MEMCAL SCHOOL
LIIBMAMT

Gift of
Richard E. Coonley

QUAIN'S

ELEMENTS OF ANATOMY

EDITED BY

EDWARD ALBERT SCHAFER, F.R.S.

PROFESSOR OF PHYSIOLOGY AND HISTOLOGY IN UNIVERSITY COLLEGE, LON'DON,

AND

GEORGE DANCER THANE,

PROFKSSOR OF ANATOMY IN UNIVERSITY COLLEGE, LONDON.

IN THREE VOLUMES.

VOL. III.— PART III.

ORGANS OF THE SENSES.
BY PROFESSOR SCHAFER.

ILLUSTRATED BY 178 ENGRAVINGS.

LONDON :
LONGMANS, GREEN, AND CO.

AND NEW YORK: 15 EAST 16th STREET.
1894.

LONDON :
BRADBURY, AGNRW, & CO. LD., PRINTERS, WHITEFRIARS.

CONTENTS OF PART III.

ORGANS OF THE SENSES.

THE EYE

THE EYELIDS AND CONJUNCTIVA

Eyelids .......

Meibomian Glands

Conjunctiva .

Vessels

Nerves .......

THE LACHRYMAL APPARATUS . . .
Lachrymal Gland .
Lachrymal Canals ... . .

Lachrymal Sac .

NasafDuct

THE GLOBE OF THE EYE

Sclerotic Coat . . . . .

Cornea .......

Membrane of Bowman

Membrane of Descemet .

Vessels and Nerves of Cornea . . .

Vascular Coat .

Choroid Coat

Ciliary Muscle .

li'is ........

Muscular Tissue of Iris .
• Vessels of Iris . . . . . .

Nerves of Vascular Coat

Retina .......

Retinal Layers .

Rods and Cones .

Mullerian Fibres .

Structure of Macula Lutea and Fovea

Centralis ......

Structure of Ora Serrata and Pars

Ciliaris ......

Vessels of Retina .
Interconnection of Retinal Elements
Vitreous Body . . . . . .

Suspensory Apparatus of Lens

Lens .......

Lens-Capsule .

Changes in Lens with Age . . .

Aqueous Humour and its Chamber

THE EAR

THE EXTKUNAL EAR .

Pinna .......

Ligaments ......

Muscles

Vessels ......

Nerves .......

External Auditory Canal

Vessels and Nerves . . . .

State in the Infant

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THE MIDDLE EAR OR TYMPANUM

Membrana Tympani ....

Eu&tachian Tube .....

Auditory Ossicles .....

Ligaments ......

Muscles ......

Movements ... . .

Lining Membrane . . . . .

Recesses .......

Vessels and Nerves ....
THE INTERNAL EAR OR LABYRINTH . .

Osseous Labyrinth ....

Vestibule . . . . .

Semicircular Canals ....

Cochlea . . . .

Membranous Labyrinth

Utricle

Saccule .......

Membranous Semicircular Canals . .

Branches of the Eighth Nerve

Vessels .......

Structure of Utricle, Saccule and Semi-
circular Canals ....

Ampullse .......

Membranous Cochlea ....

Limbus .......

Basilar Membrane ....

Membrane of Reissner . . . .

Spiral Ligament .....

Organ of Corti

Rods of Corti

Hair Cells and Cells of Deiters .

Lamina Reticularis ....

Tectorial Membrane . ...

Nerves of Cochlea .....

Vessels of Cochlea . ....

Development of Organ of Corti

Measurements of Cochlea . . . .
THE NOSE

Cartilages . ,

Nasal Fossa? ......

Mucous Membrane .....

Olfactory Mucous Membrane .

Olfactory Cells

Olfactory Nerve .....

Organ of Jacobson ... .

Vessels of Nasal Fossa1 ....
THE ORGANS OF TASTE . ...

Gustatory Cells .....

ARRANGEMENT OF SENSORY CELLS AND

NERVE FIBRES IN THE DIFFERENT

ORGANS . ....

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ORGANS OF THE SENSES.

IN this Part will be described the organs of sight, hearing, and smell, and also
the taste buds which are found on the tongue and other parts endowed with the
sense of taste. The terminations of sensory nerves in the skin and elsewhere have
already been described in Vol. I., Part 2, and will only be briefly alluded to in
reviewing the whole subject of the ending of nerves of special sense.

THE EYE.

The organ of vision, strictly speaking, consists only of the ball or globe of the

CORRIGENDA.

Pa<je 16, line 14 from top, for "(p. 25)" read "(p. 24)."
,, 44, footnote l, for " tvos " read " Iv6s."
,, 59, title of fig. 6S,for " HUMOURS " read st HUMOUR."

80, line 13 from bottom, for " auditus " read "aditus."
,, 147, line 2 from top,/or " Uber" read " Ueber."

line 9 from top, for " nebcnMhlc " read " Nebenhb'hle."

line 5 from bottom, for "vergkichend-anatome" read " vercjlrichcnd-anatomische.'

line 2 from bottom, for " pathologlsch" read "patholvyiscfw."

The upper lid is larger and more moveable
than the lower, all the transparent part of the
globe being covered by it when the eye- is
closed ; it is chiefly by the elevation of this lid
that the eye is opened, the movement being
effected by a muscle (levator palpebra) devoted
exclusively to this purpose. At the outer and
inner angles (canthi) of the eye the eyelids are
united. The interval between the angles varies

in different individuals, averaging about 28mm. (Fuchs), and, according to its
extent, gives the appearance of a larger or a smaller eye, the size of the globe being
nearly the same in all. The greater part of the edge of each eyelid is flattened
and angular, but towards the inner canthus it is rounded off for a short space, at
the same time that it changes its direction, so that a rounded bay is here left
between the two eyelids ; this bay has been termed the lachrymal reservoir (lacus
lacrimalis) • at this point there is seen on each lid a slight elevation (papilla
lacrimalis)) — the apex of which is pierced by the aperture (punctum) of a small
canal (canalwulus lacrimalis) which serves to convey away the fluid which moistens
the conjunctiva (fig. 1, Pli, Pis}. (See also figs. 9, 10, and 11.)

In the greater part of their extent the lids are applied to the surface of the eye-
ball ; but at the inner canthus, at the lachrymal lake, there intervenes a vertical fold

VOL. III. — PT. 3. 9 B

OKGANS OF THE SENSES.

IN this Part will be described the organs of sight, hearing, and smell, and also
the taste buds which are found on the tongue and other parts endowed with the
sense of taste. The terminations of sensory nerves in the skin and elsewhere have
already been described in Vol. I., Part 2, and will only be briefly alluded to in
reviewing the whole subject of the ending of nerves of special sense.

THE EYE.

The organ of vision, strictly speaking, consists only of the ball or globe of the
eye ; but connected with the eyeball externally are muscles, nerves, and blood-
vessels, elsewhere described, as well as other parts specially destined for its protec-
tion (tutamina oculi), of which an account will first be given.

THE EYELIDS AND CONJUNCTIVA.

The eyelids (palpebrce) are moveable folds of integument, strengthened towards
their margins by a thin lamina of dense fibrous tissue (tarsus). They are about
3mm. thick near their free edge. A mucous membrane (conjunctiva) lines their
inner surface, and is reflected thence on the front of the eyeball. The line of
reflection is termed thefornix conjunctives.

Fig. 1. — FRONT VIEW OF THE RIGHT EYE, WITH THE

EYELIDS DRAWN APART BY BLUNT HOOKS. (Merkel.)

Ps, plica semilunaris ; Pis, Pli, punctum lacrimale
sup. et inf. ; Car, caruncula lacrimalis ; Lpm, interna
tarsal ligament.

The upper lid is larger and more moveable
than the lower, all the transparent part of the
globe being covered by it when the eye- is
closed ; it is chiefly by the elevation of this lid
that the eye is opened, the movement being
effected by a muscle (levator palpelra) devoted
exclusively to this purpose. At the outer and
inner angles (canthi) of the eye the eyelids are
united. The interval between the angles varies

in different individuals, averaging about 28mm. (Fuchs), and, according to its
extent, gives the appearance of a larger or a smaller eye, the size of the globe being
nearly the same in all. The greater part of the edge of each eyelid is flattened
and angular, but towards the inner canthus it is rounded off for a short space, at
the same time that it changes its direction, so that a rounded bay is here left
between the two eyelids ; this bay has been termed the lachrymal reservoir (lacus
lacrimalis) ; at this point there is seen on each lid a slight elevation (papilla
lacrimalis), — the apex of which is pierced by the aperture (punctum) of a small
canal (canaliculus lacrimalis) which serves to convey away the fluid which moistens
the conjunctiva (fig. 1, Pli, Pis). (See also figs. 9, 10, and 11.)

In the greater part of their extent the lids are applied to the surface of the eye-
ball ; but at the inner canthus, at the lachrymal lake, there intervenes a vertical fold

VOL. III. — PT. 3. B

THE EYE.

of conjunctiva, the plica semilunaris (fig. 1, Ps), which rests on the eyeball ; whilst
occupying the recess of the angle at the border of this fold, is a spongy-looking
reddish elevation (caruncula lacrimalis, Car) formed by a small isolated portion
of skin containing a few large modified sweat glands, as well as a group of sebaceous
glands which open into the follicles of very fine hairs. There is further found in it
a small amount of plain muscular tissue (H. Miiller), as well as some cross-striated
muscular fibres. A few plain muscular fibres are also to be found in the plica
semilunaris.

The plica semilunaris is the rudiment of the third eyelid (membrana niclitans]
found in many animals ; and in some animals, and occasionally in man, the carun-
cula lacrimalis retains its connection with the skin at the inner canthus. The
muscular tissue of the nictitating membrane of animals, and presumably, therefore,
of the semilunar fold of man, receives its nerve supply through the cervical sympa-
thetic. In many animals, and occasionally in man (in the negro constantly, accord-
ing to Griacomini), the plica semilunaris contains a plate of hyaline cartilage.

Structure of the lids. — The skin covering the eyelids is thin and delicate, and
covered with fine downy hairs (fig. 2, i, i). These are provided with sebaceous
follicles ; small sweat-glands are also present. At the line of the eyelashes the skin
joins the conjunctival mucous membrane which lines the inner surface of the lids.
The cutis vera contains a number of ramified pigment cells, and pigment is also
frequently found in the Malpighian layer of the epidermis, especially near the inner
angle of the lids. Beneath the skin is a quantity of very loose connective tissue,
entirely free from fat and containing the fasciculi of the orbicularis palpebrarum
muscle (&), and beneath the mucous membrane on the posterior surface is the
lamina of dense connective tissue before mentioned, and known as the tarsus (e), or
from its consistence, the tarsal cartilage, which thins off near the attached margin
of the eyelid into the palpebral fascia connecting it with the margin of the orbit.
In the tarsi are imbedded the Meibomian glands (/). In the upper eyelid there is,
in addition, the insertion of the levator palpebrae superioris, attached to the upper
or anterior surface of the tarsus by fibrous tissue and smooth muscular tissue (see
below) and further sending a well-marked flat tendinous expansion, the bundles of
which pass between the bundles of the orbicularis palpebrarum muscle, and are
attached to the skin of the middle of the eyelid (fig. 6). There is nothing corre-
sponding to this in the lower lid, but the inferior rectus and oblique muscles send
strands of fibrous tissue forwards to be attached to the tarsus and palpebral ligament.

The orbicularis muscle is attached to the skin by loose subcutaneous connec-
tive tissue, but glides loosely on the tarsal cartilages. A marginal fasciculus lies
within the line of the eyelashes, separated by the bulbs of the lashes from the other
fibres, and constituting the ciliary bundle or muscle of Riolan (b1). The fibres of
the orbicularis are very small and pale in colour. Its attachments have already
been described in Yol. II., Part 2.

The tarsi (tarsal cartilages) are two thin elongated plates formed of dense
connective tissue, without any intermixture of cartilage-cells. They are placed one in
each lid, to which they give shape and firmness. The upper one, the larger, is half
oval in form, being broader near the centre and narrowing towards the angles of
the lids. The lower is thinner, much narrower, and more nearly of a uniform
breadth throughout. Their free edges, which are straight, are thicker than any
other part. At the inner canthus they are fixed to the nasal process of the superior
maxillary bone by the internal tarsal slip ; and at the outer angle are attached to
the malar bone by a fibrous band termed the outer tarsal ligament (Yol. II., p. 281).
Groups of fat-cells are found in the tarsus both near its attached border and
scattered over its anterior surface (Merkel).

THE EYELIDS.

The palpebral fascm (septum orbitale) is a fibrous membrane placed beneath the
orbicularis muscle, attached on the one hand to the margin of the orbit, and on the
other prolonged towards the attached border of each tarsus. In the lower lid its
tissue is continuous with that of the tarsus, but in the upper lid it blends with the
tendon of the levator palpebrse. The membrane is thicker at the outer part of the
orbit, where it forms the lateral (outer) palpebral or tarsal ligament (figs. 4, 12).
The mesial (internal) palpebral ligament, to which the fibres of the orbicularis
palpebrarum are attached (see Vol. II. p. 281), is not formed from the general
palpebral fascia, but lies altogether in front of it (fig. 4). The palpebral fascia

Fig. 2. — VERTICAL SECTION THROUGH THE UPPER
KYKUD, HUMAN (after Waldeyer). Mag-
nified.

a, skin ; l>, orbicularis ; l>', ciliary bundle ;
c, involuntary muscle of eyelid ; d, conjunctiva ;
e, tarsus ; /, Meiboniian gland ; y, sebaceous
gland near eyelashes, with modified sweat-gland
opening with it ; h, eyelashes ; i, small hairs iu
outer skin ; j, sweat-glands ; k, posterior tarsal
glands.

extends downwards from the crista
lacrimalis posterior, between the osseous
boundary of the nasal duct and the
origin of the inferior oblique muscle, to
reach the lower border of the orbit
(Merkel).

The palpebral fascia thus acts as a
kind of fibrous septum between the
cutaneous and the conjunctival parts
of the eyelid at its attached border : it
was therefore termed the septum or-
bitale by Heiile. It is perforated above
the internal tarsal ligament by the
termination of the ophthalmic artery,
with a considerable anastomotic vein
between the superior ophthalmic and
the angular, and its attachment to the
supra-orbital margin is interrupted in-
ternal to the centre by the passage of
the supraorbital nerve (in one or two
pieces) with the accompanying artery.

On the ocular surface of each lid
are seen parallel vertical rows of what,

seen through the conjunctival mucous membrane, look like yellow granules.
There are twenty to thirty of these rows in the lower lid, somewhat more in the
upper lid ; they are the Meibomian or tarsal glands (fig. 3). These are long
sebaceous glands, imbedded in the tarsi ; and they open on the free margin of the
lids by minute orifices, generally one for each. The glands consist of nearly straight
tubes, closed at the end. with numerous small caecal appendages projecting from the
sides. Sometimes, however, they are not straight, but are bent round at the blind
end, as is shown in some of those represented in fig. 3. The mouths of the tubes are
lined by stratified epithelium continuous with that of the skin ; but the ducts and
the glandular recesses have a lining of cubical epithelium filled with the f itty

B 2

1.

THE EYE.

secretion. According: to Colosanti the glands have a basement membrane, and a
muscular layer outside this : he further describes a network of fine nervous fibrils
amongst the epithelium-cells.

A layer of unstriped muscular tissue is contained in each eyelid (H. Miiller) :
that of the upper (fig. 2, c ; fig. 13) arising from the under surface of the levator
palpebras, that of the lower from the neighbourhood of the inferior oblique muscle,
and each being inserted near the attached margin of the tarsus. According to
Henle, some of the fibres have a transverse course.1

The eyelashes (cilia) are strong short curved hairs, arranged in two or more
rows along the margin of the lids, at the line of union between the skin and the
conjunctiva. The upper lashes are more numerous and longer than the lower ; they

Fig. 3. — MEIBOMIAN GLANDS OP THE LEFT EYELIDS

AS SEEN FROM BEHIND.

a, a, palpebral conjunctiva ; 1, lachrymal gland ;
2, openings of seven or eight of its ducts ; 3, upper
and lower puncta lacrimalia, ; 6, 6, ends of the
upper and lower Meibomian glands, of which the
openings are indicated along the margins of the
eyelids.

are curved in an opposite direction in the
two lids : so that their convexities are
directed towards one another. The
extremity of the lid, in which the follicles
of the eyelashes are set, is composed of
a dense fibrous tissue, somewhat similar

in nature to that of the tarsus, with which it is, in fact, in the upper lid continuous
(Merkel). The hair follicles are of some length (To to 2*5 mm.), penetrating
obliquely from the outer edge of the lid nearly to the tarsi.

Near the inner canthus the hairs are weaker and more scattered. Immediately
within the eyelashes, between them and the ciliary bundle of the orbicularis, is a
row of large modified sweat glands (glands of Moll), which sometimes open into the
mouths of large sebaceous glands (fig. 2, g) (not the Meibomian).

The conjunctiva consists of the palpebral part (conjunctiva pafyelrarwn), with
which may be included the plica semilunaris and caruncula, and of the ocular part
(conjunctiva lulbi), in which may be distinguished the sclerotic and corneal
portions : each of these parts has distinctive characters. The epithelium of the
conjunctiva varies somewhat at different parts ; that of the eyelids is columnar,
with smaller cells between the fixed ends of the columnar cells. Near the skin and
cornea it shades oif into the stratified epithelium which covers these parts.

The palpebral portion of the conjunctiva is thicker and more vascular than the
rest of the membrane, and is freely supplied with nerves. Through the puncta
lacrimalia and canaliculi, it is continuous with the lining membrane of the
lachrymal sac. Although closely united to the tarsi, it exhibits, nevertheless,
numerous small creases or folds, which are visible with a lens. A layer of small
racemose or tubulo-racemose glands (posterior tarsal] is found on the ocular surface
of the lids, immediately under the conjunctiva, and beyond the blind ends of the

1 It may be mentioned in this place that H. Miiller also described a layer of unstriped muscle
bridging over the spheno-inaxillary fissure, corresponding to a more largely developed layer found in
the extensive aponeurotic part of the orbital wall of various mammalia (H. Miiller, Wurzburg Sitzungsb.,
1858 ; Turner, Nat. Hist. Ilev., 1862). These involuntary muscles receive their nerves through the
cervical sympathetic ; the spheno-maxillary muscle, when contracted, causes the globe of the eye to
project more from the orbit.

