corneas spread over the eyes of mono-
culi. In the compound eyes of the branchipus stagnalis, how-
ever, it has been recently observed that, behind the smooth
surface of the corneas, there are distinct round or ovate
lenses supported each on the anterior end of an elongated
vitreous humour. This vitreous body tapers backwards to
the optic nerve, it is enclosed in a hyaloid membrane which
embraces also the posterior half of the lens, and it is entirely
covered externally by a retinal expansion of the optic nerve
as far as the middle of the lens ; thus presenting a structure
similar to that lately detected in the compound eyes of several
insects. There are about five thousand eyes in the two com-
pound organs of the lobster. The optic nerves in the
Crustacea, as in insects, enlarge into an optic ganglion
within the globe of the compound eye, from which ganglion
the small filaments radiate outwards to the separate lenses
of the component eyes, and each minute eye appears to have
a pupilar extension of the choroid around the anterior surface
of its lens. Thus the compound eyes of the Crustacea and of
insects are but repetitions of the simple organs of the leech
and the planaria, and probably of the ocular papillae of the
hydatina, the medusa and the monad. The mobility so re-
markable in the pedunculated eyes of the decapods is already
perceptible in the elevation and retraction of the isolated
organs of the annelides, and this power of varying the direc-
tion of the organs is greatly en creased in the pedunculated
eyes of mollusca and even of some fishes. In the great deve-
lopment of the cornea and the lens throughout the articulated
classes, we observe the early perfection of the most dense
and refractive parts, on which the optical properties of this
organ chiefly depend.

The organs of vision are less required and less generally
developed in the slow moving or fixed molluscous animals

ORGANS OF THE SENSES. 1?59

than in the active articulated classes, and they are never
aggregated together to form groups of simple eyes, like those
of myriapods or arachnida, nor compound organs like those
of insects and Crustacea. Where they occur in the acephalous
mollusca they are numerous, simple, and separate as in worms,
but in the higher forms of gasteropods, pteropods and
cephalopods their structure is more complex and their num-
ber is reduced to two, which are symmetrically disposed
on the sides of the head, as in all the vertebrated classes.
The tunicated animals, like the cirrhopods in their adult
state and like most of the entozoa, fixed and buried under
an opaque covering, appear to be destitute of visual organs,
and for the same reason these organs are as little required
and are wanting in most of the inhabitants of bivalve shells.
In the free and quick moving pectens, however, which swim
rapidly backwards by the quick and repeated contractions of
their valves, there are numerous distinct pedunculated eyes,
placed at the bases of the palleal tentacula all around the
free margins of the mantle, and these have long been figured
and recognised by naturalists as organs of vision common to
many of the conchiferous mollusca. They are placed in the
most exposed and the most sensitive part of the animal, and
by their pedunculated character and their position beside the
tentacula they resemble the eyes of gasteropods. They are
nearly a quarter of a line in diameter and more than fifty in
number in the pecten maximus. They have a round promi-
nent smooth cornea and contain an opaque shining choroid
embracing a small crystalline lens. Their nerves are probably
as in the gasteropods, derived from the tentacular branches
passing along the bases of their peduncles. Their forms, dis-
tribution and structure are the same in the spondyli as in the
pectens, and their shining lustre, in both these genera, is
compared to that of the emerald by Poli who has given en-
larged views of their microscopic structure. The eyes of the
gasteropods are always two in number, placed on the ante-
rior part of the body, moveable, and generally pedunculated.
Some of the naked dorsibranchiate gasteropods as the eolis,
the doris, and the glaucus appear to be destitute of these
organs. In the naked aplysia they appear as minute black
points on the smooth surface of the neck. In the pectini-
branchiate species they are most frequently placed on tuber-

s 2

260 ORGANS OF THE SENSES.

cles extended from the bases of the two tentacula, as seen
in the annexed figure of the common cyprcea tiff res (Fig 102.)

FIG. 102.

from the South Seas, where the two long tentacula (102. «,
a,) present near their bases two prominent, round, black and
moveable eyes (102. c, c,) with smooth glistening transparent
cornese. The tentacula being extended above the mouth
(102. b,) and anterior to the syphon (102. d), the eyes,
which are raised on tubercles at some distance from the base
of the long slender tentacula, have a considerable range of
vision. Above the large expanded foot (102. g, #), is seen
the inner surface of the mantle (102. e), turned up over a
portion of the shell (102. h)9 and covered with small ramified
tentacular extensions (102. /), which apprise the animal of
danger from behind. In some of the gasteropods, as the
haliotis, Umax, helix, and onchidium, the peduncles of the
eyes are as long as the tentacula themselves. According to
Chiaje the doris and the thetis have pedunculated eyes, and
Ehrenberg has observed organs of vision in the hexabranchus
and the phyllidia. The position of these small dark eyes at
the exterior of the base of the tentacula is already represented
in the buccmum undatum (Fig. 22. d, d), and in the harpa
elongata (Fig. 92. s, s,) where they are a little further re-
moved from the base ; and in the carinaria mediterranea
(Fig. 89. f, /), where the optic nerves are seen passing to
them directly from the cerebral ring (89. i). The internal
structure of these simple eyes of the gasteropods much re-
sembles that of the large ocelli of the scorpions and other
arachnida. In the eyes of the helix pomatia, which are
raised to the ends of long tubular muscular peduncles exceed-
ing the length of the tentacula, Swammerdam observed a
thin aqueous humour, a more consistent vitreous humour,

ORGANS OF THE SENSES.

a pupil and iris, and a distinct crystalline lens ; and in the
eyes of the cyclostomum viviparum, as well as in that anato-
mised by Swammerdam, a distinct crystalline lens, a coloured
choroid coat, and also an iris were detected and described
by Stiebel. The structure of the eye in the helix pomatia and
in the murex tritonis has also been described and represented
by Muller (Fig. 103). The eye of this helix (103. A. a), is
attached to one side of a large moveable bulb (103. A. b),
and presents a compressed crystalline lens (103. B. a), a
thin aqueous fluid, and a larger vitreous body (103. B. b),
covered by the dark choroid coat. This ocular bulb (103. A.
b), with its attached eye (103. A. «), can be extended from,
or retracted into the sheath of its tubular peduncle, and is
supplied with a large nerve (103. A. d), which gives off the

FIG. 103.

optic (103. A. c), as is done by the tentacular branch in most
other gasteropods. A similar bulb is seen attached to the
eyes in some other mollusca (Fig . 93. A. c). Blainville ob-
served a large crystalline lens in the eye of the voluta cym-
bium, which projected anteriorly like that of a sepia, a small

26*2 ORGANS OP THE SENSES.

pupilar opening of the choroid behind the transparent skin
which formed a distinct convex corneee over the organ, and
two small muscles behind for the motion of this sessile eye.
A similar structure nearly was found by Muller in the large
eyes of the murex tritonis (Fig. 103. C. D. E), where they
occupy their most frequent position at the outer part of the
base of the tentacula (103. C. a). In a few of the gastero-
pods they are placed on the inner part of the base of
the tentacula. The delicate skin of the tentaculum (C. a),
forms a thin transparent cornea (C, b), over the eye and
leaves a considerable chamber for the thin aqueous fluid
anterior to the iris (103. D. b,) and the pupil (103. D. a).
The eye is lengthened in the direction of its visual axis, and
the black circular iris (103. C. d. D. b), continued from the
coloured choroid, presents a large round pupil directed
obliquely outwards from the base of the tentaculum. The
interior of the large cavity surrounded by the choroid and
its pigment, appears to be chiefly occupied by the irregular
round pellucid amber-coloured mass of the crystalline lens
(103. E), and the optic nerve (103. C. e), which comes off
from the common tentacular nerve, enters the eye-ball ob-
liquely on the outside of the axis of vision. The organs of
vision, two in number and placed on the sides of the head in
the pteropods, though small in their dimensions, have pro-
bably an internal structure similar to that found in most of
the gasteropods. The position of these organs is seen in the
cymbulia of Peron (Fig. 24. c) and in the clio of the South
Seas (Fig. 6J. A, b), they are also obvious on the head of the
cleodora. In the cephalopodous animals these organs pre-
sent the greatest size and the most complicated structure met
with in any of the invertebrated classes, and they are even of
great size in proportion to the magnitude of the head and to
the general bulk of the body. As in the higher Crustacea,
and in some of the gasteropods and cartilaginous fishes, the
eyes are sometimes pedunculated in the animals of this class
as in the nautilus and the loligopsis (Fig. 93. A. c), and they
already present distinct external muscles for their movements,
and palpebral folds of the surrounding skin, which passes
transparent like a conjunctiva over their anterior surface to
form a smooth cornea, as in other mollusca. Like the eyes
of fishes, they are generally flattened in front from the defici-
ency of aqueous humour, and they are of great size from the

ORGANS OF THE SENSES. 263

magnitude of the optic ganglion (Fig. 93. C. c), which is
greater than the brain (93. C. a), and from the glandu-
lar masses (93. C. e, e,) contained within the outer layer
of the choroid and the thickened posterior portion of
the sclerotic (93. C. b), behind the retina and the inner layer
of the choroid as in the eyes of fishes. But a small part
therefore of these large organs is occupied with the trans-
parent optical apparatus, and their movements are nearly as
limited as those of a murex or a buccinum. There is a rudi-
ment of the membrana nectitans, or third eye-lid so gene-
rally developed in the vertebrated classes^ and the eye-lids,
like the iris, are still almost motionless. The ciliary pro-
cesses, as in the higher cartilaginous fishes, are remarkable
for their great development, and the crystalline lens for its
double structure and its great posterior convexity; it occu-
pies two thirds of the axal diameter of the eye in most of the
naked cephalopods, and consists of two plano-convex hemi-
spheres of unequal size applied to each other by their flat
surfaces. The vitreous humour, of a thin fluid consistence,
is enclosed in a distinct cellular hyaloid membrane, and the
soft loose pigment of the inner layer of the choroid is gene-
rally of a deep purple colour. In the loligo there is a small
aperture on the surface leading to the glandular cavity of the
eye like a lachrymal pore. The retina of the cephalopods is
placed, as in other animals, within or anterior to the pigment
and the inner layer of the choroid, as shown long since by
Chiaje, and the crystalline lens is composed of concentric
layers of minute transparent fibres, like that of vertebrated
animals. Thus in the isolated organs of vision of the mollus-
cous classes we constantly observe a crystalline lens and
transparent parts anterior to the optic nerves as in the
higher articulata; and in the general plan of their formation
and the higher complexity of their structure they form a
nearer approach to the ordinary condition of these organs in
fishes and higher vertebrated classes.

The eyes are two in number and symmetrically disposed
on the sides of the head in all the vertebrated classes and
nearly in all the species, and the differences which they pre-
sent relate chiefly to the density of the media through which
the various animals receive the rays of light, and the extent of
development of the external protecting parts of these delicate

264

ORGANS OF THE SENSES.

organs. From the imperfect development of the nervous
system of fishes and the obscurity of the element through
which they move, their organs of vision are of great size, and
from the density of the watery medium around them, they
have little necessity for aqueous humour in the eye, and their
cornea is flat. To preserve the eye of fishes flat in front,
the sclerotic is thickened and consolidated, as in the cetacea,
and it is also to prevent its assuming the spherical form in
birds, by the equal pressure of the contained fluids, that the
sclerotic is there strengthened with osseous plates, which pre-
serve the tubular form of the eye and the great convexity of
the cornea in that class. This thickness of the sclerotic coat
and the presence of the choroid gland and adipose substance
between the layers of the choroid coat behind, and the flat-
ness of the cornea in front shorten very much the visual
axis of the eye and diminish the space for containing the
vitreous humour ; hence a completely spherical form and
great size and density of the crystalline lens are here required
to bring the rays of light more quickly to a focus as seen in
the eye of the perch (Fig. 104. A. e). The crystalline lens is

composed, as in other classes, of minute transparent fibres,
which are disposed in concentric layers and variously united
by their serrated edges, the layers encreasing in density from
the surface to the centre of the lens. The diameter of the
lens (104. A. e) is often greater than that of the aqueous and
the vitreous humours, and concentrates the rays of light to a
focus before the retina, so as to form an inverted image on
that membrane. The conjunctiva is now more easily sepa-
rated from the cornea than in the cephalopods, and the
choroid and retina are here remarkable for the distinctness of

ORGANS OF THE SENSES* 265

the coats of which they are composed. Their eye-lids are
still as rudimentary as in the cephalopods, and the liquid
element around them is their only lacrymal as well as their
salivary fluid. The pupil is large in fishes and the iris is
almost motionless. The outer layer of the choroid passes
with its shining pearly lustre over the front of the iris, and
the dark inner layer lines the posterior surface of the uvea.
This inner layer forms a kind of pecten, passing obliquely
forwards to- the lens, but without the pigment which covers
it in birds. The ciliary ligament is always present, but the
ciliary processes are rarely developed, and the foramen
centrale is not perceptible in the axis of vision. The eyes
are generally quite lateral in their direction, and notwith-
standing the great irregularity of their outward form, the
sphericity of the retina is generally preserved by the glandu-
lar and adipose substances interposed behind between the
layers of the choroid coat. The sclerotic is easily perceived
to be continuous with the sheath of the optic nerve and the
dura mater, and sometimes, as in the xiphias, the consoli-
dated portion of the sclerotic envelopes the ball of the eye
like an osseous band, with a thickened anterior round margin
to receive the circumference of the cornea and to support the
periphery of the iris. The fatty substance commonly depo»-
sited between the layers of the choroid at the back of the eye
in fishes is traversed by numerous branches from the ocular
artery, and by the ciliary veins returning to the choroid
gland. The inner of the two layers of the choroid is often
distinctly separable into two, an exterior formed by the
straight parallel ciliary veins, and an interior, formed by the
ramifications of the ciliary arteries, on which the pigment
rests. The optic nerve (104. A. g), generally presents a con-
tracted appearance at the place where it penetrates the vas-
cular layer of the choroid (104. A. k)9 and expands into a soft
and pulpy retina which terminates by an even margin near
the base of the uvea. The organs of vision are smallest in
anguilliform fishes and such as burrow in the mud or sand ;
they are larger in predaceous fishes which frequent the dark
depths of the wide ocean than in those which reside on the
shallow coasts or in fresh waters ; their mobility is encreased
in the active muscular plagiostome fishes by being supported
on cartilaginous peduncles ; they are moved in fishes by

266* ORGANS OF THE SENSES.

four recti and two ooliqui muscles as in higher vertebrata ;
they are very rarely directed to one side of the head, as in
the pleuronectes ; sometimes the eye-lids are so perfect as to
be provided with distinct orbicular or sphincter muscles 5
and in several fishes the upper edge of the iris extends down
in form of a vine leaf over the middle of the pupil. The
pearly lustre of the exterior choroid seems due to crystalline
spicula, and from the deficiency of internal pigment the eyes
of many cartilaginous fishes have an internal shining lustre,
like the tapetum of the eye of quadrupeds.

The eyes of amphibious animals are generally interme-»
diate in their form and structure between those of fishes
which receive the rays of light constantly through the dense
medium of water, and those of the higher air-breathing
classes which receive them through the rare medium of
the atmosphere. These organs are still therefore of great
size, and flat in front from the small quantity of aqueous
humour, especially in the perennibranchiate species which
more constantly reside in the water. From the imperfect
ossification of the orbit the eyes have great lateral extent
of motion, they are provided with an upper and lower eye-lid,
and a very complete membrana nictitans, and as in other
oviparous vertebrata the lower eye-lid is more developed and
more moveable than the upper. The eye is large and provided
with a thick and firm sclerotic, as in fishes, in the frog
and the toad, but is very small in the pipa where it is
destitute of eye-lids, and the crystalline lens is spherical,
as in most other amphibia and in fishes. The outer layer
of the choroid has the pearly lustre of that of fishes and
passes shining over the fore-part of the iris around a pupil
still almost motionless, the ciliary processes are not developed,
and the retina forms a thick and pulpy external layer like that
of fishes. The eyes appear to be still destitute of lachrymal
apparatus, as in the former class, and in the proteus the
organs of vision are covered over by the opaque integuments
of the head.

The eyes of reptiles are more adapted to receive the
rays of light from the rare medium of the atmosphere than
those of fishes or amphibia, their cornea is therefore gene-
rally more convex, their aqueous and vitreous humours
more abundant, and their lens less spherical in form. They

ORGANS OF THE SENSES. 26*7

are generally provided with the ordinary straight and oblique
muscles, a distinct lachrymal apparatus, two moveable eye-
lids, and a membrana nictitans. In serpents the skin forming
the eye-lids passes transparent and continuous over the
eyes and their lachrymal organs, and the epidermis is thus
shed from the closed eye- lids as from the rest of the skin ;
the tears here bathe the concealed conjunctiva, and pass by
the lachrymal duct into the nose, as in higher animals. But
in the slow-worm, the eye-lids and the membrana nictitans
are formed as in saurian reptiles. The sclerotic is sometimes
firm and cartilaginous, sometimes it contains adipose sub-
stance behind the retina as in fishes, and in many as the
crocodilian reptiles, the iguana, the lizard, and the monitor,
and the tortoises and turtles, the fore part of the sclerotic
supports a circle of osseous plates which surround the
transparent cornea, as in birds. These plates around the
cornea existed also in the ichthyosaurus. The ciliary pro-
cesses are now considerably developed around the margin
of the flattened lens, especially in the crocodilian reptiles,
and the greater freedom and mobility of the iris from the
abundance of aqueous humour, allows of more extensive
and quick changes in the diameter of the pupil than in
the inferior vertebrata. The pupil is often extended vertically
in saurian and ophidian reptiles, as in many carnivorous
mammalia, and a dark pecten in many lacertine and cro-
codilian reptiles, is prolonged from the choroid coat into
the vitreous humour, as in birds. The pulpy and fibrous
layers are obvious in the retina, and its central foramen
is seen in many of the species. The eyes of the chamseleon
do not move simultaneously, the two eye-lids are united
over the eye excepting a small vertical slit opposite to
the middle of the pupil, and the concealed membrana
nictitans is nearly as large as in birds. In the eye of
emys europaea (Fig. 104. B.) the cornea («) is pretty convex
from the abundance of aqueous humour (b) in the anterior
chamber, and the margin of the cornea is supported by
ten osseous plates (104. C. d.) imbricated like those of birds,
and placed in the anterior part of the sclerotic (104. B. d, d,)
near to the ciliary processes, (104. B. /.) and to the fixed
margin of the iris (104. B. e.) The crystalline lens (104. B.
g.) has a compressed eliptical form, and a smaller axis than

268 ORGANS OF THE SENSES.

the vitreous humour (104. B. h.) The retina terminates
with a thickened edge at the beginning of the ciliary pro-
cesses, and a similar structure is presented in most of the
chelonian reptiles.

The eyes of birds are adapted in all their parts for the
rare medium through which they receive the rays of light,
and for sudden changes in the density of that medium,
and in the intensity of light, and for the varying distances
and directions of their objects of vision, and by their high
development and their magnitude they compensate for the
imperfect condition of most of the other organs of sense.
From the lateral position of the eyes and the great projection
of the cornea they command an extensive field of vision,
and from this circumstance and the great mobility of their
head and their long neck the large organs of vision of
birds are less moveable in their orbits than those of qua-
drupeds. They are the most remote in structure and
form from those of fishes, which accords with the difference
of density in the media of vision, and the fluids now
most abundant in their interior are the least refractive,
the aqueous and the vitreous, while the crystalline lens
is flattened in its form and reduced in the density of
its texture and in the space which it occupies in the
axis of the eye. To prevent the sphericity of the eye,
from the equal pressure of the contained fluids, and
to preserve a great convexity of the transparent cornea
especially in rapaceous birds, the anterior margin of the
sclerotic is strengthened by a circular series of quadrangular
moveable imbricated osseous plates, disposed between its
coats around the edge of the cornea as in many reptiles,
and which often give a conical or even a tubular form
to the fore-part of the eye, as seen in the large nocturnal
eyes of the long eared owls. The tough posterior mem-
branous part of the sclerotic, forms a great hemisphere
occupied almost entirely by the vitreous humour, and filling
the very large orbits of the cranium, and from the quantity
of space occupied by the thin and yielding aqueous and
vitreous humours in the eyes of birds, they are probably
more easily and quickly adjusted to the different distances
of surrounding objects, and to the varying density of the
medium through which they see. The thin convex dense

ORGANS OP THE SENSES. 269

cornea is here removed to a distance from the iris by
the abundant aqueous humour occupying the anterior chamber,
and from the rapid evaporation of this fluid it quickly sinks to
flatness or to a concavity externally after death* The cornea is
least convex, and the eyes are smallest in the aquatic birds,
where the food is often distinguished more by the sen-
sibility of the lips than by the organs of vision, and they
are largest in the nocturnal birds of prey where they are
directed forwards, with their axes nearly parallel, and the
pupils are of great size, to receive the strongest impression
from a feeble light. The choroid coat, consisting as usual
of two layers, of a dark colour, is lined internally with
a thick deposit of black pigment which appears to be com-
posed of globular particles with a transparent centre, and
a prolongation of this dark membrane covered with its
pigment, is extended forwards through the vitreous humour,
from the lineal entrance of the optic nerve to the capsule
of the crystalline lens to which its anterior margin is attached.
This folded marsupium or pecten, continued from the
vascular layer of the choroid through the axis of the eye
to the lens, may convey the central nutritious vessels
of these humours, or moderate the intensity of the light
admitted into the eye, or may assist in adapting the eye
to different distances by affecting the position or the form
of the lens to which it is attached. From the ciliary liga-
ment which unites firmly the choroid to the sclerotic, the
large ciliary processes extend freely inwards to form a corona
around the margin of the lens ; the ciliary nerves unite
to form plexuses at this ciliary ligament, and the retinal
expansion of the optic nerve appears to terminate internally
at the same place. Plexuses are formed on the ciliary
arteries, as in similar delicate organs, before penetrating
the delicate textures of the eye to spread on the ciliary
processes, the marsupium, and the iris which is here remark-
able for the diversities of lively colours which it presents
in the different species. From the great mobility of the
iris, the round pupil of birds is susceptible of great and
rapid changes of dimension, which are very extensive and
almost voluntary in the parrots. The optic nerve penetrates
the choroid by a lengthened fissure, as in many of the lower
animals, and from this lineal perforation the falciform qua-
drangular pecten extends forwards through the thin and

/ ORGANS OF THE SENSES.

liquid vitreous humour. The bright coloured and highly
moveable iris, with its black uvea, appears sometimes de-
tached from the free anterior margin of the choroid, and
its coloured surface presents aggregations of minute globules
like those of the choroidal pigment. The number of folds
in the pecten varies from three or four observed in the
goat-sucker to nearly thirty observed in several singing birds.
The eyes of birds are moved by the ordinary four straight
and two oblique muscles, they are provided with lachrymal
glands above and glandulae Harderi beneath as in many
reptiles, their conjunctiva forms always a large pellucid and
highly elastic membrana nectitans at the inner angle of the
eye moved by two distinct muscles, and their lower and
upper eye -lids are very perfect, being already provided with
tarsal cartilages, Meibomian glands, and even eye-lashes,
besides the ordinary muscles for their elevation and de-
pression.

As some of the mammalia are organized to fly through
the air, some to walk on the earth or burrow in the interior,
and others to swim through the dark abyss of the ocean,
their organs of vision are very differently constructed to
adapt them for receiving visual impressions in these different
situations. They are generally more spherical in their form
and consquently more thin and membranous in their tunics,
and better provided with external means of motion and
of protection, than in the oviparous classes of vertebrata.
They have generally a lateral aspect to give greater extent
to the field of vision, but in nocturnal quadrupeds and
in quadrumana and man they are directed forwards with
more parallel axes to give greater precision and strength
to the visual impressions. The eyes are large in most
of the lower herbivorous mammalia, as the ruminatia, the
rodentia and most of the pachyderma, and also in most
of the nocturnal species, as we generally find in other classes ;
and they are very small in the adult state of many of
the burrowing quadrupeds, as moles and shrews, in the
larger pachyderma and cetacea, in the highest mammalia,
where their axes are nearly parallel, and in the cheiroptera,
where, as in aquatic birds, their deficiency is compensated
for by other organs of sense. The same circumstances
which modify the form of the eye and the proportions of
its refractive parts in other classes of animals affect the organ

ORGANS OF THE SENSES. 27 1

in this : thus in the visual organ of swimming mammalia
we observe many affinities with the eyes of fishes, those
of bats approach to those of birds, and intermediate forms
are allied to the eyes of reptiles. In cetaceous animals,
which constantly reside in the water and receive the rays
of light through that dense refractive medium, the eyes
have little aqueous humour, the cornea is flat, the crystalline
lens is large, dense and spherical, and the vitreous humour
is less abundant than in terrestial quadrupeds ; and in order
to preserve this flatness of the fore-part of the eye, the
sclerotic coat, like that of fishes, is here thick, firm, and
elastic, especially over the back and the anterior parts of
the eye. The sclerotic is an inch thick at the back part of
the eye in the whale. The superior oblique muscle of the
eye appears still destitute of a pully for its tendon in the
cetacea, these lowest aquatic mammalia, and they are almost
in the condition of fishes in the imperfect development
of their eye-lids and even of their lachrymal apparatus ; but
the smallness of their visual organs compared with those
of fishes, accords with the higher development of their in-
ternal organs of perception, and their whole nervous system.
Many intermediate forms of the organs of vision between
those of cetacea and those of land quadrupeds are seen
in species which have only semi-aquatic habits, as in walruses,
otariae, seals, otters and beavers, where the eye gradually
becomes more spherical in form, its coasts around the middle
of the eye more thin and membranous, the cornea more
convex, the crystalline lens more compressed from before,
backwards, and of a softer texture, and the glandular and pro-
tecting apparatus of the eye more complicated and more
perfect in structure. The large eye of the ruminatia and
most other herbivorous quadrupeds accord with the imper-
fect development of their intellectual organs, and they
often present a greater lateral than vertical extension
of the transparent cornea, the pupil, and even of the
whole eye-ball, by which the lateral range of vision is
extended in these timid and watchful animals during the
inclined position of the head. The prominent cornea of
carnivorous quadrupeds covers a pupil most frequently ex-
tended in a vertical direction which is that most suited
to their leaping and predaceous habits, and in the back part

272 ORGANS OF THE SENSES.

of the eye their thick and tough choroid, destitute of the
pigment which lines the other parts, shines with a blue
or green coloured metallic lustre, a tapetum lucidum which
is not seen in the lowest nor in the highest terrestrial
animals of this class, and which often presents a red colour,
as in albinos, from the exposed vascular layer of the choroid.
The ciliary ligament is less and the processes are more de-
veloped than in the inferior classes. The iris presents less
varied and deep hues than in birds, its free edge, in the em-
bryo, supports the membrana pupillaris which closes the
pupil as the inter-pulpibral membrane closes the eye-lids
at the same period of life, and where the pupil is elongated
transversely, as in the horse, the upper free margin of the
iris presents pendent processes, as in the cartilagenous fishes,
which hang down more or less over the pupil, and sometimes
they rise up also from the lower edge. Between the sclerotic
and the choroid is a thin brown coloured layer connecting
these coats and considered as continuous with the delicate
arachnoid covering of the brain and optic nerve, at the ciliary
ligament the minute canal of Fontana is still often per-
ceptible though less than in birds, and the canal of Petit
surrounds the lens between the vitreous and the aqueous
humour. The optic nerve penetrates the choroid by a round
aperture on the nasal side of the axis of vision ; but in some
of the rodentia, as the marmot, it enters by a lineal slit in the
choroid, as in birds, and sometimes a rudimentary trans-
parent pecten is observed in the embryos of mammalia
extending forwards through the vitreous humour, as in the
lower oviparous vertebrata. As we ascend through the quadru-
manous animals to man, the eye becomes smaller and more
spherical, its membranes thinner, the vitreous humour more
abundant, the crystalline lens smaller and more compressed,
the pupil more circular, the ophthalmic ganglion larger, the
retinal surface more extensive, the eyes more approximated
and parallel, their orbits more completely surrounded with
bone, and the circular suspensory muscle extending forwards
from around the optic foramen to the sclerotic in the inclined
heads of inferior mammalia, is no longer developed or required
for the small eyes and elevated orbits of the quadrumana and
man. It is however in the visual apparatus of man (Fig. 105.)

ORGANS OF THE SENSES.

organized for seeing in the erect position of the trunk, that
we find the most complete protection of the orbits by solid
osseous parietes and the most parallel direction of their
axes. Shaded externally by the eye-brows which are moved
by corrugator muscles, and protected by two highly moveable
eye-lids formed by the common integuments which continue
thin and transparent, as a conjunctiva, over the fore part of
the organ, the human eye presents in form of a plica semi-
lunaris, only a small rudiment of the third eye-lid or
membrana nictitans so highly developed in most of the
inferior vertebrata. The upper eye-lid is now the largest
and the most moveable ; both eye-lids are supported by tarsal
cartilages, they are provided with long cilia symmetrically
formed and disposed, arid with numerous glandular follicles
or meibomian glands, which pour out their secretion by
minute pores along the inner margins of the eye-lids, and
the eye-lid is perforated within by the several ducts pro-
ceeding from the lobules of a large lachrymal gland situate
in the upper and outer part of the orbit. There are three
or four irregular rows of cilia in each eye-lid, which are more
numerous and larger in the upper than in the lower, and in-
crease in size from the two angles to the middle of the eye-lids,
the large upper eye-lid has its proper levator muscle which
is not required in the lower, and both are closed by the
orbicularis palpebrarum. The glandula Harderi so large in
the inferior quadrupeds and birds, where the third eye -lid

PART ill. T

274 ORGANS OF THE SENSES.

is fully developed, is here as in the quadrumana reduced to
the small follicles of the caruncula lachrymalis, as the great
membrana nictitans is now merely a small plica semilunaris
at the inner angle of the eye. The lympid fluid from the
bilobate lachrymal gland, conveyed by the upper eye-lid
over the conjunctiva, passes through the two puncta lachry-
malia near the inner angle of the eye, and through the two
small lachrymal ducts to their dilated sac and tapering canal
from which it is poured by a valvular orifice into the anterior
part of the inferior meatus of the nose. The eye-balls,
nearly spherical in form, with their axes parallel, and
perforated behind by the optic nerves on the nasal side
of their axes, are supported on the l>ack part by a large
deposit of adipose substance (105. /. /.) and are moved
by four recti and two oblique muscles; the tendon of
the superior oblique is not perforated by the rectus su-
perior (105. o.) as it is in many feline animals. The
muscles are inserted into the white anterior part of the
sclerotic, called tunica albuginea, and the optic nerve per-
forates a circular cribriform portion of this membrane behind,
the central minute aperture of which is occupied by the
central artery of the retina which passes through the middle
of the optic nerve (105. a.) The transparent cornea, com-
posed of homogeneous concentric laminae, thicker and more
convex than the sclerotic, has still its transverse diameter
a little more extended than its vertical. The choroid is
firmly united to the sclerotic at the white ciliary ligament
a line in breadth, and is perforated by a circular aperture
behind for the transmission of the optic nerve, and from
the anterior margin of this ligament proceed the numerous
minute folds of the corpus ciliare which give attachment
to about seventy ciliary processes (105, /.) extending with
their convex margins internally to be united to the capsule
of the crystalline lens. The villous internal surface of the
vascular layer of the choroid secretes, a layer of variable
thickness, of a muscous and viscid pigmentum nigrum
this appears to be immediately lined with the delicate
transparent membrane of Jacob, within which are the me-
dullary and fibrous layers of the retina (105. d.) and the
several concentric layers of the hyaloid membrane of the vi-
treous humour. The iris, composed chiefly of radiating vessels

ORGANS OF THE SENSES.

and nerves disposed in two concentric rings, is attached
to the anterior part of the choroid around the ciliary liga-
ment, arid divides the cavity for the aqueous humour into
two unequal chambers which communicate by the pupil ; it
is variously coloured on its anterior surface, and supports
on its back-part the uvea which is covered with the black
pigment of the choroid. A little exterior to the entrance
of the optic nerve a small fold of the retina is observed,
and a yellow spot, with a minute round transparent portion
of the retina, the uses of which are unknown. The vitreous
humour (105.^.), of a gelatinous consistence and contained
within the concentric folds of the hyaloid membrane, occu-
pies about two-thirds of the axis of the eye, and its delicate
membrane embraces also the crystalline lens with its firm
capsule and forms around its edge the circular canal of
Petit. The crystalline lens, here comparatively small and
soft, has its posterior surface as usual more convex than
the anterior, and both are most convex at the earliest periods
of life. The aqueous humour, enveloped in a delicate capsule,
which forms the membrana pupillaris by extending over
the pupil in the embryo, occupies a large anterior and a
smaller posterior chamber, giving the necessary convexity
to the cornea and facilitating the free motions of the iris.
Thus we observe these complicated optical instruments, the
most universal and the noblest organs of sense, gradually
advancing to perfection from the monad to man, where all their
internal essential parts, and all their external accessary appa-
ratus are the most exquisitely finished and adjusted, and it
is chiefly through their means that he is enabled to provide
for his wants, to acquire the materials of thought, and to
enjoy the sublime spectacle of nature.

THIRD SECTION.

Organs of Hearing*

The organs of hearing are next to those of vision in
their importance and in the universality of their occurrence
in the animal kingdom, where they are distinctly perceived

T 2

276 ORGANS OF THE SENSES.

both in the molluscous and articulated tribes, and they
relate to movements of the surrounding element which give
notice of objects at a distance. The percussions given
by outward bodies to the air or water in which animals
reside, are communicated, like undulations of light, to the
general surface of their body, and may produce some feeble
sensation where there are yet no distinct acoustic instru-
ments developed, as light appears to affect many organized
beings without eyes. But most of the higher invertebrated
animals and all the vertebrata present at the distal expanded
soft extremities of distinct auditory nerves, more or less
complicated acoustic instruments adapted to receive and
transmit sonorous undulations, and to render more distinct
the perception of their force, their direction and their ra-
pidity of succession. These, like most of the other organs
of sense, are disposed symmetrically on the two sides of
the head,, and the impression of sound may be communicated
to the auditory nerves without passing through the external
acoustic apparatus, as by means of the solid parietes of the
head, or by direct impression on the nerves from within.
From the structure of the organ of hearing it is more adapted
for communicating aereal vibrations than those of water, and
it is most general and most developed in the air-breathing
classes. The sudden percussions communicated by various
means to the dense watery element in which most of the
lower invertebrata reside, may affect rapidly and powerfully
the whole surface of their body, whether naked or covered
with hard vibratile parts, and through that means the most
sensitive internal parts, without these animals having special
acoustic organs to concentrate the undulations and direct
them to particular nerves, and we ascend as high as the
active-air-breathing insects before we perceive distinct organs
appropriated to this sense. Many insects have hard organs
for producing audible sounds by their rapid attrition against
each other, and these sounds are often heard and repeated
by their mates, being a means of communication between the
sexes, especially in the darkness of the night. The organ
of hearing in insects already presents not only a distinct
auditory nerve and vestibule, the first and most essential
elements of all this acoustic apparatus, but also the rudi-
ments of two semicircular canals, according to the obser-

ORGANS OF THE SENSES. 2/7

vations of Camparetti on that of the scarabseus and several
other genera of insects. At the lower and lateral part of the
head there is a minute round passage closed externally by
a membrane, and leading on each side of the head to an
internal vestibular sac, with two small curved canals ex-
tending from it. These vestibular cavities are furnished

O

with distinct nervous filaments, which appear to be branches
of the antenneal nerves, and they constitute an acoustic
organ which has been observed in many different forms of
this class. They are placed more anteriorly on the head of
the locusts, where the minute canals are thin, membranous,
and transparent, and this organ presents different degrees
of development in different species of locusts. Similar audi-
tory organs have been detected in the cicada, vespa, libelluke,
and at the sides of the base of the long spiral proboscis of
the papiliones ; they are perceived also in ants, flies, and
other insects belonging almost to every order of this great
class. This delicate organ contained entirely within the
cranial cavity of insects is provided with a vestibular opening
or fenestra ovalis covered with a thin and tense membrane
to receive the sonorous undulations of the air and to convey
them to the ento-lymph of these membranous cavities, and
so to the expanded surface of the surrounding delicate
auditory nerves. These organs have been also dissected and
described in many insects by Ramdohr, who observed them
in the common bee placed near the base of the maxillae.
Treviramus found those of the blatta orientalis placed behind
the basis of the antennae and closed by an oval, white,
concave, vestibular membrane, and Blainville found them
in the cicadae, which distinctly hear, on each side of the
back part of the head, in form of two minute open stigmata
leading to vestibular sacs, but many entomologists, as Straus
and Burmeister, are inclined to place the auditory organs of
insects in the antennae themselves. In the class of arachnida,
which also breathe and reside in air, organs of hearing very
similar to those of insects were detected by Camparetti in the
spiders, placed near to the mouth at the bases of the palpi
and consisting of a vestibular sac covered by a transparent
membrane, through which the auditory nerves could be per-
ceived. The density of texture and the deep hues of the

'2j& ORGANS OF THE SENSES.

exterior covering of the head in these air-breathing entomoid
classes, and the softness and transparency of the vestibular
membrane which receives the sonorous vibrations, render
more obvious the position and nature of the organs of
hearing in them, than if the whole exterior of the body were
covered with a more soft and uniform skin, and it is pro-
bably in part from this circumstance that a more simple
rudiment of these important organs has not hitherto been
observed in the higher forms of helminthoid animals which
already present the rudiments of almost all the complex
organs of insects. From the thick and solid calcareous
covering of the body in the higher Crustacea, their organs of
hearing, with their exposed vestibular membrane, are most
obvious, especially in the active macrurous decapods, as
the lobster and cray-fish, where they present a prominent
circular aperture covered with a thin membrane and situate
at the bases of the outer pair of antennee. This exterior
covering is calcined in some of the brachyurous species, as
the maja, and appears to form a loose operculum provided
with distinct muscles for its movements. Within this
simple vestibular cavity is a white, soft, lengthened sac,
or membranous labyrinth, filled with a transparent ento-
lymph, and supporting the small fibrils of an acoustic nerve
derived from the great supra- oesophageal ganglia. It passes
obliquely upwards for a short distance into the first segment
of the antennae, and appears to be still destitute of those
solid internal lapilli or cretaceous substances which are
commonly found in the labyrinths of higher animals. By
opening on the lower and not the upper surface of the
antennee, the position of its aperture corresponds with the
inverted position of nearly all the other organs of these
animals. The exterior margins of this vestibular opening,
or fenestra ovalis, are often prominent and almost tubular,
as in the pagurus, where the covering membrane appears
fibrous like the membrana tympani of mammalia. The
concealed condition of this organ under a solid calcified
covering in the brachyurous species, accords with their more
limited powers of swimming, and is analogous to the con-
cealed position of the organs of hearing within the cranium
of cephalopods and osseous fishes. These organs have a

ORGANS OF THE SENSES.

large vestibular membrane in the palinurus, they appear as
small tubercles in the palaemon, and in most of the inferior
orders of Crustacea no trace of them can be perceived.

The slow-moving molluscous animals are less provided
with organs for perceiving the properties of outward bodies
than the active articulated classes ; but many of the higher
pulmonated gasteropods seem both to hear and to smell,
although the precise seats of these feelings have not been
determined, and the tritonia arborescens emits audible sounds
under water, which are, without doubt, intended to be heard
by others of the same species, as we see in insects, and
probably to serve as a means of communication between
these hermaphrodite and almost blind animals, although the
organs have not been detected which are appropriated
to their perception. The cephalopods which, of all the in-
vertebrata, approach the nearest to fishes in their general
form, structure and movements, come next to them in the
complexriess of their organs of hearing as well as in those
of sight. These organs in the cephalopods, as in osseous
fishes, are symmetrical and double, placed within the pa-
rietes of the cranium, and destitute of external meatus or
vestibular membrane. On the sides of the great cephalic
cartilage through which the oesophagus passes, and which
envelopes the brain, we observe two depressions within the
cranial cavity, at its lower part, which are separated by a
tough dura mater form the cerebral ganglia. These cavities
are separated from each other, and from the exterior mus-
cular parts, by the cartilaginous substance of the skull, and
they contain each a membraneous sac, or soft labyrinth,
which is surrounded by the exterior lymph of Cotunnius,
or peri-lymph. The membranous labyrinth on which the
acoustic nerves are distributed is filled with a thin ento-
lymph, and encloses a solid chalky lapillus, of various forms
in different species, composed of carbonate of lime, pre-
senting sometimes the appearance of a crystallized rhomboid,
and suspended by nervous filaments. Numerous minute
blood vessels are seen accompanying the filaments of the
acoustic nerves on the parietes of these vestibular sacs.
This calcareous substance, like that of the sacculi in the
labyrinths of higher animals, serves to communicate more
uniformly and distinctly to the accoustic nerves the vibra-

-b'O ORGANS OF THE SENSES.

tions transmitted to this part of the head, the organs of
hearing being here enclosed in the thickest and densest
part of the great cephalic curved plate into which the strong
muscles of the arms are inserted. In the octopus ven-
tricosus, this cretaceous body is conical like a limpet, of
a rose-red colour on its round exterior tapering surface,
white and hollow on the base which rests on the vestibular
membrane, and it is connected, as in higher animals, to the
side of the vestibule by numerous nervous filaments. The
ento- and peri-acoustic lymph seen here in the vestibule
corresponds with that found in the entomoid articulata and
in the ears of vertebrated animals, and notwithstanding the
magnitude and constancy of the auditory organs in the
naked cephalopods, and their presenting the most complex
form met with in the invertebrated classes, they are yet
reduced almost to the first rudiment or most essential
element of the auditory apparatus — the vestibular sac with
its acoustic nerve.

In tracing this organ upwards through the vertebrated
classes we find it gradually perfecting the semi-circulajr canals,
developing a cochlea from the vestibule, and enveloping the
whole of this complex labyrinth within the solid texture of
the cranium. It acquires in the air-breathing animals a
tympanic cavity communicating with the fauces by the
Eustachian tube, and containing ossicula auditus which
transmit the vibrations of the membrana tympani to the
vestibule and the whole internal labyrinth. And in the
highest conditions of the organ a still more exterior meatus
auditorius and complicated moveable concha are added to
complete this acoustic instrument. Fishes, like the cepha-
lopods, receive their auditory sensations through the dense
watery element they inhabit, the undulations of which strike
forcibly the whole surface of their head and trunk, so that
they less require any external means of concentrating sono-
rous vibrations or a complicated internal auditory apparatus,
than animals which hear through a thin and rare aerial
medium. In the lowest cyclostome cartilaginous fishes, as
the lamprey, the whole internal ear is nearly in the same
condition as in the cephalopods, consisting of a simple shut
vestibule, without fenestra ovalis, enclosed in the cartilagi-
nous substance of the cranium, without internal calcareous

ORGAN'S OF THE SENSES. 281

concretions, and even without distinct semi-circular canals,
these canals being only represented by three perceptible folds
of the vestibular membrane. These two vestibular cavities
lodged in the lower and lateral parts of the skull are still
separated from the cranial cavity only by the dura mater,
and are pierced only by the acoustic nerves and blood vessels
which spread on the vestibular membranes, between the
peri- and ento-lymph. But in the higher osseous fishes, we
find in addition to a highly developed vestibule containing solid
calcareous bodies and even sometimes perforated externally by
a fenestra ovalis, distinct, large, free, semi-circular canals with
considerable ampullae at their terminations, as in other ver-
tebrated classes. These parts, however, of the acoustic
apparatus are not yet imbedded in or surrounded by the
solid bones of the head, but are simply lodged in a de-
pression on each side within the general cavity of the skull.
There is generally no external fenestra or vestibular opening
in osseous fishes, and the sonorous impulses communicated
to the body of the animal through the dense medium of the
water, are commonly conveyed to the air-sac of the trunk,
which is often bifurcated or even ramified, and from that
forwards to the base of the skull or into its interior near the
ear, and sometimes distinct small costal bones detached
from the transverse processes of the anterior vertebrae assist
in communicating these vibrations from the air-sac to the
organ of hearing. These bones, however, are ordinary ele-
ments of the vertebrae, and the air-sac is the rudiment of
the lungs and not analogous to the tympanic cavity of air-
breathing animals. The great size and length of the semi-
circular canals within the cranial cavity of osseous fishes,
where they are not yet enclosed within the substance of the
temporal bone, corresponds with the great development exter-
nally of the tympanic ossicula composing the opercular bones
which are likewise unrestrained by any tympanic membrane
or osseous walls in their extension outwards. Although in the
osseous fishes the whole labyrinth lies in an open groove on
each side, entirely within the general cavity of the skull,
separated from the brain only by the dura mater, and con-
nected only by ligaments with the temporal bone, we find in
the sturgeon, an operculated cartilaginous fish, that the
labyrinth is already partly buried in the substance of the

282 ORGANS OF THE SENSES.

temporal bone, which envelopes the three semi-circular canals
and leaves the vestibule still free within the cavity of the
cranium. In the higher forms of cartilaginous fishes, how-
ever, in the rays and sharks, the whole labyrinth is at length
found to be completely surrounded by the firm elastic car-
tilaginous substance of the skull, excepting at the internal
entrances of the vessels and nerves and at the fenestra ovalis
which now communicates with an external meatus. The
external meatus is already seen in some of the osseous fishes,
as in the large ears of the lepidoleprus ; in the sharks it is
more distinct though closed externally by the skin, and in the
rays it is even double on each side as if to form a rudiment
of the Eustachian tube, the spiracula of these animals
having no relation to the organs of hearing. This imbedded
condition of the organ in the cartilaginous fishes better
enables them to perceive all the sonorous vibrations com-
municated to the soft substance of their skull, and we find
the whole internal ear preserve this position, so favourable
for receiving vibration, even in the densest forms of the
skull, from the cartilaginous fishes up to man. The cre-
taceous substances, generally three in number, found within
the vestibular succulum and its communicating smaller
sacculi, are soft and pulpy in the cartilaginous fishes and
of a stony density in those which have an osseous skeleton.
They vary in shape according to the species ; they are
normal parts of the auditory organ in most animals from
the cephalopods to man; they are composed of minute
rhomboidal crystals of carbonate of lime and are desti-
tute of internal organization like the excreted shells of
molluscous animals. The succuli of the vestibule in these
lowest forms of the ear appear to form the first rudiment
of a cochlea, and a rudiment of the tympanum is seen in
the subcutaneous passage destitute of air, leading from
the fenestra ovalis to the surface of the head in the highest
cartilaginous fishes. The acoustic nerve comes off sepa-
rately in fishes from the inferior part of their lobed medulla
oblongata beneath the cerebellum, and sends branches to be
distributed on the ampullae of the semi-circular canals, on
the vestibule, and on the sacculus or the yet undivided and
unconvoluted rudiment of the cochlea, so that its branches
are most affected by vibrations in these two last cavities by

ORGANS OF THE SENSES. 283

the solid cretaceous bodies they contain, and the vestibule and
semi-circular canals are the first parts which become imbedded
in the substance of the temporal bone. In some fishes, as the
lophius, where the skeleton is of a semi-osseous consistence
the canals are already partially imbedded in the substance of
the cranial parietes, by their passing round a process of the
temporal bone.

The perennibranchiate amphibia being, like the fishes,
permanent inhabitants of the water, and receiving their so-
norous vibrations through that dense medium, are still
destitute of a tympanic cavity, and consequently of a Eus-
tachian tube, which are parts of the organ first required and
first developed in those species which lose their gills and
change their aquatic for an aerial element. In these aquatic
species the labyrinth is still imperfectly enclosed in a
spacious general cavity of the temporal bone, the vestibule
communicates externally by the fenestra ovalis, to which
the stapes is applied as in all the higher classes of animals,
but is here in form of an operculum as in fishes. There is
no tympanic cavity or membrane ; the semi-circular canals
and the vestibule with its sacculus and lapilli, are formed
like those of osseous fishes, but with the sacculus propor-
tionably small, and the muscles and integuments still cover
the exterior of the organ without leaving a trace of external
meatus ; so that the auditory vibrations from without are
here obscurely conveyed, as in fishes, through the solid
walls of the cranium. The same simple condition of these
acoustic organs is seen in the caecilia, and appears to be
possessed by the larvae of all the higher caduci-branchiate
amphibia. But in the adult state of the frogs and sala-
manders we find the semi-circular canals already imbedded
in the substance of the temporal bone, and the rest of the
labyrinth still free in the original general cavity of that bone,
as we observe in the sturgeon among the cartilaginous fishes.
The lapilli here form a soft white pulpy calcareous substance,
and a small tympanic cavity filled with air, communicating
with the fauces, and confining the small united ossicula, is
now found between the labyrinth and the skin of the head.
The Eustachiaii tubes leading from the tympanum to the
fauces, are generally separated throughout, wide, and short,
sometimes they unite to open by a single aperture on the
median plain as in several frogs and in the pipa, and in

284 ORGANS OF THE SENSES.

some a canal is found prolonged outwards from the fenestra
rotunda. The thin and naked skin forms in these air-
breathing amphibia a large membrana tympani on a level
with the general surface of the head to the centre of which
membrane the bent cartilaginous malleus is attached, and
from the soft condition of the tympanic ossicula the sonorous
vibrations communicated from without to the large expanded
membrana tympani are obscurely conveyed to the fenestra
ovalis to which the broad base of the stapes is applied.

In the air-breathing reptiles the organs of hearing present
a higher condition of development than in the semi-aquatic
tribes of amphibious animals, especially in the parts which
more immediately relate to the rare medium through which
their sonorous impressions are received. The tympanic por-
tion of the ear is still however so imperfectly developed in
the serpents that we find it covered externally not only
by the skin and muscles, as in fishes and branchiated
amphibia, but also by the hard scales of the head. The three
tympanic ossicula are united together into a single piece as
in the frogs, which is still cartilaginous at its distal or malleal
extremity where it is attached to the inner surface of the
membrana tympani. The semi-circular canals, with their
ento- and peri-lymph as in fishes and amphibia, are imbedded
in the dense petrous portions of their solid temporal bones.
The vestibule is still lodged in a capacious cavity of the tem-
poral bone, and its sacculus contains a large and solid creta-
ceous body, so that the solid lapilli of serpents more resemble
those of osseous fishes, while the soft and pulpy cretaceous
substances of the labyrinth of amphibia are allied to those of
cartilaginous fishes, and they are softer in the chelonian than
in the saurian reptiles. The cavity of the tympanum is ge-
nerally much larger in the saurian than in the ophidian
reptiles, and is covered externally by a thin, projected, trans-
parent, naked, membranous continuation of the skin, placed
on a level with the general surface of the head, so as yet to
present no external auditory meatus. This cavity communi-
cates freely with the fauces by a separate Eustachian tube
and by means of the fenestra ovalis with the labyrinth, which
still presents only a rudimentary undivided cochlea closed
externally by the membrane of the fenestra rotunda, and a
solid calcareous lapillus as in the serpents. The stapes
with its base applied to the fenestra ovalis, continues

ORGANS OP THE SENSES. 285

to be the principal ossiculum ossified in the tympanum,
and the tympanic cavity begins to assume a more
lengthened tubular form towards its exterior membrane
preparatory to the formation of an external auditory
meatus and expanded concha to collect and direct the vibra-
tions of the air. In some of the saurian reptiles the mem-
brana tympani is still covered, as in many serpents, by the
ordinary scales of the head, in most it is quite naked and
exposed as it is in the frogs and the salamanders, and in the
most elevated forms of the sauria it begins to be protected
by external overhanging elastic folds of the skin, forming
thus a distinct rudimentary concha, as seen in the crocodiles,
the gavials, and the alligators. The internal parts of the ear
are nearly in the same condition in the chelonian reptiles,
which present a more narrow and lengthened tympanic
cavity covered externally by the loose integuments of the
head, and communicating with the fauces by a wide semi-
cartilaginous and distinct Eustachian tube. The three
anchilosed tympanic ossicula still constitute a long stiliform
bone with its opercular or stapeal piece applied to the fenes-
tra ovalis and attached by its outer rounded malleal ex-
tremity to the middle of the membrana tympani as in the
other orders of reptiles. The vestibule, enveloped with its
sacculus and the semi-circular canals, in the substance of the
temporal bone, is provided with solid lapilli supported by
the filaments of the acoustic nerves, and with a compara-
tively large cochlea, though still undivided by an internal
lamina and unconvoluted in its form, so that the cochlea
appears to be the last part of the internal ear which acquires
its normal and perfect form ; but in the crocodilian reptiles
it already presents a slightly curved form, and an internal
membrane which supports branches of the acoustic nerves and
divides it into a scala tympani communicating with the fe-
nestra rotunda and a scala vestibuli continuous with the
general cavity of the vestibule and membranous labyrinth.
Notwithstanding the gelatinous consistence of the ento-
lymph which fills the membranous labyrinth of the cold-
blooded as well as the higher vertebrata, resembling the
vitreous humour of the eye, no cellular tissue or folds of a
hyaloid membrane have been observed to pervade its sub-
stance, nor in the more abundant and fluid peri-lymph which

ORGANS OF THE SENSES.

envelopes these delicate parts and separates them from the
solid parietes of the osseous labyrinth. The soft lapilli of
the labyrinth of vertebrated animals appear to consist of
minute rhomboidal crystals of carbonate of lime like those often
found lining the intervertebral foramina in other parts of the
vertebral column.

The dense bones of the skull of birds closely envelope
every portion of their internal ear with a vibratile covering
of great hardness, and corresponding with the rare elastic
medium they inhabit. The semi-circular canals, so large and
free in the cranium of osseous fishes, are here even more
reduced in their dimensions than in reptiles, especially in
the water birds, but with enlarged ampuke at their ends for the
auditory nerves. The vestibule is narrow but more lengthened,
and the cochlea has assumed a more curved and spiral form
than even in the crocodiles, its spiral partition, formed by
two triangular cartilaginous folds extending nearly to its
apex, partially divides it into a vestibular and a tympanic
portion, communicating with the two foramina of the vestibule
and communicating with each other at the apex in the dilated
infundibulum or lagena. The cretaceous lapilli so large in the
membranous labyrinth of fishes and amphibia are now greatly
reduced and appear only in the form of strata of minute calcar-
eous crystals. The semi-circular canals are long and narrow
in the rapaceous birds, large and wide in the singing birds,
and comparatively small, short, and wide in the grallatores, the
palmipeds, and the gallinaceous birds. The tympanic cavity,
lengthened like the vestibule, has here a short external
meatus beyond the projecting convex membrana tympani to
which the cartilaginous malleal end of the anchylosed
tympanic ossicula is attached. Not only the tympanic
cavity is here surrounded by solid bone, but also the short
wide Eustachian tubes which sometimes unite together be-
fore they open into the posterior nares, and the drum of the
ear has its internal dimensions greatly encreased by the nu-
merous air-cells of the diploe, over the greater part of the
cranium, which now communicate freely with the interior of
both tympana. The short external auditory meatus removes
the membrana tympani from the level of the general surface
of the head, and the exterior concha, the last part of the
auditory organ to be developed, presents itself as a simple

ORGANS OF THE SENSES. 287

crescentic fold of the skin extending upwards from the su-
perior margin of the external meatus. This rudimentary
concha is perceptible in most birds, which can erect or de-
press the feathers which bound its upper margin, but it is
most developed in the nocturnal predaceous birds, which
most require this sense to direct them to their prey in the
night. The extent of this crescentic membranous concha is
encreased in some of the owls by the long feathers which
radiate from around its free margin, and it is raised or
depressed at will like a valve or an eye-lid. The solid pa-
rietes of the tympanum are pierced by several foramina
which lead to the large cells between the two tables of the
skull, as those in the tympanum of man and quadrupeds lead
to the mastoid cells, and the tympanic cavity is here traversed
by the vidian nerve as in mammalia. The cartilaginous
malleal portion of the single long tympanic ossiculum divides
into three parts where it is attached to the inner surface of
the membrana tympani, but in place of the three muscles of
the malleus observed in man and quadrupeds, there is here
but one long muscle which extends forwards from near the
occipital condyle to the exterior end of the malleus.

We thus arrive at the most perfect condition of this com-
plex acoustic instrument presented by the inammifervus
animals, where all its internal essential parts and all its
external accessory apparatus have attained their full deve-
lopment. The petrous portion of the temporal bone, of
great density, embraces closely all the most important in-
ternal parts, and the exterior concha for collecting the
sonorous vibrations and directing them to the membrana
tympani, is generally of great size. The thin membranous
labyrinth, highly vascular and of exquisite delicacy, is filled
with a fluid ento-lymph enveloping two cretaceous bodies
composed of minute calcareous crystals, and analogous to
those found in the labyrinth of fishes and even of many in-
vertebrated animals. These two cretaceous bodies, nearly of
equal size, are contained, one in the large sacculus of the
vestibule, and the other in the long elliptical sacculus
formed by the meeting of the semi-circular canals near their
ampullae, and they are supported by the delicate expanded
extremities of distinct branches of the acoustic nerves as in
the inferior classes. The membranous labyrinth is surrounded

12SS ORGANS OP THE SENSES.

externally with a copious transparent, thin and colourless
peri-lymph which separates it from the periosteum, lining the
interior parietes of the osseous labyrinth. The membranous
semi-circular canals and their ampullae are comparatively
slender, their median portion forms the larger part of the
broad, short, and irregular vestibule, and its lapillus corres-
ponds with the utricular of fishes. The sacculus vestibuli
and its lapillus are proportionally small, and the cochlea
forms a large turbinated cavity divided longitudinally
throughout by an internal solid spiral lamina, forming from
two to four spiral turns ; but in the ornithorhyncus it is as
simple as in birds. As in the inferior vertebrata the exterior
semi-circular canal extends outwards horizontally and at
right angles to the other two, and the anterior and posterior
unite together to form a common canal before entering the
vestibule, their direction being nearly vertical with relation
to the floor of the cranium. The nerves of the membranous
labyrinth are chiefly confined to the ampullae of the semi-
circular canals and to the two sacs containing lapilli, and
the two lapilli are proportionally larger in the foetus than
in the adult. The osseous spiral lamina dividing longi-
tudinally the interior of the convoluted cochlea is still
membranous at its peripheral margin, and the scala vestibuli
communicates freely with the scala tympani at its dilated apex
where it receives a branch of the acoustic nerve, but no
nervous brandies are perceived on the membranous semi-cir-
cular canals. The two vestibular openings vary much in their
form and size in different mammalia, and the aqueducts of the
vestibule and cochlea appear connected, the one inter-
nally with the dura mater and the other externally with
the periosteum. The cochlea is of a narrow lengthened
spiral form in many of the rodentia, more short and orbi-
cular in the cetacea, and in most of the higher orders of
quadrupeds it forms a turbinated cavity with about two turns
and a half as in the human ear. The tympanic cavity, im-
bedded in the temporal bone, communicating by several aper-
tures with the mastoid cells, and by a lengthened ossified
Eustachian tube with the fauces, is bounded by a thin fibrous
membrana tympani concave externally, and contains four
ossicula articulated moveably with each other and provided
with distinct muscles for their movements. The external

ORGANS OF THE SENSES. 28i>

meatus is now increased in length, bounded by ossious
walls, defended internally by short hairs and by an acrid
secretion from its parietes, and generally terminated ex-
ternally by an expanded cartilaginous concha variously
formed and developed, which is adapted by its mobility
and its conical shape to collect the sonorous vibrations from
different directions and to convey them to the internal ear.
The concha is generally very small or wanting in the aquatic
mammalia. In the cetacea, where the cochlea is often
very large and the semi-circular canals comparatively small,
we observe only a narrow winding perforation leading out-
wards from the membrana tympani to the surface of the head,
there is no external concha, and the minute entrance to the
meatus is scarcely perceptible on the surface of the skin.
The concha is still wanting in the seals and walruses, and
is very small in otarise, beavers, otters, and other diving
mammalia. It is deficient in the ornithorhyncus, and in
several digging animals, as the mole and the manis. The
monotrema are also distinguished by several other marks
of inferiority in their organs of hearing by which they are
allied to birds and reptiles, as the shortness of the external
meatus, the anchylosis of the ossicula auditus, the rudi-
mentary state of the cochlea, and the free projection of the
osseous semi-circular canals into the cavity of the cranium.
As we ascend through the tribes of mammalia that live more
exclusively upon the land, we find the exterior cartilaginous
concha acquiring greater magnitude and symmetry, and, by
the articulation of the cartilage and the great development
of its muscular apparatus, it acquires the means of more
varied and extensive motion. It is largest, most moveable,
and, commonly directed backwards, in the timid and feeble
rodentia, ruminantia, pachyderma and other herbivorous
quadrupeds where the cerebral hemispheres are proportionally
small, and it is least and directed forwards in the carni-
verous tribes where the brain is large. It is large, however,
in the bats and most nocturnal quadrupeds, and we observe
it in the quadrumana, especially in gibbons and orangs,
gradually acquiring the short, flat, round form and motion-
less character of the human concha. The internal ear of
man, like that of inferior mammalia, has its membranous
labyrinth filled with an ento- lymph and separated by a thin

PART III. U

290 ORGANS OP THE SENSES.

peri-lymph from its osseous parieties. The auditory nerves,
as in other vertebrated animals, spread on the ampullae of
the semi-circular tubes and supporting the cretaceous lapilli
of the median sinus and the succulus, can receive their im-
pressions only from the undulations of this fluid medium.
The minute component crystals of the two cretaceous lapilli
of the vestibule are loosely aggregated together as in the
cartilaginous fishes and in all the higher vertebrata, and
the membranous labyrinth is separated from the fenestra
ovalis by the peri-lymph and by the membrane of that
orifice, so that this thin enveloping peri-lymph receives
the sonorous vibrations from the tympanum and transmits
them to the sensitive parts of the membranous labyrinth.
The aqueducts appear to be but vascular foramina. The
anterior auditory nerve, accompanied by the facial, passes
to the two anterior ampullae and to the cretaceous lapillus
of the median sinus, and the posterior auditory branch
passes to the posterior ampulla, to the saccular lapillus,
and to the cochlea, as in the inferior vertebrated classes.
So that there is great uniformity of plan in the structure
of this delicate acoustic organ from the simple vestibule
of the articulata to its most complex form in the highest
mammalia, where the different densities and forms of the
pulpy granular lapilli, the gelatinous ento-lymph, and the
thin fluid of Cotunnius, regulate and limit each others vi-
brations, and approximate the phenomena of hearing to
the undulations of light through the various humours of
the visual organs.

FOURTH SECTION.

Organs of Smell.

The organs of smell, which are destined to receive and
transmit the impressions of odorous particles diffused through
the medium in which animals live, are much simpler in
their structure, and more difficult to determine, in the in-
ferior tribes of animals than those of sight or hearing, and
they appear also to be less important for the preservation of
life, and less general in their occurrence throughout the
animal kingdom. It does not appear that the radiated

ORGANS OF THE SENSES. 291

'animals have distinct organs to enable them to be sensibly
affected by odorous effluvia, but the air-breathing annelides
among the articulata have been supposed to perceive them
by the parietes of their mouth or by the lateral pores of
their air- sacs. The sense of smell so distinctly manifested
and so delicate in insects, has also been referred to the
same parts of their body, or to their palpi, or to their
cesophageal sacs, or to the delicate subdivided laminated
extremities of their long flexible antennae, and the inner
pair of these organs in the Crustacea have been considered
as the seat of the same sense. The labial appendices of the
conchifera and other molluscous classes, the entrance of
the respiratory sacs in pulmonated gasteropods, the highly
sensitive tentacula covered with a delicate mucous mem-
brane, and even the whole surface of the skin in the higher
mbllusca, have been regarded as the organs through which
these animals receive impressions of odorous emanations.

The organs of smell, on which the olfactory nerves are
entirely distributed, are very obvious in fishes, although
they do not communicate with the respiratory organs or
with the cavity of the mouth. They are laminated organs
placed in cavities or depressions excavated on the anterior
part of the face and protected by cartilages as in higher
animals, but have yet no posterior opening into the interior
of the body on account of the density of the element here
respired. The olfactory nerves, arising alone from the
rudimentary hemispheres of the brain and provided with
large olfactory tubercles, perforate the anterior part of the
skull corresponding with the ceribriform plate of the ethmoid
bone, and immediately spread upon the numerous parallel
or radiating laminae covered with a delicate and extensive
mucous membrane. These numerous nasal laminae covered
with the petuitary membrane are thus more or less exposed
on the surface of the face to the contact of the surrounding
element, and a fold of the integuments supported by a
cartilaginous plate generally hangs like a valve over the
middle of each nasal cavity. The nasal cartilage protecting
each cavity partially divides its entrance into two, so that
the water passes freely through its interior and over the
extensive' surface of the olfactory laminae during the lateral
motions of the head and the progressive movements of the

u 2

292 ORGANS OF THE SENSES.

body. By the separation of the organs of smell from the
respiratory passages in fishes, as in other water-breathing
animals, their great sensibility and delicate structure are pro-
tected from the violent and incessant action of the currents
of water required for respiration. In most osseous fishes there
is an anterior contractile and a posterior open or valvular
orifice placed superficially apart from each other, and leading
into each nostril from the upper part of the muzzle, but in
the lampreys both nostrils open by a common orifice on the
upper part of the head. In the plagiostome species the
wide plicated valvular nostrils open on the under surface
of the face anterior to the mouth, and in some of the eels
an approach is made to the structure of these parts in
the lowest amphibia by having the posterior orifice of their
nostril placed internally under the upper lip.

In the amphibious animals, where the respiration of air
begins to be effected through the nostrils, the olfactory
organs become more complicated in structure and more
internal in their position. The cartilaginous plicated portion
of the organ of fishes now begins to assume the more
compact tubular and convoluted form which the osseous
plates present in the higher classes of animals, and the sen-
sitive surface of the organs increases in extent as we ascend
through the vertebrated classes. In the perennibranchiate
amphibia the nostrils still form on each side a simple sac,
without internal convolutions, and having their posterior
opening so far forward in the mouth as to be immediately
under the upper lip, as in some fishes. In the larva state
of salamanders and frogs the nostrils are still, as in fishes,
confined to the exterior of the head, and even in the adult
forms of these animals the posterior openings of the nostrils,
though within the cavity of the mouth, are much advanced
in their position, and distant from the median line of the
body. The exterior nares which are muscular and contrac-
tile, have now almost lost the cartilaginous valve of the fishes,
but the turbinated bones even in a cartilaginous form, scarcely
yet extend the interior surface of the organ, and the cavities
of the nostrils in the proteus are still laminated as in a fish,
although they open posteriorly under the upper lip.

In the serpents the organs of smell have their internal
surface extended by the rudimentary turbinated bones, and

ORGANS OF THE SENSES. 293

by enlarged nasal cavities which open posteriorly both by
a common orifice on the median plain, near the anterior
part of the palate. These cavities are increased in the
sauria where the turbinated bones begin to be strengthened
by ossific matter and to assume a more convoluted form.
They extend from the point of the muzzle nearly along the
whole head, separated by the vomer, in the alligators,
gavials and crocodiles, where they generally open externally
by expanded, contractile, valvular sacs, as in many cetacea.
The anterior and posterior openings of the nares, in the
saurian reptiles, are wider than in the ophidia, the whole
organs are situate more internally and are more protected
by the expanded nasal bones. The whole organs of
smell are still more covered and concealed by the osseous
walls in the consolidated head of the chelonian reptiles,
where the olfactory surface is encreased in extent, the
anterior nares are very small, and the posterior openings
are placed further backward from their primitive anterior
position in the inferior vertebrata.

The olfactory nerves and the whole internal organs of
smell are comparatively small in birds, and their imperfect
development of this sense is compensated for by their high
powers of vision, which is better adapted for their active
life and the great distances at which they generally require
to distinguish their food. The exterior openings of the
nostrils are generally large and oblique for the more free
respiration required during their rapid movements; they
perforate the horny mandible or the cere, or the feathered
skin, and the various forms and positions of these exterior
openings present useful characters for the distinction of
species in this class. There is commonly a nasal gland of
considerable size in or near each orbit. The cartilaginous
alae of the nose are seldom moveable or prolonged, the
septum is often more deficient below than that between
the orbits, and the posterior nares, prolonged backward to
near the glottis, often terminate by a single opening covered
with protecting papillae. The turbinated bones are larger
than in reptiles, and the convoluted portion of the ethmoid,
though they are still but partially ossified, and the olfactory
nerves pass from their long ethmoidal tubes, through the back
part of the orbits, into the convoluted plate of the ethmoid.

294 ORGANS OF THE SENSES.

These convoluted parts for the highly vascular petuitary
membrane, and corresponding in magnitude with that of
the olfactory nerves of birds, are for the most part still
cartilaginous and very limited in their extent, and the
imperfect development of this organ is often compensated
for by the extensive distribution of the fifth pair of nerves
on the upper and lower jaws, as in many aquatic species
which seek their food in mud.

All the internal parts of the organs of smell become more
complex and elaborate in the mammiferous animals, new
and enlarged cavities open into their interior, as the frontal,
maxillary, and sphenoidal sinuses, the large nasal glands of
birds are here reduced to follicles, and the exterior nares
assume a more lengthened and expanded form than in the
oviparous classes. The large olfactory nerves here pene-
trate the numerous openings of a broad cribriform ethmoidal
plate, excepting in the cetacea, arid spread over the very
extensive surface of the convoluted cellular part of the
ethmoid, and the two turbinated bones on each side. The
turbinated bones are most lengthened and simple in form
in the long-muzzled ruminantia, pachyderma, and other
herbivorous quadrupeds, where the various communicating
sinuses are largest, arxl these bones form the most com-
plicated labyrinths in the short-muzzled carnivora, where
the sense of smell is most acute, and by which they pursue
their prey through all their windings and concealments, or
seek them by night. The exterior openings of the nostrils
are valvular in the beavers, seals, and other diving quadru-
peds, to protect them during their rapid movements through
that dense element ; they are almost as valvular in the camels
and dromedaries for the sands of the desert, and in many
scraping and burrowing quadrupeds, and they are prolonged
in many cetacea into wide valvular and contractile sacs,
which enable them, like the crocodiles, to breathe freely
with every other part of their body concealed under the
surface of the water. The nostrils terminate in vertical
foliated membranous expansions in the phyllostoma and
many other bats, and in fimbriated radiating margins in the
condylura ; they form the digging instruments in the hog
tribe ; they are long and flexible in the nasua, more muscular,
prolonged, and mobile in the tapir, expanded into a bottle-

ORGANS OF THE SENSES. 295

shaped cavity in the cystophora, and most extended in the
elephant where they serve as organs of prehension both for
fluid and solid food. Where the cerebral hemispheres in
this class are largest, the olfactory, like most of the other
sensorial organs, are comparatively small, as in the quadru-
mana and man, and they are proportionally large in the
human foetus and in the negro, as in the inferior orders of
mammalia.

FIFTH SECTION.

Organs of Taste.

The organs of taste are situate in the mucous membrane
of the mouth, especially in the papillae and calyces of the
tongue, and are adapted to convey a knowledge of many
properties of sapid bodies applied to these parts ; so that,
as the organs of smell watch over the respiratory organs
and the properties of the surrounding element, those of taste
are situate at the entrance of the digestive apparatus where
they can best examine the materials to be conveyed into
the alimentary canal. According to the extent and delicacy
of these parts of the mouth, and their supply of blood
vessels and nerves, the sense of taste appears to be de-
veloped in animals, and the gratification of this sense forms
an incentive towards supplying the necessary wants of the
body. Although these organs appropriated to our sense of
taste are more rarely met with in the inferior animals than the
organs of the former senses, it is difficult to conceive animals
with a mouth and stomach without supposing that they derive
some sensations of taste from the substances they introduce
as food into these cavities, and such sensations have been
ascribed even to the polygastric animalcules, from their
apparent selection of proper food, and their rejecting hurtful
substances. Where delicate buccal organs, of doubtful
function, are directly applied to the food in the lowest tribes
of animals, it may be inferred that they communicate some
impressions of this kind, as the prominent lips of many
polypi and acalepha, the minute tubular organs around the
mouth of ophiurae, asteriae, spatangi, arid most other echino-
derma, and the tongue and lips of most articulated and
molluscous animals. Notwithstanding the shortness and

296 ORGANS OF THE SENSES.

density of the tongue, and the horny prehensile or masti-
cating organs which often cover its surface in higher classes,
we can perceive distinct gustatory villi on that of the ce-
phalopods and the cold-blooded vertebrata, which are suc-
ceeded by larger papillae and calyces in the birds and
mammalia. These highly vascular and sensitive papillae
which terminate the gustatory filaments of the fifth pair of
nerves gradually assume the arrangement and forms which
they present on the human tongue as we ascend through the
quadrumana to man.

SIXTH SECTION.

Organs of Touch.

The most general sense in animals is that of touch, of
which all the others may be mere modifications, and it is
situate in the highly vascular and sensitive surface of the
skin which covers and protects the entire machine. This
general sense relates to the most common physical properties
of bodies, as their form, their consistence and their tem-
perature, without some perception of which animals
could scarcely provide for their own subsistence or the con-
tinuance of their race. It constitutes the simplest form of
an organ of sense, where the minute cutaneous vascular
papillae are scarcely yet apparent, which form by their
development on the ends of sensitive nerves the more com-
plicated organs of the higher senses ; and the contact of
the outward object, required in all, is most obvious in
this sense. As the sensitive surface of the skin, the vascular
layer of the corium, exudes upon its exterior an insensible
and extra-vascular cuticle and rete mucosum, which vary
much in their thickness, and in the nature and quantity of
the materials which often consolidate them, the effect of
external impressions in exciting perceptions of touch must
chiefly depend on the structure and sensibility of the parts
touched and on the general condition of the nervous system
in animals. Those invertebrated animals therefore, of each
class, which have their exterior naked and soft, will have a
more general and acute sense of touch than such allied forms
as have their bodies covered with dense substances, although
in the latter animals the higher development of the other

ORGANS OP THE SENSES.

297

organs of sense may compensate for the deficiency, and
enable them amply to provide for all their wants. The
naked surface and long cilia, almost developed into ten-
tacula, of most polygastric animalcules, the long sensitive
tentacula of most zoophytes and acalepha, and the fleshy
tubular feet of higher radiated animals, are the parts most
adapted to receive impressions of this kind, although we
perceive no distinct organs in these animals appropriated
solely to the sense of touch. These sensitive organs con-
tinue soft in the helmmthoid articulata, but become con-
solidated and jointed in the entomoid classes where they
constitute the various forms of palpi and antennae. There is
one pair of these antennae in the myriapods as in most of
the annelides, and the same number is seen in the insects,
but they are deficient in the arachnida, and two pairs are
found in the Crustacea where they are generally more ex-
tended than in insects. In the molluscous classes they
again assume the soft, sensitive and fleshy condition of
tentacula, destitute of articulations, as we observe around the
orifices of the respiratory sac in unicated animals, and around
these orifices and the margins of the mantle in conchifera.
In the gasteropods there are commonly two of these ten-
tacula, as seen in the cyprcea erosa, (Fio. 106. c. c.9) they

extend from the sides of the

FIG. 106.

neck or the mouth, (106. b.,)
supporting the eyes (106.
d. d.}) near their base, and
are often surmounted by the
ciliated syphon (106. a.) for
the passage of water to the
respiratory organs. The
muscular foot (106. e.) pos-
sesses exquisite sensibility ;
there is frequently a second
pair of tentacula at the sides
of the mouth, and numerous
fleshy extensions, simple or
ramified (106. /.), are often
seen prolonged from the
sides or the general surface,
of the mantle. Similar fleshy
cephalic tentacula are seen

298 ORGANS OP THE SENSES.

in the pteropods, and the whole surface of the body is
exquisitely sensitive in the naked cephalopods where the
flexibility of the long arms and tentacula will enable them
to obtain more accurate perceptions of the forms and di-
mensions of outward objects.

Among the vertebrata, as in the inferior classes, many
animals are covered externally with hard and insensible
parts which must greatly obscure their impressions of touch
derived from the contact of surrounding objects. The large
solid calcareous scales of many fishes, the smaller horny
scales of most ophidian and saurian reptiles, the large plates
of crocodilian and chelonian reptiles, the compact and dense
plumage of birds, the thick hides or shaggy furs of many
quadrupeds, and the long spines or broad horny scales of
others, must act like the insensible sheaths of many radiated,
articulated, and molluscous animals, in shielding their skin
from impressions of touch. Many fishes have the scales
so minute that their body, with relation to touch, is almost
as naked and sensitive as that of the amphibia above them ;
others have only the lower surface of their body or the
periphery of their mouth covered with a naked and
sensitive skin to compensate for the want of adaptation
of the arm and hands to the sense of touch, and
in many species of fishes the tentacula of the in-
ferior classes are still seen in the form of fleshy filaments
around or near the mouth. The long divided exsertile
tongue of serpents and the worm-like flexibility of their
trunk compensate for the want of hands as organs of touch.
The flexible prehensile tails of many climbing saurian and
mammiferous animals, the palmated feet and sensitive lips
of many aquatic birds and mammalia, and the delicate ex-
posed skin, the extended labial bristles, the long flexible
tongue or lips, or the extended proboscis of many quadru-
peds, contribute to extend this sense. The osseous foramina
for the branches of the fifth pair, even in animals now
extinct, enable us to judge of the development of these parts
relating to the sense of touch. But, from the cold-blooded
amphibious animals through all the higher forms of ter-
restrial vertebrata, we observe the hands to become more
exquisitely organized and more fitted for communicating
delicate impressions of the forms, dimensions, temperature,

ORGANS OF THE SENSES. 299

consistence, and other physical properties of external bodies.
The almost naked skin of apodal anguilliform fishes, and the
great flexibility of their trunk, compensate, as in the per-
eimibranchiate amphibia and in the cetacea, for the imper-
fect development of their members as tactile organs, and
many fishes possess tentacular filaments of great sensibility,
and often very numerous near the mouth, as the sturgeons,
the silurus, the cod, and the lophius where they extend also
from along the sides of the body. The clawless feet, the
naked and delicate skin, and the broad fleshy tongue and
lips of the caducibranchiate amphibia greatly extend their
means of receiving impressions of touch ; and the long
forked tongue of serpents, during their intercourse with each
other, and during their progressive movements, is constantly
darted out and retracted, and employed as an organ of touch,
like the antennae and palpi of insects under similar circum-
stances. The soft webbed feet and partly clawless toes of
the crocodilian reptiles, and their broad fleshy tongue and
lips, compensate for the diminished sensibility produced by
the large ossious plates and horny scales covering the greater
part of their body, and enable them better to feel their prey
under the dark and muddy waters they inhabit. The broad
digital expansions of geckos and phylluri, the soft fleshy
feet and thin cutaneous coverings of the chamseleons, the
iguanas, the lizards, and other climbing sauria, and the broad
intercostal membranes of the dragons, contribute also to ex-
tend their sense of touch. As in all other aquatic animals, it
is chiefly among the aquatic forms of birds and mammalia that
we observe the naked and soft condition of the skin most
conducive to its sensibility, and the most extensive develop-
ment of this delicate organ of touch especially between the
digital phalanges, and the tentacular developments of the
invertebrata so often seen in the fishes, are still observed in
various fleshy prolongations from the face of birds, and even
of some quadrupeds as the condylura. It is, however, chiefly
in the long divided hands of carnivora, quadrumana, and all
the hightr forms of quadrupeds that we find the organs of
touch acquire their most appropriate and exquisite structure.
And in proportion to the high nervous development and
that of the sensitive cutaneous papillee, to the sensibility,
the vascularity, the flexibility and the softness of the fingers,

300 ORGANS OF THE SENSES.

the hands and other cutaneous parts, this most general
sense of touch, so closely allied to common nervous sen-
sibility, encreases in power and extent as we ascend to man,
who surpasses all other animals in the exquisite and equal
development of all his organs of sense, and in the perfection
of all those higher organs of relation by which animals are
more immediately connected with surrounding nature.

PART SECOND.

ORGANS

OF

VEGETATIVE OR ORGANIC
LIFE.

ORGAN'S OF DIGESTION. 303

CHAPTER FIRST.

ORGANS OF DIGESTION.

FIRST SECTION.

General Observations on the Organs of Digestion.

As an animal is but a moving sac, organized to convert
foreign matter into its own likeness, all the complex organs
of relation or of animal life serve but to administer to this
digestive bag. The bones, connected together by their
ligaments, are but the solid levers which enable the muscles
to move it to and fro, and the nervous system, with its
various organs of sense, serve but to direct its movements
in quest of food. The unorganized food of plants is placed
by nature in contact with the exterior surface of their body,
and their vessels are directed thither to select and absorb it,
which roots them through life to the soil where they grow ;
but as animals place their food within their stomach and
have their roots directed inwards to that central reservoir,
they can change their place and move about in quest of
what is most congenial to their nature. The organs of
animal life relate to this difference between the two organic
kingdoms, to the locomotive powers of animals for the
selection of their food; but the organs of vegetative life
relate merely to the assimilation of food when already within
the body, and are, therefore, common to animals with

804 ORGANS OP DIGESTION.

plants. The alimentary surface of the plant is the exterior
of its root, ramified and fixed in the soil which affords it
food, so that a vegetable is like an animal with its stomach
turned inside out. As the organs of relation are those most
immediately connected with the varying external circumstan-
ces of animals, they are the most variable in their character
and inconstant in their existence ; but those of vegetative or
organic life relating to the more common and necessary
functions of assimilation are much more regular and constant
in their character. No organ, indeed, is more universal or
essential in animal bodies than that internal digestive cavity
by which they differ so remarkably from the species of the
vegetable kingdom. This internal sac is but an extension of
the primitive absorbent surface of the skin, which, in
animals, passes into or through the homogeneous cellular
tissue of the body. And, although in the simplest forms of
animals, this primitive sac performs alone all the assimilative
functions, we find it, as we ascend in the scale, giving
origin to various other organic systems, to which distinct
parts of the complex function of assimilation are successively
entrusted. Thus the peripheral nutrition of the plant passes
gradually into the central mode of the animal, and the
organs of organic or vegetative life, whether they open
internally into the digestive cavity, or on the mucous surface
of the skin, may be considered as originating from the
exterior integument, which is itself only a portion of the
primitive cellular tissue of the body, modified by the
stimulating contact of the surrounding element. As the
various tubular prolongations of the alimentary canal become
more and more developed and isolated from their primitive
source, they assume properties and functions more and
more peculiar and distinct, and thus form the numerous
follicular and conglomerate glandular apparatus, and the
various vascular systems, of animals. An alimentary cavity
is observed in every class of animals and almost in every
species, and its form and structure vary according to the
situation of animals in the scale, or according to the kind
of food on which they are destined to subsist, and the extent
of elaboration it requires to undergo to assimilate it to the
animal's body. The peculiarities presented by the digestive
organs are, therefore, intimately connected with the diversi-

ORGANS OF DIGESTION. 305

ties of form manifested by the organs of animal life, and
with all the living habits and instincts of animals.

SECOND SECTION.

Digestive Organs of the Cyclo-neurose, or Radiated Classes.

In the lowest tribes of animals the internal organization
relates almost solely to digestion, and the food consists
almost entirely of the simplest forms of animal matter. The
alimentary cavity has often but one orifice, it is seldom
provided with masticating organs, and scarcely a trace of
&ny glandular organ is yet observed to assist in the process
of assimilation. Like the exterior form of the body, the
digestive apparatus is more varied in this than in any of the
higher divisions of the animal kingdom.

I. Polygastrica. Internal digestive cavities are seen in
the simplest monads ; and they are so numerous in almost
all the higher forms of animalcules, that the class has been
termed polygastrica from this character. From the great
transparency of these microscopic animals, their digestive
sacs, when empty, or when filled only with water as they
often are, appear like portions of the common cellular
substance of the body, or like gemmules, or internal animaU
cules, and from not being easily or generally recognised as
alimentary cavities, many, like Lamarck, were led to believe
that these animals were without a mouth or any internal or-
gans, and were nourished by superficial absorption, like marine
plants. Lewenhoeck, however, observed that they possessed
an internal cavity, and devoured each other ; the same was seen
by Ellis ; Spallanzani perceived them swallowing each other
so voraciously that their bodies became distended with their
prey ; and Goetze designated the trichoda cimex the wolf of
infusions from its rapacity among the smaller animalcules.
Gleichen placed animalcules in infusions coloured with
carmine in order to discover the forms of their digestive
cavities, and he has figured many trichocke, vorticella, and

TART III, X

30G ORGANS OF DrQESTION.

other animalcules with their internal sacs filled with this
coloured matter ; the same was done by Trembley ; and
these stomachs are figured by Miiller, Bruguiere, and most
others ; but Miiller supposed that they fed upon water, from
their stomachs being most frequently filled with that fluid.
Ehrenberg has more extensively employed opaque colouring
matter to detect the forms of these internal cavities, and by
using principally carmine, sap-green, and indigo, carefully
freed from all impurities which might prevent their being
swallowed, he has succeeded better than his predecessors in
unfolding the structure of the digestive organs of animal-
cules. Such coloured organic matter, diifused as fine
particles mechanically suspended in the water in which
animalcules are placed, is readily swallowed by them, and
renders visible, through their transparent bodies, the form
and disposition of their alimentary cavities; but, how-
ever long they remain in these coloured infusions with their
stomachs distended with the colouring matter, it is not
perceived to communicate the slightest tinge to the general
cellular tissue of their body. They appear to possess an
acute sense of taste in rejecting coloured metallic and other
substances which might prove hurtful to them, and their food
appears to consist chiefly of smaller animals of the same
class and of particles of mucus or other decomposed organic
matter found in the water.

In most of the polygastric animalcules there is an ali-
mentary canal, with an oral and an anal orifice, which
traverses the body, and is provided with numerous small
round coecal appendices, which open into its parietes
throughout its whole course, and which appear to perform
the office of stomachs in receiving and preparing the food.
In the simplest forms of animalcules, however, as in the
monas atomus (Fig. 107- A.), there is but one general
orifice (107. A. b.) to the alimentary cavities (107. A. d.)9
which is placed at the anterior extremity of the body and is
surrounded with long vibratile cilia (10J. A. «,) which serve
both as organs of motion and tentacula. The several
stomachs (A. d.) covered by the general wide integu-
ment, (A. e.) open by distinct short cesophageal canals
(A. c.) into the common buccal orifice (A. #.), and
there is no separate anal aperture for the excrementi-

ORGANS OF DIGESTION.

307

tious residue of digestion. This simple form of digestive
apparatus found in the monads appears to belong to about
forty other genera of this class, which, from this circum-
stance of having no intestine passing through their body,
have been formed into a group designated anentera. In the
monas termo which is only about the two-thousandth of a
line in diameter, four to six of these small round stomachs
have been observed filled with colouring matter, although
they did not appear to be half the number which might be
contained in its bodyj each of these stomachs, of about the
six-thousandth of a line in diameter, appears to open, as in
other anentera, by a narrow neck into a wide funnel-shaped
mouth, surrounded by a single row of long vibratile cilia,
which attract the floating organic particles, or minuter
invisible animalcules, as food. This anenterous form of the
digestive apparatus, constituting almost the entire organiza-
tion, is found both in the sheathed or loricated and in the
naked forms, belonging to the lowest genera of this class,
many of which, however, have been found to be only the
young of supposed higher genera.

The intestine which traverses the interior of the body in
all the higher forms of polygastrica, and communicates with
all the internal stomachs, presents very different forms in

x 2

308 ORGANS OF DIGESTION.

different genera. In the vorticella citrina (Fig. 107- B.) the
intestine (b, c, d, e.) passes downwards without dilatation,
and after bending round in the lower part of the body,
it ascends more narrow to terminate at the same lateral
oral funnel-shaped ciliated aperture (B. a.) at which it
commenced, having numerous coecal dilatations or stomachs
(B. f.) communicating with its interior throughout its
whole course. This circular form of intestine, opening at
both its extremities in the same ciliated aperture, is per-
ceived also in the carchesium, zoocladium, ophrydium, vagini-
cola, and other genera, which from this character form the
group termed cyclo-cala. In some animalcules of this
group, as in the stentor polymorphus, (Fig. 107- C.), the
circular intestine is regularly sacculated, or alternately
dilated and contracted, throughout its whole course
(C. b, c, c, d.), and from these dilated parts the little
stomachs (C. f.) take their origin. In other species of
stentor the intestine is twisted in a spiral manner through-
out its circular course. Many of the polygastric animalcules
which approach nearer to the helminthoid classes in
the lengthened form of their body, have the mouth and anus
placed, as in higher classes, at the opposite extremities of
the trunk, as seen in the enchelis pupa (Fig. 107. D0> where
the intestine, passing straight and cylindrical through the
body, from the wide ciliated terminal mouth (D. «.), to the
opposite dilated rectal termination (D. £.), gives off very
numerous coecal cavities (D. /, /.) along its whole course.
Such animalcules form the group termed ortho-coela from
the straight course of the intestine. In others, however, as
the leucophrys patula (Fig. 107. E.), the intestine passes in
a spiral course through the short and broad trunk of the
animalcule, giving off digestive coeca (E. f.} in all parts of
its course, from its ciliated wide oral extremity (E. a.) to the
saccular rectum (E. b.) at the opposite end, and such animal-
cules as present this spiral form of the alimentary canal com-
pose the group of campylo-ccela, of which there appear to be
few known genera. About thirty-five genera of polygastric
animalcules appear to have an intestine of some form (ente-
rodela), passing through their transparent body, and deve-
loping from its parietes minute globular coeca, which are
regarded as stomachs, from the quickness with which the

ORGANS OF DIGESTION. 309

food is conveyed into them, and from its not being ac-
cumulated or retained in any other part of the digestive
apparatus. Nearly two hundred stomachs have been count-
ed in a paramcecium and in an aurelia, filled with food at the
same time, and there may have been many more, unseen from
their empty and collapsed state. These digestive sacs are
contracted filiform and almost invisible when empty, but they
are susceptible of remarkable dilatation, and are sometimes
seen distended with water, or smaller animalcules, or portions
of confervre swallowed as food ; and the forms of these minuter
animalcules can often be detected in the half-digested masses
expelled from their posterior opening. Viewed through the
microscope, the polygastric animalcules present very dif-
ferent appearances, according to the quantity and the kind of
food contained in these digestive sacs, and from deceptions
of this kind twelve different species of animalcules, belong-
ing to six supposed distinct genera, have been formed of the
single species vorticella convallaria. Although no muscular
apparatus is perceptible in the transparent bodies of the
polygastrica, distinct maxillary or dental organs are seen in
many species belonging to very dissimilar genera. They
consist of numerous long straight, stiff, elastic spines, dispos-
ed parallel to each other, and arranged so as to form an oral
cylindrical proboscis, capable of being extended, widened, or
contracted, to seize and compress the soft prey. No gland-
ular organs to assist in digestion have been observed in this
class of animals, notwithstanding their dental apparatus and
the multiplied cavities of their alimentary canal. They are
often observed to swallow animalcules nearly as large as
themselves, and which could not be lodged in any of the
digestive sacs ; these appear to remain in the distended ali-
mentary canal, and they render them, for a time, inactive*
One polygastric animalcule often contains many hundreds of
smaller prey within its body, and, notwithstanding the
almost invisible minuteness of the animals of this class, and
the great simplicity of their structure,, they appear to be at
once the most numerous, the most active, the most prolific,
and the most voracious of all living beings. In some of the
minutest forms of monads we are often unable to perceive
any internal cavity ; in others, from one to a very variable
number of cavities are rendered visible by coloured food — an

310 ORGANS OF DIGESTION.

anenterous monad with a single cavity presents the simplest
form of the digestive apparatus known among animals. In
some of the larger paramfecia the food appears to move freely
in round masses through the general internal cavity of the
body, and these are sometimes accumulated at one end of
the animal and sometimes at the other. The straight ali-
mentary canal with its numerous lateral appendices in the
orthoccela, approaches most nearly to that of many hel-
minthoid articulata, as the halithea, the leech, and many
inferior forms of annelida, rotifera, and entozoa. The open-
ing of these coeca on the surface of the body, and changing
the direction of the food's motion, would produce the form
of alimentary organs presented by the poripherous ani-
mals.

II. Poriphera. The alimentary apparatus of poripherous
animals, by the peculiarity of its form and the simplicity of
its structure, approaches the nearest to that of plants ; the
cellular tissue of their body is permeated in all directions by
ramifying and anastomosing canals, which begin by minute
superficial pores closely distributed over every part, and
terminate in larger orifices variously placed according to the
exterior form of the entire animal. In the minute superficial
absorbent pores we can generally perceive a fine transverse ge-
latinous net-work (Fig. 2.N.) an dprojectingspicula, to protect
these entrances from the larger animalcules and from noxious
particles floating in the water. The internal canals, like the
veinous system, leading from capillaries to trunks, are bound-
ed internally by a more condensed or more highly organised
portion of the general cellular substance of the body, and
are incessantly traversed by streams of water, passing in-
wards through the minute pores, and discharged through the
larger orifices or vents ; but no polypi have been observed in
any of those parts, nor even cilia, although from analogy we
may suppose them necessary as the active agents of the
currents. In this simple organization there appears to be
only an increased extent given to the general cutaneous
absorbent surface; there are yet no distinct cceca or
stomachs for receiving and retaining the aliment that has
been conveyed into the body along with the currents
of water. These animals in their earliest free and
moving condition, while they are in the state of gemmules.

ORGANS OF DIGESTION. 311

and for some time after their development in a fixed condi-
tion has commenced, present no perceptible canals or cavi-
ties of any kind in their body 5 nor do the polypipherous
animals while they continue in the same free state of ciliated
moving gemmules. As the development of the porifera
proceeds, minute openings are observed to form on the sur-
face, which extend gradually through the body, producing
internal canals which terminate superficially in vents or fecal
orifices. From the incessant currents conveyed through the
body of these animals, it would appear that all parts of their
interior, like the exterior surface, of their general cellular
tissue, are adapted to admit by endosmose, and to assimilate
nutritious matter to the texture of their body. On watching
the streams of water that issue from the vents, minute floc-
culent particles are observed incessantly detached from the
interior, and thrown out with the currents, these appear to
be fine mucous pellicles excreted from the surface of the
internal canals, as the residue of digestion thus detached
from the body. A similar mode of excretion is often seen
on the naked mucous surface of zoophytes, where thin
pellicles are -periodically detached from the soft exterior of
the body.

In the spreading sessile species of porifera, as in the halina
papillaris (Fig. 108.) so common on all parts of our coasts, both
the small absorbent pores (108. «, a, a.) and the larger fecal
vents (108. b, b.) are necessarily disposed on the same general
external free surface, the inferior surface (108. g.} being fixed
to the rocks or other sub-marine bodies and thereby com-
pletely closed. The upper free portion of the body, as in
most other animals, is more appropriated to nutrition, and the
lower or posterior part to generation. A vertical section of
the body, shows the continuation of the pores (108. d.) which
lead to the larger branches, canals (108. e.) and vents (108.
b, b.). Along with the small portions of feculent matter
(108. b. b.) are seen propelled from the vents numerous
ovate reproductive gemmules (108. c. c.) after they have
been developed in clusters (108. /.) in the deeper parts of
the body, and have escaped into the internal canals (108.
/*•/*•)• In the tubular species, as in the leuconia com-
pressa (Fig. 3.), the whole outer surface or periphery of the
body is appropriated exclusively to the absorbent pores

312

ORGANS OF DIGESTION.

FIG. 108.

whicn lead obliquely upwards through the parietes to the
general internal cavity, and from this cavity the currents
pass out by an inferior orifice (Fig. 3 d.), the upper part
(Fig. 3. c.) in such forms being the closed part of attach-
ment. The proper vents in such tubular species are there-
fore only seen upon opening the parietes and observing the
inner surface (Fig. 3 b.} which is entirely covered; with
orifices of a larger size than the exterior pores. In the
branched forms of poriphera, which, from the softness of:
their texture, appear always to hang downwards from their
point of attachment, the whole outer surface is closely
studded with minute pores, as in the haliclona oculata (Fig.
2 A. «.), and from these pores the anastomozing canals
wind through the interior to open on the margins of the
branches by wide prominent vents (Fig. 2 b. b.). The
vents are disposed in all the different forms of porifera so as
least to incommode the absorbent pores by the flocculi of
matter constantly discharged from them with the currents.
The vents are raised from the general absorbent surface to
the ends of projecting papilke (Fig. 108. b. b. c. c.) in those
species which are attached to the acclivities of rocks ; there

ORGANS OF DIGESTION. 313

are no such papilla) on those which fix on the under surface ;
the vents open on the outer margins of the ramified forms
(Fig. 2 b. b.), and they open into the interior of the tubular
species (Fig. 3. b.), so as to be most free from the absorbent
pores which would readily be obstructed by the mucous
flocculi and particles of foreign matter propelled from the
large orifices. The absorbent canals of poriphera are like
the ramified roots of a plant turned inwards, and from the
simplicity and similarity of their structure in every part they
are susceptible of infinite division without destroying their
vitality, and distinct individuals, by coming into contact in
the progress of their growth, easily coalesce to form one
mass.

III. Polypiphera. In the polypipherous animals or zoophy-
tes the digestive organs are more distinct from the common
cellular tissue of the body, and present a more complicated
form than in the porifera, as the margins of the pores are
here lengthened out to form little stomachs or polypi, or-
ganised to select, and seize, and digest living animalcules ;
parts of the lips of these polypi are also still further extend-
ed to form sensitive prehensile tentacula, and the sides of
these tentacula develope numerous minute filiform cilia, by
the rapid vibration of which currents are produced in the
water to attract prey. In the hydra or fresh-water polype,
the whole digestive apparatus consists of a simple sac, exca-
vated in the cellular substance of the body, and destitute of
all cceca or glandular appendices, and even of a distinct
anus. The parietes of this simple polype appear to possess
the same properties in every part, as they continue to seize
and digest food when the animal is turned inside out, and
each part of the animal, when cut to pieces, is found to
develope itself to a perfect polype. What was formerly the
internal digestive surface is found also to become the genera-
tive, and to produce gemmules and young polypes when the
animal is turned inside out. They feed chiefly on larvae and
annelides which they search for and seize by the long tenta-
cula developed from the sides of their mouth, and they often
swallow animals many times larger than their own body, by
stretching their thin elastic parietes over their prey. The
digested part of the food passes through the common cellular
tissue of their body, and through their tubular tentacula,.

311 ORGANS OF DIGESTION.

and the residue is thrown out by the mouth. In most of
the soft flexible vaginated forms of zoophytes, or keratophy-
tes, the posterior part of the polypus, which is the surface
of attachment in the hydra, is perforated by a pyloric orifice
to allow the digested part of the food to pass backward into'
the circulating system, as shown by Cavolini in sertularia,
plumularia, campanularite, and most other forms. The
polypi in those vaginated forms of keratophytes are the only
parts of the fleshy substance of the body which come into
free contact with the surrounding element, and they con-
stitute highly irritable and sensitive sacs, the tentacula
surrounding the margins of which are generally provided
with vibratile cilia to produce currents, and attract prey
within their grasp. The whole digestive and circulating
cavities ramified through the body of these animals form an
approach to those ramified through the common cellular
substance of poriphera, but here there are no common vents
or fecal orifices. From the transparency of the polypi and
of their horny enveloping cells, we can easily perceive the
contained food while it is being digested, and that the excre-
mentitious residue is thrown out by the same orifice by
which it entered, while the digested nutritious portion is
successively transmitted backwards through the pyloric
orifice, to be circulated through the central fleshy cavity
pervading all the ramifications of the body. These move-
ments of the digested matter through every part of the
fleshy substance of keratophytes, appear to depend on in-
ternal vibratile cilia, as the movements of similar globules
in the tubular fleshy feet of echinoderma, and in many
other parts of radiated animals. The polypi of the alcyonella
have a distinct lateral anal termination of their digestive canal,
and they further approach to the vorticella in their double
series of tentacula, which are here provided with vibratile
cilia. The digestive polypi have a more complicated and
isolated structure, in the cellaria andflustra as in iheflustra
carbesia (Fig. 63.), where the stiff elastic tentacula (63. d.)
disposed in a campanulate form and furnished with vibratile
cilia, are supported on a dilated portion of the body like a
head, and where the alimentary cavity has not only a length-
ened cylindrical curved intestinal form, but is even provided
with a distinct coecal or glandular appendix (63 b.) opening

ORGANS OF DIGESTION. 315

into its posterior portion. This small coecum, the rudiment
of a liver, presents a continued revolution of the particles
contained in it, and is sometimes seen to pulsate like a
heart. It is smaller in .the flustra foliacea where the lower
curved part of the polypus is dilated into a wide gastric
cavity. These polypi have also distinct bands passing
from their body to the aperture and to the base of the cells,
apparently to assist in their rising and retreating ; the polypi
appear to be capable of subsisting in an isolated condition,
when detached from the cells to afford space for the develop-
ment of the gemmules, as I have often found them
swimming free in the water by the rapid contraction and
extension of their tentacula. It is chiefly in the lowest zoo-
phytes and in the smallest and simplest forms of polypi that
the tentacula are furnished with vibratile cilia, as in sertula-
ria, plumularia, cellaria, flustra, alcyonium, alcyonella ; in
some, as campanularia and tubularia, the cilia are disposed
round the extensile lips, and the tentacula are simple ; and
in many higher forms of polypi, as in madrepora, gorgonia,
and lobularia, where the cilia have generally a similar dispo-
sition around the mouth, the tentacula are furnished with
lateral appendices which are not vibratile, and the stomach
open at both ends, forms a separate internal sac, as in
actinia, allowing the gemmules of each separate polypus to
escape through this open passage. The large polypi are
more nearly isolated in their condition in many of the
massive lithophytes, as in the large deep-green polypi of the
astrea viridis (Fig. 109. A. B. C.), where they are more
than six lines in length, and protected in deep laminated poly-
gonal cells (109. A. g. h.) two lines in diameter, they are
striated with longitudinal (109. A. b.} and transverse (109. B.
C. d. d.) bands, and are connected only by a thin fleshy layer
(109. A. /.), covering the dark brown coral, and scarcely
perceptible when the polypi are retracted into their cells
(109. A. e.f.}. The numerous bright-green tentacula (C. c.),
alternately large and small, disposed around the very pro-
minent blue mouth (C. a.) of the polypus, appear to
constitute a double row of simple arms as in the tubularice,
and the surface of the polypi in their contracted state is
marked with regular vertical rows of prominent tubercles
(6. d.). The polypi of lobularia are provided externally

316

ORGANS OF DIGESTION.

FlG.

with regular vertical series of dense white glistening calcare^-
ous spicula, attached to their parietes, and the internal
cavities of these polypi are continuous with the long tubular
radiating canals which traverse and almost constitute the
entire fleshy mass of the body. The internal structure is
very similar in pennatulce and viry.ularue, where the mature
free ciliated gemmules also pass out through the open cavity
of the stomach. In many zoophytes, each polypus forms a
separate animal, as in several tubularm^ caryophyllice, and
fungi® where the cells are as isolated as the polypi. The
caryopfayllia cyathus is composed of an isolated calcareous
cell, containing a large polypus with a double row of conical
tubular tentacula destitute of cilia or any kind of lateral
appendices, and altogether constructed like an actinia in its
digestive sac and its vertical ovarial partitions. In the
winding superficial concavities of the meandrime is protected
the variously-coloured fleshy mass of the animal, with
numerous short conical polypi form orifices having generaUy
eight marginal lobes, the remnants of the eight fimbriated
short teotacula so common in the higher forms of zoophytes,
and along the margins of the prominent calcareous ridges

ORGANS OF DIGESTION.

317

are seen numerous conical tubular fleshy tentacula, like the tu-
bular feet of a holothuria. In the still deeper and more isolated
concavities of the pavonice are found the large depressed ex-
panded polypi, with eight-lobed orifices, and closely re-
sembling the sea-anemonies in their exterior form and
internal structure, as seen in the deep-green polypi of the

FIG. 110.

pavonia lactuca (Fig. 110. a. «.), from the shores of the
South Sea Islands. The transparent, common, connecting,
fleshy substance of these polypi, becomes a thin arid almost
imperceptible layer at its exterior margins, but rises, in the
expanded condition of the animal, even beyond the extreme
edges of the delicate calcareous foliated expansions (110. c.)
which compose this elegant lithophyte, and thus extend their
limits by the addition of calcareous matter. The eight short
lobes (110. b.) of the oblong oral disc of these broad depressed
Npolypi (110. a. «.), are the only traces of marginal tentacula
which they present. The cavities containing the polypi are
almost destitute of those vertical prominent sharp ridges
and depressions, which mark both surfaces of the undulating

318 ORGANS OF DIGESTION.

foliacious expansions, and which increase in depth towards
their free elevated dentated edges (110. c.), and the nu-
merous brown-coloured papillae, spread over the yellowish-
green surface of the polypi are the rudiments of the conical
tubular feet so largely developed on many other lithophytes.
From the magnitude and muscularity of the polypi in most
of the larger forms of lithophytes, and from the increased
number and strength of their prehensile organs, they are
adapted for seizing and digesting more highly organized prey,
than those delicate minute cellular forms which attract the
smaller floating animals by vibrating the cilia of their tenta-
cula. The most complicated forms of fixed polypi, and
those which approach the nearest in structure to the free
and independent actiniae, are generally those which have
the largest and most isolated cells, as we observe already in
the prominent lips and internal partitions of the polypi of
tubularice, and their double row of tentacula destitute of cilia.
In the caryophyllue, where the whole animal is sometimes
composed of a single polypus with its cell, as in caryophyllia
cyathus, the tentacula are not only disposed in a double
series around the flat disk of the polypi, but are also short,
thick, membranous and tubular as in most actinia, and
ciliated internally like the tubular conical feet of most echi-
noderma, and the corresponding hollow organs of the higher
zoophytes. In the turbinolia, likewise, which consists of a
single conical calcareous cell with thin vertical radiating la-
mellce, there is but one large actiniform polypus with a flat
disk, a transverse oral aperture, and a sub-duplicate series
of long tubular conical tentacula, disposed around the margin
of the fleshy disk; the exterior surface of these tubular tenta-
cula is sometimes irregularly tuberculated, like those of
many inferior vaginiform zoophytes, and as we perceive in
those of the simple hydra. The polypi of fungia more
closely resemble actinia than those of any other lithophyte,
as seen in those of fungia actiniformis (Fig. 111. A.) and
fungia crassitentaculata (Fig. ill. B.), from the South
Pacific. In these broad expanded isolated polypi, envelop-
ing a solid lamellated calcareous axis (ill. D. C.), the
transversely-elongated central mouth is lobed on the margin
(111. A.), or surrounded with lively-coloured tubercles (ill.
B.), as in many actiniae ; and the whole surface of the fleshy

ORGANS OF DIGESTION.

319

FlG. 111.

disk is covered with long muscular tubular conical prehensile
tentacula, disposed irregularly, with minute terminal aper-
tures, striated with transverse muscular bands, and pro-
truded by the injection of water into them from below, like
the tubuliform feet of echinoderma. In the fungia actini-
formis (111. A. D.) the tentacula are very numerous, long,
brown-coloured, slender, sub-cylindrical, and terminated by
a yellow-coloured, dilated, perforated disk ; the general
surface of the polypus is yellowish-coloured with green
striae; the long, convoluted, white ovaries, like those of
actiniae, are protected between the vertical plates of the cal-
careous axis (111. D.) ; the flesh passes likewise over the
inferior surface of the axis which is concave, and laminated
on that part as above ; and when the animal is alarmed the
tentacula are withdrawn between the upper vertical lamellae,
the flesh shrinks downwards between these plates and is
found accumulated chiefly on the under concave laminated
surface of the axis. The tentacula are larger, fewer in num-
ber, more muscular, thick, and conical, in the fungia crassi-
tentaculata (111. B. C.) ; they rise from a yellowish-coloured
flesh covering the flat upper surface of the lamellated orbi-
cular axis (111. C.) ; they are formed like leeches, striated
transversely, of a brown colour, and terminate in a greenish-

320 ORGANS OF DIGESTION*.

yellow perforated disk capable of seizing and conveying to the
central mouth of the polypus the smaller crustaceous or mol-
luscous animals brought within their reach. The most com-
plicated and most isolated forms of the polypi, or digestive sacs
of zoophytes, are the free, locomotive actinia, destitute of a
calcareous axis, and where the muscular and nervous sys-
tems, and the organs of digestion, generation, and respira-
tion are already distinctly developed. Strong muscular
bands surround the coriaceous external contractile covering
of the body, and others extend vertically to the spreading flat
base ; a thick muscular sphincter, to enclose all the delicate
parts of the disk, surrounds the upper and exterior margin^
and another the entrance of the stomach ; and numerous ver-
tical muscular partitions, extending from the upper disk to
the base of the actinia, and from the exterior skin inwards to
the gastric cavity, divide this peripheral space, as in most of
the higher zoophytes, into numerous genital compartments
occupied by the long, white, convoluted, filiform ovaries, or
gemmiparous sacs, attached to the inner free margin of mem-
branous alternate folds extending inwards from the skin.
The capacious stomach, provided with a muscular and mucous
coat lined with vibratile cilia as in other zoophytes, and
striated with vertical opaque bands and plicae, occupies the
axis of the body, and communicates as in other highly-or-
ganized polypi, with the genital cavities below. These lateral
cavities between the stomach and the skin, communicate
with each other, and with the numerous muscular conical
tubular tentacula which are lined internally with vibratile
cilia and are perforated at their free apex, like the tubular
feet of higher radiata : so that every part of the actinia is
capable of being bathed and distended with the surrounding
element like a respiratory organ, and the stomach is easily
protruded from the mouth by the distension of the genital ca^
vities behind with that fluid. The actinia, like the hydra, free
and unfettered by a solid axis, stretches its elastic body over
prey many times larger than itself, and by the great digestive
powers and copious secretions of its most capacious stomach,
it quickly extracts nourishment from all kinds of animal sub-
stances, living or dead, which are brought within the reach
of its adhesive poisonous secretions and its expanded tenta-^
cula by the ceaseless motions of the tide. The sand, gravel)

ORGANS OF DIGESTION. V2 1

and broken shells, often swallowed with the food and found
distending the stomach, are thrown out by the same oral
aperture when the stomach is protruded. The margins of
the oral disk, supporting the tentacula, are sometimes found
extended in foliaceous expansions, and covered with minuter
forms of these sensitive organs, by which the prehensile and
respiratory surfaces are also increased in extent. In others
the tentacula aie tuberculated on the surface, or are length-
ened and ramified with the luxuriance of many inferior
alcyonia, or like the roots of a rhizostoma, or the radiating
divisions .of a euryale, as we see in the actinia alcyonoidea
(Fig. 112. A. C.) and the actinia arborea (Fig. 112. B. D.),

FIG. 112.

two large species from the South Pacific. The cylindrical
body of the actinia alcyonoidea (112. A.) striated longitu-
dinally with numerous undulating brown-coloured bands,
terminates above in a circular green disk spotted with
deeper shades of the same hue, and presenting a lively rose-
coloured oral aperture in the centre. From the outer margin
of the disk sixteen large cylindrical ramified tentacula extend
to the distance of half-a-foot from the mouth, and have all
their divisions terminated by rasemose enlargements (112.
C.) which are closely covered with minute pedunculated
suckers (112. C. b. c.), by which the sensitive, the prehen-
sile, and the respiratory surface of this remarkable zoophyte
is greatly increased, and it is better enabled to perceive and
to grasp larger prey floating or swimming freely through the

PART III. Y

322 ORGANS OF DIGESTION.

sea. The ramifications of the long, thick, and longitudinally
striated tentacula of the actinia arbor ea (Fig. 112. B.) render
that isolated polypus, which is more than a foot in height,
still more dendritic in outward form than the last species ;
and the smaller size of its body (B. a. b.) makes it more nearly
approach to the higher stellated echinoderma, as the ophiura,
comatula, and euryale, where the nutritive organs are con-
fined, as here, to a small central disk. The deep blue-colour-
ed disk around the mouth (112. D.), between the thick bases
of the ramified tentacula, is here also marked with numerous
brown-coloured spots, regularly disposed on yellow bands
radiating from the mouth to the margin of that surface, and
the dichotomous character of the branched tentacula (112. B.
b. c.) is seen even in the minute fleshy tubular filaments (B.
d. d.) which cover the terminal tubercles of all the branches.
The adhesive mucous exudation from the surface of all those
ramified tentacula, as in other actinia, inflames and irritates
the human skin, and may serve alike to seize and to destroy
the victims which fall within their grasp. In the pedun-
culated form of the lucernaria, with its soft irritable body
and central digestive simple sac like an actinia, and its
connected radiating pedigerous divisions, we are also ap-
proximated to the condition of the higher stellated echino-
derma, and especially to the pedunculated crinoid family, so
that, from the simple isolated sac of the hydra, which is
alike generative and digestive in every part, we pass through
a great and most diversified series of zoophytic forms, to the
complicated structure of these large independent actiniform
polypi, where separate parts of the body are already dis-
tinctly appropriated to the most general and important
functions of organic life.

IV. Acalepha. The soft transparent gelatinous acalepha, float-
ing like large animalcules through the sea, are but free digestive
cavities, like inverted zoophytes detached from their stony
axis, and have their alimentary organs extended through every
part of their mantle, their long filiform tentacula, and their
pendent ramified peduncles. Among the ciliograde acalepha,
the beroe'pileus has a straight alimentary canal passing through
the long axis of its body, commencing at the lower part with four
thin prominent contractile and highly irritable lips surround-
ing the wide oral aperture. The contracted oesophageal part is

ORGANS OF DIGESTION. .32.1

succeeded by a gastric expansion of this straight canal, contain-
ing frequently minute entomostracous Crustacea which have
been swallowed as food, and a narrow straight intestine ter-
minates in a prominent anal orifice at the upper part of the
body. The numerous ciliated canals conveying currents and
globules through every part of the animal appear to be
connected with the alimentary cavity, as in zoophytes and
in other acalepha, and currents of water appear to flow
through the alimentary canal in its empty state. In the
aldnoe vermiculata, provided also with eight longitudinal
bands of vibratile cilia, the alimentary canal passes straight
through the axis of the body, surrounded below, at its oral
entrance, as in beroe, with four prolonged marginal lips,
but here of a lengthened conical form like the tentacula of
polypi. Numerous coecal prolongations from the cavity of the
stomach are seen in physalia extending into the abdomen and
are generally found to contain portions of the digested food.
The digestive sacs of the physophora resemble the polypi of
companularia, but destitute of tentacula, and their contrac-
tions are seen to aid the progressive motions of the animal in
floating through the water, as the contractions of medusa
and of some heroes assist in their progression. The wide
tubular proboscis in the centre of the lower surface of the
velella (Fig. 6. 1.) leads to a capacious stomach occupying
the middle part of the body, from which minute orifices
appear to extend to the numerous small tubular suckers
placed around the mouth ; and the same structure is seen in
the porpita where the digestive cavity, the only important
system yet developed, is protected above, as in velella, by
the firm internal skeleton. Around the delicate margin of
the berenice, which was thought to be agastric, there are
numerous prominent papillae, the tubular passages of which
lead to a wide central stomach. Most of the small physo-
grade acalepha, as well as the larger pulmodrade medusaria,
like inverted zoophytes torn from their fixed attachment and
floating through the sea with their polypi extended in all
directions, have numerous small pendent orifices at the
extremities of peduncles more or less ramified and extended,
and these polypiform mouths lead by narrow canals to
a central sac, from which the nutritious matter is sent by
numerous radiating ramified ducts to all parts of the body.

324-

ORGANS OF DIGESTION.

Larger and more direct openings, varying in number in
different animals, are also generally observed leading into
this gastric cavity, which is sometimes central and single,
and in others is divided into compartments disposed around
the vertical axis of the disk. From the transparency of
every part of the body in the rhizostoma Cuvieri (Fig. 113.
A. B.) the limits of the central gastric cavity (A. d.) and of
the four surrounding ovarial sacs (A. e* e. e. e.) can be
easily perceived through the thick parietes of the mantle, and
also the numerous ramifications of wide vessels which extend
from the circumference of this quadrangular stomach to the
purple-coloured, lobed, highly vascular, and respiratory
margin of the disk (A. B. h. h.). The peduncle hanging
from the centre of the disk divides into eight branches (A. r.

FIG. 113.

ORGANS OF DIGESTION. 325

c.), which terminate below in simple lobed dilatations (A.
a. a. a. a.} having their surface marked with numerous
depressions which are the orifices of internal canals (A. a. b.
c.) leading upwards to the stomach. In the middle and
upper parts of these eight branches there are fimbriated
membranous extensions (A. /. B. /. k.) the numerous
vessels of which also anstomose with the principal ascend-
ing trunk of each peduncle. On making a vertical section of
this rhizostome through the centre of the disk (113. B.) we
observe the internal canals (B. b. c.) commencing from the
polypiform orifices of the branches (B. a. a.) receiving all
the lateral absorbent or respiratory canals (B. f. /. k. k.} in
their course, and uniting above to form one large oesophageal
passage (B. ra.) before entering the wide central gastric
cavity (B. d.) There are more than twelve open
pores, the polypiform orifices of these digestive tubes,
perceptible on the lobed trilateral dilated base of each
peduncle (A. B. a. a.} and the delicate mucous
lining of all these digestive cavities can scarcely be
detached from the general cellular tissue of the body which
they traverse. Thin membranous partitions (B. /. /.)
separate the cavity of the stomach (B. d.) from the four
surrounding ovarial sacs (B. e. e.) which open externally
by distinct apertures (B. i. i.) and sixteen canals radiate
from the periphery of the stomach, dividing and anastomos-
ing as they proceed towards the outer margin of the disk
(B. h. h). The myriads of minute ramifying canals, anas-
tomosing freely with each other, form a continuous compli-
cated plexus around the free margin of the mantle, and
spread extensively on the coloured lobes (B. h. h.) which
bound its periphery, thus forming, as in the pteropods,
a respiratory apparatus of the most active organ of locomo-
tion. In many of the higher medusa, as in the medusa auri-
ta (Fig. 113. C. D.) the mouth is single and opens directly
from the centre of the inferior surface of the mantle, into a
capacious stomach from which numerous vessels radiate to
a circular canal surrounding the margin of the disk. The
mouth • of the medusa aurita is of a quadrangular form,
supported by four curved cartilaginous plates, from which
are suspended four lengthened tapering lips or tentacula
(C. D. p. p.] as we find on the sides of the mouth in most

326 ORGAN'S OF DIGESTION.

*'

conchiferous mollusca. On inverting the disk (D) we
observe the short quadrangular oesophagus in the centre,
leading to a capacious gastric cavity partially divided into
four sacs (C. d.) and from each of these sacs numerous
alimentary canals (D. q. q. q. g) radiate towards the mar-
gin of the mantle, ramifying with great regularity, but pre-
senting few anastomoses compared with those of the rhizos-
tomes. Around the lower part of the stomach are disposed
the four ovarial sacs (D. e. e e. e) containing the coloured
ovaries, and opening externally each by a distinct aperture
as in other medusae. The inner surface of the stomach has
a spotted follicular appearance, and this divided cavity is
separated by a double membrane from the open ovarial sacs
beneath. From around the margin of the stomach there
come off sixteen canals, alternately simple and ramified, which
end in the circular vessel (D. r. r.) passing round the mar-
gin, and by placing the living medusa in sea water tinged
with indigo, the stomach (C. d.) the radiating vessels (D. g.
g. g. g.) and the circular marginal canal (D. r. r.) are soon
found filled with the blue coloured infusion while the rest
of the animal remains colourless. A nervous circle is seen
around the oral passage from which the long tentacula (C. D.
p. p.) are suspended; another nervous cord accompanies
the circular canal (D. r. r) around the free margin of the
mantle which is fringed with a rowT of minute tentacula (D.
o.o.) highly sensitive and in constant motion ; the organs of
vision (D. n. n.) are placed in the sight depressions around
the free edge of the disk ; and in the middle of each of the
eight lobes of the mantle, between each pair of eyes, is
seen the dilated anal termination of a simple excrementitious
canal (C. D. o. o. o. o.) generally containing the indigesti-
ble remains of very minute articulated and molluscous ani
mals, which are thrown out by these eight marginal ani on
alarming the medusa. Currents of digested matter are seen
moving through the radiating ciliated canals of medusae, as
in those of the ciliograde acalepha and the corresponding
organs of other radiated classes. In the carybdea marsupia-
lis, which was thought to be agastric, there is a central infe-
rior oral aperture, surrounded by four short conical tentacu-
la, the stomach is partially divided into four compartments,
from each of which a canal extends to the free margin of the

ORGANS OF DIGESTION. 327

mantle; these four radiating alimentary canals are conti-
nued down through the four long marginal tentacula which
extend 'from the edge of the disk, and the parietes of the
stomach appear to be already provided with ramified biliary
follicles which pour their secretion into its cavity. From the
remains of minute rotifera, Crustacea, and mollusca, found
in the alimentary cavities of the rhizostome forms of acale-
pha they appear to subsist on animal matter more highly
organised than' themselves, and already divided into very mi-
nute ^parts, so that they require neither masticating nor
glandular organs to assist in digestion ; but in the monosto-
matous species adapted for larger food, the cartilaginous
parietes of the mouth may compress or divide the prey,
and the biliary follicles aid in its assimilation.

V. Echinoderma. The structure of the digestive organs
in these fixed or slow-moving, thick-skinned, predaceous
animals is as various as their outward form and their liv-
ing habits, and presents the links of transition from the
broad and radiated alimentary cavity of the acalepha to
the long cylindrical narrow intestinal canal common to the
articulated classes. In many of the stellated echinoderma,
as the euryale, the ophiura, and the asterias, we observe a
simple sac with one orifice, as in the hydra and the simplest
polypi of zoophytes ; in others, as the comatula and encrinus,
the digestive canal is more lengthened and curves upon
itself, as in alcyonella smdflustra, and has an anal opening
distinct from the mouth ; and in the echinida and holothur-
ida there is a long narrow convoluted intestine passing
through the body, with as little gastric enlargement as in the
long straight intestine of a worm. But in these various forms
of echinoderma the digestive cavity is always bounded by
parietes distinct from the common integument of the body,
as in all the higher classes of animals, and is generally
connected with them by means of a highly vascular mesen-
tery. The mouth of the asterias, surrounded with long tu-
bular tentacula and protected by fasciculi of calcareous
spines, is situate, as in most cyclo-neurose animals, in the
centre of the inferior surface of the body, and by a short
oesophagus leads to a wide and most dilatable stomach
provided with a distinct internal mucous lining and an
exterior muscular tunic, and occupying the whole central

32iJ ORGANS OF DIGESTION.

part of the body from which the marginal divisions ori-
ginate. In the ophiura and euryale the digestive sac, with its
ten small rudimentary cceca, are entirely confined to the central
disk, but in the asterias two long tapering ramified coeca,
like the biliary follicles of higher classes, commencing by a
single trunk, extend from the stomach to a very variable
length into each division of the body. Each of these rami-
fied coeca of the asterias is attached to the integument along
the upper part of the ray by a delicate vascular membrane,
and its lateral ramifications terminate in small vesicular en-
largements generally filled with digestive matter, or the
secretion of their own parietes. The stomach is also
furnished with small short coeca at its upper part within the
disk, and at its sides between the great coecal trunks of the
rays, which likewise vary much in their forms and dimen-
sions in different species. Above the stomach and towards
the side is situated the small glandular sac covered externally
with a solid calcareous plate and containing numerous
minute crystalline calcareous spicula. In the comatula there
is a distinct gastric cavity, and an alimentary canal long and
cylindrical, forming two convolutions round the stomach in
the central disk or abdomen, and open at its anal extremity.
The mouth forms a large circular aperture towards one side
of the centre of the inferior surface, and a small sub-
marginal anus is seen at the opposite side, not far from the
mouth, and opening at the end of a prominent papilla. The
same structure of the alimentary cavity with its two distinct
and approximated openings is seen in the pentacrinus, and it
appears to have been the common form of the digestive
canal in that great and almost extinct family of crinoid ani-
mals.

The mouth becomes furnished with strong masticating and
salivary organs in the higher forms of echinida; and while it
preserves its central position on the lower or anterior surface
of the body, the anal orifice leaves that surface to assume a
diagonally opposite position in the centre of the upper or pos-
terior part, which prepares the structure for the lengthened
horizontal forms of the holothurida and the articulated classes
of animals where the axis of the trunk ceases to preserve the
vertical position so general in the radiata. In the sou-
tellum and the clypeaster both orifices still preserve the

ORGANS OF DIGESTION.

inferior surface, the anal aperture has acquired a sub-dorsal
aspect in the spatangus and many of the genera now extinct,
and in the cidaris and echinus the mouth and anus occupy
the opposite poles of a vertical axis. In the spatangus,
which burrows in the moist sands and passes that substance
constantly through its body in order to derive nourishment
from the innumerable minute animals contained in it, the
mouth, destitute of teeth and furnished with numerous long
tubular tentacula, is placed on the lower flat surface towards
the obliterated ambulacrum, and leads to a long convoluted
black-coloured delicate alimentary canal which performs two
revolutions in opposite directions, attached by a thin vas-
cular mesentery to the upper part of the shell, and terminates
at the marginal aperture on the posterior part of the body.
The slight gastric enlargement at the commencement of this
long intestine receives the opening of a single lengthened
hepatic follicle or coecum. The mouth of the echinus., which
subsists chiefly on young mollusca and Crustacea, is provided
with a strong dental apparatus (Fig. 8. 2. 3.) embracing
the commencement of the oesophagus, and is surrounded
with delicate fimbriated contractile lips and numerous long
tubular tentacula. The intestine, with a slight gastric dilata-
tion and of variable diameter in its course, forms a double
convolution in a waved direction round the axis, and is
attached by a short vascular mesentery, containing minute
tubercles like glands, to the interior of the shell. The anal
aperture, at the upper pole of the vertical axis, is surrounded
by a membranous expansion, sometimes with valvular
folds, and is provided, like the mouth, with circular and ra-
diating muscular bands for its contraction and dilatation. The
structure is nearly the same in the cidares which present the
most globular forms of the echinida, but the forms of the
slight saccular enlargements in the course of the alimentary
canal, and the zig-zag manner in which the intestine ascends
and descends in performing its revolutions round the axis,
vary much in the different species of cidaris and echinus. In
its general conformation the holothuria is like a lengthened
echinus deprived of its calcareous plates, and with the axis
of the trunk extended in a horizontal direction. The mouth
and anus are placed at opposite ends of the body, with a
long convoluted alimentary canal, almost destitute of gastric

330

ORGANS OF DIGESTION.

cavity, and connected to the sides of the abdomen by a vas-
cular mesentery, passing from the one aperture to the other,
as seen in the annexed figure of the holothuria elegans
(Fig. 114.) by W. Bell. The mouth (114. a.) is generally
surrounded with long tentacula in form of ramose tufts (holo-
thuria of Lam.) in others the tentacula are simple, and
expand only at their free ends (fistularia of Lam.), and some-
times long saliyary follicles (b.) open into its parietes. The ten-
tacula, capable of complete retraction within the oral aper-
ture, are supported by the circle of osseous plates to which
the strong longitudinal muscular bands of the trunk are

FIG. 114.

ORGANS OF DIGESTION. 331

also attached. The oesophagus leads to a slightly enlarged
gastric portion (114. b. d.) of the intestine, which receives
the secretion of a large biliary follicle (114. c.) The
intestine is generally filled with sand and comminuted
shells, and the holothuria commonly lie among the ejecta-
menta of the sea where they appear to partake of a very
mixed and heterogeneous kind of food. The whole surface
of their body is traversed by longitudinal rows of long fleshy
tubular feet for progressive motion and to secure attachment ;
and on the lower surface, near the anterior extremity of the
trunk, is the common opening of all the divisions of the
ovary (114. k. k.} as in many of the entozoa and annelida.
The tentacula, like the tubular suckers along the body,
are protruded by the injection of a fluid into them from
their base. The long convoluted intestine (1 14. d. d.) passes
backwards along the whole extent of the abdomen, then
returns to near the mouth, and again turns backwards to ter-
minate in the middle of the cloaca (1 14,/.), connected along
this course, by a short delicate vascular mesentery (114. e. e.)
to the sides of the trunk. The two long ramified tubular
branchiae (1 14. h.) terminate in the cloaca by separate orifices
on each side of the rectal extremity of the intestine ; after
receiving the orifices of several small follicles (U 4. i). A
mucous, a muscular, and a peritoneal coat can be detected
on the delicate intestine of the holothuria, as in several other
echinoderma. The nutritious part of the food is taken
from the intestine by the mesenteric veins (114. /.) and
conveyed, with the venous blood of the system, to the long
ramified internal branchiae (114. h. h.), from which it is
again collected by the branchial veins (114. m.) to be dis-
tributed through the great systemic arteries without the
aid of a heart. As the cloaca (114,/.) is a capacious cavity
which inhales the water to be sent through the tubular
ramified gills (114. h. A.), the rectal portion of the intestine
(114. d.) is protruded through that cavity to the external
opening of the anus (114.^.) in evacuating its shelly con-
tents, as in the oviparous vertebrata. The whole digestive
apparatus of the holothurice are often forced out from the
body, through the mouth, by the contractions of the strong
muscular parietes of the abdomen, before death, and I have
found even the dental plates and their attached tentacula,

332

ORGANS OF DIGESTION.

protruded with the intestines in such circumstances. The
mucous coat of the intestine, near its commencement,
sometimes presents internal longitudinal plicae. The ali-
mentary canal is most variable in its extent and convolutions
in different species of holothurite, and also the forms of
their dental plates, according to the nature of their food.
In the holothuria ananas (Fig. 115) which is nearly two

FIG. 115.

feet long, found in the South Sea, and prized as an article
of food in the Molucca islands, there are twenty long
pedunculated tentacula (115. b. b.) around the mouth (115.
a.) which terminate each in a concave disk, embracing nu-
merous red-coloured tubercles. The tubular fleshy feet
here cover irregularly the delicate inferior or ventral surface
^f the abdomen ; and those of the upper coriaceous surface

ORGANS OF DIGESTION. 333

of the animal, having a flat foliaceous tapering form, are dis-
posed like imbricated scales, and are perforated like the
abdominal feet. Numerous long salivary follicles (1 15. d. d.)
pour their colourless secretion into the mouth, and near
them are placed the two long ramified coloured ovaries (115.
e. e.} as in other holothurise. From the dental apparatus, sur-
rounded by the muscular parts and integuments of the
mouth (115. a. c.), the narrow oesophagus (115./.) leads
to a capacious and lengthened stomach (115. g.) with nu-
merous vessels (115. h.) extending from its parietes along
the reticulate mesentery. The intestinal canal (115. f. g. i.)
which in some species is more than ten times the length
of the whole body, is here only about twice that length,
and was found turgid with sand. The rectum 115. k.) with
strong parietes, terminates at the upper part of a long
cloaca (115. /.) which is supported by numerous lateral
bands (115. m. m.) and presents on its two sides the wide
orifices (115. r.) of the long ramified arborescent branchiae
(115. p. p. o. o.) which ascend as high as the mouth.
The anal opening (115. n.) of the cloaca, and the orifices
(115. r.) of the two gills, are here so wide and so constantly
open, that Crustacea more than a quarter of an inch in
diameter, were found living and residing in these passages,
and this active cloaca was found to retain its high irrita-
bility after the animal had been cut to pieces. The dental
organs, so powerful and complicated in the cidaris and
echinus, and so variable in their extent of development in
the holothur'uB and fistularia, have lost their calcareous
matter in the priapulus, and are wanting in the long ver-
miform sipunculi which present a lengthened retractile tu-
berculated head, a wide funnel-shaped oesophagus, and a con-
voluted alimentary canal many times the length of the body,
destitute of gastric dilatation, furnished with a few biliary
follicles, and returning from behind to open externally near
the mouth. Thus the digestive cavity, from the condition
of a simple monostome sac, filling the whole abdomen, in
the lower stellated forms of these animals, has gradually
acquired the form of an elongated tubular narrow canal, open
at both ends, and furnished with biliary and salivary follicles,
in the helminthoid echinoderma, as in many helminthoid
articulata.

334 ORGANS OF DIGESTION.

THIRD SECTION.

Digestive Organs of the Diplo-neurose or Articulated
Classes.

The lengthened cylindrical and articulated form of the
body in the helminthoid and entomoid classes, is that best
suited for the creeping, piercing, parasitic and carnivorous
habits, so characteristic of this great division of the ani-
mal kingdom, and the internal organs of these animals,
especially the digestive, partake of this straight and ex-
tended form of the trunk. In the radiated animals, which
are almost all stomach, the shortness and the vertical
position of the axis, and the lateral expansion of the
alimentary cavity, often enable them to dispense with a
second orifice to their digestive sac, and better adapt them
for seizing and swallowing entire the smaller animals so
numerously spread through the waters of the globe. The
carnivorous character, so general in the articulated classes,
and even the highly organized condition of their prey, are
indicated by the limited capacity and by the short and
straight course of their alimentary canal, which almost uni-
versally opens at the two opposite extremities of the body,
and by the numerous prehensile and destructive instru-
ments so commonly placed at its commencement. As they
are nearly all free animals, with power of rapid locomotion,
and with a relatively high development of their nervous
system and of their organs of sense, they are well adapted
by their instincts and their organs of animal life to admi-
nister to the vegetative, by distinguishing and overtaking
the most suitable and highly organized prey. As the sim-
ple and straight form is a character impressed upon the
alimentary canal of the articulata, both by the narrow
cylindrical form of the trunk and by their predaceous ha-
bits, we observe greater uniformity in its plan of structure
than in the other divisions of the animal kingdom, although
the endless modifications of their organs of relation enable
them to seek their prey in every element and in every situa-
tion. The mouth is here generally provided with masticating

ORGANS OF DIGESTION.

335

organs which move laterally and are provided with palpi ;
and hard parts subservient to this function are often found
in the cavity of the stomach. The mucous lining of the
alimentary canal exhibits few developments of villi, folds,
or follicles, the salivary and pancreatic glands are rarely
perceptible, and the liver has generally the simplest folli-
cular form.

VI. Entozoa. The entozoa, subsisting on the living
fluids of animals more highly organized than themselves,
present generally the simplest condition of the alimentary
apparatus met with in the articulated classes, and from the
facility of assimilating the nutritious fluids which they
absorb, many of these animals dispense with a separate anal
orifice, and their digestive organs are thus often closely
approximated in form to the vascular or sanguiferous sys-
tem. In the cystoid forms of intestinal worms, as in the
simplest polypi, there is only , a buccal entrance to the di-
gestive sac, and that orifice is often numerously repeated
on the same sac, like the polypi of a zoophyte or the absor-
bent orifices of a rhizostome. In the hydatids, as in the
hydras, there is a simple digestive cavity destitute of an
anal aperture, but here, as seen in the cysticercus longicollis
(Fig. 116, A.), the buccal apparatus (A. a. b. c.)} is in form

d—

336 ORGANS OF DIGESTION'.

of a small white prominent head or papilla terminated anteriorly
with a double row of minute, sharp, conical recurved spines
(A. «.), and presenting around its sides four circular ab-
sorbent orifices (A. b.) From these orifices (A. b.} the ab-
sorbed fluids are conveyed by four slender canals through
a narrow neck (A. c.) into a thin transparent white mem-
branous sac (A. d. e.} more or less distended or contracted,
according to the state of repletion, and according to the pe-
culiar forms of the species. In the collapsed state of this
digestive bag, its anterior part (A. d.) assumes a narrow,
elongated, and corrugated form, and becomes more dense,
white, and opaque, with numerous transverse constrictions
which give it already an articulated appearance. A more
compound zoophytic form is seen in the ccenunts where nu-
merous minute heads, similarly constructed to those of the
cysticercus, open into the same common digestive sac or
vesicle. These heads are disposed in numerous groups over
the surface of a large transparent gastric cavity, and appear
as clusters of opaque white points. A small detached por-
tion of the general digestive sac of the ccenurus cerebralis,
highly magnified, and with three of the absorbent heads
preserved in different states of extension, is seen in Fig. 1 16 B.
The anterior terminal papilla of each head is surrounded,
as in the cysticercus, with a double row of recurved spines
(B. a. «.), and around the dilated part of the head are the
usual four perforated suctorial disks (B. b. b.) The head is
attached to a narrow neck (B. c. c.)9 capable of consider-
able elongation and contraction, and these passages all lead
to the same capacious general digestive vesicle (B. d.)
In the long flat cestoid forms of parenchymatous entozoa,
the structure of the head, with its absorbent pores, is very
similar to that of the hydatids. Around the anterior
median papilla of the tcenia, which is sometimes perforated
with a small pore, there is a double range of minute re-
curved sharp spines, and the four lateral perforated suckers,
disposed on the four angles of the head, lead to as many
canals, as in the cysticercus. The upper and lower canal
however on each side unite with each other to form one, and
these two lateral canals, thus constituted of the original
four, extend along the two sides of all the segments of the
body, as seen in two of the segments magnified of the tania

ORGANS OF DIGESTION. .1*

solium (Fig. 116. C. a. a.) These lateral digestive and
contractile tubes communicate with each other by a trans-
verse branch (C. c. c. c.) at the lower end of each segment
where they are constricted and valvular, and they open
externally by one or more lateral orifices (116. C. h.) on
the sides of each division of the body. The dendritic
ramifications of the ovary (C. d.) occupy the central part
of each segment, and open externally beside the intestinal
pore (C. h.), by a small distinct genital orifice (C. i), from
which likewise extends a styliform tubular duct (C. k.)
considered as a male organ (C./.) Besides the delicate exterior
skin covering all these organs, there is an outer transverse
and an inner longitudinal layer of muscular fibres which
produce the varied movements of this aggregate animal, so
that each segment of the teenia, which worm often exceeds a
hundred feet in length, possesses all the requisite organs
for nutrition and generation, as an entire animal, and no
gastric enlargement is developed in the whole course of
this alimentary tube. The four cesophageal canals however,
of the tcenea dispar, descending from the four lateral
cephalic pores, unite together in the middle of the neck
to form one median canal, which enlarges in each division
of the animal, and passes thus sacculated and continuous,
through all the segments of the body. Besides • the usual
lateral pores of the head a minute opening and canal are seen
in the apex of the prominent papilla in the middle of the
head of the botkryocephati, as in some of the tcenice. The
alimentary organs of the trematode worms are more ramified
and sanguiferous in their appearance than those of the ces-
toid entozoa; they commence by one or more orifices near the
anterior part of the trunk, and pass backwards ramifying and
anastomosing freely along the lateral parts of the body, des-
titute of an anal opening, as in the other parenchymatous
species. In the distoma hepaticum they form two parallel
trunks near the middle of the body, and ramify into minute
capillaries on the lateral parts, as they proceed tapering back-
wards to the posterior extremity of the animal. In the penta-
stoma they unite to form a single straight median canal in the
back part of the body ; so that we still observe the tendency
to form a simple longitudinal median canal in all these forms
of parenchymatous entozoa, as in the higher orders of this

PART III. Z

338 ORGANS OF DrGESTION.

class, and in the higher forms of articulata. The distoma
hepaticum is like a more highly organized segment of a tcenia,
in which we perceive a broad funnel-shaped oesophagus lead-
ing to two wide ramified alimentary canals occupying the
middle part of the body, while the ovaries here occupy the
sides, and two parallel ventral nervous filaments unite below
the oesophagus and ramify as they extend around that wide
passage. In the echinorhynchus there is a minute pore in the
centre of the armed head, which leads to a single alimentary
canal extending along the middle of the trunk and dividing,
before it terminates, as in the other parenchymatous worms.

In all the nematoid and more perfect forms of entozoa the
alimentary canal passes simple through the body, presenting
a distinct oral and anal aperture which are generally at the
opposite ends of the trunk, as in the higher articulata. The
ascaris, like the other nematoid worms, has a single oral
aperture at the anterior extremity of the body ; the three
marginal lobes of the mouth are provided with minute teeth
and moved by distinct muscles, so that the mouth somewhat
resembles that of the leech in its masticating apparatus.
The oesophagus forms a wide elongated muscular sac, like
that seen in the halithea and some other annelides ; it is con-
tracted at its lower part, and opens into a straight and wide
intestinal canal with thin parietes, and where the limits of
the stomach are seldom indicated by an inferior constriction.
The digestive canal passes straight through the middle of the
trunk, surrounded by the tubular windings of the testicle or
ovaries, to the posterior extremity where it opens by a small
traverse aperture on the inferior surface. In the strongytus
armatus (Fig 1 16. D.) the hemispherical disk of the head is
surrounded by dense, sharp, vertical teeth (D. a.), and the
short oesophagus (D. c.) opens into a wide intestine (D. d.)
without a distinct gastric portion and continued straight
through the trunk to the anus (D. e.) at the opposite end
of the body. The two long convoluted ovaries (D. h. h.)
wind round the alimentary canal in its whole course through
the trunk in the female, and unite to form a single vaginal
orifice (D. g.) below the middle of the body, the single
tubular testicle winds round the intestine in the same man-
ner in the male, and opens by a long projecting hollow
styliform organ of intromission at the posterior end of the

OKUAXS OF DIGESTION. .W.)

body. The straight and wide intestine of the stronyylus yi-
yas appears to be surrounded with short biliary follicles
during the greater part of its course through the body. In
the highest animals of this class, as the achtheres, ierntea,
peniculus, tracheliastes, brachiella and chondracantfyus, which
have a more entomoid form, and suck the vital fluids from
the delicate exterior parts of the skin of aquatic animals, the
mouth is already provided with small lateral unciform mandi-
bles, adapted to tear the surface to which the animals are
fixed ; and their alimentary canal, wide and short and with a
terminal anal aperture passes straight through the body,
surrounded by the biliary follicles and by the genetal organs,
as in higher articulated classes.

VII. Rotifer a. In the minute and transparent bodies of
the wheel-animalcules we observe the digestive, like the other
organic systems, to present the typical forms of the articulat-
ed animals. Their large transverse maxillae (Fig. 12.) are
moved by a powerful muscular apparatus (Fig. 11. b.) and ap-
pear in incessant action while they are surrounded by minuter
animalcules. Their carnivorous character is seen alike in the
living and mangled contents of their transparent stomach
(Fig. 1J. A.), and in the short and straight course of their
alimentary canal (Fig. 82. B). The alimentary cavity in
some, as the hydatina sent a (Fig. 11 7- A.) passes straight,
simple, and uniform from the narrow ossophagus (11 7- A. f.)
to its'posterior cloacal termination, without any perceptible
lateral coaca or follicles. They pursue their prey by vibrat-
ing the anterior circles of cilia (117- A. a.) by the muscular
lobes at their base which are attached to ligamentous bands
(117. A. b.) The large cerebral ganglion (11 7- A. c.) and
the smaller lateral ganglia (117- A. d.) surround the strong
muscular pharynx (117- A. e.) which is capable of being
protruded and retracted to a great extent and with great ra-
pidity. The living animalcules (11 7- A. g.) contained in the
stomach are easily perceived, and the whole internal structure,
through the hyaline texture of their body, and small glandu-
lar sacs (117. A. h.) are seen at the sides of the oesophagus
(117. A./.) which appear to send ducts to the muscular
pharynx (117- A. e.) embracing the masticating organs. The
dorsal vessel (117- A. L) extends along the middle of the
back, sending off numerous lateral branches in its course

z2

34o

ORGANS OF DIGESTION.

FIG. I;7-

forwards, and the sides of the abdominal cavity are occupied
chiefly by the large lobed sacs of the ovaries (11 7- A. k.) and
the long winding glandular sacs, considered as testicles (llj*
A. /.), which terminate behind the cloaca in a small vesicle
like a vesicula seminalis ( 1 1 7. A. m.) Their food is often brought
from a distance by vibrating their anterior cilia while their
body is attached to some motionless surface by the two long
terminal fleshy retractile peduncles (117- A. n.) In some,
as the stephanoceros, the food is collected in a large buccal
cavity, anterior to the maxillae and behind the tentaculiform
ciliated arms, before it is submitted part by part to the act of
mastication. The gastric portion of the alimentary canal va-
ries much in its form in different rotiferous animalcules. In
the diglena, enteroplea, synchaeta, and brachionus, it presents
a less uniform and more globular form than in the hydatina
(Fig. 82. B-.) In the diglena lacustris (Fig. 117- B.) the
sharp pointed maxillee (117- B. a.) arid their muscular appa-
ratus (117. B. b.} are succeeded by a lengthened and narrow
oesophagus (117« A. c.) which opens into a short denned glo-
bular stomach (11 7. B. d.) From different parts of the

ORGANS OF DIGESTION. 341

stomach two large (117- B. e.) and five small (117. B. f.)
elongated coeca arise, which appear like hepatic or glandular
follicles, and do not admit into their interior the larger undi-
vided portions of the food contained in the general gastric
cavity (117- B. d.) From the pylorus, the intestine continues
downwards, narrow and nearly straight, to terminate (117-
B. ff.) in the cloacal opening at the posterior end of the body,
close to the two fleshy peduncles. The whole alimentary
canal, from the mouth to near the anus, is narrow and cylin-
drical in the rotifer vulgaris, and follows a slightly winding
spiral course through the body, closely surrounded with large,
short, biliary follicles. At its rectal termination, however,
it suddenly enlarges to form a wide globular colon. The
same structure, nearly, is seen in the alimentary cavity of the
philodina roseola (Fig. 11 7. C.) where the maxillae (117- C.
a. a.) and their muscular apparatus (117- C. b.) and the two
pharyngeal sacs or glands (117- C. h.) are succeeded by a
narrow and straight oesophagus (117- C. c.) and intestine
(1 17. C. d.) The narrow intestine is closely surrounded by in-
numerable short straight biliary follicles (! 17. C. e. e.) or glan-
dular cceca, throughout its whole course from the oesophagus
(117.C. c.) to the short dilated colon (117. C./.) which opens
by its rectal orifice (l 17. C. g.} into the cloaca where the genital
organs also terminate, as in most of the higher articulata.
The lower part of the intestine is slightly curved upwards
upon itself, so as to lengthen its course, in the brachionus
urceolaris and pterodina patina. The stomach and the
whole alimentary canal of the rotiferous animalcules move
freely and loosely backwards and forwards, to a great extent
in the wide and ciliated cavity of the abdomen, during the
contractions of the long, slender, transparent muscles which
extend longitudinally from the anterior end of the body,
and the two glandular pharyngeal sacs of very variable form
accompany them in their motions to and fro. The whole
cavity of the abdomen, as well as the wide cavity of the
intestine, in these transparent and colourless animals, appear
generally as if distended with pure water, and vibratile cilia
appear to be in rapid action both on the mucous kand the
peritoneal coats of the alimentary canal.

VIII. Cirrhopoda. The masticating and digestive appa-
ratus of the cirrhopods present the same close affinities to

ORGANS OF DIGESTION.

those of the articulated classes which we observe in the ex-
ternal form of their body, and in all their organs of relation.
The mouth, as seen in the pentalasmis (Fig. 11 7. D. E. F.
a. a. 0.), provided with serrated mandibles which move
transversely, and with a pair of maxillae with rudimentary
palpi attached to them, opens by a short contracted oeso-
phagus (117- E. b.} with longitudinal internal folds, into
a capacious sacculated stomach (11 7- E. c.) furnished with
t\vo large ccecal appendices and closely surrounded by the
numerous small lobes of the liver (117- F. c.) Two distinct
lobulated salivary glands (1 17- D. h. F. b.) pour their secre-
tion into the mouth, and the numerous small compacted
lobes of the liver (117- D. e. F. c.) open freely by short ducts
with wide orifices (117- E. d. d.) into the cavity of the
stomach, as in most invertebrated classes. From the con-
tracted pyloric orifice of the stomach, the wide and corrugated
intestine (117- D- b. c. E. e. F. d. d.) passes along the dorsal
convex part of the body, presenting an annulated appearance,
and having a distinct muscular coat of transverse fibres and
longitudinal bands, but without convolutions or a distinct
mesentery. The concavity left on the fore part of the
body, by this wide curved intestine, which follows the course
of the closed posterior portion of the shell (Fig. 13. i. e.),
is occupied chiefly with the mass of the ovary (Il7« D. k.)
and the wide oviduct (117- D- 2.) surrounded with the
testicle. The rectal portion of the intestine (117. D- c. F. d.)
opens, along with the oviduct, into the base of the long
capilkited muscular tubular proboscis (117- D- c. d.), by
which the residue of digestion is conveyed freely from the
interior of the shell to which the animal is fixed. The food
is brought within the cavity of the mantle, and within the
reach of the three pairs of maxillae, by means of the respi-
ratory currents and by the incessant movements of the long
curled ciliated feet, and it appears to be recognized by the
palpi, the upper and lower lip, and rudimentary antenna,
without the aid of organs of vision which are here oblite-
rated in the fixed adult animals, as they are in the fixed
adult state of the epizoa. By the lobulated or conglomerate
form, and the great development of the biliary and salivary
glands, and by the numerous wide ducts by which the liver
communicates with the cavity of the stomach, the cirrhopods

ORGANS OF DIGESTION. 343

are allied to the molluscous classes, which they also resemble
in their fixed condition and their testaceous covering, in
the adult state.

IX. Annelida. Notwithstanding the difference in the
forms, habits and food of the annelides, there is great
similarity in the structure of their digestive organs, which
generally pass straight through their elongated body, with
the mouth and anus at the opposite ends, with slight gastric
dilatations in their course, and with an imperfect develop-
ment of the hepatic and salivary glands. This simple
condition of the alimentary canal, accords with the animal
nature of their food ; but as that food is received in various
conditions, sometimes mixed in minute particles with earth
or sand, and sometimes consisting of larger animals, there
is greater diversity in the masticating organs which, in some
of the higher annelides are numerous and complicated in
structure, and in others are altogether wanting as in the
earth-worms and many of the tubicolous species. The
masticating organs generally consist of numerous pairs of
lateral superimposed horny unciform maxillae as in higher
articulated classes; but in those provided with a sucking
organ, as the leech, the mouth is furnished with numerous
approximated, hard, sharp, recurved teeth, like those common
in the molluscous classes. In some, as the earth-worm, the
mouth presents a distinct upper and lower lip, as in the
entomoid classes, and in others as the phyllodoce the interior
of the mouth is capable of being protruded in form of a large
proboscis or like the head of a sipunculus. The wide and
capacious mouth of the earth-worm (Fig. 82. D. a.) is
furnished with a large upper and a smaller lower lip, soft,
fleshy, and of great sensibility, and a small salivary gland,
and leads by a narrow oesophageal portion of the canal to a
slightly enlarged sacculated stomach, consisting of three
continuous cavities, placed immediately behind the genetal
organs, about a third from the anterior end of the body.
The second of these muscular digestive cavities is lined
with a tough coriaceous easily detached coat to protect it
from the earthy matter taken in with^the food. The stomach
opens into a narrower part of the intestine which continues
along the middle of the trunk (82. D. a. b. b.) slightly tor-
tuous in its course, and gradually enlarging as it descends

344 ORGANS OF DIGESTION'.

to the anus, where distinct levator and sphincter muscles
are perceptible. The exterior of this intestinal portion,
from the stomach to near the anus, is surrounded with small
short biliary follicles, generally filled with their yellowish-
brown coloured secretion. The whole alimentary canal of this
animal is commonly found filled with the moist black earthy
soil in which it lives, and which it incessantly conveys
through its body to derive nourishment from the organized
particles so abundant in that matter. The alimentary canal
is more tortuous in its course, more capacious throughout,
with its gastric portion less distinctly marked, in the delicate
transparent short body of the pectinaria, and even in the
long distensible trunk of the arenicola, which, like many
other worms and echinoderma, transmit incessantly the
moist sands of the sea through their intestine, to extract
as food the innumerable minute animals contained in that
medium. The coriaceous lining is seen in the lower portion
of the more lengthened stomach of the arenicola, as in the
earth-wrorm ; and below this part are the openings of two
yellow-coloured biliary follicles, lengthened in form like
those of insects. Within the muscular sucking disk of the
mouth, in the medicinal leech, there are three crescentic
horny jaws, supporting each a row of sharp acuminated
teeth, with which it files its triradiate wound. The intestine
passes straight through the long axis of the body, sacculated
in a regular manner, and furnished with short wide lateral coeca,
nearly throughout its whole course. There are ten of these
coeca on each side, and smaller enlargements of the intestine
are interposed between each pair ; the coeca increase gradually
in size from the first or anterior to the ninth pair ; and the
two posterior coeca, which are much larger than any of the
others, extend backwards along sides of the remaining
short portion of the intestine. This sacculated part of the
intestine occupies about two thirds of its whole length,
and terminates, like a stomach, in the succeeding straight
portion, by a narrow elongated valvular pylorus. The short
and wide oesophagus is marked internally with longitudinal
plicae of its mucous coat, and the duodenal portion of the
intestine, beyond the pyloric valve of the long sacculated sto-
mach, is furnished with numerous transverse folds confined
also to its inner membrane. The colon enlarges into a small
round sac before it reaches the anus. The number of the gas-

A.\S C;F LMOKSTION. 345

trie coeca varies in different species, the long posterior pair are
the most constant. These sucking annelides live chiefly on
the smaller aquatic animals which swarm around them in the
stagnant waters they frequent. I have taken the entire legs and
other parts of the common triton cristatus from the stomach
of the hirudo sanguisuga so abundant in our fresh water pools.
The intestinal canal is sacculated nearly through the whole
extent in the pontobdella ; but the numerous cells are here
more short and round than in the leech where they gene-
rally taper to a point. The small mouth of the halithea acu-
leata, furnished with two conical tentacula or antennae, opens
into a short membranous oesophagus, which terminates in a
large muscular stomach with thick firm parietes and a strong
coriaceous lining. The entrance of this muscular cavity is
furnished with four sharp, triangular, converging, horny teeth
analogous to those of the gastric toothed cavity of insects
and Crustacea ; and this sac is also analogous to the muscu-
lar stomach of the arenicola, lumbricus, and many other
annelides, and to that of the ascaris and other nematoid
entozoa. From this muscular gizzard, the intestine passes,
thin, membranous and wide, through the middle of the
trunk nearly in a straight course to the posterior terminal
orifice, giving off from the dorsal aspect of its sides, at
regular and short distances, long narrow cceca which send
out numerous branches and terminate in elongated sacs.
These two rows of elongated ramified coeca, coming off near
to each other from the dorsal side of the intestine by long
narrow ducts, and generally filled at their vesicular termi-
nations with a soft turbid brownish-coloured matter, like
that found in the coeca of an asterias, present a more ex-
tended, divided, and isolated condition, of the short coeca
of the leech and the simpler biliary follicles of inferior anne-
lides. In the halithea, which appears to subsist on a mixed
kind of food, like the pectinaria, form the sand and frag-
ments of shells commonly found in its intestine, the duo-
denal portion of the canal generally forms a slight redupli-
cation, as in that animal, by folding backwards upon itself;
but in the long articulated myriapodous forms of the tere-
bell&i amphitrites, and nereides the alimentary canal pre-
sents a more narrow and elongated character, and assumes
a zig-zag or tortuous course in its distended state, and es-

34(3 ORGANS OF DIGESTION.

pecially in the contracted state of the trunk. In the nereides
there is generally an exsertile broad proboscis (Fig. 14. 1. a.)
at the anterior end of the head, numerous lateral jaws which
are remarkable for their frequent unsymmetrical number
and development on the two sides of the mouth, a distinct
gastric cavity furnished with longitudinal internal folds and
with numerous sharp horny teeth, and an elongated intestine
furnished throughout the greater part of its extent with
lateral cceca, or biliary follicles, as in most of the higher
annelides.

The digestive organs of the entomoid classes, like most
of their other organic systems, are characterized by a more
elevated grade of the same plan of development followed
throughout the helminthoid articulata ; and by the higher
condition of their organs of sense and locomotion, they are
better enabled to select their food, and to overcome more
highly organized prey.

X. Myriapoda. In the long, equally developed, vermi-
form bodies of the myriapods, we still find an imperfect
condition of the masticating organs, and the most simple
helminthoid form of the alimentary canal, which accord
with the characters of inferiority marked in their other
organs, and with the cruel and carnivorous propensities
these animals display in the living state. The masticating
organs of the scolopendrae (Fig. 15), consist of a small pair
of mandibles and a similar pair of maxillae, which are fol-
lowed by two pairs of larger jointed organs formed by the
metamorphosis of the two first pairs of feet into masticatory
jaws. The mouth is furnished with an upper and lower
lip, and with long, simple, salivary follicles, like those of in-
sects, enlarged at their closed extremities. The alimentary
canal, like that of most of the higher annelides, passes
through the whole longitudinal axis of the body, with thin
membranous parietes, with little appearance of gastric en-
largements, and without convolutions. The contracted oeso-
phagus opens into a wider lengthened gastric cavity with
thin parietes, and this elongated membranous stomach is
succeeded, as in serpents, by a narrow small intestine which
terminates in a perceptibly wider colon : so that the alimen-
tary canal here presents affinities both to that of the higher
forms of worms, and to that of the vermiform ophidian rep-

ORGANS OF DIGESTION. 347

tiles. There appear to be three pairs of salivary glands of
unequal lengths, extending along the sides of the oeso-
phagus, in the scolopendra gigantea, besides two poison-
glands placed along the lower maxillee, which send their se-
cretions to the two strong piercing grooved articulated hooks
situated at the base of the jaws. From the elongated form
of the stomach in the scolopendrae, the two wide extended
biliary follicles have a low entrance into the alimentary
canal, as in most insects. The stomach has the same broad
elongated form in the iulus, where it is followed by a short
small intestine, and a more wide and lengthened colon
marked internally with transverse folds, and the biliary
tubular follicles enter the lower end of the stomach. The
single gastric cavity of the lithobius also receives, at its
valvular pyloric extremity, the terminations of the two bi-
liary tubes which extend forwards in a tortuous manner
towards the head, and are supported by a small ligament
at their closed anterior end. So that the two long terminal
cceca of the stomach of the leech have now assumed the
form of lengthened tortuous biliary vessels, as in the highest
winged insects, and they here open into the lower end of
the chylific stomach,, as in most of the animals of that class.

XL Insect a. The digestive organs have arrived at a high
degree of development in insects, and already present, in an
embryo-state, almost all the assistant chylopoietic organs of
the highest animals, as the liver, the salivary glands, the
pancreas, and many other parts important in the process
of assimilation. They vary much, however, in their form
and extent of development according to the consistence and
the nutritious quality of the food, the peculiar living habits
of the species, and the condition of the animals with regard
to their metamorphosis. The mandibulate forms of the
masticating organs are best adapted for comminuting hard
substances, and the 'tubular form or proboscis for sucking
food in a soft or fluid state, but even suctorial insects re-
quire some form of these hard parts to pierce the surface
from which they are to obtain their liquid food. The mouth
of insects is furnished with an upper and lower lip (labrum
and labium), a pair of strong proximate mandibles arid a pair
of exterior maxilke which move transversely. The labium
and the maxillee support each a pair of palpi ; the dense pos-

348 ORGANS OF DIGESTION.

terior part of this lower lip forms the mentum, and its soft
anterior portion supports the fleshy prominent tongue. The
masticating organs present infinite varieties of form accord-
ing to the difference of food in insects, as in other classes of
animals, but the same constituent parts of the mouth can
be recognized in all the different forms of mandibular and
haustellar apparatus. The same buccal organs form broad,
short, and strong cutting instruments, which move trans-
versely, in those insects which subsist on hard food, and
a long, slender, tubular apparatus, capable of extension and
retraction, in those, which suck fluid or soft substances.
These parts often change from the one form to the other in
the same insect, while it changes its kind of food in the pro-
gress of its metamorphosis ; and where the food is the same
in the larva and imago, the masticating organs preserve the
same form in these two conditions of the insect. The food
reduced by the mandibles and maxilla and mixed with the
secretion of one or more pairs of salivary glands, is trans-
mitted by a pharynx of variable length, to the oesophagus
and alimentary canal. The oesophagus commences by a
narrow canal which generally forms an enlargement of crop
at its lower part, for receiving and collecting the food when
first swallowed ; this enlargement of the oesophagus is often
covered with minute short glandular follicles which open
into its interior. Below the crop is a small but strong mus-
cular gizzard, with thick parietes, and provided internally
with numerous longitudinal rows of hard sharp conical horny
teeth. This muscular triturating stomach is most developed
where the hardness of the food most requires its aid, as in
most of the orthopterous and coleopterous insects ; but
where the food is liquid, as in most of the sucking hemiptera,
the gizzard is scarcely perceptible. The largest, the most
constant, and the most important gastric cavity in insects,
is the long, wide and highly glandular chylific stomach which
extends generally from the gizzard to the insertion of the
hepatic ducts. The chylific stomach is, for the most part,
amply furnished with considerable glandular follicles, which
are developed from its whole parietes, arid open by separate
orifices into its interior. This cavity is frequently of great
length, and partially divided by numerous transverse con-
strictions, it is then most wide and glandular at its anterior

ORGANS OF DIGESTION. 3 \*J

or proximal part, becoming narrower like the intestine at
its lower portion. The intestine, from the termination of
the chylific stomach to the anus, is most variable in its
length and capacity, and in the number and extent of its di-
latations. Like the masticating organs, the gastric cavities
and the whole alimentary canal have their forms regulated
and impressed by the kind of food which they are destined
to assimilate, or the quantity they are adapted to consume.
In the voracious and inactive condition of the developing
larva, the stomach is often found of enormous capacity com-
pared with the diminutive size to which it is reduced in the
more parsimonious and active state of the mature winged
imago.

The alimentary canal of insects presents a distinct in-
ternal mucous lining, an external peritoneal coat, and mus-
cular fibres, both transverse and longitudinal can be easily
perceived in its parietes. The interior of the mucous coat
presents a smooth surface, as in most of the lower inverte-
brate, having neither plicae, nor valvulse, nor villi, to increase
its extent, and exterior to this there is commonly a loose
cellular or follicular enveloping tissue. The exterior peri-
toneal coat forms a distinct thin mesentery, which is co-
vered with the minute ramifications of tracheae, and which
connects the convolutions of the intestine with the interior
of the abdominal segments. The ramifications of these
white opaque air-vessels on the mesentery are seen in the
common blue fly, and in most of the larger insects, without
the aid of a lens, and appear like the branches of blood-
vessels. The peristaltic motion of the intestine is obvious
on opening the abdomen of the living insect ; and in the
short trunks of many of these animals, the intestine measures
several times the length of the whole body. In insects, as in
other classes of animals, the simplest forms of the alimentary
canal, and of all the glandular organs connected with digestion,
are those belonging to carnivorous species, from the already
highly organized condition of their food requiring the least
delay and the least change for its assimilation. In the cicin-
dela campestris (Fig. 118. c.) which preys on other insects,
the digestive canal passes nearly straight through the body.
The oesophagus, commencing narrow as usual from the pos-
terior opening of the head (C «.) dilates below into a wide

350

ORGANS OF DIGESTION.

FIG. J13-

crop (C. c.} presenting several longitudinal rows of very
minute follicles. The crop is succeeded by a short muscular
gizzard (C. d.) and this by a capacious chylific stomach (C.
e.) covered with numerous glandular follicles, and tapering
downwards to its pyloric extremity (C./.) where it is per-
forated on each side by two simple convoluted hepatic ves-

ORGANS OF DIGESTION. .ol

sels (C. m.) From the chylific stomach the intestine con-
tinues downwards very narrow, and nearly straight, to a
short dilated colon (C. h.) which contracts before it termi-
nates in the cloaca. In the common blood-sucking bug, cirnex
lectularius (118, D.) the whole digestive apparatus is more
simple in its structure though more extended longitudinally,
the alimentary canal being about three times the length of
the short body of this insect. The mouth, armed with
piercing and sucking organs, receives the secretions of two
pairs of small salivary glands (D. n. o.) in form of simple
follicles terminated by minute vesicles at their closed ends-
The short capillary oesophagus forms a small conical crop
(D. c.) before entering the lengthened cavity of the chylific
stomach (D. e. f.) which is most dilated at its upper part
(D. e.) but is susceptible of considerable distension through-
out its whole course when filled with blood. The lower in-
testiniform portion of the chylific stomach, though here
represented for greater distinctness as drawn out nearly to
a straight course, is more convoluted in the short abdomen
of the living bug, and receives on each side at its narrow
pyloric termination (D./*.) the two orifices of short and sim-
ple hepatic vessels (D. m.) The remaining short and wide
intestine (D. h.) generally distended with a thick reddish-
brown coloured paste, the residue of digested blood, receives
obliquely the pyloric end of the stomach (D. f.) above and
contracts below into a narrow rectum before it terminates.
Although the biliary vessels (D. m.) here, as in most insects,
terminate in the stomach by separate orifices and without
cystic enlargements, distinct reservoirs for receiving and
collecting the bile are often developed at the insertion of
these tubes. In the pyrrhocoris aptera (Fig. 118. F.) which
feeds on the juices of the ripe fruits of malvacious plants,
and the intestinal canal of which, though more lengthened
and capacious, very much resembles in its whole structure
that of the cimex, the chylopoietic glands are much more
developed. There are three pairs of elongated salivary
glands opening into the mouth, and on the lower pyloric
extremity of the chylific stomach several minute simple pan-
creatic follicles (F. g.) are observed to open into its interior.
The biliary vessels (F. m.) are not only lengthened and wide,
but have thick glandular parietes, and they terminate on

352 ORGANS OF DIGESTION'.

each side in a single vesicular enlargement or gall-blad-
der (F. /.) before entering the stomach, which is here suc-
ceeded, as in the former insect, only by a short and capacious
colon (F. h.} and narrow tapering rectum. In the geocorises all
the lateral hepatic vessels terminate in a single median gall-
bladder. In the mandibulate herbivorous insects, which sub-
sist on coarser vegetable food, as the common coleopterous
cockchaffer, melolontha vulgaris (Fig. 116. A.) which feeds on
the leaves anil shoots of our garden plants, the whole digestive
apparatus is long, complicated, and capacious. The oesophagus
passes out narrow from the head (A. a.) and dilates below
into a short conical crop (A. c), which is succeeded by a very
minute gizzard (A. d.) and a long convoluted chylific stomach
(A. d. e. e. /.). The anterior portion of this lengthened
glandular stomach is wide and sacculated by numerous
transverse strictures, and terminates insensibly in a narrow
convoluted pyloric part, which dilates into a small round
vesicle at the lower end, where it receives the openings of
the hepatic vessels (A./1.). The two hepatic vessels (A. i. I.
m.) on each side are here, in accordance with the coarse
nature of the vegetable food, very long, wide, and convoluted,
and have their secreting surface greatly extended by the
development of innumerable small lateral follicles (A. i. k. I.)
which give them a pinnated form throughout the greater
part of their course ; thus presenting the most complicated
condition of the liver met with in insects. The lower portion
of the intestinal canal has also its capacity increased by
distinct dilatations on the parts analogous to the colon
(A. g.) and the rectum (A. m.} In the powerful, aquatic,
insectivorous naucoris aptera (Fig. 118. E.) the whole form
of the digestive organs closely resembles that of the cimex,
but there is a short, narrow, small intestine between the
chylific stomach (E. e.) and the colon, the pyloric end of
the stomach dilates, as in many insects, into a small oval
sac where it receives the hepatic vessels, the cardiac part
of the stomach is wide and partially sacculated, and the
crop (E. c.) forms an almost imperceptible dilatation at the
lower end of a small elongated oesophagus. The posterior pair
of salivary glands (E. p.) form wide cylindrical tubes which
terminate by short narrow ducts in the mouth, and the two
anterior shorter pairs (E. o. n.) divide at their closed extremities

ORGANS OF DIGESTION.

into clusters of small follicles, already forming lobules, like the
lobules of the tubuli biliferi in Crustacea. There are three pairs of
salivary glands, lengthened and complicated, in the scutellera
mgrolineata which feeds on the young seeds of growing corn.
The biliary tubes of this insect are very small, and they ter-
minate in a single median vesicular enlargement, forming a
minute gall-bladder. The chylific stomach, with its several
convolutions and enlargements, composes, as in most insects,
the greatest part of the alimentary canal. In the herbivorous
coreus marginatus, which feeds on the juices of several plants,
the digestive canal is more lengthened, but similar in
structure. There are four pairs of large elongated salivary
glands ; two pairs of short simple biliary follicles pour their
secretion into a single gall-bladder, and a pair of long
sacculated pancreatic follicles terminate separately in the
stomach above the entrance of the short cystic duct. This
simple form of the pancreas is seen also in the leptis, bomby-
liuSy chrysotoxum, and many other insects. In the cicada
orni (Fig. 118, B.) which appears to feed on the juices of the
pine, and not of the ash tree, the long narrow tubular
stomach (B. t), after forming numerous convolutions, returns
to terminate in itself, like the intestine of a vorticella or the
tubuli of many glands. In this, as in many other insects,
there are two distinct forms of salivary glands which unite
together to enter the mouth by a single duct on each side.
One of these glands is a simple convoluted follicle (Fig. 118.
B. p.) like the biliary and urinary tubuli, and the other gland
on each side of the oesophagus forms a posterior (B. o.) and
an anterior (B. n.) lobule, composed of small short follicles,
before terminating in the common duct. The long capillary
ossophagus dilates into a small crop (B. c.) before entering
the coecal cavity with which the chylific stomach (B. e. t.)
commences, and from which the intestinal canal (B. u.}
originates. The stomach (B. e.f, /.) in place of forming a
continuous canal, as usual, from the oesophagus to the in-
testine, here turns off suddenly from the direct course of the
alimentary canal, and, after forming numerous convolutions
as a small tube (B. t.), it returns, to terminate in its proximal
extremity (B./.), thus forming a circular elongated tubular
coecum. At the commencement of this long circular coecum,
the stomach receives the termitnaions of four isolated monili*

PART IV. A A

354 ORGANS OF DIGESTION.

form biliary vessels (B. m. m. /.). The small intestine
(B. u.) originates from a coecal cavity below the crop, and
forms a narrow convoluted tube, which dilates into a small oval
colon (B. h.) near the anus. This tubular anastomosing form
of the stomach, with four similar sacculated biliary vessels en-
tering its commencement, is seen in the aphrophora salicina
and other insects of this family. In the dorthesia characias,
the biliary vessels enter the narrow middle portion of a
similar anastomosing convoluted . gastric tube, and the
stomach describes the same circular course in the psylla ficus
where the biliary vessels are reduced, as in many other
insects, to four short isolated follicles.

The salivary glands are nearly as general in the class of
insects, as the biliary vessels, and they are often accompanied
in predaceous insects, as in the nepa, with distinct poison-
glands, which present the same simple follicular structure.
Although the biliary vessels are most frequently four or six
in number, and terminate generally in the phyloric extremity
of the stomach, they often exceed a hundred, and terminate
around two or more distinct parts of the lengthened gastric
cavity. Where these primitive tubuli biliferi are very nu-
merous, as in many orthopterous, neuropterous and hyme-
nopterous insects, they are generally small, short, and separate
at their distal extremity ; where they are more lengthened
and complicated they often anastomose at their free ends, as
in the glands of higher animals. In most of the coleopterous
insects with two sets of biliary vessels, whether simple or
rammed, the ends of the anterior set anastomose with the
posterior as in separate lobules. By the low and oblique
insertion of the small intestine into the wider inferior portion,
a distinct and often capacious coscum-coli, analogous to that
of vertebrated animals, is formed in many insects, as in
pelogonus marginatus, ranatra linearis, nepa cinerea, and
other species. The lower part of the intestine, also, fre-
quently receives one or more urinary follicles, or tubuli urini-
feri, which are found to secrete urea as in higher animals,
and on which a small vesicle or urinary bladder is sometimes
distinctly formed as in ditiscus marginalis and several other
coleopterous insects. The alimentary canal of insects termi-
nates in the cloaca along with the genital organs, as in ovipa-
rous vertebrata.

ORGANS OF DIGESTION. 355

XII. Arachnida. The carnivorous character of the
arachnida is indicated by the shortness and straightness of
their alimentary canal, and by its small capacity, as well as
by the poison-instruments with which they are often furnished,
and by the imperfect development of their chylopoietic
glands. They prey chiefly upon living insects, which their
cunning instincts, and their offensive weapons enable them to
ensnare and to overcome, and many parasitic species suck the
living fluids from the surface of higher animals. The mouth
of the arachnida, like that of insects, is furnished with a pair
of strong articulated mandibles, which are here often per-
forated near the point for the transmission of a poison-duct,
as seen in the spiders. The mouth is likewise furnished with a
small pair of palpigerous maxillae, a labium or inferior lip,
and a lingua. The pharynx of the spiders leads to a short
oesophagus, on which there are two pairs of small proven-
tricular sacs, opening together into the same part of the
canal, and which sometimes have the form of elongated
follicles. The oesophagus continues narrow from this multiple
crop, through the cephalo-thorax to the large abdominal
cavity, which is chiefly filled with the biliary lobules and
with the genital organs. The intestine here forms a small
round stomach, and continues straight to the anus at the
posterior end of the trunk, exhibiting a small dilatation or
colon before it terminates. The palpi in the male spiders
end in a wide oval bulb, containing the sexual organ, and
in the female the terminal joint of the palpi is slender and
elongated. In the parasitic acari the palpi are simple pedi-
form extensions of the maxillae, as in the spiders, and do not
terminate in prehensile pincers, like the large palpi of the
scorpions. There are several distinct follicular salivary
glands in the trombidium and other genera, which pour their
secretion into the mouth, like the two salivary glands of the
scorpions. The maxillae and tongue sometimes form a
lengthened piercing and sucking proboscis, as in sucking
insects. In the simpler tracheated species, the mouth ap-
pears sometimes to open by distinct orifices on both sides of
the head, and their small stomach is furnished with numerous
biliary follicles. The anal portion of the intestine in the
spiders receives the secretion of several urinary follicles,
which terminate in a small sac. or bladder, before opening

A A 2

356 ORGANS OF DIGESTION.

into the canal, as in many insects. The strong short mandi-
bles and the large palpi of the scorpions terminate in prehen-
sile organs, like the pincers of a crab, and embrace a capa-
cious buccal cavity like the stomach of a crustaceous animal.
From this wide oral sac, which is surrounded above by the
ganglionic cerebral ring, the alimentary canal passes, narrow,
tubular, and equal, through the abdomen and the tail, to the
beginning of the last caudal segment, where it opens on the
lower surface. In its course from the narrow oesophageal
part, which passes through the nervous collar to its anal
termination, the intestine of the scorpions forms neither crop,
gizzard, nor gastric enlargement ; but the portion contained in
the abdomen, like a tubular stomach, is surrounded with the
numerous lobes of the liver, which communicates with its
interior by five pairs of short wide ducts, opening at regular
distances along its sides. These five pairs of hepatic lobules
are more isolated conditions of the ramified intestinal cceca of
the halithea and other annelides, and at the lower part of
this elongated stomach originate also four distinct ramified
vessels, like some of the branched biliary vessels of insects,
but which here communicate with the two anterior compart-
ments of the heart, and with other parts of the vascular sys-
tem, as if they conveyed nutriment to the blood. Thus,
while the masticating organs of the arachnida approach these
carniverous animals more nearly to insects, their straight and
narrow alimentary canal, and the compact lobulated condition
of their liver, connect them with the Crustacea.

XIII. Crustacea. Like the spiders and scorpions of the
land, the crustaceous inhabitants of the waters are cunning,
cruel and carnivorous animals : with means of rapid locomo-
tion and numerous acute organs of sense, and with a solid
exterior protection and strong organs of prehension and
mastication, they are well fitted for preying on all kinds of
animals in the rich element they inhabit. They subsist on
living or dead animal food both higher and lower than them-
selves in organization ; most of them are in constant warfare
with each other, and many, from being free, become fixed and
parasitic in their adult state. The mouth in the higher
Crustacea is generally furnished with a pair of strong palpi-
gerous mandibles, and five or more pairs of jointed extended
maxillae, which move transversely, and support likewise articu-

ORGANS OF DIGESTION. 357

lated palpi ; the three inferior or outer pairs of maxillee are
the largest and the most convertible in their forms, and
support branchiee at their base like the ambulatory feet. The
entrance of the mouth presents an upper lip, a bifid tongue,
and sometimes a small under lip, formed by a pair of maxillae.
The .maxillae are often reduced to one or two pairs, or are
wanting, in the lower Crustacea. One or more of the anterior
pairs of ambulatory feet generally terminate in strong pincers
like the palpi of the scorpions. The wide buccal cavity of
the decapods, surrounded with complicated organs of sense
and of mastication, opens by a very short and narrow oeso-
phagus into a capacious stomach, provided internally with
several pairs of solid calcareous teeth, and occupying the
anterior part of the cephalo thorax. As their watery element
almost bathes this gastric cavity, they require no salivary
glands to soften their moist food. The gastric teeth, colored
and shed like the exterior shell, are symmetrically disposed
near the pylorus, and are supported by thin elastic calcareous
laminae, to which powerful muscles are attached, and which
cause the teeth to meet with precision in grinding the con-
tents of the stomach. In many of the parasitic species
attached to the surface of fishes, the mouth forms an extended
syphon composed of the prolonged lips, and embracing the
long, sharp, piercing mandibles, and in the limuli all the
masticating organs around the mouth have the form of ambu-
latory feet, terminating in pincers.

As in most other carnivorous articulata, the alimentary
canal of the Crustacea passes, without convolutions, through
the longitudinal axis of the body, and opens by distinct
apertures at its two extremities. The mucous coat forms
often rugae or folds in the wide oesophagus and stomach, but
passes smooth through the rest of the canal ; the muscular
layer is strongest at the orifices of the stomach, and the
peritoneal covering, as in insects, forms no mesentery in the
abdomen. The pyloric extremity of the stomach, near which
the gastric teeth are disposed, receives on each side a short
and wide duct from the large and lobated liver which en-
velopes this part of the cavity and the beginning of the
intestine. The gastric teeth are common to the Crustacea
with insects and other articulata, and many molluscous
animals. The hepatic duct on each side of the narrow

358

ORGANS OF DIGESTION.

muscular pyloric extremity of the stomach divides into
numerous smaller branches; these terminate in groups of
minute follicles, which compose the lobes and lobules of the
liver. The hepatic lobes in the larger decapods envelop the
oesophagus and sides of the stomach, extend backwards above
or between the branchial cavities, and beneath the heart and
genital organs, and fill the greater portion of the abdominal
cavity, as seen in the annexed figures of the male lobster,
astacus marinus (Fig. 119. A. B.) by W. Bell, where A re-
presents a vertical longitudinal section of the trunk viewed
laterally, and B a dorsal view of the principal thoracic and
abdominal viscera. The maxillae (119. A. a.) and mandibles,
with their palpi, are placed on the inferior aspect of the head,

FIG. 119.

between the anterior large ambulatory limbs and the two
pairs of antennae (119. B. a. b.). The two pedunculated

ORGANS OF DIGESTION. 359

compound eyes (B. c. c.) are lodged in orbital cavities above
the broad peduncles of the large exterior antennae (B. b.}, and
are protected by a spiny prominent median rostrum. The
short vertical oesophagus opens into a capacious muscular
stomach (A. b. B. d.) in which the teeth are disposed in pairs
near the contracted pyloric extremity, and which is surrounded
by the numerous lobes of the liver (A. B. n. n. n.). The
intestine (A. c. B. e.} receives at its commencement the two
hepatic ducts, and passes beneath the heart, (A. e. B. g.)
the testes (B. o. o.), and the posterior aorta (A. h. B. £.), fol-
lowing nearly a straight course to the anus (A. d.) which
is situate below the last segment of the trunk. The ab-
dominal cavity, containing these viscera is separated from
the thoracic containing the branchiae (B. /. /.) by a strong
tendinous diaphragm (B. m.). The colic portion (B. /*.)
embraced by the bifurcation (A. i.) of the posterior aorta
(B. k.) is more wide and dilatable than the rest of the canal,
like the colon of insects, and it is provided below with its
muscular sphincter, and sometimes with a valvula coli at its
commencement. Besides the biliary tubuli which compose
the large symmetrical lobes of the liver, and which are some-
times reduced to a few pairs of simple follicles in the lower
Crustacea, two or three pancreatic tubuli, lengthened and
isolated, are occasionally observed to enter the pyloric por-
tion of the intestine in the higher decapods, and the soft
rudiments of salivary glands are perceived at the sides of the
oesophagus in the same animals. The stomach and alimen-
tary canal (119. A. b. c. B. d. e.} occupy the dorsal portion of
the trunk in the Crustacea, and not the ventral part, as in the
vertebrata, which corresponds with the general inverted con-
dition of the other organs of the body in the articulated
classes. Although the stomach is thus large and powerful in
the higher mandibulated predaceous forms of this class, there
is often no perceptible gastric enlargement in the short
straight intestine of the lower sucking parasitic species. Thus
the alimentary canal and the chylopoietic glands are com-
paratively limited in their development in all the entomoid,
as in the helminthoid forms of articulata, which corresponds
with the general carnivorous character of these animals, their
inferior position in the scale, and the highly organized con-

ORGANS OF DIGESTION.

dition of the animal matter on which they commonly sub
sist.

FOURTH SECTION.

Digestive Organs of the Cydo-gangliated or Molluscous

Classes.

The low development of all the organs of sense and loco-
motion throughout the molluscous classes, compared with
those of the articulata, renders them less able to select and
overcome the higher forms of animals as prey, and requires
their digestive apparatus to be adapted for a more coarse and
varied kind of food. The slow moving or fixed animals of
this division, subsisting on organic matter in a lower con-
dition of development, and consequently more remote from
their own nature, possess a more extended and complicated
alimentary canal, and a higher development of biliary, salivary,
pancreatic and other glands, to assist in the complex process
of assimilation. The digestive canal of the mollusca almost
never passes straight through the body, nor is the posterior
orifice terminal, as it is in most of the articulata. The gastric
cavities are more distinct, more numerous, and capacious; the
intestine is more lengthened and convoluted, and the chylo-
poietic glands are not only larger, and developed on a higher
plan, but are more constant throughout the cyclo-gangliated
classes, than in the long extended trunks of the active and car-
nivorous worms and insects. The softness or subdivided
nature of their food, and the magnitude of their hepatic,
salivary, and other glands, enable the molluscous animals to
dispense with the numerous solid instruments of mastication
and prehension disposed around the mouth in the articulated
tribes, and their whole economy being thus adapted for the
absorption and solution of the softer and inferior kinds of
organized matter, teeth or other dense parts are more rare
in their digestive sacs, than in the entomoid and even the

O *

helminthoid classes.

XIV. Tunicata. The tunicated animals, the lowest and
simplest of the molluscous classes, subsisting on the minute
organic materials suspended in the waters of the sea, and

ORGANS OF DIGESTION. 361

having their buccal aperture situate at the bottom of a deep
respiratory sac, through which the aqueous currents are con-
veyed, exhibit no prehensile nor masticating apparatus nor
distinct organs of sense connected with the mouth. Delicate
tentacular filaments (Fig. 88. c.), analogous to the palleal
tentacula so common and numerous in the conchifera, are
generally disposed around the interior of the ciliated branchial
orifice (88. a.), and also of the anal aperture (88. b) or of the
anus (88. i)9 to guard these passages from the intrusion of
noxious bodies ; both these orifices serve sometimes for the
entrance and sometimes for the exit of the currents which
aerate the branchiae and bring food to the mouth. The oral
tentacula are wanting in the pyrosoma ; they are simple fila-
ments in the phullusia, and are ramified in some of the
cynthue. They are generally more simple around the vent and
around the anus than at the respiratory orifice, and in some
species small red ocular points are seen around both the
respiratory orifice and the vent. There are six of these red
ocular points around the vent, and eight around the branchial
orifice in the common soft transparent green-coloured ascidia
intestinalis of our coasts, and they resemble the rudimentary
eyes met with in many of the simpler forms of radiated and
helminthoid animals. The inner surface, and marginal
tentacula of the respiratory aperture, are ciliated to pro-
duce the currents, as in conchifera. The mouth, or entrance
of the oesophagus, generally forms an oblique transverse
aperture, with loose sensitive lips, at the bottom of the
respiratory sac, as seen in the cynthia (88. t/.), so that the
food arrives at that aperture directly from the respiratory
orifice, (88. #.), before the currents have passed out through
the minute ciliated perforations of the branchial cavity. The
short and wide oesophagus leads to a distinct gastric cavity
(88. h.) sometimes plicated longitudinally, and perforated at
its pyloric extremity with the orifices of the wide ducts from
the biliary follicles. No teeth, nor jaws, nor salivary glands are
perceptible at the entrance of this very simple alimentary
canal, but the stomach forms a distinct enlargement, even in
the lowest species, and the liver is nearly as constantly
observed under some follicular form, opening into its cavity
as in the stomach of conchifera and almost all the higher
mollusca. The pyloric portion of this simple membranous

362 ORGANS OF DIGESTION.

stomach, and also a part of the intestine, are generally sur-
rounded with the soft granular substance of the liver, which
presents an appearance of minute lobules from the grouping
of its component follicles. The intestine, on leaving the
stomach, forms a sigmoid curvature in the abdominal cavity
on the back part of the respiratory sac, ascending towards the
exterior vent near which it generally terminates with a
fringed margin (88. «.). The intestine, covered with perito-
neum, highly vascular, without mesentery, and without coecal
or other enlargements, occupies a cavity not traversed by the
respiratory currents, and has on its convex posterior part, the
heart and aorta, and on its upper or anterior part, the ovaria
(88. k.) and oviducts (88. m.)9 as in the bivalved mollusca.
The respiratory currents, after traversing the ciliated perfora-
tions of the branchiae, pass out by a distinct canal, over the
anal aperture and the generative orifices, to the exterior vent,
so that the ex-currents, aided by the contractions of the
general muscular tunic, assist in expelling the products of
generation and the residue of digestion, as in the conchifera.
The respiratory orifice, for the entrance of the currents and
of the food, is generally larger than the vent by which they
are expelled, and the two apertures of the alimentary canal,
the mouth and anus, are variously approximated to the
exterior orifices of the enveloping tunic in the different species
of this class. The anal aperture of the intestine, which pro-
jects free into the expiratory canal, is generally lobed or
fimbriated or valvular as in many of the higher mollusca. In
some of the compound tunicata the liver is not distinguish-
able ; in the pyrosoma it is divided longitudinally into several
lobes which communicate with the intestine by distinct ducts ;
in some cynthiae it forms a glandular layer of minute follicles
over a part of the intestine, or of the stomach, as in the
cynthia canopus, and in others, as the cynthia momus, the
liver presents a more definite character and form, as in higher
classes. The convoluted alimentary canal is commonly filled
with a dark-coloured flocculent mucous matter, like that
found in the intestine of most conchifera, and although the
nature of the food is not distinguishable in this soft digested
matter, small entomostracous Crustacea are often found within
the respiratory sac, and probably form a principal part of
their food. This dark matter filling the intestine renders

ORGANS OF DIGESTION. 363

visible the course of the convoluted digestive canal through
the abdominal cavity, where it is generally found ascending
on the right side of the respiratory or thoracic cavity in the
higher isolated forms of tunicata, and is contained beneath
that cavity in many of the lower compound forms. As the
short component follicles of the liver open freely into the
alimentary canal, their contents are often tinged with the
colour of the food, and thus give rise to a diversity of colour
in the liver of these animals. In the cynthia dione, the
hepatic follicles are long and isolated, and envelop the
stomach, as the pancreatic follicles or caeca pylorica envelop
the pylorus in most osseous fishes, and in this cynthia, as in
some others, the turns of the intestine are in contact with
each other throughout their course, and the buccal and anal
orifices are nearly approximated. In the botryllus and other
compound tunicata, each component animal has its own
distinct organs for nutrition and generation, constructed on
the same plan as in the isolated species, the respiratory
orifices of the botryllus open separately on the surface, around
a large central aperture which gives exit to all the ex-currents
of the separate vents. The prominent papillae which cover
the exterior surface of the pyrosoma (Fig. 119. 2 c.) have
each a respiratory orifice near their apex, and the currents
pass through the body of each component animal to the anal
apertures situate in the interior of the general tube formed by
the aggregation of all the individuals. Near the bottom of
each reticulated ciliated respiratory sac is the small round
buccal orifice leading by a short narrow O3sophagus to a
simple globular stomach ; the intestine, furnished with a
distinct liver, forms a single convolution, and terminates near
the vent. On opening the general tube of the pyrosoma the
numerous small vents of the respiratory sacs are observed, by
which the currents pass into the tube and move it through
the sea.