BLOOD-VESSELS OF THE EYELIDS. 5

Meibomian glands (fig. 2, &). Their minute ducts open near the line of reflection
of the conjunctiva upon the globe of the eye.

Harderian g-land. — All animals which possess a well-developed membrana nictitans have
also, situated at the mesial angle of the eye, a special gland, the duct of which opens beneath
the third eyelid. The gland has a racemose structure, and secretes a mucus-like fluid, thus
differing from the serous-secreting lachrymal. It is not found in primates, unless in an
extremely vestigial form.

The ocular portion. — The conjunctiva changes its character at the line of reflec-
tion from the eyelids, becoming thinner and being loosely connected to the sclerotic
coat of the eyeball by submucous tissue. But over the cornea it consists only of a
prolongation of the epithelium, which is closely adherent to the anterior layers of the
cornea, in connection with which it will be described.

Blood-vessels. — The blood is supplied to the eyelids mainly by the internal and
external palpebral arteries ; the former being derived from the ophthalmic artery

Pronto-nasal
-Superior paljgebral

Transverse,
faciai"

Infra-orbital

ligament
Fig. 4. — DISSECTION SHOWING THE ARTERIES AND VEINS OF THE EYELIDS. (After Testut. )

and the latter from its branch, the lachrymal. The internal palpebral are usually the
larger, and consist of two vessels, a superior and an inferior, one for each lid, which
they reach by piercing the palpebral fascia, one a little above and the other just
below the mesial palpebral ligament (fig. 4). In the eyelid each vessel runs with a
tortuous course near the free border between the tarsus and the bundles of the
orbicularis, forming the so-called tarsal arches. At the outer side they anastomose
with the external palpebrals, which are derived from the lachrymal. The superficial
temporal and transverse facial also send branches to join this anastomotic chain at
the outer part of the orbit.

In the upper eyelid there is a secondary arterial arch formed by a branch of the
superior palpebral, and running just in front of the upper or attached end of the
tarsus, between the tendon of the levator palpebrae and the plain muscular sheet
which passes from it to join the tarsus. Sometimes there is a similar secondary arch

THE EYE.

POST.ETHM.

-SUP.EXT.MUSC.

O MENINGEAL.

branches from the Meibo-
mian glands and from the
orbicularis and integument,
below which it forms a
tortuous venous plexus, with
large and irregular meshes.

Fig. 6. — SECTION OF THE UPPER

EYELID, WITH THE ARTERIES

INJECTED. (Modified from
Merkel.)

The course of the nervous twigs
is also shown.

The blood from this plexus
passes externally into the
superficial tsmporal and in-
ternally into the facial vein.

Lymphatics. — There are
two networks of lymphatic
vessels in each eyelid, one
in front of, the other behind
the tarsus. The former re-
ceives lymph from the in-
tegumental and muscular
structures of the lid, the
latter from the Meibomian
glands and conjunctiva. The
networks are connected by
vessels which pierce the tarsi,
but less freely in the lower
than in the upper eyelid.
The efferent lymphatics find
their way mesially along the

in the lower lid. The two arches in the
upper lid are joined here and there by small
anastomotic arteries. Branches pass in
each lid from the tarsal arches, 1, for-

Fig. 5. — PLAN OF THE OPHTHALMIC ARTERY, SHOW-
ING THE TYPICAL MODE OF ORIGIN OF ITS

BRANCHES. (G. D. T. after Meyer. )

wards to supply the orbicularis muscle, and
the integumental structures ; 2, backwards
into the tarsus to supply the Meibomian
glands ; and 3, backwards around the upper
and lower edges of the tarsus to supply the
conjunctiva palpebrarum. The veins of
the eyelids are disposed in two series or
networks. The one, post-iarsal, receives
branches from the conjunctiva and a few
from the Meibomian glands ; its blood
passes for the most part into the ophthal-
mic vein. The other, or pre-tarsal, receives

-^ Muscle of ~RLolasi,

QlounoL of Moll

THE LACHRYMAL APPARATUS.

7

facial vein and its tributaries towards the submaxillary lymphatic glands, laterally
into the pre-auricular and parotid lymphatic glands.

Nerves. — The levator palpebrse is supplied by the upper branch of the third
nerve, the orbicularis palpebrarum by the upper branches of the facial nerve ; the
plain muscular tissue of the lids, like that of the orbit generally, by branches of the
sympathetic.

The sensory nerves come from branches of the fifth. The upper lid is mainly
supplied by the frontal and supra-orbital, the lower lid mainly by the infra-orbital
branches, but at the inner or nasal part the supra- and infra-trochlear branches of
the ophthalmic division come to the surface, and assist in supplying the lids and
the adjacent lachrymal apparatus, whilst laterally the lachrymal branch of the

Fig. 7. — NERVES OF THK EYELIDS. LEFT EYE. (From Merkel.)

ophthalmic sends ramifications to the skin over the external angular process, some
of which may pass into the upper eyelid (fig. 7).

The principal nerves run in front of the tarsi between these and the fibres of the
orbicularis (fig. 6). From here their branches pass forwards to the skin and back-
wards, piercing the tarsi, to the Meibomian glands and conjunctiva. Near the edge
of each eyelid, between the tarsus, the orbicularis, and the muscle of Kiolau, is an
anastomotic chain of nerve-fibres, the marginal plexus of Mises, from which nerves
are supplied to the surrounding parts and to the hair-follicles of the eyelashes.

THE LACHRYMAL APPARATUS.

The parts which constitute the lachrymal apparatus are the following, viz. : —
The gland by which the tears are secreted ; the two canals which collect the fluid
near the inner canthus, and the sac with the nasal duct continued from it, through
which the tears pass into the inferior meatus of the nose.

The lachrymal gland (fig. 3, 1), an oblong flattened body, about the size of
a small almond, is placed in the upper and outer part of the orbit, a little behind the
anterior margin. The upper convex surface of the gland is lodged in a slight
depression in the orbital plate of the frontal bone, to the periosteum of which it is
united by fibrous bands; the lower surface is adapted to the convexity of the
eyeball, and is in contact with the upper and the outer recti muscles. The fore
part of the gland, separated from the rest by a thin layer of fascia, and sometimes
described as a distinct gland (glandula lacrimalis inferior of Rosenmliller), is

THE EYE.

closely adherent to the back of the upper eyelid, and is covered on the ocular
surface merely by the conjunctiva ; its lobules are small and separate, with minute
ducts, some opening separately, others joining the ducts from the principal gland,
which are also very small. The number from both divisions of the gland seldom
exceeds twelve. After running obliquely under the mucous membrane, and
separating at the same time from each other, they open in a row at the fornix con-
junctivae, by separate orifices, at its upper outer part.

Structure. — The lachrymal gland is a compound tubulo-racemose gland
resembling the serous salivary glands in general structure. Its alveoli are bounded

Fig. 8.— ALVEOLI OF THE LACHKYMAL GLAND OF THE DOG : A, FROM A GLAND IN THE RESTING

STATE ; B, FROM ANOTHER GLAND WHICH HAD BEEN SECRETING FOR THREE HOURS PREVIOUSLY.

(E. A. S.) Highly magnified.

The glands were hardened in chromic and osmic solution. In A the cells are filled with the
materials of secretion ; in B, these are mostly discharged, and the cells are shrunken and vacuolated.

by a basement membrane formed of ramified flattened cells ; and the secreting cells
exhibit changes in the different states of rest and activity of the gland similar to

Fig. 9. — FRONT OF THE LEFT EYELIDS WITH THE LACHRY-
MAL CANALS AND NASAL DUCT EXPOSED.

1,1, upper and lower lachrymal canals, showing towards
the eyelids the narrow 1 ent portions and the puncta lacri-
raalia ; 2, lachrymal sac ; 3, the lower part of the nasal
duct ; 4, plica semilunaris ; 5, caruncula lacrimalis.

those seen in most other glands (see fig. 8 and
Vol. I., Part 2, p. 396). No rod-like structure has
been noticed in the epithelium of the ducts. The
arteries of the gland are derived from the lachry-
mal, and the veins pass into the ophthalmic vein.
The nerves come from the lachrymal branch of
the ophthalmic and from the sympathetic.

Lachrymal canals. — These commence as
already mentioned by a minute aperture (punc-

tiun) on the margin of each lid, near the inner angle (figs. 9, 10 and 11). The
upper punctum is slightly smaller and is situated rather more mesially than the
lower one. The upper canal is rather the smaller and longer of the two ; it
first ascends for 2 mm. from the punctum ; then makes a sudden bend, and

THE LACHRYMAL APPARATUS.

is directed inwards and slightly downwards for 6 to 7 mm. to join the lachrymal sac
(fig. 11). The lower canal descends from the corresponding punctum and then
takes a nearly horizontal course inwards. Both canals are smallest at the punctum,

Fig. 10. — SECTION OF THE EYRLIDS, PASSING ALONG
THE LACHRYMAL CANALS. (Grerlach. ) Magnified.

c., inner canthus of eye ; s.c., i.e., superior anil
inferior canals respectively ; l.s. , lachrymal sac ;
orb., fibres of orbicularis muscle.

and here they are a little wider at the
mouth than at the base of the papilla
lacrimalis, where they only measure
O'l mm. in diameter ; they then become
enlarged and present a further enlarge-
ment at the bend, where each has a
marked dilatation, enlarging to 1 mm.
diameter or more (fig. 10). The bend is
sharper in the embryo than in later life.
From this the horizontal limb passes off

as a nearly cylindrical tube of about 0*6 mm. diameter, gradually narrowing to
half that size. A part of the orbicularis palpebrarum (pars lacrimalis, tensor
tarsi) runs parallel to the horizontal limbs, which are embraced by some of the
muscular fibres, and when the orbicularis contracts the canals may be compressed by
these fibres (Merkel). The canals either unite near their end, or they open
separately, but close together, into a diverticulum of the nasal sac which is known
as the sinus of Maier.

Fig. 11. — SECTION SHOWING

THE COURSE AND RELA-
TIONS OF THE NASAL SAC
AND DUCT. (E. A. S.,

slightly modified from
Merkel.)

Zcichrr/mal canals ;/'" „

^

The mucous mem-
brane in the canaliculi
is lined by a stratified
scaly epithelium set on
a corium rich in elastic
fibres.

The lachrymal sac
and nasal duct con-
stitute together the
passage by which the
tears are conveyed from
the lachrymal canals to
the cavity of the nose.
The lachrymal sac (fig. 9,

2 ; fig. 11), the slightly dilated upper or orbital portion of the passage, is situated at
the side of the nose, near the inner canthus of the eye, and lies embedded in a deep
groove in the lachrymal and superior maxillary bones, from which it is separated by
a thin layer of the orbital periosteum. When distended with tears it forms a distinct
swelling here at the side of the nose. It is about 15 mm. long, and about 5 or 6 mm.
wide, and is sometimes narrower below where it passes into the nasal dnct. Its

10 THE EYE.

upper end is closed and rounded, forming a cul-de-sac ; the lower end gradually
narrows into the nasal duct. On the outer side, and a little in front, it receives
the lachrymal canals ; and here it is placed behind the internal tarsal ligament, and
some of the inner fibres of the orbicular muscle of the lids ; while on its orbital
surface is the tensor tarsi muscle. The nasal duct, very variable in length (12
to 24 mm.), and 3 or 4 mm. wide, grooving the upper maxilla, descends to the
fore part of the lower meatus of the nose, the osseous canal being completed by
the lachrymal and lower turbinate bones. Both sac and duct are composed of
fibrous and elastic tissues, adhering closely to the bones above mentioned, and
strengthened in the case of the lachrymal sac by a fibrous process sent from the
internal tarsal ligament, which crosses it a little above its middle. The inner
surface is lined by a mucous membrane, which is continuous through the canaliculi
with the conjunctiva, and through the nasal duct with the mucous membrane of the
nose.

At the opening into the nose the lining membrane is often arranged so as to form
an imperfect valve (Hasner). Other valvular folds have been often noticed and
described, but they appear to be less constant. The nasal duct is rather narrower
in the middle than at either end ; its direction is not quite vertical, but inclined
slightly backwards. Its direction is indicated by a line joining the mesial
canthus of the eyelids with the anterior edge of the first molar of the upper jaw
(Testut). The lower orifice of the nasal duct is very variable in position, but is
usually from 80 to 35 mm. behind the posterior margin of the anterior nasal opening
(Arlt). It may open by a simple round orifice close under the inferior turbinate.
or by an oblique or slit-like orifice or groove in the mucous membrane somewhat
lower. In rare cases two lower openings have been described. This condition is
always present in some animals (e.g., dog).

The nasal sac and duct are lined by a columnar epithelium, which may be
ciliated here and there, but does not appear to be covered everywhere with cilia as is
the case on the adjacent mucous membrane of the nose. The lower part of the
nasal duct has numerous glands similar to those in the nasal meatus into which it
opens. The arteries come from the nasal and inferior palpebral. The veins are
very large and numerous on the nasal duct (as in the adjacent nasal mucous mem-
brane). The nerves are derived from the infratrochlear branch of the nasal
division of the ophthalmic.

THE GLOBE OF THE EYE.

The globe or ball of the eye is supported by a quantity of fat and loose connective
tissue in the fore part of the orbital cavity, somewhat nearer its lateral and inferior
walls than its mesial and superior. The recti and obliqui muscles closely surround
the greater part of the eyeball, and are capable of changing its position within
certain limits : the lids, with the plica semilunaris and caruncle, are in contact with
its covering of conjunctiva in front ; and behind it receives the thick stem of the
optic nerve.

The eyeball is composed of segments of two spheres, of which the anterior is the
smaller and more prominent ; the segment of the larger posterior opaque sphere
corresponds with the limit of the sclerotic coat, and that of the smaller sphere with
the cornea. The junction of the two is marked by a broad shallow groove which
has been named sulcus sderce.

The eyeball measures nearly an inch (24*5 mm.) across from side to side, but
slightly less from before back (24 mm.), and still less from above down (23'5).
It weighs about 7 grammes, and has a volume of about 6 -5 cubic centimetres.

CAPSULE OF TENON. ] 1

Except when directed towards near objects, the axes of the eyes are nearly
parallel ; the optic nerves, on the contrary, diverge considerably. Each nerve
enters the corresponding eye about 2 to 8 mm. to the inner or nasal side of the
axis of the eyeball.

The eyeball consists of three concentric coats, and of certain fluid and solid
parts enclosed by them. The coats are (1) an external fibrous covering, forming
the sclerotic (tunica sclera) and cornea, (2) a middle vascular, pigmented, and in part
also muscular membrane, the cJioroid and iris (tunica uvea), and (3) an internal
nervous and epithelial stratum, the retina. The enclosed refracting media, three
in number, are the aqueous humour, the vitreous lody, and the lens.

Around the posterior two-thirds of the eyeball there is a tunic of fascia, tunica
vaginalis oculi, or capsule of Tenon, which is perforated by the tendons of the recti

Tcwsi

Outer palpebrctl
tiqatnent.

tocUl of muscle
orbit

Fig. 12. — HORIZONTAL SECTION OF ORBIT. (After Gerlach.) Magnified.

and obliqui muscles, along which it sends sheaths which blend with the perimysium
of the muscles (figs. 12 and 13). It is connected with the sclerotic by delicate con-
nective tissue (adventilia oculi, Lockwood), except posteriorly, at the entrance of the
ciliary vessels and nerves, where it blends with the sclerotic. Anteriorly the capsule
of Tenon is continued into the conjunctiva. This capsule is lined by flattened
endothelial cells, and encloses a lymph-space, which separates the eyeball from the
orbital fat. It is strengthened just behind the places where the recti muscles
perforate it, by bands of fibrous tissue (figs. 12 and 13,), and it is attached on
either side to the malar and lachrymal bones by elastic ligamentous structures, which
also receive fibrous slips from the internal and external recti. These structures
serve as check-ligaments (fig. 12) to these muscles. They are stated by Sappey to
contain plain muscular fibres. Fibrous slips also pass from the sheaths of the
superior and inferior rectus, and are attached to the conjunctiva palpebrarum and

12 THE EYE.

to the connective tissue of the eyelid (fig. 13). Below and in front of the anterior
end of the inferior rectus the capsule is strengthened by a band of fibrous tissue,
which is stretched like a sling from one side of the orbit to the other, and is
inserted at its ends to the lachrymal and malar bones. This band — the ligamentum

•Frotvtxdis

Fig. 13. — SAGITTAL SECTION THROUGH THE MIDDLE OP THE GLOBE OF THE EYE WITHIN THE OKISIT.
(E. A. S.. from a figure by Merkel, enlarged and modified.)

suspensorium oculi of Lockwood — serves to aid in maintaining the eye in position ;
it is joined anteriorly with the tarsus of the lower lid (see fig. 13). Lastly, another
band passes from the anterior border of the sheath of the inferior oblique muscle
forwards, downwards, and outwards, to be attached to the lateral part of the lower
border of the orbit (fig. 13). For further details regarding these structures consult

THE SCLEROTIC COAT.

Lock wood, Journal of Anatomy and Physiology, 1885 ; Merkel, Handbuch der
topograph. Anatomic ; and Testut, Traite d'Anatomie. See also Vol. IT., p. 292

^ Tern/oara-l
LcL.ckryrna,L nerue{ \ mu*scle

W1

y «\>1o«-i •

'Extzrnod. rcctuz

Fig. 14. — CORONAL SECTION THROUGH THE RIGHT EYE AND ORBIT.
(E. A. S., from a figure by Merkel, enlarged and modified.)

THE SCLEROTIC COAT.

The sclerotic coat, the tunic of the eye on which the maintenance of the
form of the organ chiefly depends, is a strong, opaque, fibrous structure. It extends
over the greater part of the eye-ball (fig. 15) joining in front with the cornea.
The outer surface is white and smooth, except where the tendons of the recti and
obliqui muscles are inserted into it. In the child the eyeball has a bluish white
colour, from the fact that the dark pigment of the choroid shows through the
sclerotic coat (which is thinner in the child). The inner surface is brown, and
rough from the presence of a delicate pigmented connective tissue (lamina fusca),
which is united by fine threads with the choroid coat. These filaments traverse a
lymphatic space through which branches of the ciliary vessels and nerves also pass
obliquely. The sclerotic is thickest at the back part of the eye, at the entrance
of the optic nerve, where it is nearly 1 mm. thick, and thinnest (0'4 mm.) at
about 6 mm. from the cornea : near the junction with the latter, it is again

14

THE EYE.