XV. Conchifera. The general plan of structure in the
digestive apparatus of the inhabitants of bivalve shells is
very similar to that of the tunicated mollusca, but they
present a more complicated and higher condition of de-
velopment in the several organs. The conchiferous ani-
mals are commonlv fixed or slow in their movements, and,

Sf)4 ORGANS OF DIGESTION

without prehensile or masticating organs, they depend on
the respiratory currents for their supply of food. The
two respiratory apertures reach to a variable extent from
the opening of the valves according to the habits of the
species, and are generally provided with tentacular filaments,
and sometimes with minute organs of vision, as in some of
the tunicata. The buccal orifice of the alimentary canal is
situate at the bottom of a large respiratory cavity, in which
the branchial folds are suspended, and is provided with two
pairs of long lateral lamelliform tentacula, which are exten-
sions of the upper and lower lips. The mouth is unprovided
with mandibles, or maxillae, or any form of solid dental
apparatus, and opens by a short and wide oesophagus into a
capacious gastric cavity, perforated, as in the tunicata, with
the numerous openings of the biliary ducts. The stomach is
generally a soft membranous or muscular cavity, destitute of
teeth, of an elongated form, and surrounded by the lobes of
a large and conglomerate liver. On opening the stomach,
several perforations are seen near its pyloric extremity, which
lead by short wide ducts to the ramifications and follicles
composing all the lobules of the liver, the liver consisting
here, as in other molluscous classes, of an aggregate of
minute follicles or coeca, the ducts of which unite into larger
trunks and terminate in the pyloric portion of the stomach.
The intestine is generally long and wide, corresponding to the
simple and inferior nature of the food brought to these
animals in small parts by the respiratory currents. On leaving
the stomach, the intestine forms a few convolutions in the
cavity of the abdomen, closely surrounded by the lobes of the
liver, then proceeding along the convex dorsal part above the
ovary and the thoracic cavity, it commonly perforates the
cavity of the muscular ventricle, and terminates near the vent
for the exit of the respiratory currents, as in the naked
acephala.

The mouth in the common oyster ostrea edudis (Fig. 120.
A. b.) is concealed, as usual, at the back part of the cavity
of the mantle, near the hinge of the valves, and is furnished
on each side with two long tapering fleshy tentacular folds
(A. a.) which are striated like gills on their inner surface and
smooth on their exterior. The buccal aperture leads almost

ORGANS OF DIGESTION.

365

directly into an elongated capacious stomach, which is per-
forated by the wide ducts of a large liver (A. n.}, and the
alimentary canal, passing through the substance of the liver
and in front of the auricle (A./*.) and ventricle A. g.} returns
upon itself on the fore part of the large adductor muscle.

T, F

(A. /. m.). After returning to the stomach and forming a
loop round that cavity, the intestine (A. c. c.) passes along
the dorsal part of the body to the anus (A. d.) without per-
forating the cavity of the heart (A./, g.} which is here en-
closed with its pericardium in a groove on the fore part of the
adductor muscle of the valves. The currents which bring

366 ORGANS OF DIGESTION.

food to the mouth are produced, as in other conchifera, and
in tunicata, by the vibratile cilia disposed on the branchial
folds (A., b.} and on the surface of the mantle (A. i.) en-
veloping the respiratory cavity. The very long labial
tentacula of the pinna nobilis (Fig. 1 20. E. b.) extend late-
rally from the lobed margin of the mouth (E. «.), and are
striated like branchiae on their inner surface. The short
narrow oesophagus (E. c.) leads to an elongated stomach, wide
at its cardiac portion (E. d.), and narrow and valvular at its
pyloric end (E. c.), where it forms a small round caecum. A
distinct pyloric valve (120. G. b.) is formed by a circular fold
of the mucous coat at the angular junction of the stomach
(120. G. a.) with the small intestine (120. G. c.), as in most
mollusca and fishes. On opening the cavity of the stomach,
strong muscular bands (120. C. c.) are seen around its
pyloric portion, and several large oblique apertures (120. C.
d. e.) leading into the lobes of the liver are found near to the
duodenum (120. C. a.). The curved duodenal portion pre-
sents a considerable enlargement (120. E. /'.), and a similar
dilatation is observed near the end of the colon (120. E. g.}
as in many insects. The colon of the conchifera generally
pierces the ventricle of the heart or the commencement of
the two aortas, and passes longitudinally through their cavity.
The part of the intestine which traverses the heart, and the
portion imbedded in the substance of the liver are commonly
found to contain food when the rest of the canal is empty.
The stomach of several of these animals is frequently ob-
served filled with mucus, sand and mud, as if they merely
strained the agitated waters of their turbid contents to obtain
their food, as the echinoderma and amielides mostly obtain
their nutriment by passing the sands of the bottom of the
sea through their intestine. The liver presents diversities of
conformation in this class as among the tunicata. In the
mactra the bile enters the stomach by a single wide duct, as
in the cephalopods, and the component coeca or biliary
tubuli are large and distinct. From the simple condition of
the liver in the conchifera, the numerous minute tubuli biliferi
which compose its lobes are easily rendered perceptible by
removing the peritoneal covering, and floating a small de-
tached portion in water, as seen at (120. H.) In most conchifera
the convolutions of the intestine are contained in an abdo-

ORGANS OF DIGESTION. 3G7

minal cavity embraced by the expanded base of the muscular
foot, which thus separates it from the respiratory or thoracic
cavity, like a diaphragm. The convoluted part of the canal
is generally either covered by the compacted lobes of the
liver, or is disposed between that organ and the ovary. The
terminal portion of the intestine or the colon, in the solen
strigilatusy traverses not only the ventricle of the heart, as in
other conchifera, but also a part both of the anterior and
posterior aortee which arise from the ventricle. In the mya
pictorum the colon passes through the middle of the anterior
aorta into the ventricle of the heart, but immediately escapes
through the parietes of that cavity and follows along its ex-
terior surface ; it again penetrates the posterior portion of
this elongated ventricle, and continues for a short distance
through the cavity of the posterior aorta.

There is a firm cylindrical stiliform body, of crystal-
line transparency, enclosed in a coecal prolongation or
membranous sheath, which opens into the cavity of the
stomach in many of the animals of this class. This
stiliform gastric dart has a tricuspid free extremity, is of
a cartilaginous consistence, and is composed of several con-
centric laminae ; it appears to be analogous to the cartilaginous
styles common in the proboscis of the gasteropods, and to be
connected with mastication; its sheath runs along the duodenal
part of the intestine, and opens into the stomach. It was
considered as a masticating organ by Meckel, and as an organ
destined to close the biliary passages by Poli, who first
described it ; it is seen in the cardium, mactra, donax, tellina,
Venus, area, solen, and its sheath has sometimes been mis-
taken for a second stomach. The rectal part of the intestine
terminates near the vent, above the posterior adductor muscle
in the dimyaria, and behind the single adductor muscle of the
monomyaria, as seen in the oyster (120. A. d.)9 and in the
spondylus (120. B. e.} The long, striated, ciliated, branchi-
form labial tentacula vary in their forms in different species,
and their fimbriated or ramified varieties lead to the forms
of the prolonged arms of the brachiopodous conchifera. In
the spondylus gaideropus (120. B. D. F.) the mouth (B. a.
F. a.) is bounded by lobed lips (F. b. b.} the lobes of which
terminate in elegant red-coloured fimbriated tufts (F. c. c.)
and the lips themselves are continued laterally into the usual
upper (F. d. d.) and lower (F. e. e.) pair of labial tentacula

368 ORGANS OF DIGESTION.

(B. b.). The narrow short oesophagus leads to an elongated
stomach (B. c.} covered by the lobes of the dark green-
coloured liver, and the intestine (B. d. e.) passing backwards
between the lobes of the ovary (B. k. k.) and forming one
convolution, returns to the upper part of the shell, or of the
abdominal cavity, where it penetrates the ventricle (B. i.) of
the heart (B. h.i.). Escaping from the cavity of the heart,
the intestine ascends, as usual, over the great adductor muscle
(B. /. s. m.) of the valves, and terminates by a simple anal
opening (B. e.) near the respiratory vent. On opening the
mouth (120. D. a. a.), the oesophagus (D. b.), and the
stomach (D. c.), we perceive the limits of the lobed lips
(D. a.) the muscular fibres and transverse rugse of the oesopha-
gus (D. b.), and the numerous apertures (D. d. d.) of the
stomach, by which the bile is poured into that cavity to mix
with the food before it is sent into the small intestine (D. e.)
The intestine (B. d. e.) is not perceptibly perforated in its
parietes in the part which is contained within the ventricle
(B. i.) in this or other conchifera. The blood from the
palleal (B. f.) and the branchial (B. g.) veins enters the two
lateral portions of the auricle (B. h.), by which it is sent into
the ventricle (B. i.), and from this it is distributed by an
anterior and posterior aorta for the nourishment of all parts of
the body. So that the digestive organs of the testaceous
acephala exhibit a higher development than is presented by
the naked species, chiefly in the large and often complicated
buccal appendices, the gastric stiliform cartilage, the con-
stant presence and great development of the liver and the
length of the alimentary canal, and it differs from that of the
tunicated species, by its passing through the muscular ven-
tricle of the heart, by the greater number of its convolutions,
and by the greater extent of its course, being enveloped in the
mass of the liver.

XVI. Gasteropoda. The numerous and diversified class of
gasteropods presents a more complicated and more varied
digestive apparatus than the acephalous mollusca, which
accords with the greater variety observed in their food and
habits ; for most of the terrestrial pulmonated species feed on
the highly organized vegetables of the land, while the naked
marine gasteropods, as the doris, eolis, scyllaa and tritonia,
subsist on the lowest fuci of the sea, and most of the pro-

ORGANS OF DIGESTION. 369

boscidian species are carnivorous and feed on living prey.
The mouth of the gasteropods is placed at the anterior
end of the body, is furnished above with one or more pairs
of tentacula and generally with a pair of eyes, and contains
often a pair of smooth horny lateral jaws, a fleshy tongue
supporting numerous recurved horny spines, or a long mus-
cular proboscis armed with numerous sharp recurved spines
at its extremity. The pharynx is generally a capacious
cavity furnished with distinct layers of circular and longi-
tudinal muscular fibres, and stronger fleshy bands to advance
and retract it. One or two pairs of salivary glands, con-
sidered by Meckel as pancreatic, extending along the sides
of the oesophagus, send their ducts into the mouth at the
base of the tongue. The oesophagus is longer than in the
acephalous mollusca, and is especially lengthened in the
carnivorous proboscidian gasteropods which mostly inhabit
turbinated shells. There is sometimes, as in the buccinum,
an enlargement or crop formed in the course of the oeso-
phagus, as is common in insects and cephalopods. The
stomach forms always a distinct cavity, often of great size,
and is sometimes divided in the phytophagous gasteropods,
as in the aplysia, into several compartments. The pyloric
end of the stomach receives by several wide ducts the
secretion of a large liver, and sometimes also that of one or
more pancreatic follicles. The interior of the stomach is
often provided with teeth, like the stomach of the Crustacea
and the gizzard of insects and sometimes with a pyloric
valve. The liver is of great size in this as in other mol-
luscous classes, its lobules are composed of more lengthened
tubuli biliferi than in the conchifera, and generally envelop
the intestinal canal as in these acephala. The gastric dart
with its coecal sheath is not developed in the gasteropods,
and the intestine, destitute of mesentery, is more lengthened
and more convoluted than in the conchiferous class, es-
pecially in those gasteropods which feed on vegetable sub-
stances. In the carnivorous species where the oesophagus is
lengthened, the stomach is generally small and the intestine
short and narrow. The intestine, supported only by vessels
and cellular tissue, is sometimes enlarged at its anal por-
tion to form a colon, but is without caecum or valvula
coli ; and instead of terminating, as in the articulated classes,

PART IV. B B

370 ORGANS OF DIGESTION.

at the posterior end of the trunk, it commonly opens, along
with the genital organs, on the right side nearer the anterior
extremity of the body. This lateral termination of the ali-
mentary and genital organs in the gasteropods, and also the
lateral position of their heart and respiratory organs, accord
with the want of bilateral symmetry remarkable in the lower
mollusca when contrasted with the articulated classes.

In the doris which feeds, like most of the naked gas-
teropods, on marine plants, the mouth is furnished with
a pair of broad labial tentacula, as in the haliotis, and
resembling those of bivalved mollusca, besides the ordinary
vertical cephalic pair, and, though destitute of jaws, it is
provided with a lengthened tongue extended through the
pharynx. The cartilaginous surface of the tongue is
covered with minute sharp recurved spines, as in most other
phytophagous species destitute of jaws, and the short wide
muscular proboscis and pharynx lead to a long, wide and
tortuous oesophagus. Both follicular arid conglomerate salivary
glands pour their secretions into the mouth, and the capacious
round membranous stomach is perforated at its pyloric
portion with the numerous wide ducts of a large enveloping
liver, and with the oblique opening of a large single pan-
creatic follicle which is wanting in some of the species.
From the stomach the wide intestine passes around the
left side of the liver to the posterior end of the abdomen
where it perforates the auricle of the heart and opens on the
dorsal aspect of the body in the space surrounded by the
branchiae. Close to the anus, in this branchial space, there
is likewise the opening of an excrementitious gland im-
bedded, like the ink-gland of the octopus, in the substance
of the liver; there is a small round sac developed on the
duct of this renal organ, like a urinary bladder. The aplysia
faciata (Fig. 121) feeds, like the doris 9 on coarse marine
plants, and therefore presents a complicated condition of
all the chylopoietic viscera. Anterior to the long conical
cephalic tentacula are a pair of minute dark coloured eyes,
and the broad labial tentacula (121. a.) are moved by strong
muscular bands (121. b.) The lips are supported by two
cartilaginous laminee, and the tongue is covered with minute
recurved teeth. The wide muscular cavity of the mouth
(121. c.) receives the terminations of two lengthened fol-
licular salivary tubes (121. e. €.), and lies over a large

ORGANS OF DIGESTION.

371

FIG. 121.

infra-cesophageal ganglion which is connected by two nervous
bands with the broad supra-cesophageal or cerebral ganglion

(12 1./.) The short
narrow oesophagus
(121. d.) passes
through the double
ganglionic ring (121
f. /".), and dilates
into a large mem-
branous crop or
curved sac (\2l.i.i.)
generally filled with
pieces of fuci. This
large crop or paunch
occupies the right
side of the abdo-
men and opens la-
terally into the
smallest or middle
stomach (121. k.)
which is provided
internally with nu-
merous broad, flat,
horny teeth of a
rhomboidal form,
which serve to com-
press the softened vegetable matter transmitted in small por-
tions from the first stomach. The third cavity (121. /.) of this
complex stomach is placed on the left side of the abdomen ;
it receives by several wide ducts placed in a valvular recess
at its pyloric orifice, the secretions of a large lobed liver
(121. o.) and of a long single pancreatic follicle; and its inner
parietes are furnished with several sharp horny spines to
subdivide the coarse food, or to pierce it for the ingress
of the solvent gastric fluids. % The intestine (121. m.) on
escaping from the third stomach forms several convolutions
round the lobed liver (121. o.), and after a lengthened course,
without forming any further enlargement or internal valve,
it opens on the right side (121. n.) near the posterior ex-
tremity of the body and immediately behind the heart (121.
q. r.) and the large pectinated branchiae (121. p.) As in

B B 2

372 ORGANS OF DIGESTION.

most of the higher mollusca, the organs of generation occupy
the posterior part of the abdominal cavity, especially the
ovary (121. s.) and the testicle (121. t.) with its convoluted
epididymis, but the common canal of both these organs ascends
on the right side to the penis (121. g.} near the head,
and the urinary sac (121 u.) opens into the same common
excretory passage.

There are four gastric cavities in the pleurobranchus
of Peron, and the capacious stomach of the pleurobranchea
extends nearly the whole length of the body. Horny teeth
are found in the stomach of the tritonia, scylloea, and
most other phytophagous gasteropods; in place of teeth
the stomach of the tethys is lined with a firm coriaceous
epithelium ; and the sides of the muscular round stomach
of the bullos are provided with two dense rhomboidal horny
plates, with their convex surfaces directed inwards towards
each other to masticate the food. In the patella the tongue
is longer than the whole body, and is covered over with
regular transverse rows of sharp recurved spines for filing
down the coarse marine plants on which it subsists. The
oesophagus is wide and sacculated at its upper part, and
passes narrow through the liver nearly to the posterior
extremity of the body before entering the capacious transverse
stomach which has an elongated form with its orifices ter-
minal, and the intestine, long and convoluted through the
mass of a large liver, terminates in a slightly dilated rectum
which opens on the right side near the head. There are two
horny maxillae in the tritonia and scylloea, besides the usual
sharp spines on the surface of the tongue, and in the limnoea
and planorbis there is a superior dentated maxilla besides
the two ordinary lateral jaws. These maxillae are articulated
together; they are moved by powerful enveloping muscles,
and they are lateral in their position like those of articulated
animals. There is a superior dentated jaw in the snails for
reducing their vegetable food ; there are three gastric sacs in
the onchidium which are pli^ted longitudinally within, and
the biliary ducts here enter the oesophagus as well as the
stomach. The rectum opens on the right side in the naked
limaces, as in the testaceous helices, on the median line in
the testacella as in the doris, and on the left side in the
planorbis which has the apex of its suborbicular shell slightly

ORGANS OF DIGESTION. 3/3

directed to that side, as in reverse shells where a similar
transposition is seen in all the viscera. The higher car-
nivorous proboscidian gasteropods, armed with an operculated
turbiiiated shell, and for the most part pectinibranchiate
and with the sexes separate, have generally sharp teeth
placed on a divided tongue at the end of the long muscular
proboscis. These teeth, like maxillse, are supported by two
long stiliform cartilaginous pieces, like the gastric carti-
laginous dart of conchifera, and are moved like jaws by
powerful muscles, as seen in the buccinum undatum (Fig. 66.
a.) Through the axis of this muscular tube passes the
oesophagus, and between them run the long ducts of the
salivary glands to the mouth at the free extremity. The
oesophagus is therefore of great length in these predaceous
animals, and is sometimes provided with a small crop on
entering the abdominal cavity. The stomach is small, simple,
and membranous, and the short intestine forms a wide colon
in advancing along the right side of the body to terminate
near the neck, on that side, under the mantle.

XVII. Pteropoda. — These small swimming mollusca ap-
pear to feed, like conchifera, on minute animals or organic
particles suspended in the waters they inhabit, and their
digestive apparatus is formed on a plan nearly as simple
as that of the inhabitants of bivalved shells or of the lowest
gasteropods. No teeth are perceptible in the triangular
fleshy mouth of the clio borealis, but long follicular salivary
glands open into the sides of the buccal cavity, as in the
pneumodermon, and the oesophagus, after passing through
the usual cerebral or ganglionic ring, dilates into a long
wide membranous stomach surrounded by the lobes of a
large liver and perforated by their ducts. From this length-
ened stomach the short intestine, still destitute of me-
sentery, turns upwards in a slightly convoluted direction,
on the left side, to terminate on the neck under the left
gill, the mantle of the pteropods being closed above, and
there being here no median open funnel for the excre-
tions as in the cephalopods. The oesophagus is generally
lengthened in the pteropods as in the gasteropods, while it
is very short in the conchifera and tunicata. The stomach
is perforated by the biliary ducts, and the intestine is en-
veloped in the hepatic lobes in the pneumodermon, as in
the clio. In the stomach of the cimbulia there are dense

374

ORGANS OF DIGESTION.

horny teeth, as in several of the gasteropods. The simple
unarmed mouth of the hyalea (Fig. 122. A. a.) leads into
FIG. 122. a narrow length-

ened oesophagus
which passes un-
der a broad cere-
bral ganglion(l 22
A. y.)y and di-
lates in the ab-
dominal cavity
into a mem-
branous crop
(1 22. A. b.) which
is slightly mark-
ed internally
with longitudinal
plicae. This first
cavity opens di-
rectly into a short cylindrical muscular gizzard (122. A. c.)
likewise marked with longitudinal folds on its inner sur-
face, and lying, like the crop, over the great retractor
muscle (122. A. h.} by which the animal withdraws its
head and fins (A. i. i.) into its shell. From the muscular
gizzard the long narrow intestine (122. A. d. e. f.) makes
a double turn round the lobes of a small liver, and continues
nearly of uniform thickness to its termination on the right
side of the neck under the right branchial fin. The mouth
of the pneumodermon is furnished with two lateral retractile
tentacular tufts composed of minute pedunculated suckers
resembling those of a naked cephalopod, and two long and
wide salivary follicles which dilate each into a small sac
before they open into the muscular buccal cavity. The
surface of the tongue is covered with small sharp recurved
spines, and the capacious membranous stomach is perforated
with numerous minute openings of the enveloping lobes
of the liver as in many of the acephalous mollusca.

XVIII. Cephalopoda. — These animals being mostly free,
naked, and predaceous, are provided with powerful organs of
prehension and of mastication, and their short alimentary
canal is furnished with highly developed salivary, biliary,
and pancreatic glands. The mouth, surrounded by strong
muscular feet, and bordered by minute labial tentacular

ORGANS OF DIGESTION. 375

filaments, is covered with sensitive and retractile lips which
move by distinct levator and sphincter muscles. The mus-
cular bulb of the mouth contains, in the naked species,
two strong, curved, sharp, "horny mandibles, like those of
many oviparous vertebrata; but in the nautilus (Fig. 122. B. a.)
the jaws are calcified and possess broad and dentated mar-
gins. The lower mandible extends beyond and curves over
the point of the upper, and both are hollow behind and
expanded at their base, like the vaginiform horny mandibles
of many vertebrata. The mandibles here move vertically
as in all the higher classes, not transversely as in articulata.
The short muscular tongue is covered with regular rows
of sharp horny recurved spines as in many molluscous and
vertebrated animals, attached to a cartilaginous base, and
the back part of the mouth receives the secretions generally
of an upper smaller pair and an inferior larger pair of salivary
glands, the component tubuli of which have already assumed
the conglomerate form and lobulated character of these or-
gans in higher classes. The inferior or large pair of salivary
glands are situate at the upper and back part of the liver,
and their two ducts early unite to ascend to the mouth
as one median canal.

The oesophagus of the cephalopods passes through the
cranial cartilage, and continues for a short distance narrow
and equal, behind the upper end of the elongated liver, then
dilates into a crop, which sometimes forms a short cir-
cumscribed membranous cavity, and in others a simple elon-
gated dilatation, as we see the forms of that organ to vary in
the class of birds, and it is generally marked with longitudinal
plicee of its internal mucous coat (122. B. b. c.) Below this
dilatable first cavity the oesophagus continues downwards
narrow, and to the right side of the dorsal part of the cavity
of the trunk, where it enters the second stomach or muscular
gizzard. The crop forms a short circumscribed cavity, and
is high in its position, in the octopus-, it is lower and more elon-
gated in the nautilus (122. B.C.) more narrow in the loligopsis
(122. D. «.), and scarcely forms a perceptible dilatation in
the loligo and the sepiola (122. C. a.) The muscular gizzard,
situate on the right side below the middle of the abdominal
cavity, varies also in its form, muscularity, and relative size,
and is provided with a thick, tough, coriaceous internal lining

376' ORGANS OF DIGESTION.

as in other classes, to protect it from the hard shells and
other dense substances taken in along with the food. This
dense epithelium is easily detached after death, and is often
found loose in the cavity of the gizzard. The muscles of the
gizzard do not form a digastric mass as in gallinaceous birds,
but commonly radiate from around a circular tendinous part
(122. B. d. D. bi) on each side, as in crocodilian reptiles
and rapacious birds, or pass continuously over the sides
of the cavity. From the left side of the gizzard a passage,
generally short and wide, leads to the third stomach (122.
B. e. C. c. D. c.) which in the most common forms of naked
cephalopods, as octopus, sepia, and loligo, has a convoluted
spiral shape, and presents internally numerous transverse
folds of its mucous coat. This third gastric cavity, which
has thin membranous parietes and which receives the biliary
and pancreatic secretions like the stomachs of other mollusca,
is but slightly curved in the sepiola (122. C. c.), it forms an
elongated simple stomach in the loligopsis (122. D. c. d.} where
the spiral marking is almost confined to the anterior parietes of
its pyloric extremity, and in the nautilus (122. B. e.} it forms
a globular sac plicated internally, as usual, with parallel
folds. It was mistaken by Swammerdam for the pancreas
of the cephalopods. The intestine is short and wide in these
rapacious animals, and is still destitute of coecum-coli; the
alimentary canal is no where imbedded in the substance of
the liver as it is in many of the inferior mollusca, and it is
not yet distinguishable into small and large intestine, as it is
in most vertebrata. Passing to the left side from the third
or spiral stomach, the intestine (122. B. /. g. C. d. d. D. /.)
generally forms a short single convolution directed down-
wards near the left branchial heart, then ascends along
the fore part of the liver to terminate between two lon-
gitudinal strong muscular bands near the base of the syphon,
by a free anal orifice protected by two lateral valvular folds
(122. C. e.) The rectal portion of the intestine in the naked
cephalopods and the argonaute receives the excretory duct
(122. C. k.) of the secreting foUicular ink-gland (122. C. h.)
near the anus, and this protecting, excrementitious anal gland
appears to be wanting in the nautilus where the enveloping
exterior shell sufficiently protects the animal without its aid.
The ink-gland, which Monro mistook for the gall-bladder,

ORGAN'S OF DIGESTION. 377

is covered by the hepatic lobules in octopus, in others, as
loligo, it is free and anterior to the liver ; and in others,
as sepia, it lies behind the posterior end of the liver, but
in none is it organically connected with that chylopoietic
gland. The colour of its inky secretion is found to cor-
respond with that of the coloured spots of the skin in
the different species, and thus to serve as a more perfect
means of concealment.

The liver is large and conglomerate in the cephalopods
as in other molluscous classes, and is generally bilobate
or quadrilobate in its exterior form. It is separable into
four distinct lobes in the nautilus and the loligopsis (122.
D. ff. g.}, and in most others it is more or less bifid at
its lower margin (122. C. f. f.) ; and these lobes consist of
numerous small aggregated lobules, the component tubuli
of which, commonly filled with a reddish brown coloured
turbid secretion, are short, wide, simple, and straight, like
those composing the hepatic acini of the higher Crustacea.
This great chylopoietic gland occupies the anterior and dorsal
part of the abdominal cavity, separated by its peritoneal
covering from the oesophagus and anterior aorta above, and
also by its muscular tunic from the gastric and circulating
organs behind arid below. As in other molluscous classes,
it is destitute of a venous portal circulation and of a gall-
bladder, as in them also it is supplied only by branches from
the aorta, and its ducts open directly into the cavity of the
stomach, not into the intestine as in the vertebrated classes.
Its higher development in the cephalopods however is
marked, as in the advanced development of this gland from
its primitive blastema in the embryos of higher classes, by its
greater separation from the contact of the alimentary cavity,
and the consequent elongation of its ducts. The bile is
poured into the third or spiral stomach by a single duct
formed by the union of two or four ducts which descend
from the lower and posterior part of the hepatic lobes ; and
the aperture by which the bile is conveyed directly into the
cavity of the stomach, is here protected by two prominent
valvular folds (122. D. d.), which are continued from the sto-
mach along the side of the intestine towards the anus. Nu-
merous small glands, sometimes in form of simple cellular
follicles ( 1 22. C. g.) and sometimes forming lobules of ramified

378 ORGANS OF DIGESTION.

tubuli (122. D. e.) encompass the hepatic ducts, and open
into them by oblique valvular apertures directed downwards.
These glands, which are common to the naked tentaculated
cephalopods of both sexes, were mistaken by Swammerdam
and Monro for generative organs, but by their structure and
anatomical relations, they must be regarded as the analogues
of the pancreas 'of other classes : they present vesicular
enlargements at the ends of their tubuli like those of the
pancreatic and salivary glands of most other animals, and
part of their lobules sometimes terminate by separate ducts
(122. D.) in the cavity of the spiral stomach. By the exten-
sion of the valvular folds (122. D. d.) from the entrance of
the hepato-pancreatic duct along the course of the intestine,
the secretions of these glands may also mingle with the food
beyond the pyloric orifice of the stomach, as in vertebrated
classes ; and in the empty and collapsed state of these parts
the bile may pass along this valvular groove towards the
anus without entering the stomach or duodenum in these
carnivorous mollusca still destitute of a gall-bladder.

FIFTH SECTION.

Digestive Organs of the Spini- Cerebrated or Vertebrated

Classes.

THE high development of all the organs and systems of ver-
tebrated animals, and the intricate constitution of all their
tissues and fluids require a corresponding complexness in
their digestive apparatus to produce those physical and
chemical changes of the food which are necessary for its
perfect assimilation to their complex bodies. Their alimen-
tary canal is extended between the spino-cerebral axis and
the heart, and terminates by distinct buccal and anal orifices
without perforating the nervous axis. It is always provided
with a distinct gastric enlargement, and with a large conglome-
rate liver, a spleen, and a pancreas. The hepatic and pancreatic
secretions are always poured into the intestine below the
pyforic orifice of the stomach, and the colon is generally
distinguishable from the more narrow anterior portion of
the intestine. The ossophageal portion of the alimentary

ORGANS OF DIGESTION. 379

canal is shorter than the intestinal portion beyond the
stomach, and numerous complicated salivary glands, which
pour their secretions into the mouth, are rarely deficient
in these classes. The chyle is now conveyed into the blood
by a distinct system of chyliferous vessels. There are no
gastric teeth, nor transverse maxillae, and the atlantal ex-
tremities often assist in the prehension and division of the
food. The jaws move in a longitudinal direction, and the
teeth, when present, are confined to the buccal cavity, and
most commonly the alveolar margins of the jaws. The
differences presented by the digestive organs in the ver-
tebrated classes relate chiefly to the nutritious quality, the
consistence, and other properties of the food, and to the
degree of development in the general organization of the
body. The alimentary canal becomes more elongated, and
the chylopoietic glands more complicated by the ramifications
of their tubuli, as we ascend through the classes ; but the
canal is proportionably most elongated, capacious, and sac-
culated, in the phytophagous tribes, where the glands are
also most developed, and the development and solidity of
the masticating organs are proportioned to the resistance
of the food and the mechanical division it requires to undergo
in the mouth.

XIX. Pisces. — As fishes are mostly predaceous animals
which swallow their prey entire, their oesophagus is short
and wide, their stomach capacious, and their intestine short ;
their chylopoietic glands are moderately developed, and their
teeth are generally in form of prehensile organs little adapted
for mastication. The exterior of the mouth is sometimes
provided with fleshy tentacular developments, like those
of mollusca, as in the Lophius, Antennarius, Batrachus, and
Cobitis, and the prehensile oral disk of many of the cyclos-
tome fishes is furnished with sharp conical curved spines,
like the arms of the onychia among the cephalopods. The
dermal nature of teeth is most obvious in the fishes, where
they develope successively and repeatedly during life from
their cutaneous pulps over all parts of the mouth, like solid
sheaths of cutaneous papillae, and they are often arranged in a
quincunx order, like hairs and feathers ; they are mere osseous
crowns of teeth, thinly covered with enamel, destitute of fangs,
laminated, deciduous, and moveable on the surface of the

380 ORGANS OF DIGESTION.

gums and other parts to which they adhere, till maturity,
when they often anchylos'e to the bones beneath by the
ossification of their pulp. They often adhere to the tongue
of fishes as in many gasteropods and birds, to the vomer as
in amphibia, to the palatine bones as in serpents, to the
pharyngeal bones and the branchial arches, as well as to the
maxillary and intermaxillary bones to which they become con-
fined in the saurian reptiles and mammalia. The dermal teeth
spread over the surface of the body in the acanthocephalous
entozoa become in like manner gradually restricted to the
mouth and jaws in higher forms of helminthoid and entomoid
articulata. Some species of fishes, and of higher vertebrated
classes, are entirely destitute of teeth ; they are most com-
monly placed in numerous contiguous rows, and are fre-
quently and variously renewed during life ; they are sometimes
confined t6 the jaws and lodged in alveoli, when the new
teeth are developed behind and displace vertically the old, as
in the crocodilian reptiles. These prehensile osseous hollow
spines or fangless teeth of fishes are not opposed to each
other so as to serve for mastication, but are most frequently
placed alternately, and recurved as in serpents, crocodiles,
dolphins, and most other predaceous non-masticating ver-
tebrata, to check the escape of their prey or to tear it to
pieces. The simple teeth are perforated for the blood-
vessels and nerve, and expand over the pulp at their base.
In many of the rays they unite to form continuous patiline
plates covered with enamel, and in some osseous fishes
the anchylosed bases of successive vertical teeth accumulate
to form elevated cones continuous with the jaws. The teeth
of the tetrodon succeed each other from behind, and the
same is observed in the component layers of those of diodon
which grow from interposed pulpy laminae at their base.
Where the food consists of very soft or minutely divided
substances the teeth are sometimes wanting, as in the
sturgeon, and they have broad strong crowns in those which
break hard substances as the testaceous coverings of mollusca
or Crustacea.

The tongue, almost destitute of gustatory papillae, is
broad, short, and cartilaginous or muscular in fishes as
in cephalopods, amphibia and many reptiles, and is often
covered with teeth supported by the large hyoid bone, and

ORGANS OF DIGESTION. 381

from the moist condition of their food, the liquid element
they inhabit, and their want of masticating organs, they are
generally destitute of salivary glands. The mouth is copi-
ously provided with mucous follicles. From the want of
means of dividing their food the oesophagus is short and
wide to receive it entire, and is bounded below by the circular
fibres of the strong cardiac sphincter. The oesophagus is
often marked internally with regular longitudinal folds which
greatly extend the surface of the mucous coat, and is some-
times also provided with rudimentary teeth, like the cu-
taneous spines often developed on the surface of the body.
The rudimentary salivary glands appear to be most distinct
where the pancreatic are least developed, and the increased
size and number of the buccal muciparous glands generally
compensate for the want of salivary glands in this class. A
small valvular fold, or rudimentary velum palati, seen as low as
the lampreys, and most developed above, as in the zeiis, com-
monly assists in conveying the food and water backwards to
the pharnyx, from which the water passes out freely between
the branchial arches, and the food is directed to the oesophagus
by the teeth of the pharyngeal bones, which are the most
constant teeth of fishes and the most analogous to the
gastric dental organs so common in the inverteb rated classes.
The alimentary canal of fishes is generally more short
and simple than in higher vertebrata, which accords with
their predaceous habits and with their inferior position in
the scale. With a short infundibuliform oesophagus, and
a capacious gastric cavity with its two orifices approximated,
the whole digestive canal of fishes is often shorter than
the trunk, and passes nearly straight through the body,
as seen in the herring, clupea harengus (Fig. 123. A.), where
the narrow cordiac part of the oesophagus (] 23. A. a.) opens
into a lengthened tapering stomach (123. A. b.) commu-
nicating by a long ductus pneumaticus (123. A. m.) with
a large fusiform air-sac (123. A. /. /.), and where the wide
duodenum (123. A. c.) provided with numerous pancreatic
tubuli (123. A. d. d.) forms the commencement of a short
intestine (123. A. e. e.) which opens into the cloaca (123.
A. /.) anterior to the aperture (123. A k.) of the urinary
organs and of the vas deferens (123. A. i) from the testes
(123. h. h.) of the male and the corresponding opening of
the ovaries in the female.

382

ORGANS OF DIGESTION,
FIG. 122.

The oesophagus of fishes, surrounded by an exterior circular
and an inner longitudinal layer of muscular fibres, and with a
white villous plicated mucous coat provided with numerous
distinct muciparous follicles, often terminates imperceptibly
in the capacious stomach, and sometimes the pyloric end of
the stomach passes insensibly into the duodenum, as in the
short straight simple alimentary canal of the lamprey. The
wide membranous cardiac portion of the stomach (123. A. b.)
is commonly directed backwards as a simple closed sac, and
the stronger narrow muscular pyloric part (123. A. c.) ap-
proaching in thickness to a gizzard, extends forward and
to the right side. This gastric sac is sometimes globular as in
the lophius, or extended backwards as in the polypterus and
the xiphias ; but the cardiac and pyloric orifices are almost
always approximated, so that the food is retained as in a
coscum continued straight from the mouth. The muscular
bands of the cardiac and pyloric sphincters are strongly marked,
the pylorus is strengthened by a cartilaginous layer between
the mucous, and the muscular tunics, and the mucous coat
around the pyloric orifice extends inwards to form a circular
valve, with a fibriated margin, at the commencement of the
duodenum as in many of the mollusca. The excretory ducts of
the liver and pancreas enter the duodenum immediately beyond
the pyloric valve, and the variously plicated mucous lining of

ORGANS OF DIGESTION. 383

the stomach is abundantly perforated by the orifices of
muciparous follicles. As in the invertebrated classes, the
mesentery is often wanting or imperfectly developed in
fishes, especially in the chondropterygii ; the intestines are
suspended by ligamentous bands which afford passage to
the vessels, and the distinction of great and small intestine
is scarcely perceptible, there being no ccecum-coli, and the
colon preserving the same width and structure as the ilion,
as seen in the annexed view of the chylopoietic viscera
of the burbot, gadus lota (Fig. 123. B.) Immediately above
the heart (123. B. «.) is seen the wide muscular oesaphagus
(123. B. b.} passing backwards over the large lobes of the
liver (123. B. g. g.) to the capacious stomach (123. B. c.) of
this fish, and close to the pyloric valve the wide duodenal
portion (123. B. d.) receives the ducts, rarely united in fishes,
of the gall-bladder (123. B. h.) and of numerous pancreatic
follicles (123. B. i.). The wide intestine (123. B. e. e.), after
forming several convolutions below the large air-sac (123.
B. /. /.), terminates in the fore part of the cloaca (123. B./.)
anterior to the common opening of the urinary organs and
of the two ovaries (123. B. n. n.)

The mucous membrane of the stomach in this class com-
monly presents an irregular plicated surface, and that of the
intestine is often plicated and villous, but without forming
valvulce conniventes like those of higher classes. At the part
analogous to the caput coli, and where there is sometimes a
small caecum as in the sole, the mucous membrane passes
inwards to form a free circular valvula coli which is often the
only perceptible mark of distinction between the great and
small intestine. The colon however is sometimes distin-
guished both by the presence of this circular valve and by its
greater width, without either external longitudinal ligamentous
bands or internal transverse folds, as seen in Fig. 124. which
represents the digestive organs as I found them in the sword-
fish, xiphias gladius. The wide plicated muscular oesophagus
(124. a.) here presents strong sphincter bands at the cardiac
orifice (124. b.) of a long flask-shaped stomach (124. c.)
with thick muscular parietes, especially at the narrow cylin-
drical pyloric portion (1 24 . c. d.) Beyond the pyloric valve
(124. d.) the three hepatic ducts (124. /.) from the liver
(124. e.} and the cystics form an irregular lobed gall-bladder

384

ORGANS OF DIGESTION.

(124. g.} open by a
short common ductus
choledochus into the
duodenum, beside the
large common opening
(124. i.) of all the con-
stituent follicles of
this great reniform
pancreas (124. h.) The
long narrow small
intestine (124. i. k.}
forms seven convo-
lutions on the right
side and presents a
distinct valvula coli
(124. L) where it ter-
minates in the short
straight colon (124. /.
m.) wider than the rest
of the intestine.

The pancreas presents every stage of the development of
this important gland, as permanent adult forms in the class of
fishes, consisting in some of mere folds of the duodenum
of one simple tubulus in the ammodites tobianus, in others as
the lophius, cJi&todon longimanus, fistularia, and pleuronectes
presenting only two simple follicles or appendicula ccecapy-
lorica, three in the perch, four in the bream, five in the
chcetodon zebra, some dozens in the clupea (123. A. d. d.) the
gadus (123. B. i.) and most of the osseous fishes, and four or
five hundreds in the scomber Mediterraneus where they
open by six short ducts ; these pancreatic follicles constitute
a large reniform mass surrounded with a strong muscular
tunic in the xiphas (124. h.) among the osseous fishes, and in
the sturgeon among the chondropterygii ; and in most of
the cartilaginous plagiostome fishes they form a compact
conglomerate gland, the component tubuli of which are nearly
as fine as those of the liver and aggregated together into
lobules and lobes. In some fishes, as the centriscus, no trace
of this organ is perceptible. The large pancreatic follicles
or appendicula pylorica of fishes, so variable in number

ORGANS OF DIGESTION. 385

and size, and form, not only in the different species, but in
the same individual, at different periods of its development,
secrete a thick turbid fluid, not unlike the product of ordi-
nary muciparous follicles, or those considered as rudiments of
salivary glands ; they are connected together by a loose
cellular tissue, and numerous plexuses of vessels, and they
admit the digested food of the intestine freely into their
interior, like the biliary tubuli of many mollusca. The spleen
is generally single, small, of various forms, attached to the
side of the stomach, as in higher classes, largely supplied
with lymphatics, and without perceptible duct ; but in a few,
as the sturgeon and the shark, it is divided into detached
lobes, as in some of the cetacea ; and in some fishes, as the
lamprey, which has neither pancreas nor gall-bladder, nor
mesentery, it appears to be wanting, as in the invertebrated
classes. The liver attached to a tendinous diaphragm,
is of great size, and of an elongated form, placed on
the median plane, of a light colour, filled with an oily
fluid, soft in texture like the spleen, deeply divided into
numerous lobes, with the acini well marked, and the compo-
nent tubuli comparatively large, provided with a portal and
arterial circulation, and commonly with a large gall-bladder,
as in other predaceous vertebrata. It is sometimes placed
more to the left than to the right side ; there are generally
several long hepatic ducts, terminating separately in the
lengthened cystic, several hepato- cystic ducts, entering the
fundus of a pyriform gall-bladder, and the common choledo-
chus, short and wide, opens along with one or more pancreatic
ducts on the anal side of the pyloric valve. The activity of
the secretions, and the muscular strength of the alimentary
canal, effect a rapid assimilation of food in the short intes-
tine of fishes ; and they disgorge by the mouth the shells or
other hard parts of their prey, like many predaceous animals
of higher and of lower classes. The air-sac, or rudimentary
lungs, generally communicates by means of a membranous
trachea or ductus pneumaticus, with the intestine, the sto-
mach, or the O3sophagus ; but however useful for progressive
motion, or the transmission of sounds, it still contributes
little to the aeration of their blood.

The form and extent of the alimentary canal of fishes and the
condition of their chylopoietic glands vary as much as their

PART IV. C C

386 ORGANS OF DIGESTION.

food which consists of everything organized in the rich element
they inhabit. The rugse of the mucous coat, which are some-
times longitudinal or transverse, or reticulate on the intestine
of osseous fishes, form a remarkable continuous, elevated, spi-
ral fold in the plagiostome chondropterygii, which winds round
the interior of the canal, from the duodenum to the rectum.
The rectum here terminates, as in other oviparous vertebrated
animals, in a common cloaca, and has behind it in both sexes
the opening, single or double, of the genital organs, the pos-
terior part being occupied by the urinary passages. On the
sides of the anus, in most of the cartilaginous and many of the
osseous fishes, as in some aquatic reptiles, there are two oblique
valvular openings, leading externally from the cavity of the
peritoneum, and affording an easy exit to matters passing in
that direction, but impeding their entrance from without. The
peritoneum lining the interior parietes of the abdomen, and
extending, like the pericardium above, over tendinous fibres
of the diaphragm, has often the shining silvery lustre and
white colour of the rete mucosum without ; the mesentery is
generally more developed in the osseous than in the cartilagi-
nous fishes, and folds of the peritoneum, charged with adipose
substance, sometimes hang from the outer margin of the in-
testine, forming a rudimentary epiloon. This imperfect con-
dition of the mesentery in the lowest fishes, where the intes-
tine is connected only by blood-vessels, approximates them to
the invertebrata, and the same is often found as an abnormal
character in man. The simple, straight, cylindrical form of
the whole alimentary tube in many of the lowest fishes like-
wise assimilates them to the earlier conditions of the human
embryo, as also the follicular character of their principal chy-
lopoietic glands. As the umbilical vesicle in the osseous fishes
passes entirely into the abdomen, to complete the intestine
and the abdominal parietes by its mucous and serous coats,
there can be no umbilical mark left in the adult, and there is
no allantois communicating with the cloaca in the young, as
they require no placental nutriment.

XX. Amphibia. The amphibious animals, like the fishes,
are mostly predaceous in their habits, and swallow their prey
entire, having loose and feeble articulations of the jaws, and
sharp, slender, prehensile teeth, ill adapted for mastication.
The teeth are placed sometimes, like those of fishes, in se-
veral rows on the palatine and both maxillary bones, as in

ORGANS OF DIGESTION. 387

the siren, or more serpent-like in single rows on the palatine
bones and both maxillae, as in the triton, or only on the pala-
tine bones and upper jaw, as in faefrog ; but they are want-
ing in both jaws in the toad and the pipa, although two small
transverse rows are seen behind the posterior nares in the
toad. The teeth have here the same osseous texture, thin
coat of enamel, and feeble superficial attachment to the jaws
as in most fishes, and these animals are almost as destitute
of salivary glands as the permanent tadpoles of the sea. The
long, free, and bifid tongue of the frog, covered with papillae
arid muciparous follicles, more nearly approaches to the
ordinary form of that organ in the serpents and many higher
reptiles than the short, thick, fleshy form of the tongue com-
mon to the perennibranchiate amphibia and the toad. The
strong muscular oesophagus, short, dilatable, and longitudi-
nally plicated within like that of fishes, leads to a narrow
elongated stomach, directed transversely from left to right,
generally with thick fleshy parietes, especially at the pyloric
portion, and covered above by the two lobes of a large liver,
which is always provided with a distinct and free gall-
bladder.

The stomach is most lengthened and narrow in the tadpole
state of the higher amphibia, and in the adult forms of the
aquatic species, as in the lower fishes and in the embryo
condition of man, and these also exhibit the least distinction
between the small intestine and the colon. In the young
tadpole (Fig. 125. B. C.) of the common frog, which sucks
with a small circular mouth (B. C. a, a,} the soft animal and
vegetable matter of our fresh water ponds, the stomach (c,
d,) is narrow and elongated, and the intestine (B. c, d, C. e,
e,) of extraordinary length, and nearly equal throughout, is
coiled up in a spiral manner, distending the capacious abdomen
and perceptible through the transparent parietes. It is only
slightly enlarged near the anus, and is attached to the verte-
bral column by an entire mesentery, as in the adults of all
the amphibia. During the metamorphosis which so remark-
ably affects every internal system, and in which the soft and
mixed food of the tadpole is changed for more nutritious
aliment, as snails, worms, caterpillars, and similar creeping
animals, the stomach and the whole alimentary canal become
gradually shortened in their proportions, and their divi-

c c 2

388

ORGANS OF DIGESTION.

sions more distinctly marked, as seen in the annexed view of
the digestive organs of the mature frog, (125. D.) At the
base of the broad bifid, reverted tongue, (125. D. b, e,) is the
short wide pharynx, (D. c,) and simple larynx leading to
complicated cellular lungs, (D./, /,) and the capacious mus-
cular oesophagus and stomach, (D. g,) adapted to receive un-
divided prey, are bounded below by a constricted thick
pylorus, (D. h,) beyond which the duodenum, (D. n,) is pli-
cated internall y with several transverse circular folds of the

FIG

...4

mucous coat, like the valvulae conniventes of mammalia. The
form of the stomach is similar in the toads, salamanders,
arid tritons, and has the narrow elongated spleen loosely
attached to its left side by cellular substance and vessels. A
slight pyloric valve is seen in the toad and pipa. The two
lobes of the liver overhang the stomach above and before ;
the intestine now forms but a few convolutions of inconsider-
able width, supported by a distinct and vascular mesentery,
(D. m) ; the pancreas, lengthened like the spleen, is situated
behind the pylorus, and the short, wide, straight colon, (D.

ORGANS OF DIGESTION. 389

I,) terminates in the cloaca, which receives also the openings
of the urinary and genital organs, as in other oviparous ver-
tebrata. The valvula coli is distinct in the frog, the hyla,
and the triton. In the pipa, the liver has a small median or
third lobe, and the lobes are more free, as in chelonia. In
the great menopoma, (125. A,) of the North American lakes,
there are palatine teeth, as well as superior and inferior
maxillary, as in the nearly allied tritons and salamanders.
The broad rounded fleshy tongue, similar to that of proteus
and siren, exhibits at its base the small opening of a simple
larynx, (125. A. e}) leading to the two long pulmonic sacs,
(A. g, y,) and the wide infundibuliform oesophagus (A. /./.)>
lying below the branchial veins (A. o, 0,) and descending aorta,
(A. n,} and above the heart, (A. p,) ends in a long narrow mus-
cular stomach (A. ^,), resting on the two lobes of the liver,
(A. /,) and tapering to its thick pyloric portion, (A. h.) The
commencement of the duodenum (A. e,), receives the end of
a long ductus communis choledochus (A. w,), and pancreatic
duct, and the intestine (A. &.), forms several convolutions con-
nectedby a distinct mesentery, before terminating in the cloaca.
Most of the chylopoietic organs here, as in other perenni-
branchiate amphibia, partake of the elongated form of the
trunk, as in the ophidian reptiles. The mucous lining of
the intestine is raised into numerous longitudinal folds in
the proteus, and also in the triton, the salamander, and the
pipa -, it forms quadrangular cells in the hyla, and transverse
folds in the frog, and is more even in the axolotle. The liver
is most numerously and deeply lobed in the caducibraiichiate
forms, as in the pipa and the frog, and most elongated and entire
in the lower amphibia, as the axolotle, the proteus and the me-
nopoma, and there is seldom a trace of pyloric valve between
the opening of its duct and the stomach. The elongated
stomach of the proteus passes insensibly into the duodenum,
and is scarcely distinguished even by the usual constriction
at its pyloric portion, but the gastric cavity is always marked
in the amphibia by the great muscularity of its parietes
when compared with the thin and delicate coats of the intes-
tinal canal, and its form, especially in the higher genera,
approaches closely to that of the chelonia.

An inferiority of character, or an approach to the class of
fishes is thus seen in the digestive apparatus of the lower

390 ORGANS OF DIGESTION.

amphibia, in the similarity and the extensive distribution
over the buccal cavity of the small conical fangless teeth, the
shortness of the tongue, the great development of the cornua
of the os hyoides, the want of salivary glands, the shortness
and width of the oesophagus, the elongated form and muscu-
larity of the stomach, the similarity of the small intestine
and the colon, the want of coecum coli and fundus of the
stomach, and the great size of the liver. In many of the
animals of this class, however, we discover approximations
to the higher vertebrata, in the more restricted distribution
of the teeth, the elongation of the tongue and the body of
the os hyoides, the greater distinctness of the gastric cavity,
and its fundus, and of the small and large intestine, the
absence of pyloric valve and valvula-coli, the development
of transverse folds in the duodenum, and of a slight ccecum
on the colon. The gall-bladder and the mesentery are now
always developed, the pancreas is always conglomerate, and
the tadpoles of all the species commence with the same short
strait, simple alimentary tube as in the embryos of all the
higher vertebrata, although some of them are destined to
undergo a double metamorphosis in this part, to adapt it
to the difference of food and habits of the larva and the
adult.

XXI. Reptilia. — As most of the ophidian and saurian
reptiles are carnivorous animals, and most of the chelonia
phytophagous, there is great diversity in the form and struc-
ture of the masticating organs, the alimentary cavities and
the chylopoietic glands in the different species of this class.
The serpents, like most of the lower vertebrata, swallow en-
tire prey, and have their teeth, like those of amphibia and
the simpler fishes, in form of mere conical crowns, sharp,
incurvated, unopposed to each other, attached to loose move-
able bones, and adapted for prehension, not for mastication.
The teeth of serpents are still attached to the palatine, ptery-
goid, and intermaxillary bones, as well as to the upper and
lower jaws ; they are wielded by powerful muscles, to enable
them to wound and secure their prey, they are deeply im-
bedded in the soft gums, but rest in shallow osseous grooves ;
they are limited to single rows, as in higher vertebrata ; the
palatine rows are more constant in their characters than the
maxillary ; they are excavated by a large nutritious canal,

ORGANS OF DIGESTION. 391

and the great anterior maxillary fangs of the noxious species
are perforated and grooved on their fore part, to transmit the
secretion of the poison gland. The scaly lips, and long,
smooth, filiform, sheathed, bifurcated tongue, employed as an
organ of touch, are li ttle adapted to give the serpents acute
feelings, from their food, which passes through their capa-
cious dilatable mouth and oesophagus undivided. The sali-
vary glands vary much in their development in different
species, but the sublingual is always present, and two large
superior and inferior labial glands send their secretions through
numerous ducts. The large poison gland, (Fig. 74. «.), the
analogue of the parotid, below and behind the orbit on each
side, is confined to the noxious species : it contains a wide
cavity, it is embraced by muscular fibres, and sends its long
duct to the perforated base of the poison fang, (Fig. 74. b.)

The lengthened oesophagus, like the buccal cavity and the
stomach, is susceptible of great distention, and in its col-
lapsed state is longitudinally plicated ; its thin elastic parietes
are lubricated by the copious secretion of innumerable mu-
ciparous follicles, and it passes insensibly into the long,
straight, and capacious cavity of the stomach, which can be
distended with prey to many times the ordinary width of the
trunk. The cardiac portion of the stomach is thin, membra-
nous, longitudinally plicated, rarely presenting a sudden en-
largement or a ccecal portion, and the posterior part of the
stomach acquires thick smooth muscular parietes, and tapers
to a narrow pyloric orifice, provided with a distinct internal
valve and sphincter bands. Beyond the pyloric valve, which
is seldom wanting, the duodenum, which presents a villous
surface, receives the ducts from the liver, and the separate
lobes of the pancreas, and the close narrow convolutions of
the small intestine are compactly united together for protec-
tion, in a distinct tubular peritoneal sheath, to the com-
mencement of the short, straight dilated colon, where there
is commonly a circular projecting valve and sometimes a
small coecum. The short, straight, and wide colon ends in
the cloaca, which receives the terminations of the two ureters,
there being no urinary bladder, and of the two oviducts, or
the two spermatic ducts ; the single or divided male organ
likewise passes out through the cloaca, as in other oviparous

392 ORGANS OF DIGESTION.

vertebrata. The liver, the spleen, the pancreas, the kidneys,
and the testes and ovaria present the same longitudinally
extended form which is seen in the oesophagus, the stomach,
and other parts of the alimentary cavity of the ophidian rep-
tiles, and in the whole conformation of their trunk. The
convolutions of the small intestine are not bound together in
a sheath, but float freely, attached to the mesentery in the
aquatic species of serpents, and in some of the higher sauroid
forms, as the anguis. The large intestine is often sacculated
by transverse constrictions approaching in form to valves,
which divide its cavity, and still further delay the passage of
the food through the ever active trunk of these animals. The
liver is generally of a lengthened cylindrical form, not divided
into lobes, provided with a distinct gall-bladder, and sends its
secretion into the duodenum, near to the pyloric valve, where
also terminate the several ducts from the lobes of the pan-
creas, which continue separate to their termination in the
intestine, and the small spleen is here often compactly united
to the pancreas by vessels and its peritoneal sheath.

The saurian reptiles are mostly carnivorous, like the serpents,
and swallow their prey undivided, and they present a corres-
ponding short and simple alimentary apparatus ; but as their
trunk is shorter, and their abdomen is not habitually pressed on
or dragged along the ground, they do not present the longitudi-
nally extended form of the viscera, nor the modifications de-
signed to protect the organs and check the rapid transit of the
food, which w£ observe in the ophidian reptiles. The teeth
are still merely prehensile organs, sharp, conical, recurved,
similar in form, and placed alternately ; but they are more
fixed in- their attachment by the outer alveolar margin of the
maxillse and by the gums; sometimes they are lodged in
deep osseous alveoli, and are generally restricted to a single
row along the margin of the jaws. Small teeth, in a few
species only, are found also in the pterygoid bones, as in
serpents ; and, as in them, the tongue is generally long and
bifid, and the salivary glands very imperfectly developed.
The oesophagus, like the neck, is short and wide, and com-
monly leads to a narrow elongated stomach, placed from left
to right, with its cardiac and pyloric orifices at the opposite

ORGANS OF DIGESTION. 393

ends, and seldom presenting any coscal portion to retard the
food in its cavity. In the crocodilian family, where the
teeth and the bones of the face are fixed, as in mammalia,
and the tongue, as in these, is short, round, and fleshy, the
stomach is in form of a round, strong muscular gizzard, with
an anterior and posterior central tendon, from which muscu-
lar fasciculi radiate to the margins, as in many lower and
higher animals, and the pyloric opening is guarded, as in
many other saurian reptiles, with a distinct circular valve.
The pyloric portion of the stomach presents a small ccecum,
like that of a heron. The small intestine is comparatively
long in a few vegetable-eating sauria, as the iguana and
scincuSy the flesh of which is edible, and it is shorter in the
more carnivorous forms, and there is commonly a small but
distinct round ccecum- as well as valvula-coli at the com-
mencement of the large intestine. The coecum-coli is large
in scincus and small in the lacerttE, and the interior of the
colon is often marked with longitudinal folds or quadrangular
cells, but it is still destitute externally of the longitudinal
bands which give this part a cellular form in the mammalia.
The wide rectum terminates in the cloaca with the urino-
genital organs, as in serpents, and the intestines are sus-
pended freely by a complete mesentery. The peritoneum is
often dark coloured or spotted, as in many other oviparous
vertebrata, and the liver, more extended transversely than in
ophidia, is always provided with a gall-bladder. The spleen
is more distinct, and generally of a lengthened form, and the
pancreas is less lobated in its exterior than in the serpents.
The stomach being less extended longitudinally than in the
serpents, the ducts of the liver are shorter, and the common
choledochus enters apart from the pancreatic at a variable
distance from the pylorus.

The chelonian reptiles subsist chiefly on vegetable food, and
present a higher development of the alimentary canal, and of
the chylopoietic glands than the more carnivorous ophidian
and saurian species ; and from the great length of the neck and
the short and broad form of the trunk, the oesophagus is
elongated as in ophidia, and the stomach, the intestine, and
the liver are most developed in a transverse direction, as seen
in the annexed views of the viscera of emys europcea

394

ORGANS OF DIGESTION.

(Fig. 126. A. B.) The wide expanded jaws, covered with sharp
horny sheaths, adapted to cut the coarse vegetable food,are mov-
ed by strong muscles, and the short, fleshy, undivided tongue
is covered with long, delicate, sheathed papillae, which are seen
likewise on the upper part of the oesophagus. The mouth
is abundantly furnished with muciparous glands, and the sali-
vary glands, especially the submaxillary, are very differently
developed in the different species. The long and muscular

FIG. 126.

resophagus is still wide, as in other reptiles, from the undi-
vided condition of the food, and it presents internally nu-
merous longitudinal folds of the mucous coat, which are seen
also extending along the thin cardiac portion of the stomach.
The longitudinal plicae of the inner membrane are percep-
tible, though smaller, along the thick, muscular, pyloric part
of the stomach. The stomach (126. A. i.) is extended trans-
versely from left to right, of great strength and capacity,
and behind the two expanded lobes of a large and broad

ORGANS OF DIGESTION. 395

liver. The long papillze which line the oesophagus are highly
vascular, and are covered with a thin but obvious epidermic
sheath. The thick, muscular, pyloric portion of the stomach
sends inwards no circular fold, to constitute a pyloric valve,
as we generally see at this part in the inferior vertebrata.
The intestine is often more than six times the length of the
trunk, and in the terrestrial forms, the colon presents a short,
round, and wide coecum, and a distinct circular valve at its
commencement ; but in the aquatic species the small intes-
tine passes often insensibly into the colon, without either
valve or coecum. The colon is now generally distinct from
the small intestine, long and wide, as in mammalia, but des-
titute of external longitudinal bands, and transverse corruga-
tions, and the interior of the small intestine is generally
marked by longitudinal folds or rugae of the mucous coat, as
in most amphibia.

The parietes of the alimentary canal are throughout mus-
cular and wide, a character which we see likewise in the
stomach, and which accords with the coarse vegetable
food on which most of these animals subsist. The abdo-
minal cavity is separated from that containing the lungs,
(126. A. g.} by the peritoneum and the rudimentary dia-
phragm. The right lobe of the liver is much larger than the
left, and between them is a small middle lobe ; the gall-
bladder is always present, and sends a short wide duct to
open into the duodenum near to the pylorus ; there is also a
distinct hepatic duct, which receives that of the pancreas
before entering the intestine. Although there are no valvulee
conniventes in the chelonia, the mucous coat of the intestine
is of great extent, as in most other phytophagous animals,
forming numerous longitudinal folds and cells, or tortuous
rugee, in its course, by which a greater extent of surface is
afforded for the secretions, and for the distribution of the
innumerable chyliferous vessels spread upon their alimentary
canal. The annexed figure, (127) from Bojanus, presents a
view of the viscera of the trunk, seen from the ventral sur-
face in the emys europaa, where the wide muscular oesopha-
gus (127. #,) behind the trachea (/",) and round thymus
gland, between the right (g,) and left (h,) lung, and posterior
to the three cavities (i. k. L) of the heart, and to the

396

ORGANS OF DIGESTION

large right (v,} and left (w)
lobes of the liver, passes
to the left side, to terminate
in the stomach (b,) which
is here as transverse in its
position as in the mamma-
lia. The convolutions of
the small intestine (c,) and
the wide colon are seen
between the developed
ovaries (y. y,) and exterior
to these, on each side, are
the long and wide oviducts
(1. 1. 4. 4.) with their ex-
panded infundibuliform
openings (z. z.) The rectum, (d,) as in higher vertebrata,
descends to the cloaca, behind the ends of the oviducts (1.1.)
and behind the large urinary bladder (#,) with its short ure-
thra, and the cloaca receives also the openings of the two
lateral sacs (2. 3.) before terminating in the transverse anal
orifice, (e^) below the base of the tail. The alimentary canal
has thus already acquired in the reptiles nearly all the divi-
sions and typical characters which it presents in the highest
of the vertebrated animals.

XXII. Aves. The alimentary apparatus of birds is
adapted for the digestion of the higher forms of animal and
vegetable matter, which their locomotive and prehensile or-
gans enable them to obtain in the air, in the waters, and in
the earth. The jaws have their alveolar margins covered,
like those of chelonia, with horny plates, which vary in their
forms, according to the kind of food, like the teeth of mam-
malia. The nearest approach to the teeth of quadrupeds is
seen in the thin horny laminae disposed along the sides of
the bills in the mallard, and some other aquatic birds ; and in
the earliest condition of the birds the laminae begin by a
series of small detached tubercles, provided each with
its pulp, its nerve, and its vessels, like the horny maxillary
plates of the whale, and the more solid calcareous teeth of

ORGANS OF DIGESTION. 397

other vertebrated animals. The broad depressed bills of
ducks, geese, swans, and many other aquatic birds, with den-
tated edges, and soft sensitive lips, are well adapted for ob-
taining worms or other small objects under water or in mud,
and they commonly present a well marked dental distribu-
tion of the alveolar nerves and blood-vessels, as well as a
high development of the second and third branches of the
trigiminal nerves. The flat spatulate jaws of the spoon-bills
are adapted for quick lateral motion in the waters, and for
extracting minute animals from the moist banks of lakes and
rivers. The submaxillary pouch of the pelican serves as a
net for seizing fishes ; the straight sharp bills of cranes and
storks dart with precision through the water upon their moving
prey, and the long compressed bills of cormorants, gulls,
albatroses, and many predaceous aquatic birds, terminate
above in a sharp inverted hook, to seize firmly the smooth
scaly bodies of fishes. The broad bills, with cutting edges,
of the strutheous birds, are adapted to prune the leaves and
shoots of plants, and the long narrow bills of woodpeckers
to be inserted into small crevices to seize minute insects ; and
most of the insectivorous order of birds have a similar struc-
ture on a smaller scale. The long tubular beak of the hum-
ming birds is suited for insertion into the corollse of flowers.
In the grosbeaks and crossbills, the sparrows and buntings,
and all the granivorous order, and in the larger gallinaceous
birds the bills form stronger and shorter cones, broader at
the base, to break down and remove the hard coverings of
grains. In the climbing frugivorous cockatoos, parrots, and
maccaws, the broad and powerful bills serve as prehensile
organs, and to break the hard shelly coverings of seeds. The
bills of eagles and vultures, hawks and owls, and other rapa-
cious birds, are strong, short, compressed, arched, curved at
the point, dense in their texture, and with sharp cutting
edges, to seize, and tear, and cut the flesh of living prey.
So that the forms of these external parts correspond with
and indicate the structure of the internal organs of digestion,
and afford useful zoological characters for the divisions of
this class. The tongue, chiefly composed of a loose cellular
texture, is here as variable in form and adaptations as the
bill, or the claws, or the food, being long and filiform, like
that of an ant-eater, in the woodpeckers, short and muscular

398 ORGANS OF DIGESTION.

in the strutheous birds, arrow-shaped in the gallinacea, long,
broad, and covered with large recurved spines in the swans,
short, round and highly flexible in the cockatoos and parrots;
but the body and cornua of the os hyoides are always com-
paratively long, slender, and flexible in this class.

As the food of birds is not masticated nor retained in the
mouth, the salivary glands are smaller than in quadrupeds,
more simple in structure, and commonly disposed in four
pairs, one situate under the sides of the tongue, another at
the junction of the rami of the lower jaw, another close to
the base of the cornua of the os hyoides, and another at the
angles of the mouth. The mouth is provided with numerous
muciparous glands, and the salivary glands are most deve-
loped in gallinaceous and frugivorous birds, as in herbivorous
quadrupeds. The closed ends of the tubuli salivarii are more
or less dilated, as in other classes of animals, and the isolated
vertical tubuli composing the first or sublingual pair open
separately into the mouth by a row of pores. The second
pair open by several ducts under the fore part of the tongue:
the third, or submaxillary pair, open behind the second,
sometimes by elongated ducts ; and the fourth pair open
within the angles of the mouth. The uvula, velum, and epi-
glottis, not being yet developed, the posterior nares and the
larynx are but little protected, and the oesophagus, with a
simple entrance, is here wide, muscular, and of great length,
corresponding with the great length of the neck in birds.

As in other classes of animals, the whole alimentary canal
of birds varies much in its length and capacity, and in the
form and development of its cavities, according to the nature
of the food, being long and capacious, with large glandular
organs and muscular parietes, in the various phytophagous
tribes, and with the reverse of these characters in those which
feed more exclusively on animal food. The long, wide, mus-
cular oesophagus, with a smooth mucous coat, and thin epi-
dermic lining, passes down behind and a little to the right
side of the trachea, as seen in the annexed figure of the vis-
cera of the gallus domesticus, (Fig. 128. a,} and about the
middle of its course, a little above the two anchylosed clavi-
cles, it presents, in gallinaceous, raptorial, and many other birds,
an enlargement, an ingluvies or crop, (128. b.) varying in form
and structure according to the difference of the food, and

ORGANS OF DIGESTION.

provided with numerous glandular follicles situate between the
mucous and the muscular coats. Continuing downwards behind
and a little to the right of the trachea, and behind the heart,
(128.m,) and great branches of the aorta, the oesophagus passes
forwards below the inferior larynx, between the two lobes of
the lungs, (128. n. n}) and to the left side, to dilate into a

second gastric cavity, the glandular stomach, proventriculus,
infundibulum, or ventriculus succenturiatus, (128. c,) which is
highly vascular and provided with more numerous and larger
follicles than open into the crop. Beneath the vertical in-
fundibulum is the powerful muscular gizzard, (128. d.) dis-
posed transversely from left to right, like the ordinary^sto-
mach of most vertebrata, covered with the lobes of the liver,

400 ORGANS OF DIGESTION.

(128. o. o. o.) and lined internally with a more or less dense
epithalium. This third cavity, the gizzard, lies in front of
the ovary (128. t. u. v.) and oviduct, (128. w. x. y. z.} in the
female, and of the testes in the male, and has its cardiac (c.)
and pyloric (e,) orifices closely approximated to each other.
The turns of the duodenum, (128. e.f. g.} on the right side
embrace the conglomerate and lobed pancreas, (128. q.q.)
which generally sends its secretion by two or more ducts,
(128. r.) alternating with the separate ducts from the liver
(128.0.0.0.), and the gall-bladder, (128. p.) The single,
lengthened, and dark coloured spleen, (seen above c. e,) is
attached near the left side of the glandular stomach, and the
divided liver (o.o.o.) has generally a free gall-bladder (128. p,)
placed under its right lobe. The intestine, (128. g. h. k.)
is still shorter than in mammalia, but its different divisions
are more distinctly marked than in the inferior classes. In
young birds a remnant of the original entrance of the yolk-
bag, or umbilical vesicle, is generally obvious in form of a
small co3cal appendage on the anterior portion of the small
intestine, and in many gallinaceous, wading, and water birds
it remains through life. At the commencement of the colon
(128. h. k,) which is here, as in lower oviparous vertebrata,
of short extent, and generally neither wide nor sacculated,
there are in most birds two coeca, (128. h. i. i. s. s.} of very
various lengths and dimensions, extending upwards, and at-
tached along the sides of the small intestine. The rectum,
(128. &,) terminates in the general cloaca (128. /,) which re-
ceives also the ends of the two ureters, the openings of the
pervious and impervious oviducts of the female, (128. z,) and
of the vasa deferentia of the male.

The least constant of these digestive cavities, and the most
variable in form, is the crop or ingluvies, the caca-coli are
likewise inconstant and nearly as variable in their extent
of development and their form 5 the gizzard presents great
differences in the thickness of its muscular and cuticular
tunics, and the ventriculus succenturiatus in the development
of its glandular follicles. The crop, which is here remarkable
for its position in the neck, receives the unmasticated food,
like the paunch of ruminantia, or the cheek pouches of many
mammalia, and moistens it with the secretion of its numerous
follicles. It forms a large globular sac, communicating by a

ORGANS OF DIGESTION.

401

narrow neck with the fore part of the resophagus in most of
the gallinaceous birds, as represented in the annexed dia-
gram, (Fig. 129. A. b,} and in the pigeons it is still larger,

FIG. 129.

and divided in front into two lateral sacs. The numerous
follicles which open into its interior, become more vascular
and enlarged at the time these birds are rearing their young ;
the milky secretion which they afford is very abundant in the
crop of the pigeon, when feeding its young, and this is the only
food they receive for the first two or three days after being
hatched. The grains which have been moistened, softened,
and partially digested in the crop, are brought up successively
from that cavity and conveyed into the mouth of the young
birds when they are further advanced. In the diurnal rapa-
cious birds, (Fig. 129. B.) the crop (£,) forms only a general
enlargement of the lower cervical portion of the O3sophagus,
into which entire prey is conveyed, and from which the hair,

PART IV. D D

402 ORGANS OF DIGESTION.

claws, feathers,, and other indigestible parts, are disgorged by
the mouth, without being allowed to pass through the alimen-
tary canal. This cavity however is entirely wanting in most
of the passerine, wading, and palmified birds, although sub-
sisting on the most dissimilar kinds of food; and it is scarcely
perceptible in the nocturnal birds of prey, or in the long-
necked struthious birds.

The glandular follicles on each side of the small ventriculus
succenturiatus (129. A. B. c. c.) are mostly disposed in vertical
rows, and have their orifices directed downwards. They are
placed, like those of the crop, between the mucous and the
muscular tunics ; they are most numerous and complicated in
the granivorous birds, where they form ramified tubuli ; and
they are simple elongated follicles in the birds of prey. They
sometimes surround the whole cavity, or are confined to a
part of the surface, and their copious secretion is required, to
assist in digestion, from the deficient glandular structure of
the gizzard itself. These glandular follicles of the ventriculus
succenturiatus, or infundibulum, of birds are analogous in
position to the cardiac glands, so large in the wombat, the
beaver, and some other mammalia.

These muscular parietes of the gizzard (129, A. d.) form
two strong digastric muscles, one anterior, the other poste-
rior, with white shining tendons, in most gallinaceous and
granivorous birds, and in many aquatic and other species. In
most rapacious and carnivorous birds, the parietes of all the
three gastric cavities are thin and highly extensible, and form
almost one continuous stomach, (129. B. b.c.d.) with slight
constrictions between its parts. The thin membranous giz-
zard however of these birds presents a distinct anterior and
posterior central tendon, (129. B. c?.) analogous to those of
the two ordinary digastric muscles, (129. A. d.}, and from
which the muscular fasciculi, more or less developed in dif-
ferent species, radiate to the margins of the cavity. When this
third gastric cavity is provided with strong muscular parietes,
as in the gallinaceous birds, its internal epidemic lining forms
a thick coriaceous dense coat, to protect the soft parts from
laceration, and to enable them to act with effect upon their
heterogenous contents. From the want of teeth in the mouth
to act upon their hard food, these granivorous birds convey
pebbles and other dense substances into their gizzard, to re-

ORGANS OF DIGESTION. 403

duce their food, like the gastric teeth of Crustacea, insects,
many gasteropods, and other invertebrata ; but in the carni-
vorous birds, with a thin membranous gizzard, no pebbles
are swallowed or required, the activity of the secretions effect-
ing all the necessary changes in the conditions of the food,
aided by the high temperature, and the movements of the
canal. From the proximity of the cardiac and pyloric orifices
of the gizzard, it forms a sac open only above, and is not
provided with the pyloric sphincter muscle, so common in
other vertebrated classes. This free and wide pyloric orifice
allows the food, partially digested in the three gastric cavities,
and reduced by the muscular action of the gizzard, to pass
out, in small successive portions, to the commencement of
the duodenum. The small internal capacity of this strong
grinding organ, which is chiefly filled with pebbles, necessi-
tates the development of other gastric cavities between it
and the mouth, to receive a sufficient quantity of coarse
vegetable food for the maintenance of these large and heavy
birds.

The duodenum forms a long narrow duplication embracing
the bilobate conglomerate highly vascular pancreas (128. <?.y.)?
the tubuli of which, like those of the salivary glands, com-
mence with small vesicular enlargements, and terminate gene-
rally in two ducts which alternate with those from the liver
and gall-bladder. The small vitelline ccecum (129. A. g.) which
remains in several adult granivorous and wading birds, early
disappears in the rapacious tribes (129. B.), and still earlier
in the mammalia and in man. The two cceca-coli (128. s. s.)
are likewise of greatest size in the gallinaceous and other gra-
nivorous birds, where they arise, like those of the manis, by
two narrow canals (129. A, i.) from the commencement of
the short colon, and enlarge into wide sacs (129. A. /.), often
exceeding several times the size of the intestine, as in the
turkey. They are very large in many of the palmipeds, as
the swans, and they are connected by mesentery along the
sides of the small intestine. In the ostrich they have a spi-
ral fold of the mucous tunic extending through them, and
several folds of the same membrane are seen in the upper
part of the colon itself, which is here of unusual length.
They have no analogy to the urinary bladder, which is
below the rectal vestibule of birds, nor are they connected

D D 2

404 ORGANS OF DIGESTION.

with the cloaca ; their duplicity is analogous to that ob-
served in the crop of pigeons, and they are found double
also in the hyrax and others among the lower mamma-
lia. The cceca-coli are least developed in the grallatores
and the nocturnal rapacious birds (129. B. k. h.), where
they generally form two small projections on the side of
the commencement of the colon. One of these only is
developed in the herons, and in several birds, as in the
lower vertebrated and invertebrated classes, and as in the
plantigrade carnivorous mammalia, there is no coecum-coli,
especially among the zygodactylous birds.

The great intestine terminates in the dilatable rectal vestibule
(l29.C.b.D.b.), which is capable of being protruded externally
through the cloaca and the anus. The distinction of the cloacal
parts of the alimentary canal is most apparent in the ostrich
(129. D.), where the rectum (D. a.) expands below into a
dilatable vestibule (D. b.) which opens into the upper and
back part of the cloaca (D. c.) This upper or first portion
of the cloaca corresponds in birds with that which deve-
lopes the urinary bladder and allantois in mammalia ; and
in the ostrich it serves for the retention of the urine as in
the higher viviparous animals. At the lower and back part
of this urinal portion of the cloaca, and separated from it
by a slight ridge, are the papillar openings (D. /../.) of the
two ureters (D. f.' f.'), and exterior to these are the open-
ings of the perforate (D. g. gJ) and impervious (D. h.) ovi-
ducts in the female, and of the vasa deferentia in the male.
To this urethro-sexual canal (D. d.) which receives the ends
of the urinary and genital organs, succeeds the preputial
cavity (D. e.), the most exterior and posterior portion of the
cloaca, which protects the organs of excitement in both
sexes, the clitoris (D. k.) of the female and the penis of the
male. These terminal parts of the digestive canal are per-
ceptible in a less developed form in most other birds, and
are represented in Fig. 129. C. as I found them in the fe-
male condor vulture, where the separation of the several
portions is less distinctly marked. The wide rectum (C. a.)
expands below into the rectal vestibule (C. b.}, the highly
vascular mucous coat of which differs much in appearance
from that of the urinal portion (C. c.) of the cloaca, and is
separated from the latter by a distinct circular ridge. The

ORGANS OF DIGESTION. 405

limits of the urethro- sexual canal (C. d.) which receives the
openings of the two ureters (C././.) and the two unequal
oviducts (C. g. g.< h.} are also perceptible ; and on the me-
dian plain, in the dorsal part of the preputial cavity, is the
opening of the Bursa Fabricii (C. e.), the analogue of Cow-
per's glands, and terminating in the same part as these
glands in the mammalia. There being no placental attach-
ment of the embryo of birds, the cloacal part of their ali-
mentary canal is not extended outwards to form an allantois
as it is in the embryos of quadrupeds.

XXIII. Mammalia. The digestive organs, like the gene-
ral form, the internal structure, and the living habits of the
species, vary more in the mammiferous animals than in any
other vertebrated class, and they present the highest type of
development in the various organs connected with this func-
tion -j but the different forms of their alimentary cavities are
most intimately connected with those of the masticating and
prehensile organs, the organs of locomotion and perception,
and more or less with all the other external and internal parts
of their economy. The high development of their organs of
sense, and the flexibility and softness of their sensitive lips and
tongue, enable these animals to perceive minuter differences
in the chemical and physical properties of their food. The
solid structure of their teeth, and their fixed condition in
deep alveoli of immoveable maxillary and intermaxillary
bones, enable them more effectually to disintegrate their
aliment, and to mix it with the secretions of the parotid,
submaxillary, and sublingual glands, which are rarely deficient
in this class. The teeth, formed in cutaneous sacs and suc-
cessively renewed during life, are disposed in single rows,
and have their forms regulated chiefly by the motions of the
jaws which support them, and their texture by the nature of
the food. They are rarely deficient as in the bird-like jaws of
the manis, myrmecophaya and echidna ; their place is some-
times supplied by horny laminae as in the ornithorhyncus and
the whale; sometimes they are simple, alternate, similarly
formed, prehensile cones, as in several of the cetacea, but
most generally they are distinguished by their forms and
positions into incisors, canine and molar teeth, of which the
last are most characteristic of the nature of the food. The
molar teeth are renewed eight times in the elephant, the in-

406 ORGANS OF DIGESTION.

cisors are shed twice in several rodentia, and most of the
teeth are renewed once in the other orders of mammalia.
Teeth are found in the lower jaw of the whale only in the
embryo state, and they are confined to this part in the adult
physeter. They are very deciduous in many of the cetacea,
edentata and cheiroptera, only two are developed in the front
of the lower jaw of the uranodon, the right upper incisor of
the monodon remains undeveloped in its alveolus, the upper
incisors are wanting in most ruminantia, and all the incisors
are deficient in the edentata, excepting the six-banded arma-
dillo ; but in the extinct anoplotherium alone among mam-
malia, the three kinds of teeth formed an uninterrupted
series around the jaws as in man. In most mammalia which
feed on animal matter, the crowns of the teeth are covered
entirely with enamel as they are likewise in the quadrumana
and man ; in the phytophagous quadrupeds, the enamel is
generally disposed in tortuous or waved vertical laminee,
which extend transversely or longitudinally according as the
motions of the jaws are longitudinal or transverse, as in
most rodentia, ruminantia and pachyderma, and in many
of the latter animals, as the elephant and capybara, several
of the molar teeth are aggregated together by a solid exter-
nal crusta petrosa to constitute a single compound masticat-
ing organ.

From the increased strength of the jaws, and the greater
density and opposable character of the teeth, the temporal,
the masseter, and other muscles of mastication are stronger
than in the oviparous vertebrata, and from the lengthened
form of the muzzle, the muscles of the lips are more sepa-
rate and extended than in man, and produce more extensive
motions of the lips. The long moveable fleshy sensitive lips,
indeed, of most herbivorous quadrupeds serve them as hands
to collect and crop their vegetable food. The long flexible
tongue of the giraffe, the thumb-like process of the upper
lip of the rhinoceros, and the elongated nose or proboscis
of the elephant, are employed for the same purpose ; and it
is chiefly by their long vermiform lubricated tongue, that
the ant-eaters secure their insect prey. The retraction of
the highly moveable lips of carnivora serves to expose their
sharp teeth for free action, and so to intimidate and weaken
their prey. The numerous muciparous glands disposed

ORGANS OF DIGESTION. 407

along the sides of the mouth in mammalia, which form large
conglomerate buccal glands in several herbivora, assist the
salivary glands in softening the food while thus delayed for
mastication, and many species of quadrumana, cheiroptera,
rodentia, and the ornithorhyncus have cheek-pouches, like
the crop of birds and the paunch of ruminantia, to collect
the food before mastication. The parotid, submaxillary and
sublingual salivary glands, so generally developed in mam-
malia, are largest in herbivorous quadrupeds where the
coarse food is longest subjected to mastication, less in car-
nivorous species where it is more quickly divided and swal-
lowed, and least in the aquatic tribes where the thin limpid
secretion of these glands is rendered less necessary by the
moist condition of their food. The velum palati is more ex-
tensive than in the former classes ; but the uvula is rarely
developed, excepting in the highest quadrumana and man,
and the cutaneous papillae, so commonly spread over the
tongue and palate, sometimes, as in the monotrema, acquire
the density of spines in their cuticular sheaths, as they do
in many birds. The tongue is supported by the short,
broad body of the os hyoides, and sometimes a vermiform
median fibre-cartilage, and the two pairs of cornua are most
developed in the herbivorous quadrupeds, where the ante-
rior pair reach the large styloid bones. The os hyoides, in
its most perfect form, consists, as shown by Geofiroy, of
twelve elements, the body of the bone being composed of a
glosso- and a basi-hyal piece, the anterior cornua consisting
each of an apo- a cerato- and a styl-hyal element, and the
smaller posterior cornua containing each an ento- and a
uro-hyal bone, and this complicated condition of the os
hyoides, common in the ruminantia, is sometimes found as
an abnormal form of that bone in man. But the cornua,
in the normal state, are least developed in man and the
orangs, and no trace of them is seen in the manis.

The pharynx of mammalia forms a distinct and wide cavity,
and the long cylindrical oesophagus, corresponding with the
length of the neck, never presents an ingluvial dilatation
above the sternum, as it does in so many birds. The resopha-
gus is wide and dilatable in the carnivorous tribes, where the
food is commonly swallowed in masses, and it is more nar-
row and muscular in the herbivorous quadrupeds, where

408 ORGANS OP DIGESTION.

the aliment is more masticated and softened in the mouth.
Its muscular tunic presents an exterior longitudinal, and an
inner transverse layer of muscular fibres ; the smooth mu-
cous coat is seldom papillated or plicated, and is lined with
a distinct epidermis which continues obvious over the three
first cavities of the stomach of ruminantia. It sometimes
passes much beyond the diaphragm into the cavity of the
abdomen, and is surrounded by the outer layer of longitudi-
nal cardiac fasciculi at its entrance into the stomach, where
its mucous coat occasionally presents longitudinal or spiral
folds. The cesophageal aperture of the diaphragm serves as
a cardiac sphincter.

As the whole alimentary apparatus is most simple in the
carnivorous mammalia, from the nutritious quality and the
complex chemical constitution of their food, so their sto-
mach consists generally of a simple globular sac, without
internal subdivision or a ccecal portion, and the same form
is seen in many insectivorous quadrupeds of different orders,
as in monotrema, cheiroptera, insectivora, marsupialia.
But where the food is of a coarser or more mixed character,
the stomach becomes elongated transversely, and a cardiac
fundus or coecal portion is developed on its left extremity,
as we find in many of the less carnivorous tribes, and in
most of the quadrumana and man. In many of the roden-
tia, the thin membranous cardiac portion forms a considera-
ble coecum, and is partially separated by a constriction from
the more muscular pyloric half of the cavity. The great
development of the gastric glands around the cardiac orifice
of the stomach in the beaver and the wombat, is required
by the coarse vegetable food on which they subsist, and
points out an analogy between this part and the glandular
infundibulum at the cardiac orifice of the gizzard in birds.
In several phytophagous mammalia, belonging to different
orders, as among the pachyderma, masupialia, edentata,
and even quadrumana, internal folds or external coeca di-
vide the cavity of the stomach to a greater or less extent,
and from the epidermic lining extending over the cardiac
sacs thus formed, we observe a gradual transition to the
complex stomachs of the cetacea and ruminantia, where the
several compartments have different structures and functions.
Although the uses and necessities of these different forms of

ORGANS OF DIGESTION. 409

the stomach are sometimes obvious, they are often as little
apparent as those of the enlargements developed on the in-
testine below that cavity ; they have generally a relation to
the digestibility and the nutritious quality of the food natu-
ral to each species. The pyloric valve, so common in the
lower classes, is still often seen in this ; the small intestine
is more distinct from the colon in form and structure, and
both are of greater extent than in other vertebrata; the
coscum-coli is single and more constant in its occurrence,
and the rectum now opens externally by an orifice almost
always distinct from that of the urinary and genetal organs.

Among the most complex forms of the gastric cavity of
mammalia are those of many cetacea, where the food often
consists of animal or vegetable matter in the lowest condi-
tion of organization. The oesophagus, like the neck, is
short and wide, as in fishes, and commonly leads, as in
them, to a large bottle- shaped longitudinal coecal cavity on
the left side, from which several successive smaller cavities
extend transversely to the right extremity of this divided
stomach. These successive gastric cavities are defined by
very narrow constrictions, and by a difference even in the
structure of their mucous membrane ; and they are some-
times succeeded, as in the porpoise, by another sac developed
on the duodenum. This multiple stomach accords with the
imperfect means which most of the cetacea possess of mas-
ticating and salivating the food in the mouth, their teeth
being mere prehensile organs, and their salivary glands being
often entirely deficient. There is yet but little difference
between the small and the large intestine ; and the ccecum-
coli is rarely developed in these animals. The ruminating
quadrupeds, on the contrary, have the masticating and sali-
vary organs most perfect, the oesophagus long and narrow,
four gastric cavities with distinct functions, the intestine
and colon long, capacious and distinct, and an enormous
ccecum-coli. The oesophagus, as seen in the annexed figure
of the stomach of the lama of Peru (Fig. 130. A. «.) enters
directly into the first large cavity or paunch (ingluvies) (130.
A. b. b.) placed on the left side, analogous to the crop of
birds, and serving the office of the cheek-pouches of other
quadrupeds. This capacious cavity is partially subdivided
by large internal folds, and is lined with closs, small but

410

ORGANS OF DIGESTION.

lengthened villi, covered with a thick epidermis. The same
epidermic covering is continued distinctly over the second
and third cavities. The second stomach or reticulum (130.
A. c.) placed more anteriorly and to the right of the former,

FIG. 130.

is much smaller, and has its mucous lining elevated into
reticulate folds forming polygonal shallow cells. This cavity
also communicates with the ossophagus, and presents two

ORGANS OF DIGESTION. 411

thick muscular valvular folds across the opening of com-
munication, by the closing of which a canal is formed
which leads to the third cavity of the stomach.

The paunch receives the crude-unmasticated vegetable food
collected in large quantity while the animal is erect and grazing,
and the process of rumination generally commences when this
cavity is filled, and the animal is reclining at rest. In rumi-
nation, small portions of the unmasticated food, moistened
and softened in the paunch, pass into the second cavity to
be sent by its contraction, as a bolus, upwards through the
muscular oesophagus to the mouth. After being thoroughly
masticated and salivated in the mouth, the bolus returns, as
a soft pulp, by the oesophagus ; and, its stimulating quality
being now altered, it finds the two valvular folds at the
lower end of the oesophagus closed, and shortened by con-
traction, and is directed by the short canal they thus form,
into the third, and thence into the fourth cavity of the sto-
mach. The third or foliated stomach (omasum) is generally
the shortest and smallest, though elongated and narrow in
the camelus and auchenia (130. A. d.), and is provided in-
ternally with numerous longitudinal, alternately small and
large folds, having their free margins directed to the centre
of the cavity. The second and third cavities have their mu-
cous membrane covered with small villi and distinct epithe-
lium, like those lining the first stomach. The third cavity
leads directly to the fourth or abomasum (130. A. e.) which
is next in capacity to the paunch, lined with a soft highly
vascular mucous coat, provided internally with large longi-
tudinal folds, and apparently destitute of epidermic lining.
The structure and form, and secretions of this fourth cavity,
placed on the right side of the others, render it the proper
digestive stomach, and the most analogous to the single di-
gestive sac of carnivorous and higher quadrupeds.

In the camels, dromedaries and lamas, numerous rows
of large, quadrangular, deep water-cells are developed on
the parietes of the second stomach, and on the parts of the
paunch next to that cavity. These cells are surrounded by
muscular fibres which, by their contraction, are capable of
excluding the food from the water-cavities ; and by the gra-
dual opening of the cells, the water is allowed to mix in
successive small portions with the digesting aliment. These
animals are thus enabled to convey and economise a large

412 ORGANS OF DIGESTION.

supply of pure water, received at long intervals in the arid
plains they inhabit. The second stomach is more appro-
priated to the retention of water than the large paunch, and
receives it directly from the mouth, unmixed with the food,
pouring over to the cells of the first stomach a quantity of
the fluid when its own are filled. The third stomach (130.
A. d.)9 which is here of a lengthened form, is provided both
with longitudinal and transverse internal folds of its mucous
coat, and the fourth cavity (130. A. e.) is of an elongated
narrow form, curved suddenly towards its pyloric end (130.
A. /.) and puckered like a colon. The fourth stomach of
the ruminantia is the first developed, the largest, and alone
employed for digestion, during the earlier periods of exis-
tence and during lactation. The milk, in suckling, passes
down through the oesophagus to the closed valvular folds,
which check its entrance into the first or second stomach,
and convey it along the canal which they form, directly to
the third or foliated cavity. The third stomach not having
been yet distended with solid food so as to separate from
each other its numerous contiguous laminae, it merely forms
a tube through which the milk passes into the fourth sto-
mach; and thus the nutritious fluid of the parent is con-
veyed directly into the proper digestive stomach of the
suckling ruminant, without being accumulated or retarded
in any of the previous cavities.

The intestinal canal of the ruminantia is of great length,
being sometimes more than thirty times the length of the
trunk of the body, as in the sheep, and the colon is always
long, convoluted, and of great width compared with the small
intestine. The long narrow small intestine has generally
thin membranous parietes, a villous internal surface, and a
short mesentery to suspend its numerous convolutions from
the vertebral column. The ccecum-coli is long, wide, and,
like the colon itself, has smooth internal parietes. The colon
is not here puckered and sacculated by longitudinal bands
as it is in many herbivorous quadrupeds, and forms nu-
merous long convolutions before it descends on the left side
to terminate in the rectum. The liver is more deeply divided
into lobes than in the cetacea, but less than in most car-
nivorous quadrupeds; many have a large and elongated
gall-bladder, while others, as the camels and deers, are des-
titute of this reservoir ; the gall-duct, whether from the liver

ORGANS OF DIGESTION. 413

or gall-bladder, commonly receives the single duct of the
bilobate pancreas near its entrance into the duodenum, and
the long flat spleen is attached to the paunch.

Although the pachyderma do not ruminate, their kind of
vegetable food, the structure of their masticating and sali-
vating organs, and the general characters of their alimentary
canal, approach the nearest to those of ruminantia ; but as
they masticate and salivate their food before it is first swal-
lowed, they do not require the arrangement of gastric cavities
given for this purpose to the latter animals. The solidun-
gulous pachyderma have, therefore, only the fourth or true
digestive stomach of ruminantia, a single undivided elongated
sac, without internal partitions or external constriction, but
they have the same lengthened narrow small intestine with
an internal villous surface, the same large coecum-coli, and
the same long wide convoluted colon. Their colon and its
capacious coecum are rendered puckered and sacculated by
the usual three longitudinal bands of muscular fibres. They
have no gall-bladder, and their hepatic duct opens, by a
common orifice with the pancreatic, within four inches of the
pylorus. The stomach is as simple, though more elongated
in form, in the elephant and rhinoceros, but is slightly tri-
partite by two transverse constrictions in the American tapir,
and is still more deeply divided internally in the pecari and
other forms of the hog tribe. The strong muscular oeso-
phagus of the pecari enters the middle large cavity of the
stomach, the left portion of the stomach forms a great cre-
scentic cavity terminated by two coeca, and the wide pyloric
portion is partially detached by the internal extension of the
mucous coat ; but the mucous coat, as in other pachyderma,
has nearly the same characters over all the partially detached
gastric cavities. The stomach of the hyrax is divided by a
narrow contraction into two almost globular sacs, the first
of which is lined with epidermis not perceptible on the
second, and the commencement of the duodenum is enlarged
to form a smaller third sac ; the intestine and the colon are
nearly of the same length, and the ilium (FiG. 130. B. a)
terminates in a large irregular sac, which is the ordinary
ccecum-coli (130. B. b) ; the commencement of the colon
forms also a wide elongated cavity, and about the middle of
its course this irregular colon forms another enlargement,

414 ORGANS OF DIGESTION.

(130, B. c), from the sides of which two small tapering cceca
(ISO, B. d) are extended, as from the colon of most birds.
The transverse valvula coli is seen at the entrance of the
ilium into the first wide coecum, but the second tapering cceca
are without valves. The two cceca-coli are seen also in the
ant-eater and the lamantin, but are placed at commencement
of the colon in these animals; they are small, without valves,
and with narrow contracted openings in the myrmecophaga,
as in birds. The stomach of the myrmecophaga, like that
of echidna and ornithorhyncus, presents the simplest undi-
vided form of this cavity, but is more strong and muscular,
like the gizzard of a bird or of a crocodile, to compensate
for the want of teeth. In the sloths the left half of the
stomach is sacculated by internal partition like that of sem-
nopitheci among the quadrumana, and its pyloric half is
puckered and spirally convoluted like that of a kangaroo.

Among the diversified forms of marsupialia, the carnivorous
dasyuri and the insectivorous didelphes and perameles have
a membranous stomach and a short alimentary canal, like
the dentated quadrupeds of similar food belonging to other
orders. In the kangaroos the stomach (130, D.) is almost
as complicated as that of the ruminantia, which they repre-
sent in Australia, and which they can partially imitate in the
rumination of their food; it is spirally convoluted, deeply
divided by transverse contractions, lined with epidermis,
puckered by three longitudinal bands like the colon of
pachyderma, sacculated by large cells (130, D. d) developed
from its sides, with a tapering winding coecum (130, D. b)
nine inches long, extending to the left of the cardiac orifice
(130, D. «), and provided with two rows of large glands
opening into its pyloric portion. The stomach is nearly
similar in the hypsiprymnus, but less lengthened and divided,
and with the gastric glands disposed in a single lengthened
narrow mass on the left portion of the cavity. The intestine
of the kangaroo corresponds in its great length and convo-
lutions with the coarse vegetable food, and the coecum-coli
is about fifteen inches in length. The coecum-coli of the
wombat (130. C.), a marsupial rodent with some affinities
to the beaver, forms a short and wide cavity (130. C. c.),
and has a remarkable small narrow appendix (130. C. d.)
opening by a valvular orifice close to the termination of the

ORGANS OF DIGESTION. 415

ilium (130. C. a.) in the colon (130. C. a.) resembling in
form the appendix vermiformis of man and the highest qua-
drumana. At the cardiac orifice of the stomach in the wom-
bat, as in the beaver, there is a large and complex gastric
gland,, forming a close analogy between this part and the
glandular infundibulum of birds, and especially required in
these quadrupeds from the very coarse nature of their
food.

The high development of all the organs of relation in car-
nivorous quadrupeds, enables them to select and obtain the
kind of food which requires least elaboration from digestive
organs for its assimilation to their body ; and their salivary,
muciparous, and other chylopoietic glands, are comparative-
ly small ; their oesophagus wide from their imperfect masti-
cation, their stomach, simple, small and membranous ; their
intestine short and narrow ; the colon small, and the coecum-
coli very short and narrow, or entirely wanting. The villi of
their long muscular tongue acquire often the density of
spines, the thick muscular fasciculi of their strong resopha-
gus have often a spiral course round that wide tube; the
soft mucous lining of their membranous stomach presents
no perceptible epithelium, and all trace of the ordinary
ccecum- and valvula-coli has entirely disappeared in the plan-
tigrade forms of these animals. The deeply lobated liver of
the carnivora is always provided with a moderate gall-bladder,
which sends its duct into the duodenum at a very short dis-
tance from the pylorus. The spleen has commonly a
lengthened narrow form with numerous round white inter-
nal corpuscules, and the two unequal lobes of the pancreas
are subdivided into smaller distinct lobules, which pour
their secretion into the duodenum, generally by two separate
ducts, a little beyond that of the gall-bladder.

The surface of the free and lengthened tongue of the insec-
tivorous bats, is likewise often provided with firm and sharp
spines, and their stomach, like that of most carnivora, qua-
drumana and man, forms generally a simple membranous
globular or pyriform sac, with a small coecal portion to the
left of the cardia ; but in the frugivorous pteropi, as in the
more elevated semnopitheci, the stomach forms a capacious
lengthened saculated cavity, puckered and winding like the
colon of a herbivorous quadruped or the stomach of a kan-

41G ORGANS OF DIGESTION.

garoo, and corresponding, as in these, with the inferior
quality of the food.

The typical forms and characters of the human digestive
apparatus (130. E.) are gradually developed and established in
the diversified order of quadrumanous animals. The cheek-
pouches, so frequent in the inferior mammalia, and so general
in the simiae of the old continent, and which are mere exten-
sions of the thin parietes of the mouth outwards and backwards
over the ramus of the lower jaw, covered and moved by nume-
rous fasciculi from the pJatysma myoides and the buccinator
muscle, are already lost in the orangs as in man ; the rounded
tubercles of the molar teeth, common to the higher quadru-
mana and man, accord with the softer condition of the food
natural to these two tribes, and the uvula and velum palati
are most developed in our species. The muciparous labial
and buccal glands, which soften the contents of the cheek-
pouches, are more constant and larger in man ; but the
parotid, sub maxillary, and sublingual salivary glands, ap-
pear to exceed the human in the more frugivorous forms
of quadrumana. The shortness of the oesophagus (130. E.
a.) corresponds with that of the neck, and the elevated posi-
tion of the head, in the quadrumana and man ; its muscular
fibres form an inner transverse and an exterior longitudinal
layer, in place of the opposed spiral fasciculi of inferior
mammalia ; ana it enters the stomach (130. E. b.) at the
shortest distance beyond the pillars of the diaphragm. The
stomach is less elongated transversely, and less generally
constricted in the middle, in the quadrumana, than in man,
but the cardiac coecum is most developed in the former, and
especially in the lowest tribes, where also the most length-
ened form of the mesentery suspends the convolutions of the
intestine. The human valvube conniventes are still wanting
in the duodenum ; but the glandule Peyeri are often much
more numerous, and more extensively spread over the intes-
tine, than in man, where they are confined to the lower part
of the jejunum and ilium. The duodenum (130. E. c.) re-
ceives the secretions of the liver (130. E. /. /.) and pancreas
(130. E. h.) by a single orifice of the united ducts, in the
simise, as in man. The gall-bladder (130. E. m.) is always
present, the liver is more deeply lobated in the lower qua-
drumana, and the spleen (130. E. i.) has generally a more

ORGANS OF DIGESTION. 417

lengthened or crescentic form, but a smaller bulk, than in
man.

The colon is most lengthened, smooth, convoluted, nar-
row, and even in its parietes, in the lowest lemurs, and be-
comes shorter, less convoluted, much wider, and more
sacculated in its parietes by longitudinal muscular bands,
in the higher simise and in man (130. E. e. g.} The crecum-
coli, which is always present, is, like the colon, more nar-
row, curved, smooth, and lengthened in the lemurs, where it
sometimes exceeds a foot in length ; it is more short, straight,
rounded, wide and cancellated, in the simise and man (130.
E. d. e.), and in several of the highest genera it is already
provided with the vermiform appendix (130. E./l) so cha-
racteristic of the human intestine. This narrow glandular
appendix is the first coecum developed in the human embryo,
and is the form presented by the adult coecum in many of
the inferior mammalia. So that while all the essential parts
of this complex apparatus of organic life pass through in-
numerable phases of development in ascending through the
various grades of the animal kingdom, all their diversified
forms are alike perfect in their adaptations to the living con-
ditions of the species, and man and the monad, at the two
extremes of this great series, are alike digestive sacs, moved
to and fro in quest of matter to prolong individual existence
and that of the race.

PART IV. E E

CHAPTER SECOND.

CHYL1FEROUS SYSTEM.

THE assimilation of foreign matter to the textures of the
body is comparatively a simple process, and effected by the
simplest means, in the lowest tribes of animals, where there
are few elements in the food, and few in the textures into
which it is to be converted ; so that the same alimentary
cavities which receive and digest the food, transmit the assi-
milated portion through their parietes, to form part of the
homogeneous tissue of their body. This low condition of
development may exist in the simpler forms of poriphera,
polypiphera and acalepha ; but in tracing the progress of the
digestive cavity through all its metamorphoses and grades
of development in the animal kingdom, we have seen it
become more extended and complicated, more finely orga-
nized, and divided into distinct parts with distinct functions,
as we ascend in the scale; follicles, cceca, tubuli, glands,
and vessels, develope from its sides, and become more or
less distinct in connection and function ; a sanguiferous
system thus becomes isolated and developed, to extend the
source of nutriment to each point of the body, and the nu-
tritive fluid of this complex hydraulic apparatus, is received
from the alimentary canal, directly by the veins, in most of
the invertebrated classes. In all the higher animals, how-
ever, constituting the vertebrated division, a distinct system
of vessels is employed to receive, and still further to elabo-
rate, the fluid product of digestion, and to convey it to the
venous system. The fluid which these vessels take up from
the intestine, being generally opaque and of a whitish colour
in quadrupeds, has received the name of chyle or lacteal
fluid, and the vessels, plexuses, glands and ducts, through
which it passes in its way to the blood, constitute the chyli-
ferous system, which like other complex systems, presents

CHYLIFEROUS SYSTEM.

419

diversities of character, and grades of development in the
different classes.

From the white serous condition of the blood in the in-
vertebrated classes, resembling the limpid transparent chyle
of the oviparous vertebrata, several parts of the former
animals have been taken for their chyliferous system,
as the mesenteric veins of echinoderma by Monro, the
radiating prolongations of the stomach of medusa by
Carus, the biliary tubes of insects by Sheldon, and even
the nervous system of conchifera by Poli. In the red-
blooded animals it is easy to distinguish, by the difference
of colour, size, structure and mode of ramification, the
numerous plexuses of chyliferous vessels spreading upon
the intestine or between the folds of the mesentery, as seen
in the annexed view (Fig. 131. h. i. k.) of those of the small

FIG. 131

intestine of the tortoise. They accompany the veins (131.
c. d. e.) and the arteries (ISl.y. g. I.) in their course along
the mesentery to the thoracic duct (h.) ; but much exceed in
thickness, in number, and in the frequency of their anasto-
moses, the blood-vessels which they accompany. The
opaque white colour of their contents, and their passage
through the mesenteric glands, render their distinction from

E E 2

420 CHYLIFEROUS SYSTEM.

the red blood-vessels still more obvious in the mammiferous
class.

The chyle contained in these vessels in the vertebrat-
ed classes, and derived from the digested chyme of their
alimentary canal, much resembles the white blood of the
lower divisions of the animal kingdonij and varies in its
composition and properties in the different tribes of animals,
and in the same animal according to the kind of food on
which it subsists, being most allied to red blood in the
reddish colour, and the abundance of its fibrinous crassamen-
tum in the highest animals, and those which subsist on the
most nutritious animal food, and most remote from that
condition in its pale and limpid character, and the 'great
proportion of its thin serum in the lowest fishes, and the
most impoverished animals. The light floating white co-
loured fatty globules, seen already formed in the chyme,
appear also to have the same relations to the chyle as to the
circulating mass of blood, in the different tribes of animals
and in the different conditions of their food. The elements
of this fluid are intimately mingled in passing through the
chyliferous vessels ; but their motions are not aided by pul-
sating ventricular sacs, like those developed on the lympha-
tics in situations where their fluids are less affected by the
movements of the surrounding parts.

The same grades of development which are perceptible in the
properties and constitution of the chyle, are seen also in the
structure, forms and number of the vessels which convey it in
the different vertebrated classes, being fewer in number, des-
titute of internal valves, and apparently composed of a single
tunic in fishes, while in the class of mammiferous animals,
their numbers exceed all calculation, their valvular structure
is most universal and complete, and their two component tun-
cis are easily separable from each other. The inner coat is
a thin, smooth, serous membrane, which, by extending
more or less in free folds into the tubular cavity of the ves-
sels, produces the crescentic or semilunar valves, so nume-
rous and important in the higher animals, in directing the
motions of the contained fluid constantly towards the recep-
taculum chyli or the thoracic duct, these motions being de-
rived chiefly from the vis a tergo of the newly absorbed chyle,
and the incessant movements of the blood-vessels and the
surrounding viscera of organic life. The exterior tunic is a

CHYLIFEROUS SYSTEM. 421

tough, thin, fibrous layer, destitute of irritability, and the
strength and elasticity of which, allows of great distention
of the vessels without rupture of their delicate parietes.

The chyliferous vessels of fishes not only appear to con-
sist of a single tunic, destitute of valves, and without those
conglomerate glands which they form in higher classes ; but
they are fewer also in number on the intestine, and between
the folds of the mesentery, and contain a more thin limpid
and colourless chyle, with less proportion of fibrin, arid
without oily globules. They are obvious in all kinds of
osseous and cartilaginous fishes, spreading on the mesentery,
and forming two layers on the coats of the intestine, com-
posing reticulate plexuses between the mucous and the
muscular tunics, and also more exteriorly between the
muscular and the peritoneal coats, where they continue
along the course of the mesentery. They appear to originate
in the highly vascular erectile villi, so commonly developed
from the mucous lining of the small intestines of vertebrated
animals, and which extend freely into the fluid periphery
of the chyme passing through the alimentary canal. The
chyliferous vessels of the intestine anastomose freely to form
numerous loops and plexuses in their course, and constitute
by their union larger and larger trunks, which pass on between
the folds of the mesentery to terminate in one or two dilat-
ed reservoirs or receptacula chyli. The only trace of the
mesenteric glands, (found on these vessels in many higher
animals) are seen in the tortuous ramifications and compli-
cated anastomosing plexuses which they often form in fishes,
in their course towards the general receptacle of the chyle ;
and indeed this the true constitution, though on a simpler
scale, of the so-named mesenteric glands of the highest
animals and man, which have never the structure or excre-
tory ducts of true glands. Two thoracic ducts proceed forwards
from the recepiaculum, and form also frequent unions by their
astomoses, as they proceed forward along the sides of the aor-
ta, to open into the branches of the superior and inferior cavte
or the jugular veins. These vessels, like the lymphatics, appear
to have communications with the veins, which accompany
them, and semi-lunar valvular folds are developed at the
orifices by which they communicate ; and although, by in-
jection, and by inflating air upon the inner surface of the

422 CHYLIFEROUS SYSTEM.

opened lacteals, we perceive that they are still destitute of
the internal folds, which form the valves throughout their
whole course in higher classes, they already present a sac-
culated or beaded appearance when injected, from numerous
small constrictions like rudimentary valves. Two or three
small lenticular glandular bodies, seen in some fishes as far
forward as the oesophagus, appear more analogous to a
thymus than to chyliferous glands.

The trunks of the chyliferous vessels communicate with
the trunks of the lymphatics, as the lymphatics communicate
with the trunks of veins, or as the ducts of chylopoietic
glands communicate with the alimentary canal ; but the dis-
similarity of function is equally obvious in the several parts
thus connected with each other. The lacteals from the in-
testine, and the lymphatics from the posterior parts of the
body, generally unite to form two great trunks before they
enter the receptaculum, and this reservoir formed by their
union, whether single or double, is comparatively very large
in fishes. The two thoracic ducts, before entering the inter-
nal jugular veins, receive the lymphatic trunks from the head
and fore part of the body, and they form several loops and
plexuses by their frequent anastomoses in this place ; and
indeed the two thoracic ducts, whether they originate from a
single or double receptaculum, communicate with each other
in the freest manner, by lateral unions, throughout their whole
course. The capillary lacteals exceed in diameter the capil-
laries of the blood-vessels, and in the frequency of their anas-
tomoses throughout their course they much exceed the veins,
which surpass the arteries in this character.

In the amphibious animals the chyliferous system is nearly
in the same condition of development as in fishes, being still
destitute of valves and mesenteric glands, and conveying only
a thin limpid chyle, like the fluid of lymphatics, from the
intestine to the blood. They appear to have a similar origin
and distribution on the intestine ; they follow closely the
C3urse of the blood-vessels, and form the same anastomoses
and plexuses on the expanded mesentery of these animals, as
in fishes. Their wide reservoir formed by the union of their
trunks, sends forwrard two thoracic ducts, to terminate in the
jugular veins, with the trunks from the anterior pair of lym-
phatic hearts. Although the lymphatic pulsating cavities.

CIIYLIFEROUS SYSTEM. 423

which collect the lymph from the external parts of the am-
phibious animals, and propel it into the veins, appear to
be extensively developed in the oviparous vertebrata, no
similar moving powers are observed in the course of the
chyliferous vessels, which occupy an internal position, the
most exposed to the influence of incessant movements from
the surrounding parts. The great tenacity of life and
irritability observed in these anterior and posterior lym-
phatic hearts of the amphibia, which continue to pulsate long
after the animals are cut to pieces, is analogous to the per-
manence of vitality observed in the chyliferous vessels even
in the higher classes of animals, where they continue to ab-
sorb chyle from the intestine long after apparent death.

Most parts of the chyliferous system present a higher
grade of development in the reptiles, which is most apparent
in the existence of distinct valves in the trunks and larger
branches of these vessels, and in the white milky condition
of the chyle from the abundance of its globules in the carni-
vorous crocodilian family. They are still, however, without
mesenteric glands, their valves are less perfect in their struc-
ture and function than in birds and quadrupeds, and allow
injections to pass easily against their course ; the chyle is
still colourless in most of the serpents, lizards, and tortoises,
and the ramifications of the lacteals (131. A.), closely accom-
pany those of the veins (131. c. m.) and arteries (131./. /.)
both on the intestine (131, a. b.), and between the folds of
the mesentery. The coarse vegetable food of the chelonia,
and the consequent great length of their intestine, give occa-
sion for the numerous large chyliferous vessels which cover
their alimentary canal and mesentery ; and from the very im-
perfect development of their valves, and the consequent faci-
lity with which injections pass from trunks to branches, these
animals present peculiar advantages for illustrating the struc-
ture and functions of this system. Besides forming nume-
rous reticulate plexuses by their anastomoses on the intestine,
and along the course of the mesentery, the analogues of
higher and more complex chyliferous glands, (131. A. e. i.),
the trunks of these vessels, by their frequent inosculations,
constitute a continuous series of arches along the entire outer
margin of the mesentery, much exceeding in number those
formed in the same situation by the veins and arteries. The

424 CHYLIFEROUS SYSTEM.

union of their trunks form a large elongated irregular reser-
voir, from which proceed two or sometimes more anasto-
mosing thoracic ducts, which form almost a continued plexus
by their frequent unions, as they proceed forwards along the
left branch of the aorta, to the anterior part of the trunk,
where they terminate in the jugular or the subclavian vein, or
in the angle of union between these vessels. The frequent
unions, and the great multiplicity of chyliferous vessels in all
vertebrated animals compared with the arteries or the veins,
are rendered necessary by their imperfect means of propelling
their contents, and by the variable pressures to which they are
subjected. From the approximation of the crocodilian reptiles
to the carnivorous mammalia, in structure, food, and habits,
they already exhibit a larger proportion of fibririous globules,
and a more sanguineous character of their chyle, than have
been observed in other reptiles. During the active feeding sea-
son of the chelonian reptiles, their lacteals are found turgid
with chyle, which can be pressed forwards, in large quantity
and repeatedly, from capillaries to trunks, and from trunks
backwards to capillaries, in the opened bodies of these ani-
mals, so remarkable for their tenacity of life. So frequent
are the anastomoses of the several thoracic ducts, which form
a plexus round the aorta in the tortoise, that when inflated
with air, they entirely cover and conceal that vessel. Before
entering the veins, these ducts receive the lymphatic trunks
from the head and arms, but no anterior lymphatic hearts
are seen, although they are seen on the posterior lymphatic
trunks of many reptiles.

The coats of the chyliferous vessels are still very thin and
distensible in birds, and their valves, which are more abun-
dant on the trunks and branches than in reptiles, are still so
incomplete as to aUow injections to pass freely against their
course, from trunks to capillaries ; and although conglomerate
glands are already perceived on the lymphatics, especially
in the neck, no similar glands are yet developed on the lac-
teals of the mesentery. The chyle is still limpid and colour-
less, as in the cold-blooded vertebrata, and the more conglo-
merate glands of quadrupeds are still represented by simple
plexuses of lacteals between the folds of the mesentery, in
this warm-blooded oviparous class. The lacteal vessels are
now more crowded in layers below the serous and above the

CHYLIFEROUS SYSTEM. 425

mucous coat of the intestine, they appear more obvious, and
have more symmetry in their distribution. Their trunks
unite with those of the lymphatics, to form a more regular
receptaculum, from which two thoracic ducts, with fewer
inosculations, advance forwards to terminate by several open-
ings on each side of the neck, at the junction of the subcla-
vian and jugular veins. This duplicity of the thoracic duct,
so general in the lower vertebrata, is occasionally found as an
abnormal character in man, when they are observed to pro-
ceed upwards on each side of the aorta, to terminate one in
each of the subclavian veins. The lacteals, like the lympha-
tics, thus accompany or envelope the trunks of arteries, to
profit by their constant pulsations, in forwarding their con-
tents to the veins, and their common trunks terminate in the
subclavian or jugular veins, as the most convenient place
near the heart and the lungs, throughout the vertebrated
classes.

The chyliferous, like the lymphatic system, is more isolated
from the sanguiferous in the mammalia than in the lower
classes, and it manifests a higher development in the more
sanguineous character of the chyle, in the increased number
and more elaborate structure of the vessels and their valves,
in the existence of mesenteric glands, and in the concentra-
tion or unity of the thoracic duct. The small semilunar folds
in the interior of the lacteals are now so numerous and com-
plete, as to check the passage of injections from trunks to
capillaries, and to assist in forwarding the chyle to the tho-
racic duct ; and the two membranes forming the parietes of
the vessels are now more obvious, and more easily separated.
The more simple mesenteric plexuses of inferior classes, now
form small condensed conglomerate masses of minute capil-
lary lacteals, interwoven with capillary bloodvessels, so as to
form distinct, firm, red-coloured, rounded bodies, enclosed in
distinct tunics, and termed conglobate or mesenteric glands,
which present a great diversity in their size, their numbers,
and their degrees of approximation to each other, in the
different orders of quadrupeds. The lacteals and chyliferous
glands are almost confined to the small intestine in the
inferior vertebrata; but as the colon is more extended
in the mammalia, they are now found also, though in
smaller proportion, on the mesocolon. The receptaculum

426 CIIYLIFEROUS SYSTEM.

chyli is frequently formed, here and in lower classes, by a
simple plexus of chyliferous and lymphatic trunks, and that
plexus is sometimes extended forwards along the aorta, dimi-
nishing the frequency of the anastomoses, to constitute one or
two principal thoracic ducts which enter the subclavian veins.
Sometimes the branches of the thoracic duct open directly
into the vena azygos, as in the hog, and a similar communi-
cation has been seen as an abnormal structure in man.

The chyle is conveyed so abundantly through the thoracic
duct, that six ounces per hour have been computed to flow
through that canal in the dog, and on tying the thoracic duct,
the chyle has been found still to pass forwards to the veins by
the enlargement of the lateral lymphatic trunks. There are
always distinct valves at the entrance of the thoracic ducts
into the veins*, to check the return of blood into these dila-
table canals, as in all the lower vertebrated classes. The
influence of the mesenteric glands on the chyle which passes
through their highly vascular and complicated • network,
is not determined; but, by their grouping and uniting
together, they often imitate the lobu'lated and conglomerate
form of other less ambiguous glands. They are of great
size in the cetacea, they are more detached in the solidun-
gulous pachyderma and in the ruminantia, and they are
often collected into a conglomerate mass, termed pancreas
Asellii, in the carnivorous quadrupeds. There are forty of
these small round lenticular glands in the bradypus ; they are
approximated into a group of about thirty in the hog tribe.
In the myrmecophaga, those of the small intestine are col-
lected into a mass, and about twenty small glands are spread
apart on the mesocolon ; they are also grouped into a
mass in the armadillo, the mole, and the nasua. In the
hyrax they are a little separate, and in the manis they are
at a distance from each other ; but in the roderitia, so infe-
rior in most of their characters, they are the smallest in
number and the least developed.

Besides the pancreas Asellii, which has always its efferent
as well as its inferent ducts, there are generally a few de-
tached mesenteric glands in the carnivora, as in the otter,
the seal, the badyer, the dog, the cat, and other species,
and the same is seen in the hedgehog ; but in the bear they
form two masses, the one belonging to the mesentery, and

CI1YLIFEROUS SYSTEM. 42J

the other to the mesocolon. In the quadrumanous animals,
as in man, they are spread at a greater distance from each
other, and more equally, over the mesentery, and in part
over the mesocolon. There are more than a hundred mesen-
teric glands on the human lacteals, and about a fourth part
of these belong to the colon; they are larger and more
crowded on the dorsal portion of the mesentery, and more
minute and dispersed towards its intestinal margin ; but
notwithstanding their greater number and development, their
uses are not more apparent here than in the simpler forms
of vertebrata. The receptaculum is still formed by the union
of the lacteal with the inferior lymphatic trunks, the primi-
tive reticulate structure and duplicity of the thoracic duct
is still perceptible in the frequent divisions presented in its
course, and it still terminates at the junction of the subcla-
vian with the jugular vein, as in most of the vertebrated
tribes. And thus the chyhferous system, though a mere
appendage to the venous, serving to convey nutriment to the
blood and performing functions assigned to the veins in the
lowest classes of animals, manifests the same laws of forma-
tion, and the same plan of perfection in the various grades of
its advancement, which we observe in all the more complex
parts of the economy, and appears like a remnant of the
simpler white-blooded sanguiferous system of the inverte-
brated tribes still on the march to a more isolated and com-
plete development.

CHAPTER THIRD.

SANGUIFEROUS SYSTEM.
FIRST SECTION.

General observations on the sanguiferous system.

THE materials elaborated by the digestive organs and
conveyed by the lacteals to the blood, are sent for the nu-
triment of each point of the body, by a vascular apparatus
almost as universal in the animal kingdom as that of diges-
tion itself, and presenting phases of development, in its
essential parts, as regular and progressive, as its general
form is varied and diversified in the different tribes. As
the fountain of all nourishment and of all development is
the blood, the peculiarities of this hydraulic apparatus in
the different classes, and the laws which regulate its distri-
bution in different animals, and in different parts of the
body, involve the chief mystery of their development and
form. Half of the animal structure, indeed, is a tissue of
minute vessels, and the healthful condition of their fluid
contents is alone preserved by the vortex-like movements to
which they are constantly subjected by muscular fibres and
the nerves, so that the life is in the blood as much as in the
heart or the brain. The sanguiferous system being but a ra-
diation of the digestive throughout the body, they keep
pace, and follow the same laws, in the march of their deve-
lopment in the animal kingdom as in the embryo. In the
embryo, as in the animal kingdom, capillaries precede
trunks in the order of formation, as the pulsating vessel
precedes and forms the ventricle. The existence of the

SANGUIFEROUS SYSTEM. 429

ventricle necessitates that of the auricle to perfect its func-
tion, and the cleaving of each produces in succession the tri-
locular and the quadrilocular heart of the cold- and warm-
blooded vertebrata.

SECOND SECTION.

Sanguiferous system of the cyclo-neurose or radiated classes.

In the radiated classes of animals, as in the earliest condi-
tion of the human embryo, vessels alone are developed to
contain and circulate the fluids, without the aid of a heart ;
and indeed, in the simplest forms, the fluids move in a
cyclosis through the general cavity of the body, like the co-
lourless blood in the cells of a plant, or the first movements
of the globules in the germinal portion of an ovum. This
constant slow revolution, forwards and backwards round the
interior of the body, is seen in the globules, suspended in a
more fluid serum, in the paramacium and other polygastric
animalcules, and appears to be produced by vibratile cilia
lining the cavity, as all the analogous movements in higher
tribes of animals ; and the same minute organs are probably
the active agents of the currents of globules suspended in a
serous fluid, which are seen in the vascular plexuses of the
stipulse and other parts of plants, and around the larger cells
which compose their structure. In some of the larger com-
pound polygastrica, as the volvox, a distinct plexus of ves-
sels, forming a reticulate texture, is seen spread over the
whole surface of the body, and apparently destined to con-
vey the fluids of the component monads over the general
mass of these remarkable aggregate beings. The same active
cilia appear to produce the circulatory movements through the
ramified and motionless canals of poriphera to nourish and
aerate the body, as they obviously effect analogous movements
in the bodies of many zoophytes.

The circulation of the blood in many zoophytes was
carefully investigated and described by Cavolini fifty years
since, especially in sertularice, plumularm, campanularite,
tubularice, and other transparent genera, and his obser-
vations have been confirmed and extended by many sue-

430 SANGUIFEROUS SYSTEM.

ceeding observers. Cavolini observed in the longitudinal
cavity of the fleshy axis of their body, a fluid in motion,
containing distinct globules like those composing the flesh,
which continued during the whole life of the animals, to
ascend and descend through all the stems, and the branches
and the polypi. These globules, he observed, were contained
in a more thin transparent and colourless fluid, not at first very
obvious, and he saw them carried upwards and downwards,
and sometimes transversely in the cavity of the fleshy axis.
The same phenomenon, he perceived, in all the tubular va-
giniform keratophytes, the transparency of whose parietes
allowed their interior to be examined through the micros-
cope, and, comparing their circulation to that of the larvee
of insects, he designated the fleshy canals through which
the blood moves as the heart of these polypipherous animals.
The same motions, indeed, in the fleshy axis of the common
sertularia geniculata had been observed by Loefning, and
described by Pallas before the time of Cavolini. Olivi, who
subsequently examined the phenomena of the circulation in
sertularice, considered them as depending on the food and
water swallowed by the polypi, which were thus subjected to a
peristaltic motion, merely to assist in their digestion. Flem-
ing pointed out a similar circulation in the fleshy axis of the
campanularia gelatinosa. Chiaje considered the ciliated ten-
tacula of zoophytes as their branchial organs, and supposed
that their circulating blood is thus transmitted to them for
aeration ; he perceived also sanguiferous vessels extending
from the base of the polypi in the coral and gorgonia, and
forming a superficial reticulate plexus in the caryophylUa.
Nordman described a similar circulation of the blood in the
alcyonella diaphana. which he compared to that seen in the
cells of the char a ; and the motions which I have long since
described in the polypi of flustra, virgularice, pennatu/ce,
and other zoophytes, I have referred to the action of minute
vibratile cilia — the common agents of all analogous move-
ments in the lowest tribes of animals, and which probably
continue to line the serous tubes of the sanguiferous system
in all the higher classes, as they are seen vibrating on the
serous lining of the cerebral ventricles, even in mammalia,
and the most complex form of the sanguiferous system in
the animal kingdom is but an extension of the simple cell of a

SANGUIFEROrS SYSTEM.

char a. The colourless chyle derived from the food digested in
the stomachs of the polypi, and transmitted in successive por-
tions by the posterior orifice of these digestive sacs, is thus
circulated for the nutriment of each part of the system, with-
out the aid of the inert canals through which it moves. In the
larger polypi, as actiniae, the vibratile cilia are still more ob-
vious, propelling the currents and globules to and fro through
the body and the tubular tentacula of these animals, as the
digested fluids were seen by Trembly to pass through the body
and the long tentacula of the hydra. And even in the acalepha,
the fluids observed meandering through the motionless canals
of their transparent texture, appear to be impelled by the
same active agents. The thin serous fluid, replete with
globules, continues moving through the longitudinal la-
teral canals of the beroe pileus, while their parietes are
seen, through the transparent body of the animal, to
remain perfectly motionless, like the sides of the cells
of a plant. The same circulation of the nutritive fluids,
sent from the stomach, was observed by Eschscholtz in
the transparent canals of the cesium, and similar currents are
seen in the wide canals of the mantle in the aurelia (Fig. 113),
the rhizostoma, and all the larger medusae, but the minuter
filaments, every where distributed through their texture, ap-
pear to have no connection with the circulating system. The
currents of nutriment thus spread through every part of the
system in the lower radiated classes, serve alike to feed and
aerate their simple textures, in the same manner as the less
isolated currents through the homogeneous texture of pori-
phera.

A more isolated sanguiferous system however, is seen in
the echinoderma, where a distinct set of vessels is appro-
priated to receive the colourless transparent chyle from the
alimentary cavity, and to convey it to the respiratory organs,
and thence through the rest of the body. These vessels are
especially obvious on the mesentery, which so commonly
suspends the intestine from the parietes of the abdomen in
the animals of this class, as in the echinus, spatangus, aste-
rias, holothuria, and allied genera, but no auricle or ventricle
is yet developed in their course, although Chiaje has assigned
these names to minute sinuses on the ends of the principal
vessel of the sipunculus. Fluids replete with globules, and

432 SANGUIFEROUS SYSTEM.

moved by the lining vibratile cilia, are seen advancing and
retreating through the transparent tubular feet of these ani-
mals, conveyed from vessels and sacs extending along their
base. But the capillary veins of the asterias arise from the
gastric coeca, extend and anastomose along the course of the
mesentery, where they are freely aerated, and their united
trunks, disposed around the central cavity, give origin to the
arteries which traverse and nourish the rest of the body.
Into each division of the body, a large intestinal artery pas-
ses from the circular trunk around the stomach, and divides
into two branches, to be distributed on the two ramified
coeca of each. A single arterial trunk is distributed to the
feet of each of the rays, and the same number of trunks con-
tinue along the whole course of the rays to be distributed
on the segments and the superficial parts of the body. The
ramifications of these vessels are distinctly seen on the
stomach, the gastric coeca, and the ovaries, and in some
astei^us a cordeform enlargement is seen on the arterial
trunk, which is not developed in other species. In the
echinus, so closely allied to the asterias in all its organs of
relation, the same plan is perceived in the distribution of the
vascular system, a circular artery is observed around the
mouth, which sends out branches to the long alimentary
canal, and five branches proceed to form a vascular ring
around the opposite axis of the trunk. A large vein passing
forwards along the inner part of the mesentery, enters the
circular trunk around the mouth, and the arteries for the
tubular feet arise from this oral ring, as in the asterias.
The numerous veins ramified on the intestine and mesentery
of the holothuria (Fig. 114. /.), replenished with chyle from
that cavity, unite to form large arterial trunks, which distri-
bute their fluids over the complicated internal branchiee
(114. h. h.)9 extended between the long turns of the intes-
tine (114. d. d.) The arterialised blood collected from the
branchial veins is sent forwards and backwards by systemic
trunks, the anterior of which forms the usual ring around the
oesophagus, while the posterior follows the course of the
intestine. The circular trunk around the oesophagus gives
off five arterial branches, which supply the apparatus of the
mouth, and the general parietes of the trunk, and extend-
ing their course backwards, parallel to the long muscular

SANGUIFEROUS SYSTEM. 433

abdominal bands as far as the cloaca, they give off numerous
branches to the superficial parts, and to the tubular ciliated
feet, which are here projected from the sides, as in other
genera. Other important branches arise from this wide,
arterial, oesophageal ring, which pass forwards and backwards
to the more deeply seated viscera. The venous intestinal
trunks follow the windings of the long alimentary canal, and
their branches anastomose most freely with each other on
the mesentery of these animals, as in the vertebrated classes.
Distinct pulsation is observed in the great arterial trunk and
circle around the oesophagus, which gives origin, as usual in
this class, to the principal arteries of the body. The blood
accumulated in the larger vessels manifests a reddish hue
during life, and abounds with globules which unite in a coa-
gulum after death. There appears likewise to be a vascular
ring around both extremities of the body in the elongated
trunk of the sipunculus, and the large connecting median
artery, like the dorsal artery of articulata, gives off numerous
lateral branches in its course forwards. This artery forms a
small sinus at both ends, and gives off the tentacular and other
cephalic branches from the cesophageal ring, which it here
forms, as in other echinoderma. Regular pulsations have
been observed in this long narrow vessel, as in the principal
trunk of holothuria, and in its terminal enlargements, and
the blood has a pale red colour, as in the large arterial trunks
of many species of asterias and other genera of this class.
The same vascular ring, sometimes double or triple, around
the oesophagus, formed by the union of the mesenteric and
the general systemic veins, observed in most of the larger
asterida, echinida and holothurida, is seen even in the smaller
forms of ophiurte, where it also radiates arterial trunks to
the superficial and the deeply seated parts, and to the vesi-
cles and ampullse of the feet. The pale red colour so gene-
rally perceptible in the blood of the echinoderma, was ob-
served by Cavolini even in that of zoophytes, especially in
the longitudinal vessels which occupy the superficial grooves
of the axis of gorgonia, corallium, and other corticiferous
forms ; and Chiaje observed a yellowish hue in the thin se-
rous fluid, abounding with blood-globules, so extensively
circulated through the superficial and the deep seated vessels
even of the minutest forms of acalcpha. There is thus in

PART V. F F

434 SANGUIFEROUS SYSTEM.

the sanguiferous system of the radiated classes, a close ana-
logy not only to the earliest conditions of this system in the
vertebrated animals, but also to the permanent conditions of
their chyliferous and lymphatic apparatus, especially in. the
composition and properties of the contained fluid, and in the
origin and simple structure of the vessels which convey it,
and their free anastomoses with each other. The cyclosis
which I have long since pointed out in the bodies of polygas-
trica, has been more recently mistaken for a revolution of
ova, which supposed ova however have never been seen to
develope. In the higher forms of these cyclo-neurose ani-
mals the afferent vessels may be regarded as veins which
proceed, whether from the alimentary canal, or the respira-
tory organs, or from the general system, towards the tubular,
pulsating, heart- forming portion of the sanguiferous system ;
and those efferent vessels may be considered arteries which
radiate to the system from this central portion, although they
appear still destitute of the strong, fibrous, middle coat, de-
veloped in the arteries of higher animals, and the veins are
still destitute of valves, and similar in structure to the arte-
ries.

THIRD SECTION.

Sanguiferous system of the Diplo-Neurose or Articulated
Classes.

The long cylindrical form of the trunk in articulated ani-
mals is observed to impress that form on the sanguiferous
system, as well as on the nervous, the digestive, and other
important internal apparatus, and is marked especially in
the longitudinal direction and the elongated form of the
great central arterial and venous trunks. The blood is more
highly organized and more deeply coloured, provided with
more abundant globules and fibrin, in the articulated than in
the radiated animals, and is more remarkable for its deep red
colour and its extensive distribution through the body in the
soft and slow moving helminthoid classes than in the more
active entomoid forms. In most of the articulated classes
the blood is observed to move forwards in one or more great

SANGUIFEROUS SYSTEM. 435

dorsal, pulsating, arterial vessels, the lateral branches of
which terminate in corresponding ventral venous trunks,
which convey it backwards to the beginning of the dorsal
vessel, and it is chiefly in the form and structure of this
great muscular pulsating centre that we perceive the higher
development of the vascular system in the entomoid than in
the helminthoid classes. The internal vibratile cilia are still
the principal agents of the circulation and respiration in many
of the lower, articulata, as in most of the radiated classes,
especially where the muscular, pulsating, arterial centre of
the sanguiferous system is not yet developed, as in the en-
tozoa and rotifera.

The exterior surface is aerated, and the interior cyclosis
is effected, by the same means, in the wide gastric cavi-
ties of the cystic entozoa, as in the ciliated abdominal sacs
of the polygastric and rotiferous animalcules. The lim-
pid serous fluids likewise meander through the inert canals
of the cestoid and trematode worms, without the aid of con-
tractile muscular parietes, as in the similarly ciliated and
inert vessels of the acalepha and most other radiated animals;
and from the extensively ramified condition of their alimen-
tary canal, the sanguiferous system is less isolated from the
digestive than in higher forms. In the diplostomum clavatum

o O J-

and diplostomum volvens, where the digestive organs are more
circumscribed, a distinct system of arteries and veins is per-
ceived to circulate most extensively through the body a thin,
red-coloured serous fluid, apparently absorbed from the pa-
rietes of the capacious alimentary sacs. A large arterial
trunk, giving off numerous lateral branches in its course, is
observed, in both these animals, to commence from the pos-
terior extremity of the body, and to advance along the me-
dian plain to near the mouth, where it is continued, with di-
minished calibre, into two great lateral venous trunks. These
great lateral veins are directed backwards along the whole
extent of the body, and receive numerous branches on each
side, many of which are observed to be continuous with the
capillaries of the median artery. A single anastomosing
canal connects the two venous trunks with each other across
the middle of the animal, and connects them likewise with
two other longitudinal veins, more central in their position,
and extending along the posterior half of the body. In the

F F 2

436

SANGU1FEROUS SYSTEM.

annexed view, from Nordmann, of the internal structure of
the diplozoon paradoxum, (Fig. 132.) which is frequently
found attached between the inner laminse of the gills of the
bream, (cyprinus brama), the circulation is observed to be
conducted in distinct arteries and veins, without the aid of
pulsating cavities or vessels, as in other species of this order ;
and not only is the same plan of the sanguiferous system
repeated in the two halves of the animal, but also on the two
sides of each half of the body. The two halves of this tre-
matode entozoon communicate freely by the digestive canal,

FIG. 132.

and have each a distinct genital apparatus, as we see also in
the several segments of the tania and other cestoid forms,
and dicephalous individuals are occasionally found in the
tricenophori and cysticerci, as abnormal forms. At the ante-
rior extremity of each of the long free tapering divisions of
the body is seen the transverse crescentic buccal orifice (132.
#,) of the digestive organs, (132. e. d. c. r.) with two lateral
suctorial disks, (132. /*,) and a salivary follicle (132. /.) ; and

SANGUIFEROUS SYSTEM. 437

together with the ramified cceca of the alimentary canal, the
two long convoluted ovaries, (132. i. k. /,) the capacious sin-
gle oviduct, (132. m. n. o,) the testicle (132. /?,) and the spiral
vas deferens (132. g,) occupy the greater portion of each ab-
dominal cavity. The oviducts have distinct openings (132. o)
at the inner margin, near the proximal end of the two poste-
rior divisions of the animal, like the marginal genital open-
ings of the tcenia. The four firm, cartilaginous, oval disks,
by which the animal attaches itself to the surface of the gills,
are provided each with four suctorial cavities (132. b. s.) j
they occupy the inferior margins of the wide posterior parts
of this bifid trunk, and these diverging parts terminate by an
expanded fold, with free reverted margins (132. a. a.), in
form of a valve or protecting mantle. Longitudinal and
transverse muscular fibres are obvious within the firm exte-
rior elastic skin, and the light yellow colour of the animal is
often changed to red, by the blood, sucked as food, filling
the ramified alimentary canal, and appearing distinctly
through the transparent texture of the body. The intestine
expands like a stomach across the place of junction of the
two lateral halves of this animal, but there is no distinct anal
opening in the body, and the residue of the digested blood is
often seen to be expelled by the buccal orifice, on disturbing
the diplozoon.

The colourless and limpid serous fluid circulating in the
vessels of this animal is carried forwards by two upper, late-
ral arterial trunks (132. u. u. v. v.) in each segment of the
body, and it is returned backwards by two corresponding,
inferior lateral veins, (132. s. s. t. /.), but there is no cordi-
form dilatation on any part of the sanguiferous system, nor is
the slightest pulsation observed in any of the vessels. As
in similar minute ' transparent animals, the ramifications and
anastomoses of the arteries and veins, and the currents of the
blood are best seen through the microscope by transmitted
light, when unobstructed by opaque contents in the ovaries
or the alimentary cavities. The two great ventral venous
trunks (132. t. s.) of each segment are observed to commence
small near the sides of the oesophagus, where they soon re-
ceive the terminations of numerous peripheral and central
veins, collected from the neighbouring parts, especially of
two long lateral branches, extending forwards parallel to the

438 SANGUIFEROUS SYSTEM.

trunks, and two shorter veins proceeding outwards from
the internal parts. Reinforced by the accession of numerous
smaller branches, the two great venous trunks pursue a
winding course backwards, receiving also large branches near
the junction of the lateral halves of the body, and they can
be traced, converging, as far as the opaque muscular organs
of attachment, at the posterior ends of the segments, ( 1 32.
a. «,) where the two arterial trunks commence. The two
great arteries (132. u. v}) lying more dorsally than the veins,
follow a similar tortuous course along the sides of the two
segments of the animal, they also are nearly of equal calibre
throughout, and their contents are observed to move from
behind forwards, while the blood moves backwards in the
venous trunks, but neither manifest the slightest systole or
diastole. The arteries give off numerous ramifying branches
in their whole course, both to the internal and the peripheral
parts, those being especially large which proceed to the ute-
rine portion, (132. m. n.) of the genital apparatus near the
middle of the body, and they become much reduced in
bulk, and at length imperceptible, before they reach the
sides of the mouth or the commencement of the venous
trunks. The; minute anastomosing branches of these great
lateral arteries and veins form superficial and deep seated
plexuses, which are most obvious in the more transparent
parts of the body, and especially a compact subcutaneous
plexus spread over the general surface ; but they here form
no median dorsal artery, as in most articulated classes, and
there appears to be little vascular connection between the
two lateral segments of this animal.

The extensive distribution of the sanguiferous system, the
rapid circulation of the blood, and the great superficial
plexuses, so conspicuous in the trematode entozoa, buried in
the substance of their food, and destitute of anal opening,
may enable them to receive or excrete matter through the
general surface of their body, as well as through their
buccal orifice. This extensive distribution of the circulating
vessels has also been especially observed in different species
of distoma and amphistoma, where, from the breadth of the
body, the principal trunks are commonly double and lateral,
and where they have sometimes appeared to communicate
directly with the exterior surface, or with internal sacs, or

SANGUIFEROUS SYSTEM. 439

with the genital apparatus. The plan of the circulating
system is similar in the polystomum and octobothrium, and
from the limpid and homogeneous character of the blood, and
the inert condition of the vessels in which it is contained,
neither the motion nor the presence of that fluid is percep-
tible in the transparent canals of the caryophyllaus, nor is
any motion perceptible in the vessels which convey the
blood in the aspidogaster. But in the lernaa, globules of
different sizes abound in the limpid blood, and distinct pul-
sations are observed in the great central artery of the trunk,
as in the higher tribes of articulated animals. In some of
the highest entomoid forms, as the achtheres, a distinct
elongated pulsating cavity is seen extending along the middle
of the anterior part of the cephalothorax, which sends two
vessels laterally to the prehensile fixed arms, and two similar
canals posteriorly to the viscera, thus approaching to the
form of the sanguiferous system of the Crustacea. By the
pulsations of the dorsal vessel the blood is sent rapidly
through the canals of the arms and of the abdomen ; but in
the following in stance it appears to re turn by the same passages,
as if they performed the functions both of arteries and veins.
From the transparency and the colourless texture of the
body in the rotiferous animalcules, vibratile cilia are percep-
tible on the exterior peritoneal surface, and the interior mu-
cous lining of their alimentary canal, and producing rapid
currents of water through the lateral brancheal tubes and
tufts disposed along with the extended testes, in the capa-
cious cavity of the abdomen. These more obvious r,espira-
tory currents appear to have been mistaken for a circulation
of blood, which has not been distinctly perceived to move in
the minute sanguiferous vessels of these animals ; and the
supposed median longitudinal dorsal artery of the hydatina,
a more careful examination has shown to be a subcutaneous
muscular band. In the extended and active state of the
body, a circular cervical plexus of minute transparent vessels
is perceptible in several genera of rotifera, as hydatina, oto~
glena, diglena, and notommata, and from this anterior vas-
cular network longitudinal vessels appear to communicate
with the more symmetrical transverse dorsal arteries of the
trunk ; but no motion is seen in these vessels, or in their
contained fluid. Vessels also appear to pass from these

440 SANGUIFEROUS SYSTEM.

peripheral parts to form plexuses around the internal nutri-
tive organs, and thence to extend to the internal respiratory
apparatus ; but many of the supposed vessels of these ani-
mals are probably, like the median dorsal, only transparent
muscular fasciculi. In the cirrhopods the sanguiferous sys-
tem, like most other parts of their economy, is constructed
on the plan of that of the higher articulata, and especially of
the Crustacea. A wide pulsating dorsal vessel, as observed
by Poli, extends forwards along the median line, apparently
receiving the blood from the branchial and the inferior sys-
temic veins, and transmitting it by large trunks into the
articulated feet and other parts of the body. Simple cur-
rents are observed to flow outwards and inwards through
the articulated feet, as in insects and the lower Crustacea,
without ramification of the two bounding canals, and the
venous blood appears to return to the fore part of the abdo-
men, as in crustacea, before being sent to the small branchial
laminoe attached to the haunches of the articulated mem-
bers.

In the annelides, as in the larva state of the higher ento-
moid animals, the blopd is extensively circulated through the
system by minute arteries and veins ; but the great centre of
the sanguiferous system is still in an inferior condition of
development, presenting only the form of an elongated,
simple, pulsating, median, dorsal artery, provided with dis-
tinct, circular, muscular fibres, and conveying a thin, red-
coloured, serous blood, with comparatively little fibrin or
globules, and without distinct cordiform enlargement in its
course. The venous blood of these animals is commonly
returned from the system to the posterior extremity of the
dorsal artery, by a median vein commonly termed vena
cava, or by two inferior lateral veins, which collect the
blood from the capillaries of the arterial branches, as they
pass backwards along the sides of the body. So that the
general plan of the circulation in the adult forms of the sim-
pler annelides (represented in Fig. 133. A, where (a) is the
median dorsal artery conveying the blood forwards, and (b.b,)
the two returning lateral veins,) not only resembles that of
insects and other entomoid animals, but also the earliest
embryo condition of this system in the vertebrated classes.
This is nearly the course followed by the red blood, observed

SANGUIFEROUS SYSTEM,

441

through the transparent body, circulating in the arteries and
veins of the common brown coloured erpobdella vulgaris,
(133. B ), found creeping on the aquatic plants of our fresh
water pools, and guided by eight eyes placed in a curved
series along the anterior part of the head, like those of a
leech. Here, according to Morren, there are two median
vessels, a dorsal and a ventral, (133. B. a,) which, by their
waves of pulsation, convey the blood into numerous lateral
branches, (133. B. b,) the capillaries of which are continuous

FIG. 133.

with those of the two great returning veins, (132. B. c. c,)
extending backwards along the sides of the body; the in-
ferior median vessel, however, is probably a returning vein.
In the prostoma and various other broad forms of pla-
nariosj the thin, red coloured serous blood is also observed
to be conveyed forwards by the contractions of a single
median dorsal artery, and backwards by two lateral infe-
rior venous trunks, which present two small vesicular en-
largements in their course, analogous to the more numerous
minute sinuses seen on the vascular trunks in the lumbri-
cus and many other annelides. The planaria viganensis
has two minute sinuses on the anterior part of each of

442 SANGUIFEROUS SYSTEM.

the lateral vessels ; and posteriorly these vessels send each a
large branch to the ovary and cloaca. In the nais, the usual
median dorsal artery, propelling the blood forwards, divides
at the anterior part of the neck, and descending on each side
of the cesaphagus, forms, as in many other elongated narrow
species, a single inferior median epi-neural vein, by which the
blood is conveyed posteriorly. This arterial oesophageal ring
of the nais exhibits the same regular systole and diastole, which
are seen in the dorsal artery, and which are obvious in the
corresponding sacculated arterial rings passing down from the
anterior part of the great dorsal artery to the ventral vein of
the earth-worm, (133. C. c, d.) Where there are two median
trunks, a dorsal and a ventral, in the sanguiferous system of the
annelides the inferior is commonly a smaller returning vessel,
extending along the motor surface of the nervous columns, as
in the entomoid classes, and analogous to the descending ab-
dominal aorta of fishes, and the embryos of higher vertebrata.
So that the position of the heart-forming dorsal trunk, the
median ventral vessel, and the vascular rings or branchial
arches which connect them, in many of the articulated classes,
correspond precisely with the inverted position which I have
shown in their moto-sensitive nervous columns, and other
important organs.

The simplest condition of the circulating system is seen
in those which have no perceptible respiratory organs, as
in the nais and planaria ; but considerable modifications
of the general plan are induced in higher genera, by the de-
velopment of organs for this function, in form of internal air
sacs, or of external cephalic or dorsal branchiae. The high cu-
taneous vascularity appears to supply their place in the abran-
chiate species, where the ramifications of the blood vessels
are quite distinct from those of the digestive apparatus. The
long dorsal artery of the nereis cuprea appears to be slightly
dilated in each segment of the body, and receives or gives
off the branchial vessels from the arterial arches which en-
compass the oesophagus ; but in other species the branchial
vessels are given off to these organs from each side of the
dorsal vessel in its whole course forwards, and small pul-
sating vesicles are generally perceptible on the lateral syste-
mic branches of the aorta. The little tubicolous clymene
likewise gives off from the great dorsal artery conveying red
blood, numerous lateral branches extending like branchial

SANGUIFEROUS SYSTEM. 443

arteries to the lateral pairs of feet. In the cephalo-branchiate
marine serpulce and sabellce, the arterialised blood is returned
by the branchial veins to two elongated sinuses placed at the
sides of the oesophagus, the aorta and vena cava occupy
the median plain, giving off symmetrical lateral branches,
and the dorsal vessel appears slightly enlarged in each
segment. The branchial veins of the amphitrite likewise
convey the arterialised blood to two vesicular sinuses which
unite below the oesophagus, and from these branchial sinuses
in the terebelloe the two lateral systemic veins take their
principal origin.

From the deep red colour of the blood, and the colour-
less transparency of the general tissues of the body, in the
common peetinaria of our sandy coasts, the pulsations of
the wide dorsal artery are easily observed, extending in
successive waves from behind forwards, and also the nu-
merous branches sent off laterally, which reduce the calibre
of this great artery at its anterior part. Besides the usual
median dorsal artery, and the median ventral trunk above
the nervous columns, in the pleione carunculata, there are
two lateral dorsal vessels which communicate freely, by anas-
tomosing branches, with the median dorsal artery, and also
two lateral longitudinal ventral veins, which send numerous
branches to the branchiae. The arterialised blood appears
to be collected from the branchise by the lateral dorsal ves-
sels, and to be transmitted partly by their internal anasto-
mosing branches, into the median dorsal artery, and partly
by their own branches to the principal organs of the body.
The venous blood of the system is collected from the super-
ficial parts and the internal viscera into the great lateral
veins, and is thence transmitted through the minute laminae
of the external branchiae, before it is received by lateral arte-
rial trunks for the nourishment of the system. The highly
sensitive and muscular pharynx is provided with a large and
distinct plexus of vessels, connected, like the numerous
plexuses of the alimentary canal, with the great inferior
lateral veins, which give origin to the branchial arteries. The
median dorsal artery is here chiefly connected with the ali-
mentary canal, as the median ventral vein is, in this and
most other articulated animals, connected with the nervous
columns. From the equal development of the great vascular
centres throughout the body of the annelides, and the nume-

444 SANGUIFEROUS SYSTEM.

rous anastomoses among the principle sanguiferous trunks,
it is easy to perceive how the circulation in these animals
can5 by the closing of the divided ends of the vessels, become
accommodated to extensive mutilations, and proceed without
interruption in a few segments detached from the trunk.
Some of the simpler forms, as stylaria, are thus enabled to
extend their means of propagation by the spontaneous trans-
verse division of their body.

Besides the ordinary dorsal artery, extending forwards
between the fifteen pairs of ramose branchiae in the arenicola,
the great subgastric vein, and two smaller vessels extending
along the sides of the nervous columns, distinct longitudinal
gastric vessels^ one superior and one inferior, are seen ex-
tending along the alimentary canal, and forming delicate
plexuses on its parietes. The numerous branchial vessels
are observed to be connected directly with the great dorsal
and ventral trunks. As in most other annelides, enlarge-
ments, here one on each side, are formed at the anterior part
of the body, on the anastomosing branches between the great
superior and inferior median vessels, and these two sinuses
have been considered as the two auricles of the heart in this
animal — cavities, however, which are not found co-existent
in the heart of animals lower than the amphibious vertebrata.
The arterialised blood from the ramified branchiee of the am-
phinome appears to be collected, as usual, into two longitudinal
lateral trunks, which convey it, by numerous anastomoses,
into the great advancing trunk of the dorsal vessel, before that
systemic artery turns downwards and backwards, to ramify on
the internal viscera ; and it is again collected from the system
into venous trunks, from which the branchial arteries convey
it to the respiratory organs. The same plan of the circulat-
ing system is seen in the leech, where the great median dor-
sal and median ventral trunks are extended along the whole
body, giving off numerous symmetrical branches on each side
in their course ; and two large lateral vessels follow along
the margins of the segments, receiving in their progress
regular alternating branches from the superior and inferior
parts of the body. The great ventral vein extended beneath
the alimentary canal, appears to be enlarged opposite to each
of the subjacent ganglia, and to encompass the nervous
columns by its numerous circles of anastomosing branches,
producing thus a hypo-neural as well as an epi-neural vein;

SAXGUIFEROUS SYSTEM. 445

its lateral branches also form regular vesicular enlargements
near the sides of the nervous ganglia. The lateral vessels
are wider than the median, their branches anastomose with
each other, and also with the dorsal vessel, and they appear
to receive the aerated blood from the respiratory vesicles, as
the lateral vessels receive it from the branchiae, in other an-
nelides. Their tapering ends are united by anastomosis
across the median plain, both anteriorly and posteriorly, so
that they form a continuous canal around the margin of the
body ; and their large dorsal branches^ at the posterior por-
tion of the body, form five long rectangular meshes by their
free junction across the segments. The dorsal vessel com-
mences posteriorly by two branches, which unite together at
the pyloric end of the stomach, and all the vascular trunks
of this animal give off or receive their branches with a sym-
metry equal to that of the nervous system.

The blood is also of a deep red colour, and charged with
globules, in the earth-worm, lumbricus terrestris (Fig. 133.
C.), and from the greater transparency of the body, the
direction of the internal currents is more perceptible than in
the more opaque body of die leech, where it is necessary to
examine this part in very young individuals, and where the
currents have appeared often to change their direction through
the vascular trunks. Successive waves of contraction are dis-
tinctly seen in the earth-worm, extending from behind for-
wards along the wide dorsal vessel ; and by removing the in-
teguments and pressing this artery between the forceps, it
becomes empty in front and turgid behind. It appears to re-
ceive the arterialised blood from the air vesicles, and sends
off numerous lateral branches in its course, especially to the
alimentary canal and the genital organs. The venous blood
is collected from the viscera chiefly by the great median sub-
gastric or epi-neural vein extending backwards between the
digestive canal and the nervous columns; and this vessel
appears to send off branches to the numerous minute res-
piratory vesicles. A small inferior median vessel or hypo-
neural vein is also perceived extending along the under
surface of the nervous chords, and an accompanying lateral
branch is seen as usual on both sides of the same columns.
Anterior to the commencement of the stomach, the great
dorsal artery, (133. C. b. b.) communicates with the median
subgastric vein, (133. C. a. a.) by five or more pairs of lateral

446 SANGUIFEROUS SYSTEM.

wide, sacculated arches, (133. C. c. d,) which embrace the
oesophagus, as the corresponding vascular arches which con-
nect these two vessels in other annelides and in the entomoid
classes. Some branches of the pulmonary arteries which
arise from the sides of the sub-gastric vein, are observed to
terminate in minute sanguineous vesicles, as in the leech and
other annelides, and this vein presents slight enlargements
opposite to each ganglion in its course, as in many other
species of this class. So that the pale red colour of the
blood, the want of a muscular cordiform cavity, the imperfect
development of valves, the frequent free anastomoses of
the great vascular trunks, and the numerous small pulsating
vesicles, seen on the sanguiferous system of the annelides,
are conditions in which it resembles also the lymphatic sys-
tem of the lowest vertebrated classes.

The uniformity of the general plan of the circulating sys-
tem is still more obvious and more constant in the entomoid
than in the helminthoid classes ; and this is especially mani-
fest in the position and function of the great median dorsal
vessel, the median sub-gastric vein, the cesophageal arches
which connect these two greaf vascular trunks, and the
lateral vessels most connected with respiration. The least
deviation from the ordinary form of the sanguiferous sys-
tem of the annelides is found in the myriapods, the most
vermiform of all the entomoida ; and it is only in the highest
forms of Crustacea that we first arrive at the development of
a strong, muscular, capacious ventricle on the great systemic,
arterial trunk. The great dorsal vessel in the myriapods is
still in form of a narrow, sacculated, pulsating tube, ex-
tended along the middle of the whole trunk of the body. In
the scolopendra this dorsal muscular vessel or heart begins
from the last or caudal segment, and is continued forwards,
segmented in appearance, but with little change of calibre,
to the second segment behind the head, where it becomes
smaller, and is prolonged in the same median line to near
the mouth. At the commencement of this narrow anterior
portion or aorta, two lateral trunks are given off, to form the
usual cesophageal anastomosing arches between the dorsal
artery and the median sub-gastric vein. The long narrow
dorsal vessel of the myriapods is retained in its situation by
the same lateral muscular bands which suspend the heart
from the dorsal part of the segments in the other entomoid

SANGUIFEROUS SYSTEM. 44?

classes. A second pair of vessels originate from the sides of
the prolonged arterial median trunk in the head, and a third
smaller pair are given off from the same vessel, as shown by
Straus and Meckel, near the mouth, which supply the neigh-
bouring parts. The oesophageal ring, which also sends for-
wards small branches, is formed as usual by lateral branches
extending from the anterior part of the aorta to the median
subgastric or epi-neural vein ; and this vein continues back-
wards, as in other articulata, along the upper surface of
the nervous columns to the posterior extremity of the body.
This small soft, pellucid vein, lying loosely on the motor co-
lumns which I have above described, and from which it is
easily lifted, appears to have been mistaken here, as also
in the arachnida, for a nervous filament imagined to have
some connection with the sympathetic system, or with the
function of respiration. It is extensively connected by
branches with the peripheral inusculo-cutaneous parts, with
the large, tortuous, ramose tracheae, and with the reticulate
peritoneal covering of the alimentary canal, but has no
resemblance to a nervous filament, in form, texture, or
mode of distribution. The elongated and simple form
of the heart in the myriapods, and the whole condition
of their circulating system appear thus, like the other
organs of their body, to be. more closely allied to those of
the inferior annelides, and of the larvae of insects, than
to the highest adult forms of the latter animals, as supposed
by Meckel.

The sanguiferous system of insects, like their nervous sys-
tem, and most other parts of their economy, not only under-
goes important changes during the growth and metamor-
phoses of these animals, but also presents various forms
and conditions of development in the adult state of the
different orders of this class. From the opacity of the inte-
guments in adult insects, and the limited distribution of
blood vessels through their highly aerated body, the course
and extent of their circulating system were long concealed
from observers, and the dorsal vessel was early believed to be
a glandular sac shut at both ends, and destined, by its con-
tinued peristaltic action on a contained honey-like substance,
to form the abundant fatty matter of their body. By examin-
ing, however, minute transparent larvae under the micros-

448 SANGUIFEROUS SYSTEM.

cope, and the soft parts of perfect insects, newly escaped
from their larva covering, it was distinctly seen by several
accurate observers, as Leuwenhock, Nitzch, and Baker, that
there is a motion of blood, containing globules, in different
parts of the living body of these winged articulata. It was
especially observed by Baker, that in certain larvee a motion
of blood globules is obvious, extending forward along the
middle of the back, and returning backwards along the sides
of the body — thus completing the circulation. The anterior
divisions of the dorsal vessel being concealed by the opacity
of the head, it was for some time supposed that that vessel
propelled its contents, by an open anterior orifice, into the
general cavity of the trunk, and that the fluid, by being re-
admitted into the posterior part of the dorsal vessel, thus
performed a circular motion. The sacculated structure of
the dorsal vessel, (Fig. 133. D. a. b,) or heart of insects, had
already been observed by Swammerdam and Lyonet, and
even by Malpighi ; but the valvular arrangements and the
lateral openings of its eight compartments, were first mi-
nutely examined by Straus.

In the larva state, as in the simpler annelides, the
dorsal vessel has a more lengthened, narrow, thin, and
uniform appearance, than in insects which have arrived
at their chrysalis or at their imago state ; and we observe
this vessel to thicken its parietes, to shorten its extent,
and to perfect its internal valves, as the muscles of the
segments, during the metamorphosis, contract and imbri-
cate the consolidating integuments, and thus shorten the
whole trunk of the body. The eight chambers of the heart
appear, like the segments of the abdomen, to be inserted
into each other from behind, and the bilabiate valves, with
their free edges directed forwards, are formed by a reflection
inwards of the tough inner parietes of this vessel, and
as they are confined to the posterior or abdominal portion
of the heart or aortal trunk, there appears to be a pulsating
muscular sac for each segment. These cavities contract in
succession from behind forwards, and convey a thin, colour-
less serous fluid, abounding with large blood globules ; they
receive this blood posteriorly from the abdominal veins, and
each cavity (133. D. a. 5.) likewise receives two lateral cur-
rents poured into its posterior end from the cavity of the

SANGUIFEROUS SYSTEM. 449

abdomen. The heart, still destitute of auricle, is attached,
as in other entomoid classes, to the upper and lateral parts of
the segments, by muscular bands extending from the sides of
each cavity ; these muscular bands have a triangular form,
tapering as they proceed laterally to the segments, and they
leave narrow openings between their broad insertions into
the tendinous, investing pericardium, to admit the lateral
abdominal currents. From this median dorsal abdominal
heart, the thoracic aorta is continued forwards, with thin
membranous parietes, and without sending off branches,
to the head where it has been shown by Carus to divide into
several lateral currents (133 D. c. d.), but the parietes of the
aorta are not perceptibly continued onwards around these
currents so as to confine them within distinct vascular canals.
The current of blood-globules from the anterior part of the
aorta is observed to divide into numerous distinct arches
(133 D. c. d.) which radiate upwards, laterally and backwards,
sending off similar isolated currents to the antennae and other
parts of the head, but there is no appearance of vascular
ramifications or capillary vessels in the sanguiferous system of
insects, which we observe so remarkably developed on their
respiratory organs, and which are obvious in the circulating
vessels even of the lower annelides.

The currents of blood, forming arches or loops in the
head and its appendices, reunite and terminate in the
two great lateral inferior returning veins which, in their
course backwards, give off similar small currents to the
legs and the wings. A single stream is observed to
enter the anterior part of the haunch in each of the legs,
(133. D./. /*.) and to flow, on the same side, towards . the
tarsi, but to a variable distance in different insects; the
current returns on the opposite part of the leg, to the haunch,
and re-enters the great abdominal vein of that side, so that a
single loop sometimes reaching to the tarsus, is thus formed
by the current in each leg. The blood, however, is more ex-
tensively distributed over the wings, especially in the soft
and pliant condition of these parts, when first escaped from
the larva covering or the chrysalis state. Although the course
which the blood follows in traversing the wings of insects,
is very different in different species, and varies according to
the form, structure, and reticulations of these organs, it is

PART V. G G

450 SANGUIFEROUS SYSTEM.

observed in all their forms, to pass by one or more wide ves-
sels, outwards from the ventral veins, along the thick anterior
or upper margin, and to return to the same great venous
currents, along the thin posterior edge of the wings, as repre-
sented in the four dissimilar wings placed in the annexed
diagram (133. D. g. g.} In the first soft rudimentary state
of the wing in the larva, the excurrent and recurrent streams
form a single undivided loop around the margin, as in the
shooting branchial laminae of the tadpoles of amphibia, and
the wings of adult insects have been compared indeed to
dried branchiae.

In the mature wings, the wide alar bloodvessels describe
various forms of curves, loops, and meshes, peculiar to
each species, and accompanying and perforated by the
ramifications of the alar tracheae; but these currents,
which are rendered visible only by the moving large ovoidal
blood-globules conveyed in the colourless serum, become
gradually obliterated, and restricted to the larger vessels, as
the wings dry and harden by use, as the respiration is in-
creased over the system by the extension. of the tracheal
ramifications, and as the necessity for nutrition and develop-
ment diminish over the system. There are sometimes hun-
dreds of blood-canals meandering through a single membra-
nous wing, and most of these canals embrace each one or
more tracheal branches which follow along their interior,
and which appear to oxygenate, while they are surrounded
by, the circulating blood. The circulating system of insects
is thus perforated and permeated by the respiratory, as the
alimentary canal of many mollusca is permeated by the great
trunks of the sanguiferous system. There are more excurrent
than recurrent streams along the margins of the wings; the
vascular parietes which bound these wide currents are not
perceptible ; and the number or size of the accompanying
atrcheae are not proportioned to the width of the blood-canals,
which embrace them. There are of course no valves in these
alar canals, and the blood is observed, on the slightest inter-
ruption to its free course, to stop, or retrograde, or ocillate
backwards and forwards in the same vessels, and by the con-
stant anastomoses of these canals a reticulate structure is
produced, like that of the adult capillaries and the first formed
embryo-vessels in the highest vertebrata.

SANGUTFEROUS SYSTEM. 451

The united recurrent or venous trunks extending along the
posterior margin of the wings return to the great lateral abdomi-
nal veins, which convey the blood backwards to the posterior
end of the dorsal vessel. Several currents, apparently continued
from the abdominal veins, are also perceived moving to and
from the principal viscera of the trunk, and exterior to these
great returning abdominal currents, two smaller veins (133.
D. h. i.) are seen extending laterally nearer to the openings
of the stigmata. These smaller accessory abdominal veins
receive the blood from the neighbouring exterior parts, and
convey it by several short canals to the great returning veins.
Abdominal currents are also sometimes perceptible, directed
to the principal viscera, especially to the genital organs and
to the biliary tubuli. As the aortal arches of the head are
observed to give off small currents to the various appendices
of its united segments, and the great returning veins to send
similar currents to the locomotive appendices of the thorax,
so we observe the caudal (133. D. k. I.) and other appendices
of the abdomen to receive small streams of blood-globules
from the great ventral veins before they open into the poste-
rior segment of the heart. The prime mover of the circula-
tion in insects is obviously the muscular structure of the heart,
and the direction is given by the numerous semilunar valves
of its compartments. From the free aeration of the circu-
lating fluid by the tracheae in every part of the body, there is
as little difference between the contents of arteries and veins,
as in the structure of these canals which perform the same
functions in ah1 parts of the body, and hence the high tem-
perature and the rapid evolution of caloric, shown by Ber-
thold, in the body of these most active of the invertebrata.
The diminished extent of the circulation in the imago state or
last stage of insects, when the organization is completed,
and the end of their career approaches, better fits these light
aeronauts to flit through the attenuated air, and corresponds
with the senile condition of this system in higher classes of
animals.

The heart of the arachnida is generally suspended, like
that of insects, by means of transverse muscular bands, from
the dorsal parts of the segments, but that of the phalangium
appears to extend free along the middle of the back. In the
short abdomen of the spiders, the heart is also short, wide,

G G 2

452 SANGUIFEROUS SYSTEM.

sacculated, and provided with a distinct muscular coat con-
sisting of strong circular fibres. It is attached by transverse
muscular bands, it terminates suddenly at its anterior part
in a narrow membranous aorta, and it gives off numerous
lateral ramifying arteries from its saccular enlargements ; it
originates posteriorly from the union of several large return-
ing venous trunks ; several of its branches are observed to
ramify minutely through the granular fatty substance of the
abdomen, and others are derived from the pulmonary sacs.
From the anterior part of the aorta, as shown by Treviranus,
two large lateral trunks diverge on each side, and the dimi-
nished median artery continues forwards to the head as in the
myriapods; he has likewise observed two lateral venous canals
extending along the abdomen. I have found four compart-
ments of the heart in spiders as in the common tegenaria,
which are each provided with distinct valves, and with
lateral narrow depressions or openings, as in the heart
of the scorpion and in that of insects. The first or
posterior chamber is very small and narrow, situate nearly
above the anus, provided with opaque muscular parietes,
and receives the thin membranous trunks of numerous
minutely ramified veins. The second compartment is
much larger and longer than the first, the third is the longest
and the broadest division of the heart; and the fourth
or anterior compartment, which is situate immediately behind
the junction of the abdomen with the cephalo-thorax, is as
short as the first, but the most thick and muscular in its
parietes. These divisions of the heart give off lateral
branches; they are dilated at their line of junction where the
valves are placed, and the narrow lateral slits which have a
dorsal aspect ; and they extend along the dorsal part of the
abdomen, immediately beneath the integuments, from the
anus to the cephalo-thorax where the short thin membranous
aorta commences.

The heart of the scorpion is, on the contrary, confined
to the anterior part of the body, or alvithorax, and con-
sists of a greater number of compartments than in the
spiders, amounting here to six or eight distinct cavi-
ties. These cavities are furnished with lateral suspensory
muscular bands, and strong muscular opaque parietes, com-
posed chiefly of transverse fibres ; they are dilated at their

SANGUIFEROUS SYSTEM. 453

extremities, and provided with terminal valves ; they present
narrow lateral openings at their dilated extremities, and they
give off symmetrical branches on each side. They constitute
a wide fusiform sac tapering much at its extremities, and
extended along the middle of the back from the proximal
caudal segment to the third pair of legs ; they are connected
with the internal organs by lateral vessels, especially with
the hepatic tubuli, the fatty substance, and the pulmonary
sacs ; and the internal terminal valves produce an articulated
appearance of the heart externally, as observed by Trevira-
nus. As in other entomoid animals, the anterior part of the
thick muscular opaque heart terminates suddenly in the thin
membranous transparent aorta which appears to widen before
dividing into lateral branches, and the small posterior com-
partment of the heart receives the great median dorsal vessel
of the caudal segments. The anterior distribution and lateral
arches of the aorta nearly resemble those of the scolopen-
dra, and the blood appears to be returned backwards chiefly
by the epineural vein, accompanying the moto-sensitive co-
lumns, as commonly seen in myriapoda, Crustacea, and
other articulated animals.

The higher crustaceans animals exhibit a more perfect
development of the sanguiferous system, in the structure of
the heart, the fibrinous character of the blood, and the extent
of the arterial and venous distribution, than is presented by
any other of the articulated classes ; but in the lower forms
of these animals, as in isopoda and stomapoda, the circula-
tion more resembles that of annelides and the larvee of insects,
especially in the elongated and simple form of the dorsal
vessel, and the absence of capillary ramifications. From the
defined nature of the respiratory organs of Crustacea, and the
imperfect aeration afforded by the medium in which they
live, the double circulation of these animals, like that of the
pulmonated arachnida, is more complete than in other articu-
lata, and the heart is systemic as in almost all the inverte-
brated tribes. The venous blood in the decapods, as in the
maja squinado, (Fig. 1 33. E.) is collected from the various
members by distinct brachial veins, (E. a. a.) and from the
upper and lower parts of the trunk by a series of superior
(E. c.) and inferior (E. b.} abdominal veins, which convey it
to capacious lateral sinuses connected freely with each other,
and situate at the bases of the several branchiee. The bran-

454 SANGUIFEROUS SYSTEM.

chial arteries, (E. e. e.) originating from these wide membra-
nous sinuses on each side, distribute the whole venous blood
of the system over the innumerable minute laminae of the
gills, and from these it is collected by the branchial veins,
(133. E./. /.) to be transmitted to the heart. The branchial
arteries follow the outer margin, and the returning veins the
inner margin of the gills, and the united trunks of the latter
vessels convey the arterialised blood, by a single orifice on each
side, into the large median muscular ventricle. (133. E. g.)

The heart, as in other articulata, is situate in the middle
of the back, as seen in the lobster, (Fig. 119. A. e. B. g,} and
consists of a single systemic muscular cavity, most concen-
trated in form in the decapods, and generally elongated like
a dorsal vessel on the inferior orders ; its thick parietes are
composed of interlaced muscular fibres, they present internal
fleshy columns, there are semilunar valves at the orifices of
the great vessels, and the heart is connected, as usual, with
the neighbouring parts by muscular bands. From the anterior
and upper margin of the heart arise three arterial trunks, (133.
E. 1. i. h. 119. B. h. h. i.) the two lateral of which send
branches to the genital organs and the stomach, and termi-
nate in the two antenna! arteries proceeding to the outer arid
inner pair of these organs, and the median vessel, (1 19. B.
d.) advancing over the stomach to the pedunculated eyes,
divides into the two ophthalmic arteries which supply these
organs. From the lower and anterior part of the heart, the
hepatic arteries (119. A. g.} originate by a single or double
trunk according to the divided condition of the liver through
which they ramify ; and from the lower and posterior part of
the same muscular cavity arises the grea,t sternal artery (119.
A. k.) which, after descending to the sternum and dividing
into an anterior, (119. A. /.) and a posterior (119. A. m )
trunk, supplies most of the musculo-cutaneous parts on the
ventral region of the body, and gives off laterally the brachial
arteries to the locomotive organs. From the middle of the
posterior margin of the heart is given off the great posterior
median systemic artery, (119. A. h. B. k. 133. E. k.) which,
extending backwards along the median and dorsal part of the
trunk, sends off numerous branches on each side to the neigh-
bouring organs, and bifurcates over the colon before distri-
buting its terminal branches on the muscles of the tail (1 19.
A. i. B/.)

SANGUIFEROUS SYSTEM. 455

The venous blood of the system is returned to the great ven-
tral and branchial sinuses and transmitted through the gills,
and when arterialized is conveyed upwards to the dorsal part
of the trunk by the branchial veins, to be poured into the cavity
of the heart by two orifices on its upper surface (1 19. B.) The
venous and the arterial openings of the heart are provided
with valves ; this organ is already furnished, as in mollusca,
with a delicate pericardium which has often been mistaken
for an auricle, and there appear to be numerous venous sinu-
ses developed on the superficial parts of the trunk, besides
those connected with the branchial arteries. There is thus
only k single cavity of the heart developed, from the gradual
concentration of the extended dorsal vessel, in the highest of
the articulated tribes, which accords with the general muscu-
lar activity of this sub-kingdom, and this single ventricle is
systemic as in other invertebrata and in the embryos of the
vertebrated classes. And in tracing the successive phases
of the development of this muscular cavity in the highest
decapods, it is observed to pass through the adult conditions
presented by the inferior orders of Crustacea, and by all the
lower articulated classes.

FOURTH SECTION.

Sanguiferous System of the Cydo-gangliated or Molluscous

Classes.

The existence of a muscular ventricle on the great vascular
trunks of the system, by interrupting the equable current of
the blood, necessitates the development of an auricle to re-
lieve the veins from regurgitation and distention, and to per-
fect its own function ; and as these two cavities are not syn-
chronous in their development, we observe a higher grade of
the sanguiferous system in the existence of an auricle, super-
added to the ventricle, throughout all the classes of mollusca.
These two cavities are systemic, as the heart in other inverte-
brata, and this high condition of the vascular system accords
with the complicated structure of, the digestive, the glandular,
and other nutritive organs of these animals. As the respira-
tion of the mollusca is almost always aquatic and limited,
their muscular energy and movements are languid, and the

456 SANGUIFEROUS SYSTEM.

systemic position of their heart is thus necessary to accelerate
the circulation and nutriment of their inert frame. The
auricle is often divided, and sometimes also the ventricle, in
the mollusca, as we find the kidney, the spleen, the liver,
and many other organs, divided into parts in their lowest or
their earliest forms, but the functions of the parts are always
the same, and this divided condition of the cavities is often
necessary from the lateral position or the distance of the
branchiae, or to suit the general form of the body. Although
abounding in fibrin and globules, and affording a white coa-
gulum after death, the blood of the living mollusca is still
thin, transparent, and colourless, or of a pale bluish- white hue,
rarely red coloured, but the parietes of the vessels which
convey it are now always distinct and their three tunics are
commonly perceptible, as in the vertebrated classes. The
diversities presented by the circulating organs are greater
than in the articulated or the vertebrated tribes, and depend
chiefly on the remarkable differences of form found in mol-
luscous animals, on the difference of position and character
of their respiratory organs, and on the various grades of deve-
lopment presented by their general organization.

The heart of the cynthia, and many other isolated forms of
tunicated animals is situated, as in the conchifera, in the ab-
dominal cavity, between the alimentary canal and the muscu-
lar enveloping mantle ; it is contained in a distinct pericar-
dium, and consists of a dilated muscular portion of the
great systemic artery, which was observed by Dicquemare
to pulsate in the living animal. This muscular pulsating and
transparent heart, consists of an elongated fusiform ventri-
cle, with a minute auricular dilatation observed by Chiaje to
be partially divided, as in the inhabitants of bivalve shells,
and to possess distinct valves at their venous orifices \ and
these cordiform cavities are so situate as to receive the arte-
rialised blood from the reticulate laminae of the gills, by two
branchial veins, into the bifid auricle, and thence into the
ventricle to be propelled through the single systemic aorta.
The auriculo-ventricular orifice is already provided with dis-
tinct valves, and the systemic aorta extends along the dorsal
part of the abdominal cavity towards the anus, between the
alimentary canal and the mantle, and following along the
course of the intestine. Both the auricular and the ventri-

SANGUTFEROUS SYSTEM. 457

cular valves were shown by Chiaje to be already sufficiently de-
veloped in ascidice to check the flow of mercury when injected
in a direction contrary to that of the natural current of the
blood. The venous blood of the system and the nutriment
absorbed from the wide and highly vascular intestine appear
to be transmitted by venous trunks to the branchial arteries
arid the gills before they are conveyed to the heart ; and the
same plan of structure is more or less perceptible in the dif-
ferent forms of simple and compound tunicata ; as shown by
Savigny, Chiaje, Cuvier, Schalck, Meckel, and other anato-
mists, although their descriptions do not always coincide.

The different parts of the heart and of the whole vascular
system are more distinct and more complicated in the conchi-
ferous animals, than in the tunicata, but they are constructed
according to the same type in these two classes of acephalous
mollusca, which consist entirely of aquatic and branchiated
animals. The heart is always systemic, and is placed as in
the former class in the dorsal part of the abdomen. It con-
sists of an auricle, commonly divided into two lateral parts,
which receives the aerated blood from the gills, and of a
ventricle, also sometimes divided into two lateral parts, which
transmits the blood to the aorta and systemic vessels. The
blood is colourless or of a bluish-white colour, and rarely of
a reddish hue. The venous blood is collected from the
system by venous trunks, and transmitted directly to the
branchial arteries to be spread over the large free pendent
reticulate and pectinated folds of the gills. From the lateral
position and the symmetrical development of the branchiae
and of the margins of the mantle, the palleal veins (Fig. 134.
a. a.) returning from the ciliated and aerated covering of the
thoracic cavity, and the branchial veins (134. b. b.) returning
the aerated blood from the gills, are separated to a distance
from each other on the two sides of the body. The two
sinuses which receive this aerated blood, and which consti-
tute the auricle (134. c. c.) of the heart, are therefore placed
apart from each other, and form two distinct cavities, in
almost all the conchifera. Their form is somewhat trian-
gular, with their largest side towards the branchial veins,
and their largest angle towards the ventricle, and their pa-
rietes, though thin, present distinct muscular fasciculi. They
have several openings for the branchial and the palleal veins,

458 SANGUIFEROUS SYSTEM.

and they communicate by a single valved orifice with the
thick- walled muscular cavity of the ventricle. In the oyster
(120. A.) where the body is much compressed and very
narrow transversely, the two parts of the auricle (120. A./.)
are united together on the median plain and constitute a
single cavity, communicating however, by two distinct ori-
fices with the ventricle (120. A, g}. The auricle and ventri-
cle are inclosed in a capacious pericardial cavity, which is
situated, in the oyster, in the concavity of the great adductor
muscle, (120. A. /.) The ventricle is generally single and
placed in the middle of the back, as seen in the spondylus
(120. B. «*.) receiving on both sides, from the divisions of the
auricle, (120. B. h.} the arterialised blood transmitted by the
palleal, (120. B./.) and the branchial (120. B.#.) veins. As
the rectal portion of the intestine (120. B. i. e.) occupies the
median line of the back, it commonly perforates the ventricle
in its course to the anus, and thus indicates a partial internal
division of this muscular cavity. In some, as the teredo,
the ventricle is cleft posteriorly into two parts, but commu-
nicates by a single opening anteriorly with the aorta ; and in
the area noa, (Fig. 134) the ventricle is entirely divided into
two distinct and separate parts, (134. d. d.) each of which
communicates by a distinct bulbus arteriosus ( 134. e. e.) with
the great trunk of the anterior (134. /.) and posterior (134.
g.) aorta. The auriculo-ventricular and aortal orifices of the
ventricle are furnished with semilunar valves which prevent
the return of the blood, and the bulbus arteriosus is most
apparent at the origin of the aorta where, as in the area noce
and the ostrea, the ventricle is not perforated by the intes-
tine. The ventricle, as shown by Cuvier, is divided into two
separate parts, also in the lingula^ among the brachiopodous
conchifera, and both the anterior and posterior aortse, as well
as the ventricle, are frequently traversed by the intestine in
the bivalved mollusca.

When the ventricle is median and perforated by the intes-
tine, it is commonly elongated and fusiform, and tapers
anteriorly and posteriorly into the commencements of the
corresponding aortae. The anterior aorta is mostly a visceral
artery, supplying the stomach, the liver, the ovaria, and
other abdominal organs, and the posterior aorta has ge-
nerally a musculo-cutaneous or a palleal distribution. In

SANGUI FERGUS SYSTEM,

459

those which, like the area noa, have the ventricle and
the bulbus anteriosus double as well as the auricle, the

FIG. 134.

anterior and posterior aortae have necessarily also a dou-
ble origin. From the bulbus arteriosus (134. e. e.) of
each side arises a large single arterial trunk, which imme-
diately divides into the usual anterior and posterior aortse
(134. f. g.} The two divisions of the anterior aorta, thus
formed, anastomose into a single median trunk (134. f.)
which advances forwards to near the mouth, sending off
numerous large arteries to the ovary, the liver, the stomach,
and other viscera of the abdomen in its course. Arrived at
the anterior part of the body, this median trunk, greatly
diminished in size, bifurcates to form the anterior palleal

460 SANGUIFEROUS SYSTEM.

arteries, which extend backwards ramifying along the anterior
edge of the mantle, and give off branches to the anterior
adductor muscle, (134. i. i.) and to the sensitive and vascular
apparatus around the mouth. The distribution of the ante-
rior aorta is nearly the same where it arises by a single
trunk from a single median ventricle, as here where it has a
double origin, and the same observation applies to the
general distribution of the posterior aorta, even when it ori-
ginates as a mere branch from the anterior or single systemic
aorta, as in the oyster.

The posterior aorta most frequently arises by a single
trunk from the posterior or anal extremity of a lengthened
median fusiform ventricle, and continues backwards along
the median plain, above the intestine, to near the anus or
the vent, where it bifurcates to form the two great posterior
palleal arteries, which follow the course of the posterior and
inferior margins of the mantle. In the bicordate forms of
this class, as the area nose, the posterior, like the anterior
aorta, commences by a double origin from the right and left
bulbus arteriosus, (134. e. e.), and the two trunks soon anas-
tomose to form the usual median posterior dorsal artery (134.
ff.) In its course towards the anus along the middle of the
back, the posterior aorta gives off numerous small lateral
branches, (134. ^7.) like intercostal^, which spread chiefly on
the muscular parts of this portion of the abdomen, and
proceeding, with the colon, over the great posterior adductor
muscle, which it also supplies, it divides above the anus
(134. /.) into the right and left posterior palleal arteries
(134. h. h.) Near to their origin, the posterior palleal arteries
give off each an anal branch, (134. k. k.) which two branches
encompass and supply the rectum and continue their course, ra-
mifying along the curvature of the posterior adductor muscle.
The great palleal trunks (134. h. h.) extend along the poste-
rior and inferior margins of the mantle, sending off numerous
branches to its appendices, and ramifying extensively over
that expanded and ciliated covering of the respiratory cavity.
From the capillaries of this almost respiratory membrane,
the blood is collected by the palleal veins, (134. a. a. 120. B.
/.) and transmitted directly to the auricle, (134. c. c. 320. B.
h.) without passing through the gills with the venous blood
of the system. The systemic veins follow nearly the course

SANQUIFEROUS SYSTEM. 461

of the systemic arteries, having their great trunks disposed
along the dorsal part of the body beneath the aortas, and
around the margin of the mantle interior to the palleal arte-
ries, and in a similar manner the branchial arteries closely
accompany the branchial veins in their distribution over the
laminae of the gills. Several enlargements are observed on
the vascular system of conchifera, as in higher mollusca,
and in some of the articulated tribes. The principal venous
trunks from the viscera appear to distribute their blood
through the reticulate tissue of a reniform organ, near the
heart, before it is collected into the two great lateral branchial
sinuses, like those of Crustacea or the branchial auricles of
cephalopods, from which the branchial arteries arise. This
minute distribution of the visceral venous blood, like a renal
portal circulation, before being transmitted to the gills, may
assist in its aeration or afford the materials of some secretion,
and the principal trunks of the palleal veins return directly
to the auricles, along with the aerated blood transmitted
by the veins of the branchiae. So that although the whole of
the systemic blood is not transmitted through the branchial
organs of conchifera the advantage of a complete double cir-
culation is nearly secured to these animals by the free expo-
sure to the surrounding element, of that portion which is
distributed over the extensive folds of the mantle.

From the undivided condition of the auricle and ventricle
in most of the gasteropods, and the uniform systemic cha-
racter of these cavities, there is greater simplicity in the ge-
neral form of the sanguiferous system in this class than in
the inhabitants of bivalve shells. As they present however,
remarkable differences in the form, the position, and the
nature of their respiratory organs, and differ not less in the
general form of their body, these circumstances materially
influence the less important peripheral parts of the vascular
system. The respiratory organs being generally unsymme-
trical, and confined to one side of the body, there is no longer
necessity for division of the cavities of the heart, and this
organ is therefore commonly single and lateral in its position.
It consists, as seen in the annexed figure (Fig. 135.) of the
harpa minor, of a distinct muscular auricle, (1356.) which
receives the arterialised blood from the respiratory organs,
(135. /.) and of a systemic ventricle, (135. c.) which trans-

462

SANGUIFEROUS SYSTEM.

mits it through a bulbus arteriosus to a great anterior, (135.
e.) and posterior (135. d.) aorta as in conchifera. These two

FIG. 135.

cavities are compactly enveloped in a tough pericardial cover-
ing, (135. a.) their parietes are strengthened by numerous
crossing fasciculi of muscular fibres, and their apertures are
well protected by valvular folds. From the varying position
of the respiratory organs, the heart is sometimes placed on
the right side of the body, sometimes on the posterior or the
anterior part of the back, but most frequently towards the
left side, and it has commonly a pyramidal or a conical form,
with its base, formed by the capacious auricle, directed
towards the respiratory organs, and its apex, formed by a
strong and angular ventricle, like that of fishes, and a dilat-
able bulbus arteriosus, directed towards the systemic aorta.
The auricle is divided into two parts in the halyotis^ the
Jissurella, and the emarginula, as in the conchiferous animals,
and the ventricle of the heart is also perforated by the rectum
in these genera, as in the former class. In the. halyotis the
arterialised blood returning from two long pectinated bran-
chiae is conveyed by two corresponding veins to two length-
ened auricles placed on the left side of the body, and much
resembling those of most conchifera. From these cavities
it is poured on each side into a lengthened fusiform single
ventricle placed between them, provided with strong muscular
parietes and fleshy columns, and completely embracing the
intestine which passes through its cavity. The ventricle
indeed, appears externally as only an enlarged or thickened
portion of the intestine, to the sides of which the auricles are

SANGUIFEROUS SYSTEM. 463

attached, and all these cavities of the heart are inclosed in a
distinct pericardium. The great aortal trunk is here given
off from that extremity of the ventricle, which the intestine
first perforates, and in passing inwards it sends off large
arterial branches to the abdominal viscera, to the round
muscle of attachment, like that of a spondylus or an ostrea,
which fixes the hatyotis to its convex shell, and the vessel
then continues forwards to supply the parts of the head, so
that this animal presents the nearest approach to the conchi-
fera in its mode of circulation. A similar division of the
auricle was observed also by Poli in the chiton, where each
division appears to communicate by two distinct openings
with the ventricle. The passage of the intestine through
the heart, thus so frequent in conchifera and gasteropoda,
may add by exosmosis further nutriment to the blood, where
an absorbent system distinct from the veins is not yet deve-
loped, or may assist in excreting some material from the
blood into the anal portion of the intestine, before that fluid
is distributed for the nourishment of all parts of the body.
It is obvious also that the constant contractions of the mus-
cular ventricle, compactly embracing the inert terminal part
of the intestine generally charged with the residue of diges-
tion, must mechanically assist the passage of that matter
through the canal.

As the branchiae in the naked tritonice are disposed along
the sides of the upper part of the body, the heart, consisting
of a single auricle and ventricle, is situated between these
organs in the middle of the back, and the aortal trunk pro-
ceeding from the fore part of the ventricle, divides at its
origin into three principal branches, the posterior of which
is distributed chiefly on the genital organs, the middle branch
on the digestive, and the anterior larger branch on the mus-
cular and sensitive organs of the anterior and lower parts of
the body. In other genera where the branchiae are thus
disposed equally on the two sides, as in scyllaa, tethys, and
others, the cavities of the heart have the same position as in
the tritonia ; but when the gills are confined to the left side
of the body, as in the great order of pectinibranchiate gaste-
ropods, the heart is found to occupy the same side, as seen
in the buccinum undatum, (Fig. 22.) where the arterialised
blood from a larger (22. g.) and a smaller (22. i.) pectinated

464 SANGUIFEROUS SYSTEM.

branchia on the left side, is transmitted to a capacious thin
auricle and a thick muscular ventricle (22. h.) on the same
side, to be distributed through the system by the great
anterior and posterior aortal branches. The auric ulo- ventri-
cular orifice is here protected, as usual, with two very distinct
semilunar folds, in the position of the mitral valves of mam-
malia. The aorta immediately divides into several large
trunks which proceed forwards to the oesophagus and head,
upwards to the large muciparous follicles and the mantle,
and backwards to the digestive and the generative organs.
The branchial tufts of the doris being placed around the anus
and protected in the same cavity of the mantle, the heart is
here situated on the median and posterior part of the back,
and receives the aerated blood from the gills into a crescentic
auricle disposed around the rectum, nearly as the ventricle of
conchifera. The short round muscular ventricle is here placed
anteriorly to the auricle, and gives origin to a large median
aortal trunk which advances forwards along the back to the
head, sending off large branches to the liver, the intestine,
the genital organs, and other parts in its course. In the pul-
monated gasteropods, as the helix, lymncea, and other genera,
and in many which breathe by gills as the aplysia, bullaea,
and others, the respiratory organs, and consequently also the
heart, are placed on the right side of the body. The arte-
rialised blood of the aplysia (Fig. 121.) collected from the
numerous laminae of the gills (121. p.) under the right margin
of the mantle, is received into a capacious auricle (121. g.)
and thence into a strong muscular pyriform ventricle, (121. r.)
like that of many fishes. The bulbus arteriosus (121. r. h.)
is of a lengthened form like that of plagiostome fishes, and
when injected or inflated appears transversely sacculated,
which induced Cuvier to believe that it was surrounded with
lateral arterial loops communicating with its cavity and des-
tined to secrete the fluid of the pericardium. The aorta gives
off a large hepatic (121. o.) and gastric (121. h.) artery, and
then directs its course downwards to advance and distribute
its branches along the ventral part of the body. The dila-
table and sacculated portion of the aorta, which appears some-
what analogous to the numerous transverse valvular folds in
the bulbus arteriosus of plagiostome fishes, here extends be-
yond the origins of the hepatic and gastric arteries.