EPITHELIUM
CONJUNCTIVA"

MUSCULUS
CILIARISv

ARTERIA

CENTRALIS

RETIN/E

Fig. 15. — DIAGRAM OP THE RIGHT ADULT HUMAN EYE, DIVIDED NEARLY HORIZONTALLY THROUGH THE

MIDDLE. (E. A. S.) Magnified five times.
The line a b passes through the equator, x y through the visual axis of the eye.

The figure has been drawn, as far as possible, to scale, the following being taken as the
average measurements of the parts of the adult eye in millimeters : —

Transverse diameter of the eyeball 24'5

Vertical diameter . . . . . . . . . ... . 23'5

Antero -posterior diameter ........... 24'0

Greatest thickness of the sclerotic, choroid, and retina together . . . . 1*4

Greatest thickness of the sclerotic posteriorly . . . . . .0*8

Thickness of the sclerotic at the equator 0'4

Thickness of the cornea in the centre ......... 0*8

Distance from the middle of the anterior surface of the cornea to the front

of the lens 3*4

Antero-posterior diameter of the lens 4'0'

THE SCLEROTIC COAT.

15

Transverse ditto

Greatest thickness of the ciliary body . . . . . . . .

Thickness of the iris ..........

Length of the radius of curvature of the anterior surface of the cornea .

Radius of the posterior surface of the sclerotic

Radius of curvature of the anterior surface of the lens

Radius of the posterior surface ........

Distance of the middle of the posterior surface of the lens from the middle of

retina
Distance between the centre of the spot of entrance of the optic nerve and

middle of the fovea centralis retinaa ........

the

the

9'1
1*1

O'l

7*8

12'5

lO'O

G'O

15'0
3-5

somewhat thickened owing to the attachment and spreading over it of the tendons
of the ocular muscles. The optic nerve pierces this coat about 2'5 to 3 mm. in-

— Anterior cJiouriber

Iris

Anterior cULcwu
- ' "

Great

-uortLcase,
ueln.

cLUcuru
Fig. 16. — DIAGRAM SHOWING THE PRINCIPAL NERVES AND BL.OOD-VESSELS OF THE EYEBALL. (Testut.

ternal to the posterior pole of the eyeball, and about 1 mm. below a horizontal plane
passing through the poles ; the opening is somewhat smaller at the inner than at the
outer surface of the coat. The outer fibrous sheath of the nerve blends with the
sclerotic at the margin of the aperture : in consequence of this arrangement, when
the nerve is cut oif close to the eyeball, the funiculi seem to enter by a group of
pores ; and to the part of the sclerotic thus perforated the name of lamina cribrosa
is given. Around this cribrous opening are smaller apertures for the posterior
ciliary arteries and the ciliary nerves. These are disposed in the manner shown in
the accompanying diagram (fig. 16). Nearer the equator of the globe the sclerotic
is pierced by four apertures which transmit veins (venae vorticosse).

THE EYE.

Structure of the sclerotic. — The sclerotic coat is formed of bundles of
connective-tissue fibres, and yields gelatine on boiling. Its white fibres are com-
bined with fine elastic elements, and amongst them lie numerous connective-
tissue corpuscles lodged in cell-spaces, but not by any means so regularly arranged
as in the cornea. Some of the cells are pigrnented. The bundles are disposed in
layers both longitudinally and transversely, the longitudinal arrangement being
most marked behind and at the surfaces, the transverse or circular near the corneal
margin. The layers communicate at intervals so as not to be separable for any
distance.

Both externally and internally the sclerotic is covered with flattened endothelial
cells, which are reflected over the muscles, vessels, nerves, and connecting bands of
tissue which pass from it to the capsule of Tenon and the choroid coat respectively.
The lamina fusca resembles in structure the lamina suprachoroidea of the choroid
coat (p. 25).

The anterior zone of the sclerotic from about the line of attachment of the
tendons of the recti muscles forwards to the cornea, is covered by the conjunctiva

Fig. 17. —TERMINATION IN END-BULBS OP THE

NERVES OF THE CONJUNCTIVA. (LongWOrth.)

which is reflected on to the globe from the
eyelids, and which is connected with the
sclerotic by loose areolar (subconjunctival)
tissue. This part of the conjunctiva is
formed of somewhat dense connective
tissue covered by a stratified epithelium
of some thickness. It is a fairly vascular
membrane, and contains a network of
lymphatics, which begin at the edge of the
cornea by tapering capillaries. Its nerves
are mostly medullated : some pass towards
the cornea, others end in the membrane
itself, many in end-bulbs (W. Krause).

A few blood-vessels derived from the
short ciliary and the anterior ciliary
arteries, permeate the fibrous texture in
the form of a network of capillaries with
very wide meshes. Those from the anterior ciliary emerge from under the tendons
of the recti muscles, dividing into branches as they pass towards the margin of the
cornea. Before reaching this, however, they dip into the substance of the sclerotic,
and they here take on a radial disposition in the thickness of that coat. Other
vessels derived from the posterior ciliary arteries form a wide-meshed network at
the surface of the sclerotic in its posterior three-fourths, and like those from the
anterior ciliary communicate freely with deeper vessels in the substance of the
membrane. At the posterior part of the sclerotic its vessels are continuous with
those of the dural sheath of the optic nerve. Around this nerve the scleral
branches of the posterior ciliary arteries form an arterial circle (circulus Zinnii),
which gives branches to the optic nerve and choroid as well as to the sclerotic. The
vessels of the conjunctival membrane, which are derived from the palpebral and
lachrymal arteries, are readily distinguishable from those of the subjacent sclerotic
by their more tortuous course, and by the fact that they shift upon the globe when
the conjunctiva is pulled upon. Near the edge of the cornea they communicate with

THE CORNEA. 17

the episcleral vessels derived from the anterior ciliary. Veins corresponding
with the arteries run in and beneath the conjunctiva, and there is a well-marked
episcleral plexus of veins behind the junction of the cornea and sclerotic. The
veins convey their blood to the anterior ciliary and the vorticose veins of the
choroid. The sclerotic receives fibres from the ciliary nerves, but it is not certainly
known how they terminate.

Hannover described the sclerotic as being: traversed in its thickness, opposite the f ovea cen-
tralis of the retina, by a strand of fibrous tissue, which unites the lamina) as it passes through
them (fun'triilus ticlew). According1 to Schwalbe the strand thus described is merely connec-
tive tissue which accompanies the most lateral group of posterior ciliary arteries as they pierce
the sclerotic.

THE CORNEA.

The cornea, the transparent fore part of the external coat, admits light into the
interior of the eyeball. It is nearly circular in shape, but is slightly wider in the trans-
verse than in the vertical direction (about 12 mm. and 11 mm. diameter respectively) ;
its arc extends to about one-sixth of the circumference of the whole globe. The
cornea has a curvature of a smaller radius than the sclerotic : the degree of its curve
varies, however, in different persons, and at different periods of life in the same
person, being more prominent in youth than in advanced age. It is also normally
a trifle more curved in the vertical than in the horizontal plane. Its thickness is
in general nearly the same throughout, viz., 0*8 mm., excepting towards the
periphery, where it becomes somewhat thicker (1*1 mm.) The posterior concave
surface exceeds slightly in extent the anterior or convex, in consequence of the
latter being encroached on by the superficial part of the sclerotic ; the cornea being
overlapped by the sclerotic like a watch-glass by the edge of the groove into which
it is received (see fig. 15) ; the tissues of the two are, however, in complete
continuity. Around the junction a slight groove is apparent in the surface of the
globe (sulcits sclerce). The tissue of the cornea readily imbibes water and becomes
opaque after death.

STRUCTUBE OP THE CORNEA.

The cornea may be described as consisting of three parts — a stratified epithelium
in front (fig. 19, 1) continuous with the epithelium of the conjunctiva ; a middle
part, substantia propria, or cornea proper (3), continuous with the sclerotic, com-
posed of modified connective tissue ; and a homogeneous elastic lamella (4), bounding
it behind, and itself covered with a simple layer of endothelium cells (5).

Epithelium of the Cornea. — The epithelium covering the front of the cornea
is of the stratified kind, the cells being in man six to eight deep (fig. 18). The
lowermost cells (c) are columnar, with a flattened base, where they rest on the sub-
stantia propria, and a rounded apex, upon which a cell of the next layer fits. To
the base of each columnar cell is attached a broad, flattened, strongly refracting
process, which projects under one of the neighbouring cells (not shown in the
figure). Above these columnar cells are two or three layers of polygonal cells, some
of the deeper of which (the fingered cells of Cleland) have projections from their
under surface which fit between the cells below. These polygonal cells (p) have
well-marked denticulations, which join one another across the intercellular spaces
which separate the cells. Quite superficially is a stratum of flattened scaly
epithelium cells, which retain their nuclei.

The proper substance of the cornea is composed, as before said, of a modified
form of connective tissue, all the constituents of which have very nearly the same

VOL. III., PT. 3. C

18

THE EYE.

index of refraction, so that in the perfectly fresh condition it is difficult, even with
the best lenses, to make out any indications of structure. After death, however,
and with the assistance of reagents, the cornea may be ascertained to consist of
alternating lamellge of fibrous tissue (about sixty in number, according to Bowman),
the planes of which are parallel to the surfaces of the cornea. The fibres com-
posing the lamellae are nearly straight and have a definite direction in each layer ;
they cross one another at right angles in the alternate layers (fig. 19, b,d). It must,
however, be understood that the layers are not individually distinct, but give off
frequent offsets to those above and below, so that they cannot readily be stripped
away for any distance. The fibrils are collected into roundish bundles, which, as

Fig. 18. — VERTICAL SECTION THROUGH THE EPITHELIUM OP THE CORNEA, HUMAN. (E. A. S.)

Highly magnified.

c, deepest columnar cells ; p, polygonal cells, immediately above them ; /, flattened cells of the
surface.

The section is slightly broken on the right of the rigure. The intercellular channels bridged across
by processes extending from one cell to another are distinctly seen.

well as the laminae they form, are, as in the connective tissue elsewhere, separated
from each other by ground-substance. The latter is in greater abundance between
the fibrous strata than elsewhere, and in these parts the cell-spaces of the tissue are
found. These cell- spaces, which are readily demonstrated by staining the tissue
with nitrate of silver (fig. 20, B), are flattened conformably with the lamellae, are of an
irregularly stellate figure, and freely communicate by their offsets both with others
on the same plane and with those above and below. The greater regularity of
arrangement which characterises them, as compared with the cell-spaces of con-
nective tissue elsewhere, is dependent on the regularly laminated structure of the
cornea.

The corpuscles of the tissue — corneal corpuscles (fig. 20, A) — lie within the cell-
spaces, corresponding generally with them in form, but without entirely filling them,
the room left serving for the passage of lymph and lymph-corpuscles. The protoplasm
of the corpuscles is clear, except in the neighbourhood of the nucleus, where it is
more granular ; the cells send branching processes along the anastomosing canals of
the cell-spaces, which join with those of neighbouring corpuscles. In vertical
sections the corpuscles appear fusiform (fig. 19, c), but horizontal sections show
them to be flattened conformably with the surface.

The cell-spaces can be filled with fluid injection by inserting- the nozzle of a fine syringe
into the tissue, and employing1 a very low pressure ; in this way a network of anastomosing
stellate figures is obtained (cell-spaces, Recklinghausen's canals). If, however, the injection-
fluid is dense or too forcibly injected, it becomes extra va sated in the interstices of the
fibril-bundles, the direction of which it takes ; and the appearance is produced of minute
swollen tubular passages running at right angles to one another in the different layers
(Bowman's corneal tubes). This appearance may still more readily be obtained if air is
injected into the tissue instead of mercury (the fluid used by Bowman), and it is seen

THE CORNEA.

19

that the injection always stops at the margin of the cornea, where the tissue becomes
closer as it passes into the sclerotic, whereas Recklinghausen's canals are continued into
the cell-spaces of the sclerotic.

Frequently in advancing- age there occurs a deposit of fatty granules at the margin of the
cornea, forming a whitish opaque ring about 1mm. from the corneo-sclerotic junction. This
ring is known as the cm •///>•

Fig. 19. — VERTICAL SECTION

OF HUMAN CORNEA FROM
NEAR THE MARGIN. (Wal-

deyer.) Magnified.

1, epithelium ; 2, anterior
homogeneous lamina ; 3, sub-
stantia propria corneoe ; 4,
posterior homogeneous (elastic)
lamina ; 5, endothelium of the
anterior chamber ; a, oblique
fibres in the anterior layer of
the substantia propria ; b,
lamellae the fibres of which
are cut across, pi-oducing a
dotted appearance ; c, corneal
corpuscles appearing fusiform
in section ; d, lamellae the
fibres of which are cut longi-
tudinally ; e, transition to the
sclerotic, with more distinct
fibrillation, and surmounted
by a thicker epithelium ; /,
small blood-vessels cut across
near the margin of the cornea.

Membrane of Bow-
man.— The part of the
cornea immediately be-
neath the anterior epi-
thelium, for a thickness
of 0*01 mm. to 0'02 mm.,
is denser than the rest of
the tissue, and entirely
free from corpuscles (fig.
18, 2), (anterior homoge-
neous lamina, membrane
of Bowman). Although
described as a separate
formation it appears not
to differ materially in structure from the rest of the corneal substance, fibres from
which may be seen passing obliquely towards, and becoming lost within it
(fig. 19, a). It is thickest in the middle, thinning off gradually towards the edges
of the cornea.

The membrane of Descemet (fig. 19, 4) (membrane of Demours, posterior
elastic lamina, Bowman), not very closely united with the fibrous part of the cornea,
is transparent and glassy in appearance. It is firm and structureless, but very
elastic ; and when shreds are removed from it they tend to curl up with the
attached surface innermost. It is not readily affected by acids, by boiling in
water, or by maceration in alkalies, but under some conditions it can be split up
into very fine lamellae. In thickness it varies from 0*006 mm. to 0'012 mm., being
thinnest in the middle and thickening towards the margin. Here also there are

c 2

20

THE EYE.

apt to develop, in adult age, low papilliform projections on the inner surface of the
membrane ; with old age these become more marked and the whole membrane
becomes thicker, and may measure as much as 0*02 mm. It is lined next the anterior

Fig. 20. — A. CORPUSCLES OP THE CORNEA. FROM A PREPARATION TREATED WITH CHLORIDE OF GOLD.

(Waldeyer.)

B. CELL-SPACES OF THE CORNEA. FROM A PREPARATION STAINED WITH NITRATE OF SILVER

(Waldeyer.;

Fig. 21. — CELLS OF ENDOTHE-

LIUM OF BIRD'S CORNEA.

(After Smirnow and Nue'l. )

chamber with an en-
dothelium (fig. 10, 5),
which resembles that on
serous membranes, con-
sisting of a single layer
of flattened polygonal
cells with distinct nuclei.
These cells are fibrillar
in structure, being tra-
versed by bundles of fine
fibrils which pass from
cell to cell across the
intercellular spaces (fig.
21), and are probably formed by threads of protoplasm, for they undergo rapid
alteration, and very soon disappear after death or removal of the globe. (Nuel,
Smirnow.)

Near its circumference the membrane breaks up into bundles of fibres, which
give attachment to the ciliary muscle (see fig. 22), but a few fine fibres are continued
into the substance of the iris, around the angle of the anterior chamber. To these
radiating and anastomosing bundles of elastic fibres prolonged from the circum-

CANAL OF SOHLEMM.

21

ference of Descemet's membrane, the name ligamentum pectinatum was given by
Hueck. They are sometimes known as the pillars of the iris. The fibres which
pass to the iris are very much more marked in the eyes of the sheep and the ox
than in the human eye. The bundles of the ligamentum pectinatum are covered
with endothelial cells, continued from Descemet's membrane, but these cells do not
stretch across the intervals between the bundles, so that the cavity of the aqueous
chamber is prolonged into, and freely communicates with spaces in the tissue

tissue of insertion of canal of canal of

sderotic. ciliary muscle. Schlemm. Schlemm.

tissue of
cornea.

I

ciliary muscl

uveal pigment of iris.

iris stroma.

Fig. 22. — SUCTION (FROM THK EYE OP A MAN), SHOWING THE RELATIONS OF THE CILIARY MUSCLE TO

THE SCLEROTIC, IRIS, AND THE CAVERNOUS SPACES NEAR THE ANGLE OF THE ANTERIOR CHAMBER.

(E. A. S.)

The figure, which is copied from a photograph, includes only a small portion of the ciliary muscle,
the fibres of which are seen to be converging to a point immediately anterior to the angle of the
anterior chamber. Here they are attached through the medium of a tongue of fibrous tissue of the
sclerotic (consisting mainly of circular bundles) to the outer part of the ligamentum pectinatum, which
forms a loose tissue with open meshes lying between the canal of Schlemm and the anterior chamber.
To the right of the figure the fibres of the ligamentum pectinatum are seen to be gradually converging
towards the posterior surface of the cdrnea, and somewhat beyond the part shown in this figure they
merge into the membrane of Descemet, The communication of the canal of Schlemm, which is double
in this section, with the endothelial-lined spaces in the ligamentum pectinatum, is seen, as also the
communications between the last-named spaces and the anterior chamber.

between the bundles (fig. 22). These spaces are much larger and more distinct
in some animals than in man, and in them they have received the name of spaces
of Fontana. A similar, but rather larger space is found immediately in front of
the ligamentum pectinatum in the substance of the sclerotic, close to its junction
with the cornea. This circular space, which is elliptical in section, is known as the
sinus circular is iridis, or canal of Schlemm (fig. 22, 4).

THE EYE.