SANGUIFEROUS SYSTEM. 465

The venous blood collected from all parts of the system in
the aplysia is transmitted to the branchial arteries by two
wide vense cavse, with thin membranous parietes ; and on
opening these two venous trunks, superficial depressions are
observed on their interior thin coats, corresponding with the
interstices of the surrounding muscular bands of the abdomen.
These depressions perceived on the serous lining of the
great systemic veins of the aplysia have been supposed to be
remarkable perforations leading into the general cavity of the
peritoneum, and probably serving the function of emunctory or
absorbent orifices, and the same anomalous structure has
been ascribed to the great systemic veins of the nautilus.
The serous lining of these wide veins of the aplysia, however,
was shown by Meckel to be entire, as in other animals. In
the testaceous and naked pulmonated gasteropods, where
there is no canal nor syphon on the left side, and in which
the respiratory sac, though opening on the right side, ex-
tends across the median plain, the two cavities of the heart
are directed transversely to the left side, between the pulmo-
nary cavity and the large muciparous gland, and the aorta
immediately divides into two great trunks, which send
branches to the abdominal viscera and the muscular parts.
The auricle is perforated by the two trunks of the pulmo-
nary veins, and two semilunar valves are seen in the ventricle
at the auriculo -ventricular orifice. The inferior of the two
aortic trunks is distributed chiefly on the liver and on the
ovary; the ascending trunk gives a branch to the sto-
mach and intestine, the right tentaculum, the dart-gland,
and the genital ducts ; another to the stomach, the sali-
vary glands, and oesophagus, and the continuation of the
trunk, after furnishing a branch to the left tentaculum, turns
backwards to spread its terminal branches on the large mus-
cular foot. The venous blood collected from the system into
a single vena cava, is transmitted by the ramifications of two
pulmonary arteries over the interior surface of the respira-
tory sac, and the capillaries reunite to form the two pulmo-
nary veins which enter the auricle of the heart.

The structure and position of the heart, and the general
distribution of the blood-vessels, appear to be the same in
the pteropods as in the higher gasteropodous mollusca ; the
venous blood of the system is propelled through the external

PART V. H H

466 SANGUIFEROUS SYSTEM.

branchiae, and, thus aerated, is conveyed to the single auricle,
and ventricle to be distributed to all parts of the body. The
thin, transparent, and tough pericardium inclosing the heart
of the clio borealiS) as shown by Eschricht, lies towards the
right and posterior part of the abdominal cavity, with its
broadest part behind, and its apex directed forwards. The
ventricle, about half a line in length, is in form of a trun-
cated triangular pyramid, with rounded Angles, as in many
gasteropods and fishes ; its parietes are thick and its cavity
small, it gives origin to the aorta at its tapering anterior
apex, and communicates posteriorly with the thin membra-
nous auricle placed at its base. The aorta, on perforating
the pericardium, continues its course forwards, sending
branches, as in the gasteropods, to the liver and genital
organs ; and advancing towards the head, gives off minute
arteries to the neck and to the large muscular lateral fins.
The heart lies also on the right side of the abdominal cavity
in the hyalea and pneumodermon, and consists of a single
systemic auricle and ventricle, inclosed in a thin transparent
pericardium, as in the clio and in most of the cephalous mol-
lusca ; and the arterialised blood is returned from the respi-
ratory organs by the branchial veins to the auricle and ven-
tricle, to be distributed through the body.

The bilateral symmetry of the cephalopods, so conspicuous
in their osseous and muscular systems, in their motor and
sensitive columns and nerves, and in their organs of sense,
is not less obvious in their respiratory and circulating appa-
ratus, and forms a closer link of connexion between them
and the fishes and other vertebrated classes, than is observed
in the inferior mollusca. The auricle in the naked cephalo-
pods, as in the conchifera, is divided into two similar and
separate muscular cavities, which here receive, as in fishes,
the venous blood of the system before it is transmitted to
the respiratory organs. The ventricle is single and systemic,
as in the other molluscous classes, median in its position,
placed with the auricles in the middle of the abdominal
cavity, and receives the arterialized blood from the branchiae,
to be transmitted by an anterior and a posterior aortal trunk
through the body. The venous blood collected from the
capillaries of the arms and suckers, is returned by the inter-
brachial veins to an irregular, transverse, circular trunk

SANGUIFEROUS SYSTEM 46/

formed by their union, and surrounding the head anterior to
the eyes and beneath the external muscular aponeurosis of
the connecting membrane of the arms. The interbrachial
veins are formed by the union of the two contiguous lateral
veins of each pair of arms, as seen in the octopus ; and the
two lateral portions of the circular cephalic vein uniting in
front, behind the syphon, to form the great anterior vena
cava, have each an internal semilunar valvular fold defending
the orifice leading into the cava. The trunk of the superior
cava continues its course downwards or backwards, on the
left side of the intestine, and exterior to the muscular apo-
neurosis embracing the liver, receiving venous branches from
the syphon, the fore part of the liver, and the muscular pa-
rietes of the mantle. After a short course along the front of
the liver the vena cava bifurcates, and its two branches proceed
laterally to the two divisions of the auricle placed at the base
of the branchiae. The muscular cavity of each of these auri-
cles is preceded by a perceptible sinus venosus, as in the
auricle of most fishes ; they have often a dark or blackish
colour, like the auricles of many conchifera, and in the naked
tentaculated species, erroneously designated decapoda, there is a
small hollow fleshy appendix communicating by a short tubular
cervix, with the cavity of each auricle. The exterior appendices
of the auricles are not found in loligopsis, octopus nor nautilus.
The trunk and bifurcation of the vena cava are covered
with saccular vesicles, cellular internally, which communi-
cate freely with the cavity of the veins, and are lodged
with them in the same two membranous thoracic venous
cavities. They form two bifid clusters on each side in the
nautilus as described by Chiaje. The wide membranous
cavities, containing these venous branches and vesicles,
communicate by two lateral tubular openings with the general
cavity of the mantle, and thereby with the exterior medium ;
and these cellular vesicles may thus be destined to secrete or
absorb some materials to affect the constitution of the blood.
Each lateral auricle, like the systemic ventricle, is here en-
closed in its distinct pericardium, and each sinus venosus
receives, besides the branch of the vena cava, a large lateral
palleal vein, returning the blood from the corresponding
side of the mantle and the suspensory ligament of the bran-
chiae. The venous blood is returned from the different

H H 2

468 SANGUIFEROUS SYSTEM.

organs of the abdomen by two great visceral veins, or poste-
rior venae cavae, which enter the two bifurcations of the ante-
rior cava near their commencement, and at an obtuse angle
calculated to retard the flow of the blood. The visceral vein
of the right side is formed chiefly by branches from the right
inferior part of the liver, from the intestinal canal, and from
the genital organs ; the left visceral vein receives its branches
from the left side of the liver, from the stomach, and from
the O3sophagus. The great trunks of the two visceral veins
are also surrounded with vesicular appendices opening freely
into their interior, as the two branches of the cava.

The two lateral auricles,of a dark grey colour and loose cellu-
lar texture, placed at the base of the branchiae, and receiving
all the venous blood of the system, are entirely foraminated or
deeply pitted on their inner surface, provided with two mitri-
form valves at the opening from the sinus venosus, and
tapering towards the commencement of the branchial arte-
ries, where they are generally provided with minute valves,
as in sepia, loligo, and argonauta. In loligopsis, the usual
detached venous vesicles are collected into four pyriform
clusters placed on the trunk and branches of the anterior
cava ; and instead of the usual sinus venosi at the entrance
of the branchial auricles, the venae cavae are here surrounded
by a spherical cluster of similar vesicles ; and the same
spherical clusters of vesicles are observed to surround the
four branches of the anterior cava in the nautilus, where the
branchial auricles have not been observed, but the usual
valves are seen at the commencement of the four branchial
arteries. The branchial arteries, two in the naked cephalo-
pods and four in nautilus, corresponding with the number of
branchiae, follow along the dorsal or fixed margin of the gills
between the suspensory ligaments and the pectinated laminae
of these organs. The branchial artery of each gill is remark-
ably wide and capacious, and gives off two lateral rows of
branches which extend ramifying along the inner margins
of the branchial laminae. The branchial nerve and the nutri-
tious artery and vein of the gill accompany the branchial
artery along the free margin of the musculo-ligamentous
band which supports the gill.

The arterialized blood is collected from the branchial la-
minae by their peripheral venous branches which unite on

SANGUIFEROUS SYSTEM. 469

the free margin of the gills to form the wide trunk of the
great branchial vein of each organ ; there are thus two bran-
chial veins on each side of the body in nautilus, and one in
the naked cephalopods. The branchial veins are directed
inwards to the median plain, to enter the great systemic
muscular ventricle, and generally dilate to form a perceptible
sinus on each side, immediately before entering its cavity.
The systemic ventricle is larger, and more muscular in its
parietes than the branchial auricles, and is extended, sometimes
transversely, sometimes longitudinally in the middle of the
visceral cavity, enclosed in its pericardium, and situated be-
hind the venae cavee and between the auricles. In sepia,
loliffo, octopus, and nautilus, the systemic ventricle is ex-
tended transversely, and the branchial veins enter its lateral
extremities. In sepiola it is pyriform and subtransverse, and
in loligopsis it is of a lengthened fusiform shape, extended
longitudinally, and receives the branchial veins on each side
of its widest middle part. The branchial vein, like the
branchial artery, is wide as a sinus in its course along the
margin of the gill, and contracts its calibre at the base of
that organ. Two semilunar valves at the entrance of each
branchial vein into the systemic ventricle, prevent the return
of the blood into these veins during the contraction of the
heart ; two semilunar valves are also placed at the orifice of
the great anterior aorta. The systemic ventricle is more
capacious than both the branchial auricles ; it is provided
with thick and firm muscular parietes, and the prominent
fleshy columns give a cellular appearance to its inner surface.
The muscular enlargement of the bulbus arteriosus is ob-
vious at the origin of the great anterior or cephalic aorta,
as in most of the lower molluscous classes and the cold-
blooded vertebrata. Two other arteries are given off from
the same systemic heart, one of which, directed backwards,
is distributed on the genital organs which occupy the bottom
of the abdominal sac, and the other forming a posterior aorta
or palleal artery, is ramified chiefly on the intestine and the
muscular parietes of the mantle. The anterior or cephalic
aorta arises from the posterior part of the heart, and at its
origin is directed backwards and to the right between the
peritoneal folds which separate the intestinal from the gastric
sacs. It passes to the right of the cardiac orifice of the giz-

470 SANGUIFEROUS SYSTEM,

zard, and penetrating a foramen of the muscular diaphragm,
it ascends on the right side of the oesophagus, in the dorsal
cavity behind the liver, as far as the oesophageal opening of
the cranium. Near its commencement this great trunk gives
off a peritoneal branch, then two dorsal palleal branches,
then some twigs to the gizzard, a little higher a branch to
the intestine and stomachs, and two branches to the liver.
Continuing upwards behind the liver, it sends off several
branches to the superior dilatation of the crop in the octo-
pus, and escaping from the dorsal cavity it divides into two
trunks, which encompass the oesophagus, like the two trunks
of the aorta in most cold-blooded vertebrata, or the first
branchial arch formed by the aorta in the embryos of higher
warm-blooded species. From this arterial oesophageal ring
two branches proceed upwards through the cranial aperture,
to supply the buccal apparatus and the upper pair of salivary
glands, and two larger branches, which pass downwards be-
hind the liver to ramify on the large inferior pair of salivary
glands and on the crop. The two trunks of the oesophageal
ring penetrate together the fore part of the cartilaginous
cranium, and then ascend, slightly diverging, to the bases of
the muscular arms, where each trunk divides into four
branches, like four branchial arches, which accompany the
brachial nerves, ramifying symmetrically along the central
cavities of the eight arms.

The smaller aorta arises from the anterior or ventral as-
pect of the heart, and immediately sends off two lateral
branches to supply the numerous glandular vesicles of the
great venous trunks. Another considerable branch from
this artery ramifies on the intestinal canal, and sends twigs
to the adjoining folds of the peritoneum ; but the principal
trunk continues its course forwards in front of the great vena
cava, and extending along the anterior connecting band of
the mantle, ramifies on the muscular parietes of that cavity.
The third arterial trunk originating from the heart, proceeds
from its inferior surface, and is directed backwards, to ramify
on the testis of the male or the ovarium of the female, and
varies in its development, as in other animals, according to
the periodical changes in the condition of these organs.

The absence of valves at the origin of the branchial arte-
ries in the octopus* is compensated for by the greater muscu-

SANGUIFEROUS SYSTEM. 471

larity of the branchial hearts in that genus. In the loligopsis
the two aortal trunks come off from the anterior and the
posterior apex of the longitudinally extended ventricle, both
have a slight bulbous enlargement at their origin, and the
genital artery forms merely a branch originating, from the
commencement of the great dorsal or cephalic aorta. So
that in this highest of all the invertebrated classes, only two
of the great cavities of the heart, a ventricle and an auricle,
are yet distinctly developed ; and notwithstanding their
diversities of form and their occasional division, these two
cavities continue with great regularity throughout the mol-
luscous subkingdom.

FIFTH SECTION.

Sanguiferous System of the Spini- Cerebrated, or
Vertebrated Classes.

There is great uniformity of plan in the different condi-
tions presented by the vascular system in the vertebrated
classes, and in the several phases of development through
which it passes before arriving at its perfect form in each of
the divisions of this subkingdom. The heart is always situ-
ated on the anterior or ventral aspect of the alimentary canal,
and its compartments are always contiguous and enclosed in
a distinct pericardium. In the species which breathe solely
by t branchiae, whether permanent or deciduous, the heart
consists of a single auricle and a single ventricle, which are
atf once, branchial and systemic, and the blood is entirely
propelled by it through these respiratory organs. But
in al^ the pulmonated tribes there is a distinct auricle
superadded, for the reception of the aerated blood from the
lungs ; and in the hot-blooded classes there is always a bilo-
cular heart for the pulmonic blood^ and a similar heart for
the systemic, which have no communication with each other,
though enclosed in the same pericardium, and formed by the
subdivision of the same original cavities. The heart in-
creases in bulk as we ascend in the vertebrata, being smallest
in the fishes, amphibia and reptiles, and largest in the hot-
blooded tribes ; and there is always a hepatic portal circula-
tion, which increases in extent as we advance from the lower

472 SANGUIFEROUS SYSTEM.

to the higher classes, and as we ascend through the succes-
sive stages of the development of the same species. The
blood contains more fibrine and red globules than in the
invertebrata, and its colour is always red, being of a much
deeper hue in the mammalia and birds than in the cold-
blooded classes, especially in the fishes, where it is also less
extensively circulated through the body.

As fishes move and breathe in a dense element, where
the air is less abundantly supplied to oxygenate their blood,
and as their respiration is still effected by branchiae, as
in most of the invertebrated classes, the heart is placed
on the branchial and not on the systemic portion of their
great aortal artery, and by contributing its impulse to
the movement of the branchial blood, the extent of respira-
tion is increased beyond that of the aquatic mollusca, where
the heart is entirely systemic. The extent and the activity
of their muscular system render less necessary, in fishes and
in the tadpoles of amphibia, an exclusively systemic heart to
propel the blood through the body, that being greatly ef-
fected by their active movements ; and the most active period
of the amphibia is the tadpole state, when the heart is en-
tirely appropriated to the branchial ramifications of the great
aortal trunk, as it is to the branchial arches of this vessel in
higher embryos.

The venae cavee of fishes generally unite to form a sinus
venosus between the tendinous diaphragm and the auricle,
and this sinus is often a capacious muscular pulsating cavity,
Like the auricle, as in the rays. Two crescentic valves com-
monly defend the entrance of the sinus venosus into the
auricle, to prevent the return of the blood during the con-
traction of the latter cavity. The heart, like the respiratory
organs, is situated far forwards under the head, between the
anterior terminations of the branchial arches; it consists of a
thin, wide capacious auricle, and a small muscular ventricle,
which are enclosed, along with the bulbus arteriosus, in a
thin pericardium. The heart is placed farther backwards
from the head in the cartilaginous than in the osseous fishes,
and still more in amphibia and in higher vertebrata. The
two cavities of the heart are not placed in the same continuous
straight line as in the gasteropods and other mollusca, and in
the earlier conditions of the vertebrated embryo ; the auricle is

SANGUIFEROUS SYSTEM. 473

here extended above the ventricle, and it advances more for-
wards over the ventricle in the plagiostome fishes, as the rays
and sharks, than in the osseous and inferior fishes, where it
has undergone a less deviation from its primitive embryo
position. In higher classes the auricles advance to the ante-
rior part of the ventricles, and the whole are compactly
embraced in a small pericardial cavity. The cavity of the
pericardium, in the plagiostome fishes, communicates by dis-
tinct openings with the peritoneal cavity of the abdomen, and,
by means of the two lateral anal orifices, with the exterior
medium, as in the cephalopods ; and the heart and bulbus
arteriosus of the sturgeon are covered with a loose glandular
mass, like the glandular vesicles enveloping the venae cavse
of the cephalopodous mollusca.

The auricle is more capacious and has thinner muscular
parietes than the ventricle, and it generally extends so much
transversely as to envelope the upper or dorsal side of the
ventricle, and to appear beyond it on each side, or to surround
it entirely during its own diastole. Although the margins
of the auricle are often angular, they do not develope the
fringed auricular extensions common in higher classes, and
the muscular bands form distinct fleshy columns in the inner
surface. The auriculo- ventricular orifice is situated near the
anterior and superior part of the ventricle, and is furnished
with two strong semilunar valves, with loose free margins,
like those of the auricular orifice of the sinus venosus. Some-
times these folds of the ventricular orifice, or mitral systemic
valve of the hot-blooded vertebrata, consist of three or four
parts, and in the cartilaginous fishes their margins are
strengthened by connecting tendinous cords. The ventricle
is comparatively small, but with thick muscular parietes
often separable into two laminae, and has generally an an-
gular and tapering or pyramidal form, in the osseous fishes,
being broad, oblique, and flat towards the tendinous dia-
phragm, and becoming smaller towards the anterior opening
into the bulbus arteriosus. In the higher cartilaginous
fishes the ventricle is more rounded, depressed and extended
transversely, like that of chelonia — a preparation for the
longitudinal division of this cavity into two parts, which is
gradually effected in the class of reptiles. Its interior is
provided with thick, prominent, fleshy columns ; its colour

474 SANGUIFEROUS SYSTEM.

is lighter than that of the auricle, and darker than that of
the bulb, which is often white ; and its opening into the
bulbus arteriosus, or thick muscular origin of the branchial
artery, is defended by two semilunar valves, which prevent
the return of the blood into the ventricle, and support the
column of that fluid during the contraction of this muscular
part of the great aortic or branchial artery. The bulbus arterio-
sus is sometimes of an ovate form, like an additional ventricle
appended to the heart, as in most osseous fishes, and some-
times cylindrical, as in the chondropterygii, where it is
furnished internally with several longitudinal rows of trans-
verse valvular semilunar folds, besides the usual valves at its
origin. The simple semilunar form of the valves through-
out the heart of fishes is similar to that observed in the
valves of the heart in the invertebrated classes, and in those
of the veins, lacteals, and lymphatics in the highest verte-
brata. The muscular arterial bulb, anterior to the ventricle,
is obvious in the acephalous and the cephalous mollusca, as
in the fishes, and prepares this great arterial trunk for its
division into a systemic and a pulmonic vessel in the higher
classes of air-breathing vertebrata.

By the contractile force of these muscular cavities of the
heart, the blood of fishes is propelled, as in the embryos of
all higher vertebrata, into a single great arterial trunk divided
on each side into branchial arches, which here however ramify
to minute capillaries, and constitute extensive respiratory or-
gans adapted to the element in which these permanent larvae
are destined to reside. No branches, however, are observed
to come off from the trunk of this great branchial artery, to
be distributed on the rudimentary lungs or air- sac of fishes,
as are seen in higher classes of cold-blooded vertebrata,
where the lungs are more distinctly subservient to respira-
tion than in this class. In order to prevent the return
of the venous blood, during the cgntraction of the mus-
cular bulb at the origin of the branchial artery, the in-
terior of that part of the vessel is furnished in the cartila-
ginous fishes with numerous small semilunar valves disposed
in longitudinal rows, which vary in number in different spe-
cies, as also the number of valves in each row. These valves
are often provided with tendinous cords to perfect their
function, and preserve the regular flow of the blood forwards
during the violent exertions of these muscular fishes. Some

SANGUIFEROUS SYSTEM. 475

sharks have only two rows of valves, others have three, and
there are five rows in the bulbus arteriosus of the skate ; in
the sturgeon there are two rows of small valves near the
ventricle, and a third row of larger valves at the anterior
termination of the muscular bulb, each row having four
valves, and all are placed in symmetrical order.

The branchial artery conveys the entire venous blood of the
system, and divides into lateral trunks corresponding with the
number of the branchiae on each side, which are only ramifi-
cations of these primary trunks. There appear to be at first
generally five branches on each side in this class, as in the
branchial arches of the aorta in the embryos of higher ver-
tebrata ; and in most of the chondropterygii these five pairs
of branchial arteries and gills continue in the adult state ; but
in the osseous fishes the anterior pair are obliterated and con-
verted into carotid arteries for the head, while four pairs are
retained for distribution on the four pairs of persistent
branchiae. The branchial artery conveying the venous blood
of each gill, occupies the exterior portion of the groove of
the osseous or cartilaginous hyoid arch, and the corresponding
branchial vein, returning the arterialized blood, runs more
concealed in the deeper part of the same marginal groove.
The branchial arteries ramify to an extreme minuteness on the
delicate bifid laminae of the gills, and their capillaries are con-
tinuous with those of the branchial veins. The deciduous ex-
ternal respiratory filaments of many cartilaginous and some
osseous fishes, being merely prolongations of the permanent
internal branchial laminae, their arteries and veins are the
same. The venous branches, reinforced by a continued ac-
cession of twigs from the branchial laminae, proceed upwards
to the dorsal ends of the branchial arches, and receiving
all the arterialized blood from the gills, they unite to
form larger trunks, which extend backwards, and anasto-
mose to form the single great dorsal artery or abdominal
aorta. The anterior pair of branchial veins thence ap-
pear to give off, at their dorsal part, the carotid arte-
ries to the head, which is thus supplied with blood newly
arterialized by passing through the giUs. The succeeding
pairs of branchial veins also send off arterial branches, which
proceed forwards to be distributed on the heart, the pericar-
dium, the operculum, and the surrounding parts. The
principal trunks, however, of the branchial veins unite below

476 SANGUIFEROUS SYSTEM.

the bodies of the dorsal vertebrae, to form the abdominal
aorta, which continues its course backwards along the median
plane, beneath the vertebrae, to the coccygeal region, where
it becomes enclosed during the rest of its course, by the
inferior converging laminae of the coccygeal vertebrse.

The great coeliac artery which supplies most of the abdo-
minal viscera, arises from the commencement of the aortal
trunk formed by the union of the branchial veins, and sends
oif numerous branches, which ramify extensively on the sto-
mach and intestines, on the liver, the spleen, the air-sac,
and the genital organs. From the principal trunk of the
aorta, within the cavity of the abdomen, and behind the
great visceral artery, several lateral branches come off at
regular distances, one pair for each vertebra, which supply
the contiguous muscular, osseous and cutaneous parts, and
send down branches as renal arteries to the long, narrow,
lobulated kidneys, extended along the sides of the vertebral
column. The brachial arteries, for the pectoral fins, origi-
nate from the aorta near its commencement, and two femoral
arteries likewise come off from the aorta in the region of the
pelvis, for the ventral fins. The coeliac artery sometimes
originates from the common trunk of the right branchial
veins before it unites with the left to constitute the aorta.
The posterior continuation of the aorta extends single along
the inferior ring of the coccygeal vertebrae, above the venous
trunk which occupies the same canal, and it sends off regular
pairs of intervertebral branches which pass upwards and
downwards on each side, to supply the muscular and other
parts of the tail.

The venous blood collected from the lower and posterior
coccygeal region of fishes, is received by numerous pairs of
lateral branches, which convey it into the inferior caudal
vein, enclosed in the lower rings of the coccygeal vertebrae.
This inferior caudal vein lies below the great arterial trunk,
enclosed in the same inferior vertebral rings, and conveys the
venous blood from the cutaneous and muscular parts of the
tail forwards to the abdomen. It forms the commencement
of the great posterior vena cava, it continues its course along
the abdomen, under the bodies of the dorsal vertebrae, and
under the trunk of the abdominal aorta, collecting the venous
blood chiefly from the surrounding muscular parts, and it
terminates in the great sinus venosus behind the auricle of

SANGUIFEROUS SYSTEM. 477

the heart. The posterior commencement of this venous
trunk in the eel was observed by Hall to present a small
pulsating muscular sinus, which accelerates the flow of the
blood towards the abdomen. The venous blood received
from the upper cutaneous and muscular parts of the coccyx,
is conveyed by numerous lateral branches into a superior
caudal vein, contained within the upper rings of the vertebrae,
and above the spinal chord in the same canal. The lobu-
lated kidneys extending along the whole abdomen to the
head, exterior to the peritoneum, and attached by cellular
substance and vessels to the sides of the bodies of the verte-
brae, receive numerous branches, and nearly the whole blood of
this superior caudal vein extending forwards above the spinal
chord. This venous blood transmitted through the lobes of
the kidneys by the superior vein, is received from the capil-
laries by lateral descending branches, which convey it into
the inferior venous trunk, to be carried forward to the sinus
venosus, thus forming a renal portal circulation, like the
portal circulation of venous blood through the liver. But
the posterior part of this vein also communicates, by direct
branches, with the inferior caudal vein.

The venous blood collected from the chylopoietic viscera of
the abdomen, is sent to be distributed through the large and
divided liver by a variable number of trunks, forming so many
venseportse; and sometimes the long lobes of the liver, attach-
ed between the turns of the intestine, receive the separate venae
portee more directly from the mesenteric veins. Sometimes only
a part of the venous blood from the viscera is conveyed through
the liver, and a part is transmitted to the vena cava, as by a
ductus venosus in higher embryos. The lungs of fishes, as
in the embryos of higher classes, not being employed for
respiration, they are nourished by the great visceral artery,
like other organs of the abdomen, and their venous blood is
transmitted by the portal veins through the liver, or some-
times is carried directly to the vena cava. This is a more
simple form of the hepatic portal circulation than is found in
higher classes, where these visceral venous trunks generally
unite to form one great vena portse before entering the liver,
and it more resembles the divided condition of the venous
portal circulation through the kidneys of fishes. In the
thynnus vulgaris Eschricht observed the liver to be composed

478 BANGUI-FERGUS SYSTEM.

of plexuses of parallel blood vessels, derived from the portal
vein, the hepatic artery, and the hepatic vein, the minute
lobules of the organ being formed by straight blood canals
opening into sinuses, like the numerous approximated, pa-
rallel, pancreatic follicles of osseous fishes. The hepatic vein
sometimes forms a distinct sinus between the diaphragm and
the liver, as in the rays, where there are also two lateral pos-
terior venae cavae with enlargements in their course. The
two anterior venae cavse extend, like jugular veins, along the
sides of the neck, receiving the venous blood from the head,,
the pectoral fins, and the anterior parts of the trunk, and
frequently form a sinus, by their union behind the head, be-
fore they open, with the posterior cavae and the hepatic veins,
often three in number, into the common sinus venosus, be-
tween the pericardium and the tendinous diaphragm. In
many fishes there are two hepatic veins, and in others they
unite into a single trunk, as in most higher animals. So
that the vascular system of fishes is advanced not only by
the development of a distinct chyliferous and lymphatic sys-
tem of vessels, but also by that of a more or less extensive
hepatic and a renal circulation of venous blood, which have
not been traced in the invertebrated classes.

The amphibious animals commence their career as fishes,
having in their tadpole state but one auricle and one ven-
tricle of the heart, breathing by means of gills, and send-
ing the whole of their blood through the branchial arches
of the aorta as in the adult state of the finny tribes, and as in
the embryos of all higher vertebrata. The heart of the tad-
pole, like that of the fish, consists of a thin capacious but
muscular auricle, which receives the entire venous blood of
the system, and a smaller muscular and commonly rounded
ventricle, which propels it into a distinct contractile fleshy
bulbus arteriosus, as seen in the larva of the triton cristatus,
(Fig. 136. a.) From the bulbus arteriosus, or commence-
ment of the great aortic trunk, the venous blood is conveyed
by three or more lateral branches, or branchial arches, on
each side, (\36.b,b,b,) both into the first and more deci-
duous external branchiae, and into the later and more durable
internal forms of these organs, as into the deciduous external
filamentous and the permanent internal laminated branchiae
of plagiostome fishes. The number of branchial arteries on

SANGUIFEROUS SYSTEM. 479

each side corresponds with that of the branchial organs when
developed ; they are generally three in number ; at first they
do not appear to communicate with the trunks of the bran-
chial veins by anastomosing canals at their base, their trunks
being nearly or entirely occupied in the formation of branchial
capillaries, and this fish-like character of the branchial
arteries of the young tadpole was found by Cuvier also
in the adult siren, where the whole blood is thus forced
through the gills. The arterialised blood returning

FIG. 13(>.

from the gills of the tadpole by the anterior branchial veins,
(136.C. c. c.} is in part sent, as in fishes, by ascending branches,
(136. l.m.n. o.) to the head and anterior parts of the body,
while the rest is collected into larger trunks, (136. d> d.)
which unite to form the descending aorta, (136. e.) At an
early period of the development of the tadpole, however,
minute anastomosing canals are formed or enlarged between
the great trunks of the branchial arteries and those of the
branchial veins, (136. b. b. g.g,} by which a preparation is made
for the gradual obliteration and absorption of the whole
branchial apparatus ; and the same canals of communication
between these trunks are found to exist in nearly all the
perennibranchiate forms of amphibia in their adult state.
From the posterior branchial artery on each side, convey-
ing venous blood in the earliest condition of the tadpole,
a minute branch (136. i.i.) descends to the rudimentary lungs,
and in its course unites with an anastomosing trunk (136. h. h.)
from the posterior branchial veins conveying the arterialized
blood from the gills, to supply these pulmonary organs.

480 SANGTJIFEROUS SYSTEM.

During the progress of the metamorphosis from the tad-
pole or larva state, the vessels proceeding to the head and
neck enlarge, as seen in the second stage of the triton cris-
tatus, (Fig. 137- /• m.n. 0,) the anastomosing canals (137- b.b.
g. g.) between the trunks of the branchial arteries and veins,
increase in size, the capillary ramifications of the gills (137. c.
c. c.) become diminished, obliterated, and absorbed ; and the
small branches on each side proceeding from the posterior
branchial arteries to the lungs, form considerable pulmonary
arteries, (137. i- *•) which ramify over the increasing surface
of these now important respiratory organs, (137. #• #•) The
venous blood of the system is now therefore conveyed in greater
quantity and by a more direct course, from the bulbus arte-
riosus (137. a,) through the communicating trunks of the
branchial arteries and veins (137- b. b. g. g.} to the branches

FIG. 137.

and trunk of the descending aorta. (13?. d. d. e.) The two
arterial trunks formerly (136. h. h.} conveying arterialized
blood from the branchial veins to the air-sacs or rudimentary
lungs, now become small ductus arteriosi (137- h. h.) con-
necting the pulmonary arteries (137. «- iy) with the branches
(g. d. g. d.) of the abdominal aorta, (137* €.) This is nearly
the condition in which the perennibranchiate species have
the development of their vascular system permanently ar-
rested, where the respiration is effected equally by pulmonic
and branchial apparatus in the adult state. By the further
metamorphosis of these vessels during the development of
the caducibranchiate amphibia, it is manifest that the ante-
rior pair of branchial arteries are gradually converted into

SANGUIFEROUS SYSTEM. 481

the great arterial trunks which proceed to the head and neck,
as seen in the third stage of the triton (Fig. 138. n. n. o. o.)
where the branchiae have been entirely absorbed, and these
pJG iag cephalic vessels have acquired a

less tortuous course. The second
pair of branchial arteries are con-
verted into the right and left
branches of the abdominal aorta
(138. b. d. b. d.), and the poste-
rior pair of branchial arteries be-
come the two pulmonary arteries
(138. i. k. i. k.) conveying mixed
blood from the heart to the lungs.
The development of the great
aortic trunks, from the previously
formed branchial arches, is effected in a similar manner, but
according to a simpler plan, in all the higher classes of ver-
tebrata, as in them the capillary ramifications for an aquatic
respiration are not developed from the branchial arches.
The anastomosing canals, therefore, observed in nearly all
the amphibia, between the trunks of the branchial arteries
and branchial veins, may be regarded as the continuations
of the primitive aortic arches, temporarily reduced in size
during the presence of the gills in the caducibranchiate
forms, and permanently kept open in those species which
preserve the branchiae through life; whilst in fishes, and
apparently in the siren, the aortic arches are entirely divided
into branchial capillaries, through which the whole blood of
the system is necessarily conveyed to increase the extent
of their aquatic respiration. The capillary branches of the
branchial arteries in the external gills of the tadpoles, do
not form ramifications as in the corresponding vessels of
fishes, but minute arches or loops which pass singly around
each small leaflet of the ramose branchiae. Although the
branchial arteries, after the metamorphosis of the frogs, and
after the functions of these vessels have changed, appear to
coalesce, and to originate on each side of the bulbus arterio-
sus by a common trunk, they are yet found in the adult
state to preserve their three canals distinct to their origin,
being separated from each other by internal septa which are
discovered on opening the two primary trunks of the aorta.

PART T. II

482 SANGUIFEROUS SYSTEM.

The bulbus arteriosus is considerable in the adult proteus,
and gives off, not only the three branchial arteries on each
side to the external gills, but also an aortic arch on each
side which unite together to form the trunk of the aorta,
as shown by Rusconi — thus combining in the same animal,
the vascular conditions of the tadpole and the adult of
the caducibranchiate amphibia, or those of the fishes and
the true reptilia; the same plan of structure appears to
exist in the other perennibranchiate forms of this class.
Even in the adult triton (138. b. b. b.) three aortic trunks
continue to originate from each side of the aorta, the third
pair (138. i. i.) being chiefly occupied in forming the two
pulmonary arteries (138. k. 7c.) which communicate by small
ductus arteriorsi (138. h. h.) with the arches of the abdomi-
nal aorta (138. d. d.) In the anourous amphibia, as the
frogs and toads, the aortic arches still further coalesce by
the metamorphosis, and externally appear to constitute, in
the adult state, only a single great trunk on each side,
divided internally by septa throughout its course, which
gives off the usual cephalic, aortic, and pulmonic arteries;
and while the external branchiae in the tadpoles of these
species are withdrawn, and are becoming absorbed, the
branchial apertures, first on the one side of the neck and
then on the other, become closed up by a thin fold of the
skin which has been mistaken by some for the analogue of
the opercular bones which support this part in fishes. Traces
of the early branchial capillaries appear to be preserved on
the carotid arteries through life, and the posterior or pul-
monic arch of the aorta gives off an artery on each side to
the back part of the head, as well as the great pulmonary
arteries to the lungs. The branchial arteries in the young
state of the coecilice are observed to ramify on internal gills,
which open on each side of the neck by cutaneous apertures,
as in the larvae of other amphibia. The bulbus arteriosus
in the menopoma (119. A.), is long, cylindrical, muscular
and provided with numerous internal valves, as in the pla-
giostome fishes ; these valves are disposed in two transverse
rows, with four in each row, and the artery is dilated at the
giving off of the aortic arches, which are four on each
side. The small posterior or proximal aortic branches, on
each side, are distributed chiefly on the simple pulmonary

SANGUTFEROUS SYSTEM. 483

sacs (119. A. q.}9 and they communicate by distinct ductus
arteriosi with the next anterior or second branches of the
aorta. The second and third aortic arches, of larger size,
unite above the oesophagus (119. A. o. o.), like the branchial
veins of fishes, to form the common dorsal trunk of the
aorta (119. A./*. /I), and their united trunks on each side
send off cephalic branches (119. A. o. o.) to the back part of
the head, as in the former class. The fourth or most ante-
rior pair, after giving off branches to the mouth, unite,
behind the aesophagus, with the cephalic branches to be
distributed on the head. The great aortic branches are
nearly similar in the amphiuma, where the proximal arches
are distributed chiefly on the long cancellated lungs, and
the two succeeding arches unite above the oesophagus to
form the descending aorta.

The heart of the larvae, before the development of the
lungs, consists, like that of the fishes, of a single auricle
which receives the venous blood of the system, and of a
single ventricle which propels it into the bulbus arteriosus
and the branchial or aortic arches ; but as development
advances, and the air-sacs assume the functions of lungs,
the arterialized blood collected from these pulmonary ca-
vities, developes a small distinct sinus or left auricle on the
united trunks of the two veins which return it to the ven-
tricle. The existence of this smaller left auricle in the
adult amphibia was first pointed out by Dr. Davy in the
caducibranchiate species, as the frogs and toads, and the
same structure of the heart was discovered by Weber, to
pervade also the perennibranchiate amphibia, as the axolotus
and the proteus. The left auricle, smaller than the right,
is separated by a thin transparent septum from the larger
systemic auricle, and is provided, like it, with distinct
valves at its entrance into the ventricle. The venous blood
of the system is generally collected into a distinct sinus
venosus in amphibia, as in fishes, before it is transmitted
to the large thin right auricle of the heart. The sinus ve-
nosus of the triton is a large round contractile cavity like
the right auricle. The blood from the right and left auricles
is mixed in the ventricle, by permeating the loose columnar
structure of its parietes, and is prevented from returning
into either aurcle, by small semilunar valves defending the

i i 2

484 SANGUIFEROUS SYSTEM.

auriculo-ventricular orifices. The auricles are more advanced
over the upper and fore part of the ventricle, than the aurcle
even of the plagiostome fishes, and the whole heart, like
that of fishes, is situated further forwards towards the head
than in reptiles or the warm-blooded vertebrata. The ven-
tricle was observed by Meek el to be partially divided by an
internal septum extending from the apex in the pipa, as in
chelonian reptiles, and he also observed the septum between
the auricles in the pipa, the siren and the axolotl, without
perceiving the difference of function in these cavities dis-
covered by Davy and Weber in both these orders of amphi-
bia. The sinus venosus of the right auricle and the bulbus
arteriosus or commencement of the aorta, are here distinctly
muscular and contractile, like the corresponding sinus and
aortic bulb in the plagiostome and other fishes.

The two aortic trunks meet behind, under the vertebral
column, as in reptiles, to form the abdominal aorta, at a point
more or less advanced towards tlie head in different species,
and in their course backwards, these two aortic vessels com-
municate with the trunks of the pulmonary arteries by means
of the two ductus arteriosi. From the commencement of each
of the two aortic trunks, a large artery originates, which
divides into a brachial and a cephalic branch, to supply the
corresponding arm and side of the neck and head, and these
primary brachio-cephalic branches of the aorta, commonly
supplying the anterior parts of the body in the amphibia, have
the same size and mode of distribution on the right and left
sides. The next great trunks from the arches of the aortee, are
the two pulmonary arteries, which descend on each side to
ramify chiefly on the dorsal and median surfaces of the lungs,
and which vary in size in different species according to the
development of these pulmonary sacs. The bulb of the
aorta often presents a rounded dilatation in the adult, cor-
responding with the part from which originated the bran-
chial arteries of the larva. At the commencement of the
great trunk of the abdominal or descending aorta, in the
anourous species, the cseliac or common visceral artery
arises, as in fishes, which gives off the gastric, the hepatic,
the mesenteric, and other arterial branches, to supply most
of the chylopoietic organs. The common trunk of the aorta
gives off several small vessels to the kidneys and the geni-

SANGUIFEROUS SYSTEM. 485

tal organs, before bifurcating to form the great iliac arteries,
and these two great trunks supply numerous branches to
the pelvic organs, before leaving that cavity to ramify on
the posterior extremities. The form and distribution of the
posterior aorta, however, in the perennibranchiate species,
and the urodelous amphibia, more closely resemble the
course of that vessel in the coccygeal region of fishes and
of the larvae of anourous species.

The sanguiferous system of reptiles is advanced to a higher
stage of development than that of the inferior classes of
cold-blooded vertebrata, and this superiority is observed
chiefly in the magnitude of the pulmonic portion, which
accords with the earlier development and the increased ex-
tent of their pulmonary organs. The whole heart is pro-
portionately larger and broader, and is situated farther back
from the head. The auricles are more muscular, more dis-
tinctly separated from each other externally, and are more
advanced to the anterior part or base of the ventricle, and
the ventricle is more divided internally by an ascending
septum, than in the amphibia. The general form of the
heart, like that of most other viscera, is modified by the
form of the trunk, being more elongated in ophidia, broader
in chelonia, and intermediate in the saurian reptiles. The
right auricle receives the entire venous blood of the system,
and the left auricle, the arterialized blood from the capacious
pulmonary sacs; the two divisions of the ventricle give
origin to the pulmonary and the systemic arteries, which
early communicate with each other by means of two deci-
duous ductus arteriosi ; and the two principal systemic ar-
teries anastamose at a greater or less distance from the
heart, to form the common trunk of the descending or
abdominal aorta, as in amphibia and fishes.

The two auricles of ophidian reptiles are generally much
extended in a longitudinal direction, and the ventricle also
has an elongated conical form; the auricles are provided
with distinct muscular bands, and prominent internal fleshy
columns ; and the right, which receives the venous blood of
the system, is more capacious than the left which receives
the arterialized blood from the lungs. The cavity of the
ventricle is partially divided by a thick cribriform pervious
septum, into a right inferior or pulmonic portion, and a

486 SANGUIFEROUS SYSTEM.

left superior or systemic portion, which communicate by a
wide opening resulting from the deficiency of the septum
near the base of the ventricle. The parietes of the systemic
portion of the ventricle are thick and strong compared with
the small interior cavity, so as to propel the systemic blood
through the whole extent of their elongated trunk, and the
numerous free fleshy columns which traverse its interior,
tend to mingle the venous with the arterialized blood poured
into its cavity. The septum of the auricles is thin and dia-
phanous, and sends from each side of its inner margin, at
the base of the ventricle, a crescentic membranous fold,
which forms a distinct semilunar valve over each auriculo-
ventricular orifice, to prevent the return of the blood during
the contraction of the ventricle. The approximated open-
ings of the two systemic aortse, in the strong upper left
compartment of the ventricle, are provided with two semi-
lunar valves, and two similar folds are observed at the
opening of the pulmonary artery in the right inferior portion
of the ventricle. The right or pulmonic portion of the
ventricle is more capacious than the left, and its parietes
are less thick, muscular, and cribriform.

The common trunk of the right and left aortee, on leaving the
systemic portion of the ventricle, soon divides to embrace the
trachea and oesophagus- in the aortic arch, as in other cold-
blooded vertebrata ; and the two trunks again anastomose a
little posteriorly, under the vertebral column, to form the pos-
terior aorta, which extends backwards along the median line of
the body to the end of the tail. The right arch of the aorta,
in its course upwards and backwards, gives off a consi-
derable thyroid branch, and a large cephalic azygous artery
from which the common carotids of both sides originate.
The common carotids divide near the head, into a larger
external, and a smaller internal carotid artery, and the lat-
ter of these branches supplies the place of the vertebrals
within the cranium. The right aortic arch also sends off,
near its junction with the left, a single median subvertebral
artery which extends forwards, and supplies the vertebral or
spinal and intercostal arteries to each side of the anterior part
of the body. The common cephalic artery in advancing to
the head, sends numerous twigs to the resophagus and the
trachea, before it divides to form the common carotids. The

SAXGUIFEROUS SYSTEM. 487

intercostal arteries of the posterior part of the body are derived
from the common trunk of the abdominal aorta, formed by
the early anastomosis of the left with the right aortic arch,
and from the length of the abdominal viscera and their dis-
tance from each other, these organs are supplied by distinct
hepatic, gastric, mesenteric, and genital arteries, which
come off, not from a common creliac or visceral artery, but
successively and directly from the long trunk of the posterior
aorta in its course backwards under the vertebral column.

The venous blood is returned from the head by two jugu-
lar veins, and from the intercostal spaces by two azygous
branches which unite before entering the right auricle. The
caudal veins returning the blood from the posterior parts
of the body appear to distribute a portion through the kid-
neys, like the renal portal circulation of fishes, and to
convey another portion to the mesenteric vein, to be sent
with the venous portal circulation through the liver. The
spermatic veins pass with the efferent renal veins into the
posterior vena cava, to be sent with the venous blood of
the superior cava and hepatic vein into the right auricle and
right cavity of the ventricle, and thence by one or two pul-
monary arteries through the single or double respiratory
sac.

The exterior surface of the ventricle in the saurians is
more generally connected with the interior of the pericardium
by tendinous threads than in the ophidian reptiles ; more
than twelve of these connecting filaments, most numerous in
the invertebrata, are found in the pseudopus, two in the mo-
nitors, and one or more in the crocodiles and most other
genera. I have found eight of these tendinous bands, arising
by separate peduncles, near the apex of the ventricle, in the
adult heart of the large gavial of India, where the pericardium
is nearly a line in thickness, white, fibrous, and of great
strength. The general structure of the heart and the distri-
bution of the great central blood vessels are nearly the same
in the lacertine sauria as in the ophidian reptiles. The peri-
cardium is generally stronger, the auricles more muscular,
short, and lobed at the margin, the ventricle with thicker
parietes, and the septum more developed between its
compartments ; the great pulmonic and systemic trunks are
bound together by condensed cellular substance and by the

488 SANGUIFEROUS SYSTEM.

enveloping pericardium, to a greater extent from their origin,
before they separate for their respective destinations. The
thick parietes of the ventricle are loose, cribriform and deeply
cancellated in their interior, from the free and detached condi-
tion of the irregular fleshy columns which compose them ;
and the pulmonic and systemic portions of the blood are
mingled together in its cavity, to a variable extent in different
species, according to the development and the direction of
its imperfect septum. The right and left aortse, provided
with semilunar valves at their origin, commence by distinct
orifices in the common cavity at the base of the ventricle,
and unite together under the vertebral column after forming
a small arch upwards on each side, the left giving off no
branches till near the place of its anastomosis with the right,
to form the common descending aorta. The two common
carotids arise from the arch of the right aorta, and the sub-
clavian arteries come off from the right and left trunks of
the aorta at the angle of their reunion. The common trunk
of the posterior aorta in passing backwards gives off the in-
tercostals on each side, a branch to the cesephagus and
another to the liver. The coeliac and anterior mesenteric
originate by a common trunk, which is succeeded by the
lumbar, the spermatic, and the posterior mesenteric arteries.
From the posterior position of the kidneys the renal arteries
come off late, and are succeeded by the two common iliacs,
the aortal trunk being here prolonged as a large median
sacral artery, corresponding with the magnitude of the caudal
prolongation of the body in these lacertine reptiles.

The heart of the crocodilian reptiles is enveloped in a very
thick and strong pericardium, which also firmly connects
together all the great arterial trunks which originate from its
cavity. The parietes of the auricles, especially the right,
are furnished with strong muscular internal bands, and there
are large semilunar valves at each of the auriculo-ventricular
orifices. The ventricle has very thick muscular parietes, and its
cavity is^divided by a strong muscular and columnar septum
deeply pitted, which extends from the apex to the base of the
heart. The right auricle is much larger than the left, which cor-
responds with the greater size of the veins and the larger
quantity of blood, which enter the former cavity, and the two
cavities of the ventricle still communicate with each other

SANGUIFEROUS SYSTEM. 48U

at the base of the heart, as in other reptiles, although here
to a smaller extent and during a limited period of life. The
venous blood of the system received from the capacious right
auricle, appears to be transmitted to the inferior right cavity
of the ventricle, which gives origin to the left aortic trunk
and also to the common trunk of the pulmonary arteries.
These vessels are provided with semilunar valves at their
origins, and the pulmonary artery arises from a small fossa
of the right ventricle, a little distant from the origin of the
left aorta. The osseous lamina observed by Bojanus in the
heart of the tortoise, between the origins of the systemic
arteries, I have found in the same situation in the adult
gavial, where it formed an irregular tuberose morbid growth,
and measured about three quarters of an inch in length
and two lines in thickness. The arterialized blood from
the lungs, received by the small left auricle, and transmitted
to the superior, or left cavity of the ventricle, although
sparingly, and perhaps for a limited time, sent through
the opening of the septum, appears to pass chiefly into
the great bulbous trunk, which gives origin to the right arch
of the descending aorta, and to the right and left brachio-ce-
phalic arteries or arterise innominatse, which supply the ante-
rior parts of the body. Two semilunar valves are also placed
at the origin of this great right systemic artery, in the left di-
vision of the ventricle. The aerated blood is thus chiefly sent
to the head and arms, by the two ascending trunks from the
right aorta, which form the common carotid and the axillary
arteries of their respective sides, and also to the legs and tail
by the right aortal trunk. The right and left aortic arches,
proceeding from distinct orifices of the ventricle, unite to-
gether under the vertebral column, as in other reptiles, to
form the common trunk of the abdominal aorta, the right
arch of the aorta conveying arterialized blood principally to
the head, legs and tail, and the left aorta chiefly venous blood
to the abdominal viscera.

All the three great trunks which originate from the
ventricles, the right and left aortse and the pulmonary
artery, form wide and elongated bulbous enlargements at
their commencement, and from this bulbous dilatation of
the right aorta arise the two large trunks, which soon
subdivide to form the common carotid and axillary or sub-

490 SANGUIFEROUS SYSTEM.

clavial artery, on each side. Sometimes the carotids of both
sides, arise by a common trunk as in serpents. The subclavian
artery gives off an oesophageal, an internal mammary, an
inferior cervical and an anterior common intercostal branch,
before arriving at the axilla, where it sends off several thoracic
branches, and forms the brachial, which divides as usual into
the radial and ulnar arteries. The trunk of the right aorta,
near its place of union with the left, gives off a considerable
posterior common intercostal artery, which is succeeded by
two smaller branches, distributed also on the intercostal
spaces. The left aorta gives off no branches before it arrives
near the place of its anastomosis with the right, where it
gives off the great coeliac, or visceral artery, which supplies
most of the abdominal organs, as the stomach, the liver, the
spleen and the pancreas, and leaves only a small and short
communicating branch to unite with the right trunk of the
aorta. The anterior mesenteric arises from the common
trunk of the united aortse at some distance below the coeliac
artery, and is followed by the supra-renal, the renal, and the
lumbar arteries, and the profunda femoris, before the aorta
gives off the great crural artery on each side to the legs.
The posterior mesenteric and the coccygeal arteries arise
from the median sacral, which here forms a large prolonga-
tion of the aorta, corresponding with the magnitude of this
part of the body in the crocodilian reptiles.

The short and broad form of the heart in the chelonian
reptiles accords with the great transverse development of
their body, and with the broad form of the auricle and ven-
tricle already seen in the highest plagiostome fishes, the
rays and sharks, which prepares for the division of the ven-
tricle into two distinct cavities in the hot-blooded classes.
The entire venous blood of the tortoise is conveyed by the
two large inferior and the two smaller superior vena cavae
(FiG. 139././. g. y.} into the common sinus venosus, and
thence by a single orifice into the capacious right auricle
(139. «.) of the heart. The smaller left auricle (139. b.)
receives the arterialized blood from the two pulmonary veins
(139. d. e.), and both auricles pour their contents simulta-
neously into the strong muscular and single ventricle
(139. c.), which propels the blood, by three distinct orifices,
into the right (139. /*.) and left (139. /.) aortee and the

SANGUIFEROUS SYSTEM.

491

common trunk (139. o.) of the two pulmonary arteries
(139. p. q.)

FIG. 139.
.ft

Two strong semilunar valves check the return of the
venous blood from the right auricle into the sinus venosus,
but the same protection is not observed at the single very
oblique orifice, by which the two pulmonary veins enter the
left auricle. The ventricle is of great size, much extended
transversely, depressed in form, with a rounded obtuse apex,
with very thick muscular parietes, especially in its left por-
tion, and the innumerable free fleshy columns reduce its in-
terior to a loose reticulate spongy texture. Its exterior
surface is generally connected with the pericardium by
several tendinous filaments, and the same are sometimes
observed passing from the ventricle to the exterior of the
auricles. The septum ventriculorum is developed to a va-
riable degree in the species of this order, being least percep-
tible in the land tortoises, and most distinct in the marine
turtles, but is less developed than in the saurian reptiles.

492

SANGUIFEROUS SYSTEM.

FlG. 140.

At the base of the ventricle, the two orifices (Fio. 140. e. d.}

leading from the right
and left auricles (140.
a. b.) are protected
by a broad membra-
nous fold (140. ^.),
which extends to the
right and left from
the septum auricu-
larum,and is strongly
connected by tendi-
nous cords (140. h.)
with the muscular
columns of the ven-
tricle (140. c. c.).
During the contrac-
tion of the ventricle,

the right portion of this broad quadrilateral valve (140.
ff.) appears to direct the current of venous blood (140. e.)
from the right auricle (140. a.) principally along the basilar
groove of the right ventricle into the now closely approximated
orifice of the bulbous commencement of the pulmonary artery,
and probably, also the left aorta ; and the arterialized blood
(140, d.) from the left auricle (140. b.) is carried through the
spongy columnar parietes towards the right side of the left ven-
tricle and the right aorta, the orifice of the left aorta being a
little nearer to the pulmonary artery than the opening of the
common right systemic trunk. The muscular valve overhang-
ing the orifice of the pulmonary artery, may tend to complete
the septum of the ventricles during the contraction of the heart,
and thus direct the two currents from the auricles into their re-
spective arterial trunks, as supposed by Meckel. Besides the
broad valvular extension from the septum of the auricles, each
auriculo-ventricular orifice is provided with another distinct
and opposite semilunar fold, most developed on the right, to
complete its protection, and a large muscular fold (HO./*.)
is seen to overhang the pulmonary artery in the right cavity
of the ventricle, extended from the septum ventriculorum,
and supported by cordse tendinise, like the muscular tricuspid
valve in the right ventricle of birds.

SANGUIFEROUS SYSTEM.

493

The three great arterial trunks which arise by distinct
orifices from a fossa on the right side of the base of the
ventricle, are provided each with a pair of semilunar valves
at their origin, and are compactly united together for a short
distance by cellular substance and pericardium on leaving the
cavity of the heart, as seen in the annexed figure (Fio. 141.
A. B.) from Bojanus, representing the ventral and dorsal
aspect of the heart and blood vessels of testudo europ&a.
The elongated right (A. a. B. a.) and left (A. b. B. b.) auricles
rest on the broad base of the ventricle (A. c. B. c.), and the
great arterial systemic trunks (A. d. e. f. g.} soon separate
for their several destinations. A strong muscular band (A. v.)
with circular fibres, embraces the origin of the great arterial
trunks (A. d. e.f. g.}, and the trunks of the coronary arteries

FIG. 141.

and veins wind round the same part of the ventricle (A. c.),
extending their ramifications towards the posterior margins
and the apex. The right systemic artery, after giving off the
right arch (A././. B./.) of the descending aorta (A. B.w. n.),
advances a little forwards, and divides into the right and left
arterise innominatse, each of which again bifurcates to form
a small ascending common carotid and a large subclavian
artery (A. B. d. e.) The common carotid, on each side, sup-
plies the parts of the neck, and is continued, ramifying like

494 SANGUIFEROUS SYSTEM.

the external carotid of mammalia, over the head and face,
the internal carotid artery being here a very small branch to
the small contents of the cranial cavity, and, as in other rep-
tiles, the vertebral artery is not required to enter the small
cranium. The subclavian artery (A. B. d. e.), on each side,
also gives off several branches to the neck, and to the scapular
and pectoral muscles, the two anterior intercostal arteries,
and the internal mammary which, in passing backwards
along the interior of the ribs, anastamoses with the inter-
costals and with the epigastric artery. A few branches to
the dorsal and scapular muscles are given off from the axillary
artery in its passage to the inner part of the head of the
humerus, where, as brachial artery, it sends off the usual
deep and circumflex branches, and on arriving at the elbow-
joint, it divides into a small radial and ulnar artery to supply
the short fore-arm and hand.

The right aorta (A. f. B. /.), after leaving the common
systemic trunk of that side, passes upwards and backwards
to unite with the left aorta (A. g. h. B. g. h.) under the ver-
tebral column, and sends off, in this course, one or more
intercostal branches. The right and left aortae unite with
the right and left branches of the pulmonary artery (B. p. q.)
by means of two ductus arleriosi (B. r. s.), which remain,
with their canal obliterated, in the adult state. The left
aorta (B. g.}, arising by a distinct orifice from the left por-
tion of the ventricle, follows a course analogous to the right,
without sending off branches to the anterior part of the
body, and is appropriated almost entirely to the abdominal
viscera, a small communicating branch (B. h.) being alone
left to anastomose with the right aorta. From the left arch
of the aorta arise three visceral arteries, the gastric or coro-
nary artery (B. /.) to the oesophagus and the stomach, the
cceliac (B. m.) which sends branches to the liver, the pan-
creas, the spleen, and the large intestines, and the mesen-
teric artery (B. i.), which is chiefly spread on the mesentery
and small intestines. The common trunk of the abdominal
aorta (A. B. n. n.}, in passing backwards, gives off a few pos-
terior intercostal branches, the two spermatic arteries, se-
veral renal branches to the lobulated kidneys, some small
lumbar arteries, and a cloacal branch like a posterior me-
senteric, and after sending out the large iliac arteries on

SANGUIFEROUS SYSTEM. 495

each side, it is continued along the sacrum and coccyx as a
small median caudal artery, as in other reptiles. The in-
ternal iliac ramifies mostly on the urinary bladder and other
pelvic viscera, and the external iliac, after giving off the
epigastric and circumflex arteries, and continuing to afford
numerous branches to the thigh and leg as crurial and an-
terior tibial artery, terminates in a dorsal arch, extending
outwards over the tarsus, from which the digital arteries of
the foot are derived.

The venous blood returned from the head and neck by
the jugular veins (B. t. u.) in the chelonia, as in other rep-
tiles, and that brought from the arms by the subclavian veins
(B. v. w.)9 is conveyed by the right and left anterior or superior
venee cavee (139. g. g.}, formed by the union of these two
veins on each side, into the common sinus venosus (141.
B. z.)} which receives the blood from the abdominal veins.
The abdominal veins receive the blood from the posterior
parts of the body, and from the renal and hepatic portal
systems, and, after communicating on each side with the
jugular veins by an anastomosing branch, they enter the sinus
venosus, which pours its contents by a single broad valved ori-
fice into the right auricle of the heart (A. a.) The two pulmo-
nary arteries (B. p. q.} arise by a lengthened single bulbous
sinus from the left inferior part of the right ventricle, and,
after communicating by the ductus arteriosi (B. r. s.) with
the two aortse (B./. #.), they follow the ramifications of the
bronchi through the extensive cavities of the lungs. The
two small returning pulmonary veins (B. 1. 2.) unite to form
a small sinus before entering by a single opening into the
left auricle. The veins of reptiles, like their chyliferous and
lymphatic vessels, are provided with scanty and ineffective
valves, which allow injections to pass readily against their
course, from trunks to branches.

In the class of birds, the septum of the ventricles is at
length completed, and the pulmonic circulation is entirely
distinct from the systemic, as in all the hot-blooded verte-
brata. The air admitted into contact with the systemic capil-
laries in the interior of the bones and in the large air-cells
extending through most parts of the body, oxygenates and
decarbonizes a larger portion of their blood, and is the source
of their high temperature, their great muscular force, and
the encreased energy of all their functions. By their

496 SANGUIFEROUS SYSTEM.

habitual great muscular exertions, the blood is determined
from the deep-seated to the superficial parts, by which
their surface-temperature is elevated for incubation, their
down and plumage are developed to equalize their tem-
perature or to aid their flight, and their perspiration
is increased to moderate their occasional heats.

The heart of birds, of a tapering conical form, with thick
muscular parietes, is placed longitudinally on the median
plain, anterior to the liver, enclosed in a thin transparent
vascular pericardium, surrounded by air-cells prolonged from
the bronchi, and still occupies, as in the inferior vertebrata,
a more advanced position in the trunk than in the mammi-
ferous tribes. The right auricle and ventricle, especially in
diving birds, have more capacious cavities with thinner pa-
rietes, than the corresponding parts on the left side, and the
venous blood of the system is received into the right auricle
from the two anterior and the larger single posterior, vense
cavee, by three distinct orifices provided with strong semilunar
valves to direct the currents and check regurgitation. The thin
muscular outer parietes of the capacious right ventricle en-
velope the greater part of the exterior of the strong left
muscular cavity, and the right auriculo- ventricular orifice
is here defended by a thick fleshy valvular fold extended
from the base of the ventricle, which probably aids in
forcing the blood through the fixed lungs of birds, where
the diaphragm is almost wanting. The arterialized blood
arrives from two pulmonary veins by a single orifice in the
left auricle, which is provided, like those of the superior
venae cavse, with only one semilunar valve, and the walls of
this auricle are more muscular and columnar than the smooth
parietes of the right cavity, but neither of these cavities yet
presents auricular appendices developed from its margins, as
in mammalia. The left auriculo-ventricular orifice is pro-
tected, as in quadrupeds, by a membranous mitral valve,
composed of two folds, and connected by its irregular free
margin, with the thick fleshy columns of the ventricle, by
means of numerous tendinous cords.

The arterial orifices of the right and left ventricles of birds
are single, and provided with three semilunar valves, as in all
the higher vertebrata, and all the parts of the heart, though
completely separated internally by the inter-auricular and
inter- ventricular septa, are now more intimately united

SAXGUIFEROUS SYSTEM. 497

together externally, and more compactly adjusted to each
other's form, than in the inferior classes. From the short-
ness of the trunk in this class, and the proximity of the
heart to its anterior part, the single great systemic artery
proceeding from the base of the thick conical left ventricle,
early divides into three principal trunks as it proceeds to the
right side of the body, along which the single abdominal
aorta descends to the pelvic region. As the arch of the
aorta is here directed to the right side, the first branch given
off is the left arteria innominata, which is the common trunk
of the carotid, the subclavian, the vertebral, and the thoracic
arteries of that side. The second branch of the aorta is the
arteria innominata of the right side, which divides in a
manner similar to that of the left. The third branch is the
great trunk of the descending or abdominal aorta which
supplies the Viscera and posterior parts, and varies less in
its magnitude than the two anterior aortic branches, which
are greatly developed in birds with large wings and powerful
flight, and very small in strutheous birds with heavy body
and feeble wings. The arteria innominata or great brachio-
cephalic trunk, on each side, sends forward the common
carotid artery which, after giving a branch to the oesophagus
and crop, generally gives origin to the vertebral artery.
The common carotids mounting along the fore part of the
neck, beneath the muscles, are most generally found both
on the left side, or with the right carotid extending along
the median plain, and near to the head they commonly divide
into the external and internal carotids, the internal being
here, as in the lower vertebrata, only a small branch of the
external trunk of the artery. Many birds have only the left
carotid, and a few only the right carotid artery developed
from the subclavian, and then dividing into two. The
principal branches of the external carotids are the supe-
rior thyroid, the lingual, the occipital which receives
the anastomosing end of the vertebral, the large facial which
forms the facial plexus behind the orbit, and the palatine
which often unites with the opposite, like the lingual, to
form a median trunk. The exterior branch of the internal
carotid artery forms the ophthalmic, and gives off an
occipital, an inferior palpebral, an ethmoidal, a lachrymal,
and sometimes an inferior maxillary, a harderian, a nasal,

PART V. K K

498 SAXGUIFEROUS SYSTEM.

and a frontal branch, and terminates in the ciliary arteries
which ramify minutely on the choroid membrane. The
interior branch of the internal carotid is chiefly occupied in
forming the cerebral arteries, and its terminal branches
entering the orbit, anastomose with the divisions of the
ophthalmic artery. The vertebral artery ascends, with
the cervical portion of the sympathetic nerves, through the
foramina of the transverse processes of the cervical vertebrae,
sending off small branches to the surrounding parts in its
course upwards to the atlas, where it anastomoses with the
occipital artery, and sends in a minute twig to the medulla
oblongata, so that the basilar artery is here formed by
communicating branches of the internal carotids; the
blood of the vertebral arteries is diverted from the internal
to the external parts of the head, as in the reptiles and the
lower herbivorous mammalia.

The great brachio-cephalic artery on each side, after giving
off the common carotid and vertebral, becomes the sub-
clavian and sends off an inferior thyroid to the lower larynx,
an internal mammary, and large thoracic and scapular arteries
to the surrounding muscular and cutaneous parts, especially
to the great pectoral muscles so important in flight, and to
the highly vascular subcutaneous incubating organ spread
over the abdomen. From the magnitude of the branches
thus sent from the subclavian, and from the smallness of the
muscular parts of the arm of birds, the axillary artery is here
greatly reduced, and after giving off the circumflex and deep-
seated branches, the brachial artery proceeds as usual along
the inner side of the humerus, and divides near the elbow-
joint into a small radial, and a larger ulnar artery which
furnishes considerable branches to the inter-osseous space
and the rest of the fore-arm, and distributes its terminal
twigs on the three fingers of the hand, and on the cutaneous
parts of the development and growth of the large feathers
of the wing.

The third or right branch of the great systemic artery
issuing from the left ventricle, is the principal continuation
of the trunk, forming the descending or abdominal aorta,
which arches upwards and backwards on the right side
of the vertebral column, over the right bronchus, and
gradually acquires a median position under the bodies
of the vertebrae, along which it proceeds to the end of the

SAXGUIFEROUS SYSTEM. 499

coccyx. The descending aorta in passing backwards, sends
out considerable cesophageal and bronchial arteries, a variable
number of intercostal trunks, and numerous smaller dorsal
and lumbar branches to the parts around the spine. The
cceiiac artery is here a considerable trunk, which is devoted
chiefly to the alimentary canal and the gastric cavities, the
branches being small which proceed to the chylopoietic
glands. This great cceiiac trunk sends a branch forwards to
the oesophagus, another the gastric to the ventriculus succen-
turiatus and the gizzard, and much smaller branches to the
spleen, the liver, and the pancras, and where the coeca-coli
are of considerable size they also receive a separate branch
from the same trunk. The chief continuation of the coeliac
artery, after giving off small branches to the oesophagus the
spleen and the liver, generally divides into a right and a left
gastric artery which spread on the corresponding sides of
the gizzard, the right sending out a branch to the duodenum
and pancreas, and another to the mtestinum ilium and cosca-
coli, and the left giving branches chiefly to the ventriculus
succenturiatus and the left lobe of the liver.

From the high origin of the external iliac or crurel arteries in
birds, only one mesenteric, the superior mesenteric artery, arises
from the trunk of the aorta, above the commencement of these
vessels, as in the class of reptiles. This vessel arises a little below
the coeliac, from the fore part of the aorta, and spreads its
ramifications over most parts of the mesentery, the intestinal
canal and the cceca-eoli, anastomosing anteriorly with
branches of the gastric arteries, and posteriorly, on the
rectum, with branches of the small posterior mesenteric
which arises from the median sacral artery. Below the
superior mesenteric, the common trunk of the right and
left genital or spermatic arteries arises from the fore part of
the aorta, and each of these arteries sends a branch to the
upper large lobe of the kidney, and another to the testicle
or to the ovary and oviduct, of its respective side, these
genital branches having a tortuous course, and being subject
to periodical enlargements with the genital organs, as in
other animals. The right and left profuncUefemoris or deep-
seated femoral arteries have separate origins from the
sides of the aorta in birds, and distribute their branches to
the muscular parts of the abdomen and femur as far as the

K K 2

500 SANGUIFEROUS SYSTEM.

knee, the epigastric arteries being derived from these deep
femoral trunks on their escaping from the pelvis. After the
giving off of the great external iliac or crural arteries, which,
from their relative size, are almost bifurcations of the aortal
trunk, the median sacral artery sends out a few lumbar
branches to the surrounding parts, a small inferior mesenteric
to the rectum and colon, and two minute internal iliacs to
the urinary and genital organs, and terminates at the end of
the coccyx by ramifying on the muscular and cutaneous
parts which it supports.

The external iliac or crural arteries, before leaving the pelvis,
send off some minute renal branches to the small inferior lobes
of the kidneys, and on leaving that cavity to become the femo-
rals, they distribute the circumflex and other branches to the
muscles of the pelvis and thighs. As popliteal artery it gives
articular branches to the parts around the knee-joint, and di-
vides behind into the anterior and posterior tibial arteries, the
posterior sending out a considerable peroneal or fibular branch,
which descends along the fibula to form articular branches
around the heel. The coarse of the anterior tibial
artery is often marked, in aquatic birds, by an enveloping
plexus of its smaller anastomosing branches, which surround
the trunk of the vessel, and reunite to it at the heel-joint,
resembling in form and use the brachial and crural plexuses
of tardigrade mammalia. The prolonged trunk perforates
the lower end of the metatarsal bone, to gain the sole of the
foot as plantar artery, where some of its branches extend
to the extremities of the toes, and others ascending behind
the metatarsus, anastomose freely with the descending twigs
of the fibular artery. There is thus a nearer approach to the
mammiferous type in the distribution of the arterial trunks,
as well as in the structure of the heart of birds, than is
met with in the inferior vertebrata, but notwithstanding the
remarkable unity of organization in this class, the diversities
observed in the distribution of the arteries in different species
of birds, is almost as great as in the diversified forms of
quadrupeds.

The venous blood is returned from the feet and legs of
birds by the deep-seated fibular and tibial veins which unite
to form the femoral trunk, and this uniting with the ischiadic
from the muscular parts around the pelvis, forms the prin-

SANGUIFEROUS SYSTEM. 501

cipal trunk of the iliac vein on each side, the course of the
superficial veins on the legs and arms imitating in some
degree their distribution in quadrupeds. After receiving the
haemorrhoidal, the emulgent, the caudal, the hypogastric, the
spermatic, and other veins of the pelvis, the two iliacs unite
to form the inferior cava, which in advancing to the heart,
receives the trunks of numerous distinct hepatic veins which
emanate from behind the liver, and the inferior cava forms
the same capacious sinus in diving birds as in other diving
animals. The smaller branches of the inferior cava anas-
tomose freely with the mesenteric veins proceeding to form
the vena portre of the liver, and others, advancing from the
posterior part of the pelvis, form two trunks which penetrate
the kidneys, and appear to form a renal portal circulation to
contribute to the secretion of these organs. The principal
part of the venous blood however, from the chylopoietic
organs, from the spleen, the pancreas, the stomach and intes-
tines, is collected into the great trunk of the portal vein, to
be transmitted with the blood of the hephatic artery, through
the lobes of the liver, and by the free communications of
these two portal systems, the renal and the hephatic, they
are capable of relieving each other, as well as the inferior cava,
the sinus venosus, and the heart.

The venous blood is returned from the hand and fore-arm
chiefly by two veins, which unite at the bend of the arm to form
the humeral vein, and these vessels accompany the correspond-
ing arteries, but in a more superficial position. The axillary or
subclavian vein on each side, after receiving the superficial
and deep-seated branches around the shoulder and fore part
of the trunk, unites with the jugular and vertebral vein to
form the superior vena cava of its respective side. The
vertebral vein of each side anastomoses freely at the exterior
of the base of the skull with the branches of the single jugular
vein, and accompanies the vertebral artery and cervical por-
tion of the sympathetic, through the canal of the transverse
processes, receiving the blood from the sinuses of the brain,
the cervical portion of the spinal chord, and the back parts
of the neck. The jugular veins are single on each side, and
anastomose freely with each other, as well as with the ver-
tebral veins, below the base of the skull, so that a free
circulation is provided for under the various circumstances

502 SANGUIFEROUS SYSTEM.

of external pressure to which the head and neck of birds are
exposed. They receive the blood chiefly from the external
parts of the head, and the oesophagus, crop, and other parts
of the neck, and, passing down superficially, along with the
pneumo-gastric nerve, they unite with the subclavian and
vertebral vein on each side, to form the right and left
superior venae cavse, as in the inferior vertebrata and most of
the lower mammalia.

The venous blood thus conveyed to the right auricle
by the single inferior and the two superior venee cavee, is
sent by the right ventricle into the pulmonary artery, pro-
vided at its orifice with three semilunar valves, like the
aorta, which immediately divides into a right and left
branch, to ramify through the corresponding lungs. The
two pulmonary veins return the arterialized blood to the left
auricle of the heart by a single orifice, which is partially pro-
tected by a semilunar valve. The pulmonary arteries of
birds communicate at an early period with the aorta, by
means of the posterior pair of branchial arches, forming a
ductus arteriosus on each side, as in the lower pulmonated
vertebrata, and the latest of these ductus arteriosi to become
obliterated, is the one upon the left side, which also remains
alone to a late period in the foetal condition of mammalia.
The two brachio-cephalic arteries result from the metamor-
phosis of the anterior branchial or aortic arches of the em-
bryo, the descending aorta from that of the middle arch of
the left side, and the pulmonary arteries, as usual, from the
posterior aortic arch. So that the peculiarities in the struc-
ture of the heart of birds, and in the course of their sangui-
ferous vessels, are alike affinities to the lower reptiles and to
the inferior tribes of mammalia, and the metamorphosis of
their branchial arches is in accordance with that of all the
other pulmonated vertebrata.

The same plan of structure observed in the vascular system
of the lower vertebrata, has arrived at its maximum of
development in the mammiferous animals, especially in the
higher quadrupeds and in man, but numerous modifications
of this complex hydraulic apparatus are necessarily presented
in this varied and extensive class, depending on differences
in the structure and condition of internal parts, or in the
general outward form of the body, or connected with pecu-
liarities in the living habits of species. The right and left

SAXGUIFEROUS SYSTEM. 503

cavities of the heart are always separated, at maturity, by
impervious septa; the descending aorta is formed by the
right arch, and not by the left as in birds ; the thick mus-
cular fold of the right ventricle of inferior vertebrata is here,
with few exceptions, as the ornithorhyncus, supplied by a
more delicate and complicated membranous tricuspid valve ;
the fibrous and serous coats of the vessels are more distinct ;
the valvular apparatus throughout the sanguiferous system
is more perfect and effective, and the valves of the veins
more numerous than in the inferior classes; the whole
heart is proportionately larger, and situate more posteriorly
in the trunk. The depressed and flattened form of the heart,
common in the chondropterygious fishes and chelonian rep-
tiles, is seen in the lowest mammalia, as in many of the
edentulous, the pachydermatous, and the cetaceous animals,
where we observe also in the adult condition of the herbi-
vorous lamantins, the rytinse, and the dugongs, the primi-
tive cleft or detached form of the two ventricles, throughout
half their extent from the apex towards the base, as in the
embryo state of this organ in higher animals and in man.
This retention of the earlier bifid condition of the apex of
the heart, resulting from the drawing up of the septum in
dividing the original single ventricular cavity into two, which
is seen also in the porpoise and slightly in the seal, is in
accordance with the general inferiority marked in the other
systems of these lower aquatic mammalia.

The first portions of the two great arterial trunks, near
their origins from the heart, are sometimes found enlarged
in cetacea, like the bulbi arteriosi of inferior classes ; and in
the diving amphibious mammalia, as the seals, besides the
usual dilated inferior vena cava or sinus venosus common in
most aquatic vertebrata, to allow of their prolonged submer-
sion and suspended respiration, we often find the foramen
ovale, the ductus arteriosus, and the ductus venosus, remain-
ing to the adult state, quite pervious as in the earlier foetus
of higher tribes. The parietes of the ventricles are thicker
in mammalia than in lower classes, the right ventricle is less
extended around the left. than in birds, and the interior
surface of these cavities is more even, and presents fewer
detached muscular chords, than in reptiles. In the lower
orders of mammalia the heart is generally more median in

504 SANGUIFEROUS SYSTEM.

its position, extending along the middle of the sternum, and
more longitudinal in its direction, with the apex at a variable
distance from the diaphragm, than in the higher quadrupeds
and man, where it is directed more transversely, inclines to
the ribs of the left side with its apex, and rests with its
pericardium contiguous to the diaphragm. The right ven-
tricle being shorter and broader than the left, the superficial
groove of separation between them lies to the right side of
the apex, and marks the direction of the coronary arteries,
which arise from the commencement of the aorta; the
coronary veins terminate by a valved orifice directly in the
right auricle, which generally presents a distinct muscular
auricular appendix, a permanent fossa ovalis, and a remnant,
more or less distinct, of the Eustachian valve so important
in the foetus. The nerves of the heart are derived from the
great sympathetic and the pneumogastric, as in other classes.
The entire heart is more oblique in its position, with its
posterior surface more approximated to the diaphragm, and
the pericardium is more intimately connected by cellular sub-
stance to the middle tendinous part of that muscle, in man
and the higher quadrumana, than in the inferior quadrupeds
where the lower vena cava is consequently longer. It is also
sinistral in its direction in the mole, from the size of the right
lung. It is also in man and the quadrumana that we find
the Eustachian valve most developed, and in several rodentia.
The muscular parietes of the right ventricle appear propor-
tionately thicker in the porpoise and other cetacea, than in
terrestrial quadrupeds. In the right ventricle of the ornitho-
rhynchus, the tricuspid valve is muscular, like that of a bird.
The semilunar valves, at the origins of the aorta and pulmo-
nary artery, are three in number, as in birds, and are provided
with the same prominent corpuscula Aurantii in the middle
of their free margin, and here also the coronary arteries, to
supply the heart, commence in the foss£e behind these valves.
In the heart of many of the adult ruminating and pachyder-
matous quadrupeds, one or two considerable cruciform
osseous laminae are almost constantly found at the base of
the septum ventriculorum, between the origins of the great
arteries from the ventricles, as seen also in the adult saurian
and chelonian reptiles.

In the mammalia as in birds, there are most generally

SANGUIFEROUS SYSTEM. 505

but two branches sent from the arch of the aorta, for the
nourishment of the anterior parts of the body, and this
structure has been observed among species the most dissi-
milar of nearly all the orders of this class. In some of the
cetacea, pachyderma, and edentata, and in most of the
rodentia, masupialia, and carnivora, the first trunk from the
arch of the aorta is the great brachio-cephalic or innominata
which gives off the right subclavian and the two common
carotids, and the second or left trunk from the aortic arch
is the left subclavian, which arises separately as in man.
In some of the cheiroptera and insectivora, as vespertilio and
talpa, the two aortic trunks consist, as in most of the feathered
tribes, of two similar brachio-cephalic arteries which divide
each into a subclavian and a common carotid. In the lowest
herbivorous quadrupeds, the ruminantia and the allied solid-
ungulous pachyderma, one trunk only arises from the arch
of the aorta as in the chelonian reptiles, but this single great
brachio-cephalic trunk here divides into two unequal branches,
the larger on the right side giving off the right subclavian
and the united trunk of both common carotid arteries, and
the smaller branch being the subclavian artery of the left
side. In the elephant, however, the right as well as the left
subclavian has a separate origin, making thus three branches
from the arch of the aorta, the middle one of which is the
united trunk of the two common carotid arteries.

In the higher quadrumana and in man, as seen in the an-
nexed figure (142) of the adult and foetalhuman vascular trunks,
there are three branches from the arch of the aorta, for the
anterior parts of the body, the first being the right brachio-
cephalic or arteria innominata (142. A. g. h.) which divides
into the subclavian and common carotid of the right side, the
second forming the left common carotid (142. A. i.), and the
third branch being the subclavian (142. A. k.) of the left
side. The same structure is seen in some insectivorous and
carnivorous quadrupeds, as the hedgehog and seal, and in
some of the lower orders of mammalia, as in the beaver, the
hamster, the rat, the sloth, the armadillo, the ant-eater, and
the ornithorynchus ; and most of the other normal forms of
these aortic trunks met with in inferior tribes, occasionally
present themselves as abnormal varieties in the human body.
So that the arterial trunks which most generally come off

506

SAXGL'IFEROUS SYSTEM.

directly or separately from the arch of the aorta, are those of
the left side, the left subclavian and the left carotid, as
might be inferred from their greater distance from the heart,
the prime mover of the circulation.

FIG. 142.

There is great uniformity in the distribution of these aortic
trunks in man and the inferior mammalia, as in the structure
of the organs which they supply. The common carotid
(142. A. k. i.) on each side divides, at the side of the larynx,
into an external and an internal carotid artery, without
giving any branch from the common trunk. The external

SANGUIFEROUS SYSTEM. 507

carotid commonly gives off, a superior thyroid to the thyroid
gland and larynx, a lingual branch to the tongue, a. facial or
external maxillary extensively ramified on the external and
internal parts of the face, an inferior thyroid which, how-
ever, in the short neck of man, is derived from the subcla-
vian, a small ascending pharyngeal to the pharynx and ad-
joining parts, an occipital to the posterior parts of the head
and neck, a posterior auricular chiefly to the external and
internal parts of the ear, a large temporal to the exterior
lateral parts of the head, and a larger internal maxillary
artery extensively distributed on the deep-seated parts of the
face, the teeth of the upper and lower jaws, and the lining
membrane of cranium. In the long necks of ruminating
quadrupeds the inferior thyroid artery is restricted to the
thyroid gland, and the superior thyroid to the larynx, and
in the myrmecophaga tridactyla both right and left superior
thyroid and the left inferior thyroid, have their place sup-
plied by a single branch from the trunk of the right brachio-
cephalic artery, which is ramified on the thyroid gland and
the larynx.

The internal carotid artery passes in a tortuous manner to
the foramen caroticum, by which it enters the cranium to be
distributed chiefly on the anterior and middle parts of the
brain, the posterior parts being supplied by the vertebral
artery, and the membranes by the meningeal branches from
the external carotid ; so that the internal carotid varies much
in its relative size according to that of the anterior parts of
the brain, being a small branch in the inferior mammalia, as
in the lower classes of vertebrata, and a large division of the
common carotid in the higher carnivora, quadrumana, and
man. The internal carotids of the ruminantia, on arriving
at the sides of the sella turcica, subdivide into innumerable
minute anastomosing twigs, forming a rete mirabile, and these
twigs again unite to recompose the arterial trunks, before
they are distributed on the pia mater to penetrate the deli-
cate texture of the brain. This structure resembles that of
the plexuses of the brachial and femoral arteries in tardigrade
quadrupeds, and serves the same function in retarding the
impetus of the blood in the long pendent neck of these
animals, before entering the brain. The same structure is
found also in some of the more powerful carnivora, and in a

508 SANGUIFEROUS SYSTEM.

few other quadrupeds, whose living habits necessitate this
protection, and whose cerebral blood is chiefly derived
from the internal carotid. In the erect bodies of man and
the higher quadrumana it is not developed, nor is it required
in the small internal carotids of the rodentia, where these
vessels are often less than the vertebral arteries, nor in the
plantigrade carnivora. On traversing the carotid canal of
the temporal bone, and the cavernous sinus of the dura
mater, the internal carotid artery, on each side, sends for-
wards an ophthalmic branch to pass, with the optic nerve,
through the foramen opticum, to the organ of vision and
the surrounding parts. It sends backwards a posterior com-
municating branch to unite with the posterior cerebral branch
of the basilar, and, advancing forwards, it gives off the
anterior cerebral which anastomoses with its opposite, by a
very short anterior communicating branch, before turning
upwards to ramify on the cerebral convolutions above the
corpus callosum. The internal carotid sends outwards like-
wise a middle cerebral artery, along the fissure of Sylvius, to
be distributed chiefly on the anterior and middle parts of the
brain. The numerous windings, anastomoses, and subdi-
visions of the internal carotid or cerebral arteries on the pia
mater of mammalia, and the more complicated retia mira-
bilia, serve to prepare these nutritious vessels, for pene-
trating in safety the delicate texture of the brain, as the
nutritious arteries of bone subdivide on its perios-
tium.

The subclavian artery on each side (142. A. b. k.} is chiefly
appropriated to the atlantal extremities, and varies in its size
and distribution according to the development and form of
these members; it sends also branches to the head and
anterior parts of the trunk, as the vertebral, the superior
intercostal, the internal mammary, several scapular and
cervical arteries, and, in man, the inferior thyroid which
in other mammalia comes from the external carotid. The
vertebral arteries ascend to the foramen occipitale, through
the foramina in the transverse processes of the cervical ver-
tebrae, giving off branches to the spinal chord and the dura
mater ; and, after winding round the articular processes of
the atlas, and entering the occipital foramen, they unite
below the medulla oblongata, to compose the trunk of the

SANGUIFEROUS SYSTEM. 509

basilar artery, which is distributed chiefly in the cerebellum
and posterior parts of the brain. In the bradypus tridactylus
the vertebral artery enters the foramen of the eighth
vertebra from the occiput, in most mammalia it enters
that of the seventh, and in man and many other species
it enters that of the sixth or the fifth cervical vertebrae.
Instead of a rete mirabile, it assumes a tortuous course, like
the internal carotid, before entering the cranium. The ver-
tebral artery is often as large as the internal carotid, as in
the guinea-pig and the agouti, where the latter artery is only
a small branch of the internal maxillary, and where the circle
of Willis is formed principally by the branches of the large
basilar artery. In some other species, as the marmot and
the porcupine, the vertebral arteries exceed in magnitude the
internal carotids. In the hybernating cheiroptera, which
generally hang suspended by the feet with their head down-
wards, and where there is no protecting rete mirabile on the
internal carotid, the cerebral blood is chiefly conveyed through
the large vertebral arteries. In the ruminantia, as in birds,
the vertebral arteries are distributed principally on the ex-
terior, and not the internal, parts of the head, these vessels
anastomosing more or less extensively with the occipital
branches of the external carotids, and not passing inwards
to form the basilar artery : so that these quadrupeds, with
their small internal carotids, have generally the exterior
parts of their head greatly developed, at the expense of the
more important intellectual organs. The great size of the
cerebellum of rodentia, and the imperfect development of
their smooth bird-like cerebral hemispheres, appear also to
be connected with the magnitude of their vertebral arteries
and the minuteness of their internal carotid or cerebral
arteries.

The superior intercostals supply the anterior intercostal
spaces ; the internal mammaries send branches to the
diaphragm, the mediastinum, the pericardium, and to the
mammary glands when pectoral, and also branches to anas-
tomose with the epigastrics from the external iliacs ; the
scapular and cervical arteries chiefly supply the muscles of
the shoulder and neck. The great trunk of the subclavian
continues its course as axillary and brachial artery, sending
off numerous thoracic and circumflex branches to the mus-

510 SANGUIFEROUS SYSTEM.

cular and deep-seated parts around the shoulder joint, and
branches to the parts along the humerus, at the lower part
of which it divides into the radial and ulnar arteries to sup-
ply the fore-arm and hand, as in the inferior classes and in
man. The ulnar artery generally sends off, near its
origin, a considerable interosseous branch to supply the an-
terior and posterior parts of the interosseous space. The
radial and ulnar arteries, after giving off several important
branches in their course to the wrist, form a deep-seated and
a superficial palmar arch, which anastomose with each other,
and supply arteries to the hand, and collateral branches to
the sides of the fingers according to their number in the
different mammalia, like the plantar arches of the posterior
extremities.

The bifurcation of the brachial artery in the short
arm of the cetacea, and in the ornithorhynchus, the
marsupialia, and several quadrumana, takes place much
higher than in man, and in the ruminantia, the solidungula,
and some of the rodentia, as the marmot, much lower on the
fore-arm. In the walrus, the brachial continues undivided
to the metacarpus. In most carnivora, and many rodentia,
edentata, monotrema, marsupialia, insectivora, and quadru-
mana, animals with free prehensile use of their arms, the
brachial artery, sometimes the ulnar, passes palmad through
the osseous canal above the inner condyle of the humerus,
accompanied by the median nerve, to protect them from pres-
sure. But in the tardigrade mammalia with a plexiform
humeral artery, the vessel is not protected by an osseous
canal, and in the myrmecophagse, where this epitrochlear
canal is present, it transmits only the median nerve, while
the plexiform brachial artery passes free over the inner mar-
gin of the humerus. The radial and ulnar arteries are equally
present, where the ulna is only rudimentary or wanting ; but
in the seal and walrus the brachial artery continues to the
wrist, and supplies their place. The hand of solidungula is
supplied with collateral branches as one finger, and that of
ruminantia as two ; but the vessels are less regular in the
rudimentary fingers. In the tardigrade sloths and loris, the
brachial and femoral arteries give off at their origins, several
trunks which subdivide into numerous anastomosing plexi-
form branches, and which follow them in their course enve-
loping the primary trunks and sending twigs to the muscles

SANGUIFEROUS SYSTEM. 511

and at length reunite with them to compose the usual trunks
which give off the arteries of the fore-arm and leg. This plexi-
form structure exists also in the extremities and tail of the
ant-eaters, in the long legs of the tarsius, in the arms of the
porpoise and the lamantine, and perhaps in many other mam-
malia, and it resembles the rete mirabile of the internal
carotids in other tribes, where the plexiform branches however,
reunite to compose the trunks of the cerebral arteries. In the
two-toed ant-eater, the arterial plexus envelopes the com-
mencement of the radial and ulnar arteries, as well as the
trunk of the brachial; but in the lamantin, and also in the
porpoise, the trunks of these arteries are entirely subdivided
into fasciculi of minute vessels, and even the branches which
they appear to give off, are only smaller fasciculi of the same
minute plexiform arteries. This structure appears to be general
in the arms of cetacea, and is probably connected with the
limited mobility of these members, as supposed by Bear ;
the plexiform condition of the arterial trunks is seen also
in the legs of many birds.

As the parts supplied by the descending aorta are more
uniform in their character, than those nourished by the
ascending branches, the arteries of the trunk are more con-
stant arid less modified than those of the extremities in the
different tribes of mammalia, and vary little from the ar-
rangement presented by these vessels in the human body. In
the thorax, the descending aorta (142. A. q. q.) commonly
gives off two or more bronchial arteries, to accompany the
ramifications of the bronchi, and nourish the lungs ; several
small asophageal branches, to that part of the alimentary
canal ; minute posterior mcdiastinal arteries, to the pericar-
dium ; and a variable number of symmetrical pairs of inter-
cost als (142. A. q. r.), chiefly to the muscular parts of the
thorax. In many of the cetacea are observed numerous
azygous intercostal arteries, arising from the posterior and
median part of the thoracic aorta, which form a compact mass
of arterial plexuses, lining the whole dorsal part of the chest,
surrounding the vertebral column, penetrating the vertebral
canal, enveloping the spinal chord, and even extending to
the interior of the cranium. They are enveloped in a loose
elastic cellular tissue, accompanied with corresponding plex-
uses of veins, and have been supposed connected with the

512 SANGUIFEROUS SYSTEM.

secretion of the large external deposit of adipose substance,
or destined to preserve the high temperature of the nervous
axis and other internal organs.

On passing into the abdomen, between the crura of the
diaphragm, the aorta gives off from its sides, the two small
phrenic arteries (142. A. above r.) to the diaphragm ; two or
more minute supra-renals to the supra-renal capsules ; the
two renal arteries to the kidneys ; a pair of spermatic arteries
(142. A. £.), to the testicles, or to their analogues the ova-
ries, according to the sex ; and a variable number of symme-
trical pairs of lumbar arteries, destined to supply the exterior
parietes of the abdomen, like the intercostals of the thorax.
The largest and most important trunks, however, arise from
the anterior median part of the abdominal aorta, and are the
caliac (142. A. r.) which sends off the coronary to the sto-
mach, the hepatic to the liver, and the splenic to the spleen ;
the superior mesenteric (142. A. s.), which arises near the
coeliac, and supplies the small intestine and part of the colon,
and the small inferior mesenteric (142. A. u.), which arises
near the commencement of the iliac arteries, and is distributed
on the colon and rectum. The direct pelvic continuation of
the abdominal aorta is the caudal or median sacral artery (142.
A. between v. w.), which, in man, and in other tail-less and
long-legged mammalia, forms but a small branch compared
with the two iliacs (142. A. v. w.), which appear to constitute
a bifurcation of the entire trunk ; but in the cetacea, and
other long-tailed species, the proportions are very different.
In man and a few of the higher quadrupeds, the aorta gives
off two large common iliac arteries (142. A. v. w.}, each of
which divides into an internal iliac (142. A. y. ?/.) appropriated
to the viscera of the pelvis, and a larger external iliac (142. A.
x. x.] to supply the leg ; but in most of the lower mammalia,
as in ruminantia, rodentia, marsupialia, carnivora, and other
orders, the internal iliac arteries arise separately from the
prolonged trunk of the aorta behind the external iliacs.
From the want of legs in the cetacea, they have no external iliacs.