The canal of Schlemm is often double (fig-. 22) ; it communicates with the spaces between
the fibres of the ligamentum pectinatum. and through these with the aqueous chamber of
the eye. But, on the other hand, the canal of Schlemm, and the other cavernous spaces in
its neighbourhood, are in communication with the reins of the anterior part of the sclerotic,
and therefore the aqueous chamber must also through them communicate with the veins.
In support of this, it was found by Schwalbe that both the spaces and the veins became
filled with coloured fluid when this had been injected into the anterior chamber. Why blood
does not find its way into the latter during life is not explained, since no valves have as yet
been discovered in these veins or spaces : the reason given being, that greater resistance is
offered to its passage here than to its return by the ordinary paths.

According to Leber, on the other hand, the results obtained by Schwalbe were due to a
diffusible colouring matter having been emploj'ed for filling the anterior chamber. Leber
affirms that when a non-diffusible one is used it never penetrates into the canal of Schlemm.
which is simply a large circular terminal vein, or a collection of two or three plexif orm veins
uniting at frequent intervals into one trunk. It is admitted, however, that fluid may pass
with extreme readiness from the anterior chamber into these veins.

The study of the development of the eye shows that the loose tissue in which the spaces
of Fontana occur, as well as the endothelium of Descemet's membrane and the membrane
itself, belong to a vascular layer of mesoblast which is continuous with the choroidal layer
of the embryonic eye, but which as development proceeds, becomes separated from the vascu-
lar layer of the choroidal coat (iris and pupillary membrane), owing to the formation of the
anterior chamber ; it then comes to form part of the cornea.

Vessels and nerves. — In a state of health the cornea is not provided with
blood-vessels, except at the circumference, where the capillaries of the conjunctiva

Fig. 23. — CORNEA OF RABBIT,

VIEWED ON THE FLAT,
SHOWING THE SUBEPITHE-
LIAL PLEXUS ; CHLORIDE
OF GOLD PREPARATION.

(Ranvier.)

n, nerve of fundamental
plexus, giving off pencils of
fibrils, a, to form the subepi-
thelial plexus, e.

and sclerotic end in
loops. Neither are any
lymphatic vessels dis-
coverable, unless the
channels in which the
nerves run, and which
are lined with flattened
cells and are indirectly in
connection with the cell-
spaces, are to be taken as representing them. The nerves, on the other hand, are
very numerous. Derived from the ciliary nerves, they enter the fore part of the
sclerotic, and are from forty to forty-five in number (Waldeyer), forming a plexus
which surrounds the margin of the cornea (plexus annularis). Continued into the
fibrous part of the cornea, partly directly, partly by passing to the adjacent con-
junctiva, they retain their medullary sheath for 1 to 2 mm., and then, becoming
non-medullated, ramify and form a plexus in the laminated structure, near the
anterior surface. From this fundamental plexus branches pass obliquely through the
anterior homogeneous lamina, where they divide into pencils of fibrils, whose general
direction is towards the centre of the cornea, and which join with one another
to form a much finer and closer plexus immediately beneath the epithelium.
From this subepithelial plexus fine, varicose, fibrils pass among the epithelium-cells,
and form here a terminal ramification which extends almost to the free surface
(figs. 23, 24, and 25).

THE CHOROIP COAT.

In addition to the nerves which are destined for the epithelium, others, for
the proper substance of the cornea, come off from the primary plexuses, and,
after uniting into one or more secondary plexuses, the cords of which are still
composite, eventually form, in and among the laminag, a terminal ramification of
ultimate fibrils, the meshes of which are much more open than those of the intra-
epithelial network (see fig. 25). An actual connection of these nerves with the

Fig. 24. — VERTICAL SECTION OF RAB-
BIT'S CORNEA, CHLORIDE OF
GOLD PREPARATION. (Ranvier.)

n, r, parts of fundamental plexus ;
a, vertical branch passing to sub-
epithelial plexus, s ; p, b, inter-
epithelial ramification.

corpuscles of the cornea pro-
bably never occurs ; although,
since the fine nerve-fibrils
run in the anastomosing cell-
spaces, they come into close
connection with the cor-
puscles and their processes,

and they have therefore been described by some observers as being actually con-
tinuous with the latter.

The larger branches of the nerves are covered with a sheath of flattened cells
which, as before mentioned, are in connection with the corpuscles of the cornea. At

Fig. 25. — CORPUSCLES AND NERVES

IN THE SUBSTANTIA PROPRIA
OF THE CORNEA OF THE FROG;
CHLORIDE OF GOLD PREPARA-
TION. (Waldeyer.)

1, bundle of fundamental
plexus ; 2, nucleus ; 3, terminal
tibril ; 4, corneal corpuscles.

the points of junction of
the plexuses nuclei are
frequently seen (fig. 25, 2),
but these appear to belong
to the ensheathing cells, and
are not interpolated in the
course of the fibres.

THE VASCULAR COAT.

The vascular coat of the eye (tunica uvea s. vasculosa] lies within the corneo-
sclerotic coat, and consists of two parts, which are continuous with one another,
viz., the choroid and iris. The choroid is applied to the inner surface of the
sclerotic, and the retina is firmly attached to its inner surface ; the iris is attached
only at its circumference, otherwise floating freely in the aqueous humour imme-
diately in front of the lens, with which it comes lightly into contact, and separated
from the cornea by the depth of the anterior chamber.

The choroid coat (tunica choroidea) is a dark brown membrane (black in most
animals) lying bettf eet^ the sclerotic and the retina. Anteriorly it is continued into the
iris, but before it passes into this it forms a number of radial thickenings named ciliary

24 THE EYE.

processes, disposed in a circle and projecting into the anterior part of the vitreous
humour. These give attachment to the suspensory ligament of the lens. The
choroid coat is thickest behind, where it is pierced by the optic nerve. The outer
surface is connected to the sclerotic by loose connective tissue and by vessels and
nerves which pass obliquely across a lymph-space which otherwise serves to separate

Fig. 26.— CHOROID MEMBRANE AND IRTS EXPOSED BY THE REMOVAL OF THE SCLEROTIC AND CORNEA.
(After Zinn.) Twice the natural size.

a, part of the sclerotic thrown back ; b, ciliary muscle ; c, iris ; e, one of the ciliary nerves ; /, one
of the vasa vorticosa or choroidal veins.

Fig. 27. — CILIARY PROCESSES AS SEEN FROM BEHIND. Twice the natural size.

1, posterior surface of the iris, with the sphincter muscle of the pupil ; 2, anterior part of the
choroid coat ; 3, ciliary processes.

the two tunics. The inner surface, which is smooth, is covered by the hexagonal
pigmented cells of the retina. These, when the retina is detached, generally remain
partly adherent to the choroid, and were formerly described as belonging to that
coat, but they are now known to be intimately related, both morphologically and
physiologically, to the retina. The ciliary part of the choroid with the ciliary
processes is often spoken of as the ciliary body (corpus ciliare).

The ciliary processes (fig. 27), about seventy in number, are arranged
meridionally, and together form a circle. They consist of larger and smaller
thickenings without regular alternation. Each of the larger ones, measuring about
2*5 mm. in length and 0'6 mm. in depth, forms a rounded projection at its inner
(anterior) end, which is free from the pigment which invests the rest of the
structure ; but externally they gradually taper, and become lost. The smaller
processes are only half as deep as the others, and about one-third as numerous. At
and near the inner ends the processes are connected by lateral projections.

Structure of the Choroid. — The choroid consists mainly of blood-vessels
united by delicate connective tissue, which contains numerous large ramified and
pigmented cells.

Externally the choroid is bounded by a non-vascular membranous layer similar
to the lamina fusca of the sclerotic, and known as the lamina suprachoroidea. This
is composed of thin membranes of a homogeneous aspect, but pervaded by networks
of fine elastic fibres, and covered by large flat cells. It contains also large flattened
pigment-cells dispersed irregularly or arranged in patches, with considerable intervals

THE CHOEOID COAT.

25

free from pigment-cells ; and lymphoid cells may occur in it here and there singly
or in groups (fig. 28). It is loosely united to the lamina fusca by vessels and
bands of connective tissue enclosing pigment-cells, and the two laminae as well as the

Fig. 28. — A SMALL PORTION OP LAMINA SUPRA-CHOROIDEA. Highly magnified. (E. A. S.)

p, pigment-cells ; /, elastic fibres ; n, nuclei of epithelioid cells (the outlines of the cells are not
indicated) ; /, lymphoid cells.

uniting structures are coated with endothelium, a lymph-space being thus formed
between the sclerotic and choroid. This space communicates, at the places where
the vessels and nerves pierce the sclerotic, with that of the capsule of Tenon
(Schwalbe).

The choroid proper resembles in general structure the lamina suprachoroidea,
but contains in addition a very large number of blood-vessels. From a difference in
the fineness of these constituent vessels, it resolves itself into two strata, outer and

^T5

>:--&/*- "-2*^

jja^EL.. .TS^'-Jfes.^^-^

&*,

Fig. 29.— SECTION OF CHOROID. (Cadiat.)

a, membrane of Bruch : the chorio-capillaris is just above it ; b, vascular layer ; c, vein with blood-
corpuscles ; d, lamina suprachoroidea.

inner ; the former containing the larger branches, and the latter the capillary
ramifications. A layer of connective tissue containing many elastic fibres which
unites the two strata, and is nearly free from pigment, is sometimes described as a
third or intermediate part.

Tapetum. — This intermediate layer is markedly fibrous in some mammals, and shines
through the layer of choroid and retina in front of it, causing the appearance known as the
tapetum. In other mammals and in fish the appearance of a tapetum is produced or

26

THE EYE.

enhanced by a layer of iridescent endothelial cells, which becomes formed immediately within
the fibrous layer (Sattler).

In the outer part of the coat are situated, as just stated, the larger branches of
the vessels. The arteries (short ciliary) are comparatively large and numerous, and

Fig. 30. — LATERAL VIEW OF THE ARTERIES OF THE CHOROID AND IRIS, (From Arnold.)

a, optic nerve ; b, part of the sclerotic left behind ; c, region of ciliary muscle ; d, iris ; 1 , posterior
ciliary arteries piercing the sclerotic and passing along the choroid ; 2, one of the long ciliary arteries ;
3, anterior ciliary arteries.

Fig. 31. — LATERAL VIEW OF THE VEINS OF THE CHOROID. (From Arnold.)

1, 1, two trunks of the venae vorticosse at the piace where they leave the choroid and pierce the
sclerotic coat. The other lettering as in fig. 30.

piercing the sclerotic close to the optic nerve (figs. 30 and 32), divide into branches
which are directed at first forwards but soon bend obliquely inwards to end in the
capillary layer; whilst the veins external to the arteries are disposed in curves (vasa

Fig. 32. — INJECTED BLOOD-VESSELS OF
THE CHOROID COAT (from Sap-
pey). 30 diameters.

1, one of the larger veins ; 2,
small communicating vessels ; 3,
branches dividing into the smallest
vessels.

vorticosa) as they converge to
four or five principal trunks
(fig. 81, I,/; fig. 26), which
pierce the sclerotic about half
way between the margin of
the cornea and the entrance
of the optic nerve. In the
intervals between the vessels
are elongated and stellate pig-
ment-cells. The veins, like
those of the pia mater, have
no muscular tissue ; they are
enclosed by an adventitious sheath, between which and the endothelium, which
forms the wall of the vein, is a lymph-space (perivascular sheath). The arteries
have, besides the ordinary circular muscular fibres, strands of longitudinally
disposed plain muscular tissue in their adventitia. As the vense vorticosa3 pass
through the sclerotic they are ensheathed by a prolongation of suprachoroidal
tissue (Fuchs).

THE CHOROID COAT.

27

The inner part of the choroid coat (tunica Ruyschiana s. chorio-capillaris,
fig. 29) is formed mainly by the capillaries of the choroidal vessels. From the
ends of the arteries the capillaries radiate and form meshes which are closer than in
almost any other texture, being especially fine at the back of the eyeball, near the
yellow spot. The network reaches as far forwards as the ora serrata, where its
meshes become elongated, and join those of the ciliary processes.

The capillaries are embedded in a soft almost homogeneous tissue, and are stated
to be enclosed within extensions of the perivascular lymph-spaces of the choroidal
veins.

Fig. 33. — DIAGRAMMATIC REPRESENTATION OF THE COURSE OF THE VESSELS IN THE EYE. HORIZONTAL

SECTION. (Leber. ) ARTERIES AND CAPILLARIES RED; VEINS BLUE.

0, entrance of optic nerve ; a, short posterior ciliary arteries ; a', branch to the optic nerve ; 6,
long posterior ciliary arteries ; c, anterior ciliary vessels ; d, posterior conjunctival vessels ; d', anterior
conjunctival vessels ; e, central vessels of the retina ; /, vessels of the inner sheath of the optic nerve ;
</, vessels of the outer sheath ; h, vorticose vein ; i, short posterior ciliary vein ; I, anastomosis of
choroidal vessels with those of optic nerve ; m, chorio-capillaris ; n, episcleral vessels ; o, recurrent
artery of the choroid ; p, circulus iridis major (in section) ; g, vessels of iris ; r, vessels of ciliary
process ; s, branch from ciliary muscle to vorticose vein ; t, branch from ciliary muscle to anterior
ciliary vein ; u, canal of Schlemm ; v, capillary loop at margin of cornea.

Fig. 34. — VESSELS OF THE CHOROID, CILIARY PROCESSES, AND IRIS OF A CHILD. (Arnold.)

Magnified 10 times.

a, capillary network of the posterior part of the choroid, ending at b, the ora serrata ; c, arteries of
the corona ciliaris, supplying the ciliary processes, d, and passing into the iris, e ; ft the capillary net-
work close to the pupillary margin of the iris.

The veins begin by the convergence of the choroidal capillaries in a whorl-like
manner (fig. 32) to form venous tributaries, which themselves converge again in a
similar manner to form the large whorled veins or vense vorticosae, by which
the blood is conveyed away from the choroid coat.

28

THE EYE.

Fig. 35. — SECTION THROUGH THE CILIARY PART OF

THE EYE, INCLUDING PART OP THE CORNEA, THE
ORA SERRATA, THE IRIS AND THE EDGE OP THE
LENS WITH ITS SUSPENSORY LIGAMENT. Magnified.

(From Fuchs.)

C, cornea ; S, sclera ; Ch, choroidea ; JK, retina ;
Pe, its pigmented epithelium ; o, ora serrata ; 0,
pars ciliaris retinae ; this is continued over the ciliary
processes ; pe, pc, pigmented and non-pigmented

cells of pars ciliaris ; L, lens ; M, ciliary muscle ; >

r, its radiating fibres ; Mu, circular ciliary muscle ;

ci, anterior ciliary artery ; s, canal of Schlemm ; z, origin of ciliary muscle ; c,c, /,/, folds and
depressions in anterior surface of iris ; cr, a crevice in this surface (? artificial) ; sp, sphincter pupillse ;
p, edge of pupil ; P, most prominent part of ciliary process ; h, pigment behind iris (pars iridica
retinae), detached at V; a, bloodvessel ; z, zonula of Zinn ; z', z', its continuation on the suspensory
ligament ; i,i, spaces between the fibres of the suspensory ligament ; k, capsule of lens.

THE CILIARY PROCESSES.

29

On the inner surface of the tunica Ruyschiana is a structureless or finely
fibrillated transparent membrane, the membrane of Bruch (fig. 29, a), which
lies next to the pigmentary layer of the retina, and, especially anteriorly in
the region of the ciliary processes, presents on its outer surface numerous
microscopic reticulations. It tends to become thickened as age advances.

The ciliary processes (corpus ciliare) have the same structure as the rest of
the choroid ; but the capillary plexus of the vessels is less fine, and has meshes
with chiefly a longitudinal direction ; and the ramified cells, fewer in number, are
devoid of pigment towards the free extremities of the folds. The ciliary processes

tissue, of
sclerotic.

\

insertion of canal oj
ciliary muscle. Schlemm.

c<inal of
Schlemm.

tissue of
cornea.

I

ciliary muscle. uveal pigment of iris.

Fig. 36. — SECTION (FROM THE EYE OF A MAN), SHOWING

THE SCLEROTIC, IRIS,

(E. A. S.)

iris stroma.

THE RELATIONS OF THE CILIARY MUSCLE TO
AND THE CAVERNOUS SPACES NEAR THE ANGLE OF THK ANTERIOR CHAMBER.

The figure (which is copied from a photograph) includes only a small portion of the ciliary muscle,
the fibres of which are seen to be converging to a point immediately anterior to the angle of the anterior
chamber. Here they are attached through the medium of a tongue of fibrous tissue of the sclerotic
(consisting mainly of circular bundles) to the outer part of the ligamentum pectinatum, which forms
a loose tissue with open meshes lying between the canal of Schlemm and the anterior chamber. To the
right of the figure the fibres of the ligamentum pectinatum are seen to be gradually converging towards
the posterior surface of the cornea, and somewhat beyond the part shown in this figure they merge into
the membrane of Descemet. The communication of the canal of Schlemm, which is double in this
section, with the endothelial-lined spaces in the ligamentum pectinatum is seen, as also the communica-
tions between the last named spaces and the anterior chamber.

are penetrated for a certain distance by glandular invaginations of the pigmented
epithelium which covers their free surface (Collins). These ciliary glands probably
assist in the secretion of the aqueous humour.

The blood-vessels of the ciliary processes (fig. 34, d} are very numerous ; they
are derived from the anterior ciliary arteries and from the vessels of the fore part of

30

THE EYE.

the choroidal membrane, Several small arterial branches enter the outer part of each
ciliary process, at first running parallel to each other and communicating sparingly.
As they enter the prominent folded portion, the vessels become tortuous, subdivide
minutely, and inosculate frequently, Finally they form short arches or loops, and
turn backwards to pour their contents into the radicles of the veins. On the free
border of the fold, one artery, larger than the rest, extends the whole length of each
ciliary process, and communicates through intervening vessels with a long venous
trunk which runs a similar course on the attached surface.

Ciliary muscle. — The anterior part of the choroid, opposite the ciliary pro-
cesses, is considerably thickened. The thickening is triangular in section, and is
produced by a zone of plain muscular tissue, forming the ciliary muscle (Bowman)
(tensor choroidecz, Bruecke). The main part of this muscle arises (figs. 35, 36) by
a thin flat expansion from the fore part of the sclerotic close to the cornea, between

A Fig. 37. — DIAGRAMS SHOWING THK

COMPARATIVE: DEVELOPMENT OF

THE CIRCULAR FIBRES OF THE
CILIARY MUSCLE IN

A, the normal or emraetropic eye ;

B, the hypermetropic eye ; and

C, the myopic eye. (Fuchs. )

the canal of Schlemm and the
anterior chamber, its fibres
being attached to the bundles
of the ligamentum pectinatum
which occupies this position.
The muscular fibres, spread-
ing radially (meridionally),
are directed backwards (fig.
35, M), to be inserted into
the choroid coat opposite to
the ciliary processes, and
partly further back. At their
insertion the fibres pass
obliquely and inter-cross so
as to form peculiar stellate
figures. According to Wal-
deyer, a small portion (the
outermost) is sometimes in-
serted into the sclerotic coat,1
but this must be very rare,
for the sclerotic always be-
comes detached with the

greatest ease from this part of the muscle. The radial fibres pass towards the iris
into a ring of fibres (fig. 35, Mu\ which have a circular course around the insertion
of the iris. This set forms the circular ciliary muscle of H. Miiller and is much
developed in hypermetropic eyes, but atrophied, or even absent altogether, in myopic
(Iwanoff) (fig. 37). It was formerly described as the ciliary ligament. In birds the
ciliary muscle is composed of cross-striped muscular fibres. When the ciliary muscle
contracts it tends to draw the choroid and ciliary processes forwards and inwards.

1 This part, if present, is the homologue of an important portion of the ciliary muscle of birds
which is known as the Cramptonian muscle.

THE IRIS. 31

The suspensory ligament of the lens is thus relaxed and the lens becomes more
convex.

The nerves of the choroid will be described with those of the iris.

The iris is the contractile and coloured membrane which is seen behind the
transparent cornea, and gives the tint to the eye. In its centre it is perforated by
an aperture — the pif/»i/.

At its circumferential border, which is nearly circular, the iris is continuous
with the choroid, and by the ligamentum pectinatum, with the cornea : the free
inner edge is the boundary of the pupil. The iris measures about 11 mm. across,
and, in a state of rest, about 5 mm. from the circumference to the pupil (slightly
less on the nasal side) : its thickness is about 0'4 mm. The anterior surface,
variously coloured in different eyes, is marked by waved lines converging towards the
pupil, near which they join in a series of irregular elevations ; and, internal to these,
other finer lines pass to the pupil. The appearance is produced by the sub-
jacent blood-vessels. The posterior surface is covered with dark pigment cells (pars
retinalis), and is marked by a number of fine converging folds or thickenings
prolonged from the ciliary processes.

Fig. 38. — CILIARY PROCESSES AS SEEN FROM BEHIND.
(Twice the natural size.)

1 , posterior surface of the iris, with the sphincter muscle
of the pupil ; 2, anterior part of the choroid coat ; 3, ciliary
processes.

The pupil is nearly circular in form, and is
usually placed a little to the inner side of the
centre of the iris. It is constantly varying in
size during life, the variation ranging from 1 mm.
to 8 mm. It is habitually wider in young than
in old persons.

Structure of the iris. — A delicate connective tissue forms the framework or
stroma of the iris (fig. 39). It contains also very numerous vessels and nerves.
The endothelial layer of the membrane of Descemet (fig. 36) is continued from
the margin of the cornea over the front of the iris ; its cells are smaller and more
granular than those which cover the membrane of Descemet, but are otherwise
similar. Depressions of some size have been described in this anterior surface of
the iris (Fuchs, Nue'l and Cornil): these have been termed stomata, but it is
doubtful if they are analogous to the openings of the same name which occur in
serous membranes and communicate with subjacent lymphatics. The posterior
surface of the iris is covered by a layer of pigmented epithelium two or three cells
deep. This is continuous with the (retinal) pigmentary layer covering the ciliary
processes, and ends abruptly at the margin of the pupil ; it forms what is known as
the pars retinalis iridis (pars iridicaretince), as distinguished from the pars choroidalis
or stroma.

The stroma consists of cells and fibres of connective tissue, the latter directed
for the most part radially towards the pupil. In the substance of the iris anteriorly
and throughout its thickness are variously-shaped ramified pigment cells like those
in the choroid. The pigment contained in them is yellow, or of lighter or darker
shades of brown, according to the colour of the eye. The colour of the iris depends
partly on the pigment in the cells of the pars retinalis, partly on that in the stroma
cells ; in the eye of the infant and in the different shades of blue eye it arises
from the black pigment of the posterior surface appearing more or less through the

32

THE EYE.

stroma, which in such cases is only slightly coloured or is colourless ; but in the
black, brown, and grey eye, the colour is due to the pigment cells scattered through
the substance of the stroma itself.

The muscular tissue of the iris is disposed as a ring (sphincter pupillce)
around the pupil, and as rays (dilatator pupillcc) from the sphincter to the
circumference.

^b

sir.

str.

Fig. 39. — Two SECTIONS OP THE HUMAN IRIS : A, RADIAL ; B, TAKEN ACROSS THE RADII (G-. Retzius).

HIGHLY MAGNIFIED.

6, basement membrane and endothelium of anterior surface; sir., stroma; s. , bundles of fibres
of sphincter pupillae, cut across (in A) ; d, layer of dilatator papillae ; r, pigment (pars iridica
retinae).

The sphincter muscle (fig. 35, sp ; 39, s, and fig. 40, a) is a narrow band about
0'5 mm. wide, situated close to the pupil posteriorly and consisting of a number
of bundles of plain muscular tissue running concentrically with the margin of
the pupil. Here the bundles are closely arranged, but further from the margin
they are more separated, and form less complete rings.

The ditator (b\ less apparent than the sphincter, begins at the ciliary or
outer margin of the iris, and its fibres form a continuous membrane close to the
posterior surface, converging towards the pupil. Here they bend round and blend
with the sphincter, some reaching nearly to its inner margin. At their origin
at the ciliary margin, they also arch round and take a somewhat circular
direction.

The majority of recent writers on the subject have failed to find evidence of the existence
of a distinct layer of dilatator fibres and have consequently denied its existence in man and

VESSELS OF THE IRIS.

mammals. It is admitted, however, to be well developed in birds (where like the intraocular
muscular tissue generally it is of the striped variety) and, amongst mammals, in the otter.
Other writers have strenuously contended for the existence of a dilatator muscle. I have
myself. obtained unmistakeable evidence of the presence of a thin layer of fibres at the back of
the iris, under the pigment-cells, having all the appearance of flat plain muscle-cells. Recently
physiological proof of the existence of dilatator fibres has been furnished in the cat and
other animals by the experiments of Langley and Anderson.

The choroidal part of the iris is often described as bein^ bounded on its anterior and

Fig. 40. — SEGMENT OF THE IRIS, SEEN FROM THE

POSTERIOR SURFACE AFTER REMOVAL OF TIIK
t VEAL PIGMENT (Iwanoff).

a, sphincter muscle ; 6, dilatator muscle of the
pupil.

posterior surfaces by special layers, which have

been termed the anterior and posterior limiting

or hyaline layers. Of these, the anterior layer

is merely the superficial part of the general

stroma, having the fibres and cells somewhat

more closely arranged ; and what has usually

been described as the posterior is probably the

thin muscular sheet of the dilatator pupillce.

There may, however, be a thin membrane corresponding to the membrane of Bruch of the

choroid immediately underlying the epithelium of the pars retinalis.

Vessels of the iris (figs. 30 to 34, and fig. 41). — The long ciliary arteries,
two in number, pierce the sclerotic a little in advance, and one on each side, of
the optic nerve. Having gained the interval between the sclerotic and choroid
coats, they extend horizontally forwards covered by loose connective tissue to the
ciliary muscle. In this course they lie nearly in the horizontal plane of the axis of
the eye-ball, the outer vessel being a little above, and the inner one a little below
the level of that line. A little behind the attached margin of the iris, each vessel

Fig. 41. — FRONT VIEW OF THE BLOOD-VESSELS

OF THE CHOROID COAT AND IRIS FROM

BEFORE. (Arnold.) Magnified 2| times.

A, choroid ; B, iris ; c, ciliary muscle ;
1,1, long ciliary arteries ; 2, 2, five of the
antei'ior ciliary arteries ramifying at the
outer margin of the iris ; 3, loop of com-
munication between one of the anterior and
one of the long ciliary arteries ; 4, internal
circle and network of the vessels of the iris ;
5, external radial network of vessels.

divides into an upper and a lower
branch, and these, anastomosing
with the corresponding vessels on
the opposite side and with the an-
terior ciliary, form a vascular ring
(circulus major, fig. 33, p, fig. 41 , 3)
in this situation. From this circle
small branches arise to supply the

ciliary muscle ; whilst others converge towards the pupil, and there, freely com-
municating by transverse offsets from one to another, form a second circle of
anastomosis (circulus minor}, from which capillaries are continued inwardly and end
in small veins.

The anterior ciliary arteries (fig. 33, c, fig. 41, 2, 2), five or six in number,
but smaller than the vessels just described, are supplied from the muscluar and
lachrymal branches of the ophthalmic artery, and pierce the sclerotic about

VOL. III., PT. 3. D

THE EYE.

2 mm. behind the margin of the cornea ; they divide into branches which supply
the ciliary processes, and join the circulus major.

Fig. 42. — PUPILLARY MEMBRANE OF NKW-BORN KITTEN,
INJECTED. (Kiilliker, from a preparation Ly
Thiersch.) Magnified.

Besides these special arteries, numerous
minute vessels enter the iris from the ciliary
processes.

The veins of the iris follow closely the
arrangement of the arteries just described.
The canal of Schlemm communicates with
this system of vessels.

Pupillary membrane. — In the foetus the
pupil is closed by a thin transparent vascular mem-
brane, the vessels in which are continued from
those of the iris and of the capsule of the lens
(which is also vascular in the foetus). Near the
middle of the pupil the vessels of the membrane loop round, leaving- the centre free from
vessels. They disappear in the seventh or eighth month of fcetal life, becoming1 obliterated
from the centre towards the circumference, and the membrane itself is gradually absorbed in
like manner. A few shreds may still remain at birth : sometimes the whole membrane persists.

Nerves of the choroid and iris. — The ciliary nerves (fig. 43), about fifteen
in number, and derived from the ciliary ganglion and the nasal branch of the

.--Anterior ehcwnber

It-is

Fig. 43. — DIAGRAM SHOWING THE PRINCIPAL NERVES AND BLOOD-VESSELS OF THE EYEBALL. (Testut. )

ophthalmic division of the fifth nerve, pierce the sclerotic near the entrance of the
optic nerve, and come immediately into contact with the choroid. They are some-

THE EETINA. 35

what flattened in form, are partly imbedded in grooves on the inner surface of the
sclerotic, and communicate occasionally with each other before supplying the cornea
and entering the ciliary muscle. When the sclerotic is carefully separated from
the subjacent structures, these nerves are seen lying on the surface of the choroid,

Fig. 44. — DISTRIBUTION OF NERVES IN THE IRIS
(Kblliker). 50 DIAMETERS.

The preparation was from the eye of an albino
rabbit ; a, smaller branches of the ciliary nerves
advancing from the choroid ; b, loops of union
between them at the margin of the iris ; c,
arches of union in the iris ; c', finer plexus in
the inner part ; e, sphincter pupil! te muscle.

into which they send branches, and
in which they form a gangliated plexus
amongst the blood-vessels, the groups

of ganglion-cells being often applied to the walls of the vessels. Within the
ciliary muscle the nerves also subdivide minutely, forming here another plexus,
which contains a number of medullated fibres, and the cells of which are smaller.
A few recurrent branches appear to pass back from it into the choroid coat, but
the greater number pass on to the iris (fig. 44, #, a). In the iris the nerves
follow the course of the blood-vessels, dividing into branches, which communicate
with one another as far as the pupil, forming a close plexus of fine non-medullated
fibres. Their ultimate destination is probably mainly the muscular tissue of the
iris and of its vessels.

THE RETINA.

The retina is a delicate membrane, which contains the expanded termination of
the optic nerve. It lies within the choroid coat, and rests on the hyaloid membrane
of the vitreous humour. It extends forwards nearly to the outer edge of the ciliary
processes of the choroid, where it ends in an indented border, named ora serrata
(fig. 45). From this border there is continued onwards a thin layer of a different
structure and containing no nerve-fibres, the pars ciliaris retince, which reaches as
far as the tips of the ciliary processes, and there gives place to the double layer of
pigment known as the urea, which is continued on to the posterior surface of the
iris (pars iridica retince). The thickness of the retina diminishes from behind
forwards, from 0*5 mm. near the yellow spot to 0*1 mm. at the ora serrata. In
the fresh eye it is translucent and of a light pink colour, but of a purple-red
colour if kept in the dark for a little while before removal. Under the influence
of sunlight it is quickly bleached and after death it soon becomes opaque. The
colouring matter was discovered by Boll and has been specially investigated by
Kiihne, who has given it the name of rhodopsin, It is absent at the yellow spot
and central fovea, and also close to the ora serrata. The outer surface of the
retina is covered with a layer of hexagonal pigment-cells which send fine offsets
between the elements of the next retinal layer : the rhodopsin becomes developed in
this layer by the agency of these pigment-cells. When the choroid is detached
these offsets are ruptured and the pigment-cells come away with it, so that this layer
was formerly described as part of the choroid coat.

The inner surface of the retina is smooth : on it the following objects may be
seen. In the axis of the ball is a yellow spot— macula lutea (Umbiis luteus,
Sommerring) — which is somewhat elliptical in shape (fig. 45), and about 1 to 2 mm.
in diameter : in the centre of this, again, is a slight hollow, fovea centralis, 0'2 mm.
to 0-4 mm. in diameter (fig. 45), and, as the retina is thinner here than elsewhere,

D 2

36 THE EYE.

the pigmentary layer is more clearly visible through it in the dead condition, giving
rise to an appearance as of a hole through the tunic. About 3 mm. inside the
yellow spot and about 1 mm. below the level of a horizontal line through the
posterior pole of the eyeball is a pale, round disc, poms options (figs. 46 and 47),

EPITHELIUM^
CONJUNCTIV/Ejj

MUSCULUS
CIUARIS^

ARTERIA /

CENTRALIS /—

RETIN/E /'/'

r.-DURAt. SHEATH

Fig. 45. — RIGHT ADULT HUMAN EYE, DIVIDED HORIZONTALLY THROUGH THE MIDDLE.
(Magnified five times.)

The line a b passes through the equator, x y through the visual axis of the eye.

where the optic nerve pierces the retina and expands to form its inner layer. The
circumference of the disc is slightly elevated to form an eminence (colliculus nervi
opt id) (fig. 45) and in its centre, which often shows a well-marked depression, is
the point from which the vessels of the retina branch.

THE RETINA.

37

When examined during life by the aid of the ophthalmoscope, the optic disc appears
of a light grey tint, contrasting strongly with the red colour of the rest of the field. In
the central depression of the disc are remnants of the tissue which, iu the foetus, accom-

nasal

temporal

FIG. 46. — VIEWS OF THE POSTERIOR PART OF THK RETINA. Variously magnified.

A. — The posterior half of the retina of the left eye, viewed from before. (Henle.) Twice the
natural size.

s, cut edge of the sclerotic ; ch, choroid ; r, retina : in the interior at the middle the macula lutea
with the depression of the fovea centralis is represented by a slight oval shade ; towards the left side
the light spot indicates the colliculus or eminence at the entrance of the optic nerve, from the centre
of which the arteria centralis is seen sending its branches into the retina, leaving the part occupied by
the macula comparatively free.

B. — Fundus of the eye, as seen with the ophthalmoscope. (Jaeger.) Somewhat magnified,
n, a, arteries ; v, v, veins ; /, fovea.

C. — The point of entrance of the optic nerve as seen with the ophthalmoscope. (Jaeger.) Magnified
still more.

A, optic nerve, passing through the lamina cribrosa, L, which shows through the disc-like expansion
of the entering nerve ; a, ring of connective tissue ; b, choroidal ring ; c, branches of the central artery
of the retina, y ; d, branches of the central vein, // ; n, inner or nasal side ; t, outer or temporal side.

38

THE EYrE.

panied the prolongation of the .central artery of the retina along the canal of Stilling
(fig. io) through the vitreous body to the capsule of the lens ; in some eyes this tissue can
be followed for some distance into the vitreous humour.

n se par fa

Fig. 47. — SECTION THROUGH THE PLACE OP ENTRANCE OF THE OPTIC NERVE (B), TOGETHER WITH THE

OPHTHALMOSCOPIC VIEW OF THE DISC (A), TO SHOW THE CORRESPONDING PARTS OF THE TWO.

(Fuchs, after Jaeger. )

c, d, lines of correspondence ; b, depression in centre of disc ; r, retina ; ch, choroid ; si, so, inner
and outer parts of the sclerotic coat, s : ci, a ciliary artery cut longitudinally ; a, r, central artery and
vein ; sd, subdural space ; sa, subarachnoid space ; du, dural sheath ; ar, arachnoidal sheath of nerve ;
p, pial sheath : n, nerve bundles ; se, septa between them.

MICROSCOPIC STRUCTURE OP THE RETINA.

"When vertical sections of the retina, i.e., sections made perpendicularly to its
surface, are submitted to microscopic examination, eight distinct; strata are recog-
nizable, together with certain fibrous structures which pass vertically through the
membrane and connect the several layers.

The following are the designations of the layers, from within outwards : —

1. The layer of nerve-fibres (stratum opticum).

2. The layer of nerve-cells (ganglion nervi optici).

3. The inner molecular layer (stratum reticulare internum}.

4. The inner nuclear layer (stratum granularum internum, ganglion retinae).

5. The outer molecular layer (stratum reticulare externum).

6. The outer nuclear layer (stratum granularum externum).

7. The layer of rods and cones (stratum bacillorum).

8. The layer of hexagonal pigment cells (stratum nigrum).

In addition to these eight strata two very delicate membranes have been
described — the one, membrana Umituns interna, bounding the retina on its inner
surface, next to the hyaloid membrane of the vitreous humour ; the other, memlrana

MICROSCOPIC STRUCTURE OF THE RETINA.

limitans externa, lying between the outer nuclear layer and the layer of rods and
cones ; but, as will be afterwards explained, these so-called " membranes " are merely
the boundary lines of the sustentacular tissue of the retina. The accompanying
figure, from Max Schultze, represents diagrammatically the general arrangement of
the layers (fig. 48).