The internal iliac artery of each side furnishes the ilio-lunt-
bar branch, to the muscles of that region ; the obturator,
chiefly to the ilio-femoral joint and the adductor muscles of
the thigh; the gluteal, to the glutei and other external
muscles of the pelvis ; the lateral sacral, to the sacrum and
its exterior muscles, and to the terminal portion of the spinal

SANGUIFEROUS SYSTEM. 513

chord ; the ischiatic, principally to the muscular parts around
the anus ; and the pudic, which commonly affords branches
to the uterus, the bladder, and the external parts of genera-
tion. The external iliac artery (142. A. x. #.), before escap-
ing from the pelvis, through the crural arch, to become the
femoral, gives off the epigastric which sends branches to the
peritoneum, the scrotum, and adjacent parts, and establishes
anastomoses with the internal mammary and the inferior
inter costals ; and the circumflex ilii, which supplies chiefly
the anterior muscular parietes of the abdomen. The femoral
artery, after furnishing several small branches chiefly to the
muscles of the groin and lower part of the abdomen, gives off
the large profunda femoris, which is extensively ramified on
the powerful muscles of the thigh ; and becoming popliteal
behind the knee, the trunk divides, at a variable distance
below that joint, into the great anterior and posterior tibial
arteries, which descend, ramifying to the toes, like the radial
and ulnar arteries of the arm.

The femoral artery divides higher in the ruminantia,
and the two tibials anastomose behind the first pha-
langes of the foot. The branches which supply the legs
of the ornithorhyncus, appear to be derived chiefly from
the internal iliacs. The femoral artery in the plantigrade
carnivora, divides into the two tibials, near the upper
part of the thigh, and the posterior tibial forms the
internal and external plantar arteries, below the middle of the
tibia. In most of the lower nocturnal quadrumana, the fe-
moral artery divides nearly as high as the crural arch, and its
branches subdivide into anastomosing plexuses, as on the
anterior extremities ; and this subdivision into minute plexi-
form branches, takes place to a greater extent in the femoral
arteries of the sloths and ant-eaters. The external iliac, in
many orders of mammalia, gives origin to the ilio- lumbar ar-
tery, and the profunda femoris to the epigastric. The epi-
gastric in the tiger arises from the internal iliac. In the
large tailed quadrupeds, as the otter, the external iliacs are
but moderate branches, from the great prolonged aorta,
which, after giving off, as in most other mammalia, the in-
ternal iliacs separately, continues its course backwards under
the bodies of the coccygeal vertebree, sending off regular pairs
of transverse branches at the vertebral articulations, like the
intercostal and lumbar arteries of the thorax and abdomen.

PART VI. L L

514 SANGUTFEROUS SYSTEM.

The internal iliacs alone arise from the aorta, in the cetacea,
there being no legs to necessitate external iliacs, and the
epigastrics take their origin from the internal iliacs. The
prolonged aorta, or caudal artery, of these animals, continues
its trunk, rapidly diminishing, under the coccygeal vertebrae
to beyond the first half of the tail, where it is at length
entirely lost in the numerous plexiform branches, which it
gives off in its whole course backwards from the abdomen.
The trunk of the artery is thus far continued amidst its
plexiform branches, as in the arms of the bradypus ; but in
the last portion of the tail, the artery is entirely reduced to
plexiform branches, as in the extremities of the loris, the
tarsius, and the myrmecophagee. This plexiform condi-
tion is seen also in the caudal artery of the ant-eaters, and
in the internal iliac arteries of the three-toed sloth. In the
marsupial quadrupeds, the great development of the external
iliac and the caudal arteries, and especially of the epigastrics
which supply the mammae and the pouch, and the small size
of the internal iliacs, and their uterine branches, render these
animals incapable of maturing a foetus in utero, and necessi-
tate an early abortion, as a normal character in that remark-
able order of mammalia.

The capillaries into which the systemic arteries ultimately
divide, after constituting plexiform ramifications in the tissue
of every organ of the body, and transuding through their
parietes the various materials of their nutriment, unite to
form the branches of the returning veins. The veins convey
the blood to the right side of the heart, from the anterior
parts of the body, by one or two superior venae cavae ; from
the parts below the diaphragm, by one inferior vena cava ;
and from the heart itself, by one or more coronary veins. In
the muscular and moving parts, as the extremities and the
lungs, the return of the blood is aided by the development of
numerous small semilunar valves in the interior of the veins,
which are not required in those of the more tranquil internal
viscera, as the brain and the liver. The venous blood col-
lected from the brain and cranial cavity, is transmitted from
the sinuses of the dura mater, through the posterior foramen
lacerum on each side, into the two internal jugular veins,
•\vhich, in descending along the sides of the neck, receive
also the lingual, the pharyngeal* the occipital, the facial, and
the superior thyroid veins, before they terminate in the great
trunks of the subclavian veins (142. A. a. b.) The external

SANGUIFEROUS SYSTEM. 515

jugulars formed chiefly by the temporal and internal maxil-
lary veins, and receiving the blood from the external and
lower parts of the neck, enter likewise the subclavian veins,
exterior to the former. In many of the inferior quadrupeds,
especially in all the hybernating tribes, the venous blood is
returned from the brain, not by the internal jugulars, but
from the anterior ramus of the lateral sinuses, through the
temporal canal on each side, into the external jugular veins,
and also by the vertebral veins which here unite with the
external jugulars.

From the anterior extremities, the blood is returned by
the cutaneous radial and ulnar, or the cephalic and basilic
veins, and by the deeper-seated anastomosing brachial veins
which accompany the corresponding arteries throughout
their ramifications, each artery being accompanied by two
veins which freely anastomose with each other around that
vessel. The union of these veins from the arm, forms the
axillary, on each side, which, after becoming enlarged by the
addition of numerous scapular and thoracic branches, is con-
tinued into the subclavian. The two subclavian veins, after
receiving the internal and external jugulars and the two
vertebral veins which follow the course of the vertebral arte-
ries, become the brachio-cephalic trunks (142. A. B. a. b.),
which form, by their union, in most mammalia, the superior
vena cava (142. A. c.) In many of the inferior species of
mammalia, however, as among the rodentia, monotrema,
marsupialia, and in the elephant, the hedgehog, and some of
the chiroptera, the brachio-cephalic veins continue separate
to the right auricle, thus constituting two distinct superior
cav(B, as found in birds and reptiles, and occasionally as an
abnormal character in man. The brachio-cephalics receive
also the inferior thyroid, and the internal mammary veins ;
and the superior vena cava, formed by their union, receives,
in its course to the heart, some small pericardial and medias-
tinal branches, and the great vena azygos, which establishes
important communications with several branches of the
inferior cava. The vena azygos, in the ornithorhynchus,
where the superior cava is double, opens into that of the left
side. The blood conveyed by the coronary arteries to
nourish the heart, is returned to the right auricle (142. A. d.),
chiefly by one great coronary vein, which enters the back part
of that cavity near the septum auricularum ; where the

L L 2

516 SANGUIFEROUS SYSTEM.

superior cava is double, the coronary vein enters the left
superior cava, as in birds.

The inferior vena cava is single, receives the venous blood
of the abdomen, pelvis, and posterior extremities, and con-
veys it to the right auricle (142. A. d.}, to be sent with that
from the superior cava, through the right ventricle and the
pulmonary organs, for respiration. In the legs, as in the
arms, the blood is returned by great subcutaneous veins,
and by deep-seated venae comites which follow, in anasto-
mosing pairs, the course of the large arteries and their
branches. The great vena saphena interna and the smaller
vena saphena externa, like the cephalic and basilic veins of
the arm, follow a superficial course on the leg ; the former
ascending along the inner part of the leg, after receiving the
superficial epigastric and pudic veins, terminates in the trunk
of the femoral vein, as high as the groin; the latter smaller
branch, following an exterior and dorsal course, ends in the
popliteal vein. The deep seated anterior and posterior
tibial veins, and the peroneal branch of the latter, likewise
unite to form the popliteal vein. Becoming femoral and
external iliac (142. A. 1. 1.), the great vein of the leg, like
the corresponding artery, receives the internal iliac vein (142.
A. 2. 2.) to constitute, by their union, the trunk of the com-
mon iliac (142. A. 3. 3.)

The large branches of the internal iliac veins, derived
from the viscera and parietes of the pelvis, anastomose
freely with each other, and form numerous plexuses
around these organs. The union of the common iliac
veins (142. A. 3. 3.), forms the great trunk of the vena cava
inferior (142. A. 4.), which in ascending along the right side
of the aorta, to perforate the diaphragm, the pericardium,
and the right auricle, receives the middle sacral, the lumbar,
the spermatic (142. A. 5.), the renal (142. A. f.), the capsular,
and the inferior diaphragmatic veins, and the numerous
trunks of the venae hepaticcs (142. A. 8. 9.), which penetrate
the inferior cava as it passes behind the liver. The veins
from the chylopoietic viscera of the abdomen, form frequent
anastomoses, and unite to constitute the two great trunks of
the splenic (142. A. 10.), and inferior metenteric (142. A. 11.)
veins. The union of these venous trunks forms that of the
vtna portce (142. A. 12.), which ramifies through the right
(142. A. 14.), and left (142. A. 13.) lobes of the liver, accom-
panied by the ramifications of the hepatic artery. The united

SANGUIFEBOUS SYSTEM. 51/

capillaries of these venous and arterial ramifications, through
the mass and around the tubuli biliferi of the liver, constitute
the roots of the hepatic veins (142. A. 8. 9.), which enter the
inferior cava before it perforates the diaphragm and pericar-
dium to open into the lower part of the right auricle.

From the right ventricle, the entire venous blood of the
system is sent through a single pulmonary artery (142. A.
/.), provided with three semilunar valves with thickened mar-
gins, with corpuscula in their middle, and with fossae be-
hind them. The pulmonary artery divides into a right and
left trunk (142. A. n. m.), each of which subdivides accord-
ing to the divisions of the bronchi which they accompany,
and to the number of the lobes of the lungs, around the
cells of which they are distributed, as around the tubuli
and cells of a gland — the lungs being merely a gland for
secreting carbon, originating with a blastema and deve-
loping as other glands, and sending its secretion in a gaseous
form through its duct, the trachea. The blood arterialized
in the capillaries of the lungs, is returned to the left side of
the heart, by a variable number of pulmonary veins, which
open commonly by four or six or sometimes by two orifices
unprovided with salves, or even by a single aperture, into
the left auricle.

There is thus great unity of plan in the distribution of the
arteries and veins throughout the vertebrated classes, and
there is much analogy between the vessels of the anterior and
the posterior portions of the trunk, and between those of the
atlantal and sacral extremities. The common iliac arteries
and veins are analogous to the arterial and venous brachio-
cephalics, and their branches mutually resemble. The
superior vena cava is single in the higher mammalia and in
man, because their heart is placed farther backwards from
the head, and the brachio-cephalic veins are thus enabled to
unite before they arrive at that cavity. But in the inferior
tribes, where the heart is situate more anteriorly in the trunk,
the two brachio- cephalics enter that organ as separate superior
venae cavfc, before the extent of their course has allowed them
to meet and unite. The posterior vena cava is longer than
the anterior, throughout the vertebrata, as the abdominal or
posterior portion of the aorta is longer than the brachio-
cephalic or anterior trunks, because the heart, in this highest
subkingdom of animals, constantly retreating from the head

518 SANGUIFEROUS SYSTEM.

as we ascend from fishes to man, has not yet reached the
middle of the trunk of the body.

The various grades of development in the sanguiferous
system, thus traced throughout the animal kingdom, are
successively represented in the transient forms which this
system assumes during its development in all the higher
animals and man. The colourless blood of the embryo at
first moves through the germinal membrane in two conti-
guous circles, like that of the lowest annelides ; and when, at
length, vessels are distinctly formed, the pale red blood con-
tinues to circulate in closed arteries and veins, without the
aid of a heart, as in all the radiated and many higher tribes
of animals* The pulsating, heart-forming centre of this
system, becomes, as in worms and insects, a dilated dorsal
vessel; and the punctum saliens forms a muscular ventri-
cle, which developes an auricle behind it, and a bulbus ar-
teriosus on its anterior part. Beyond this bulb, the
aorta early divides into five successive pairs of deciduous
branchial arteries, and the embryonic branchial open-
ings on the sides of the neck have been retained to ma-
turity, as an abnormal condition, in the human body.
The cavities of the heart lose their primitive rectilineal posi-
tion, which they retain in the gasteropods ; the auricle gra-
dually doubles up behind the base of the ventricle, and
arrives at that dorsal position, with regard to it, which it
retains in fishes; the two ends of the primitive, conti-
nuous, heart-forming, dorsal vessel, are now become posterior
vena cava and aorta, where the blood still moves through
the cavities of the heart, as in insects, from behind forwards.

The three anterior branchial arteries, forming simple
aortic arches in man, as in mammalia, birds, and rep-
tiles, are successively converted into the ascending trunks
from the arch of the aorta. The fourth arch forms the
descending aorta, and the posterior arch the pulmonary
arteries, as during the metamorphosis of a frog. So
that man's vascular system, arrived at the possession
of a single muscular ventricle, represents that of the
highest Crustacea ; with an auricle and ventricle placed
in a line, it becomes that of a gasteropod ; and with a
developed bulbus arteriosus, an auricle advanced upon
the ventricle, and the aorta divided into branchial arches,
it is raised to that of fishes — the embryos of all

SANGUIFEROUS SYSTEM. 519

higher vertebrata. The development of a second auricle by a
septum rising through the first, the partial division of the
ventricle by a muscular septum, the imperfect separation of
the venous from the arterialized blood, the entire metamor-
phosis of the branchial arches, and the development of the
pulmonary arteries, change, at length, this system of the
human embryo to that of an air-breathing reptile. The
ascending septum of the yet single ventricle, draws up and
cleaves the apex of the embryo's heart, and makes it double,
like that preserved through life in the lamantin and the
dugong ; and this septum, on reaching to the origin of the still
single systemic artery, divides it also to the extent of the
ductus arteriosus, arid entirely severs that portion, con-
taining the pulmonary arteries, from the primitive bulb of the
aorta. The septum of the auricles is developed in man, as
in the reptile, before that of the ventricles; but the sep-
tum of his ventricles is necessarily completed, before the
entire separation of the auricles, at birth, by the closing
of the foramen ovale; and the reptile circulation of man in
the amniotic fluid, must be continued for a time, by a diffe-
rent route from that followed in the air-breathing animal.

The arterial blood of the human foetus (142. B. C.), as of
other mammalia, aerated and replenished by traversing the
placenta, is returned by the umbilical vein (B. 4.), to be sent,
along with the visceral blood poured into it from the vena
portce (B. 1.2. 3.), through every part of the liver (B. 5. 6).
A small portion only of the placental fluid now follows its
primitive course, from the umbilical vein (B. 4.) directly
through the ductus venosus (B. 7-)> into the inferior vena cava
(B. 11.) The portal blood (B. 1. 2. 3.) entering the dilated
sinus (B. 5.) of the umbilical vein (B. 4.), is distributed with
that of the minute hepatic artery, chiefly through the right
lobe (B. 6.) of the liver, which here is less than the left.
The arterialized fluid received from the hepatic veins, (142.
C. c.) and the ductus venosus (C. b.), is conveyed, along with
the blood of the abdominal cava (C. «.), into the great vena
cava inferior (C. d.) and the right auricle (C. e.) of the heart.
By the aid of the Eustachian valve, it is directed from the
right auricle (C. e.), through the foramen ovale (C. p.), into
the left auricle (C. /.), where it mingles with the blood from
the yet small pulmonary veins (C. v.) From the left auricle
(C./.), this aerated placental fluid is conveyed through the

520 SANGUIFEROUS SYSTEM.

left auriculo-ventricular orifice, into the left ventricle (C. a.)
of the heart, by which it is propelled into the aorta (C. h)
and into all the branches (C. i. k. I.) ascending from its arch,
to nourish and develope the brain, the organs of the senses,
and all the important anterior parts of the body, so early
and largely developed in the foetus.

The blood thus rendered venous by affording nutri-
ment to the larger anterior half of the body, is returned,
in an impure state, by the superior vena cava (C. ».),
to the right auricle (C. e.) By the right auriculo-ventri-
cular orifice it passes directly into the right ventricle
(C. o.), which propels it into the pulmonary artery (C. r.)9
the ductus arteriosus (C. /.), and the descending aorta
(C. m.), to afford a scanty nutriment to the small pos-
terior parts of the trunk and the limbs, and to proceed in
mass through the large umbilical arteries (142. B. u. v.) for
fresh oxygenation in the placenta. A small portion only of
this blood is yet sent by the right (C. s. B. h.) and left (C. u.
B. i.) branches of the pulmonary artery (C. r. B. g.}, to the
rudimentary and ineffective lungs; and the external and
internal iliacs are yet but small branches of the great umbilical
arteries which here form the bifurcation of the aortal trunk.
Both ventricles thus combine, to propel the vital fluid through
the system of the foetus, and through the long and tortuous
windings of the umbilical and placental vessels, and a mixed
blood circulates through the arteries of the body, as through
the body of a cold-blooded reptile. It is only by the subse-
quent closing of the umbilical arteries and vein, and the obli-
teration of the ductus venosusy the foramen ovale, and the
ductus arteriosus, that man's circulating system is raised to
the mammiferous type, after a proteus-like career through
every inferior form presented by this system throughout the
animal kingdom.

ORGANS OF RESPIRATION. 521

CHAPTER FOURTH.

ORGANS OF RESPIRATION.

FIRST SECTION.

General observations on the Respiratory Organs.

As the function of respiration is that by which the fluids of
living bodies are oxygenated and decarbonized, and which
renovates their vital properties, and prepares them for afford-
ing the materials of their various secretions, it is one of the
most influential and most general in both kingdoms of organic
nature. Every living plant has the power of decomposing
the atmosphere, to effect its respiration, and every animal,
from the monad to man, has the power of renewing the stra-
tum of the surrounding element in contact with its exterior
or its interior surface, to aerate the fluids of its body. The
monad excites currents in the water around it, to aerate its
surface, by the rapid vibration of its cilia, and man produces
similar currents in the air, for the same purpose, by the
alternate motions of his ribs and diaphragm, and by the
myriads of vibratile cilia which line the mucous membrane
of the passages and cells of his lungs. The absorption of
oxygen from the atmosphere into the system, and the secre-
tion of carbon from the living fluids, being always effected
through delicate membranes constituting a respiratory surface,
it is obvious that this chemical function may alike be per-
formed by the general surface of the skin, or by the mucous
lining of the alimentary canal, or by any external or internal
organ especially appropriated to it. The lowest animals
respire by their general cutaneous mucous surface, without a
special organ for the convenient exposure of their fluids to
atmospheric influence, and the external skin, or its internal
mucous prolongation, is the origin of most forms of respira-
tory organs met with in higher tribes. The gills of aquatic
animals, and the pulmonic cavities of the invertebrated tribes,

522 ORGANS OF RESPIRATION.

opening on the sides of their body, are but extensions of this
general secreting integument. And the complicated lungs of
the highest classes are but internal developments of its con-
tinuation, the alimentary canal, which, though they are
adapted for an aerial product, present extensive secreting
surfaces, with excretory ducts, and vesicular terminations of
the tubuli, like other glands, to which they are allied in
function, and in mode of development, as well as in general
form and structure.

The respiratory apparatus of animals increases in extent
with the general advancement of their organization, and the
respiration is directly proportioned to their muscular force,
to the temperature of their blood, and to the general energy
of their functions. In the lowest animals, where the limited
circulation and the limited sphere of activity, require no
special respiratory organ, this function is effected by means of
vibratile cilia disposed on their exterior, which are their
common organs of locomotion, and which renew the stratum
of the surrounding element in contact with their general sur-
face; or it is effected by similar organs disposed on the
mucous lining of their alimentary canal, which cause the
external element to traverse and oxygenate that cavity. In
most aquatic animals, however, with a distinct sanguiferous
system, respiration is performed by more circumscribed
branchiae, developed from the exterior skin, like everted
lungs, on which the blood is more or less extensively distri-
buted, or by similar gills in the interior of the body, as in
echinoderma and rotifera.

Air-breathing animals are furnished with pulmonary or-
gans or lungs, closely allied to secreting glands, placed
internally, lined with vibratile cilia, and opening either on
the sides of the body, as in the invertebrata, or into the
mouth, as in the vertebrated classes. The lungs present,
as other glands, an extensive surface for the distribution
of capillary blood vessels, and they are stimulated to
activity by their own accumulated secretion. Their com-
plicated function, embracing many mechanical and chemical
changes, necessarily involves moto-sensitive, excito-motory,
and sympathetic nerves, with voluntary and involuntary
muscles, and the activity of this function in animals, is in-
versely proportioned to their tenacity of irritability and of
life. The chemical changes effected by respiration are under
the control of the minute grey filaments of the sympathetic

ORGANS OF RESPIRATION. 523

nerves with their microscopic ganglia, as all the other che-
mical functions of animal bodies. In the invertebrated classes,
the heart is systemic, and rarely assists in transmitting the
blood through the respiratory organs, but in all the verte-
brated animals these organs receive the blood directly from a
muscular ventricle, which thus contributes its force to aug-
ment the respiratory function. Respiration is the chief
source of animal heat, it is a means of conveying odorous
effluvia to the organs of smell in air-breathing animals, it is
the principal stimulus to development in all classes, and its
organs, by producing vocal sounds, give expression to the
inward feelings, and afford a means of intellectual communi-
cation at a distance through the organs of hearing.

SECOND SECTION.

Respiratory Organs of the Cyclo-neurose or Radiated
Classes.

As there is no distinct sanguiferous vascular system in
poly gastric animalcules, they appear to possess no special
organ appropriated to the function of respiration, and the
aeration of their fluids is effected through the thin pellicle
which covers their exterior, or through the mucous lining of
their alimentary cavities. The respiratory currents are pro-
duced by minute vibratile cilia, variously disposed over the
surface of the body, or around the buccal orifice ; and pro-
bably lining the alimentary canal, and the peritoneal cavity
where a cyclosis of particles is observed. These vibratile
filaments, thus early connected with the function of respi-
ration, and here serving also as organs of locomotion and even
of prehension, appear to form a part of the respiratory ap-
paratus of all the higher aquatic invertebrata, and line the
pulmonary organs throughout the vertebrated classes. Those
polygastrica which are covered externally with a horny sheath,
or with articulated laminae of silica, appear to respire by
internal currents through the buccal orifice, as in vaginiform
zoophytes. The internal cyclosis of the larger forms, as par-
ameecium, and the reticulate cutaneous connecting vessels of
the compound forms, as volvox, may also aid in this function.

The entire gelatinous substance ofporiphera is respiratory,
and the incessant currents of water through the pores, canals,

524 ORGANS OF RESPIRATION.

and vents oxygenate every part of the exterior and interior of
their body. Vibratile cilia are also the agents of the respira-
tory currents in the adult and the embryo-state ofpolypiphe-
rous animals, where these minute organs are disposed along
the sides or around the external periphery of the tentacula,
or line their interior ; and they line the buccal and gastric
cavities of the polypi, and their prolonged canals which circu-
late nutriment through the body. In hydra and actinia, the
respiratory currents of water enter the stomach by the mouth,
and are seen passing to and fro within the ciliated cavities of
their tubular tentacula ; and indeed nearly the whole exterior
surface of the body and every internal organ, in the latter
genus, are closely covered with very minute vibratile cilia,
and are bathed by the aqueous currents of respiration.

Although almost every kind of zoophyte is cilio-brachiate,
like actinia, and is amply provided with these minute organs
on the interior mucous lining of its alimentary apparatus,
the larger forms of symmetrically disposed brachial cilia are
generally confined to the lateral margins of the tentacula,
along which they move in very regular waves, following
always the same apparent direction, from the mouth of the
polypus on one side of the tentaculum, and towards the
mouth on the other ; but the direction in which these cilia
actually more is nearly vertical to the apparent plain of the
entire waves. The vibratile cilia are thus disposed on the
sides of the arms in most of the lower zoophytes, as alcyo-
nium, flustra, cellaria, serialaria, plumularia and sertularia,
which extend their elastic tentacula in a regular campanulate
form, while the ciliary currents flow towards the polypi,
aerating their surface and bringing food to their mouths from
a distance. These tentacula when severed from the body of
the polypi, continue to vibrate their cilia, and swim by their
action like worms through the water : thus showing, as in the
vibratile cilia of the mucous and serous membranes detached
from the body in all higher animals, the independence of
their movements on consciousness or volition, and their simi-
litude, in this isolated condition, to reflex or sympathetic phe-
nomena.

The number of tentacula, like the number and size
of the cilia, varies much in different zoophytes, there
being but six tentacula in some hydrce, eight in plumularia
falcata, serialaria lendiyera, and many of the higher genera
as, lobularia, ptnnatula, virgularia, isis, corallium, and gor-

ORGANS OF RESPIRATION. 525

gonia, ten in alcyonium gelatinosum, fourteen in cellaria avi-
cularia, twenty- two in flustra carbesia, and higher numbers
in alcyonella, tubularia, caryophyllia, actinia, where they
form two or more series around the mouth. In some polypi-
phera, as lobularia, pennatula, gorgonia, where the large ten-
tacular cilia are not vibratile organs, the respiratory currents
and food are directed to the mouths of the polypi, by the
minute vibratile cilia which line the buccal and gastric cavi-
ties. So that the whole interior of the polypi, and their
prolonged tubular canals, are aerated by the ciliary currents
of the surrounding element, in the minutest compound zoo-
phytes, as in the larger isolated forms of actinise.

The large fin-like vibratile cilia of beroe and other
ciliograde acalepha, disposed in symmetrical longitudinal
columns, and serving as organs of locomotion, like those
of polygastrica, must also contribute to the respiratory
function, by constantly renewing the stratum of water in
contact with the thin pellicle covering the exterior of their
soft body. These organs, however, are not branchial la-
mellee, destined to support the ramifications of blood ves-
sels, as in Crustacea and fishes. In the empty state of
the alimentary canal, the currents of water directed over
its ciliated surface, passing straight through the axis of
the body, will likewise aerate the mucous lining of that pas-
sage, as in polypi, and even in fishes. In the gaseous
swimming vesicles of the physograde species, as the physalia,
we already observe the analogue of the air-sac of fishes, and
the first rudiment of the lungs of higher vertebrata, although
they are not yet subservient to aerial respiration. In many
of the palliograde species, as aurelia, the four ovarial sacs
opening around the stomach, below the mantle, and sepa-
rated from the gastric cavity by thin septa, appear to extend
the respiratory surface ; but the greatest respiration of these
animals is probably effected by the vascular and active peri-
pheral margin of the mantle, and by passing currents of the
surrounding element through the whole ciliated interior of
their body, as seen when they are placed alive in sea water
artificially coloured.

More distinct and more complex organs are appropriated to
the function of respiration in the echinoderma than in any other
radiata, which accords with the higher development of all
their other organs. In the asterias, the upper surface of the

526 ORGANS OF RESPIRATION.

body is covered with innumerable minute transparent colour-
less fleshy tubes, which, in the living state, are seen to rise
and sink incessantly through openings of the skin, conveying
water by their ciliated parietes, for respiration, into the inte-
rior cavity of the body. Though very minute, these respira-
tory tubes resemble in form, the large inferior prehensile feet
extended through the ambulacral apertures, being, like
them, nearly cylindrical and provided with terminal open-
ings. The whole exterior and interior surfaces of the body,
and of its internal organs, and of the long ambulacral feet,
are likewise provided with vibratile organs and aerated
by ciliary currents, like the mucous and serous surfaces of
other radiata, and of most aquatic invertebrata. They cover
the exterior of the prehensile tubular feet of echinoderma,
and even the investing cutaneous membrane of the spines
on the exterior of echini. The prehensile ambulacral feet are
extended by having fluid injected into them from vesicles at
their base, and these communicate by membranous canals
with a vascular apparatus disposed around the mouth. The
surrounding element enters the peritoneal cavity by nume-
rous small membranous tubes, disposed around the lower
aperture, and bathes the abdominal viscera, in the echinida,
as in the asterida, and the vibratile cilia covering all the in-
ternal and external parts of the body, incessantly renew the
stratum of water in contact with their surface, so as to aerate
every part of the vascular system and the various tissues of
the body.

The whole irritable exterior surface of holothuria is res-
piratory, and the ciliated tubular feet which extend in lon-
gitudinal rows from its surface, and the ramified, ciliated
sheathed tentacula which surround the mouth, as the external
parts of other echinoderma and most radiata, as seen in the
annexed figure of holothuria spinosa (Fig. 143. A. B. C.) from
Port Jackson, of a red colour, and covered with calcareous
spines, like an asterias ; but the internal apparatus ap-
propriated to this function, and their communication
with the surrounding element, are more circumscribed,
and they approach nearer to the type of these organs in
higher animals. Instead of entering the general cavity
of the peritoneum by numerous minute orifices, as in
asterida and echinida, the water is inspired by holothuria
solely through the cloacal aperture (143. B. C. e. <?.),

ORGANS OF RESPIRATION.

527

and is confined to the interior of one or two hollow
ramified tubular branchiae (143. B. /. /. C. /. /.) at-
tached by a fold of peritoneum to the sides of the abdomen,
and which communicate externally only by one or two ori-
fices leading into the cloaca (143. B./".) The parietes of these
internal branchiae, which ramify throughout the whole interior
cavity of the body, like the tracheae of insects, have distinct

transverse and longitudinal muscular fibres, and support the
ramifications of the sanguiferous vessels containing the venous
blood of the system, like the internal pulmonary organs of
air-breathing animals, which they also resemble in their
rythmic movements of dilatation and contraction ; and many
larvae of aquatic insects inspire, like holothuria, through the
anus and the cloaca.

528 ORGANS OF RESPIRATION,

THIRD SECTION.

Respiratory Organs of the Diploneurose or Articulated
Classes.

In the sluggish helminthoid classes of articulata the respi-
ration is nearly always aquatic, but in the active entomoid
classes it is most generally aerial; and in the simpler forms of
ivorms, as in the lower radiata, no special organ appears to be
appropriated to this function. From the internal habitation
of the entozoa, and the general softness and vascularity of
their exterior covering and their component tissues, they
appear to be oxygenated directly by the contact of the fluids
of the animal in which they are parasites, like a foetus in
utero, an ovum, a gemmule, or a portion of the body itself;
the possession of special pulmonary or branchial appa-
ratus, would be unavailing in animals permanently buried in
the substance of the brain, the liver, or similar internal
organs, and with so limited a circulation of the blood, and
where their temperature is not dependent on their own vital
functions.

The subcutaneous situation of the transverse abdo-
minal blood vessels of the rotiferous animalcules, and of
their vascular plexus around the neck, their thin soft and
generally naked skin, and the ciliary currents almost con-
stantly flowing over its surface, together with the ciliary
movements produced in their wide buccal and gastric cavities
and even in their general peritoneal abdominal cavity, contri-
bute to the extensive aeration of their ever-active body, inde-
pendently of the distinct branchial organs which have been
detected in several species. The branchiae are here placed in
the interior of the abdominal cavity, as in holothuria ; they
are furnished with large vibratile valvular cilia, like many
Crustacea; they communicate with the exterior medium by
a single median dorsal aperture near the neck, and they are
symmetrically disposed on the two sides of the abdominal
cavity. Eight of these branchial organs, placed apart from
each other, and attached to internal lateral tubes, apparently
the testes, are seen in the transparent abdomen of the hyda-
tina sent a, with their vibratile laminae in constant action.

The branchiae of the cirrhopods are short laminated

ORGANS OF RESPIRATION. 529

pyramidal organs, varying in number, size, and form,
in different species, attached to the sides of the trunk,
or to the bases of the proximal pairs of articulated feet, like
those attached to the haunches of the ]egs in the higher forms
of Crustacea ; and they aerate the blood spread upon their
numerous component laminae, before it is transmitted to the
pulsating dorsal vessel for distribution through the system.
The red-blooded worms have the greatest activity, and the
most extensive sanguiferous system of all the helminthoid
classes, and they present a corresponding development of the
respiratory organs, which are most generally branchial,
sometimes external, sometimes internal ; some respire by
the naked ciliated surface of their body, and a few possess
internal pulmonary sacs for an aerial respiration. The
vascularity of the skin, and the incessant currents of water
over its exterior, produced by minute vibratile cilia which
cover its naked surface, appear sufficient to oxygenate the
fluids in some of the lower annelides, as the planarice, which
present no special organ appropriated to respiration. No
distinct branchiae have been seen in the nais, the gordius,
and some other genera of the abrunchia of Cuvier; but the
tubicolons annelides, whether secreting calcareous shells, or
constructing adventitious tubes of sand or mud, are generally
distinctly cephalo-branchiate, having regular ramified tufts,
or elegant plumose expanded branchiae, covered with vibratile
cilia, and symmetrically disposed on the head or anterior
part of the body, as in sabella, serpula, terebella, amphitrite,
and pectinaria. These organs, in the living animals, are
commonly a little extended from the orifice of the tubes,
and expanded to receive the full influence of the ciliary
currents, on the red blood distributed through their minutest
ramifications. Most of the naked and burrowing aquatic
annelides are dorsibranchiate, having the branchiae in elegant
arborescent tufts, symmetrically arranged along the exterior
and dorsal aspect of the segments, or in form of more simple
branchial sacs confined to their interior. In amp/iinome,
hipponoe, pleione, and nereis, these ramose branchial tufts
accompany the upper pairs of lateral feet nearly along the
whole extent of the trunk. They are more concentrated in
their distribution in arenicola, where they are confined to a
limited number of the segments in the middle portion of the

TART VI. M M

530 ORGANS OF RESPIRATION.

trunk, but they are individually more ramified and length-
ened, and they exhibit most regular movements of expan-
sion and contraction as they receive or expel the red blood
transmitted by the branchial vessels. In the common areni-
cola piscatorum, there are thirteen pairs of these branched
organs along the dorsal part of the body, and three or four
segments of the trunk intervene between each pair of bran-
chiae. In polynoe, the branchiae are in form of thin dilatable
membranous sacs disposed externally along the whole extent
of the sides of the trunk. The branchiae are also in form of
membranous sacs placed along the dorsal part of the body in
aphrodita (halithea, Lam.) where they are sometimes con-
cealed by an external fibrous reticulate covering, as in halithea
aculeata, or exposed on the exterior of the back, as in hali-
thea squamata. There are thirty compressed dorsal respi-
ratory sacs in the halithea aculeata, disposed in fifteen sym-
metrical pairs, along the whole extent of the body, with
fourteen pairs of much smaller crested or serrated sacs
interposed between the larger. They all communicate, at
their inferior margin, with a distinct closed dorsal respiratory
cavity, extending along the whole body, and separated by its
thin parietes from the abdominal cavity, and from the re-
ticulate texture covering the back. The sacs open also
externally by minute compressed lateral stigmata concealed
in deep depressions between each pair of feet, and there are
t\vo large openings into the general respiratory cavity, placed
at the sides of the buccal orifice.

There are nearly twenty pairs of isolated internal, highly
vascular, respiratory sacs, disposed along the whole abdomi-
nal cavity of the leech, hirudo, lined each with a soft se-
reting mucous membrane, covered with a peritoneal coat,
supplied with vessels from the great lateral trunks, opening
by small round stigmata on the ventral surface of the body,
and the pairs separated from each other by about five seg-
ments of the trunk. Similar minute, isolated, internal, late-
ral, respiratory sacs are disposed in regular pairs along the
whole extent of the abdominal cavity in the earth-worm,
lumbricus, which, like those of halithea, and hirudo, are
largest in the middle portion of the trunk ; they become
almost imperceptible towards the ends ; they generally con-
tain a white mucous fluid, and they open separately by

ORGANS OF RESPIRATION. 531

small round stigmata on the sides of the segments. These
simple internal sacs of the earth-worm and the leech, opening
by minute stigmata on the surface of the skin, and receiving
a large portion of the venous blood of the system on their
highly vascular mucous lining, may be adapted both for an
aerial and aquatic mode of respiration, or they may receive
air from the water itself: and there is thus a gradual transi-
tion from the external and internal branchial sacs of polynoe
and halithea, to these internal rudimentary lungs of the
highest pulmonated annelides, where we already observe the
commencement of the spiracula, and even of the tracheae of
the entomoid classes.

In the entomoid classes, the respiration is generally aerial
and extensive, which accords with their increased muscular
energy, and with the high temperature they often exhibit
in their living and active state. In the myriapods, the most
vermiform of all the entomoida, the respiratory organs are
adapted solely for atmospheric air, and consist of ramified
tracheae, which commence by stigmata opening on the sides
of the segments, or sometimes, as in scutigera, on the
middle of the back, where they lead to small air-vesicles.
These air-tubes in the scolopendra, open on each side of
the alternate segments along the whole extent of the body,
and they divide immediately at their origins in the stigmata,
into numerous large branches, which form partial anasto-
moses with those of the adjoining segments, without con-
stituting, as supposed by Meckel, the large continuous
lateral trunks seen in the tracheae of insects.

Insects are generally provided, in the larva as well as in
the adult state, with nine or ten pairs of valvular spiracula,
defended externally by firm margins, sphincter apparatus,
and surrounding converging hairs, disposed on the sides
of most of the abdominal and thoracic segments, and leading
to tracheae which ramify through every point of the system.
They exhibit rithmic contractions and expansions of the
abdominal cavity during respiration, as in pulmonated ver-
tebrata; and many, especially of the neuropterous larvae,
possess also branchiae for aquatic respiration, which are
sometimes deciduous and sometimes permanent, as in the
caducibranchiate and perennibranchiate amphibia. The
branchiae appear to separate air from the water and convey

M M 2

532 ORGANS OF RESPIRATION.

it to the internal tracheae, and some coleopterous insects and
dipterous larvae inhabiting the water, come, like cetacea, to
the surface to inhale atmospheric air. The branchiae, indeed,
are mere external prolongations of the commencements of
the internal air-tubes, and assume the form of capillary
filaments, or ramose tufts, or lamellae, through which the
tracheae pass ; at their metamorphosis, they often lose these
branchial terminations of the tracheae, and acquire spiracula
for aerial respiration. The aquatic larvae of the common
gnat, and of the hydrophilus, chironomus, and dytiscus,
inhale air by stigmata near the anus, and the last segment of
the trunk is prolonged into an air-tube in the stratiomys and
in the larvae of eristalis, which they extend to the surface of
the water. The deciduous external branchiae prolonged from
the internal tracheae of the larvae of many insects, thus
resemble the external deciduous branchiae prolonged in
filiform tufts from the permanent organs in many of the
higher fishes.

The tracheal openings of perfect insects are provided with
muscles to open and close them, as shown by Lyonet ; they
are often extremely minute or entirely wanting on the pos-
terior segments of the abdomen and of the thorax, and they
are generally largest on the anterior rings of these two divi-
sions of the trunk, even where the posterior have been largest
in the larva. The tracheae are lined internally with a soft,
white, mucous tunic ; externally they are covered with a more
dense, shining, serous coat, and between these is an elas-
tic fibrous tunic, composed of continuous spiral filaments,
twisted closely, like those of a plant, around all the ramifi-
cation of the tracheae, from the spiracula to their minutest
divisions, thus giving the necessary elasticity for the free
passage of air through all parts, as the cartilaginous rings of
the trachea and bronchi of vertebrata. These air-tubes ra-
mify, like blood-vessels, through all parts of the head, the
antennae, the palpi, the legs, the tarsi, the wings, the muscular
system of the trunk, the interior of the blood-canals of the
wings, the surface of the alimentary canal, the ovary, and on
almost all the internal organs, as seen in the annexed figure
(Fig. 144,) of the tracheae of melolontha vulgaris. From the
stigmatic origin of each tracheae, there generally extend forwards
and backwards several large longitudinal trunks (144. b. c.)

ORGANS OF RESPIRATION.

533

which, by anastomosis, establish a free communication with the
adjoining stigmata of the same side ; there are also several
transverse anastomosing branches, (144. h. I.) which unite
below (144. k.) with those of the opposite side, to form a free
communication between the two sides of the body ; and there
are numerous other branches (\44.f.g.) from the same trachea!

FIG. 144.

origins, which ramify directly on the various organs of the
body.

Sometimes, as in blatta and locust a, the longitudinal
branches form but one dorsal and one ventral median trunk,
from which branches are distributed to the organs, and be-
tween which a free communication is established by regular
transverse anastomosing branches. The longitudinal lateral
trunks are often much dilated in aquatic insects, to render them
buoyant, and to provide for their interrupted respiration ;
and the aquatic larvae of several insects, as of libellula,
inspire air solely from water regularly introduced and ex-
pelled through the anus, as holothuriae inspire water for res-
piration by the same orifice. In the rectum or cloaca of
these larvae, indeed, there are several compact rows of trian-
gular branchial lamellae, which line its whole parietes, and
which support the capillary extremities of the abdominal tra-
cheae ; some have as many as eighty of these plates, dis-
posed symmetrically in rows of pairs within the rectum.
Besides the minute cells, (144. d. e. f. g.) in which, as in the
lungs of vertebrata, the tracheal ramifications of the higher
insects frequently terminate, there are often more consider-
able vesicular dilatations on the great lateral longitudinal

534 ORGANS OF RESPIRATION.

trunks, and other large tracheae, as in many adult dipterous
and hymenopterous species and aquatic coleoptera ; such vesi-
cular enlargements of the tracheal trunks of insects are seen
in the head, the thorax, (144. b.), and especially the anterior
part of the abdomen ; they lighten the body in flying forms ;
they are covered with minute transparent spots like perfora-
tions ; they are not developed in larvae ; and they often give
origin to the visceral branches. The common entomoid form
of the respiratory organs is seen even in the apterous spe-
cies, as the louse, pediculus, where there are seven pairs of
lateral stigmata, opening into two longitudinal tracheae, which
extend, without dilatations, along the whole body, and com-
municate with each other by numerous anastomosing branches*
And thus the limited circulation of the blood in insects is
compensated for by the extensive ramification and distribu-
tion of the respiratory organs through every texture of their
body, and the necessary lightness, elasticity, and muscular
energy are imparted to these invertebrated winged inhabitants
of the air, and hence the high temperature which their body, as
has been long known, often acquires.

In the arachnida, the more extensive circulation of the
blood through the body is accompanied, as in annelides,
myriapods, and Crustacea, with a more concentrated form of
the respiratory organs than occurs in most insects ; and, as
in insects, they are always adapted for aerial respiration,
whether they belong to aquatic or terrestrial species. Some
aquatic forms of arachnida, as some aquatic insects, appear
to respire under water by means of the globules of atmo-
spheric air which they carry with them into that element,
entangled among the hairs of their surface. In the phalan-
gium, and other tracheated species, the air- tubes divide into
branches from their commencement in the lateral stigmata,
as in myriapods, and these branches communicate freely
with each other by transverse and longitudinal anastomoses.
The stigmata have generally a more ventral aspect in the
arachnida, especially in the higher pulmonated forms, as the
scorpions and spiders, where no tracheae extend through the
body. Some arachnida, as the dysdera and segestria, have
been shown by Duges to be at the same time possessed
both of ramified tracheae and pulmonary sacs, the two pos-
terior of their four stigmata opening into branching air-

ORGANS OF RESPIRATION. 535

tubes, and the two anterior into circumscribed pulmonary
cells.

Of the pulmonated forms, some, as the scorpion, have eight
distinct internal respiratory sacs, opening by separate stig-
mata ; others, as mygale, have four sacs, and the most con-
centrated form of these organs is that of the spiders,
which have only two symmetrical pulmonary cells. On
the ventral surface of the abdominal segments of the scor-
pion, four pairs of elongated oblique stigmata open into eight
broad short quadrangular sacs, each of which is divided into
nearly twenty small flat cells, by internal parallel septa,
giving a pectinated appearance externally to the shut margin
of the sac, which may be compared to the incipient develop-
ment of peripheral cells in the lungs of reptiles. Four simi-
lar sacs, also with soft white vascular parietes, open, by
four stigmata, on the ventral surface of the abdomen in the
mygale, and one similarly divided pulmonary sac opens, in
spiders, by a transversely elongated stigma on the anterior
part of the ventral surface of the abdomen. There is thus,
in passing through the tracheated, the pneumo-tracheated, and
the pulmonated forms of arachnida, a gradual transition from
the highly ramified and extended condition of the respira-
tory organs of insects, to the more concentrated and laminated
structure presented by the branchiae of Crustacea.

As the blood is most extensively circulated through the
body in crustaceans animals, and their respiration is only
aquatic, their branchiae present an extensive surface, and
consequently a laminated structure, to receive a larger portion
of venous blood in capillary vessels, for aeration. The gills
are here generally attached to the bases of the articulated
feet, whether these lateral appendices of the segments be
masticatory, ambulatory, natatory, ovigerous, or simply res-
piratory ; and they receive the venous blood of the system
before returning to the heart, for distribution through the
body. In the lower orders of Crustacea, the branchiae are
commonly confined to the appendices of the segments near
the caudal end of the trunk, where they hang free in the sur-
rounding element, and are rapidly moved to and fro by the
organs which support them, as by vibratile cilia. But in the
higher species, they are attached to the ambulatory and mas-
ticatory appendices near the cephalic extremity of the body,

536 ORGANS OF RESPIRATION.

where they are concealed beneath the sides of the dorsal
carapace, in a thoracic cavity separated by a tendinous
diaphragm from the abdomen.

In many of the lower suctorial parasitic Crustacea, as the
califfus, no special organs for respiration have been detected,
and they may be aerated through the soft naked surface of
their body. The branchiae have the simple form of flat vas-
cular membranous folds, or vesicular lamellae, attached to
the thoracic feet in most of the branchiopodous species.
They are also, in the amphipoda, in form of membranous
foliated expansions, highly vascular, attached naked to the
thoracic feet, and rapidly moved to and fro by them, for the
aeration of the venous blood extensively spread on their sur-
face ; they form small membranous sacs attached to the tho-
racic appendices in the laemodipoda. They are exposed
membranous, sometimes ramified laminae, attached to the
abdominal feet, in the isopods ; and, with the same position,
in most of the stomapods, as in the squillae, they consti-
tute flabelliform series of small pectinated tubes, while in
others of the same order, as the cynthiae, they form a small
pedunculated membranous cylinder. The five pairs of broad
natatory abdominal feet of the limulus support, on their
posterior surface, innumerable delicate exposed branchial fila-
ments, composing the respiratory organ; and the anterior
five pairs of abdominal feet, in the squilla, support as many
pairs of peniform ramified tubular branchiae.

The branchiae, or the elementary pieces of the feet sub-
servient to respiration, are, in the decapods, more developed
and more complex, though not more numerous, than in most
of the inferior Crustacea ; and they are disposed in two lateral
longitudinal rows of vertical laminated pyramids, attached to
the bases of the five pairs of ambulatory, and the three outer
pairs of masticatory, appendices. They are concealed in a
respiratory cavity, formed by the lateral overhanging folds of
the carapace, which gradually extends downwards, to cover
them during their earlier development ; and in this cavity
they are fixed below by the bases of the several branchial
foliated pyramids, and their free apices converge above. In
the brachyourous decapods, the branchial laminae composing
the ten or eleven vertical pyramids on each side, are more
simple, and present a smaller extent of surface for the distri-

ORGANS OF RESPIRATION. 537

bution of blood-vessels, than in the macrourous species,
where there are about twenty-two pyramids on each side, and
their component lamince are subdivided into innumerable
small filaments, so as to present a more extended respiratory
surface. The laminae of each pyramid are disposed in two
vertical rows, with their flat surfaces superimposed; there
are sometimes two hundred laminae in a single row ; and
between the branchial pyramids of each pair of feet, a long
horny lamina is extended upwards, by the constant action of
which the currents of water are directed forwards over the
branchiae. In many of the brachyourous decapods, where
the branchial cavity and its openings are more circumscribed,
the currents are generally directed inwards through an infe-
rior orifice on each side, by the movements of a small horny
valvular lamina attached to the base of a maxilla, and the
water passes out by a superior vent, on each side of the
mouth, after bathing the surface of the gills. During the
development of the complex branchial apparatus in the
decapods, the highest order of Crustacea, they are observed to
pass through successive conditions of structure, much re-
sembling the various permanent forms presented by these
organs in the lower orders of this class. For a time,
they are not developed from the feet of the embryo ; next,
they are observed as simple rudimentary processes, of inde-
terminate function; later, they become distinct, vascular,
naked, respiratory laminae ; and lastly, they fold up under
the projecting carapace, and become concealed under its
margins.

FOURTH SECTION.

Respiratory Organs of the Cyclo-Gangliated or Molluscous

Classes.

All molluscous animals, excepting a few pulmonated gas-
teropods, are aquatic, and breathe by means of branchiae,
which present no less striking diversities of form and struc-
ture than are seen in most other organs of the body in this
most diversified subkingdom. From their aquatic and limited
respiration, their muscular energy is more feeble, their move-
ments are more slow, their whole functions more languid,

538 ORGANS OF RESPIRATION.

and their temperature lower than in most of the active, air-
breathing articulated tribes. As the development of vibratile
cilia, on the respiratory apparatus of animals, is generally
inversely proportioned to the other means of activity pos-
sessed by these aerating organs, they are most developed, most
numerous and constant, and most extensively distributed on
the branchial apparatus of the languid and inert molluscous
classes, where they were already observed and described on
the branchiae of conchifera, before the time of Leuwenhoek.
These minute vibratory organs not only cover the filaments
of the branchiae, and line the whole respiratory cavities, but
are seen also on most of the naked parts of the exterior, and
even in the alimentary canal, as in many lower invertebrata ;
and the involuntary character of their movements was known
to Leuwenhoek, who saw them moving on pieces of the
branchiae of the common muscle, mytilus edulis, detached
from the body. The respiratory currents of tunicata, when
their body is perfectly motionless, were known to Cavolini,
who justly compared those of ascidia to the currents which
bring food to the polypi of zoophytes ; and Basterus referred
to the ciliary movements of the branchiae extending a little
beyond the edge of the shells, the spontaneous motions
which he often observed in newly hatched embryos of the
oyster.

The tunicata breathe by reticulate branchiae, occupying
the interior of a large thoracic cavity, which receives the
ciliary currents by the large respiratory orifice, and expels
the water by the common vent of the branchial, the alimen-
tary, and the generative organs. In the long narrow cavity
of the salpa, they are disposed transversely in rings or spiral
turns, giving an anriulated appearance to that cavity, com-
pared to a trachea by Chamisso, as seen through the trans-
parent parietes of the body. In the higher forms of this
class, the branchiae generally constitute a more continuous
lining of the respiratory sac ; and the inhaled currents pass
through their elongated oval or quadrangular meshes, to
arrive at the efferent canal and exterior vent. Although the
elasticity of the exterior tunic of these animals is capable of
assisting in inspiration, and the contraction of the muscular
tunic or mantle, everywhere attached to its interior, contri-
butes occasionally to rapid and powerful expiration, yet the

ORGANS OF RESPIRATION. 539

orifices are most open, and the respiratory currents are most
active, when aU these parts are entirely quiescent. The same
currents which aerate the branchiae by passing through their
innumerable meshes, bring also floating particles of food to
the mouth, placed in a recess at the bottom of the respiratory
cavity.

The vibratile cilia, which alone produce these equable
and constant currents, I have found of minute size, com-
pactly disposed over the entire breadth of the reticulate
filaments of the gills, lining the smooth parts of the branchial
sac, covering even the tentacular filaments at the orifices, and
moving in most regular waves around all the meshes of the
branchiae, as around the arms of a polypus. On being irritated,
the ascidiee contract the mantle forcibly, and throw the
contained water to a distance from both orifices, the direction
of the respiratory currents being determined not so much by
valvular structure, as by the impulse of the waves of minute
vibratile cilia, which here, as in all other cases, continue to
vibrate on small pieces detached from the gills. The vibra-
tile cilia, in these inert and often fixed animals, thus serve to
aerate the venous blood of the system, before being trans-
mitted to the heart, and they bring food to the mouth with
the respiratory currents ; in the swimming species, they are
also, as in the ciliograde acalepha, the means of locomotion ;
in the luminous tunicata, as pyrosoma, they appear to be
connected with that remarkable property of emitting light,
as I have found them to be on the surface of beroe, and in
the ciliated intestine of some luminous annelides ; and they
assist in removing all excretions and foreign particles from the
interior of their body.

In the respiratory organs of the conchifera, as in most
other organs of their body, the general plan of structure is
nearly the same as in tunicata, and they are very uniform
throughout the class. Here, as in tunicata, the mantle pre-
sents two apertures, a respiratory orifice and a vent, commu-
nicating with the branchial cavity, for the reception and exit
of the ciliary currents, and the buccal orifice of the alimentary
canal is situate at the bottom of this cavity. The vibratile
cilia, often of great size and bent, as in mytilus, cover closely
the whole surface of the branchial meshes, line all parts of
the respiratory cavity, extend over the mucous covering of

540 ORGANS OF RESPIRATION.

the viscera, the labial appendices, the mantle, and its fimbri-
ated tentacular prolongations, and even line the interior of the
alimentary canal. A pair of double pectinated branchial folds,
on each side of the foot, within the mantle, are suspended
in the branchial cavity, fixed by their two contiguous upper
margins, free below, and at their two upper remote margins,
each fold forming a loose, compressed, reticulate sac, and
supporting on its innumerable minute elongated meshes the
capillaries of the branchial blood vessels. In the conchifera,
which burrow in rocks, timber, mud, sand, or other materials,
the mantle and the respiratory cavity are necessarily pro-
longed, to bring the two orifices of the palleal cavity within
reach of the surrounding element, and the branchiae are
greatly elongated.

Each pendent gill is composed of two nearly contiguous
pectinated laminae, united to each other below, enclosing
between them a narrow space, widening above, and allowing
the transmitted aqueous currents to pass over one free upper
margin, into the canal of the expiratory vent. As the conti-
guous sides of each lateral pair of gills are continuous at
their upper margin, where they are fixed, and at their free
margins below, the entire pair of one side in the conchifera
may be considered as only a puckered or folded condition
of the simple expanded reticulate membrane lining either
of the two sides of the respiratory cavity of a cynthia
or other tunicated animal. The compressed filaments which
compose the branchial laminae are slightly connected toge-
ther by regularly disposed tubercles, whose contiguous sur-
faces appear to be also provided with minute slow moving
cilia ; these component fibres of the branchiae are nearly free
in pecten, area, and spondylus, and are united only at their
distal ends in the malleus. The branchial laminae are some-
times unequal in size, as in cardium, where the exterior are
not half so large as the interior laminae. The branchial
currents of conchifera bring food to the mouth placed at the
bottom of the respiratory sac, they assist in removing the
excretions and the ova or embryos from the cavity of the
mantle, and they may aid in clearing or enlarging the per-
forations made by burrowing species. Small portions of the
branchial laminae, detached from the body, continue long
their ciliary movements, and present the most favourable

ORGANS OF RESPIRATION. 541

means of examining this unexplained phenomenon. In marine
species, their movements are quickly arrested by immersion
in fresh water, and by sea water in the palustrine forms.

Nearly all the gastcropods breathe, like the other mollus-
cous classes, by means of branchiae, which are disposed
externally in the naked species, and are generally concealed
under the mantle in the testaceous forms ; a few species only
breathe air by a pulmonic cavity opening on one side, some
of which are aquatic in their habits, others terrestrial. The
naked gasteropods, like the naked annelides, have greater
latitude of surface than the testaceous forms, for the distri-
bution of their external ciliated branchiae, and of their
general ciliary currents ; and, indeed, their whole surface
is often ciliated and respiratory. The branchiae in these
species are generally disposed, as in the dorsibranchiate
annelides, in ramose tufts, symmetrically arranged over a
greater or less extent of the dorsal or lateral parts of the
body; but the modifications of form and structure which
they present are too numerous and diversified to afford satis-
factory means for the zoological subdivision of this class.
In scyllaa, they are disposed in isolated, ramified, small tufts
on the outer surface of the extended dorsal folds of the
mantle, and on the surface of the back ; in tritonia, as in
arenicola among the annelides, they rise more directly
in elegant ramifications, along each side of the back; in
eolidia and cavolina, they form numerous rows of small
simple clavate projections, similarly disposed along the back;
and in tergipes, a single row on each side; in tethys, the two
dorsal rows are composed of alternately disposed tufted and
crested branchiae ; and in glaucus, they form long filiform
extensions from the ends of the lateral palleal appendices.
In the tritonia and similar forms, the number of branchial
pairs varies with the degree of development of the body,
and they are developed successively from the front pair back-
wards.

In the doriSy the branchiae form elegant plumose or ramose
tufts around the anal opening on the posterior part of the back ;
they constitute a single penniform organ, under the margin
of the mantle, on the right side, in pleurobranchus and
pleitrobranchaa ; they are protected by a thin pellucid shell,
on the right side of the body in aplysia, and on the middle

542 ORGANS OP RESPIRATION.

of the back in carinaria. In patella and chiton, they form a
circular range of branchial laminae around the body, between
the margins of the mantle and foot ; but in pleurophyllidia,
they are confined to the two sides of the body, the circle
being interrupted before and behind. In the haloitis, they
constitute two unequal penniform organs, placed under an
extended fold of the mantle, on the left side of the body ;
and the same character is found in the pectinibranchiate
gasteropods, inhabiting nearly all univalve, unilocular, turbi-
nated shells, and forming the largest order of this class.
The branchiae when confined to the right side in gasteropods,
are commonly single, and when confined to the left side,
they are thus generally double penniform organs. The two
penniform pectinated gills of the pectinibranchiate species,
are placed in a recess on the left side of the back, under the
open parieties of the mantle, and, as usual, near to the
auricle and ventricle of the heart, which receive the aerated
blood.

The muscular and ciliated syphon, prolonged from the
left side of the mantle, and extended through the canal
or groove of the shell, directs the respiratory currents in-
wards over their surface ; and the water, interrupted by the
closed cavity of the mantle behind, after bathing the entire
ciliated branchial laminae, and the ciliated respiratory cavity
in which they are lodged, passes outwards over the right side
of the palleal cavity, and over the muciparous follicles and
the excretory orifices there placed. The development of
the vibratile cilia over all parts of the branchial apparatus
and external soft parts of gasteropods accords, as usual, with
the limited means otherwise provided for renewing the
stratum of the surrounding element in immediate contact
with their surface. Here also they are seen on the mucous
lining of the alimentary canal ; they are early developed on
the mantle and branchiae of the embryos in ovo, and serve,
for a time, as natatory organs in the young when hatched ;
and by the continuance of their action on portions detached
from the body, they exhibit the same independence of voli-
tion as in other classes.

A transition from the branchiated to the pulmonated
gasteropods is effected by the naked, amphibious, marine
onc/iidium} in which, besides about twenty pairs of small

ORGANS OF RESPIRATION. 543

dorsal ramified branchial tufts, a distinct pulmonary sac,
lined with vascular network, is observed, opening by a single
spiracle, above the anus, on the median line, at the posterior
end of the body ; and both kinds of organs exhibit rhithmic
respiratory movements of dilatation and contraction, in their
respective elements. Some pulmonated gasteropods, breath-
ing solely by lungs, live in the fresh waters, as lymnaa and
planorbiSy the exterior surface of whose body, and the mucous
lining of the alimentary canal, are covered with vibratile cilia,
as in the branchiated marine species ; others are terrestrial,
and testaceous, as helix, or naked, as Umax, and these likewise
breathe solely by means of a large single pulmonary cavity
placed in the middle of the back, and opening by a single
small round spiracle on the right side, near to the head. The
interior surface of this sac is highly vascular, from the numerous
large reticulate branches of the pulmonary arteries and veins
there distributed ; the aerated blood is transmitted to the
auricle and ventricle, to be sent through the system, as in
other mollusca ; and the external aperture of the respiratory
organ is here approximated to the anus, as in onchidium, and
as these two passages are in most of the internal forms of
respiratory organs of invertebrata. And thus, in the air-
breathing gasteropods, the highest pulmonated invertebrata,
the lungs already form a circumscribed cavity, extended
along the middle of the back, with one tracheal opening, as
the air-sac of fishes and the embryo lungs of all higher
vertebrata.

All the pteropods are marine, branchiated, swimming
mollusca, with a closed cavity of the mantle necessitating an
external disposition of the branchiae, and whose naked sur-
face, or extensive palleal fold enveloping a thin shell, may
assist in the aeration of the body. The branchiae of the
small naked pneumodermon form two considerable crescentic
laminated organs extending freely from the surface of the
mantle at the caudal extremity of the body. In the testa-
ceous hyalea, they form an elliptical ring of branchial laminae
disposed on the back, between two folds of the mantle, and
the lateral apertures of the shell appear to transmit the
respiratory currents to this open cavity of the mantle. In
clio and cimbulia, the natatory fins, developed from the sides
of the neck, appear to support, on their striated or laminated

544 ORGANS OF RESPIRATION.

surface, the branchial vessels destined for the aeration of the
blood.

The cephalopods are also entirely marine and branchiated
mollusca, but with the palleal cavity open anteriorly, and the
branchiae, symmetrically developed on the two sides, are
suspended by peritoneal and muscular folds along the dorso-
lateral part of the abdominal cavity. The respiratory currents
enter by the anterior lateral valvular openings of the mantle,
and after bathing the branchial laminae, they escape from the
palleal cavity by the median valved orifice of the syphon.
The large respiratory cavity is separated from that containing
the nutritive and generative organs, by muscular aponeuroses
and folds of the peritoneum. The branchiae have a pyramidal
form, with the free apex directed anteriorly ; they consist of
numerous superimposed laminae, diminishing in size ante-
riorly ; and they support the trunk of the branchial artery
along their fixed upper margin, and the branchial vein along
their pendent inferior free border. There are two of these
organs on each side of the body in the nautilus, consisting,
as on the left side of the pectinibranchiate gasteropods, of a
larger and a smaller branchia — the bilateral symmetry esta-
blished in the cephalopods, and the median position of the
syphon, allowing of the equal development of these organs
on both sides of the body. In the argonauta, another testa-
ceous form, there is but one branchia on each side of the
palleal cavity, and the same structure is seen in all the naked
cephalopods ; these organs vary, however, in their relative
magnitude, and in the number of laminae of which they are
composed^ in different species. There are only about twelve
laminae in each branchia of octopus* about fifteen in argo-
nauta, about forty in sepia, and as many as ninety are some-
times found in one of the long narrow branchiae of loligo,
the branchial laminae being generally smaller and narrower
in proportion to the increase of their number.

The branchial circulation is accelerated, and consequently
the extent of respiration increased, by the force of the two
lateral muscular cavities of the heart ; and the arterialized
blood is sent by the branchial veins to the median single ven-
tricle, for distribution through the body. The branchial lami-
nae, supported each around a central cartilaginous hoop like
the arches of the gills in fishes, and minutely subdivided into

ORGANS OF RESPIRATION. 545

smaller lamellae, present an extensive surface for the branchial
vessels ; and the currents are directed over them, as in fishes,
by the rhythmic contraction and expansion of the surrounding
parts. The loose valvular margins, extended from the broad
base of the syphon, allow of the free ingress, and check the
egress of the respiratory currents, by the sides of the palleal
opening; and the valvular fold, directed forwards, in the
canal of the syphon, prevents the entrance of the water by
that passage during inspiration : so that there are already
two lateral and one median opening employed in the respira-
tion of cephalopoda, as of fishes, although the currents here
take an opposite direction ; and the bilateral symmetry of
the respiratory organs, perfectly established throughout this
class, accords with the numerous other approximations of
the cephalopods to fishes, and to the vertebrated sub-
kingdom.

FIFTH SECTION.

Respiratory Organs of the Spini-Cerebrated or Vertebrated

Classes.

The higher vertebrated classes, like the entomoid classes
of articulata, are mostly composed of air-breathing animals,
the high development and activity of all their organs re-
quiring this more effective mode of respiration; but the
lowest vertebrata, like the lowest invertebrated tribes of
every subkingdom, are limited to an aquatic respiration, in
accordance with their simpler structure, and the diminished
energy of all their functions. The blood is always propelled
through the respiratory organs by the contractions of a
muscular ventricle, and these organs always communicate di-
rectly with the cavity of the mouth, through which the respira-
tory currents, whether of air or water, are chiefly conveyed.
As in most of the invertebrata, the respiratory organs are
here always placed near the heart, but their openings are
never approximated to the anus, as they most generally are
in the molluscous classes. The branchiae of vertebrata are
always double and symmetrical, like those of the cephalopods,
the highest of the invertebrated classes ; and the pulmonary
organs, which are sometimes single as in fishes, and even un-

PART VI. N N

546 ORGANS OF RESPIRATION.

symmetrical as in ophidia, are here always placed in the dorsal
region of the trunk, as in the highest pulmonated mollusca.
Some vertebrata, as the lowest fishes, are exclusively
branchiated; others, as reptiles, birds, and mammalia, are
exclusively pulmonated ; others pass, by development, from
the one mode of respiration to the other; others remain
pulmo-branchiated, or truly amphibious, through life. But
the temperature of the blood, and the energy of the muscular
organs, directly correspond, in all, with the extent and acti-
vity of the respiratory system.

Although thus elevated in the scale, the respiration of
fishes, like that of the lowest worms, is only aquatic and
branchial ; but in order to render this mode of respiration as
effective as possible, the surface of these aquatic organs is
here greatly extended, the surrounding element is rapidly
renewed on their exterior, the whole blood of the system is
sent through them for aeration, and its velocity is accelerated
by the entire force of the heart. The respiratory organs of
fishes consist of variously formed gills, attached to osseous
or cartilaginous branchial arches, extending from the sides of
the os hyoides upwards to the sides of the cranium. In the
osseous fishes, there are four of these branchial arches sus-
pended, free and moveable, under a wide opercular covering
on each side of the neck. The branchiae consist of numerous
small, flat, tapering, cartilaginous laminae, approximated closely
to each other, bifurcated at their free ends, or cleft to their
base, and arranged in a regular series, like the teeth of a comb,
over the whole exterior convex margin of each branchial arch.

Over the very extensive surface presented by these
innumerable, free, pendent laminae, the whole venous
blood of the system, sent from the heart and bulbus
arteriosus, is conveyed by the minute ramifications of the
branchial artery. The water inhaled by the mouth, is con-
veyed backward by an act like deglutition, and escapes on
each side, between the separated branchial arches, and over
all the vascular laminae of the gills ; and thus the venous
blood of fishes is oxygenated, and decarbonized, and fur-
nished with nitrogen for the gaseous secretion of their air-sac.
Vibratile cilia have been detected both on the external and
internal mucous surfaces of fishes. Some fishes are observed
to swallow atmospheric air, to be conveyed through the

ORGANS OF RESPIRATION. 547

ductus pneumaticus, to the air-sac, or to aerate the vascular
mucous lining of their intestine. As the great artery pro-
ceeding from the heart of fishes is entirely subdivided into
branchial capillaries, and leaves no pervious anastomosing
trunk communicating with the veins, as in amphibia, all the
species are necessitated to retain permanently the aquatic
character of the earliest tadpole state, incapable of undergoing
metamorphosis by the absorption of the branchiae. The
trunks of the branchial veins returning the arterialized blood
to the descending aorta, occupy the bottom of the marginal
concavities of the branchial arches; the branchial arteries
are exterior to them in these grooves ; and in each small
leaflet of the gills the arterial twig occupies the inner margin,
and the returning vein the exterior edge.

The number of branchial arches varies in fishes, as in amphi-
bia ; in some plectognathi, as the diodon, there are only three
pairs of gills ; there are three pairs in the lophius, with the rudi-
ment of an anterior fourth pair ; most osseous fishes present
four complete pairs ; several present the rudiment of an ante-
rior fifth pair ; and a greater number is seen in many of the car-
tilaginous fishes. In the operculated fishes, whether osseous
or cartilaginous, there are only two branchial openings, one on
each side of the pharyngeal cavity ; in the long cylindrical
ffastrobranchus, likewise, there are but two small round
branchial openings, which are the terminations of two com-
mon lengthened canals, which receive the whole of the branchial
currents, and convey them to the surface. In the sturgeon,
the chimaera, and the spatularia, though cartilaginous fishes,
the branchiae are free at their margins, with a single opercular
opening on each side of the neck ; in the rays and sharks, where
there is no free operculum, there are five narrow transverse
openings on each side ; and the outer edges of the branchiae
are fixed to the integuments between the several openings ;
so that the inhaled water is divided into five streams, passing
over the surfaces of all the separate gills. In the lampreys* also
with fixed branchiae and without a free operculum. there are
seven of those separate branchial cavities on each side,with as
many small round openings, through which the respiratory
currents pass to and fro, as in the lateral respiratory sacs of
a leech or a worm. In place of the usual pectinated gills
seen in other osseous and cartilaginous fishes, the lopho-

N N 2

548 ORGANS OF RESPIRATION.

branchiate species, the syngnathus, peyasus, and hippocampus
present a regular series of ciliated filamentous tufts, disposed
along all the branchial arches, and much resembling the
ramified branchial tufts of many gasteropods and annelides ;
these filaments are free at their ends, concealed in a branchial
cavity, and communicate externally by a single operculated
opening on each side, as the gills of other osseous fishes.
In the heterobranchus anguillaris, there are also small acces-
sory ramified branchial tufts, in addition to the usual
laminated gills.

Besides the ordinary internal, covered, laminated branchiae,
many cartilaginous fishes, as the rays and sharks, and some
osseous fishes, present, in the foetal state, long, external,
simple, branchial filaments, continuous with the internal
laminae of the permanent gills, and hanging down free from
the sides of the exterior branchial openings. These deci-
duous, exterior, branchial filaments are lost in the foetus of
the rays and sharks, before they escape from the ovum ; and
in the osseous fishes, where they have been observed, they
disappear by absorption at a very early period of foetal life.
In watching the development of the permanent branchial
apparatus of fishes, the outer surface of the neck appears,
at an early period, to have no branchial openings ; but there
are soon after formed five small separate holes on each side,
even in the operculated osseous fishes. The branchial
arches at length make their appearance, and the minute
constituent laminae of the gills begin to bud out from their
edges. The laminae increase in number, in extension, and in
firmness of texture, and hang free from the sides of the neck ;
the opercular apparatus now begins to be developed, and by
the gradual extension of its branchiostegous membrane and
rays, the branchial organs are covered and concealed.

Most fishes have an air-sac in the abdomen, extended
longitudinally under the vertebral column, exterior to the
peritoneum, and containing a gaseous secretion, differing in
its constitution from atmospheric air. The air- sac is most
developed in species which frequent, or feed at the surface of
the water, and is least developed or wanting in those which
lie at the bottom or burrow in mud ; its secretion contains
a larger proportion of oxygen in the powerful predaceous
fishes of deep seas, and nitrogen predominates in the feebler

ORGANS OF RESPIRATION. 549

species which frequent shores and shallow waters. Being
developed, like the lungs of higher animals, from the alimen-
tary canal, the air-sac of fishes generally communicates with
the oesophagus or stomach, by means of a short trachea or
ductus pneumaticus ; in some, however, this tracheal commu-
nication becomes completely obliterated, and the sac remains
an isolated, closed cavity, filled with its gaseous secretion,
as in the xiphias. It is often provided with distinct mus-
cular bands for its compression, and when largely developed,
it is often capable of producing sounds, either under water
as in pogonias, or in the air as in trigla, but there is yet no
adaptation of laryngeal cartilages for systematically vocalizing
these sounds.

The air-sac of fishes presents great diversities of general
form, as well as of extent of development, being sometimes a
single simple elongated sac, or provided with tubular or ramified
appendices, or divided into sacculi by transverse constric-
tions, or symmetrically divided into two lateral cavities like
the lungs of higher animals, as seen in several of the plectog-
nathi. The highly vascular glandular organ, which secretes
the gaseous contents, is most developed and distinct where
there is no ductus pneumaticus, and is generally imper-
ceptible where that tracheal canal exists. The air-sac is
supplied with branches from the pneumogastric nerve, like
the lungs of higher vertebrata ; like the lungs of tritons,
water-snakes, turtles, and other aquatic pulmoniferous ver-
tebrata, this sac assists in poizing the body in that dense
element ; and it often communicates with the organ of hear-
ing, like the respiratory passages of higher animals. In the
herring, the long fusiform air-sac communicates by a narrow
ductus pneumaticus, with the fundus of the stomach ; in
the sturgeon it opens by a short wide duct into the cardiac
portion of the stomach ; in the diodons, which inhale air at
the surface of the water, and thus render their body tense
and buoyant, the large air- sac communicates with the an-
terior portion of the oesophagus. In rays, frog-fishes,
flounders, lampreys, and many others which lie at the
bottom of the water or reside in mud, there is na air sac
developed. The tracheal duct of many fishes already receives
atmospheric air, sometimes pure, and sometimes derived
from the inspired water, as that sent into the tracheae from
the minute openings of the branchial apparatus of some

550 ORGANS OF RESPIRATION.

aquatic insects in the larva state ; it is still membranous,
like that of a proteus, or of a lepidosiren ; generally it is
single, as in most higher vertebrata, but is sometimes double,
as it is in many chelonia ; and in some fishes it opens as
high as the pharynx like the trachea of other vertebrated
classes.

Thus, while the conditions of the branchial and pulmonary
organs of fishes present a perfect adaptation for the dense ele-
ment they are destined permanently to inhabit, they have many
analogies with the forms of the gills and air-sacs of mollusca,
and other invertebrated tribes, and also the closest affinities
with the deciduous and permanent respiratory organs of the
amphibia next above them in the scale. In the successive
development, and in the different permanent forms of the
branchial subdivisions of the great aortal trunk issuing from
their single ventricle, they exhibit the embryo conditions
of this vessel in all the higher vertebrata ; and in the various
conditions of their air-sac and ductus pneumaticus, they
imitate the embryo forms of the pulmonary organs in all the
higher air-breathing classes.

The amphibious animals breathe at first, like fishes, by
means of branchiae ; their air-sac is double, and is now more
obviously subservient to aerial respiration, and they respire
also by the entire surface of their naked, sensitive, and
vascular skin. In the earliest condition of the tadpole, when
the whole body is covered with vibratile cilia, small ciliated
branchial filaments are seen extending from the sides of
the neck, which produce currents of water over their surface
by the action of their minute vibratile organs ; and in this
first external filamentous condition of the gills, they may be
compared to the earliest deciduous external branchial filaments
seen in many cartilaginous and osseous fishes. Around the
margin of each of these short simple primary filaments, a single
capillary blood-vessel extends ; and by the successive forma-
tion of loops on this vessel, small ramifications originate and
develope along the sides of each branchial filament — each
branchial ramification having only a single capillary blood-
vessel around its margin. Before the development of the
pulmonary organs and the left auricle, the venous blood of
the system in the tadpoles of amphibia, is sent through a
bilocular heart, a bulbus arteries us, and branchial arteries,
as in the class of fishes ; and in many of the larvee of am-

ORGANS OF RESPIRATION. 551

phibia, as in the fishes, the primary free external filiform
branchiae are changed at a later period, for more circum-
scribed internal forms of these organs.

In the perennibranchiate amphibia, the branchiae are
retained, along with the pulmonary organs, through life; and
in the caducibranchiate species, every trace of these organs
becomes absorbed, and the respiration is effected in the
adult state solely by the developed pulmonary cavities. The
branchiae here, as in fishes, are supported by cartilaginous
arches connected with the posterior cornua of the os hyoides,
and vary in number and form and relative development in
different species ; there are three or four of these arches on
each side, composed each of one or more pieces, presenting
often rudimentary teeth along their inner margin, supporting
the free pendent gills along their outer convex edge, and
protected anteriorly by a rudimentary cutaneous operculum.
The branchiae are retained longer in the larvae of the urode-
lous forms, as the tritons, than in those of the anurous species
as the frogs and toads ; and the branchial arches, in both
tribes, during the metamorphosis, are gradually absorbed
with the gills, so as to leave only the os hyoides with its
curtailed cornua, in the adult state. In the external forms
of the branchiae, the ciliary currents are directed outwards
over their surface to the free ends of the branchial laminae,
and the ciliary actions continue on portions of the gills, and
on portions of the general skin, detached from the body,
as the ciliary actions in other classes of animals.

The branchial arches of amphibia, as of fishes, generally four
in number, do not always support effective respiratory gills ;
thus there are four branchial arches in the triton, and only
three of these are furnished with gills ; the posterior arch is
that most generally destitute of branchial laminae. There
are likewise only three gills on each side in the siren, the
proteus, and the oxolotus, where they are permanent in the
adult state, and hang freely exposed from the sides of the
neck ; there are four gills on each side in the larvae of anurous
amphibia. Muller observed distinct branchiae within a round
opening, a line in width, on each side of the neck, in the
larvae of ccecilia already three inches long. The branchiae
are not composed of closely approximated lanceolate parallel
laminae as in fishes, but are here cutaneous penniform ex-

552 ORGANS OF RESPIRATION1.

tensions, with a middle stem from which the soft ramified
compressed filaments or laminae hang free on each side.

By the movements of the lower jaw and os hyoides, the
respiratory currents of water are directed inwards by the
mouth, and outwards by the lateral branchial openings, as in
fishes ; and the stratum of water in contact with the surface
of the external pendent branchiae, is further renewed by the
constant vibration of the minute cilia closely covering their
whole exterior, as in the branchiae of inferior classes. Al-
though the branchial laminse are not here fixed at their outer
ends as in cyclostome and in plagiostome fishes, the number
of exterior lateral branchial openings varies in different
species, there being but one on each side of the neck in the
larvae of anurous amphibia, two in the proteus, three in the
siren, and four in the triton. The branchiated period of the
larvae of salamandra is commenced within the oviducts of the
female, and that of pipa is passed within the cells of the
parent's back ; in most others it is passed in the water, where
the ciliary action of the entire naked cutaneous surface of the
body, compensates for the imperfect development of other res-
piratory organs. Even in the adult state, frogs have lived
thirty hours after the entire removal of their lungs, breathing
then solely by their naked cutaneous surface, which is also
their sole respiratory organ during months of hybernation,
immersed in mud under water during winter.

In the proteus, the axolotus, and other amphibia which
permanently retain the gills, there are two long membranous
respiratory air-sacs, rudimentary lungs, extending, like the
air-sac of fishes, far backwards into the cavity of the abdo-
men, above the other viscera, but freely moveable in the
cavity of the peritoneum, and covered with that serous mem-
brane. The small pulmonary arteries descend from the
posterior branchial trunks of the aorta, their ramifications
form a close network over the entire surface of the pulmo-
nary sacs, and the aerated blood is returned by the pulmo-
nary veins to the small left auricle of the heart. The lungs
are here simple sacs, without internal cells, and they commu-
nicate with the pharynx by thin membranous smooth ductus
pneumatici, or tracheae, still nearly destitute of all cartilaginous
rings or annulated appearance. This simple condition of the
lungs and trachea is seen also in the triton in the adult state,
but is only a transient condition of these organs in the larvae

ORGANS OF RESPIRATION*. 553

of salamandra and of the anurous amphibia. These organs
are much more developed in the adult frogs, toads, and sala-
manders, where the lungs are capacious, broad, short, entirely
subdivided internally into large cells, and more confined to
the anterior portion of the trunk.

Along the sides of the short membranous trachea, both of
the caducibranchiate and perennibranchiate amphibia, irregu-
lar longitudinal continuous tracheo-laryngeal patches of carti-
lage are seen extending, and these shoot out transversely
small processes, which in higher animals become, by absorp-
tion, distinct isolated tracheal rings. The upper portion of
these two lateral tracheo-laryngeal cartilages already become
separated to form arytaenoid cartilages in all the amphibia,
as shown by Henle, and the rudiments of cricoid and thyroid
cartilages are generally perceptible, thus composing a rudi-
mentary larynx or organ of voice ; the lower portions, descend-
ing along the lower sides of the trachea, become broad, and
their lateral processes almost divided into distinct transverse
pieces, the rudiments of tracheal rings, in the salamanders, and
they are more distinct in the pipa and in the ctecilia. In the
frog, the small cornicula laryngis are already detached from the
ends of the arytaenoid cartilages, as in mammalia.

The larvae of frogs and other caducibranchia, breathe for a
time, both by lungs and branchiae, and by the naked surface of
the skin, as the perennibranchia ; the branchiae of the frog are
early withdrawn into a capacious pharyngeal cavity, commu-
nicating externally, as in cartilaginous fishes, by small lateral
cervical openings, which soon close up entirely, and the
cavity remains capacious in the male, for the production of
the croaking sounds. As the ribs, when present, are ineffec-
tive for respiration in amphibia, the lungs are gradually filled
with air by the successive movements of the os hyoides and
pharynx, as in chelonian reptiles where the ribs are entirely
immoveable, hence they are unable to breathe when the
mouth is forcibly kept open. The higher amphibia thus
exhibit remarkable metamorphoses in their respiratory organs,
commencing their career while yet in the ovum, with cuta-
neous vibratile cilia, like the respiratory organs of the lowest
radiated animals, then acquiring external branchial tufts like
those of the lowest worms or gasteropods, then internal
covered branchial laminae like those of fishes, and at length
internal cellular lungs like those of the higher vertebrata.

554 ORGANS OF RESPIRATION.

The reptiles breathe solely by means of pulmonary cavities,
no branchiae having been hitherto detected in any condition
of animals higher than amphibia, and the thick scaly cover-
ings of serpents, saurians, and chelonians, preventing respi-
ration through their skin. The form of the lungs of reptiles
as that of their other organs, accords with the general form
of the body, being long simple sacs in the serpents, broad
cellular organs expanded over the whole dorsum of the trunk
in chelonia, and approaching nearer to the mammiferous
type in the higher sauria. The want of bilateral symmetry
in the pulmonary organs, often produced in quadrupeds by
the sinistral position of the heart, is greater in serpents than
in all other vertebrata, as they are here sometimes developed
only on one side of the body, and that the right, on which
side alone they exist in the highest pulmonated invertebrata,
the air-breathing gasteropods, and on which side they are
largest in the mammalia. In many saurians also the right
lung is much larger than the left. These proportions of the
two lungs, however, appear to be reversed in some ophi-
dian reptiles, without the law of this variety being apparent.

The lungs of serpents are generally composed of two une-
qual, long, narrow, cylindrical or fusiform sacs, extending far
back in the cavity of the abdomen, above the other viscera,
surrounded with the serous lining of that cavity, without
internal cellular divisions, excepting at the dorsal portion of
their anterior end. In different species of coluber, typhlops,
and vipera, the lung of one side only is developed, and in
other genera, as boa and python, they are developed nearly
equally on the two sides. They communicate by a long
narrow, single, firm, annulated trachea, surrounded by dis-
tinct, though incomplete rings, with the back part of the
tongue, where the larynx already presents the aryteenoid,
cricoid, and thyroid cartilages, and is sometimes fur-
nished with a distinct epiglottis, as shown by Henle in the
large crotalus durissus. The annulated marking of the
almost membranous trachea, is sometimes, as in python,
continued perceptibly over the long cylindrical pulmonary
sacs. On opening the lungs of the boa or python, as in
most other ophidia, a beautiful cellular and highly vascular
appearance is presented in the interior of the upper and back
part of these organs, somewhat resembling the interior
polygonal cells of the second stomach of ruminantia, and

ORGANS OF RESPIRATION. 555

consisting of innumerable delicate septa of small open
air-cells extending into that part of the cavity, like
the embryo air-cells in all higher animals, and greatly
extending the surface over which the pulmonary capillaries
are spread. The rest of the lung, on each side, presents a
continuous simple internal cavity, with smooth parietes,
covered by the reticulate ramifications of the pulmonary
vessels. A larger quantity of air is taken into the lungs of
serpents and other reptiles, especially of aquatic species,
than can be effectively employed in oxygenating their blood,
and this may give tension to the body to aid their progres-
sive movements, or buoyancy and lightness for swimming,
or resistance to assist in the generative and fecal discharges,
or the means of longer suspending respiration when required,
or of increasing and prolonging their defensive hissing sounds.
Although distinct branchiae are not developed in any of the
true serpents (the naked serpents or cceciliae being now
properly removed to the class amphibia) the great branchial
trunks of the aorta, and the branchial openings on the sides
of the neck, are seen in the embryos of these animals, as of
all the higher vertebrata, and of man. In the embryo of the
python, Meckel detected three branchial openings on each
side of the neck; in the embryo of the coluber natrioc, Baer
observed the aorta, at its exit from the heart, divided into
four pairs of branchial arteries ; and similar observations
have been made by Rathke and others.

In the saurian reptiles, as in the ophidians, the ribs being
moveable, the respiration is chiefly effected by the action of
the intercostal muscles, without the aid of a diaphragm,
which does not yet separate the thoracic from the abdominal
cavity. The lungs of sauria are more equally developed on
the two sides of the body than in serpents ; they generally
extend far back into the abdomen, their lower and posterior
part is often scarcely divided into cells by any internal par-
titions, and their upper and dorsal portion is minutely cel-
lular. In many of the higher species, however, as the lizards
and crocodiles, the lungs are entirely subdivided internally
into small cells, and they are confined to the anterior thoracic
region of the trunk, as in mammalia. Each lung of the
scincus offidnalis forms a single continuous cavity, but the
entire inner surface of the parietes is cancellated by small
projecting reticulate septa, like the developing peripheral cells

556 ORGANS OF RESPIRATION.

in the embryo lungs of birds and mammalia, and the cancel-
lated portion of the lungs of most serpents. The upper and
dorsal part of the lungs of the chameelion are, as usual in the
sauria, minutely cellular, lower in their cavity the cells become
much larger, and at their lower extremity, the internal septa
have entirely failed, and the ends of the lungs are prolonged
over the whole fore part of the abdominal viscera, in the form of
long free saccular digitations, forming lengthened, undivided,
continuous cells. The long sacs extending free over the
whole abdomen from the cellular lungs of the chameelion, are
analogous to the abdominal air-cells of birds prolonged from
the terminal ends of their bronchi ; but where the diaphragm
is completed, in mammalia, the pulmonary organs are en-
tirely restricted to the thoracic division of the trunk, and are
everywhere minutely divided internally by the ramifications
and cells of the bronchi, to increase the extent of surface for
the distribution of blood-vessels.

A rudimentary diaphragm is already seen in the crocodilian
reptiles, extending in radiating peripheral muscular bands over
the inferior part of their minutely cellular and entirely thoracic
lungs ; the rudimentary diaphragm is seen also in the chelo-
nians, and in many birds, especially in the ostriches. In the
gecko fimbriatus, as in the emeu of New Holland, there is a
wide separation of the rings of the trachea, and a membranous
portion, capable of distension, passing between the widely
separated ends of the rings, about the middle of the course
of the trachea. In different species of chameelion, there is
a considerable round membranous laryngeal sac, opening
into that canal by a transverse valvular slit, between the
lower margin of the larynx, and the upper margin of the
first tracheal ring, on the fore part of the neck. The trans-
verse valvular margins of the two cartilages bounding the
slit, project into this laryngeal sac, like a rudimentary
epiglottis, and the cavity of the sac is partially divided by a
median crescentic septum extending inwards from its upper
and anterior part. The anterior tracheal ring is complete in
the geckotida, but is still incomplete in most saurian genera ;
the anterior tracheal rings are incomplete in the crocodilians
and most chelonia, but gradually become united towards the
bronchial end of the trachea.

The branchial openings on the sides of the neck, and
the subdivision of the aortal trunk into regular pairs

ORGANS OF RESPIRATION. 557

of lateral branchial arteries, have been often observed in
the embryo of the common lacerta agilis] five pairs of
branchial arteries were perceived by Baer; three bran-
chial openings have been observed, at the same time, on
each side of the neck, in saurian, as in ophidian reptiles ;
a smaller fourth opening makes its appearance at a later
period. In the substance of the first or most anterior of these
pharyngeal folds, thus formed by the successive fissuring of
the outer serous layer of the neck, in the embryo of verte-
brata, are developed the two lateral portions of the lower jaw ;
in the second fold, are formed the cornua of the os hyoides ;
and in the succeeding folds are developed, in- branchiated
animals, as fishes and amphibia, the true branchial arches and
gills for aquatic respiration.

The lungs of chelonian reptiles still extend over the whole
dorsal part of the trunk as far as the pelvis ; they are fixed
by the pleura to the ribs, which also separates them from the
cavity containing the digestive and generative organs ; they
are symmetrically developed on the two sides, largely cellular
internally, very capacious, and still composed of a single
distinct undivided lobe on each side. The large-celled
capacious lungs of turtles, expanded over the whole dorsal
region of the trunk, serve most advantageously to poise their
heavy body and its members while swimming, or floating
asleep in the water, like the air- sac of fishes, or like the
extensive pulmonary organs of birds, which poise their
suspended heavy parts while swimming in the light air.
The extent of respiration corresponds, not with the quantity
of air taken into the body of an animal, but with the extent of
surface over which the aerated blood is spread, the rapidity
of the blood's course over that surface, and the frequency of
the renewal of air in the pulmonary organs. The small, but
minutely subdivided cellular lungs of a rabbit, present a
much more extensive surface for the distribution of pulmo-
nary blood-vessels, than the capacious lungs of a turtle ten
times its size ; and although the quantity of air taken in by
the quadruped is less, it is entirely employed in effecting the
aeration of the blood, and hence its higher temperature,
activity, and general development. As the ribs of chelonia
are immoveable, the lungs fixed to their interior, and the
diaphragm consists only of a few muscular bands extending

558 ORGANS OF RESPIRATION.

over their inferior surface, inspiration is effected, as in frogs,
by the movements of the os hyoides and the pharynx, and
expiration chiefly by the abdominal muscles ; and from the
fixed condition of the osseous elements surrounding the
trunk, the resistance of the distended capacious lungs is
necessary to assist in all discharges from the body.

From the length and movements of the neck, the trachea is
generally elongated in fresh water and marine chelonia, as
in birds, and is surrounded, as in them, with complete cartila-
ginous rings ; it sometime divides, in the land species, into
two bronchial branches nearly as high as the larynx, one of
which proceeds along each side of the neck, protected from
compression during the retracted state of the head, by entire
tracheal rings. The epiglottis is only a membranous fold
across the anterior part of the opening of the glottis, but the
rudiments of the vocal chords extend further into the larynx,
and are more developed in chelonian than in other reptiles.
The vibratile cilia, which line the nasal and buccal passages,
the pharynx and oesophagus, and the larynx, trachea, and
interior of all the pulmonary organs of amphibia and reptiles,
are most remarkable for their tenacity of life in the lungs of
chelonia, where they have been observed in activity for seve-
ral weeks after death, and on portions detached from the
body, even when putrefaction had commenced. The two
bronchi of chelonia, enter the inner portion of their corres-
ponding lungs, and in traversing the whole extent of these
organs, they open as in birds, by numerous lateral perfora-
tions, into the large saccular cells of the lungs, which are
regularly disposed in outer and inner series, as shown by
Bojanus in the emys.

In birds, as in insects, the inspired air is transmitted through
almost every part of the body, and the blood sent through
the branches of their systemic vessels is freely aerated, as
well as that contained in the vessels of the lungs. The
pulmonary organs of birds present a form intermediate be-
tween those of reptiles, extended through the abdominal
cavity, and those of mammalia, confined to the thoracic por-
tion of the trunk. The large cells prolonged from the ends
of the bronchi, still reach the posterior part of the abdomen,
like the lungs of fishes, amphibia, and reptiles ; and as the
lungs are not collected into the anterior part of the trunk,

ORGANS OF RESPIRATION. 559

as they are in quadrupeds, there can yet be no muscular septum
or diaphragm separating its cavity into a thoracic and an
abdominal portion.

As in most reptiles, the pulmonary organs of birds are
composed of an anterior minutely subdivided cellular portion,
and a posterior largely sacculated part, but slightly partitioned
by internal septa, and contained, as usual in oviparous verte-
brata, in the same cavity with the digestive organs. The
highly vascular parietes of the abdominal air-sacs, or enlarged
pulmonary cells, covered with peritoneum, and lined with
the ciliated mucous membrane of the lungs, extend forwards
and backwards around the chylopoietic viscera, and reach in
every direction beyond the cavity of the trunk, as into the
axilla, the neck, the vertebrae, and the bones of the extre-
mities. Their interior is partially subdivided by imperfect
septa, the first rudiments of all pulmonary cells, which begin
to develop from the periphery ; and they communicate by a
few large round openings, on the inferior surface of the lungs,
with the ends of the wide bronchial tubes, which traverse these
organs, with little subdivisions, and nearly in a straight
course.

These air-sacs, and their free communications with the lungs
and trachea, were familiar to Harvey, who regarded them
as the principal parts of the lungs of birds, and who found
their bronchial openings in the ostrich so wide as to admit
the finger. The air-sacs are generally in contiguous pairs,
separated by a median septum, and opening each by a dis-
tinct foramen into its corresponding lung. One large
cell on each side extends forwards, under the sternum and
coracoid bone, supplying with air the bones of the shoulder
and arm, enveloping the heart, the bronchi, and the inferior
larynx, and extending into the axilla. Another extends into
the neck above the clavicles, forming various enlargements in
different species, on each side of, or beneath the crop ; ano-
ther beneath the sternum, extends also behind the heart and
oesophagus, to the vertebrae of the neck, thus enveloping the
great vascular trunks of the heart. Another large pair, some-
times subdivided into an anterior and posterior compartment,
extends backwards along the dorsal and lateral parts of the
abdomen, enveloping most of the viscera, forming air- sacs
in the pelvis, and extending into the bones of the legs.

The bones of the head, neck, trunk, and extremities, are thus

560 ORGANS OF RESPIRATION.

permeated with air from the pulmonary organs, to a variable
extent in different tribes of birds, according to their power of
flight, and their necessity for extensive aeration of their fluids.
As these cells and cavities are filled with heated air from the
lungs, the whole body is thereby rendered more light and
buoyant for progression through the colder and denser ex-
ternal medium. The highly vascular entosteal lining of the
bones, like the vascular mucous lining of the great air-sacs of
the trunk, contributes to the aeration of the systemic blood ;
and the extensions of the air-sacs thus penetrate the tissues of
the body, as they do in insects. When the trachea is tied, birds
can still inhale air, and inflate their cavities, by the broken
ends of the humerus or femur, and when the bones of the extre-
mities are fractured in flight, they are thus quickly precipitated
to the earth. The bones which receive air in birds, have a
more dry, white, and less oily appearance, than those which
permanently preserve their marrow. The air admitted into the
interior of the bones during the development and growth of
birds, causes, to a variable extent, the gradual absorption of
the thin serous marrow, which originally occupied all their
cavities.