The several layers of the retina will first be considered successively as they are
met with from within out, after which the sustentacular fibres or fibres of Miiller,
which traverse several of the layers, and the connection of the nervous elements

Outer or choroidul surface.

. Layer of pigment cells.
7. Layer of rods and cones.
..Membrana limitans externa.

) 6. Outer nuclear layer.

5. Outer molecular layer.
\ 4. Inner nuclear layer.

3. Inner molecular layer

2. Layer of nerve-cells.

1. Layer of nerve-fibres.

. . . Membrana limitans interim

Inner or vitreous surface.

Fig. 48. —DIAGRAMMATIC SECTION OF THE HUMAN RETINA (Schultze).

throughout the retina with one another will be described. Finally an account will
be given of those parts of the retina which present points of difference from the rest,
especially the central fovea, and the ciliary part.

1. Layer of nerve-fibres. — The optic nerve passes at the porus opticus
directly through the thickness of the retina to reach its inner surface (fig. 47)
on which it spreads out in the form of a membrane which extends to the ora
serrata. Its fibres, which are destitute of a primitive sheath and vary much in
size, but are mostly small, lose their medullary sheath on reaching the retina,
consisting there normally of axis-cylinder only (Bowman). In rare cases some of
them may retain their medullary sheath for a short distance. They are collected

THE EYE.

into small bundles, which, compressed laterally, intercommunicate and form a
delicate web with narrow elongated meshes (fig. 49). At the yellow spot this layer
is almost wanting, and indeed it ceases at the central fovea, but elsewhere it forms
a continuous stratum, gradually diminishing in thickness in front, interrupted only
by the enlarged ends of the fibres of Miiller to be afterwards described (fig. 48, 1).
The nerve-bundles, as well as the cells of the next layer, are partially supported by
neuroglia-cells (spider-cells). Most of the fibres are continuous with the axis-
cylinder processes of the cells of the next layer (fig. 50, i.), but some are con-
tinued through the second and third layers, and end by ramifying either in the
inner molecular layer or amongst the elements of the fourth layer (inner granules),
the terminations being frequently somewhat knobbed or enlarged (fig. 50, i., m).

2. Ganglionic layer. — Immediately external to the nerve-fibre layer is a
stratum of nerve-cells (fig. 48, 2), having in the fresh condition a pellucid aspect.
The cells vary much in size and in figure, some being spheroidal, others more pyri-
form. Each cell has a single unbranched nerve-fibre process extending obliquely

Fig. 49. — MAGNIFIED VIEW OF THE INNERMOST LAYER OF THE RETINA, SHOWING THE BUNDLES OF

C'l'TIC NERVE FIBRES RADIATING FROM THE PAPILLA. (Merkel.)

from its rounded inner extremity amongst the fibres of the preceding layer, with
one of which it is continuous. From the opposite end of the cell, which is fre-
quently imbedded in the substance of the succeeding layer, one, two, or more much
thicker protoplasmic processes extend outwards for a variable distance into that
stratum, and branch in its substance (fig. 50, v., vi., vn.). The branching occurs
at different levels for different cells, the smaller cells as a rule having the terminal
ramification of their protoplasmic processes nearer the ganglionic layer, the larger
ones nearer the inner nuclear layer. The arborisations are mostly flattened
conformably with the retinal strata, and in sections of retina produce the appearance
of coarse lines in the molecular stratum. The number of nerve-cells and con-
sequently the thickness of the ganglionic layer in the different regions of the retina
varies largely. Over the greater part of the retina they form a single stratum,
but in the neighbourhood of the yellow spot they are placed two or three deep. At
the spot itself (fig. 60, 2) they are very thickly set ; the cells are also smaller here.
Towards the ora serrata, on the other hand, there is but a single stratum, and that
frequently incomplete.

LAYERS OF THE RETINA. 41

The gang-lion-cells of the retina may be classed into those the protoplasmic or peripheral
processes of which ramify in a diffuse manner in the inner molecular layer, and those the
protoplasmic processes of which are ramified horizontally in one or more of the strata of that
layer, where they interlace with similar ramifications from the cells of the inner nuclear layer.
The diffusely ramifying- cells (fig-. 50, VII., •/) are usually small and with slender processes, and
this is also the case with some of the cells with stratified processes (fig. 50. v.. <i ; vi., e], but
many of the latter are larger, sometimes very large (giant cells), and with comparatively
coarse processes.

The cells with stratified processes are classified by R. y Cajal according to the stratum of
the inner molecular layer in which these processes ramify. Some ramify, however, in two.
and even in more layers (bi- and multi-stratified). Three types of the stratified cells can
usually be distinguished. They mav be termed ///v.7. xc<-o/i<L and third, or from their relative
size, hirt/c. »//'rfiini/. and xm«/I, and some of each type appear to belong, as regards the dis-
tribution of their arborescence, to each stratum of the inner molecular layer.

I-'irxt t !/]»'. — Those of the large type have a thick axis-cylinder process and one, two, or
more coarse protoplasmic processes, varying in vertical extent in different cells according to
the stratum of the inner molecular layer for which they are destined. Their terminal
arborescences extend over a considerable area, and are open in nature. The largest cells of this
type (giant cells) send their processes to the outer strata of the molecular layer (fig. 53, vii.,
ii. c. c*) ; processes to the inner strata come from cells of the same type but of smaller size.

Second type. — The ganglion-cells of this type (fig. 50, vi., vn., /, y, A) vary in size of
cell-body, but are usually smaller than those of the first type, and of pyriform shape, the stalk
of the pear being directed outwards for a variable distance in the molecular layer according
to the position within this of the terminal arborescence. The latter is composed of moderately
fine varicose filaments which form a compact, closely interwoven ramification, occupying some
thickness of the molecular layer, the arborescence being less flattened out than is the case
with those from many of the cells of the first and third types.

Third t;/jn'. — This is represented by cells usually pyriform with small cell-bodies and
correspondingly fine moderately arborescent processes which may radiate from the end of a
straight outwardly directed stalk, as in the case of those which ramify in the outer strata of
the molecular layer (fig. 50, vi., «)> or maJ spring in a similar radiating manner from the body
of the cell itself, as with those ramifying in the inner strata (fig. 50, vn.. b~).

3. Inner molecular or inner plexiform layer, neurospongium. — Next in
order to the ganglionic layer comes a comparatively thick stratum of a granular-
looking1 substance, which as preparations treated by the methods of Ehrlich or of
Golgi show, is mainly made up of the arborescent terminations of the processes of
the cells in the layers which bound it internally and externally. A few branched
cells, apparently of nervous nature, occur within the layer (fig. 50, in.) ; these are
probably allied to the amacrine cells of the layer next to be described. The inter-
laced arborisations of the ganglion-cells, amacrine cells, and bipolars form within it
definite strata which, according to R. y Cajal, are altogether five in number. There
are a few blood-vessels in this layer, and the fibres of Muller pass through it as fine
vertical filaments with delicate lateral offsets.

4. Inner nuclear layer. — This is composed of a number of closely-packed
cells, which are frequently known collectively as the " inner granules," but are of
several distinct kinds. Some are bipolar nerve-cells, and it is the presence of these
which has led to the name ganglion retina being applied to this layer. They occupy
the bulk of the stratum and send processes inwards and outwards into the respective
molecular layers. Others are multipolar nerve-cells, the processes of which ramify
in the molecular layers ; they form incomplete strata close to and partly imbedded
in the molecular layers. Others, again, are nucleated enlargements belonging to the
fibres of Muller. The structure and arrangements of each of these elements must
be separately considered.

a. Bipolar -celh. — These, by far the most numerous, are round or oval clear cells
(fig. 50, i., in. ; fig. 51, 4), prolonged at either end into a fibre.

Of the processes or fibres which proceed from these cells, the inner one, or that
extending into the inner molecular layer, is finer than the other, is always unbranched
until reaching that layer, and often exhibits varicosities similar to those on nerve-

THE EYE.

Fig. 50.

INNER NUCLEAR LAYER OF THE RETINA. 43

fibrils. It is regarded as the axis-cylinder process of the cell, and extends usually
to the inner part of the internal molecular layer, within which it ends in a terminal
ramification of varicose fibrils which is frequently in close proximity to the outer
surface of one or more of the ganglion-cells of the layer. The outer prolongation
or process of the bipolar cell is not varicose, is usually thicker than the inner one,
and in some cases passes undivided into the next layer, in others divides before
reaching it. Having arrived at the outer molecular layer it breaks up into an
arborisation within this layer, which is interlaced with arborisations of fibres
belonging to the horizontal cells presently to be described, and with the termina-
tions of the rod- and cone-elements of the bacillary layer. It has been shown
by R. y Cajal that the bipolars are of at least two kinds, distinguishable by
the character of the terminal arborescence of the outwardly-directed protoplasmic

Fig. 50. — ELEMENTS OF THE RETINA OF MAMMALS DISPLAYED BY THE CHROMATE OF SILVER METHOD

OF GOLGI. (Cajal.)

I. Section of the dog's retina, a, cone-fibre ; 6, rod-fibre and nucleus ; c, d, bipolar cells (inner
granules) with vertical ramification of outer processes destined to receive the enlarged ends of rod-fibres ;
e, bipolars with flattened ramification for ends of cone-fibres ; /, giant bipolar with flattened ramifi-
cation ; ff, cell sending a neuron or nerve-fibre process to the outer molecular layer; h, amacrine cell
with diffuse arborisation in inner molecular layer ; i, nerve fibrils passing to outer molecular layer ;
j, centrifugal fibres passing from nerve-fibre layer to inner molecular layer ; ra, nerve-fibril passing into
inner molecular layer ; n, ganglionic cells.

II. Horizontal or basal cells of the outer molecular layer of the dog's retina. A, small cell with
dense arborisation ; B, large cell, lying in inner nuclear layer but with its processes branching in the
outer molecular ; a, its horizontal neuron ; C, medium sized cell of the same character.

III. Cells from the retina of the ox. a, rod-bipolars with vertical arborization ; b, c, d, e, cone-
bipolars with horizontal ramification ; f, y, bipolars with very extensive horizontal ramification of
outer process ; h, cells lying on the outer surface of the outer molecular layer, and ramifying within it ;
i, j, m, amacrine cells within the substance of the inner molecular layer.

IV. Neurons or axis-cylinder processes belonging to horizontal cells of the outer molecular layer, one
of them, b, ending in a close ramification at a.

V. Nervous elements connected with the inner molecular layer of the ox's retina. A, amacrine cell,
with long processes ramifying in the outermost stratum ; B. large amacrine with thick processes
ramifying in second stratum ; C, flattened amacrine with long and fine processes ramifying mainly in
the first and fifth strata ; D, amacrine with radiating tuft of fibrils destined for third stratum ; E,
large amacrine, with processes ramifying in fifth stratum ; F. small amacrine, branching in second
stratum ; Gr, H, other amacrines destined for fourth stratum ; a, small ganglion-cell sending its
processes to fourth stratum ; 6, a small ganglion-cell with ramifications in three strata ; c, a small cell
ramifying ultimately in first stratum ; d, a medium sized ganglion-cell ramifying in fourth stratum ;
e, giant cell, branching in third stratum ; /, a bi-stratified cell ramifying in second and fourth strata.

VI. Amacrines and ganglion-cells from the dog. A, amacrine with radiating tuft ; B, large amacrine
passing to third stratum ; C and Gr, small amacrines with radiations in second stratum ; F, small
amacrine passing to third stratum ; D, amacrine with diffuse arborisation ; E, amacrine belonging to
fourth stratum ; a, d, e, y, small ganglion-cells, ramifying in various strata ; i, f, large ganglion- cells,
showing two different characters of arborisation ; /, bi-stratified cell.

VII. Amacrines and ganglion-cells from the dog. A, B, C, small amacrines ramifying in middle of
molecular layer ; b, d, y, h, i, small ganglion-cells showing various kinds of arborisation ; ft a larger
cell, similar in character to #, but with longer branch ; a, c, e, giant cells with thick branches ramifying
in the first, second, and third layers ; L, L, ends of bipolars branching over ganglion-cells.

process, and by the position in the internal molecular layer in which the axis-
cylinder process terminates. In one kind this arborescence is composed of a
dendritic tuft of vertical fibrils, somewhat varicose and enclosing amongst them the
end-knobs of several (3 to 20) of the rod-fibres of the bacillary layer ; and the axis-
cylinder process ends in a varicose ramification over a body of a cell of the
ganglionic layer. These may be termed, therefore, the rod-bipolars, or bipolars with
vertical arborescence (fig. 50, i., c ; in., a). In the other kind (cone-bipolar s) this
terminal arborescence is horizontal (fig. 50, I., e ; in., b, c, d, e), and abuts against
or interlaces with the ramified foot of one or more cone-fibres, and the axis-cylinder
process usually extends to a less depth of the internal molecular layer, and is not
constant in position as is that of the rod-bipolar ; the axis-cylinder process of either
kind may give oif short collaterals in traversing the inner molecular layer. Some of

44

THE EYE.

the cone-bipolars have their horizontal arboresceiice extending over a large area of
the outer molecular layer (fig. .")(), i.,/, in.,/, y)9 and probably come into contact with a
considerable number of cone-feet.

In birds, reptiles, and amphibia some of the bipolar cells— probably correspond-
ing to those described above as cone-bipolars— give oft' from their arboresceiice
within the outer molecular layer an uubranched irregularly varicose fibril as far as
and just beyond the meinbrana limitans externa (fibril of Land oil,}, where it usually
ends in a clavate enlargement (fig. 51, E). According to Cajal it is absent in
mammals and teleosteans.

The relative length of the inner and outer process of the bipolars naturally
differs according to the position of the individual cell in the nuclear layer : if the
cell is near the inner molecular layer the outer process will have a longer course to
reach the outer molecular layer, and, conversely, if the cell is near the latter. At
and near the central fovea these processes or fibres of the inner nuclear layer have a

Fig. 51. — SECTION OF

KKTJXA, PREPARE!) BY
GOLGl's METHOD. (11. V

Cajal.)

A, i), Inrge spongioblasts
of inner nuclear layer ; C,
smaller spongioblast of the
same layer ; D, small bi-
polar cells with one process,
a, b, ending in terminal rami-
fications in the inner molecular
layer, and the other process
ending partly in a flattened
ramification in the outer mole-
cular layer and partly in a
filament which ends at the
external limiting membrane
in an enlarged extremity
(at E) ; F, Gr, rod and cone
nuclei ; H, I, cells with
ramifications in the outer
molecular layer ; J, fibre of
M tiller.

markedly oblique direction, in other parts of the retina they run nearly vertically to
the surfaces.

In the frotf and lizard it is common to find bipolars amongst the outer granules as well as
in their ordinary position in the inner nuclear layer. Such cells are spoken of as displaced
bipolars.

b. HponyioWasts (of inner molecular layer) of "VV. Miiller : amacrine * cells of
Cajal. — These, which are placed in the inner part of the inner nuclear layer, form
an almost complete stratum, which is termed by Cajal the layer of amacrine cells.
As this name implies, it has not hitherto proved possible to demonstrate the
existence of an axis-cylinder process in these cells (which are nevertheless regarded
by Cajal as nerve-cells 2), but they possess, on the other hand, extensively ramified
protoplasmic processes which are wholly included within the inner molecular layer,
and mostly form horizontal arborisations in the several strata of that layer.
There are several kinds of these cells, which differ amongst one another much in the

' a, privative ; /istKpds, long ; tt>os, fibre.

2 In birds, reptiles, and amphibia there are a certain number of large cells in this layer which have
an undoubted axis-cylinder process extending into the nerve-fibre layer (Dogiel) (see fig. 51, A), but
they have not been found in mammals.

LAYERS OF THE HKTTXA. 45

same way as do the cells of the ganglion-cell layer, that is to say, partly in the
varying size of the cell-body, and the character of the cell-processes, partly in the
position of their terminal arboresccnces within the inner molecular layer.

The varieties of amacrine cells described by Cajal are firstly, those with diffusely ramified

their arbore.scence extending? throughout the whole depth of the molecular layer

(tig. .10. !..//; vi., D). and secondly, those having their terminal arborescences horizontally

placed in the several strata of the molecular layer. Of these so-called stratified amacrines

there niv. ,-i> in the case of the ganglion-cells, three principal types —

(1.) Those of the first type (fig. 50, v., B, E ; vi., B) have for the most part very large
cell-bodies and a thick stalk-like process, sometimes more than one, extending into the inner
molecular layer, and ramifying in one or other of its strata over a considerable extent of area,
but with comparatively few and relatively coarse processes. A good deal of variation is,
however, met with in the character and extent of these processes.

(2.) Those of the second type (Jig. .10, v., F, G, H ; vi., E, F, G ; vn., B, C) have a pyriform
cell-body of medium size with a straight stalk passing into the molecular layer, and ending in
one of its strata in a moderately extended close interlacement of fibrils.

(8.) Th'1 amacrines of the third type (fig. 50, v.. D ; vi., C) are of small or medium size,
usually with a fine stalk-like process passing into the molecular layer. From the lower
inner) end of this process a terminal tuft of very fine radiating fibrils spreads out in one of
the strata of the molecular layer, the extent of the arborescence thus formed being often very
considerable. When, however, the arborescence ife near the inner nuclear layer, the fibrils
may come off from the body of the cell (fig. 50, v., vi., A),

r. X/)o /tf/t n h lasts of outer molecular layer : horizontal cells of Cajal : basal cells. —
These are flattened or irregularly projecting cells, the bodies of which occupy the
outermost part of the inner nuclear layer, whilst their greatly ramified processes
i \tctnl into and end in the outer molecular layer. The stratum in which they lie is
termed by Cajal the layer of horizontal cells; it was previously described by
\V. Krause as the membrana fenestrata.

T\vo kinds of these cells have been noticed by Cajal in mammals, and by their
situation they serve to subdivide the layer into two strata, an inner and an outer.

(1.) The cells in the inner stratum of the layer are large and broadly pyramidal in shape.
the base being directed towards the outer molecular layer, and resolving itself into a large
number of coarse but rapidly tapering processes which end in small tufts of thort varicose
vertical fibrils at about the level in the outer molecular layer in which the knobs of the rod-
fibres occur. The apex of the pyramid is sometimes truncated, but in other cases can be
traced as a thick vertical process down into the inner molecular layer, where it ends in
horizontal branches. Each cell has a long axis-cylinder process, which extends for a con-
siderable distance within the outer molecular layer to end in a closely interlaced terminal
ramification (fig. 50, II., B, C ; IV., a).

(2.) Semilunar cells, from the upper (outer) flattened surface of which a thick brush of
closely interlacing radiating filaments comes off and passes vertically outwards towards the
base of the rod- and cone-fibres (fig. 50, II., A). These also have an axis-cylinder process
which passes horizontally and a little upwards to end in the outer part of the outer molecular
layer.

5. Outer molecular layer. — The outer molecular layer is much thinner than
the inner, but otherwise presents, in vertical sections of hardened retina, a similar
granular appearance.

This layer (fig. 50, n.) is largely formed of the processes of the horizontal cells
which have just been described, and also of the outwardly directed protoplasmic
processes of the bipolars, which ramify within it and interlace with similarly
ramifying fibres from the cones, and with the knobbed ends of the rod-fibres.

In some mammals there are cells with widely extending branched processes
resting upon the outer surface of the outer molecular layer (fig. 50, in., h), much in
the same way as some of the amacrine cells rest upon the inner molecular. The
outer molecular layer also receives fine axis-cylinder processes which pass into it from
the inner molecular (fig. 50, r., /'), but whence they are derived is not known.

46

THE EYE.

The layers hitherto described contain structures (cells and fibres) which are undoubtedly
of nervous nature, and which appear to be developed in the same manner as corresponding-
structures in the brain. Those next to be described are of epithelial nature, and constitute
collectively what is sometimes known as the cyitJieliiim of tlic rttiiui. in contradistinction to
the more strictly nervous or cerebral part. The outer nuclear and bacillary layers are
morphologically but one, being composed of long cells, visual cells, which extend through
both layers. Each cell is drawn out into a fibre, and furnished with a nucleus in its inner
portion (rod- or cone- fibre and its outer granule), and is peculiarly modified both in shape and
structure in its external portion (rod or cone proper).

In most vertebrates no blood-vessels penetrate into this epithelial layer, but a remarkable
exception is stated by Denissenko to occur in the retina of the eel, in which the retinal
capillaries extend nearly to the limitans externa.

6. Outer nuclear layer. — This (figs. 48, 50, 52) resembles very closely at first
sight, in sections of retina stained with hasmatoxylin or carmine, the inner nuclear

Fig. 52.— DIAGRAM OF SOME OF THE NERVOUS AND EPITHELIAL
ELEMENTS OF THE RETINA. (Modified from Schwalbe. )

The numbers are the same as in fig. 47.

layer ; appearing, like that, to consist of clear, oval or
elliptical, nuclear corpuscles (outer granules), from the
ends of which delicate fibres are prolonged. These
outer granules differ, however, essentially from the
inner granules, and may be readily distinguished from
them. They are of two kinds, which present well-
marked differences, and are known respectively as the
rod-granules and cone-granules, accordingly as they
are connected with the rods or with the cones of the
next retinal layer. Those which are connected with
the rods are, in most parts of the retina, by far the
more numerous, and form the main thickness of the
outer nuclear layer. They may be regarded as enlarge-
ments or swellings in the course of delicate fibres (rod-
fibres), which extend from the inner ends of the rods
at the membrana limitans externa through the thick-
ness of this layer to the outer molecular layer. The
enlargements, of which there is but one to a fibre,
situated at any part of its course, are each occupied by
an elliptical nucleus, and, in the fresh condition,
exhibit a remarkable cross-striped appearance (Henle),
the strongly refracting substance which mainly com-
poses the enlargement being interrupted by bands or

disks of a clearer, less refracting material, usually two in number, one on each side of
the middle line (fig. 52), but occasionally single and median (see the left-hand one
in fig. 52). The rod-fibres are of extreme fineness, and exhibit minute varicosities
in their course : each is directly continuous at the outer end with one of the rods,
but at the inner end terminate in a somewhat larger varicosity (end-knob). These
end-knobs lie in the outer part of the outer molecular layer, and are embedded in
the tufts of which the terminal arborisations of the rod-bipolars are formed. In
amphibia and birds (bat not in nocturnal birds) fine fibrils radiate from these
end-knobs (fig. 51), but in mammals and teleosteans these fibrils are absent
(Cajal).

Those outer granules which are connected with the cones are, in most parts of
the retina, much fewer in number than the rod-granules, from which they are dis-

RODS AND CONES OF THE RETINA.

47

tinguished by their shape, which is somewhat pyriform, by the absence of transverse
striatiou, and by their position — for they occupy the part of the outer nuclear layer
nearest the membrana limitans externa,1 and the larger end of each is thus in close
proximity to the base of the corresponding cone (fig. 48), with which it is directly
connected, or there is at most a short, comparatively thick stalk uniting the two
(see fig. 52). At the macula lutea, however, where only cone-granules are met with,
many of them are further removed from the limiting membrane, and the stalk is
then longer (fig. GO). The nucleus of each cone-granule, which, as in the case of
the rod-granules, occupies almost all the enlargement, is spheroidal, and contains a
distinct nucleolus. The cone-fibre is very much thicker than the rod-fibre above
described, and is itself finely striated or fibrillated. It passes from the smaller end
of the pear-shaped enlargement straight through the outer nuclear layer to reach
the outer molecular layer, upon which it rests by a somewhat pyramidal base (cone-
foot), from which ramifications may be traced into the substance of the molecular
layer where they interlace with the ramifications of the peripheral processes of the
cone-bipolars (see above) (fig. 52).

7. The layer of rods and cones. — The elements which compose this layer
are, as their name implies, of two kinds, those of the one kind — the rods — having an

Fig. 53. — OUTER SURFACE OF THE COLUMNAR LAYER OF
THE RETINA (Kblliker). 350 DIAMETERS.

a, part within the macula lutea, where only cones
are present : ?>, part near the macula, where a single
row of rods intervenes between the cones ; c, from a
part of the retina midway between the macula and
the ora serrata, showing the preponderance of the
rods.

elongated cylindrical form (about 0'060 mm. long and 0*002 mm.
diameter) ; the cones, on the other hand, being shorter (0'035 mm.),
much thicker (O'OOG mm.), bulged at the inner end or base, and
terminated externally by a finer tapering portion. Both rods and
cones are closely set in a palisade-like manner over the whole extent
of the retina between the membrana limitans externa and the pig-
mentary layer (fig. 48, 7). Except at the macula lutea, where only
cones are met with, the rods far exceed the cones in number. Their
relative number and arrangement is well exhibited when the layer is
viewed from the outer surface, as in fig. 53, where a represents a portion
of the layer from the macula lutea ; Z>, from the immediate neighbour-
hood of the latter ; and c, from the peripheral part of the retina.

Fig. 54. — A ROD AND A CONE FROM THE HUMAN RETINA (Max Schultze).

(Highly magnified. )

In the rod the longitudinal striation of both the outer and inner segments is
shown ; in the cone the transverse striation of the outer segment and the longitudinal
of the inner segment ; Z, limitans externa.

The total number of cones in the human retina has been calculated to exceed three
millions ; and of rods many times this number. It may be of interest here to note that the
number of fibres in each optic nerve is about half a million (Salzer).

The rods and the cones, although differing thus in shape and size, agree in many
points of structure. Thus, each consists of two distinct segments — an inner and an
outer ; the division between the two occurring, in the case of the rods, about the
middle of their length (in man) ; in the cones at the junction of the finer tapering

In Teleostei the cone-nuclei lie outside the limitans externa.

48

THE EYE.

end-piece with the basal part ; consequently, the outer and inner segments of the
rods are nearly similar in size and shape, the inner being, however, slightly bulged,
whereas the inner segment of each cone far exceeds the outer one in size, the latter
appearing merely as an appendage of the inner segment (fig. 54). The two
segments both of the rods and cones exhibit well-marked differences in their
chemical and optical characters, as well as in the structural appearances which may
be observed in them. Thus, while in both the outer segment is doubly refracting in
its action upon light, the inner is, on the contrary, singly refracting : the inner
becomes stained by carmine, iodine, and other colouring fluids, whilst the outer
remains uncoloured by these reagents, but is stained greenish-brown by osmic acid.
The outer segment in both shows a tendency to break up into a number of minute
superposed disks. The inner segment of each is distinguishable into two parts —

[ ffllTF1

Figs. 55 and 56.— SECTIONS OF FROG'S RKTINA SHOWING THE ACTION OF LIGHT UPON THE PIGMEXT-
CKLLS, AND UPON THE RODS AND CONES, (v. Grenderen-Stort. )

Fig. 55, from a frog which had been kept in the dark for some hours before death.

Fig. 56, from a frog which had been exposed to light just before being killed.

Three pigment cells are shown in each section. In Fig. 55, the pigment is collected towards the
nucleated part of the cell, in Fig. 56 it extends nearly to the bases of the rods. In Fig. 55 the rods,
outer segments, were coloured red (the detached one green), in Fig. 56 they had become bleached. In
Fig. 55, the cones, which in the frog are much smaller than the rods, are mostly elongated, in Fig. 56
they are all contracted.

an outer part, composed, according to Max Schultze, of fine fibrils, and an inner parr,
homogeneous, or finely granular, and, at the membrana limitans externa, directly con-
tinued into a rod or cone-fibre, the disposition of which in the outer nuclear layer
has been already described.

In the outer segments of the rods there can be detected, by the aid of a
powerful microscope, besides a delicate transverse striation (fig. 52), corresponding
to the superposed disks of which, as above mentioned, they appear to be formed,
also fine longitudinal markings which are due to slight linear grooves by which
they are marked in their whole extent. The ends of the segments are rounded and
project into the pigmentary layer, The purplish-red colour of the retina before
mentioned (p. 35), resides entirely in the outer segments of the rods (Boll, Kiihne).
A few of the rods are, however, at least in some animals, of a green colour. The
outer segments of the cones taper gradually to a blunt point, and do not exhibit

EODS AND CONES OF THE RETINA. 49

superficial groovings, but the transverse markings are somewhat more evident than
in the rods (figs. 52, 54). There is a delicate covering of neurokeratin investing
the outer segments of both rods and cones, and this is somewhat more pronounced
on the cones, so that a post-mortem separation into disks does not take place so
readily as in the rods. From their behaviour to staining reagents and the readiness
with which they become altered after removal from the body, it has been conjectured
that the outer segment contains materials similar in chemical nature to those com-
posing the myelin of the medullary sheath of nerve-fibres.

In the inner segments, the proportion which the fibrillated part bears to the
homogeneous basal part differs in the rods and cones. In the rods the fibrils
usually occupy only the outer third of the inner segment (fig. 52), ceasing
abruptly at its junction with the middle third ; in the cones, on the other hand,
they occupy about the outer two-thirds of the segment, only the part nearest the
membrana limitans remaining free from fibrils. The fibrils in question are for
the most part straight and parallel, and strongly refracting. Sometimes, in the
cones, instead of this outer part of the inner segment being fibrillated, it appears

Fig. 57. — PlGMENTED EPITHELIUM OF THE HUMAN RKTINA (Max Schultze). HIGHLY MAGNIFIED.

(t, cells seen from the outer surface with clear lines of intercellular substance between ; b, two cells
seen in profile with fine offsets extending inwards ; c, a cell still in connection with the outer ends of the
rods.

homogeneous, but is nevertheless well marked oft from the inner part by its strong
refractivity.

This condition of a part of the inner segment of the cones is much better marked in other
mammals and in the lower vertebrata, where there occurs a distinct strongly refracting body,
situated in the middle or outer part of the segment, and known from its shape as the
•; ellipsoid," a name which is also extended to include the fibrillated part of the cone in the
human retina. In reptiles an oval body, coloured red by iodine, takes the place of the
ellipsoid (Merkel). In lower vertebrata, as well as in most other mammals, the fibrils are
absent from the inner segments of the rods also, a peculiar, strongly refracting, lenticular
body (" rod-ellipsoid ") being met with at their outer part, corresponding to the ellipsoid of
the cones. Further, in birds, reptiles, and amphibia, in ganoid fishes and in marsupials (but not
in other mammals), there is found in the extreme outer part of the inner segment of each
cone a minute globular body, apparently of a fatty nature, which in some is clear and colour-
less, but in many cones is brightly coloured of a tint varying in different cones from red to
green — red and yellow being the most common. Blue and violet are not met with, but by
the action of iodine the colours of all become changed to blue. Sometimes the whole inner
segment is found to be slightly tinted of the same colour as the " oil-globule." In birds
there are two kinds of cone : in the one kind, the cone-fibre passes straight down to the outer
molecular layer ; in the second kind, obliquely. In all vertebrates below mammals, double-
or twin-cones are here and there met with ; these usually have, the one a straight the other
an oblique cone-fibre. Numerous other differences and peculiarities are found in animals :
thus in birds and reptiles the cones are more numerous than the rods ; in many reptiles (e.g.,
lizard) only cones are met with ; while in some fishes (sharks and rays), in most nocturnal
mammals, and in the owl, the cones are either altogether absent or are but few and rudi-
mentary (M. Schultze). This statement has, however, been denied by W. Krause so far as
nocturnal mammals are concerned. In the size of the elements there is also much variation :
the rods being very large in amphibia, and especially long in fishes. In the frog there are three

VOL. in., PT. 3. E

50 THE EYE.

kinds of rods, one kind having a long outer segment of the usual red colour (when not exposed
to light), whilst in the others the inner segment is lengthened and either fine or of the usual
thickness, whilst the outer segment is short and of a green colour. The rod-fibre is straight
in the red variety and in those of the green kind with the larger inner segments, but oblique
in the green rods, with finer inner segments.

In the frog the cones were observed by Engelmann to shorten on exposure to light and to
lengthen in the dark (figs. 55. 56). This change occurs through the nervous system, for it
will take place equally well if the head of the animal be kept in the dark and only the skin
of the trunk and limbs exposed to the action of light.

8. The pigmentary layer.— This layer, which bounds the retina externally,
and was formerly described with the choroid coat, consists of a single stratum of
hexagonal epithelium cells separated from one another by a perceptible amount of
clear intercellular substance (fig. 57). The outer surface of each cell — that which
is turned towards the choroid — is smooth and flattened, or slightly convex, and the
part of the cell near this surface is devoid of pigment, and contains the nucleus
(figs. 55, 56) ; the inner boundary, on the other hand, is not well marked, for the
substance of the cell, which here is loaded with pigment, is prolonged into fine,
straight, filamentous processes (fig. 57, &), which extend for a certain distance
between and amongst the outer segments of the rods and cones — indeed the
outer parts of the rods may be said to be altogether imbedded in the pigment-
cells (c).

The pigment-cells are not everywhere quite regularly hexagonal, but here and
there cells are found, singly or in patches, which are larger or smaller than the rest,
and of a more rounded or of an irregularly angular shape.

The pigment granules, which are in the form of minute crystals, are placed for
the most part, both in the cells and cell-processes, with their long axes at right
angles to the surface of the retina. The distribution of the pigment granules
within the cells varies during life and immediately after removal of the eye
according as the retina has been shaded from the light or exposed to its influence.
In the former case the pigment is mainly accumulated in the body of the cell (or
at least its inner zone), and is withdrawn to a great extent from between the
rods ; but after exposure to light, a large amount of pigment is found between the
rods, and some of the granules may even extend as far as the external limiting
membrane (fig. 56). This has the effect of causing the pigmentary layer to adhere
more firmly to the rest of the retina than when the pigment granules are accumu-
lated in the body of the pigment-cell. The pigment appears to have inter dliis
the function of renewing the colour (visual purple) of the outer segments of the
rods after these have become bleached from exposure to the light. This renewal
of the colour will take place for a short time after the death of the animal, or the
excision of the eye (Kiihue).

In some animals, e.g., frog, coloured oil-droplets and particles of a highly
refracting myelin-like substance (myeloid granules, Kiihne) occur in the non-
pigmented portion of the cells, which are further covered next to the choroid by a
clear homogeneous cuticular layer.

The intervals between the rods and cones are only partially filled by the pro-
cesses of the hexagonal pigment-cells ; the remaining part appears to be occupied
by a clear substance, which, according to Henle and H. Miiller, is of a soft elastic
consistence during life and in the fresh condition, but soon liquefies after death ;
but according to Schwalbe, is normally liquid. In the embryo, between the
hexagonal pigment and the remainder of the retina, there is a distinct cleft filled
with fluid (remains of cavity of primary optic vesicle), homologous with the
ventricular cavities of the brain, with which it is originally in continuity.

The sustentacular tissue of the retina : Miilleriaii or radial fibres. —

PIGMENTARY LAYER OF THE RETINA.

51

In addition to the eleoients which belong specially to the layers above described,
there are certain other structures which are common to nearly all the layers,
passing through the thickness of the retina from the inner almost to the outer
surface, and, although not actually of the nature of connective tissue, serving
the same kind of purpose, namely to bind together and support the more
delicate nervous structures of the membrane. These mstentacular fibres or fibres
of Miiller (figs. 48, 58), commence at the inner surface of the retina by a broad
conical hollow base or foot, which may be forked (fig. 58), and often contains
a spheroidal body, staining with haematoxylin (pseudo-nucleus). The bases of

.l.e.

Fig. 58. — A FIBRE OF MiJLLER FROM THE POCr's RETINA, SHOWN

BY GOLGI'S METHOD. (R. y Cajal.) Highly magnified.