The proper cellular lungs of birds, like those of chelonian
reptiles, are excluded from the peritoneal cavity, and bound
by cellular tissue to the inside of the ribs and the sides of the
dorsal vertebne, being covered only on their ventral surface with
peritoneum, which is prolonged also from the large bronchial
apertures overall the abdominal air-sacs. They were considered
by Bartholinus as fixed to the upper and dorsal region of the
trunk, in birds, to balance their body in flight. They consist of a
single long, flat, nearly triangular, undivided lobe on each side,
and have a more light florid red colour than in other vertebrata;
their minute cells have a parallel and methodical arrangement,
around the bronchi, and freely communicate. The bronchi,
thin and membranous, with annulated markings on one side, tra-
verse chiefly their ventral and median portions, dividing in each
lung, into about seven branches, perforated in their dorsal as-
pect with numerous foramina, leading to the minute pulmonary
cells, and terminating below in the wide oblique orifices of the
great air sacs. Their narrow, thin, inferior, and outer mar-
gins are traversed by the radiating peripheral muscular bands,
composing the rudimentary diaphragm, as in saurian and
chelonian reptiles, and by their thin tendinous expansions ;

ORGANS OF RESPIRATION'. 561

their interior is more uniformly cellular throughout than in
reptiles, and the cellules are larger than in mammalia, giving
a light spongy texture to these organs, which occupy a com-
paratively small space in the alvi-thorax of birds. Meckel
found the lungs of an emaciated eagle to weigh only -^ of the
entire carcase, and those of an equally spare heron -i-H- j they
are proportionally largest in the singing birds, and least in
the strutheous and other heavy species.

The trachea, like the neck, is necessarily lengthened in this
class, and the tracheal rings, like the cartilages of other parts
of their body, are generally ossified, and thus preserve a free
passage during the various contortions and pressures to which
this part is exposed. Surrounded with entire ossified rings
throughout its course, it descends along the left side of the
oesophagus and crop, into the cavity of the trunk ; commencing
above in a larynx, simple and uniform in structure, and much
resembling that of chelonian reptiles, it terminates below
the clavicles in a complicated osseous moveable apparatus, the
inferior larynx, for modulating the vocal sounds ; here the
trachea bifurcates to form the two soft and partially annulated
bronchi, which, without any previous subdivision, penetrate
the ventral surface of the lungs, a little behind their thick
anterior margin. The trachea is often lengthened by convo-
lutions at its lower part in aquatic birds, as swans, cranes,
geese, pintados, demoiselles, and spoonbills ; the larynx and
tracheal rings, are cartilaginous in the strutheous and some
other birds, as in mammalia. The canal of the trachea,
though commonly cylindrical, is often varied, especially in
the male, by constrictions and dilatations in its course, as
in mergus, anas, and other palmipedes, where the rings con-
tinue complete around the dilated parts. The tracheal
rings are sometimes incomplete and open at the dilated part,
as first shown by Fremery, in both sexes of the emeu of
New Holland, where they leave a free membranous tracheal
pouch a little above the sternum. The rings are often sutured
on one side ; they are remarkably destitute of bilateral sym-
metry in cranes and some other wading birds ; and the lower
part of the trachea is sometimes divided internally by a longi-
tudinal membranous septum, as in procellaria and aptenodytes.
For the retraction of the long trachea of birds, it is commonly
provided with a superficial and a deep-seated pair of retractor

PART VI. O O

5G2 ORGANS OF RESPIRATION.

muscles, the ypsilo- and sterno-tracheales, which are some-
times of great length. The tracheal differences of the sexes,
and of nearly allied species, affect, also, the inferior larynx,
and are greater in birds than in any other classes ; and they
are sometimes connected with differences of the voice. The
superficial retractor muscles are often wanting, especially in
wading birds, as in the long necked phcenicopterus, where
there are, at least, three hundred and fifty tracheal rings ; a
number not surpassed in any other bird.

The inferior larynx of birds, like other vocal organs, is a
mere accessary development of the trachea, placed on that
tube to take advantage of the elasticity of the transmitted
air, for the purpose of producing sounds, and thereby giving
audible expression to the inward feelings. The ordinary and
most convenient seat of these sounds, the superior larynx, is
developed in birds, as in other air-breathing vertebrata, and
its vibratile margins can partially vocalize the transmitted air,
like the larynx of many reptiles, to which that of birds is
most closely allied in structure. But the great length, and
the varying dimensions of the trachea, the unsuitable form of
the tongue and buccal parietes of birds for modulating sounds,
and the demand for extensive vocal intercourse in this class,
necessitate the development of a new organ of voice, an in-
ferior larynx, placed nearer to the lungs and air-cavities.
This inferior or bronchial larynx, situated at the bifurcation
of the trachea, and involving the commencements of the two
bronchi, consists of enlarged, ossified, often much altered and
anchylosed, tracheal and bronchial rings, with great mem-
branous interspaces. The lowest tracheal ring, by extending
centrad before and behind, bisects its canal with an osseous
septum ; and the membranes of the interspace, by passing
centrad from each side, form two free internal crescentic vocal
ligaments. Two semilunar membranes also extend, in sing-
ing birds, from each side of the median septum, to meet the
lateral folds, and complete the vibratile lips of these two
rimae ; two simpler vocal folds, at the narrow membranous
origin of each bronchus, are likewise added to this complex
wind-instrument. There are five pairs of muscles for the
various movements of the inferior larynx in singing birds ; in
parrots, where this part of the vocal apparatus is more simple,
theree are thre pairs of muscles ; in many rapaceous, grallato-

ORGANS OF RESPIRATION.

rial and other birds, with less power of modulating their
sounds, there is but one pair of these inferior laryngeal
muscles, and in the gallinaceous and a few other birds, there
are no special muscles for the movement of the inferior
larynx, distinct from the ordinary muscles of the trachea.

The superior larynx is still very simple in birds ; it is much
more uniform throughout the class than the inferior, and it
more nearly approaches to that of reptiles, especially of che-
lonia, than to that of mammalia. The large thyroid cartilage
forms the anterior part, and the entire base resting on the
first tracheal ring, and its two lateral quadrangular pieces,
often detached when ossified, have commonly been mistaken
for the cricoid cartilages. These three principal constituent
parts of the thyroid, remain united through life in swans,
pelicans, parrots, ostriches, and some other birds, especially
where they retain their primitive cartilaginous condition ; but
where they become ossified, the broad pentagonal anterior,
and two lateral four-sided pieces, leave greater or less cartila-
ginous interspaces between them, which have impeded the
identification of the laryngeal elements of birds. The rudi-
ments of tracheal rings are generally seen at the base of the
large middle anterior piece of the thyroid, indicating the
mode of development and separation of the more perfect in-
ferior rings. The thyroid pieces are disunited on the median
line behind, though generally in contact ; and on dissecting
the inner and upper part of the anterior piece, the cartilagi-
nous rudiments of the epiglottis, are seen extending upwards
and inwards. In the storks and herons, the processus epiglot-
ticus rises upwards broad, like that of an agama among the
sauria, and is already ossified in these birds, like most of their
tracheal and laryngeal parts. In many gallinaceous and
other birds, the epiglottis is flat, thin, and flexible, like that
of mammalia ; and the most perfect forms of the epiglottis
observed by Henle in the birds, were those of sterna, rallus,
and larus} where it is detached from the thyroid cartilage, and
extends free, flexible, and cartilaginous, into the pharyngeal
cavity.

Between the posterior ends of the thyroid cartilage, in the
angular space commonly left behind by the meeting of its
edges, is situated the small cricoid cartilage of birds, of a
quadrangular, or triangular form, often ossified, tapering

oo2

564 ORGANS OF RESPIRATION.

downwards, and supporting the arytaenoid cartilages above,
attached to each side of its free projecting margin. It
presents a middle, and two lateral centres of ossification,
sometimes separated from each other by vertical fissures,
and is often partially attached to the basilar ring of the
thyroid, and to the lateral quadrangular pieces of the
thyroid, which has induced many to consider the whole
of these pieces as forming together the cricoid cartilage
of birds. The long, narrow, triangular, arytsenoid car-
tilages, tapering forwards, broader, and united together
behind, generally ossified, bound the rima of the glottis with
their straight inner margin, and are attached to the thyroid
by their outer edge. Though generally ossified, like the
other laryngeal and tracheal parts of birds, the cricoid and
other laryngeal cartilages remain soft, flexible, and cartilagi-
nous in the strutheous birds, as in mammalia. The larynx
and trachea are raised chiefly by the hyothyrioideus and the
thyriotrachealis muscles ; the laryngeal opening is widened
by the thyrioarytcenoideus posticus muscle, and is com-
pressed by the thyrioarytanoideus lateralis, as in the higher
reptiles. The muscles of the upper larynx of birds appear to
be supplied chiefly by the superior laryngeal nerve, which pro-
tects the passage of the glottis, and the muscles of the lower
larynx, or organ of voice, by the inferior laryngeal, or vocal
nerve.

In the embryo of birds, the lungs appear as two small sacs
or follicles, developed from the oesophagus or pharynx; their
apertures coalesce and elongate, to form a tracheal duct, on
the median plain; the interior parietes of these primitive
pulmonary sacs, develope peripheral septa or follicles, to form
the rudiments of their internal cells, which are arranged with
great regularity, though subdivided and ramified, around the
bronchial canals ; and the membranous tracheal duct, or
ductus pneumaticus, becomes cartilaginous, segmented, and
divided into a distinct superior and inferior larynx, with a
more simple intermediate, lengthened, annulated trachea.
Before the branchial openings have formed on the sides of
the neck, the integuments appear entire on both sides, and
when the embryo is more advanced, three lateral passages
are discovered on each side, leading into the cavity of the
pharynx. They are seen in the chick on the third day of in-

ORGANS OF RESPIRATION. 565

cubation, and they continue open to the eighth. The aorta
divides from its origin, into two great lateral arches, each of
which subdivides into the five branchial arteries of its own
side, which receive the entire blood of the heart. Between
the second and third days of incubation, four pairs of
branchial arteries are observed to be produced in succession
from before backwards ; and the first, or anterior of these
pairs, has disappeared before the fifth pair of branchial
arteries is developed, behind the others, on the fifth day of
incubation. The same order of succession is observed in
the development of the pairs of branchial openings in the
neck, from the anterior to the posterior pair. The vibratile
cilia are seen in active motion, on the mucous lining of every
part of the respiratory organs of birds, from the openings of
the nostrils and the interior of the eustachian tubes, to the
minutest divisions of the bronchi, and the closed extremities
of the great air-sacs extending through the trunk.

The respiratory organs of mammalia are confined to a
distinct thoracic cavity, separated from the abdomen by a
complete muscular and tendinous diaphragm ; and as this
function is not extended to their systemic vessels, as it is
in birds, they manifest a lower temperature of the body, and
a diminished energy of their muscular system, and of almost
all their vital properties. The lungs here are covered on all
sides with pleura, and float free in the cavity of the chest ;
they no longer communicate with abdominal air-sacs, or
with the cavities of the bones ; they are entirely divided
into more minute cells, so as to present a more extensive
respiratory surface than in inferior classes, and they are
larger in the male than in the female sex. They are more
minutely and equally divided into cells, and into lobes, and
present a larger respiratory surface, and occupy a larger
thoracic cavity, in the more powerful carnivorous quadrupeds,
than in the feebler herbivorous tribes, where the more
limited development of the respiratory organs is accompanied
with a diminished energy of all their movements and func-
tions. The contiguous minute terminal cells of the lungs
appear to communicate with each other, like the ultimate
tubuli of many other glands. The lung of the right side is
generally larger than the left, from the sinistral position of
the heart, especially in the higher mammalia and man^ and

566 ORGANS OF RESPIRATION.

the number of lobes on each side generally corresponds with
that of the primary divisions of the bronchi.

In the cetacea, they present the most firm compact texture,
the largest cells, and the least division into lobes ; they are
also but slightly lobed in many of the ruminantia, pachy-
derma, and even chiroptera, and in some of the larger her-
bivora they present no lobular divisions on either side ; thus
approaching, in the lower mammalia, to the undivided con-
dition of the lungs in birds. The bronchi ramify to a great
degree of minuteness before ending in the small vesicles, or
terminal air-cells, on the parietes of which the pulmonary
capillary vessels are chiefly distributed. The mucous mem-
brane, lining all the nasal passages, the eustachian tubes,
the larynx, trachea, and bronchial ramifications, is covered
with active vibratile cilia, as in inferior vertebrata, and which
continue their active movements on detached portions, long
after death. Although the lungs of mammalia do not extend
beyond the cavity of the thorax, the air is admitted in some
chiroptera, as first shown by Geoffroy in the nycteris, into
large cellular sacs surrounding the trunk of the body, be-
tween the skin and the muscles, especially of the back and
sides in the common plecotus, which assists in bracing the
muscles, and probably in aeration, and lightens the body by
the retention of heated air, as in birds. The air is intro-
duced into these subcutaneous cells of the bats, by a small
round aperture, provided with a sphincter, and situated at
the bottom of each of the two cheek-pouches. The entrance
to the respiratory organs in most aquatic mammalia, as seals
and beavers, is protected by the valvular structure of the
nostrils, which they can completely close against the water
through which they move with rapidity ; and a similar
structure is seen in the nostrils of the camels, and some
other ruminantia, to protect them against the drifting sands
of the deserts. In several cetacea, as the porpise, the
nostrils form two elongated moveable muscular sacs, as in
some crocodilian reptiles, by extending which to the surface
of the water, they can respire freely, while the rest of their
body is entirely immersed.

The trachea of mammalia varies with the length of the
neck, in the different species, and is generally shorter and
more straight than in birds ; it is nearly of equal calibre,

ORGANS OF RESPIRATION. 567

without convolutions or enlargements in its course, or an
inferior larynx ; it is frequently directed a little to the right
of the oesophagus, and is closely surrounded with rings,
for the most part incomplete on their posterior aspect, some-
times incomplete in front, as in many of the cetacea, and of
a cartilaginous texture, though often becoming ossified in
advanced age. It divides in the cavity of the thorax com-
monly into two, sometimes into three bronchial tubes, which
again subdivide before entering the substance of the lungs.
The bronchi often continue their cartilaginous rings, with
their intervening fibrous structure, through their minuter
divisions in the lungs. The posterior vacant spaces between
the ends of the tracheal rings, present distinct transverse
connecting fibres, and longitudinal fasciculi of fibres are seen
passing between the margins of the successive rings. The
tracheal rings are completed behind in the most diversified
forms of mammalia, as in the long-necked rumiriantia, and
the short-necked cetacea, in burrowing rodentia, and in
flying chiroptera, and probably relates to the extent of
motion or pressure to which this part may be exposed by
the living habits of the species. The trachea appears to be
somewhat elongated and curved in the thorax of bradypus,
as common in the feathered tribes to which they are so
much allied.

The larynx of mammalia, like that of inferior vertebra ta,
is formed by the development and consolidation of tracheal
rings, and presents the most complex and perfect form of
this part, being formed on the anterior and lateral parts by
the thyroid cartilage, on the posterior and inferior parts by
the cricoid, and on the upper and inner part by the arytee-
noid cartilages. The thyroid cartilage, which meets behind
in birds as well as in front, is always widely deficient on the
back part in mammalia, where the interspace is occupied by
the now greatly developed cricoid. The two posterior pieces
of the thyroid of birds, as shown by the careful researches of
Henle, have here coalesced with the cricoid, to compose a
part of that cartilage, as the styl-hyoid bone of inferior
quadrupeds separates from the os hyoides, and anchyloses
with the temporal in man, to form a process of that bone.
The posterior margin of the thyroid is extended downwards
on each side, to form the narrow inferior cornu for the

568 ORGANS OF RESPIRATION.

attachment of the cricoid cartilage, and the same posterior
margin is prolonged upwards to form a superior cornu for the
attachment to the os hyoides. The thyroid cartilage is still
sometimes divided vertically on the median plain, by a
distinct suture, into two lateral halves, as it is in many of
the reptiles ; and although it no longer manifests a division
into its primitive separate tracheal rings, the perforation for
the inferior laryngeal artery is considered by Henle as
indicating an earlier separation at that point. The thyroid
cartilage of the ornithorhynchus is a small, simple, flat, arched
piece, without either superior or inferior cornua, and its
firm ligamentous connection with the hyoid bone, was sup-
posed by Meckel to be a peculiar extension of the thyroid
cartilage, embracing the oesophagus, in this animal.

The cricoid cartilage of mammalia, always most developed
behind, where it rises upwards between the posterior edges
of the thyroid, and tapering forwards, where it is often
deficient, as in many carnivora and cetacea, is formed by the
union of the small cricoid of chelonia and birds with the
detached posterior, or lateral pieces of the thyroid seen
in the latter class. It here commonly forms a complete
ring, united though small in front, resting on the first tracheal
ring, attached to the inferior cornua of the thyroid, and by
a small vertical median ridge behind to the oesophagus, and
supporting on its upper convex posterior articular surfaces,
the two arytaenoid cartilages. There are commonly two
small round inter articular cartilages, discovered by Brandt,
like sesamoid bones, between the upper edge of the thyroid
and the articular surfaces of the arytsenoid ; these are largest
and triangular in the hedgehog, and are transversely elongated
in the vampire. Similar small inter articular pieces are also
frequently found between the posterior and inner edges of
the arytaenoid cartilages, which in the ornithorhynchus, the
opossum, and some other mammalia, are consolidated into a
single piece on the median plain.

The two arytaenoid cartilages preserve their elongated
triangular form and their general connections, most con-
stantly throughout the pulmonated vertebrata, being less
extended longitudinally in mammalia than in birds. Resting
by their grooved and smooth articular bases on the back
part of the cricoid, and extending forwards, with their flat

ORGANS OF RESPIRATION. 569

inner margins parallel and approximated, they commonly
present, at their tapering anterior ends, the small capitula
santorini, which are attached to their apices by distinct
articular surfaces, and ligamentous fibres. The capitula are
merely continuous, curved, terminal processes of the
arytsenoid cartilages in the ruminantia and solidungula, as in
the lower classes, and become distinct cartilages in the higher
mammifera, where we observe also, for the first time, two
small detached cuneiform cartilages lying between the folds of
the mucous membrane, the li 'g amenta aryepiglottica, extending
from the arytsenoid to the epiglottis. The highly elastic
fibro-cartilaginous epiglottis, rising upwards from the ante-
rior and superior part of the thyroid, and capable of covering,
during deglutition, the entrance of the glottis, is now almost
always distinctly separate from the thyroid cartilage. In
the cetacea, however, the epiglottis, as shown by Rapp and
Henie, is still a mere process continuous with the thyroid
cartilage, as in the lower vertebrata, and is in the dolphin and
porpise, a thick firm cartilaginous mass, almost destitute of
its usual elastic tissue.

As we ascend in the vertebrated classes, the distance be-
tween the arytsenoid and the thyroid cartilages increases,
and the connecting mucous fold, the lig amentum aryepiglotti-
cum, on each side becomes, in proportion, more expanded
over the entrance of the larynx, and now affords space for
the development of the cuneiform cartilages, which are not
found in inferior classes. The upper and lower pair of vocal
ligaments, or chorda vocales, and the intervening ventricula
morgagni, are found in almost all mammiferous animals
above the cetacea. The inferior vocal ligaments of mamma-
lia are the analogues of those of reptiles, and principally
form the rima of the glottis.

The three laryngeal muscles of birds and reptiles, are
represented by three groups of muscles in mammalia. The
hyo-, crico-y and sterno-thyrioidei muscles, He in front, and the
two last of these represent the thyrio-tracheales of birds ; and
the glosso-epiglotticus of mammalia is regarded by Henle as
only a fasciculus detached from the hyo-thyrioideus, as the
epiglottis here represents merely the anterior point of the
thyroid cartilage of lower tribes. The cricoarytaenoidei postici,
ascending from the cricoid to the arytsenoid cartilages in
mammalia, (where we have already seen that the lateral

570 ORGANS OF RESPIRATION.

pieces of the thyroid cartilage of birds, have united to the
cricoid,) dilate the entrance of the larynx. Now that the
epiglottis is a distinct, detached and moveable part, the ary-
epiglotticus, which in inferior classes acted only on the
arytaenoid cartilages, serves in mammalia, to depress the
moveable epiglottis. The crico-arytcenoideus lateralis has
also shifted from the thyroid to the cricoid cartilage, and
serves to compress the passage of the larynx, and a similar
function is performed by the thyrio-arytcenoideus, and the
arytaenoideus transversus and obliquus. And with this elastic,
vibratile, and muscular apparatus, developed at the entrance
of the respiratory organs of air-breathing vertebrata, they
are enabled to regulate the quantity of air sent to or from
the lungs, to protect these organs against the intrusion of
foreign matter from the buccal or nasal cavities, and to
vocalize the air transmitted through the trachea, so as to
produce the various sounds of animals.

The development and metamorphosis of the branchial
arteries, and the successive formation and closing of the
branchial openings of the neck in the mammalia, present the
same phenomena as in the inferior air-breathing vertebra ted
classes, and have often been observed and described in the
human body, as well as in inferior quadrupeds, by Rathke,
Baer, Ascherson, Burdach, Meckel, Miiller, and other
anatomists. The branchial arterial arches are successively
formed from before backwards, and successively metamor-
phosed into the ascending cephalic and brachial arterial
trunks, the descending aorta, and the pulmonary arteries,
but no true branchiae have yet been detected in this class,
nor above the amphibia. Three or four branchial openings
on each side of the neck, are commonly observed present at
the same time, in mammalia, as in the lower classes ; they
appear and disappear in succession from before backwards,
and the anterior openings on each side are generally much
larger than the two posterior. In a human embryo three
lines long, Rathke found the sides of the neck not yet per-
forated by the branchial openings ; in the hog, they were
open in an embryo only six lines long, also in an embryo of
the horse only eight lines in length, and at an early period
in the embryo of the sheep. Baer perceived three pairs of
branchial openings, the anterior pair being much larger than
the posterior, in a human embryo at the fifth week; and in

ORGANS OF RESPIRATION.

a dog's embryo of three weeks, he detected four branchial
arteries co-existing on each side, with the minute rudiment
of a posterior fifth pair. Four pairs of these openings were
observed present at the same time, by Miiller and by Bur-
dach, in the human embryo about the fourth week ; Rathke
found three pairs of unequal openings in the human embryo,
about the sixth week; and Ascherson has observed arid
described several abnormal cases, where remnants of these
branchial openings were preserved through life, forming
permanent congenital fistulas in the human neck.

The same simple and uniform plan, followed by nature in
the construction of all animal organs, is not less apparent
in the development of the pulmonary organs of man and
mammalia, than in that of their branchial apparatus. The
lungs begin by a single simple follicle, as other glands,
originating on the median plain, in a vascular blastema,
on the fore part of the oesophagus, and soon extend down-
wards, bifurcate, and enlarge at their closed extremities, so
as to constitute two simple pulmonary sacs, with a single
membranous trachea, like that of fishes, or the lowest am-
phibia, or a lepidosiren. Peripheral septa begin to appear
on the inner surface of their dilated part, the rudiments of
future terminal cells. The trachea elongates, and irregular
continuous spots of cartilage are perceived extending on its
two sides, which rudiments of tracheal rings as yet neither
meet in front nor behind, a condition preserved in the adult
pulmonary organs of many amphibia, and the lowest reptiles.
The peripheral septa extend inwards, to cancellate the pul-
monary sacs, proceeding from their proximal towards their
distal ends, as in reptiles. The lateral tracheal primitive
cartilages, now extending their development upwards and
downwards along the sides of that tube, become divided
transversely, by absorption, into separate pieces, to form
imperfect and incomplete tracheal rings. By the gradual
approximation of these imperfect rings, on the median plain,
before and behind, by their increased size and number, and
by their enlargement and coalescence at the beginning of
the air- tube, the annulated trachea and the laryngeal carti-
lages are distinguished and completed, as the uncancellated
membranous tubular bronchi had been previously rendered
distinct from the capaceous cancellated lungs. The tracheal

572 ORGANS OF RESPIRATION.

cartilages and fibrous structure are continued along the
bronchi, and their ramifications, in the substance of the
lungs. The laryngeal cartilages, by the successive formation
and detachment of new elementary pieces, and the coalescence
of others, pass through every inferior vertebrated form to
the human type. The few simple laryngeal muscles and
ligaments of amphibia and reptiles, become necessarily
broken up into distinct parts, to form new muscles and
ligaments, with different attachments and different functions.
And thus, by a series of changes, complicated but uniform,
of which no limit has existed in the past conditions or can
be conceived in the future, the respiratory organs of animals
have arrived at the type of the human pulmonary apparatus,
by which his vital fluids are purified and replenished, his
muscular system is furnished with its capability of action,
his high temperature is preserved in every condition of the
surrounding element, and his means of oral communication
are established, which enable him to express his feelings
and his wants, to communicate his accumulated knowledge,
and to enjoy the most refined physical and intellectual
pleasures of which his nature is susceptible.

ORGANS OF SECRETION. 5/3

CHAPTER FIFTH.

ORGANS OP SECRETION.
FIRST SECTION.

General Observations on the Secreting Organs.

THE blood, replenished with fresh materials from the
lacteals, and oxygenated by respiration, is fitted to be sent
through the system for the nourishment of all the organs,
and to afford the materials of all the secretions. But every
living membrane in contact with a fluid, whether in the
interior or on the surface of the body, exhales its own pecu-
liar secretions ; and in the lowest tribes of animals, all the
requisite secretions are furnished from the fluids of the body,
often without even the presence of a distinct sanguiferous
system. The materials thus transuded through the porous
texture of membranes, or the parietes of capillary vessels,
are sometimes destined to form directly a part of the living
system, sometimes to assist in the complicated process of
the assimilation of foreign matter, and sometimes to form
excretions to be discharged from the body. The secretions,
however, are not mere transudations of the constituent
materials of the fluids which afforded them, unchanged in
composition and properties ; they are generally altered, both
in chemical and physical properties, during their transmis-
sion by nervous influence, or by the peculiar texture and
form of the secreting membranes, or by the mode of distri-
bution of the vessels. They are poured out alike by the
external cutaneous surface of animals, and by its internal
continuation the mucous lining of the digestive canal, or into
the shut cavities of serous membranes, to lubricate the

574 ORGANS OF SECRETION.

surface of internal organs. The secerning membranes most
generally present a tubular form, open at one end, and closed
at the other, forming cells, or sacs, or follicles, or tubuli, or
conglobate, or conglomerate glands, by which the largest
secreting surface is accommodated in the smallest space, and
the readiest transmission is afforded to the secreted matter ;
and the whole form and structure of these glands appear to
become more complex, as the fluids they produce differ more
from the constitution of the blood which affords them.

The alimentary canal traversing the interior of animals,
itself lined with a secreting membrane, is the common pas-
sage for foreign matter through their body, and into which
the most numerous streams of secreted fluids are incessantly
pouring from all sides. Most of the glandular secretions
poured into this canal, assist in the conversion of this ma-
terial into chyle, to replenish the blood ; and these chy-
lopoietic glands, the most essential to life and growth, are
the first formed in the animal body, and the most universal
in their occurrence in the animal kingdom. Indeed, the
whole processes of the nutrition and growth of every part
of the organization, though not effected by distinct glands,
may be considered as a series of secretions of their own
materials, by all the different constituent tissues of the be dy.
The first-formed secreting surface, and the most universal in
animals, is the skin, and next, its internal continuation, the
digestive canai ; and nearly every distinct gland of the body,
is developed from one of these two surfaces, which in most
of the lower animals, are very similar to each other.

A mucous membrane, a mucous follicle, and a muciparous
gland, are but different forms of the same surface, more or
less extended, and more or less isolated, and adapted alike,
under every form, for the distribution of capillary blood-
vessels, and for affording their peculiar secretion. When
these common secreting membranes have acquired a com-
plicated and isolated form, so as to present, in small space,
a large surface for the distribution of the capillaries, which
afford the materials of the secretion, they constitute glands,
which may thus be developed as isolated follicles, or the
most ramified tubuli, from every mucous^ cutaneous, or serous
surface of the body. The adult forms of all glands in the
lowest tribes of animals, and the earliest transient rudi-

ORGANS OF SECRETION. 575

mentary forms of the most complicated glands in the highest
classes, are merely simple co3ca prolonged from the surface
on which they open. The transition from secreting lining
or investing membranes, to secreting glands, is gradual and
almost imperceptible, and the most complicated glands of
the highest animals, as the liver and the pancreas, scarcely
merit the name of glands in their first stages of development,
or in the lowest tribes of animals.

As digestion is the most important function of organic
life, and the digestive organs the most universal in animals,
the largest, the most numerous, and the most important
glands of the body, are developed from, and communicate
with the interior of the alimentary canal. The duct of a
gland is the gland itself, which may be a simple follicle, or a
tubulus ramified so as to compose a conglomerate mass, like
the liver ; but this membranous duct, with its vessels and
nerves, appear to be alone, though mysteriously, concerned
in the production of the secretion. Not only are the liver,
the pancreas, the salivary, and other chylopoietic glands, but
ducts developed from the digestive canal, and minutely
ramified towards their closed extremities, but even the
urinary, the genital, and the pulmonary organs themselves,
may be regarded as developments of the same kind. As the
digestive canal is not only lined with a secreting membrane,
continued through all its glands, but is also provided with a
muscular tunic to move its contents; so we observe this fibrous
contractile coat continued along the ducts of glands, to an
indefinite extent, to expel the secretions from their interior.

In the first development of glands, the part from which
they are to originate, becomes thickened, soft, and highly
vascular, and constitutes a blastema or nidus through which
the growing ducts are to ramify. The blastema somewhat
indicates the form of the future gland, by its early division
into corresponding lobes and lobules ; and it becomes gra-
dually absorbed, as the developing tubuli ramify through its
substance. The glands which first make their appearance
in the lowest animals, are those most important in the eco-
nomy, those most constant in all the higher classes, and
which attain the greatest magnitude and complication in
quadrupeds and man ; and there are many considerable
temporary glands in the embryos of the highest animals,

576 ORGANS OF SECRETION.

which appear to attain no farther development than that of
a simple deciduous blastema.

As a follicle implies merely a more elevated condition of a
secreting surface, than a simple flat membrane, an aggregate
follicular gland, merely a more advanced condition of a
follicle, and a conglomerate glandular mass, merely a further
development of a follicular gland ; and as the same gland
passes through all these forms, in the course of its develop-
ment : so we find the highest of these conditions, the con-
glomerate form, to characterise the glands of the highest
animals ; and, in the lowest radiata, the cutaneous and the
mucous surfaces afford all the requisite secretions, without
even assuming the follicular form. All secreting glands, so
far as their structure can be perceived, being thus merely
membranous coecal tubes, with highly vascular parietes, their
peculiarities relate chiefly to trivial differences of form, size,
situation, and products, throughout the animal kingdom,
which admit of being considered either in zoological order,
or by following separately, through all classes, the history of
every individual gland.

SECOND SECTION.

Secreting Organs of the Cycloneurose or Radiated classes.

In the radiated classes of animals, which constitute the
first stages of animal organization, the glandular form ap-
pears rarely necessary for affording the various secretions of
their cutaneous or mucous surfaces ; a copious mucous
secretion is poured out from every part of their soft smooth
cutaneous exterior, and from the mucous lining of their
digestive cavities, without their appearing to require distinct
cryptee, or other forms of glands for its formation. The
earliest developed, and the most constant gland in the animal
kingdom, is the liver, the first formed and the most compli-
cated in the highest animals, and the most important in the
process of nutrition ; and in the radiated, as well as in most
of the articulated animals, this organ, so complicated and
enormous in the vertebrata, generally consists of simple
isolated follicles, more or less numerous, opening directly
into the cavity of the stomach. The numerous intestinal
coeca, or stomachs of poly gastric animalcules, opening into

ORGANS OF SECRETION. 577

their alimentary canal, and the only distinct follicles per-
ceptible in their body, may be considered as analogous to
the hepatic coeca developed from the sides of the intestine, of
long gastric cavity, of annelides. The hepatic follicles in most
of the lower invertebrata, and in the first stages of their de-
velopment in the highest vertebrated animals, admit the
contents of the intestine into their interior, as well as in
polygastrica. Were the secretions furnished by the interior
lining of these follicles in the polygastrica, different in their
characters towards the anterior and posterior ends of the
digestive canal, the follicles nearest to the masticating organs,
might be considered as salivary, and those nearest to the
anus, as urinary glands, as in many articulata, but these
differences and analogies are not established in this class.
A larger single or double follicle, more various in form
and colour, than the intestinal, and the small contractile
follicle, seen in most polygastrica, have been imagined to be
connected with the generative system, and the former to
represent a testicle, and the latter a vesicula seminalis, but
with as little evidence of such analogy. As the whole inter-
nal cavity of polygastrica, whether a canal as in the diaccelous
and cyclocoelous forms, or a mere concavity as in the anen-
terous species, is most analogous to the gastric sac of higher
animals ; so are all its follicles most analogous to hepatic or
biliary tubuli, forming the simple condition of the liver in
these animals. Some polygastrica, as peridinium, synchseta,
prorocentrum, illuminate the seas where they occur, but
the source of their luminous secretion, is as little known as
that of many higher animals. The flesh of poriphera forms
a universal blastema for all the glands and other organs or
higher animals, but in which none are yet developed ; and if
its constituent granules enjoy an independent existence, like
the individuals of aggregate animalcules, they probably
exhibit also in their interior, the hepatic follicles, or so-
named stomachs of all other known polygastrica. Fine
pellicles of mucus or epithelium are secreted by the sides
of the internal canals of poriphera, and are constantly thrown
out, along with the respiratory currents, from the numerous
large vents of their surface.

From the fleshy surface of lobularia, and other polypiphera,
thin mucous pellicles are periodically formed and detached,

PART VI. P P

ORGANS OF SECRETION.

like the periodical cuticular separations of most vertebrata.
Some as pennatula, when excited, emit a bright luminosity,
which is secreted by the individual polypi. These luminous
secretions, so common in the radiated and the molluscous
classes, appear to accompany the mucous secretions of the
skin, or of the alimentary canal. Numerous zoophytes
secrete from their surface large quantities of calcareous
matter, mixed with a coagulating muco-gelatinous substance
to form the solid extravascular skeleton of lithophytes, and
others pour out upon their surface, or into their interior, a
soft homogeneous coagulable matter, which soon hardens to
constitute the flexible sheath or the axis of keratophytes.
Many secrete colouring matters of various and vivid hues,
sometimes along with the earthy matter of the skeleton, as
the purple of corallium, tubipora, melitcea, and sometimes
without it, as in the deep hues of actinia, zoanthi, pennatula.
The interior of the stomach of many zoophytes, as actinia,
produces a copious secretion which appears to prove quickly
fatal to, and quickly to dissolve their victims when seized and
swallowed alive, and these parts of the stomach appear striated
with thick opaque patches, like a blastema of future follicles.
This condition of the secreting surface of the stomach, is more
follicular in appearance in many sertularite, where it is reduced
to minute aggregated coloured spots, like rudimentary biliary
tubuli filled with their coloured secretion ; and from the sto-
mach of the polypi ufflustrce, a distinct hollow follicle extends,
forming an arrested development of a liver. We may regard,
however, most of the glandular or secreting organs of these
lowest classes, as still in their simplest condition of flat
smooth secreting membranes, which have not yet developed
even cryptee or follicles to extend their surface, and to pro-
vide for the different kinds of products, and yet their secret-
ing powers are often very considerable, and their products
most varied. They present no distinct glandular structures
for elaborating those very different materials from the food
which they take in. Each species developes its gemmules
always from determinate points of the body, and not indis-
criminately from every part of the fleshy substance. We
may consider, therefore, that even the ovariuni, or the gland
for secreting ova which is developed in higher classes of
animals., presents itself here in a rudimentary state, as a

ORGANS OF SECRETION. 579

series of gemmiparous points of the common fleshy sub-
stance.

Most of the acalepha exhibit tubular prolongations, sim-
ple or ramified, extending from the periphery of their great
gastric sac, by which the absorbent and secreting internal
surface is increased, and the nutriment is distributed to a
greater distance from the central cavity. These become
more circumscribed tubular coeca, like biliary tubuli, in the
stomach of physalia, carybdea, and other genera, and the
analogies of these gastric coeca to the liver, have long been
suggested by Eschscholtz, Edwards, and others. The mar-
ginal, cylindrical, opaque, granular bodies around the disk
of many medusa, have been regarded as the liver of these
animals. Most of the species are known to secrete upon
their surface a matter of a highly acrid, poisonous, and
stinging quality, which appears to be furnished by every
point of their surface, and which exerts peculiarly irritating
effects on the human skin and other parts. I have expe-
rienced the violent inflammation and burning torture resulting
from its application to the surface of the eye. Another de-
fensive secretion of these animals, is the luminous material
which appears to be connected with the mucous secretion of
their surface, and to pervade nearly the whole class. The
brilliant hues emitted by day, and the vivid light emitted in
the dark, by beroes and other ciliograde forms, appear to be
confined to the large vibratile cilia. The physograde species,
secrete a gaseous fluid into their air-sac to assist in swim-
ming, and some others as physophora, porpita, and velella,
secrete a firm horny skeleton to support their soft parts.
Some secrete a bright blood-red matter into their long slender
tentacula, and the velellce are covered with a soft substance
of a deep violet-blue colour.

The small follicular coeca, sometimes ramified, which open
into the digestive canal of holothuria, and into the wide
gastric cavity of stellerida, are considered by Chiaje as con-
stituting the liver of the echinoderma ; but the hepatic tubuli
of higher and lower allied classes have still more close analo-
gies with the ordinary large ramified gastric coeca extending
into the rays of asterias, and in other genera. If a difference
of function existed in these gastric appendices, the smaller
isolated follicles would rather represent a pancreas in these

p p 2

'580 ORGANS OF SECRETION.

animals, and the larger ramified cceca the liver. There are
numerous distinct matters eliminated from the food by the
vital processes of echinoderma, but very few developed
glandular organs appropriated to their formation; the
various colouring materials of the surface, of vivid hues,
both in the naked and the testaceous forms ; the numerous
calcareous deposits of granules, spines, and shells ; the co-
pious solvent secretions of their digestive cavities, and the
mucous secretions poured out on the surface of holothurw,
and other naked species ; the supposed calcifiant gland of the
stellerida, which is a small vascular sac filled with a thick
grumous secretion, consisting chiefly of minute calcareous
crystals ; and the numerous distinct sacs or tubuli, for the
periodical development of ova. The internal branchiae of
holothurue have the form of long hollow ramified tubuli, and
into their wide ducts, close to the cloaca, open several small
isolated follicles, like a rudimentary kidney or renal tubuli ;
small isolated salivary follicles are observed also in some of
the species, opening into the cavity of the mouth.

THIRD SECTION.

Secreting Organs of the Diploneurose or Articulated Classes.

The glandular organs of articulata are more distinct, more
numerous, and more constant than in the radiated classes,
but they still manifest the simplest follicular character, both
in the ordinary chylopoietic, and in the newer and peculiar
glands, and this simple condition of their chylopoietic glands
accords with the nutritive character of the food in most of
these parasitic or carnivorous tribes. The liver is rarely
imperceptible in the entozoa, and has been long since shown
by Rudolphi, Bojanus, and others ; and salivary glands have
also long been observed in the animals of this class, as in
the trematode diplozoon, described by Nordmann, and in the
pentastoma, by Cuvier. In most of the trematode and
lowest forms of parenchymatous entozoa, as in many echi-
noderma and annelides, the liver consists of numerous
ramified coeca prolonged from the sides of the digestive
canal ; and in the higher nematoid species, the biliary tubuli
are restricted to small short follicles surrounding the long

ORGANS OF SECRETION. 58l

gastric sac, or straight alimentary tube. The salivary glands
consist of one or more simple undivided tubuli opening into
the mouth, and even the testis and ovary have still the
simplest glandular form of elongated tubuli.

The liver is not less obvious in the rotiferous animalcules,
where it consists of isolated tubuli, varying much in their
number and size, and opening directly into the wide gastric
cavity. Two of these hepatic tubuli are seen in brachionus
urseolaris, four in megalotrocha alba, seven in diglena lacus-
trisy nine in enteroplea hydatina, some dozens surround the
stomach in rotifer vulgaris, and in philodina roseola the
entire length of the digestive cavity is closely enveloped
with simple, short, straight, parallel biliary follicles, as in
many of the higher annelides. These various tubuli are
commonly dilated at their closed ends, as in most other
glands ; and the difference of form and place of insertion of
these tubuli, would induce a belief of their having sometimes
different functions, and representing both liver and pancreas,
as in the enteroplea hydatina, where seven long narrow
biliary tubuli open into the upper cardiac portion of the
stomach, and at some distance below two very different short
wide follicles, like the rudiment of a distinct pancreatic
gland. The salivary glands are generally represented in the
rotifera by two simple dilated follicles connected with the
sides of the masticating apparatus. The male and female
genital organs have also here a simple tubular structure, the
internal branchiae are in form of ramose tufts, the vesicula
seminalis is a single median follicle, and a few of the species
secjete upon their surface extravascular silicious laminae,
forming an enveloping sheath, like the polygastrica.

The high development of the chylopoietic glands of the
cirrhopods, and the form and connexions of these organs,
constitute further affinities between them and the mollus-
cous classes, and accord with their imperfect means of select-
ing and obtaining the more nutritious kinds of aliment.
The liver is of great size, and consists of innumerable small
biliary follicles or cryptae, arranged in clusters or acini, which
form several lobes on each side of the stomach. These
lobes surrounding the stomach open into different parts of
its cavity by short wide biliary ducts, as in most mollusca.
Two large conglomerate salivary glands pour their secretion

582 ORGANS OF SECRETION.

into the mouth near the masticating apparatus. The male
and female genital glands have assumed a more complicated
form, and the exterior secreting surface of the mantle pours
out the calcareous matter of their complicated shell, and the
dark coloured epidermis covering the peduncle of anatifee.

Numerous small coeca, or biliary tubuli, are seen extending
from the periphery of the digestive canal of many annulida,
as the common earth-worm, which generally assume the
saccular form of dilated follicles, as the gastric follicles of
polygastrica, and are commonly filled with their yellowish-
white coloured bilious secretion. These tubuli are very short,
wide, and rudimentary along the sides of the stomach of the
leech, excepting the last pair, near the pyloric valve, which
have the narrow lengthened form of the hepatic tubuli of
insects. In halithea, they arise by narrow openings from
along the sides of the dorsal aspect of the stomach, they are
much elongated, slightly ramified, and enlarge at their ex-
tremities into vesicles generally filled with digested or
secreted matter. They are ramified also in planarise and
other annelides, as the prolongations of the stomach in many
of the parenchymatous entozoa. From the biliary tubuli,
such as they are, in the leech, extending along the entire
length of the stomach, and ceasing to be developed at the
pyloric valve, we more distinctly perceive the great extent of
the alimentary canal which here corresponds to the gastric
cavity of higher animals, and the relations of the hepatic
tubuli to that cavity. The higher development and greater
constancy of the salivary glands in annelides than in entozoa,
corresponds with the higher condition of their masticatory
and other organs, and the more mixed character of their
food. Several salivary follicles open into the mouth of the
earth-worm, as shown by Morren ; I have observed two
elongated salivary tubuli in the arenicola ; and Brandt found
them composed of clustered follicles in the leech. Besides
the internal chylopoietic, and the male and female generative
glands, we often find the naked surface of their body lubri-
cated by a copious, thick, viscid, mucous secretion poured
out from distinct glandular cutaneous orifices ; and this is
sometimes mixed with an acrid colouring matter, as we
observe in the deep yellow secretion thrown out from the
surface of the arenicola. Numerous distinct small round

ORGANS OF SECRETION. 583

muciparous follicles pour out a copious secretion generally
near the orifice of the organs of generation, as seen in the
earth-worm. Many annelides secrete from the surface of
their skin calcareous or other matters to form exterior enve-
loping tubes for protection, and many minute marine species,
when irritated, give out a brilliant fluctuating light of a
bluish -white colour, extending in waves along 'the whole
length of their body, and apparently subjected to the will of
the animals. The testes and the ovaria, and even the pul-
monary cavities, are still in form of simple glandular sacs, as
in the earth-worm.

The liver of the myriapods, as in the scolopendra and the
iulus, consists of long isolated biliary tubuli opening into the
pyloric end of the elongated gastric cavity, as in insects, and
the mouth is furnished with several pairs of long simple
salivary follicles. In the scolopendra gigantea, there appear
to be three pairs of elongated unequal salivary tubuli extend-
ing along the sides of the oesophagus, and opening into the
mouth. The chilopoda have two poison-glands placed along
the lower maxillee, which convey their acrid secretion into
the two unciform palpi placed at the base of the jaws. The
genital glands are placed on different sexes, and are fur-
nished with several accessory follicles ; the pulmonary sacs or
follicles of the annelides, have here become elongated tubuli, or
ramified tracheae ; in the chilognatha, small glandular follicles
open by minute orifices along the sides, near the haunches of
the legs, which secrete an acid and strongly odorous fluid ;
and many myriapods emit a bright luminous appearance.
Urinary tubuli are already observed in the iulus opening
into the lower part of the alimentary canal at the beginning
of the dilated colon or rectum, as in many insects.

The hepatic, salivary, pancreatic, and urinary glands, are
distinctly developed in insects, and have generally the form
of long isolated tubuli, often provided with small reservoirs,
forming a urinary- and a gall-bladder, for the reception and
accumulation of their respective secretions before being sent
into the digestive canal. The salivary glands form one or
more symmetrical pairs of simple tubuli, or clustres of fol-
licles, opening by single ducts on each side of the mouth ;
and the dilated part of the oesophagus forming the crop, is
generally surrounded with numerous minute muciparous

584 ORGANS OF SECRETION.

glandular follicles, which open into its interior. The long,
capacious chylific stomach is also well provided with similar
small, short, isolated follicles, the proper gastric glands,
which open around its whole inner surface.

The liver of insects consists always of long biliary tubuli,
varying much in their number, sometimes simple, sometimes
with small follicles developing along their sides, sometimes
isolated and free at their extremities, often anastomosing
and continuous at their distal ends, and opening into one or
more points near the pyloric extremity of the stomach.
There are often two, or four, or six tubuli on each side of
the stomach, and when thus few, they are very long and
convoluted, and frequently united in pairs by the anasto-
mosis of their distal ends, so that each tubulus returns to
terminate in the part whence it originated. Sometimes there
are several dozens of these tubuli, and when thus numerous,
they are generally quite free, shorter, and separate at their
closed ends, and open around more than one point of the
stomach. These tubuli sometimes form a small sac, or
gall-bladder, to collect their secretion before transmitting it
to the stomach. By opening the stomach of the bombyx,
and compressing the biliary tubuli, Malpighi in 1687, observed
the yellowish coloured bile flow by a distinct aperture into
the cavity of the stomach. The liver is least developed in
carnivorous insects, as seen in cicindela (Fig. 118. C. m. m.)
and in cimex (Fig. 118. D. m. m.), and most developed in
the phytophagous species, as seen in melolontha (Fig. 118.
A./c.l.m.); and the gall-bladder is sometimes double, as
already seen in pyrrhocoris (Fig. 118. F./).

The pancreas is less developed and less constant in insects
than the liver, and commonly presents itself in the form of
one or more simple follicles, opening into the pyloric portion
of the chylific stomach, near to the entrance of the hepatic
tubuli, as in pyrrhocoris (Fig. 118. F. q.), where, at least, six
small pancreatic follicles are seen entering the stomach, close
to the opening of the long hepatic tubuli. Numerous other
relations of the chylopoietic glands of insects belong to the
general account of their digestive organs already given.

The urinary organs, like most other glands of insects,
consist of one or more elongated isolated follicles, or simple
tubuli uriniferi, which open into the lower or cloacal portion

ORGANS OF SECRETION. 585

of the intestine, and sometimes develope a small vesicle, or
urinary bladder, as in ditiscus, destined to receive their
scanty secretion, which is found by analysis to contain urea,
or a suburate of potash and ammonia, as the renal secretion
of higher animals. Many coleopterous insects, especially
the carnivorous species, possess glandular tubuli which pour
a very acrid matter into the rectum, and in the hymenoptera
there is frequently a poison-gland developed in the last ab-
dominal segment, which sends its secretion through a perfor-
ated sting of great density and sharpness. The testes and
the ovaries themselves, though more subdivided and compli-
cated, present the same elongated follicular character of
glandular tubuli. There are often numerous tubuli in the
male, like vesiculae seminales, connected with the vasa
deferentia ; and in the female we often observe, in the course
of the oviduct, one or more glandular organs, apparently
destined to secrete a fluid. to envelope the ova, as they pass
through the trunk of the united oviducts.

Many insects form a glutinous secretion from distinct
glands, as from the two long tortuous labial glands of the
silk-worm, which, after being thrown out from small aper-
tures, hardens into fine silken filaments, destined sometimes
to assist in their progressive motion, or to suspend their ova,
or to entangle their prey, or to envelope and protect their own
body while in the torpid pupa state. As in the lower classes
of animals, numerous species of insects, when excited or
alarmed, produce vivid flashes of light, which they are capable
of prolonging for some time. There are often cutaneous
follicles, which pour out on the surface, secretions possessing
every variety of odour, as a means of protection when irri-
tated; frequently the odorous glands contained within the
segments, near the anus, can be protruded from the body
and retracted at pleasure. Some insects have the odorous
follicles placed near the head, or on the back, or along the
articulations of the trunk and of the extremities. Glandular
follicles on the lower part of the abdomen of the bees, secrete
the wax in which they envelope their ova, and their honey
is elaborated in the digestive organs, from the juices they
have collected in sucking the flowers of plants.

The chylopoietic glands are but imperfectly developed in
the carnivorous tribes of arachnida, where, however, we

586 ORGANS OF SECRETION.

observe several distinct salivary follicles in the trombidium,
and other genera, and two in the scorpion ; the liver consists
generally of clusters of small follicles, which, in the scorpion,
open into the stomach by five pairs of short hepatic ducts ;
and the urinary tubuli of the spiders form a small bladder,
as in many insects, before sending their secretion into the
cloacal part of the alimentary canal. The generative organs
of both sexes still present the tubular character of elongated
follicles, and poison-glands with poison-instruments are
developed in these animals, sometimes at the anterior and
sometimes at the posterior end of the body. In the scor-
pion, as in many insects, the last segment of the trunk is
converted into a sharp, piercing poison-sting, which is here
external, curved, solid at the point like the fang of a serpent,
grooved at each side, and provided with two lateral canals
continued from these grooves to the two poison-glands,
which are situate above the broad dilated bulbous base of
this exposed terminal sting. In the tarantulee and spiders,
as in the scolopendree, among the myriapods, the poison-
glands are situate at the sides of the mouth, and pour their
secretions through the perforated, sharp, curved, maxillse.
There are four small follicular glands in the lower and back
part of the abdomen in the spiders, which secrete the fine
glutinous threads that compose the webs, and send their
secretion through four ventral papillae, in front of the anus,
which are perforated with numerous very minute orifices, like
the nipples of many mammalia. These filamentous glands can
be suddenly compressed by the spiders, so as to throw out
the threads to some distance when required.

Most of the numerous glands developed in insects and
other air-breathing articulata, are incompatible with the
aquatic life of the Crustacea, which have fewer secreting
organs than any other entomoid class. From the limited
circulation of the blood in myriapods, insects and arachnida,
their glands have generally a simple, isolated, elongated,
tubular form, adapted to reach the fluids of the body ; but
in the aquatic forms of Crustacea and annelides, where fewer
glands are required, and where the sanguiferous system is
more extensively distributed through the tissues for their
nutrition, the secreting organs have a more subdivided,
ramified, or conglomerate character, as the blood can be here

ORGANS OF SECRETION. 587

more easily sent to all their minutest subdivisions. In the
simplest forms of the chylopoietic and intestinal glands in
the lower articulata, the analogies of these minute secreting
tubuli were determined chiefly by the parts of the alimentary
canal into which they open, the salivary follicles opening into
the mouth or oesophagus, the hepatic, gastric, and pancreatic
into the long cavity of the stomach, and the urinary into the
terminal or cloacal part of the intestine.

In the Crustacea, however, not only are the different parts
of the digestive canal more denned, but the character of the
glands is also more distinct and obvious. From their aqueous
habitat and the moist condition of their food, these animals,
like fishes and cetacea, require no salivary glands, and rarely
present a rudiment of these organs even in the highest
decapods ; the pancreatic glands, so nearly allied to them in
function, follow nearly the same law of development, and
only equivocal traces of them are perceptible in some of the
entomostracous and higher species ; and the rudimentary
condition of these two important chylopoietic glands, corres-
ponds also with the nutritious character of the food of these
predaceous inhabitants of the waters. The chemical part of
their digestive process depends, therefore, almost entirely on
the liver, which is generally of great magnitude, minutely
subdivided, and possessed of an immense secreting surface,
as in the aquatic mollusca.

In the lower forms of amphipodous and isopodous
Crustacea, two or three pairs of isolated simple biliary tubuli
opening into the elongated stomach, still compose the entire
liver, as in insects ; and in the simplest parasitic species, this
organ is represented merely by a follicular development, or
cellular covering, investing the parietes of the stomach, as in
some of the annelides. The liver in the higher orders con-
sists generally of a single duct on each side of the stomach,
more or less subdivided and ramified, and with its ultimate
tubuli disposed with perceptible symmetry, in lobules and
lobes. In the most developed forms of decapods, both ma-
crourous and hrachyourous, the mass of small, short, straight,
parallel tubuli biliferi arranged in lobules, and these in larger
lobes, constitutes the largest organ of the body. These
innumerable hepatic coeca are the terminal ramifications of
two short wide ducts, which open into the narrow muscular

588 ORGANS OF SECRETION.

pyloric extremity of the capacious masticating stomach. They
are connected together by their points of junction, by their
common peritoneal covering, by a loose interposed cellular
tissue, and by the minute ramifications of the hepatic arteries
which afford the materials of their secretion. The branches
of the two primary ducts determine the lobes, and their
branches, the minuter lobules, and the terminal tubuli are
commonly filled with their yellowish-brown coloured secre-
tion. By removing a portion of the peritoneal investment,
and agitating a small piece of the liver gently in water, the
component tubuli, which are disposed with their shut ends
around the periphery of the lobes, are easily separated from
each other, and rendered obvious to the naked eye.

The soft green-coloured pulpy substance on each side of
the oesophagus, composing the salivary glands in many of
the decapods, more resembles a vascular blastema than rami-
fied tubuli; and the pancreas of these highest Crustacea,
consists only of two or three elongated, simple, isolated
tubuli, opening into the digestive canal, beyond the entrance
of the hepatic ducts. The generative glands, the ovaria and
tesles, present a greater subdivision of their terminal, secre-
ting, coecal portion, and a greater distinction of this part
from the efferent ducts, than in most of the inferior articulata.
From the simple tubular structure thus presented by the
various glands of the articulated classes, they not only ex-
hibit permanent types of the primary transient stages of
these organs in higher animals, but afford most instructive
analyses of all the most complex conglomerate forms of
secreting organs met with in the animal kingdom, and in the
regularity of their forms and their bilateral symmetry, they
surpass the glands of all other tribes of animals.

FOURTH SECTION.

Secreting Organs of the Cyclogangliated or Molluscous

Classes.

The high development of the sanguiferous system in the
molluscous classes, their mixed and inferior kind of food,
and their imperfect means of locomotion, prehension, and

ORGANS OF SECRETION. 589

.mastication, require a greater development and a more com-
plex condition of the chylopoietic glands, than in the active
and predaceous articulated tribes. Their slowness of motion
or fixed condition, and their aqueous medium, are incompati-
ble with many of the glands connected with the organs of
relation, developed in the air-breathing animals of the former
subkingdom, as the poison-glands of myriapods, insects and
arachnida, the cutaneous follicles for odorous or acrid secre-
tions to be poured on the surface of the skin, the filamentous
glands for the webs of spiders, or the cocoons of insects.
The molluscous animals are, therefore, provided with few
secreting organs not immediately connected with nutrition
or generation, and the great chylopoietic glands, the hepatic
and salivary, are remarkable for their size, their constancy,
and their conglomerate character, in this great subkingdom of
aquatic animals. The liver is always contiguous to the
stomach, and opens directly, for the most part by numerous
wide orifices, into its cavity. The salivary glands are some-
times simple tubuli, sometimes conglobate clusters of short
follicles, sometimes both these forms occur together, and
they open generally by long ducts into the cavity of the
mouth. The pancreas presents both the tubular and lobu-
lated forms, opening, like the liver, into the cavity of
the stomach, and the urinary organs terminate near the
anus.

In the tunicated animals those glands only are developed,
which are most essential to digestion and generation. The
small short tubuli biliferi, sometimes as isolated follicles, and
sometimes composing lobules, closely surround the greater
portion of their stomach, and open into its cavity by nume-
rous orifices ; so that the liver in these lowest of the mollusca,
presents nearly the divided and the concentrated forms, the
two extremes of development, met with in the aquatic
articulata, the lowest annelides and the highest Crustacea.
No salivary or pancreatic glands are perceptible here, or in
the allied conchiferous mollusca. Besides their common
genital glands, and the secretions of their mucous surfaces,
pallial and intestinal, and the bright luminosity exhibited by
many of the species, as salpa and pyrosoma, many of these
animals attach to the exterior surface of their tunic, by means

590 ORGANS OF SECRETION.

of a glutinous secretion, particles of gravel, shells, and other
substances, for concealment and protection.

The liver of the conchi/era, as in the higher tunicata, con-
sists of numerous small lobes, compactly united together,
surrounding the pyloric portion of the stomach and part of
the intestine, and opening freely by numerous short wide
ducts into the capacious gastric cavity. The lobes consist of
racemose groups of small dilated short biliary follicles, filled
with their dark-coloured secretion, and opening into common
anastomosing ducts, which penetrate the coats of the
stomach by separate wide oblique orifices. In the situation
of the pancreatic gland of higher mollusca, there is a single
elongated and wide follicle opening into the stomach of many
conchifera which secretes the firm cartilaginous material of
the gastric dart, and salivary follicles are seen in some of the
brachiopodous species, as in the lingula, A copious secre-
tion of calcareous matter for the increase of the shell, is
thrown out from the vascular exterior of the mantle, and a
mucous secretion from its interior. In the abdomen, below
the heart, is a considerable reticulate soft glandular organ
and sac with two narrow orifices, near those of the oviducts,
generally charged with calcareous particles and uric acid,
and regarded by Swammerdam as the calcifient gland, by
Blainville as a urinary apparatus, and by Bojanus as respi-
ratory. Many genera, especially those provided with thin
delicate shells, are fixed by a byssus, composed of strong
dense filaments, secreted by a distinct gland at the base of
the foot, and these filaments appear to be intimately united
to the muscular or tendinous fibres reaching from the foot
to the shell. The pearls formed by these animals are com-
posed of spherical concentric layers of nacreous matter,
secreted around foreign particles by the outer surface of
the mantle, or in some by appropriate calcifient glands, and
the same parts afford the various colouring matters which
decorate the shells.

The glandular organs of the gasteropods are more numerous
and distinct, and correspond with their more varied and
active life. The hardness of their food now necessitates
masticating apparatus, and these necessitate salivary glands,
which keep pace with them in development. The salivary

ORGANS OP SECRETION. 591

glands, commonly one or two pairs, disposed along the sides
of the oesophagus, and opening by long ducts into the mouth,
consist sometimes of simple single elongated tubuli, as in
bullosa, aplysia, and other genera, sometimes of racemose
clusters of follicles, forming a compact lobulated organ, as in
ariorii buccinum, and many others, and sometimes these two
forms occur together as in the doris. The liver, as in other
mollusca, is of great size, consisting of numerous aggregated
lobes, composed of small short tubuli filled with their biliary
secretion, surrounding the greater part of the stomach and
intestine, and opening by one or more oblique, wide orifices,
into the pyloric end of the gastric cavity. The pancreas
consists of a small single glandular coecum, with thick folli-
cular parietes, opening by a wide distinct orifice into the
cavity of the stomach, close to the openings of the hepatic
ducts, as in the doris and aplysia. The urinary glands are
found to contain uric acid, as in conchifera, they consist
generally of a conglomerate mass of small follicles, with a
single efferent duct or ureter which opens externally near
the anus, as in arion, umbrella, pleurobranchus, doris,
aplysia, and other genera, and sometimes a small vesicle,
or urinary bladder, is developed in the course of the ureter.
These have also been regarded as calcifient glands.

Both in the naked and testaceous gasteropods, there are nu-
merous muciparous follicles disposed on the surface of the
body, to lubricate and protect the skin. In the testaceous
pectini-branchiale tribes, there are often considerable mucipa-
rous glands disposed under the mantle to lubricate the interior
of the pallial and respiratory cavities, and to protect them from
the irritation of excrementitious and foreign matters. Many
species present also at tno bottom or near the margin of the
pallial cavity, soft follicuiar glands destined to afford secre-
tions of various and often lively colours, as the blue of the
janthinte, the yellow of the bulla, and the purple of the mu-
rices. Thejantkina and the glaucus appear to derive their
deep blue colouring matter, from feeding on the deep blue
velellae, which float with them near the surface of the sea.
Chiaje found the purple secretion of the myrex tritonis to be
produced by the parietes of a glandular sac, situate at the
bottom of the pallial cavity, and communicating with that
cavity by a small foramen. The float of the janthina, by

592 ORGANS OF SECRETION.

which it suspends itelf and its spawned ova at the surface of
the sea, is formed by a glutinous secretion of the mantle,
enclosing globules of air.

The small swimming pteropods, both naked and testaceous,
are, at least, provided with distinct chylopoietic glands. In
the clio and the pneumodermon, single long salivary tubuli
open into each side of the buccal cavity, and numerous hepatic
lobes, composed of compact clusters of biliary follicles, and
enveloping a large part of the intestine, open freely by short
separate ducts into the cavity of the stomach. The liver of
hyalea likewise consists of small aggregated biliary follicles,
forming a compact lobulated mass investing the intestine, as
in most inferior mollusca, before opening into the stomach.
And the genital glands, both oviferous and seminiferous,
have still the simplest follicular structure of isolated tubuli,
or of a few racemose groups of small follicles, the ovary being,
as usual, the more complex gland.

The secreting organs of the cephalopoda approach nearer
to the vertebrated type in their form, structure, and con-
nections, than those of all the inferior invertebrata. Their
diminished cutaneous mucous secretion is a further affinity
with higher tribes, and is compensated for by the copious se-
cretion of muciparous follicles in every part of the digestive
apparatus, as well as by the higher development of all the
normal chylopoietic glands. Two large pairs of lobed salivary
glands, analogous to the parotid and submaxillary, consisting
of aggregated lobules of small white dilated follicles filled
with their salivary secretion, open by lengthened ducts
into the back part of the buccal cavity, and correspond with
the sharp and powerful cutting maxillae, and the numerous
recurved lingual teeth of these predaceous, though generally
naked, mollusca. In the great size and the conglomerate
character of the liver, and in its opening by a single length-
ened duct near the pylorus, they indicate affinities to the
fishes as well as to the lower mollusca. The short dilated
parallel tubuli biliferi, filled with their brownish-yellow
secretion, and directed with their shut ends towards the
entire periphery of the organ, and of its component lobes,
are easily seen with the naked eye, by removing carefully
the thin, soft, investing peritoneum, and then floating a
small piece of the liver in water. The pancreas here presents

ORGANS OP SECRETION. 593

itself sometimes in form of numerous isolated follicles, par-
tially divided internally by peripheral septa, and opening
separately into the hepatic ducts, as in sepiola, and some-
times in the more conglomerate form of distinct ramified
tubuli, forming isolated lobes of racemose bundles of dilated
follicles, opening by several common and slightly elongated
ducts, into the trunks of the hepatic ducts, and also directly
into the cavity of the third or spiral stomach, as in loligopsis.
The pancreas, therefore, exhibits nearly the same variable
character of development, and nearly the same connections
as in fishes, and corresponds with the more advanced condi-
tion of the salivary glands in cephalopods ; its connection
with the biliary duct is that common in the vertebrated
classes, and the cephalopodic type is repeated in the hepato-
pancreatic duct of the dolphin and some other mammalia. The
spleen, of which no trace has been detected in some of the
lowest cyclostome fishes, appears also to be deficient in this,
as in all the other invertebrated classes.

The ink-gland, developed as a means of protection in
the naked cephalopods, and probably serving also as a
urinary apparatus, consists of a highly vascular, simple
cancellated sac placed on the ventral surface of the liver,
and terminating by a single wide fibrous duct, in or near
the anus, like the urinary and pigment-glands of gas-
teropods, and the anal or odour-glands of many verte-
brata. The dark-coloured gelatinous pigment secreted by the
parietes of the peripheral cells of this gland, and conveyed by
the expired water through the syphon, to be diffused, for
protection, through the surrounding element, corresponds in
colour with the changeable cutaneous coloured spots, but no
organic connection has been discovered between these dis-
tant parts. The ink-gland is deficient in the thick-shelled
nautilus, and present in the thin-shelled argonaula as in the
naked genera. The coloured secretion forming the changeable
cutaneous spots, appears to be confined to small, isolated,
highly expansible cells, situate on the vascular and sensitive
surface of the cutis, and beneath the soft layer of epidermis.
These small coloured cells continue to dilate and contract,
and thus to vary the colour of the surface, even on small
pieces of the skin detached from the body, and in the living
state they appear to be regulated by the will of the animal,

PART VI. Q Q

594 ORGANS OF SECRETION.

like the vibratile cilia of many inferior tribes. The cellular
follicles covering the great venous trunks on the ventral
surface of the liver, and communicating freely with their
interior, have been compared by some to urinary organs,
and by others to the rudiments of a portal circulation. The
genital glands here manifest the same elevated character of
development as most of the other secreting organs ; the tes-
ticle forms a large conglomerate mass composed of long,
small, divergent, ramified tubuli seminiferi, with their closed
extremities forming the periphery of the organ. The long
vas deferens is convoluted like an epididymis, and is ac-
companied with a vesicula seminalis and a prostate gland.
The ovary forms a large cluster of highly vascular secreting
follicles, and the oviducts are furnished with distinct glands
to secrete the enveloping materials of the ova, as in the
plagiostome cartilaginous fishes.

The higher development of the secreting organs of the
molluscous classes, is thus indicated by the greater number
and greater sub-division of their component tubuli, and
the more extended surface thence presented for the dis-
tribution of the blood-vessels which supply the materials
of the secretions. It is seen in the concentration of all the
constituent follicles and tubuli into single efferent ducts,
and in the elongation of these ducts, by which the secreting
glands are removed to a greater and more convenient dis-
tance from the parts whence they originate and which
receive their secretions. The increased extent likewise of
the vascular system in the molluscous classes, and the minute
distribution of arterial capillaries through the glandular
tissues, augment the products of the secerning organs. The
efferent ducts are more distinct in form, structure, and func-
tion, from the follicular secerning portion of the glands; they
terminate with more oblique and valviform orifices, and the
analogies of form, connections, and function more closely
approximate the glands of mollusca to the vertebrated type,
than those of the articulated or radiated animals.

FIFTH SECTION.

Secreting Organs of the Spini-cerebrated or Vertebrated
Classes.

As the general development of the glandular system of

ORGANS OF SECRETION. 595

animals keeps pace nearly with that of the entire organism,
the highest condition of all the normal secreting organs is
presented hy the vertebrated sub-kingdom ; and as the laws
are most uniform by which the secreting surface of glands
is gradually increased to the greatest extent, and the secreting
organ itself is confined to the smallest space, it is in this
division of the animal kingdom that most glands have per-
manently assumed their most compact and most conglo-
merate forms. The vertebrata, like the entomoid articulata,
being chiefly active air-breathing animals, with a high de-
velopment of the. organs of relation, they exhibit a cor-
responding high condition of all the secreting organs con-
nected with the functions of animal life. They have there-
fore the most numerous and the most varied forms of glands,
and the most diversified in function connected especially with
their cutaneous covering, their tegumentary apparatus, their
organs of the senses and of locomotion, besides the highest
condition of all those secreting organs more immediately con-
nected with individual nutrition and with generation.

The fishes, like the uterine embryos of higher tribes, are,
from their aquatic habitat, still nearly in the condition of the
molluscous classes, with relation to their secreting organs,
and they exhibit chiefly those most essential to nutrition and
generation. From the moist condition of their food, and
their want of proper masticating teeth, from the shortness
and width of their oesophagus, and their swallowing their
food almost without division, from the aqueous constitution
of saliva, and the constant streams of water flowing through
their mouth for respiration, fishes require no salivary glands,
and they are more appropriately provided with numerous and
large buccal muciparous follicles, which lubricate and protect
the capacious cavity of the mouth and pharynx. Similar
mucous glands are developed along the parietes of the oeso-
phagus, and they abundantly perforate the mucous lining of
the stomach and intestine, as indeed in all the vertebrated
classes, and on most mucous surfaces throughout the animal
kingdom. As the aquatic respiration of the mollusca is not
effected through the mouth, this function does not interfere
with the great development of their salivary glands ; but in
fishes where the dense aqueous element is respired solely by
the mouth, this function is incompatible with the ordinary

Q Q 2

596 ORGANS OP SECRETION.

salivation of food, and the development of salivary glands.
The imperfect aeration of their blood by means of this
aquatic respiration, is probably also connected with the pre-
ponderant development of their liver, that great emunctory,
supplemental to the lungs and branchiae in decarbonizing the
blood.

The liver is large in fishes, as in mollusca, of a soft texture,
divided into numerous lobes, its tubuli are filled with a very
light coloured oily secretion, and there is generally a distinct
gall-bladder superadded to the ordinary biliferous cosca com-
posing the entire liver of invertebrata. The gall bladder is
sometimes wanting as in ammocetes, or a mere dilatation of
the hepatic duct as in petromyzon. The great size of the
gall-bladder and its constancy in this class, accord with the
carnivorous habits, and the consequent irregularity in the
supply of food, in most of the species, as seen also in the
reptiles and the predaceous tribes of other classes. As the
capillary blood-vessels furnish incessantly the materials of
the secretion, and the tubuli of the liver as constantly form
bile, the interruptions to the demand for that fluid, by the
irregular feeding of almost all carnivorous animals, necessi-
tate the development of a reservoir in the course of the
efferent duct, to prevent the bile from irritating the empty
intestine in time of fasting, and to afford a sufficient supply
for their excessive meals. In most herbivorous animals, with a
constant abundance of food, and an unceasing process of
digestion, no reservoir or gall-bladder is wanted, but rather
a constant and copious supply of bile direct from the tubuli
and ducts of the liver ; and thus the presence or absence of
this appendix, and its extent of development, are related
more or less obviously to the food and habits of animals.

The liver of fishes is often disposed on the left side, or on
the median plain, or towards the right side of the abdomen,
being suspended by broad ligaments from the tendinous
diaphragm, and is generally deeply lobated, extending back-
wards, in front of the alimentary canal, as far as the pelvis,
and often partially enveloping the intestine as in the mollusca,
but without the central excavation often seen in the liver of in-
vertebrata. There are commonly one or more long hepatic ducts,
which unite with a long cystic duct from the large gall-bladder,
to form a short and wide common ductus choledochus which
opens into the commencement of the duodenum, immediately

ORGANS OF SECRETION. 597

beyond the pyloric valve, and close to the opening of the
pancreatic duct. Besides the hepatic artery, common to the
invertebrated classes, in which it alone furnishes the materials
of the bile as well as the nourishment of the liver, this organ in
fishes is supplied with several portal veins, derived chiefly from
the chyloposetic viscera, which ramify with the hepatic artery
along the pinnated tubuli of the liver, affording the bile from
the mixed blood of their capillaries. The portal veins are
less extensively ramified through the liver in fishes and the
lower vertebrata than in the higher warm-blooded classes, as
in the earlier conditions of the human embryo. There are
frequently hepato-cystic ducts in fishes which convey the
bile directly into the fundus of the gall-bladder, as well as
the usual hepatic ducts leading to the cystic ; and sometimes
as in the orthagoriscus, the bile is still poured directly into the
cavity of the stomach, as in most of the invertebrated classes.
From the aqueous nature of the pancreatic secretion, that
gland, like the salivary, is little required in fishes, and is
there found, as in the mollusca, chiefly in the simplest folli-
cular form, occurring as a single pyloric follicle in the ammo-
dites, and arriving at the most conglomerate form in the highest
cartilaginous fishes. In some fishes where the free pancreatic
tubuli are still wanting, as the cyprinus, esox, murrena and
ophisurus, their place is supplied by a simple cellated or
follicular structure of the internal lining of the duodenum.
The pancreatic follicles of this class open into the duodenum,
close to the biliary duct, beyond the pyloric valve, by a most
variable number of orifices, according to the degree of de-
velopment or concentration of the organ. The follicles, when
simple, are commonly cylindrical, aggregated into groups, and
open into the duodenum by several apertures sometimes
nearly as wide as the intestine itself; but in the most con-
glomerate form of this organ, in the plagiostome fishes, the
common duct of all the minute tubuli composing the lobules
of the pancreas, terminates by a single and narrow orifice.
The spleen first makes its appearance in the class of fishes ;
it is sometimes wanting as in the lamprey, the myxene, and
the gastrobranchus, generally it is small and single, but in
some cartilaginous species it is divided into detached lobes,
as in some of the cetacea ; it is appended to the left side of
the stomach, and is highly vascular and largely supplied with
lymphatics.

598 ORGANS OF SECRETION.

Notwithstanding the scaly covering of fishes, their exte-
rior surface is generally lubricated by a copious viscid mucous
secretion poured out on different parts of the body, from long,
ramified, subcutaneous, muciparous glands. These simple
glands are especially distinct and numerous on the head and
sides of cartilaginous fishes, where they form long tortuous
tubes filled with their white mucous secretion. In many of
the osseous fishes they form a continuous tube extending
along each side of the body to the end of the nose, and
sending down branches along the operculum and the lower
jaw. These muciparous vessels, like other secerning tubuli,
secrete at all points of their course, and pour out their secre-
tion on the surface from distance to distance as they proceed
below the skin, and they are often seen following the course
of the longitudinal lateral line on both sides of the body.

Besides the ordinary secretions of the pulmonary, the
urinary, and the generative apparatus, many fishes both of
fresh water and of the sea, and both osseous and cartilagi-
nous, are provided with complicated electrical organs, pre-
senting an immense secreting surface in small space, and by
which they are able to communicate violent shocks to ani-
mals which touch or approach them. In the gymnotus
these organs consist of an upper larger and a lower smaller
pair, and occupy the inferior part of the whole caudal region
of the body. They are divided by numerous closely approxi-
mated transverse membranous folds, and these horizontal
compartments are further subdivided by innumerable thin
vertical laminee like the plates of a galvanic pile, with a
mucous secretion interposed between the layers, and filling
all the cells thus formed, and they are largely supplied with
nerves, as are all the electrical organs of fishes. The
two distinct electrical organs disposed along each side
of the body, are separated from each other by firm ten-
dinous membranes and by muscles, and they extend ta-
pering to the end of the tail. The membranous septa are
highly vascular to furnish their abundant secretion, and they
are supplied with symmetrical pairs of spinal nerves derived
from the whole course of the spinal chord. In the torpedo
the electrical organs occupy a large space on each side of the
head ; they are composed of numerous small vertical com-
partments, each of which is regularly subdivided by a series
of horizontal parallel septa or thin membranous lamina^

ORGANS OF SECRETION. 599

enclosing the mucous secretion, and they are supplied with
large branches from the fifth and eighth pairs of nerves.
The frequent excitement of the electrical organs appears to
exhaust rapidly the influence of the ganglionic nerves
of digestion and secretion, and to arrest these processes.
The highly vascular secreting organ, connected with the/
parietes of the lungs of fishes, and which appears to
produce the gaseous contents of the air sac when destitute
of ductus pneumaticus, has been considered analogous to
the thymus gland of higher vertebrated classes, but it is here
a permanent and essential part of the pulmonary sac.

From the aquatic habits and the imperfect masticating
powers of the amphibious animals, their salivary glands are
nearly as little required and as little developed, as in fishes
or in cetacea, but their buccal cavity, like the naked surface
of their skin, is abundantly provided with muciparous follicles,
and the whole course of their digestive canal. The liver, as
in fishes, is proportionately large and always provided with
a large gall-bladder, and it is partially divided into two lobes,
as in most reptiles. In the pipa there is a third intermediate
lobe, and they are more free, as in the chelonia. The liver
commences in the tadpole by a small pit or crypta on the
side of the intestine, like the concavity left in the adult
liver of many mollusca ; from this a few small simple short
follicles gradually extend ; these increase in number, elongate,
and divide to constitute at length the entire mass of the
adult organ. The pancreas is always conglomerate, as in the
plagiostome fishes, and opens into the duodenum beside the
biliary duct. The highly vascular spleen, is single as in
reptiles, of an elongated form like the stomach, and is
attached by cellular tissue and vessels along the left side of
that organ, as in higher vertebrata. The muciparous glands,
so largely developed and extensively ramified immediately
beneath the skin of fishes, assume a more divided form on
the naked skin of amphibia, where they pour out their viscid
and sometimes acrid secretion, by open pores dispersed over
all parts of the surface. The excretory orifices of these
cutaneous follicles are large and obvious over the back of
the land salamander, and their acrid product in the toad is
alkaline, not acid like most other excretions. The glandular
follicles which secrete this bitter, oily, and poisonous fluid
on the back of the toad, are chiefly disposed on the dorsal

GOO ORGANS OF SECRETION.

part of the broad short neck, and appear to serve as a means
of defense. No unequivocal thyraus gland appears to be
developed in the amphibia or in the fishes, and it is only a
deciduous organ of the foetus in higher vertebrata.

The impervious scaly covering of terrestrial air-breathing
reptiles, is less compatible with the high development of
cutaneous muciparous glands, than the soft and often naked
skins of aquatic vertebrata, and this external deficiency is
compensated for by the increased secretions of internal glands;
nearly similar conditions exist in most birds and mammalia.
The sublingual salivary glands are always distinct in serpents,
and also the superior and inferior labial glands, and the parotids
or foliated temporal glands in the noxious species, transmit
their poisonous secretions through the perforated fangs. The
poison gland of serpents occupies the situation of the paro-
tid, below and behind the eye, on each side of the head,
and consists of numerous symmetrical compressed Iobes3
each composed of minute diverging branched follicles, and
the common duct of all the lobes passes forward along the
side of the upper jaw to the base of the perforated fang,
where it enlarges to form a wide reservoir for the secretion,
and is surrounded with muscular fibres to compress it when
required, and force the poison into the tooth. The upper
and lower labial or maxillary glands consist of vertical,
parallel, simple, contiguous lobes opening into the mouth by
separate orifices. The salivary and muciparous glands are
also distinct in the saurian, and especially in the chelonian
reptiles where the submaxillaries are most developed.

The liver of reptiles is large, little divided externally into
lobes, composed of minutely pinnated follicles or acini, pro-
vided with a gall-bladder, and an extensive portal circulation,
and there are commonly hepatic ducts passing directly from
the liver to the duodenum, besides the duct from the gall-
bladder. This organ varies its external form with the general
form of the animals, being remarkably elongated in the
ophidian, broad in the chelonian, and intermediate in the
saurian reptiles. The hepatic ducts of the ophidia alternate
with the separate ducts of the pancreatic lobes, in their
points of entrance into the duodenum, near the pyloric
valve. The pancreas presents a more concentrated form in
sauria and chelonia than in ophidia, and the spleen is also
relatively small in serpents where it is closely united to the

ORGANS OF SECRETION.

601

pancreas, sometimes divided into separate lobes, and some-
times it is quite imperceptible.

The relative position of the ducts of the chylopoietic
glands, as viewed from behind in the emys europaa, is seen
in the annexed figure from Bojanus (Fig. 145) where a. b.

FIG. 145.

represent the elongated stomach, c. d. the small intestine,
e.f. the coecum and colon, g. the gall-bladder opening by
two ducts into the duodenum h. one of which ducts receives
the hepatic and may be considered as its continuation. The
pancreas (i.) intimately connected with the stomach, the
duodenum and the colon, opens by three separate ducts
(u. u.) into the duodenum, and has the spleen (k.) compactly
united to its inferior lobe. The gastro-epiploic (q.) the
coeliac (?*.), and the mesenteric (/.) arteries ramify as indicated,
the upper lobe of the pancreas receiving the pancreatic artery
from the coeliac, and the inferior lobe receiving branches from

602 ORGANS OF SECRETION.

the mesenteric artery, along with the spleen. The veins
(o. p.) returning from the alimentary canal, the spleen, and
the pancreas, unite below the liver to form the vena portarum
(h.) which ramifies through the right (m.) and left (n.) lobes
of that organ.

As the alimentary canal passes straight through the body
in the embryos of vertebrata, the great chylopoietic glands,
the liver and the pancreas, are developed from its anterior
part, on the median plain, like the lungs from the oesophagus.
In the embryo of the lizard, the liver appears at first as a
short, hollow, bifid follicle continued from the intestine, and
numerous tubuli bud out from the whole surface of its thick
vascular parietes, which extend, ramify, and compose the
entire lobules and lobes. The thymus gland, which first
makes its appearance in the reptiles, is there a permanent
organ, as it is also in some of the lower mammalia, as the
cetacea and the rodentia. Some predaceous saurians, as
the aligators, possess distinct anal glands, like many carni-
vorous quadrupeds, which secrete a strongly odorous subs-
tance, having the odour of musk, and the same structure
appears to belong to some chelonian reptiles, and to the
rattle-snakes and many other serpents, both noxious and
innoxious. Besides these anal musk-glands, most of the
crocodilian reptiles present two simple follicular glands under
the lower jaw, which pour out on the surface of the skin a
thick fluid with a similar musky odour. In some lizards,
these odorous glands open by distinct external apertures on
each side of the anus, and in most of the saurian reptiles
there are numerous external inguinal pores for the discharge
of a similar strongly odorous secretion at the breeding season.
The cutaneous follicles of the Indian gecko secrete a fluid
which is said to have the same acrid and poisonous pro-
perties as that of the toad. The glandula lachrymalis and
, Harderi are already distinct in the orbit of reptiles, and even
in serpents where the skin passes transparent and conti-
nuous over the front of the eye-ball ; and the urinary and
genital glands have here attained a high development.

The liver is already perceptible in the embryo of birds, as of
the fowl, on the third day of incubation, and appears as a
simple bifid hollow projection from the anterior median aspect
of the straight alimentary canal. These two follicles or primi-
tive lobes extend, enlarge, draw out the digestive tube to in-

ORGANS OF SECRETION. 603

crease their internal cavity, develope from their vascular and
thickened periphery innumerable rudimentary tubuli, the prox-
imal cervix becomes contracted and extended to form the duct,
and from the parietes of the duct a small diverticulum pro-
trudes to constitute the future gall-bladder. In the substance
of the vascular enveloping blastema, the minute plumose
ramifications of the tubuli, of which the adult organ is chiefly
composed, are observed compactly aggregated together, and
apparently as yet without internal cavities, and they are
destitute of the terminal vesicular enlargements seen at the
closed ends of the pancreatic and salivary tubuli. The liver
in birds is still relatively large, variable in form and in the
number of its external divisions, with the left lobe generally
smaller than the right, and a distinct middle lobulus Spigelii.
There is still a separate hepatic duct which passes into the
duodenum above the entrance of the cystic, one or more
hepato-cystic ducts end in the fundus of the gall-bladder,
and the separate hepatic and cystic ducts open into the in-
testine at a considerable distance below the pyloric orifice of
the stomach. The gall-bladder is often wanting in this
class.

The pancreas still opens as in reptiles by several ducts,
which penetrate the duodenum between the openings of the
hepatic and cystic ducts. The small spleen of birds is some-
times divided into separate lobes, as in some fishes, serpents,
and cetaceous mammalia. The thymus gland is a transient
organ in birds, as it is in most mammalia, and it makes its
appearance late in the progress of development in these
classes, as it appears late in ascending through the classes of
the animal kingdom. Two small thyroid glands are recog-
nizable in many birds near the inferior larynx ; and most
birds, especially the aquatic species, present over the dorsum
of the coccyx, two contiguous pyriform oil glands, composed
of straight parallel tubuli ; which open on the skin by several
papillar orifices, and afford the unctuous secretion with which
the feathers are dressed to render the plumage impermeable
to water. In most birds the rudiment of Cowper's glands
is observed as a single or bifid follicle, bursa Fabricii, opening
into the median dorsal part of the cloaca, between and behind
the openings of the two ureters.

All the ordinary secretions of birds, from the high tempe-

604 ORGANS OF SECRETION.

rature of their body and their great muscular activity, are
formed, expended, and reproduced with comparative rapidity,
the mucous secretions of their buccal, nasal, and intestinal
cavities, the serous transudations into shut cavities, as the
abdomen and the pericardium, and especially the oily syno-
vial secretions into the capsules of their ever-active joints.
The fluids of the eye, the ear, the lachrymal, the Harderian,
and the nasal glands, the cesophageal, ingluvial, and gastric
or proventricular glands, and the secretions of the oviducts,
are all rapidly expended and reproduced in this most active
and hot-blooded of all the vertebrated classes. This condi-
tion of the secreted fluids of birds is not dependant on a
more highly developed or complicated structure of their
glands, which are still comparatively simple, but rather on
the rapid transmission of highly arterialized and heated blood
through their texture, and the high development of the
nervous system on which the secretions so immediately
depend.

The secreting organs have mostly arrived at their greatest
complexness in the mammiferous tribes, as indicated by the
number and minuteness of their ultimate tubuli, their sepa-
ration from the surface from which they originate by the
elongation and concentration of their ducts, by the formation
of reservoirs to retain and accumulate the secretions, and
by the size and vascularity of the entire glandular masses.
The plan of development, however, in every gland, appears
to be the same as in lower classes, commencing by simple
follicular protrusions from the formative surface, which acquire
thickened vascular parietes, forming a blastema, for the
further production of coeca and ramified tubuli, to compose
the lobules and lobes of the gland, and thus to increase the
extent of surface over which the capillary blood vessels are
spread to afford the materials of the secretion. The salivary
glands commence from the mucous membrane of the mouth
as simple follicles, these bud out from their periphery further
follicles and ramified tubuli, which extend through the soft
vascular and lobulated blastema, the closed ends of the tubuli
forming small vesicular enlargements, and the blastema gra-
dually disappearing as its space becomes occupied with the
developing secerning tubes. The blastema early assumes a
lobulated exterior form, corresponding with the future lobed

ORGANS OF SECRETION. 605

structure of the gland, and the minute terminal vesicles of
the ultimate tubuli appear clustered in racemose groups
forming small lobules or acini. The parotid, submaxillary
and sublingual salivary glands attain the greatest develop-
ment in the herbivorous quadrupeds where there is longest
mastication and the coarsest food ; they are smaller in the
carnivorous tribes where there is less mastication and richer
food, and they are deficient in the cetacea where the moist
food is mostly swallowed entire.

The liver begins in man and mammalia, as in other ver-
tebrata, by a simple follicular protrusion, like the embryo
condition of the pancreas, from the anterior median surface of
the yet short straight intestine. Its parietes thicken to cons-
titute a soft vascular blastema, and new follicles and ramified
tubuli are prolonged through the substance of this deciduous
formative nidus. The primitive follicle becomes narrow and
elongated to form a duct, and thus to separate the gland from
the surface of the intestine, the duct develops a small filiform
diverticulum, which widens and elongates to form a gall-
bladder and cystic duct. And in the adult state of this most
complicated of all glands, in this highest class of animals,
where the tubuli have arrived at their maximum of sub-
division, they are still perceptible, larger than capillary
blood-vessels, constituting in groups the acini and nearly
the entire mass of this large organ, and when success-
fully inflated with air, their shut ends have appeared to
Krause to form minute dilated vesicles, like the lungs and
most other glands. The arrangement of the minute ccecal
tubes, forming the lobules or acini by their grouping, is
perceptible on the outer surface of the liver through the
transparent peritoneal covering, or on cutting open the larger
trunks of the vena portee or venae hepaticee and carefully
inspecting their inner transparent parietes. This minute
lobulated appearance, seen on all the peripheral parts of the
liver, was shown by Malpighi to be produced by the innu-
merable small ramifications of the proper secreting ducts,
which he found to constitute the essential part and the mass
of all secreting glands, and which here generally assume the
symmetrical forms of foliaceous or pinnated expansions of
small white cylindrical secerning tubuli, in all parts of the
organ. Into these minute terminal follicles, and their con-
necting continuous secerning trunks, the bile is transuded

606 ORGANS OF SECRETION.

from the mixed blood conveyed by the united capillaries of
the vena portae and hepatic artery, the diameter of the ulti-
mate divisions of the tubuli, as in other glands, much ex-
ceeding that of the capillary blood vessels which afford them
the materials of the secretion. But although the more trivial
circumstances of the size and mode of grouping of the tubuli,
and the outward form and bulk of the entire mass, vary in
the different tribes of mammalia, and the mode of distribu-
tion of the blood vessels through the organ, we still find this
largest and most complicated gland to consist, in the highest
as in the lowest animals, merely of a membranous duct, or
prolongation developed from the parietes of the alimentary
canal, destined to augment the secerning surface, for the
more extensive distribution of capillaries, and to form a more
convenient reservoir of this stimulating and solvent secre-
tion. From the chemical composition of the bile, the liver
appears to perform a function somewhat similar to that of
the lungs, and its development in animals is generally in the
inverse ratio to that of their respiratory organs.

The secretion of the liver, which in the lowest animals is
poured directly into the stomach, to reach the food early,
and to act upon it during the whole of its short passage
through the body, now always enters the alimentary canal at
some distance beyond the stomach, the food being here acted
upon by numerous other secretions, and having a long
course to pass through after leaving the stomach. As all
parts of the liver, like the parts of the lungs or other secret-
ing organs, have the same function to perform, they are
shaped or fissured into lobes, according to the forms of the
surrounding parts or other convenience in the different
tribes, being least lobed in the inactive abdomen of the low-
est aquatic mammalia, the cetacea, more divided in the
herbivorous quadrupeds, and most fissured in the active
trunks of many carnivora and rodentia, where its primitive
peripheral lobules sometimes remain distinct through life.
But even the external forms and peripheral divisions of
glands, manifest the same uniformity of plan, as other the
most trivial parts of the economy, as the position of the
intestinal turns in the abdomen, the cerebral convolutions
in the cranium, or the direction of the hairs on the several
parts of the skin.

The gall-bladder is most generally deficient in the her-

ORGANS OF SECRETION. 607

bivorous tribes, and in some its place is supplied by a mere
dilatation of the hepatic duct, as in the horse and elephant,
and the same is seen in the dolphin ; it is most constant
and most developed in the carnivora ; it is sometimes double
or even triple as abnormal varieties ; and its fundus still
often receives several hepato-cystic ducts as in lower classes.
In the dolphin and grampus, where, as in most cetacea,
there is no gall-bladder, nor pyloric valve to mark the termi-
nation of the gastric cavities, the united duct from the liver
and pancreas opens directly into the muscular duodenal
dilatation, commonly termed the fifth stomach, and the dilated
reservoir supplying the place of gall-bladder in the dolphin,
as in the elephant, is an enlargement of the common trunk
of the hepato-pancreatic duct, receiving, like the duct of a
cephalopod, the secretions both of the liver and pancreas.
The vena portae forms a sinus in the dolphin before di-
viding in the liver, and in the diving seals and otters
the trunks of the hepatic veins are surrounded with a con-
tractile muscular tunic, which is immediately invested with
an exterior plexiform layer of the small returning anastomosing
branches of the intra-lobular hepatic veins, to allow of the
safe contraction of these muscular hepatic trunks. In the
echidna and ornithorhyncus the gall-bladder is present, along
with a dilatation of the common biliary duct, seen also in
several marsupialia, before piercing the duodenum ; the pan-
creatic and common choledochal ducts continue separate,
and have distant terminations, in the echidna, but these two
early unite in the ornithorhyncus, to form a common hepato-
pancreatic duct.

The liver is proportionately large in the human embryo,
as in the lower vertebrata and the molluscous animals in
their adult condition. The follicular structure of the embryo-
liver was already observed by Malpighi in the chick,
before the end of the first week of incubation, and before
the end of the first month, the liver in the human embryo
has attained nearly half the weight of the entire body, and is
lobulated like the kidney of a bear, and extended backwards
to near the pelvis. The gall-bladder early makes its appear-
ance as a developing cylindrical tubulus, and gradually be-
comes more elongated, conical, hollow, rnuciparous, rugous
internally, and at length biliferous ; the liver becomes less

608 ORGANS OF SECRETION.

gelatinous and pellucid, more firm, opaque, red and vascular,
and the biliary and pancreatic ducts, originally separate,
coalesce by the drawing out of the intervening portion of
intestine during development.

The pancreas opens by a single duct, sometimes into the
ductus choledochus, and sometimes separately into the duo-
denum, although the division of this organ into two lobes is
perceptible in most of the mammalia ; these lobes consist of
smaller aggregated lobules or clusters of ramified tubular
coeca, ending in vesicular enlargements like the salivary
follicles ; and the organ commences its development, like the
liver, from a small median coecal protrusion from the fore
part of the intestine, which sends out follicles and ramified
filiform tubuli through the thickened soft vascular blas-
tema. The spleen, in many of the cetacea, is divided, as in
many lower vertebrata, into several detached, small, round,
portions, connected only by sanguiferous and lymphatic
vessels ; it is single and large in the ruminantia, of a regular
elongated form, and attached along the side of the paunch.

The mucous surfaces of mammalia are every where pro-
vided with muciparous follicles, presenting the simplest
forms of glands, and the alimentary canal has its simple
follicular glands of Lieberkuhn andofPeyer; more compli-
cated forms of these muciparous organs exist in the labial,
buccal, palatine, molar, and amygdaloid glands, the caruncula
lachrymalis, and several connected with the urinary and geni-
tal apparatus. The serous membranes have also their secret-
ing surfaces and bursse, to preserve the mobility of the viscera
and joints. The mammary, urinary, and genital glands present
numerous modifications in this class ; and the tegumentary or-
gans are every where provided with their simple sebaceous folli-
cles, and their more complicated sudoriferous and oil glands, as
the eyes are furnished with their simple Meibomian and com-
plicated lachrymal glands, and the external meatus of the
ears with their ceruminous glands.

From the different habits and external circumstances of
the animals of this most varied class, many of the secreting
organs are so modified as to appear special developments
limited to tribes or to individuals. The most odoriferous
parts of the skin of mammalia are sometimes developed into
distinct follicles or more complicated glands, as in the inter-

ORGANS OF SECRETION. 609

digital spaces in most ruminantia where we observe between
the hoofs a tubular and slightly ramified glandular cavity,
which affords an oily secretion of a strong and peculiar
odour, to lubricate and protect the hard extravascular hoofs,
and by which the carnivorous quadrupeds are better enabled
to trace the footsteps of their prey. Some of these rumi-
nating quadrupeds also exhibit simple cutaneous odorous
inguinal glands, opening on the surface near the mammae,
and developed in like manner from odoriferous parts of the
skin. The strongly aromatic musk of the musk-deer is
secreted by two glandular sacs, opening near the prepuce of
that animal. The spur of the ornithorhyncus was shown by
Meckel and Rudolphi to transmit through its tubular canal
the poisonous secretion of a large gland placed in each thigh.
In rodent quadrupeds there are numerous glandular follicles,
situate near the anus or near the prepuce, which secrete
strongly odorous, sebaceous, or oily fluids. Two plicated
glandular sacs are found on each side of the genitals of the
male and female beaver, which pour out, near the organ of
excitement, the well known fatty and resinous secretion, the
castoreum of medicine ; and the most conglomerate form of
the gastric glands is seen at the cardiac orifice of the stomach
in this animal and in the wombat, which aids the digestion
of their coarse vegetable aliment, and points out a closer
analogy between this part and the glandular stomach, or
ventriculus succenturiatus of birds. In many rodentia the
shut extremity of the long ccecum-coli is closely covered
with small simple glandular cryptee, which open into its
cavity, and similar rudimentary glands, in clusters of simple
follicles, occur in various parts of their alimentary canal.
Anal glands, secreting odorous substances, are also met with
in several of the marsupialia and pachyderma, but they are
most developed in the carnivorous quadrupeds, where their
secretion is remarkable for the intensity of its odour in the
civets, badgers, hyaenas, and some other genera. In the
elephant, similar odorous glands are seen in the region of
the temples, opening externally on each side by a small
round orifice, between the eye and the ear.

But notwithstanding the infinite diversity of form, struc-
ture, and position of these secreting tubular membranes,
forming glands throughout the animal kingdom, and the

PART VI. R R

(510 LYMPHATIC SYSTEM.

various modes in which the blood-vessels and the nervous fila-
ments are distributed on their surface, no general or determi-
nate relation has been discovered between these structural con-
ditions and the peculiar properties of the secretions they pro-
duce. In their most complex conglomerate forms, the bilife-
rous, uriniferous, seminiferous, and other secerning tubuli, like
so many vascular systems, convey their fluid contents, elimi-
nated from the blood, always in one direction, from the san-
guiferous system, as the chyliferous and lymphatic systems
convey theirs to the mass of the blood. And although the
mode of action of these various emurictories of the circula-
tion, in producing chemical changes in the fluids they
transmit through their parietes, be, like the transmissive
powers of nervous filaments, yet unexplained, the most per-
fect regularity of system and unity of plan are not less
apparent in the development of secreting organs throughout
the classes of the animal kingdom and the embryos of indi-
viduals, than in the nervous or other important systems of
the animal economy.

CHAPTER SIXTH.

LYMPHATIC SYSTEM.

IN the lowest tribes of animals, all the assimilative func-
tions are performed by the same simple digestive cavity
which receives the raw material from without ; but as we
ascend in the scale of organization, the functions become
more complicated in their result, and special organs are
appropriated to the several portions of the complex process
of nutrition. In the first condition of the vascular system in
the radiated classes of animals, the arteries are scarcely
distinguishable from the veins in structure or in function,
and to this simple plexus of ramified tubes, in which the
blood often takes a retrograde course, are confided the func-
tions of chylification, sanguification, circulation, and even
absorption. And throughout the highest of the inverte-
brated classes, the absorption of nutriment from the intes-
tine, and the absorption of the decayed materials from

LYMPHATIC SYSTEM. Gil

all parts of the body, appear still to be confided to the
ordinary sanguiferous vessels. In the complex systems
of the vertebrata, however, a distinct chyliferous appa-
ratus is appropriated to the absorption of the nutritious
part of the food, and to its conversion into chyle or almost
into blood, and in the same elevated tribes of animals a dis-
tinct vascular system, the lymphatic or absorbent, is allotted
to receive the decayed materials from every point of the
body, and to convey them to the blood, to be discharged
with the excretions.

The lymphatics appear to be porous or absorbent at all
points of their surface, as the tubuli of glands are secern-
ing throughout their course, and probably both these sets
of permeable tubes are equally closed at their commence-
ments. By the introduction of these absorbents into all
the tissues of the body, they are enabled to grow by in-
tus-susception, and to retain all their proportions while they
increase in bulk. From their function they have been termed
absorbents, and lymphatics from the limpid fluid they convey.
Though differing in function from the lacteals, as the lacteals
from the veins, or the liver from the kidney, they have nearly
the same relation to the venous or sanguiferous system, and
enter it at the same place, through the medium of the
thoracic ducts, which are canals common to the chyliferous
and lymphatic apparatus. While the lacteals convey only
chyle to the blood, and originate solely from the alimentary
tube, the lymphatic absorbents convey the dissolved tissues
of every living organ, and originate from or traverse every
point of the body ; and although these two systems first
appear simultaneously in the class of fishes, the plexiform
convolutions of their vessels, forming their so-named ganglia
or conglobate glands, appear earlier in the lymphatic than
the chyliferous system. The limpid contents of these vessels
are sometimes yellowish, reddish from the presence of blood
globules, or whitish in colour, they contain albumen and
fibrin and easily coagulate, and they convey globules, like
chyle, blood, or milk.

The lymphatics abound in the tissues of all the verte-
brated classes, following the course chiefly of the larger
and deep-seated arteries and veins, and occurring over all
the subcutaneous parts, so that they appear to confer the

R B 2

612 LYMPHATIC SYSTEM.

property of rapid absorption on all the mucous and se-
rous membranes, and on all the other tissues of the body,
by their quickly conveying the transuded matters to the
circulating blood, and they become exquisitely sensitive in
the inflamed state. They commonly exhibit two distinct
coats, an outer dilatable fibrous tunic, and an inner smooth,
less elastic, serous coat which forms internal crescentic folds
or semilunar valves. The valves are commonly in pairs,
directed towards the heart, less numerous than in the lacteals,
and apparently deficient in some of the viscera, as the lungs,
the liver, and the uterus. The anastomoses of the lympha-
tics are much more frequent than those of the veins, which
occur much oftener than in the arteries ; they probably com-
mence by closed orifices, like the tubuli of glands. The lym-
phatics form numerous so-named conglobate glands or gan-
glions, consisting of plexiform sub-divisions convoluted into
small tubercles, with afferent and efferent lymphatics leading
to and from these pseudo-glands, like the nervous filaments
in sympathelic ganglia ; and muscular pulsating cavities are
sometimes developed on the lymphatics, like the pulsating
sacs on the sanguiferous system of many invertebrata.

In the class of fishes, where the existence and the extensive
distribution of the lymphatics have been long known, they
have been observed in almost every form of osseous and car-
tilaginous species, excepting in the lowest cyclostome fishes,
as the myxine and the lampreys, but they have not been
detected in the invertebrated tribes, where their function,
like that of the lacteals, appears to be performed by the
sanguiferous capillaries. The lymphatics of fishes were early
examined and described by Monro, Hewson, Fohmann,
Meckel, and others, who injected them with fluids, inflated
them with air, and pointed out their yet simple structure,
apparently consisting of a single very thin tunic, their want
of internal valves, excepting at their entrance into veins
where there are generally valves, their distribution throughout
the textures and organs of the body, especially over the super-
ficial parts, and their supposed free communications with the
venous system. Instead of the distinct compact conglobate
glands presented by this system in the warm-blooded classes,
we here observe occasional groups of crowded tortuous
anastomosing lymphatics, presenting a kind of analysis of

LYMPHATIC SYSTEM. 613

the higher forms of these so-named lymphatic glands or
lymphatic ganglia. The few small lenticular bodies like
lymphatic ganglia observed in the neck of the roach have
been considered by some as mesenteric glands, and were
regarded by Meckel as the- first rudiment of the thymus
gland, which he considered, as well as the spleen, as merely
a lymphatic gland. Monro observed the deficiency of the
ordinary lymphatic glands in fishes, and considered the long
subcutaneous muciparous follicles as lymphatic vessels opening
by large orifices on the surface of their skin, and thence
supposed that all lymphatics must have similar open orifices.

Besides extending as a continuous network over all the
deep-seated and superficial parts of fishes, they already
cover by their numerous plexuses, as shown by Fohmann,
the entire surface of the larger veins, especially when they
are distended with injected matter, and from the exten-
sibility of their soft thin coats, they generally appear very
wide and sacculated, and present numerous transverse con-
strictions of their parietes, at irregular distances, as if from
the commencing development of valves. The direct com-
munications of the lymphatics with many branches of veins
pointed out by Fohmann, have been more recently as-
cribed by Panizza and others, entirely to rupture of the
injected vessels and to transudation, not only in fishes but
in all higher classes. The large sacs and receptacles com-
monly observed on the injected lymphatics of fishes, are,
for the most part, produced by the pressure of the injected
matter on the thin distensible sides of these vessels. There
are commonly two great lateral plexuses of lymphatics 011
the trunk of fishes, passing forwards to terminate with the
anterior ventral plexus, in the thoracic ducts behind the
heart ; and the lymphatics of the head and dorsal parts of
the body enter the ducts anterior to this point, after forming
considerable plexuses near their entrance into the anterior
cavra or into the jugular veins. The lymphatics from the
posterior parts of the body unite with the lacteals from the
intestine, to form two great trunks before ending in the re-
ceptaculum, which forms the commencement of the two
anastomosing plexiform wide thoracic ducts. They form a
compact layer of plexiform vessels around most of the organs
of the abdomen, as around the spleen, the large pancreatic

614 LYMPHATIC SYSTEM.

tubuli, the liver and gall-bladder, the testes and ovaria, and
even the minute laminae of the gills where their larger
branches follow the course of the branchial arteries along the
concavities of the arches.

The lymphatic vessels have been shown by the numerous
careful injections of Panizza, Muller, and others, to be no
less extensively distributed through every part of the body
in the naked batrachian animals or amphibia, than in the
fishes, and they are maintained by Panizza to be here, and
in all higher classes, a distinct, isolated system of vessels,
from their origin to their termination, by great trunks, in the
venous system. He has represented, in his splendid plates,
taken from his own preparations, the crowded distribution
of these plexiform and beaded vessels, over all the subcuta-
neous parts of the body, and forming compact layers around
the interior viscera, especially on the spleen, in frogs and
salamanders among the amphibia, as well as in serpents,
lizards, crocodiles, and tortoises, among the true reptiles ; he
considers the skin as altogether different in properties from
mucous membranes, and that the batrachia are incapable of
respiring through their soft and naked skin. Between the
skin and the subjacent muscles of the higher amphibia there
are large lymph spaces which appear to communicate freely
with the lymphatic vessels, they are readily filled by inflation
of the lymphatic hearts, and they usually contain a consider-
able quantity of lymph which escapes on cutting the skin.
The great receptacle or thoracic duct of the frog, forms a
wide continuous sac extending along the whole dorsal region
of the cavity of the trunk, above the abdominal viscera ; the
large receptacle of the salamander, in extending forwards,
divides and reunites, and again bifurcates before entering the
two subclavian veins.

Muller at Berlin and Panizza at Pavia discovered, about
the same time, two symmetrical pairs of pulsating muscular
cavities, on the large brachial and crural lymphatics, in
the regions of the neck and pelvis in the naked amphibia,
and similar pulsating sacs have also been detected on the
lymphatics of some reptiles and birds. The pulsations of
these lymphatic sacs are not synchronous with those of the
heart, nor even with each other ; and they continue after the
heart has been dissected from the body, or the body cut to

LYMPHATIC SYSTEM. 615

pieces. In the frog the anterior pair are situate below the
posterior edge of the scapula, and above the broad transverse
processes of the third cervical vertebra, the posterior pair
on each side of the free end of the long coccygeal bone, quite
superficially near the sides of the anus ; they are seen pul-
sating, about sixty times in a minute, through the skin of
the entire animal without dissection, and they propel the
lymph collected from the anterior and posterior parts of the
body and extremities, into the neighbouring venous trunks.
They contain only the usual colourless lymph, and by dis-
tending them with air the lymphatics of the extremities
become inflated, and also the lymph spaces beneath the skin.
The anterior pair of these lymphatic hearts propel their con-
tents, on each side, into a branch of the jugular vein, which
becomes distended by each contraction of the sac, and the
posterior pair send their lymph on each side into a branch
of the ischiadic vein. The posterior pair of these pulsating
sacs are the more constant in their development, and have
been observed, where the anterior were imperceptible, in
salamanders, serpents, and saurian reptiles. They are pro-
vided with simple valvular folds at their orifices in the
python, where they send their lymph into branches of the
renal veins.

The structure and distribution of the lymphatic system of
reptiles have been illustrated by the researches of Bojanus,
Panizza, and other anatomists, especially in the chelonia,
where they present great facilities for their investigation,
from their great size, their extensive distribution, and the
still imperfect development of their valves. The imperfect
development of the valves in the lymphatics of all the rep-
tiles, still allows injections to pass from the larger trunks of
these vessels towards their branches and capillaries, and
hence the convenience and the facility of illustrating their
distribution through the textures and organs, by preparations
from this class, especially from the vegetable eating chelo-
nian reptiles, where they are largest and most extensively
developed. They are always wide and dilatable vessels, and
they present a knotted or beaded appearance, most conspi-
cuous when filled, injected, or inflated, from the constric-
tions caused internally by the valves, and the dilatations of
the elastic parietes of the vessels between the valves. Sue-

LYMPHATIC SYSTEM.

cessfully injected preparations of the lymphatics in the che-
lonian reptiles, show almost every organ of their body, to be
permeated and covered over with a compact layer of these
wide absorbent vessels. They are remarkably crowded on
the surface and in the interior of the spleen in the chelonia,
as in the amphibia ; and Tiedemann supposed that all the
chyliferous vessels of the mesentery in these cold-blooded
classes, pass through the spleen before entering the thoracic
ducts. The thoracic ducts form generally two wide irregular
anastomosing canals, most dilated at the receptaculum,
which convey the lymph and chyle to the veins of the neck.

The lymphatic glands or ganglia are not yet developed in the
reptiles, and their place is supplied by the tortuous windings
and subdivisions of parts of the vessels themselves, as in the
lower cold-blooded vertebrata, which indeed is but a less
concentrated or a more unravelled and simple condition of
the compact lymphatic ganglia of higher animals. Panizza
detected a small pulsating muscular sac on the lymphatics
proceeding from the posterior part of the trunk on each side,
in the coluber flavescens, like those discovered in the amphi-
bia, and they are found in many of the saurians ; they are
nearly an inch long in the python. He has not been able,
by all his injections, to discover a single direct entrance of a
lymphatic vessel, or of a lacteal into a vein, even in the
lymphatic and mesenteric glands of the higher vertebrata,
and he ascribes the communications pointed out by other ob-
servers, to the rupture of vessels, and the extravasation of
the injected matters, especially in the glands, where the
minute lymphatic capillaries twine round and interlace with
the veins. The more recent researches of Muller and other
anatomists have also tended to establish the isolated condi-
tion of the absorbents, in all the vertebrated classes, through-
out their entire course to the great normal trunks by which
they terminate in the venous system ; and Duvernoy sup-
poses that such free communications as have been presumed
between absorbents and veins, at least between the lacteals
and the branches of the vena portoe, would tend to dimmish
and deteriorate the chyle destined to nourish and replenish
the blood, by expending its principal constituents in the for-
mation of bile.

The spleen of the tortoise, by successful injection, is made

LYMPHATIC SYSTEM. 617

to appear like a mass of absorbents, where the finer in-
ternal vessels accompany the divisions of the veins through
its texture, and the larger exterior lymphatics form by
their confluence, a considerably superficial sinus. They
abound on the mucous and serous membranes and through-
out the adipose substance of this animal, they present
a regular arborescent appearance on the testicle, and are
comparatively rare on the liver, the gall-bladder and the oeso-
phagus. The distinct compact external intestinal layer of
absorbents, probably belongs to the lymphatic rather than
to the chyliferous system. In the crocodile and the green
lizard, Panizza found the lymphatics particularly abundant
and forming distinct layers around the cloaca and the termi-
nal portion of the intestine, the heart of the crocodile ap-
peared enveloped in a plexiform layer of these vessels, but
he could not inject those of the liver, the testicle, or the pe-
ricardium. In the turtle, the crural plexuses derived from the
lymphatics of the posterior extremities, together with the
renal, the rectal, the cloacal, and the sacral plexuses, unite
with the lymphatics of the peritoneum, the adipose substance
of the abdominal parietes, and part of the lungs, and the
great chyliferous trunks, to form the wide reticulate commen-
cement of the anastomosing thoracic ducts, which envelope
and almost conceal the abdominal aorta, as they advance
forwards, collecting the lymphatics from all surrounding parts,
to terminate in their respective subclavian veins. In the alli-
gator, four great chylo-lymphatic trunks unite and separate
several times, before they collect on each side to constitute
two lateral thoracic fasciculi, which receive the neighbouring
lymphatics as they advance, and terminate in the two sub-
clavians. In the lizard the thoracic duct advances single
through part of its course, but divides anteriorly into the
usual two branches, before ending in the veins ; in serpents
they continue separate from the receptaculum.

In the class of birds the lymphatics are less wide and sac-
culated than in the chelonia, their parietes are more firm ;
they are smaller and more numerous than in reptiles, and
the valves formed by crescentic folds of their serous lining
are more developed. Their course is now generally more di-
rect, and their plexuses in the neck are occasionally deve-
loped into distinct small lenticular conglobate glands, though

618 LYMPHATIC SYSTEM.

they are not yet developed on the chyliferous vessels of the
mesentery. They are here seen, as in other classes, clus-
tered in reticulate plexuses around the great blood ves-
sels of the extremities and of the trunk. The lymphatics
from the lower extremities and the posterior parts of the
trunk, enter a large plexus or receptacle at the origin of the
coeliac artery, along with the lacteals from the lower portion
of the intestine. Those from the head and anterior parts of
the body enter the two great trunks of the thoracic ducts, to
pour their contents along with the chyle into the angle
between the subclavian arid jugular veins. As many as six
lymphatic glands have been detected on each side of the
neck, in some of the larger predaceous birds. Injected mat-
ters can still occasionally be forced to pass through the lym-
phatic vessels, from trunk to branches against the direction
of the valves, and Lauth sometimes found the injections ex-
travasated between the two coats of these vessels in birds.
In the goose, he observed the lymphatics extending along the
sides of the toes and over the interdigital membrane, form-
ing a plexus on the tarsus and lower part of the leg, collected
behind the knee into a single femoral trunk, which enters
through the crural arch into the pelvis ; here they form a
plexus, on each side, enveloping the renal veins, and send
their principal trunks into the renal or the sacral veins. The
chyliferous plexuses chiefly envelop the mesenteric, coeliac,
and aortic trunks, and, after receiving several lymphatics
from the abdominal and pelvic viscera and the posterior
parts of the trunk, they collect to form the commencement
of the thoracic ducts. The lymphatics from the lungs and
oesophagus, and from the wings, enter the thoracic ducts be-
fore their termination in the jugular veins, and the same
ducts receive also the lymphatic trunks from the sides of the
head and neck, excepting a branch from the right cervical
trunk which opens separately and directly into the right ju-
gular vein, and the left thoracic duct sometimes sends bran-
ches to open separately into the left subclavian.

The fibrous and serous coats of the lymphatics, and their
general external cellular investment, are more distinct, espe-
cially in the larger trunks, in the mammalia, than in lower
classes ; their symmetrical pairs of opposed semilunar valves
are more numerous, more complete, and more effective in

LYMPHATIC SYSTEM. 619

guiding the course of the contained lymph, and in prevent-
ing the flow of injected fluids against their natural direction.
The compact aggregate masses of convoluted lymphatic ca-
pillaries, forming the conglobate glands, so rarely met with
in lower vertebrata, are now general, distinct, large, and nu-
merous in the course of these vessels. They abound especially
in the inguinal and axillary regions, on the sides of the neck,
and along the course of all the great veins. The lymphatic gan-
glia of mammalia are common in the general cavities, and
around the great viscera of the pelvis, abdomen, and tho-
rax, and even in the interior of organs, as along the divi-
sions of the bronchi in the substance of the lungs. They are
commonly more concentrated, fewer, and larger in the infe-
rior quadrupeds than in man ; and from their deficiency in
the cranial cavity, where lymphatic vessels abound, their
office appears to be incompatible with the delicate functions
of the brain. They are often tinged by peculiar contents of
their vessels or by the colours of the surrounding parts, es-
pecially after death, as in the vicinity of the liver, the spleen,
and the bronchi, and they often acquire a cellular appear-
ance internally, as in the cetacea, from dilatations of their
minute convoluted tubes, or of their connecting cellular tis-
sue. Though they do not occur within the skull, the lym-
phatic glands are common on the exterior parts of the head,
as behind the ears, beneath the lower jaw, and on the in-
side of the parotids.

The lymphatic vessels not only form integrant parts of all
the organs and tissues of the body, but by injection many
of them appear to be almost entirely composed of these ves-
sels. Though smaller in mammalia than in lower classes,
they are more numerous and more extensively distributed,
they are much larger than the capillary blood-vessels which
spread on their parietes, they are wider than the terminal
tubuli of most glands, and their minutest branches are per-
ceptible by the naked eye. Their subcutaneous layer now
forms a more compact and continuous stratum over all the
superficial parts of the body, as they appear also over all the
mucous and serous membranes of the interior, forming an
inextricable network as little provided with, and as little re-
quiring villous commencements or orifices as the sanguife-
rous capillaries they accompany, and in which the limpid,

620 LYMPHATIC SYSTEM.

colourless, coagulable, imbibed fluids are moved forwards
to the blood by the vis absorbendi, the pressure and move-
ments of all surrounding parts, and by the direction of the
valves now crowded in their interior. The valves, as in por^
tions of the venous system, are sometimes deficient in their
interior, as in the lungs, the liver, and the uterus, and not-
withstanding their distinct fibrous coat, considered by Meckel
and others to be muscular, and the obvious rithmic pulsa-
tions of their muscular sacs in many of the lower vertebrata,
no pulsatory movements or spontaneous contractions have
yet been discovered in any portion of the lymphatic system
of man or mammalia.

The general distribution or the typical form of this vast sys-
tem in the mammiferous animals, is seen in that of the human
body where, as usual, they have been detected and most in-
vestigated, after their discovery in inferior tribes. Collecting
the lymph from the superficial parts of the feet, these vessels
form an outer cutaneous group, ascending behind the exter-
nal ankle and the back part of the leg to the small popliteal
glands, and an inner cutaneous group, ascending along the in-
ner side of the knee and forepart of the thigh, to the superfi-
cial inguinal glands. From the deeper parts of the feet the
lymphatics collect around the arterial trunks, as the cutaneous
do with the great veins, and ascending with the peroneal, the
anterior and the posterior tibial arteries, they traverse the
popliteal glands, and continue their course with the femoral
artery to the smaller and deeper seated glands around that
vessel in the inguinal region. Throughout their whole course
these lymphatic trunks are reinforced by numerous branches
from all the surrounding parts, and numerous lymphatics
from the exterior of the pelvis, the abdomen, and the ge-
nital organs, likewise meet to traverse the inguinal glands.
The efferent lymphatics from both sets of inguinal glands
enter the pelvis, through the crural arch, with the great
blood-vessels, and proceed along the external iliac artery to
the large and numerous lumbar glands, and all the arte-
rial trunks issuing from the pelvis are accompanied by nu-
merous lymphatics from the neighbouring parts, proceeding
inwards to the same destination, and thence to the thora-
cic duct.

The absorbents from the urinary bladder, the prostate, the

LYMPHATIC SYSTEM. 621

deeper parts of the penis, the clitoris, and the vesiculee
seminales, like those of the uterus, enter the glands
along the internal iliac artery, the ovarian have a higher
termination; the large rectal lymphatics proceed to the
sacral and lumbar glands, and those of the testes accom-
pany the spermatic arteries to enter the latter glands, and
the renal and suprarenal lymphatics have the same termina-
tion. The splinic absorbents accompany the blood-vessels,
form a series of small glands ; receive the lymphatics of the
pancreas, and part of those from the stomach, and pro-
ceed with the lacteals towards the general receptaculum ;
those from the superficial and the interior parts of the
liver, proceed partly through the diaphragm and medias-
terium to the right lymphatic duct, and partly backwards
to the great left thoracic or chylo-lymphatic duct, both
sets forming numerous glands in their course. Both the
superficial and the deep-seated absorbents of the lungs
meet in the bronchial glands, and the efferent ducts of
these small glands ascend to terminate respectively in the
right and left thoracic ducts ; the lymphatics of the heart
accompanying the coronary vessels to the base of that organ,
and forming glands in their course, likewise ascend by the
sides of the trachea to open into both thoracic ducts, and
those cf the thyroid gland have a similar double termination.
The lymphatic glands or ganglia thus extensively developed
on all the absorbent trunks in man and mammalia, appear to
exert an influence in animalizing the serous residue of nutri-
tion which they convey, as the chyliferous glands exert on
the chyle they convey to nourish the blood.

As in other parts, the absorbents from the head and neck
follow chiefly the course of the sanguiferous vessels, the su-
perficial generally accompanying veins, and the deeper-seated
the arterial trunks, and forming numerous small glands in
every convenient part of their course. The lymphatics
which descend with the temporal artery on each side, tra-
verse the zygomatic and parotid lymphatic glands, and con-
tinue to the numerous glands of the neck lying near the
junction of the external jugular with the subclavian vein ;
those which descend posteriorly with the occipital artery, tra-
verse the post- auricular glands, and terminate with the former
in the cluster of cervical glands. The numerous exterior ab-

622 LYMPHATIC SYSTEM.

sorbents accompanying the facial vein traverse the submaxil-
lary lymphatic glands and those seen over the buccinator
muscle ; the deeper branches of the face pass likewise through
the glands at the angle of the jaw, in their course downwards to
the mass of lymphatic ganglia at the base of the neck. And the
efferent vessels from these glands which receive most of the
absorbents from the head and neck, unite on each side
to form single trunks which enter the right and left thoracic
ducts, or sometimes directly the subclavian or the jugular
veins. The anterior termination of the great chylo-lympha-
tic duct is still irregular and divided, like its posterior com-
mencement ; and although this common centre of the chyli-
ferous and lymphatic systems is now single in most of its
course, it exhibits traces of its double and plexiform condi-
tion in most lower vertebrata, by the divisions and anastomo-
ses which it still seldom fails to present in different parts of
its course in mammalia and in man.

The course and distribution of the lymphatics of the arms,
correspond much with those of the posterior extremities,
forming a superficial series mostly accompanying the cuta-
neous veins, and a deep seated group following the course of
the great arteries. The principal cutaneous absorbents of
the anterior extremity ascend on the palmar side of the
hand, wrist, and fore- arm to the bend of the elbow, where
they form one or more glands, seldom seen in lower mamma-
lia, and continue their course on the inside of the arm, en-
larging by the accession of branches from all surrounding
parts, to the cluster of glands in the axilla. The smaller su-
perficial group proceeds along the dorsal part of the hand and
arm, and along the course of the cephalic vein to the subcla-
vian glands. The deeper-seated lymphatic trunks accompany
the radial, ulnar, inter- osseous, and brachial arteries, commu-
nicating with the cutaneous absorbents, and terminating in the
group of axillary glands, which receives also the lymphatics
from the anterior and posterior parietes of the thorax. The
efferent trunks from these large axillary glands follow the
course of the subclavian artery, on each side, and open with
other lymphatic trunks into the right and left thoracic
ducts, or sometimes directly into the subclavian veins.

The axillary and inguinal lymphatic glands are more
subdivided and detached in man than in most lower mam-

EXCRETING ORGANS. 623

malia, where they are seldom observed in the ulnar or the
popliteal regions. These glands are also more compactly
united together, and into fewer groups, on the head and
neck, and in most parts of the body, in the lower qua-
drupeds than in man, as shown by Gurlt in several of
the domestic species; this accords with their smaller
number of lymphatic absorbents, and of convenient places
for their assuming the glandular form. In like manner,
where the intestines and mesentery are long, and afford ex-
tended space for the distribution of chyliferous vessels, as in
herbivora, quadrumana, and man, the mesenteric glands
are numerous, small, detached, and spread separately over a
large surface ; and where the alimentary canal and mesen-
tery are shorter, as in carnivora, these glands are more
approximated, aggregated, and often compactly united into
the so-named pancreas Assellii. And thus the lymphatic
system, though late in its commencement in the animal
kingdom, and still mysterious in its function, has advanced
by regular and progressive stages to a condition more uni-
form in character than the chyliferous, and higher in deve-
lopment, by the possession of a rudimentary heart, and has
approached the sanguiferous system in the elaboration of its
parts, and in its vast distribution through the organs and
tissues of the body.

CHAPTER SEVENTH.

EXCRETING ORGANS.

THE residue of the nutrition of all the organs and tissues,
and the decayed materials of animal structure, imbibed by
the parietes of lymphatics from all points of the body, and
conveyed by them to the blood, prepare that fluid to afford
the materials of various excretions, to be removed from the
system by distinct internal organs or by the general surface
of the skin. But animals without lymphatics, and even
without blood-vessels, alike possess the means of dissolving
and separating from their fabric the old materials which for

624 EXCRETING ORGANS.

a limited time have formed part of their system, and this
endowment is essential to their development and growth, and
constitutes the principal phenomenon of their nutrition and
of their life. The effete materials of their nutrition are pouring
incessantly in a gaseous or in a fluid state, from the exterior
cutaneous surface of the body, or from the internal mucous
surface of the alimentary canal and its appendages, in all
classes of animals, from the polygastrica to the mammalia,
however inappreciable those products may often appear. Re-
pair and decay, nutrition and excretion, may alike be re-
garded as secerning processes, where dissolved materials
permeate the parietes of capillary tubes ; and where those
secreted materials do not appear subservient to some useful
purpose in the maintenance of the individual or of the spe-
cies, they are regarded as excretions, and the parts which
form them excrdlny organs, whether they communicate with
the internal mucous lining of the alimentary cavity or the
exterior cutaneous covering of the body.

All excreting organs, by extracting their products from
capillary blood-vessels spread on their surface, have a se-
cerning function, whether performed by simple membranes,
follicles, tubuli, or other forms of glands, and a precise
limit can scarcely be assigned to the excrementitious cha-
racter of glands and secretions. The luminous, the elec-
trical, and the stinging materials evolved by many of the in-
ferior tribes, are but little connected with the processes of
nutrition or of generation, as are also the numerous poiso-
nous fluids, inky secretions, and odorous materials formed
by animals for self-defence, but unequivocally less are the
gaseous and aqueous materials evolved by the respiratory
organs, the fluids perspired by the skin, and the heteroge-
neous product of the kidneys. As in all other glands con-
nected with organic life, the most important and the most
developed forms of excreting glands originate from the in-
terior of the alimentary canal, and are safely protected in
the deeper cavities of the body, while the more simple and
minute forms of these organs, and the most numerous, are
developed from the skin and spread over the whole exterior
of the body.

EXCRETING ORGANS. 625

FIRST SECTION.

Internal Organs of Excretion.

The most complicated and the most distinct of all emunc-
tory apparatus developed in animals, are the urinary organs,
which early appear in the animal scale and in the embryo,
and exert the most immediate and extensive influence over
the condition of the vital fluids, and the entire economy.
Developed in the vertebrated tribes, from the cloacal end of
the alimentary canal, like the lungs from the buccal extre-
mity, the urinary, like the pulmonary organs, excrete largely
the aqueous constituents with other materials of the blood,
and both these complex secerning organs remove their hete-
rogeneous products by the terminal openings of the diges-
tive tube. As carbonic acid is the most characteristic in-
gredient of the pulmonary excretion, so are uric acid, or urea,
and lithic acid, both abounding with nitrogen, the chief
urinary products ; and as the structure of no gland is yet
indicative of its function, the lowest and most ambiguous
forms of the urinary organs are determined rather by their
general analogies of form and connections, and the chemical
nature of their products, than by any peculiarity of internal
structure. The urinary organs thus corresponding in func-
tion, and complimentary, to the respiratory, commonly how-
ever exhibit less tendency to ramification and vesicular
dilatation in their ultimate tubuli, than the lungs and most
other complex glands.

The means of respiration possessed by the simplest
forms of animals, whether internal or external, may serve
likewise as general emunctories for the urinary and other
excretions, without the necessity of special organs for each
of these products. As all parts of the body in the radiated
classes of animals, the cutaneous, mucous, and serous
surfaces, are constantly bathed by ciliary currents of the sur-
rounding liquid element, the excretions may be removed di-
rectly from every point of the system without distinct organs
for their elimination. The tubular, ramified, internal respira-
tory organs of holothuria (Fig. 114. A.), developed like renal
glands from the cloacal end of the alimentary A canal, and ex-
tending like the kidneys of vertebrata along the interior of the

PART VII. S S

626 EXCRETING ORGANS.

trunk, have obvious affinities, both to urinary and branchial
organs, and may perform the function of both these great
emunctories. Distinct isolated follicles, (Fig. 1 14. z.), however,
more resembling simple urinary tubuli, are already perceptible
in this animal, developed from the cloacal end of these large or-
gans, and to which the urinary function may be confined. The
calciferous gland of the asterias may have a similar function.
Although numerous salivary, mucous, and biliary
follicles pour their secretions, partly excrementitious, into
the alimentary canal in the helminthoid animals, no distinct
formation of uric or lithic acid has hitherto indicated a
urinary function in any of these simple glands. Among the
entomoid articulata, many insects and arachnida exhibit,
besides the ordinary biliary tubes opening into the higher
chylific portion of the alimentary canal, distinct small
secreting follicles or tubuli developed from the lower ex-
cretory part of the intestine, like the renal organs of verte-
brated animals, and these structural analogies have been
confirmed by their chemical products, by the uric and lithic
acids discovered in their secretions. These simple tubuli
uriniferi pour their secretion into the cloacal part of the
intestine near the anus, and in some of the coleopterous
insects, as in ditiscus, there is a distinct small vesicle or
urinary bladder into which one or two renal tubes convey
their secretion, before opening into the terminal part of the
intestine. The renal tubuli were pointed out by Treviranus
in the iulus among the myriapods, they have been detected
in some of the Crustacea, as the pagurus, and they are seen
in the spiders among the arachnida. The urinary organs,
like other glands of mollusca, have seldom the form of
elongated isolated tubuli, as they have in the articulated
tribes, but generally present the form of short wide secreting
sacs, opening near the anus or the genital organs. Such
sacs are seen in many conchiferous mollusca, situate in the
dorsal part of the body below the heart, and opening by
two short ducts along with the oviducts, near the anus ;
these are often charged with earthy particles, and have been
generally considered as destined to secrete the calcareous
nratter of the valves. In several of the terrestrial and fresh-
water gasteropods breathing atmospheric air by pulmonary
sacs, uric acid has been detected in the secretion of a small
excretory gland, laminated internally, filled with solid

EXCRETING ORGANS. 627

granules, and opening near the anus, and which thus pre-
sents a close analogy to the renal organs of higher animals.
The muciparous gland of the turbinated testaceous gaster-
opods, pouring out so copious a secretion under the mantle,
near the anus, may perform a similar office, and also the
glandular sac opening near the anus in the doris and some
other naked species. The poison glands of scorpions and
insects, the glands for the deep-coloured excretions of certain
gasteropods, the anal ink-glands of cephalopods and the
muciparous glands of their oviducts, have likewise some
analogies to urinary organs.

In the vertebrated classes, no organs are more constant
than the two essential urinary glands, the kidneys, and the
more accessory urinary bladder is one of the most variable
and inconstant. The urinary organs are generally of larger
size, and of a simpler internal structure, in those animals
which have a limited extent of respiration, so that their bulk
is commonly in the direct ratio of that of the biliary organs.
The urinary organs of vertebrata, like their genital organs,
are developed in the embryo from the cloacal end of the
alimentary canal, and in all the oviparous tribes, they con-
tinue in the adult state to communicate directly with that
cavity. The kidneys of fishes have a lengthened lobulated
form, extending along the sides of the vertebral column as
far forwards as the cranium, exterior to the peritoneum, and
behind the air- sac. In their elongated form, and in their
proximity to each other along the median plain, as well as in
their lobed structure, and in the parallelism of their compo-
nent tubuli uriniferi, they resemble the embryo-state of
these organs in mammalia. They extend forwards above
the heart and branchiae, and backwards into the pelvic cavity
behind the anus, bound to the sides of the bodies of the
vertebrae by the peritoneum, separated from each other by
the interposed vena cava, and by the two ureters which run
along their whole extent, as narrow tubes, without forming
a distinct enlargement or pelvis. The great size of these
emunctories of the aqueous part of the blood in fishes, may
have relation to their aquatic habitat, and the quantity of
fluids constantly taken with their food. The kidneys consist
of subdivided ureters, the tubuli of which are variously
disposed, and produce, by their subdivisions and convolu-

s s 2

628 EXCRETING ORGANS.

tions, the tabulated exterior so constant in the oviparous ver-
tebrata. The secreting surface of these ducts is thus greatly
extended for the reception of a larger distribution of renal
capillary arteries and veins over their parietes, and the diffe-
rent modes of distribution of the blood-vessels in the interior
of these organs in the different classes, contributes to the
differences perceptible in the intimate texture of the kidneys,
as of other glandular organs. The tubuli uriniferi are almost
always long, cylindrical, narrow, and more or less tortuous
in the adult lobules of the kidneys of the plagiostomi, and
the higher osseous fishes, and more short, straight, parallel,
and wide, in the earlier stages of their development, and in
the lowest cyclostome species. Each lobule of the adult is
composed of the tubuli proceeding from a single branch of
the common duct or ureter, and appears, in the embryo, to
consist of a single lamina of the formative blastema. The
primitive vascular blastema of the embryo divides into
laminae, and each lamina developes a cluster of tubuli, which
open by a common orifice, or short duct, into the cylindrical
narrow ureter extending along the whole kidney. The group
of tubuli uriniferi, composing a renal lobe, are held together
by the remaining portion of the soft formative blastema.
The blastema at first extends undivided on the median plain,
along the middle of the back, between the mucous and serous
layers of the embryo ; a duct for each kidney is, at length,
perceived extending through it longitudinally, and giving off
lateral tubuli in its course, which develope through the sub-
stance of the lobules.

In the rays and sharks, the kidneys are composed of long,
fine, very tortuous and convoluted tubuli, which open
separately along the course of the ureter, and in the early
embryo, they appear, as in higher classes, to be accompanied
with a corpus Wolffianum, composed of very minute convo-
luted tubuli. In the torpedo marmorata, the kidneys form two
tabulated organs extending along the outside of the ureters,
and consist of large tubuli, about Tv of a line in diameter, long,
and remarkably convoluted like the tubuli seminiferi of mam-
malia. In many of the long, equal, contorted tubuli, forming
the entire mass of the kidneys in the cyprinus carpio, Muller
observed a distinct dichotomous division, at some distance
from their closed extremities, preserving, however, as usual in

EXCRETING ORGANS. 629

tubuli uriniferi, the same diameter throughout their entire
course. The secretion of all the tubuli of each kidney is poured
directly into the long narrow ureter, which, without forming
a pelvic enlargement, and often without forming a urinary
bladder, opens into the cloacal termination of the intestine,
posterior to the rectal opening, and posterior to the genital
openings, whether male or female, as in the embryos of higher
vertebrata. Frequently, however, a urinary bladder is
developed, which is comparatively small in fishes, its orifice
then receives the terminations of the two ureters, and it
opens by a short wide passage at the back part of the cloaca.
The long narrow kidneys of many osseous fishes are approx-
imated and more .or less united on the median plain, without
any anastomosis of their internal tubuli. In the plagios-
tome fishes, the kidneys are smaller and shorter, as in che-
lonian and other reptiles, and the ureters enter, as usual, with
the vasa deferentia into a common short urethral passage,
without forming a urinary bladder. The kidneys of fishes
thus already present a very large secreting surface for the
distribution of capillary blood-vessels, which are always much
more minute than the tubuli on which they spread, as in
other secreting organs. The numerous arteries which supply
the renal lobes of fishes, come off directly from the trunk of
the descending aorta, or from the intercostal arteries which
are given off from its sides, and the renal veins mostly enter
the vena cava, as it passes forwards between the lobes of
these organs. The venous blood distributed through the
lobes of the kidneys, by the branches of the great superior
spinal vein, is received also by the vena cava, thus forming a
renal portal circulation.

The kidneys in amphibia are less elongated and less lobu-
lated in form than in most fishes, and the urinary bladder
is of greater size and more constant in its occurrence. These
glands originate early in the embryo, before the genital
organs; they are developed more towards the dorsal and pelvic
portion of the trunk than the corpora Wolffiana, and in the
adult state they neither extend forwards to the cranium, nor
backwards to the posterior end of the abdominal cavity, as
they do in most fishes ; so that the ureters have here a longer
free course before reaching the back part of the cloaca,
where they open at the sides of the wide orifice of the large
urinary bladder. They are at first, as in fishes, narrow, flat,

630 EXCRETING ORGANS.

approximated laminae, extending longitudinally along the
whole extent of the abdomen, under the vertebral column,
and from the periphery of the organ towards the lateral
portion of each tube or ureter, numerous minute tor-
tuous tubuli uriniferi are developed to extend the se-
creting surface. Their structure much resembles that of
the corpora Wolffiana of birds, which were thought to be
deciduous kidneys, but the kidneys are here developed much
posteriorly to the situation of these remarkable deciduous
glands. The kidneys retain their primitive foetal condition
to a much later period in the tritons than in the frogs and
toads, and their adult form is more elongated in the perenni-
branchiate species, as the proteus and siren, than in those
which lose the gills. The closed vesicular terminations of
the tubuli are perceptible around the periphery of the soft
vascular blastema, earlier than the narrow tubular necks by
which they communicate with the ureters, as the develop-
ment proceeds from the circumference to the centre of these
organs, and the development of the ureters appears also to
proceed from their renal ends backwards to their open
cloacal extremities. The form of the kidneys is more
elongated and narrow in the ccecilia and triton than in sala-
mandra and the anurous species, and the urinary bladder
of ccecilia is bilobate in form, like that of other caduci-
branchiate amphibia. The urinary bladder has a simple
and elongated form in the species which retain the bran-
chiae, as the axolotuSy siren, and proteus. The tubuli
are unusually large in the adult pro feus. The dichotomous
division of the tubuli uriniferi, near their closed ends, has
been observed by Huschke in some of the amphibia, and
also vesicular peripheral terminations, which latter are gene-
rally confined to the earlier stages of the development of
the tubuli. The small round corpuscula Malpighiana turgid
with red blood, are already abundant and conspicuous in
the texture of the kidneys of amphibia, as in higher
classes.

In the ophidian reptiles, as in fishes and birds, the urinary
bladder is very rarely developed, and the ureters terminate
as usual, directly and separately in the cloaca. The kidneys
of serpents, like most other organs of the body, partake of
the elongated form of the trunk; the left is situated farther
backwards than the right ; they are surrounded entirely with

EXCRETING ORGANS. 631

peritoneum, and suspended freely in the cavity of the abdo-
men, to allow of greater motion of the vertebral column with
safety, where there is yet no fixed sacrum. They have a
deeply lobulated or folded structure, consisting of a long
series of flat imbricated tortuous transverse lobes, or regular
sinuous folds of their exterior tubulated portions, resembling
externally so many small kidneys pressed closely together.
The contorted and convoluted tubuli composing each of
these lobes, pour their thick white viscid secretion, consist-
ing chiefly of uric acid, by a single orifice into the common
ureter, without forming a pelvic enlargement, and without
the calices developed in the more concentrated forms of the
kidneys of mammalia.

The narrow tubular ureters follow along the inner margin of
the kidneys, receiving successively the short wide common
ducts of all the separate lobes, and open by distinct orifices
into the back part of the cloaca, as in other oviparous ver-
tebrata, whether provided with, or destitute of, a urinary
bladder; sometimes, however, a small vesicular dilatation
is formed on each ureter before it opens into the cloaca.
The blood-vessels penetrate from the exterior of the kidneys
between the lobes, and appear to have been mistaken by
Huschke for tubuli uriniferi ramifying through the lobes.
The affinity of the anguine serpents to saurian reptiles, so
obvious in most parts of their structure, is seen also in the
presence of a urinary bladder in these species, which is of
considerable size in the pseudopus ; and the two short
kidneys of the anguis are placed on the same transverse
plain of the body, as in higher reptiles. The small white
tortuous tubuli uriniferi preserve the same size and diameter
throughout the substance of each lobe, and the same tortuous
diverging course to their periphery, so that there is yet no
distinction of cortical and medullary portions of these organs,
as is seen in the kidneys of mammalia. In the long narrow
kidneys of the embryo, the tubuli are short, cylindrical, and
straight, and extend separately from the ureter, through the
soft blastema, with little regularity in their arrangement or
in their course ; they commence in the embryo earlier than
the suprarenal capsules, near to the cloacal end of the trunk,
on the dorsal side of the corpora Wolffiana, as two narrow
white opaque bands of blastema, along the inner edges of
which, the ureters and the rudimentary tubuli make their

632 EXCRETING ORGANS.

appearance. Their distance from the cloaca increases, the
ureters elongate, especially that of the right side, a lobulated
or convoluted surface is developed, the ureters open into
the cloaca, close to the ducts of the deciduous kidneys or
corpora Wolffiana.

In the saurian reptiles there is more generally a urinary
bladder, and the kidneys are less elongated, and situated
farther backwards in the pelvic region of the trunk, than in
ophidia. In the crocodiles, however, and some others,
where there is no urinary bladder, the ureters open sepa-
rately into the dorsal part of the cloaca, as in bird^ and many
inferior vertebrata. And even where there is a urinary
bladder in the sauria, the ureters do not open directly into
its cavity or fundus, as they do in most mammalia, but into
the dorsal part of the cloaca near the neck of the bladder,
as is seen likewise in fishes amphibia and chelonia. The great
size of the urinary bladder in these animals results from its
containing the entire allantois, which is not protruded from
an external umbilicus, nor constricted and obliterated to
form a urachus as in mammalia. The kidneys of the cro-
codilian sauria are surrounded with tortuous superficial folds,
and appear more deeply lobulated externally, like those of
serpents, and from the ureters sending off numerous lateral
ducts, they are more complicated in the internal arrange-
ment of their tubuli, than in the lizards. Their tubuli
uriniferi, however, do not form tortuous groups arising from
short wide primary ducts, in each of the several lobes, as in
serpents, but diverge regularly in straight radiating lines
from around a central wide duct, which traverses the whole
extent of the axis of each lobe ; so that a vertical section of
a part of one of the lobes presents a pinnate appearance, with
parallel straight tubuli extending to the periphery from the
central duct. The kidneys are more developed at their
anterior part in some of the lizards, as they are in birds, and
taper backwards to their posterior ends, being shorter in
sauria than in ophidia, and longer than in chelonian reptiles.
In the embryo, the kidneys are more elongated, as in ser-
pents, and their short simple tubuli extend directly from
the side of the ureter, without indication of the lobulated
structure seen in the adult Jacertee,

The kidneys of chelonian reptiles have a more concen-

EXCRETING ORGANS. 633

•

trated and shorter form, and are less distinctly lobulated
than in most inferior vertebrata ; their surface presents a
convoluted appearance, as in crocodiles, from the tortuous
forms of their component lobules. The tubuli uriniferi are
more tortuous in their course in the chelonian than in the
crocodilian reptiles, but arise in a similar manner from the
ramified ureters. Their urinary bladder is of greater size
than in any other vertebrata, which accords with their suc-
culent vegetable nutriment and their limited cutaneous per-
spiration ; generally it is partially divided into two, and some-
times into three lobes at its upper part. Like the respira-
tory allantois of the foetus of higher classes, it is a great folli-
cular or hernial development from the cloacal part of the
intestine, and although, as usual in oviparous vertebrata,
the ureters do not terminate directly in it, but behind its
cloacal orifice, uric acid is found in its viscid contents, as in
the similar large urinary bladder of the batrachian animals.

The kidneys of birds are still constantly and deeply
divided, especially at their posterior ends, into numerous
lobes of considerable size, covered on their ventral surface
only with peritoneum, and lodged immediately behind the
lungs in the deep fossae along the sides of the sacrum. They
are elongated in form, diminishing in size from before back-
wards, constricted in their middle, symmetrical, placed be-
tween the same transverse plains of the body, deeply sulcatedon
their dorsal surface by the transverse processes of the sacrum.
The component lobes are most numerous and distinct in the
ostrich, and least apparent in some of the palmipeds, as the
pelican. The largest anterior lobe of each kidney receives
a distinct renal artery from the trunk of the aorta, and the
smaller succeeding lobes receive branches from the femoral
arteries, or from the sacra media prolonged from the aorta.
The surface of the lobes, when closely examined, presents a
convoluted appearance, as in many reptiles, from the tor-
tuous distribution of the small lobules, formed by the shut
ends of the ultimate tubuli uriniferi, as shown by Ferrein,
and tufts of these tubuli end in small calyces, as in mammalia.
The simple narrow ureters collecting the secretion from the
renal lobes, and extending along the ventral and inner surface
of the kidneys, without forming a pelvis, open directly into
the dorsal and lateral part of the cloaca, by two prominent

634 EXCRETING ORGANS.

papillae, and, there being no urinary bladder in birds, the
urine, containing a large proportion of urea with little aqueous
constituents, is mixed with the other excretions in the cloaca.
The openings of the ureters thus preserve the same relative
situation as in reptiles and lower vertebrata. But in the
ostrich, which presents so many other affinities with the
mammalia, the two ureters open at the lower margin of
the large cloacal cavity, which allows the secretion to ac-
cumulate as in a distinct bladder. The bladder, indeed,
in its most normal form, is only a development of the
cloacal part of the intestine, and the want of a urinary
bladder in adult birds, is due to the extent of oblitera-
tion of the allantois and urachus originally continued
from their cloaca. The minute cylindrical uriniferous tubuli,
much larger than the capillary blood-vessels, and directed in
a pinnate manner to the surface of the renal lobules, leave
perceptible interlobular spaces for the blood-vessels, as in
other glands, and the small sanguineous vesicles, or corpus-
cula Malpighi, are seen on these vessels in the tissue of the
organ, as in mammalia. The larger branches of the urinife-
rous ducts unite to open by prominent papillae into the
ureters, and small calices were already detected by Ferrein
in the pigeon, and are seen in the kidneys of the cassowary,
the falcon, the pintado, and other birds.

The kidneys of birds first appear in the embryo as a soft
transparent, almost homogeneous mass, in which the convo-
luted and foliated structure is gradually evolved, and the
extremities of the uriniferous tubes which compose the
lobules become perceptible in the periphery of the vascular
blastema. For some days after escaping from the egg, in
the larger birds, the delicate convolutions on the surface of
the renal lobes, and the elegant pinnate arrangements of the
ultimate tubuli, are beautifully manifested to the naked eye,
by means of the natural secretion of white inspissated urea
which fills and distends all these parts ; but by immersion
in alcohol, this beautiful appearance is soon effaced, by the
uniform whitening of the whole surface. These organs are
preceded in their development by the two elongated follicular
glands, the corpora Wolffiana, the ducts of which proceed
likewise along with the ureters to the cloaca. The deciduous
corpora Wolffiana, composed of simple tortuous follicles pro-
ceeding transversely from their common marginal duct, and

EXCRETING ORGANS. 635

extending along each side -of the vertebral column, precede
much the development of the kidneys, and disappear before
the bird escapes from the ovum : they are more connected
with the evolution of the genital glands, the testes and
ovaria, than of the urinary organs, in the classes where they
are observed. As in other glands, the tubuli of these deci-
duous bodies appear at first as pedunculated peripheral
vesicles, which become gradually elongated and constricted
to form straight narrow tubes, and, at length, long narrow
tortuous and interwoven tubuli extending to the interior
edge of the organ from the exterior marginal duct. Their
structure resembles that of the kidneys of amphibia, but
they are not organically connected with the urinary tubuli,
and appear to assist in the development of the genital
glands.

The urinary organs of mammalia generally present a more
compact and simple external form, and a more extensive
secreting surface by the minute divisions and the compact
arrangements of their tubuli, than in lower vertebrata ; they
eliminate a larger proportion of the aqueous constituents of
the blood, and they are always provided with a distinct
urinary bladder. The lobed condition of the kidneys, so
constant in lower classes, is still, however, observed as a
normal adult character in many of the inferior mammiferous
tribes, as in the cetacea, many ruminating and pachyderma-
tous herbivora, the slow-moving plantigrade carnivorous
quadrupeds, and in the amphibious mammalia and the otter.
In the higher tribes, the kidneys pass early from the primi-
tive lobulated condition to a more concentrated form, by
the union of the lobes into a single compact organ, which
generally presents internally a distinct cortical and medullary
portion, resulting from the straight and parallel course of the
minute tubuli in the central part, and their tortuous inter-
woven course in the exterior portion. These two portions
are alike perceived in the separate renal lobes of the human
foetus, and in the component lobes of the adult lobulated
kidneys in lower mammalia. The right kidney is generally
more advanced in the trunk than the left, and impresses the
liver ; they are covered only on the ventral surface with peri-
toneum ; they present a depressed and rounded form more
or less elongated in different species, and they are largest

636 EXCRETING ORGANS.

and most divided into lobes in the aquatic and the larger
terrestrial forms of this class. In several of the cetacea,
there are more than two hundred deeply isolated lobes in a
single kidney, but in the monotrema, they are united into a
simple compact organ ; in the lobulated kidneys, the number
of papillae and infundibula corresponds with the number of
lobes, but in the compact forms of the organ, the number of
these conical tufts of tubuli is often reduced to a single
papilla, and the entire pelvis to a single calyx. The relative
development of the cortical and medullary portions, varies as
much as the outward form of the organ in different mam-
malia. The structure and relations of the straight and
tortuous tubuli uriniferi of the simple and lobulated kidneys
of mammalia and lower vertebrata, and the connections of
the small round vascular corpuscules with the arterial
branches, were already investigated and described by Mal-
pighi.

The kidneys of mammalia, as of lower vertebrata, are
preceded in the embryo by the corpora Wolffiana, composed
each of elegant series of simple transverse tubuli opening
into a common longitudinal duct, which extends along the
outer margin of these deciduous glands and terminates in
the cloacal end of the intestine ; these bodies are interposed
between the situations of the renal and genital glands, they
are most developed long before the middle of foetal life, and
they have entirely disappeared before birth. The kidneys
appear at first as consisting each of a congeries of minute
tortuous follicles radiating to the periphery of a small round
soft gelatinous blastema, and terminating around the ex-
terior surface of this primitive mass in minute closed pyri-
form sacs, like the vesicular terminations of the bronchial
tubes of the lungs or of the early tubuli of most other glands.
The peripheral terminal vesicles diminish in size and disap-
pear, as the tubuli become lengthened, tortuous, and inter-
woven, and there is no trace of distinction between cortical
and medullary portions in the interior, nor of lobes on the
surface. The tubuli in the central part of the kidney become,
at length, more straight and parallel, and grouped into conical
fasciculi, which compose the medullary portion, while the
tortuous interwoven peripheral parts of the tubuli form the
cortical portion of the organ. These conical groups of

EXCRETING ORGANS. 637

straight converging tubuli meet at their open extremities,
and terminate, as shown by Malpighi, in prominent papillae,
which are surrounded by calyces opening generally, by in-
fundibula, into a common wider receptacle, or pelvis, from
which the ureter commences. The tubuli often divide
dichotomously, both in the medullary and the cortical part
of the kidney, without changing their diameter. The de-
velopment of the ureters in the embryo, begins from their
renal ends and proceeds downwards, being at first solid,
then tubular, then opening into the bladder, which, in some
abnormal cases, they do not reach. The urinary bladder is
developed from the cloacal end of the intestine, as the pe-
duncle of the allantois and the urachus, but its early commu-
nication with the alimentary canal is at length entirely cut
off in most mammalia, by the separation of the rectal portion
of the intestine above from the uro-genital canal below. In
the monotrema, however, they continue to communicate, as
in reptiles, through the whole of life.

Many internal secreting glands already considered, may
likewise be viewed as partly internal excretory organs. The
internal tubuli and cells of the lungs, by the carbonic acid
and aqueous part of the blood which they so largely eliminate
from the system, may be regarded as presenting an extended
internal excretory surface ; and from the composition and
functions of the bile, the tubuli of the liver may be viewed
nearly in the same light. The various kinds of odorous
and poison-glands at either end of the alimentary canal, and
even the muciparous glands throughout its entire course,
have partly an excretory function. The surface of all mucous
membranes lining internal ducts and cavities which communi-
cate externally, and serous membranes lining closed cavities,
even the interior lining of blood-vessels, by constantly excret-
ing and detaching globules, cytoblasts, or scales of epithelium,
may also be considered as exerting an excretory function on
the circulating fluids of the body.

638 EXCRETING ORGANS.

SECOND SECTION.

External Organs of Excretion.

As the larger and more complex internal excretory organs
are developed from the common mucous lining of the diges-
tive canal of animals, the smaller and more numerous exter-
nal forms of these organs are developed from the cutaneous
covering of the body. The naked surface of the skin in most
of the lowest animals, being both respiratory and secerning,
may likewise be regarded as a general excretory surface, and
the various forms of extravascular scales, shells, and other epi-
dermic materials, poured out as nuclei or in a fluid state from
its capillaries, and growing or concreting into granules, cells, or
cytoblasts, have also a close analogy to excretions. The sub-
cutaneous muciparous glands so large and complex in fishes,
and so numerously spread over the naked surface of am-
phibia, and various other cutaneous glands of higher animals,
eliminating materials little subservient to individual nutrition
or to the race, are partly excretory in their function. The
cutaneous glands most special and distinct in their excretory
function, and the product of which is most analogous to the
urine of the kidneys, and the carbonic acid and halitus
expired from the lungs, are the small, simple, convoluted,
sudoriferous follicles, or sweat-glands, perforating the epi-
dermic layers, and so numerously spread over the entire
surface of the body in the warm-blooded vertebrata. The
innumerable minute ramified sebaceous glands, which pour
their oily secretion, by distinct ducts, into the wider cuta-
neous follicles for the hairs, to lubricate and protect the skin
and its epidermic developments, may likewise be considered
as partly cutaneous emunctories, eliminating the oleagenous
materials of the blood ; so that these external forms of ex-
cretory organs become almost essential constituents of the
cutaneous or tegumentary parts of animals.

TEGUMKXTARY ORGANS. 639

CHAPTER EIGHTH.

TEGUMENTARY ORGANS.

THE animal body being an aggregate of numerous compli-
cated and delicate apparatus, nicely adjusted to the various
mechanical and chemical functions necessary for the sup-
port of life, is always protected externally from the action
of the surrounding elements and from accidental injuries,
by some common investing tegumentary organs. These ex-
ternal investments consist generally of a compact reticulate
fibrous, elastic, highly sensitive and vascular cutis, corium,
or true skin, and a more superficial, extravascular, insensible,
scaly cuticula, epidermis, or scarf-skin ; and to these are- often
superadded various forms of horny scales, plates, spines, hairs,
feathers, or other accumulated epidermic exudations from the
vascular secreting surface of the true skin. The cutis or true
skin of the higher classes of animals, developed, like the
osseous, the muscular, and the nervous systems, from the
exterior or serous layer of the germinal membrane of the
ovum, continues in the adult as the most exterior of the
sensitive and vascular tissues of the body. It is not only
the seat of the sense of touch, by the innumerable sensitive
vascular and erectile papillae developed over its surface, but
likewise of various secretions from myriads of minute glands
imbedded in its substance, and whose ducts traverse in a
straight or tortuous direction its fibrous tissue. These ducts
open on the surface of the epidermis, as seen in the annexed
views (Fig. 146.) from Gurlt, of the simple piliferous follicles
(146. A. C.f.f.) and the more complex sebaceous glands (146
A. h. C. e.) and sudoriferous glands (146. A. d. C. b. b.), com-
municating with the exterior surface of the skin (146. A. B.
C. a. a. «.). Besides the piliferous follicles, the sudoriferous
and oil-glands, and the numerous capillary blood-vessels,
nerves, and lymphatics which every where permeate the
fibrous texture of the skin, it has been considered as the seat

640

TEGUMENTARY ORGANS.

of a distinct chromatogenous apparatus for secreting the
carbonaceous colouring matter or pigment-cells of the

FIG. 146.

-d

epidermic scales, and of distinct blennogenous glands for
secreting the constituent matter or cytoblasts of the epider-
mis itself.

Resting immediately on the subcutaneous cellular and
adipose substances (146. A. c. B. /.) is the inferior fibrous
reticulate layer (146. A. b. B. e.) of the cutis, of very variable
thickness in different animals, permeated by the subjacent
cellular substance, and in which are generally imbedded the
minute oil-glands (146. A. h.) of the piliferous follicles (146.
A./.) which contain the hairs (146. A. g.). The exterior
papillated layer (146. B. c.) of the cutis is more thin, compact

TEGUMENTAHY ORGANS. 641

and homogeneous, covered with sensitive papillae, traversed
by the piliferous follicles, the hairs, and the long tortuous
ducts of the sweat-glands (146. B. h.), and is in contact with
the rete mucosum (146. B. d.) of Malpighi, or the soft infe-
rior layer of epidermis. The prominent conical sensitive
papillae of the surface of the skin are most developed on the
naked palmar and plantar surfaces of the hands and feet in
the soft-footed animals, as seen on the palm of the human
hand (146. B. c.) ; and on many parts of the skin they are
not perceptible, as on the human scalp (146. A. a.).

The sudoriferous glands have been detected by Gurlt in all
parts of the surface of the body, placed generally deeper than
the piliferous follicles, and imbedded in the subcutaneous
cellular substance. They are large and obvious to the naked
eye, beneath the soft skin of the genital region of the horse
(146. G. h.)9 and nearly as large under the plantar surface of
the dog's foot, and they are of smaller size in other parts of
the hairy skin of the horse (146. F. e.), and in the skin of
the hog (146. C. b.). They are small and round in the palm
of the human hand (146. B. h.), more elongated in the human
scalp (146. A. d.)y minute, simple and uniform under the skin
of the ox (146. E, c.), and under the hairy skin of the dog,
and they are very large and equal under the thin soft skin of
the sheep (146. D.y. g.}. They consist each of a single
transparent long follicle, more or less convoluted into a mass
at its closed extremity, like the tubuli of the testis, and their
single tortuous duct, lined with epidermic cytoblasts or epi-
thelium, opens by a dilated conical orifice on the surface of
the skin (346. A. e. E. d.), or continues its spiral windings
(146. B. g.} through the strata of thickened cuticle (146.
B. a. b.).

The small elongated racemose clusters of minute transpa-
rent white follicles, composing the conglomerate sebaceous
glands (146. A. h. C. e.), are situate more superficially in the
texture of the skin, than the piliferous follicles (146. A.
C././.) or tfie sudoriferous glands (146. A. d. C. £.), which
extend more deeply into the subjacent cellular substance.
The sebaceous glands and the piliferous follicles occur over
most parts of the body, excepting on the naked palmar
and plantar surfaces of the hands and feet in man and car-
nivora, where neither are observed. In some naked parts of

PART VII. T T

642 TEGUMENTARY ORGANS.

the skin the sebaceous glands abound without piliferous fol-
licles, but the piliferous follicles, when present, are always
accompanied with one or more, generally with two, sebaceous
glands. The numerous small follicles composing each of
these conglomerate sebaceous glands, communicate 'generally
with a single duct, sometimes with several ducts, which open
directly into the piliferous follicles, where they are present,
or on the surface of the skin in many hairless parts ; and
these glands vary in magnitude generally according to the
size of the hairs they accompany, but they are very minute
in the hog (146. C. e.) which has large hairs (146. C. d.).

The piliferous follicles (146. A. C././.) are appropriated to
the development of the hairs, and to the reception of the
oily secretion of the sebaceous glands. They are elongated
simple sacs, widest at their deeper closed extremity, and nar-
rowest at their orifice, where they embrace closely the con-
tained hair. They penetrate vertically through the skin to
the subcutaneous cellular substance, and they correspond in
size and form with the contained hair. They are prolonga-
tions of the vascular secreting surface of the cutis, and they
receive the secretions of the sebaceous glands, which can be
pressed out from their orifice. Like all the ducts of cuta-
neous glands, they have a distinct lining of epithelium, which
can be drawn out entire, continuous with the epidermis, from
the macerated skin of the foetus, and coloured portions of
the cuticle can often be distinctly traced into their cavity.
The epidermic linings of these various small cutaneous
ducts, appear as so many minute connecting fibres, when the
cuticle is being gradually drawn off from the surface of the
cutis.

The most exterior continuous tegumentary layer of animals,
as of other organized bodies, is the insensible extra vascular
epidermis, poured out as granular nuclei in a fluid medium, from
the reticulate, vascular, sensitive surface of the cutis, or secreted
by its capillaries. Like most internal organized tissues, the
exterior epidermic covering originates from minute cells, or cy-
toblasts, which possess, like entozoa, an independent means of
growth, and undergo various changes in the course of their de-
velopment ; and all the different cuticular appendages, as hairs,
spines, nails, hoofs, horns, feathers, and scales, are merely
aggregations of the same epidermic cells. The epidermic
nuclei when first formed, exhibit internally a granular struc-

TEGUMENTARY ORGANS. 643

ture, and are contained in a soft gelatinous connecting sub-
stance, a cytoblastema, which enables them to grow, and to de-
tach concentric layers or enveloping cells from their surface.
The exterior cells grow more rapidly than the contained nuclei
which first developed them, and there are commonly minuter
pigment-cells, like internal parasites, free in the contained fluid
of these cytoblasts. The soft, round, loosely aggregated, newly
produced, growing cytoblasts, forming the lower strata of epi-
dermic cells, compose the rete mucosum of Malpighi, where the
various hues of the contained pigment-cells, in all deeply- co-
loured animals, are most fresh and intense, and where the cu-
ticular cells are still most agglutinated to the surface of the
cutis. As the epidermic cells, by their own independent vitality,
enlarge, and thicken in their parietes, the connecting gelatinous
matter, or cytoblastema, disappears, they become contiguous,
compressed, and polyhedral, and the nuclei are still perceptible
towards the centre of the thus flattened cells, attached to their
interior surface. In the outer strata of the epidermis, the cells
are thin, empty, flattened disks, bleached, deprived of their
colouring matter, compressed into a continuous layer, and
they at length fall from the surface as dried, isolated scales,
with their opposite parietes coherent, and with single persist-
ent nuclei. The black pigment-cells of the cuticle of the
tadpole, undergo remarkable changes of form, like a poly-
gastric proteus, and they contain numerous, minute, parasitic,
spontaneously moving cells, in their interior.

The epithelial cytoblasts of internal parts present similar
phenomena of growth, development, and metamorphosis, to
those of the exterior epidermis ; they are seen on the lining
membrane of the heart, in veins, on the chorion, the amnion,
and on all mucous and serous surfaces ; their form is some-
times lamellar, sometimes conical or cylindrical, and they
often exhibit distinct vibratile cilia at their free extremity on
mucous membranes. Cytoblasts abound in all secretions,
they constitute the first rudiment of the ovum, and the
globules of blood, milk, and other animal fluids ; they give
origin to capillary vessels, to cartilage, to the fibres of the lens,
of the teeth, of cellular tissue, of nerves, muscles, and most
other tissues of animal bodies. The primitive germinative
nuclei often develope two or more concentric enveloping cells
around each, these concentric spheres often coalesce and

T T 2

6-11 TEGUMENTARY ORGANS,

unite to thicken the parietes of the general cell, two or more
nuclei are often found within the same cell, and the nuclei
generally retrograde in their development, or entirely dis-
appear, when the cells they produce have arrived at their
maturity.

The successive strata of epidermic cytoblasts are most
accumulated, and retained, in a condensed form, on parts of
the skin most exposed to pressure and friction, as on the
palmar and plantar surfaces of the extremities, and on the
whole surface of thick-skinned naked animals, as rhinoce-
roces, hippopotami, manati, and other pachy derma and ceta-
cea. The difference of colours in the contained parasitic
pigment- cells of the epidermic cytoblasts, which are most
vivid and most lively in the soft, loose cytoblasts of the rete
mucosum, gives rise to the varied hues of all the tegumen-
tary parts of animals. In the interior even of these parasitic
pigment- cells, are sometimes seen numerous other minute
cells in active movement. The colour of the pigment-cells
often varies in different parts of the skin, giving rise to cor-
responding differences in the colour of the hairs, spines, and
other epidermic developments ; their excess produces the
intense colour of the rete mucosum of the negro, and other
deeply-coloured animals; their deficiency produces the various
tegumentary peculiarities of albinos ; and the ephemeral
existence of these coloured parasites, causes the outer strata
of epidermis to be shed colourless, from the most deeply
coloured skins of animals, as salamanders, serpents, and
negros. The epidermis is already a thick layer on the pal-
mar and plantar surfaces of the extremities in the early con-
dition of the embryo, and the coloured parts of the integu-
ments of quadrupeds are distinctly marked at an early period
of the foetus in utero.

The cytoblasts of the epithelium, at the exterior open-
ings of mucous cavities, have mostly the same flattened form
and stratified arrangement as in epidermis, as seen on the
interior of the nostrils, the lips, the mouth, the tympanic
cavity and the mastoid cells, and on the surface of the con-
junctiva and cornea, where they were observed and described
by Leuwenhoek, as forming a hundred strata of superim-
posed scales ; but in most other parts of the mucous surfaces
they present a conical or cylindrical form, are compactly

TEGUMENTAHY ORGANS. G45

arranged with their long axes vertical to the surface on which
they rest, and have often distinct vibratile cilia at their broad
free end. The vibratile cilia of the epithelial cytoblasts, are
larger and more extensively distributed in the foetus than in
the adult, as shown by Henle on the human epiglottis ; and
they are continued vibratile on the epithelium through the
larynx, trachea, and the minutest ramifications of the bronchi,
and the cells of the lungs, where the ciliated cytoblasts have
the usual cylindrical form.

The epithelial cytoblasts continue cylindrical in the
ducts of most glands, in the stomach, and along the whole
intestine to the anus, where the epithelium abruptly
unites with the flat-celled exterior epidermis, and they
have the same cylindrical form in the interior of most of
the uro-genital passages. In the female, however, the flat-
celled epithelium lines the entire vagina, and the cylin-
drical cytoblasts with vibratile cilia, perceptible in the adult
state, begin about the middle of the cervix uteri, and con-
tinue throughout the body of the uterus and along the
Falopian tubes and their fimbriated terminations. The
epithelium of serous membranes consists of flat cells, with a
distinct central nucleus in each, and arranged in a tesselated
form, as seen on the peritoneum, pleura, pericardium, tunica
vaginalis testis, synovial membranes, and membranes of the
brain. Vibratile cilia are more rarely observed 011 the epi-
thelial cytoblasts of serous membranes, and exist on the
lining membrane of the ventricles of the brain, and on the
exterior peritoneal surface of the fimbriated ends of the Fal-
lopian tubes. The epithelial cells detached from the parietes
and ducts of secerning tubuli, and from other mucous sur-
faces, are observed isolated and mixed, like corpuscles, with
the various secretions and excretions, as in mucus, saliva,
lachrymal fluid, bile, and urine, and they appear to form the
nuclei of morbid irritation, and the corpuscles of morbid
secretions, in various pathological states.

Hairs, bristles, and spines are merely epidermic appen-
dages, developed, like teeth, in highly vascular cutaneous sacs
or follicles ; they are formed by the successive aggregations of
cytoblasts, and are gradually protruded from the piliferous
follicles by the growth and elongation of their constituent
cytoblasts, and by the addition of new layers to their ex-

646 TEGUMENTARY ORGANS.

panded, soft and hollow base, the apex and shaft of the hair,
or spine, being formed before the bulb, like the crown of the
tooth before its fang. They are continuous, at their base, with
the epidermis lining the enveloping follicles ; they are com-
posed of the same cells or cytoblasts, which are commonly
arranged in rectilineal series ; and they generally present a
more dense exterior laminated cortical part, inclosing a loose
granular medullary portion. The component cytoblasts are
more round and loose at the soft, dilated base of the hairs,
as in the rete mucosum ; and they are compressed, elongated,
and more compactly united, in the denser shaft of the hairs.
By the rectilineal arrangement of the component cytoblasts,
the hairs possess a fibrous structure, and greater elasticity
and strength, they are more permeable to the oily secretion
of the sebaceous follicles, and they exhibit a filamentous de-
composition, often seen in the spontaneous longitudinal
fissuring of the human hairs. The soft dilated bulbs of the
hairs, beneath the cutis, are alone developed, and are con-
fined to their follicles, in the smooth -skinned piscivorous
cetacea. But in the rough-skinned herbivorous species of
these animals, the shafts of the hairs are partly protruded
from their follicles, like short, hard spines, and are especially
developed on the upper lip, as they are also in amphibious
carnivora. The almost horny epidermic integument of the
herbivorous cetacea, has long been compared to the con-
tinuous horny hoofs covering the piliferous follicles and
their contained hair-bulbs, on the feet of solidungula and
ruminantia.

Hairs are successively reproduced in the same follicles, when
shed periodically in mammalia, or when forcibly torn from
their cavities, like the teeth of crocodiles in their alveoli. The
hairs of mammalia grow and enlarge in their follicles, and are
gradually protruded through their constricted apertures, by
the addition of successive layers of epidermic cytoblasts,
lineally aggregated, to the hollow interior and base of their
soft, white, expanded bulb, and by the enlargement of the
individual cytoblasts. The constituent cells are connected
together, as in other epidermic parts, by the remains of
the soft adhesive cytoblastema, which originally afforded
them nutriment. By the great elongation and compres-
sion of the cells as they proceed oiJtwards from the bulb,

TEGUMENTARY ORGANS. (J47

the shaft of the hair becomes much more narrow than the
base from which it originates, and the fibrous structure is
most apparent on the peripheral or cortical portion of
the shaft. The fibrous composition of hair was described
and figured by Leuwenhoek. The nuclei of the cytoblasts
almost disappear, in the elongated cells forming, by their
lineal aggregation, the ultimate filaments of hair; and the
artificial separation of the constituent filaments, is ren-
dered much more easy, by macerating the hairs in dilute
muriatic acid, when they are seen to be disposed in a longi-
tudinal, rectilineal and parallel order, from the bulb to the
point of each hair. The filamentous structure and fibrous
decomposition of hairs were familiar also to Hooke in 1667.
The diameter of the ultimate fibrils of a hair is about the
two thousandth of a line, and a human hair of one tenth of
a line in thickness, has about two hundred and fifty fibrils in
its mere diameter, and about fifty thousand in its entire
calibre : so that these ultimate fibrils are finer than those of
almost any other known tissue, from the great elongation
and narrowing of their constituent cells, as they are drawn
out into the shaft of the hair during growth ; and hence the
expanded bulb of the hair, where the cells are yet spherical
and soft.

In the larger hairs, bristles, and spines there is generally
a more compact, thin, dense cortical part, inclosing a loose
cellular medullary portion, not perceptible in the human
hairs ; so that they more resemble the shafts of feathers des-
titute of lateral barbs. The highly vascular and sensitive
hair-pulp in the long whiskers of carnivora, extends through
the bulb into the shaft, and increases the sensibility of these
parts, while it adds to their strength of attachment, and to
their surface of increment. The nails and claws of mam-
malia and other vertebrata are composed of the same epider-
mic cells, %nd grow in reduplications of the skin forming
compressed, curved follicles, like the cylindrical hairs and
spines in their circular cavities. The successive strata of
polygonal cells, which are most easily separable in the embryo
and foetus, are added, in lineal aggregations, to their covered
base, and their compact, dense, free portion is gradually pro-
truded from the compressed enveloping follicle. The con-
stituent cytoblasts with their nuclei and fluid contents, are
most distinct at the soft, white base, and at the inferior sur-

648 TEGUMENTARY ORGANS.

face of the nails, and become compressed, flattened, and
compactly agglutinated together on the upper surface and the
protruded part, where the stratified arrangement is most
apparent, and where the nuclei and contents of the cells have
mostly disappeared. Layers of cells are secreted and added
along the whole inferior attached, concave, lamellated surface,
to compensate for the flattening and thinning of the upper
convex strata of cells, first added from behind and from be-
neath, and thus to preserve the equal thickness and strength
of the nail at its free, exposed part. The nails b.eing thus
only the thickened epidermis of the parts which support
them, they adhere in the same manner as epidermis, to the
subjacent sensitive and vascular laminated surface of the
cutis, by means of the soft, homogeneous, adhesive cytoblas-
tema which envelopes, nourishes, and unites together the
growing component cells.

The anterior vertical portion of the hoofs of ruminantia
and solidungula consists merely of a large curved nail, and
the inferior horizontal portion, which is partially attached to
the former along its anterior thick margin, is only the usual
thickened epidermis, covering the lower surface of the toes.
The vertical curved portion of the hoof, analogous to the
human nail, embraces a large part of the anterior and lateral
surface of the toe, is more deficient behind, and extends
downwards beyond the plain of the inferior basilar plate, so
as to defend the entire lower margin of the hoof, which is
most subjected to pressure and attrition. In the feet of
solidungula the entire anterior portion of the hoof is formed
as a single investing independent nail, and extends beyond
the inferior thickened epidermic plantar portion. The sharp,
dense, compressed, curved claws of feline carnivora, are nails
which almost invest the terminal phalanges of the toes, and
have their base and its containing follicle supported by an
osseous sheath; they are kept sharp at the point by the
periodical shedding of their terminal laminee. Even the per-
manent vaginiform horns of antilopes and other ruminantia,
are formed and developed like conical nails around the
tuberosities of the frontal bone, receiving their means of
increment in their interior cavity and around their follicular
base, like the tusk of an elephant, or the bill of a bird, a
tortoise, or a cephalopod, or the conical shell of a gasteropod.
And the solid nasal or frontal horn of the rhinoceros is

TEGUMENTARY ORGANS.

developed from the subjacent periostium, like a large hair
from its follicle, or like the horny coverings of the papillae
on the plantar surface of the feet in carnivora ; and it exhi-
bits the same fibrous structure and filamentous mode of decay,
as in other epidermic parts composed of recti-lineal aggre-
gations of cytoblasts. In these various forms of epidermic
developments, the polyhedral form of the compressed cells,
their nuclei and fluid contents, and their lineal arrangements,
are most apparent in their primitive soft condition in the
foetus, or in the recently formed portions in the adult ; and in
their subsequent metamorphoses their internal fluid and nu-
clei disappear, the empty cells become elongated or flattened,
with their interior parietes contiguous, they are aggluti-
nated into laminae by the remains of the cytoblastema, and
their conformable stratified superposition is- rendered more
distinct.

The feathers of birds, like the • hairs of mammalia, are
epidermic developments contained in cutaneous follicles; they
are provided with their vascular secreting pulp, their hollow
bulbous base of increment, and their solid exposed shaft ; and
like them, they are composed of extravascular organized
independent cells, or cytoblasts, which were already figured
and described by Hooke, and by Leuwenhoek, as composing
the entire microscopic structure of the feather, Like other
epidermic structures, feathers are first formed and most
developed on those parts where they are first and most
required, and their horny composition and tubular structure
are those best adapted to combine strength with lightness.
The strong diaphanous tubular empty quill (147-A. o.) in
the adult bird, is deeply imbedded in the cutaneous pen-
niferous follicle, as the point of attachment and of nutriment
of the feather, and contains only a few dried remains of the
primitive secreting pulp-cells. The tapering light elastic
conical shaft (147. A../, b.) is occupied internally with white
dried aeriferous cytoblasts, which were described before the
time of Leuwenhoek, and gives a firm support to the two un-
equal sides of the vane (14?. A. c. d.). The vane is composed of
barbs (147. A. rf.) or laminae placed vertically to afford the
greatest resistance in flight, closely applied to each other,
continued from the sides of the shaft, and connected toge-
ther by barbules developed from each side of their dorsal or

TEGUMENTARY ORGANS.

exterior margin. The barbules again develope, from their
margins, minute curved, hooked filaments, or barbulinae, to
complete this delicate structure for hooking together and
uniting the barbs into a continuous membrane, as shown by
Hooke, who carefully investigated, described, and figured this
complex mechanism in 1667, and accurately compared each
barbule, with its barbulinse, to the structure of an entire
feather. In most feathers the proximal part of the vane
(147- A. d.} has its barbs and barbules long, loose and floating,
so as to form a compact downy mantle next the skin of the
bird, to retain the high temperature of the body. In the rest
of the vane the barbs are more firm, straight, regular and
united, to assist in flight, or to protect the body.

The parts of the feather, as shown by Dutrochet, Blainville,
and F. Cuvier, are at first formed within a thick closed epider-

TEGUMENTARY ORGANS. 651

mic capsule (147. B.) embracing in its axis two concentric
striated membranes, (147. B. b. d.), and a highly vascular, se-
creting, formative pulp (147. B. d. e.), and contained in a deep
penniferous follicle. This exterior epidermic capsule, perfo-
rated below by the vessels and nerves of the organized pulp,
elongates, opens above, and allows the newly formed parts of
the feather to escape from the opening of the cutaneous follicle.
This general extra- vascular enveloping capsule, (147- C. c.),
is entirely composed of strata of large flattened cytoblasts,
which grow by their independent vitality, are united by their
cytoblastema, and give a necessary brittleness to the texture
of this deciduous membrane. On cutting open the exterior
capsule of the young feather, the two more delicate tonics
are seen investing the pulp, and connected together by nu-
merous septa ; the soft, newly formed barbs, (147. B. c. c.)
moulded between these septa, are thus found folded around
the central organized matrix, being developed in a polythala-
mous cavity filled with the granular secretion of the vas-
cular pulp. The pulp developes a series of superimposed
conical capsules, and traverses their axis in a continuous
canal, as seen in the annexed figures from F. Cuvier (147. E.
F. G.). The dense tubular elastic quill is formed by the
meeting of the edges of the exterior horny dorsal lamina of
the shaft, after the completion and convergence of the two
sides of the vane ; and an exterior opening, or upper um-
bilicus, is left at this point for the admission of air to the
interior and cells of the quill and the shaft. The membranous
cells (147. K. L.), disengaged from the distal extremity of
the organized pulp, and occupying at first the cylindrical
cavity of the folded barbs, are successively detached, ex-
posed, and lost by the unfolding of the barbs, and the rest
are confined and retained, dried, and collapsed, within the
closed tubular quill, after the shaft is completed.

The large polyhedral pith- cells of the growing shaft con-
tain, at first, a fluid substance ; they are provided each with a
distinct nucleus adhering to its inside, and within the nuclei
are seen one or two comparatively large nucleoli ; the cells
are easily separable from each other ; they have firm exterior
parietes, and in the adult state, like the few large ceUs of the
quill, they contain only air, and have nearly lost all traces of
their nuclei. As the internal constituent cytoblasts of the shaft-

652 TEGUMENTARY ORGANS.

pith are successively derived from around the apex of the con-
tained central organized pulp, they are most developed towards
the outer dorsal convex part of the shaft, and are smallest near
the central cavity, which is indicated only by an inferior longi-
tudinal groove in the adult expanded feather. More nearly
in contact with the formative matrix, indeed, are found mere
granular nuclei, contained in a fluid cytoblastema ; and these
organized, though extravascular, independent nuclei, pass
through the ordinary phases of development and growth,
seen in other epidermic and epithelial cytoblasts. These
epidermic cells composing the white friable corky pith of the
shaft, were accurately described by Hooke in 1667, and
Leuwenhoek described and figured the cytoblasts, or glo-
bules, composing the barbs.

The formation of a distinct, thin, dense, interior epidermic
layer, in the concavity of the growing shaft, and around the
exterior surface of the secreting matrix (147- H. I. a. b.)
completes the inferior concave surface of this part of the
feather, and prepares for its gradual protrusion, with the per-
fected and unfolding barbs continuous with its sides. On
opening the. organized pulp (147. D. b. b.), innumerable ves-
sels, turgid with red blood, are seen forming a continuous net-
work over every part of its interior parietes, and their trunks
are observed entering the convex conical part of its base where
a terminal opening or inferior umbilicus is left in the adult
quill (147. A. e.). The outer strong elastic layer forming the
dorsal fibrous covering of the shaft, between the outer ends of
the septa, or barbiferous cells, is early developed, and origi-
nates from cytoblasts, which undergo changes very similar to
those which give origin to the minute fibres of cellular tissue.
From their primitive rounded form, these cells are observed
to elongate, to become flattened, and gradually to subdivide
each into numerous longitudinal fibres ; their nuclei disap-
pear, their parietes become absorbed or fissured, and they at
length constitute the compact horny fibrous covering of the
dorsum of the shaft, and the entire parietes of the quill,
which is merely a cylindrical continuation of that portion of
the feather. The inferior grooved surface of the shaft is
covered by a similar deposition of granular independent
animated cells, with their nutrient fluid cytoblastema between
the lower ends of the grooved barbiferous septa, or compli-

TEGUMENTARY ORGANS.

cated cavities in which the apparatus of the vane is moulded.
On examining even the minutest parts of the barbules of
feathers, the constituent elongated compressed angular cyto-
blasts, compactly and symmetrically arranged, and provided
with persistent central nuclei, are distinctly perceptible. A
second shaft, furnished with all the apparatus of the vane, is
generally more or less developed from the superior umbilicus or
distal opening of the quill, and this supplementary shaft some-
times, as in the emeu, equals in length that of the primary feather.
The rudiment even of a third shaft is sometimes developed
from the feather, and the entire plumage of a bird is some-
times renewed once or twice in a single season. But not-
withstanding the endless diversity of form and the intricate
structure of these organs, and the remarkable changes they
undergo during their development, growth, and moulting,
they present only a more complex form of the ordinary insen-
sible, extravascular, epidermic tissue, forming the exterior
integument of most organized bodies.

In the simple organizations of the lowest animals, the dif-
ference is less marked, between the exterior cutaneous and
the interior mucous coats, and between the epidermic and
the epithelial developments they form on their surface; and
as most of them are inhabitants of an aquatic medium, their
epidermic covering generally retains the soft condition of a
rete mucosum, or of a mucous deposit, as seen in the naked
forms of radiated, helminthoid, and molluscous animals. It
is shed in flocculi from poriphera, and in larger pellicles from
the surface of many zoophytes, as lobularia, and its con-
stituent cytoblasts were observed by Gade in acalepha. In
many vaginated forms of polygastric and polypipherous ani-
mals, it composes a firm, elastic, often articulated, almost
horny sheath, over the entire surface of the true skin ; and
in the entomoid and testaceous animals, it becomes consoli-
dated by the addition of various earthy materials, to compose
their enveloping extravascular skeletons. Its granular nuclei
are constantly pouring from the vascular secreting surface of
the cutis, its condensed accumulations adhere to the skin by
means of the cytoblastema, and these accumulated epidermic
masses are periodically thrown off from the body in the
articulata, but are consolidated, collected, and permanently
retained in the testaceous mollusca and radiata. The resplen-

654 TEGUMENTARY ORGANS.

dent hairs of halithea, the setae of armelides, and the agglu-
tinating matter of their tubes, the down and hairs of larvse,
and those common on adult insects, arachnida, and Crustacea,
the byssus of coiichifera, the horny opercula of gasteropods,
the horny mandibles of cephalopods, the lingual spines of
many mollusca, the gastric teeth of aplysia, the spines of the
gizzard of insects, the gastric plates of bulla, and the animal
matter of all testaceous coverings, may be considered as parts
of the same epidermic or epithelial tissue, having the same
extravascular and cytoblastic character, and the same or-
ganization and independent vitality.

The tegumentary organs of the vertebrata are closely re-
lated to the temperature of the body, and to the density of
the surrounding medium, those of the warm-blooded classes
being slow conductors of caloric, in order to preserve the
high temperature of their body, and those of the cold-blooded
being indifferent in their conducting power, as they are also
in most in vertebrata. The sensitive vascular skin of fishes,
is thick, soft, gelatinous, and closely connected by tendinous
intersections with the subjacent muscular system. The
cuticle, as in the naked aquatic mollusca, forms a thin, soft
layer ; and by its periodical shedding, the lively colours of the
inferior loose strata of cytoblasts, or rete mucosum, are
allowed to shine more distinctly through the pellucid scales,
and this increased brilliancy of colour is most marked at the
spawning season. The imbricated scales of fishes, which are
wanting in the cyclostome and very minute in the plagios-
tome species, but generally cover their surface, are consoli-
dated by phosphate of lime, detected also in the hairs of
mammalia ; and they grow, like the human nails, or the wing
scales of lepidopterous insects, by successive layers added
by the squamiferous follicles of the cutis, in which they are
fixed.

From the soft, thin, and granular condition of the newly
formed epidermic and epithelial coverings of membranes, the
secretion of glandular tubuli, and the respiration of pul-
monary ceils, or branchial laminae, are easily effected through
these coverings. And from the necessity for free respiration
by the entire cutaneous surface of the body in the amphibia,
their highly sensitive and vascular cutis is destitute of scales ;
it is covered only with a thin, soft epidermis, which is cast

TEGUMENTARY ORGANS. 655

rapidly and frequently, that of the frog and triton being
apparently shed every month. Their copious exterior secre-
tions, perhaps, also demand a higher cutaneous oxygenation
and a thinner epidermic covering. The epidermis of the
triton is shed in an entire piece, as in serpents. On the
surface of the tough, thick, fibrous, papillated cutis of ophi-
dian and saurian reptiles, the soft rete mucosum, composed
of newly-formed cytoblasts, generally presents the most in-
tensely and lively coloured pigment-cells, which fade or die
before they are shed with the concrete outer layer of epider-
mis. As the apparent scales and scuta are only elevated
papillae or tubercles of the vascular secreting cutis, some-
times partially imbricated, the epidermis passes continuously
over them, and is thus cast from the entire body without
perforations or scales, and even from the united transparent
eye-lids or conjunctiva of serpents, as from the compound
eyes of articulata. The tortoise-shells, or epidermic plates,
covering the osseous elements of the carapace and plastron
of chelonia, are permanent accumulations of cytoblasts,
formed in successive and increasing layers from the subjacent
vascular periosteum, like the nasal horns of the rhinoceros, or
the permanent vaginiform horns of ruminantia; and the
limits of the successive layers of growth, are here commonly
indicated by peripheral ridges on the exterior of the plates,
as on the shells of conchifera and of gasteropods.

The sparkling and resplendent surface of most fishes, ac-
cords with the liquid element and its pebbled bed ; the dull
and sombre surface of most amphibia and serpents, accords
with their concealed habitats; and the more lively colours
of many climbing ophidia and lacertine sauria, are adapted to
their arboreal life. The mutable colours of the cham3elion,
conceal it from its insect prey ; the dark rough surface of
crocodilian sauria, conceal them on the muddy banks of
rivers, or among the decayed trunks of fallen trees ; the dark
dull surface of most terrestrial chelonia corresponds with their
lurking and burrowing habits ; the lustre, transparency, and
mottled brown colours of marine turtles, pervading the whole
substance of their large, permanent, epidermic plates, resemble
those of the dark fuci, on which they rest and feed. The
parasitic pigment-cells of epidermic cytoblasts, are little de-
veloped amid the snows and darkness of arctic regions, where

656 TEGUMEXTARY ORGANS.

albino peculiarities are naturalized, as in the wild swan, the
snowy owl, the alpine hare, the arctic fox, the polar bear.
Dull and sombre hues best suit nocturnal animals, as moths
and owls, rats and mice, bats and lemurs ; and the darkest
colours conceal the inhabitants of burrows and subterranean
caves, as beetles, toads, and moles, and the huge inhabitants
of the dark abyss, as walruses, seals, and cetacea. The most
lively and varied colours, and the brightest metallic lustres,
are developed in the diurnal species of tropical climes, as in
parrots and cockatoos, humming birds, and birds of paradise ;
and the hues appear often to be regulated by those of the
accompanying vegetation. The metallic lustre, so rare in
mammalia, is splendid in the chrysochloris. The reddish-
brown fleece of lions and pumas, caracals and tigers, and
most feline inhabitants of the deserts, resembles the decayed
leaves, or the light of the setting sun, or the sandy plains on
which they lie in watch for their prey. So that the proper-
ties of these extravascular parts, have extensive relations
to the internal economy of animals, and to surrounding
nature.

The colours of the tegumentary parts of animals, depend-
ing upon living parasites in the body of the epidermic cells,
are most distinct in the plump condition of these in the rete
mucosum, and are alike obvious in the chick in ovo, on the
foetus in utero, in the developing feather yet concealed in its
thick sheath and deep cutaneous follicle, and in the hairs of
subcutaneous cysts, to which the chemical influence of light
has never penetrated. Indeed the entire structure, proper-
ties, and forms of the tegumentary parts of organized beings,
are regulated by laws as simple and uniform as those of the
most essential organs of vegetative life, and they are most
intimately connected with the living habits and the entire
history of the species.

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