1, nerve-fibre layer ; 2, ganglionic layer ; 3, inner molecular
layer; 4, inner nuclear layer ; 5, outer molecular layer ; 6, outer
nuclear layer ; m.l.e., membrana limitans externa ; 'in.l.i., mem-
brana limitans interim ; b, nucleus of the fibre ; a, process extend-
ing from nucleated part into inner molecular layer.

adjoining fibres are united together at their edges
(fig. 59), so as to give, in vertical sections of the
retina, the appearance of a distinct boundary line
(fig. 48) ; this has been named membrana limitans
interna, but, as may be inferred from the above
description, it is in no way a continuous or inde-
pendent membrane. The Miillerian fibres pass through
the nerve- and ganglionic layers, either with a smooth
contour, or with but two or three well-marked lateral
projections from which fine lamellar processes extend
amongst the elements of these layers : gradually
diminishing in size they then traverse the inner
molecular layer. In the mammalian retina the fibres
may be marked by slight projections in passing
through this layer. In the inner nuclear layer they
again give off delicate flattened processes from their
sides, which pass round the inner granules and
serve to support them. Moreover, each Miillerian
fibre is here characterised by the presence of a
clear oval or elliptical nucleus (already mentioned
in the description of the inner nuclear layer), con-
taining a nucleolus, and situated at one side of, and in close adherence to the fibre
to which it belongs (fig. 58, b). On reaching the outer nuclear layer (after passing
through the outer molecular) the fibres of Miiller break up into fibrils and thin
lamellae, and in this form they pass outwards through the layer, between the outer
granules and the rod- and cone-fibres, enclosing these structures, filling up the
intervals between the granules and forming partial sheaths for them. At the level
of the bases or central ends of the cones and rods, the numerous offsets terminate
along a definite line which marks the boundary between the outer nuclear
layer and the layer of rods and cones, and has been termed membrana limitans
externa. This also, like the m. I. interna, is in no way a continuous membrane, nor
is it isolable from the Miillerian fibres ; indeed, numerous fine fibrillar offsets of
these pass a short distance beyond the so-called limiting membrane, and closely
invest the bases of the inner segments of the rods and cones.

The Miillerian fibres exhibit a fine striation. They swell up and become

E 2

THE EYE.

indistinct on treatment with acetic acid and dilute alkalies, but much more slowly
than connective tissue fibrils ; moreover, they are not dissolved by boiling- in water.
They are much less developed in the central and posterior part of the retina than in
the peripheral and anterior part ; towards the ora serrata they are very distinct and
closely set.

Fig. 59. — INTERNAL LIMITING MEMBRANE OF THE RETINA TREATED WITH SILVER NITRATE, SHOWING

THE OUTLINES OF THE BASES OF THE MC'LLERIAN FIBRES. (RetzillS. )

At the lower pait of the figure some of these fibres are seen separated.

Structure of the macula lutea and fovea centralis (fig. GO). — The
peculiarities in structure which these present have partly been incidentally
noticed in the preceding description of the retinal layers. In the fovea no
rods are met with, and the cones, especially their inner segments, are much
longer and narrower than elsewhere. All the other layers are much thinned, but
towards the margin of the fovea they rapidly increase in thickness, and in the rest
of the macula lutea most of them are thicker than at any other part of the retina.
The ganglionic layer (fig. GO, 2) is especially thickened at the edge of the fovea,
the cells being from six to eight deep. They are smaller here than nearer the centre
of the fovea. The nerve-fibre layer (1) gradually thins and disappears as a distinct
layer near the edge of the fovea as the fibres join the central ends of the ganglion-
cells. The opposite end of each ganglion-cell is directed vertically towards the inner
nuclear layer. The bipolar inner granules are somewhat obliquely disposed. They
are smaller than the outer granules and, as elsewhere, much smaller than the ganglion-
cells. At the centre of the fovea they are but thinly scattered, and the inner and
outer molecular layers appear to join between them. At the middle of the fovea the
retina is very thin, consisting here mainly of the cone-cells (i.e., cones with their
nucleated fibres) and pigmentary layer, but a few of the inner granules are also
present, and one or two isolated nerve-cells (perhaps amacrine cells) may also
be seen very near to the centre. According to the figures and description given
by M. Schulbze the membrana limitans externa is also cupped in at this place, and the
cones, both inner and outer segments, are considerably longer than elsewhere, so that

STRUCTURE OF FOVEA CEtfTKALIS.

53

the line of pigment remains level. Hulke figured the limitans externa as plane, and
others (e.g., Merkel, Kuhnt, Schwalbe) have formally denied this cupping of the
m. limitans externa. Undoubtedly, however, it exists and may, as a glance at fig. 60
will render evident, be as deep as that of the limitans interim or true fovea, from
which for purposes of description it may be distinguished by the name of fovea
c.rlt'rna. On the other hand, the inner segments of the cones are not longer here
than elsewhere, but are if anything somewhat shorter than at the edge of the fovea,
but this is more than compensated for by the greater length of their outer segments.
The cones are also more slender in the very middle of the fovea than elsewhere, here
measuring not more than 0'002mm., whereas at the edge of the fovea they arc
double this in diameter. The outer nuclear layer (fig. 00, 6) of the macula lutea is

•m.l.c.

m.ll

Fig. 60. — DIAGRAM OF A SECTION THROUGH THE FOVKA OKNTKALIS. (The outlines of this figure have
been traced from a photograph.) Magnified 350 diameters. (From a preparation by C. H.
Golding-Bird.)

2, ganglionic layer ; 4, inner nuclear ; 6, outer nuclear layer, the cone-fibres forming the so-called
external fibrous layer; 7, cones; 7/t.l.e., mernbrana limitans externa; m.l.i. membrana limitans
interna.

occupied in the greater part of its thickness by the very long and obliquely
disposed cone-fibres ; the nuclei are only two or three deep, and take up a compara-
tively small portion of the layer, which was termed the outer fibrous layer by Henle.
Over most of the yellow spot the cone-nuclei are placed close up to the limitans
externa, but a short distance from the middle of the fovea they begin to be removed
from the limitans, and at the centre of the fovea they are close to the outer molecular
layer. The cells of the pigmentary layer are smaller but deeper (O'Olmm. x
0*01 6mm.) and more strongly pigmented in the macula lutea than in the rest of
the retina. The hyaloid membrane of the vitreous humour is very thin over the
centre of the fovea. The choroid coat is thickened opposite the fovea, the
thickening being due to an accumulation of capillary blood-vessels, which here
occupy not only their usual position but also that of the layer of larger blood-
vessels, and even encroach on the lamina suprachoroidea (Nue'l).

54

THE EYE.

The yellow tint of the macula is absent at the centre of the f ovea : it is said to be due to
a diffuse colouring- matter which is seated in the interstices between the elements of the four
or five inner layers. The yellow colour of this part of the retina is peculiar to Primates : in
man it develops after birth. A corresponding area is found however in all mammals,
characterized by a lack of dark pigment in the pigmentary layer, while in some mammals
(Chievitz) as well as in birds, reptiles and amphibia (H. Mliller, Hulke, W. Krause), a
Jovea has been described within such a central area. In some birds two foveas are present,
one being near the ora serrata : in some cases several fovese are found (Chievitz). The central
area is always characterized by containing relatively smaller visual cells. The occurrence and
relative development of the central area and f ovea in vertebrata has been specially investigated
by Chievitz (see Bibliography).

Structure of the ora serrata and pars ciliaris retinae. — At the line of the
ora serrata the numerous complex layers of the retina disappear, and in front of it,
the retina is represented merely by a single stratum of elongated columnar cells with
the pigmentary layer external to it (pars ciliaris retina}. The transition is, in man,
somewhat abrupt, all the changes being met within a zone of about 0*1 mm. in
breadth. The layer of rods and cones (fig. 61, #) first disappears as a complete
layer, the cones continuing rather further than the rods, but being imperfectly
formed and lacking the outer segments ; the nerve- and ganglionic layers, which
were already very thin and incomplete, cease altogether at the ora, the inner

Fig. 61. — VERTICAL SECTION THROUGH THE CHOROID AND RETINA NEAR THE ORA SERRATA (Kolliker). CO

DIAMETERS.

a, hyaloid membrane ; b, limiting membrane and nervous layer of the retina ; c, ganglionic and
inner molecular layers with closely set Miillerian fibres ; d, inner nuclear ; e, outer molecular ; /, outer
nuclear layer ; g, columnar layer ; h, pigment ; i. Jc, choroid ; I, part of one of the ciliary processes ;
TJi, pars ciliaris of the retina. (The recess shown at a' is not constant. )

Fig. 62. A SMALL PORTION OF THE CILIARY PART OP THE RETINA (Kolliker). 350 DIAMETERS.

A, human ; B, from the ox ; 1, pigment-cells ; 2, columnar cells.

molecular layer (c), which is now largely occupied by Miillerian fibres, retains its
thickness up to a certain point, and then abruptly terminates (a1), as do also the
nuclear layers, outer and inner (f, d,). The columnar cells of the pars ciliaris,
which appear directly to continue these layers of the retina, are at first of con-
siderable length, but become gradually shorter anteriorly ; they are finely striated
(fig. G2, 2), and each cell has a clear oval nucleus at the outer part of the cell, near
the pigmentary layer. The inner end may be rounded, pointed, square, or even
branched ; the sides of the cells, too, are sometimes uneven.

This double layer of cells is continued as before said over and between the ciliary
processes to join the uveal layer upon the posterior surface of the iris (pars iridica
retince). On the ciliary processes, and especially their anterior aspect, glandular
depressions of the epithelium occur which may be solid or may be provided with a

VESSELS OF THE RETINA.

55

lumen like true tubular glands (E. T. Collins). The function of these ciliary glands
is not certainly known, but they are believed to take part in the secretion of the
aqueous humour.

Vessels of the Retina. — A single artery (arteria emir alls retina) passes
between the bundles of fibres of the optic nerve to the inner surface of the retina
at the middle of the papilla optici (fig. 64). It enters the nerve about
15 — 20 mm. from the globe of the eye, being accompanied by the corresponding
vein and giving off small branches to supply the central part of the nerve.
Emerging at the papilla oculi the vessels divide into branches (fig. 63), usually
two, one above, the other below (superior and inferior papillary branches), each of
these again almost immediately dividing into two branches which arch out towards

nasal

temporal

Fig. 63.— RETINA AS SEEN WITH THE OPHTHALMOSOOPE. (Jaeger.)
a,a, branches of central artery ; v,v., branches of central vein ; /, fovea.

the sides (superior and inferior nasal and temporal branches) • the outer ones are
somewhat the larger, and as they bend round the macula lutea they send numerous
fine branches into it which end, a short distance from the centre of the fovea, in
capillary loops. The macula is also supplied by small vessels which pass directly
to it from the papilla. The middle of the fovea centralis has no blood-vessels. The
main branches of the vessels pass forwards in the nerve-fibre and ganglionic layers,
dividing dichotomously as they proceed, and giving off fine offsets to the substance
of the retina, where they form two capillary networks, the one in the nerve- and
ganglionic layer, the other in the inner nuclear layer. The capillaries of the former
are mainly connected with the arteries, and those of the latter with the veins, the
communication between the two networks being effected by vertically and obliquely
coursing capillaries which traverse the inner molecular layer. No vessels penetrate
the outer molecular layer (His, Hesse), so that the outer retinal layers are entirely
destitute of blood-vessels. The retinal arteries have no anastomoses, thus resembling
those of the grey matter of the brain.

The vascular system of the retina is nowhere in direct communication with the
choroidal vessels. Near the entrance of the optic nerve, however, it comes into
communication with some offsets from the posterior ciliary in the sclerotic coat, and
the choroidal vessels also send branches to join the long-meshed network in the optic

56

THE EYE.

nerve furnished by the central artery. The arteries of the retina have the usual
coats, but the veins resemble capillaries in structure, their walls consisting- of a
single layer of endothelial cells without any muscular tissue. Outside the endothelial
layer is a space (perivascular lymphatic space, His) both in the veins and capillaries,
bounded externally by a second endothelial layer (forming the wall of the lymphatic
space). Outside this again is found, in the case of the veins, a layer composed of a
peculiar retiform tissue. These perivascular lymphatic spaces are in communication

nasal

Fig. 64. — SKCTJON THROUGH THE PLACE OP ENTRANCE OF THE OPTIC NERVE (B), TOGETHER WITH THK

OPHTHALMOSCOPIC VIEW OP THE DISK (A), TO SHOW THE CORRESPONDING PARTS OP THE TWO.

(Fuchs, after Jaeger.)

c, d, lines of correspondence ; b, depression in centre of disk ; r, retina ; ch, choroid ; si, so, inner
and outer parts of the sclerotic coat, s ; ci, a ciliary artery cut longitudinally ; a, v, central artery and
vein ; s, d, subdural space ; sa, subarachnoid space ; du, dural sheath ; ar, arachnoidal sheath of nerve ;
p, pial sheath ; n, nerve bundles ; se, septa between them.

with the lymphatic spaces of the optic nerve, and may be filled by injecting coloured
fluid under the sheath which that nerve derives from the pia mater. Other lymph-
spaces also become injected by the same process, viz., the interstices between the
nerve-bundles which radiate from the papilla optici, the capillary space between
the limitans interna and the hyaloid membrane of the vitreous humour, and
finally even the irregular interstice between the pigmentary layer and the layer
of rods and cones (Schwalbe). With one or two exceptions (Chelonia, eel) no
vertebrates below mammals have blood-vessels in the retina : even in some
mammals the distribution is restricted to the posterior part of the eye and to the
nerve-fibre layer.

Interconnection of the retinal elements. — It is only comparatively
recently, by the aid of the method of Ehrlich (staining intra vitam with methyl-blue)
and that of Golgi (chromate of silver impregnation), that histologists have been able

INTERCONNECTION OF RETINAL ELEMENTS.

57

definitely to trace the course and connections of the fibres which pass from and to
the several retinal elements. The most fruitful applications of Golgi's method have
been made by Ramon y Cajal, following up investigations by Dogiel, which
were made by Ehrlich's method ; it is the account given by the first-named
observer which will here in the main be followed.

In the first place, it would appear that there is no direct anatomical continuity
between the elements of the several layers, with the exception of some of the
nerve-fibres of the first layer and the ganglionic cells immediately outside them.
As with other parts of the nervous system (see Part I. of this volume) the
nerve-elements of the retina are anatomically isolated units, merely coming into
connection with one another by the interlacement of their arborescent processes.
These interlacements occur in two places, viz., in the two molecular layers. In the

Fig. 65. — DIAGRAM SHOWING THE MODE OP CONCATENATION OP THK

VISUAL NERVOUS ELEMENTS IN THE VERTEBRATE TYPE.

outer molecular layer is found the interlacement by
which the rod- and cone-elements are brought into
connection with the inner granules. In the inner
molecular layer there is a series of interlacements
running mainly in planes parallel to the surfaces of the
layer, and serving to bring the elements of the inner
nuclear layers into connection with those of the gang-
lionic layer. Finally, some of the nerve-fibres of the
first or innermost layer ramify directly in the mole-
cular layer or pass through this layer and ramify
amongst the inner granules (figs. 50, 51, 64).

The retina, therefore, is essentially formed by a
number of nerve-cell chains, the elements of which are
arranged in three series from without in. The first of
these is formed by the rod- or cone-element. One
end of this element abuts against or is imbedded
in a pigment-cell, the other end interlaces by the
terminal arborisation of the rod- or cone-fibre within
the outer molecular layer, with the peripheral arborisa-
tions of the next elements. The latter are the bipolar inner granules (fig. 65, gr.i).
These, by the peripheral process just mentioned, interlock with the arborisations
of the rod- and cone-fibres and in some animals also send the fibres of Landolt
as far as the membrana limitans externa. By their central processes they ramify
within the inner molecular layer (m.i.) and interlace with the peripheral processes
of the ganglion-cells (g). The last-named form the third of the concatenated
elements. Their peripheral processes spread out in the inner molecular layer, and
are connected with the central processes of the inner granules in the manner just
stated. Their central process (n) is an axis-cylinder of one of the fibres of the
optic nerve, and its terminal ramification is to be found in the grey matter of the
superior corpora quadrigemina, or of the lateral geniculate bodies. The functions
of the other cell elements in the retina, such as the horizontal cells, which ramify
in the outer molecular layer, and the amacrine-cells of Cajal, which are distributed
in the inner molecular layer, are still quite obscure.

58

THE EYE.

THE VITREOUS BODY.

The vitreous body occupies the greater portion of the eyeball. It is quite
pellucid in aspect, and of a soft gelatinous consistence. Sub-globular in form, it
fills about four-fifths of the ball, and serves as a support for the delicate retina, but
it may be readily separated from the latter, except behind, at the entrance of the
optic nerve, where the connection is closer, the retinal vessels having here entered
it in foetal life. At the fore part it is hollowed out (fossa patellaris) for the
reception of the lens and its capsule, to which it is closely adherent. The vitreous
humour contains 98*5 % of water. The solids are chiefly salts and extractives,
with a trace of proteid and nucleoalbumin.

The surface of the vitreous humour is covered everywhere by a thin glassy
membrane, named hyaloid, which lies between it and the retina. In the last edition

Fig. 66. — HORIZONTAL SECTION OF THE HORSE'S! EYE
HARDENED IN CHROMIC ACID (after Hannover).

The vitreous humour appears concentrically and me-
ridionally striated throughout its whole depth.

of this work it was stated that, according to
the most recent observations, there is no binding
membrane between the vitreous humour and the
lens capsule, but it has been shown by Anderson
Stuart that the older view regarding this subject
is more correct, for after removal of the lens
within its capsule it is still possible to demon-
strate the existence of a delicate glassy mem-
brane over the fossa patellaris in the front of the vitreous humour, and this can
be none other than a continuation of part of the hyaloid membrane. No vessels
enter the vitreous humour in the adult, and its nutrition must, therefore, be
dependent on the surrounding vascular structures, viz., the retina and the ciliary
processes.

Although in the fresh state apparently structureless, or at least presenting under the
microscope but faint traces of fibres and a few cells — the so-called corpuscles of the vitreous

Fig. 67.— TRANSVERSE SECTION OF HUMAN EYE HARDENED IN CHROMIC ACID,
SHOWING RADIAL STRIATION OF THE VITREOUS BODY (after Hannover).

humour to which we shall immediately recur, — yet in preparations
hardened in weak chromic acid, or acted upon in certain other ways,
it is possible to make out a more or less distinct lamellation of the
vitreous body, especially in its peripheral part, that, namely, nearest
the retina ; which part in the human eye has a somewhat firmer
consistence than the more central portion. From the appearances
(figs. 66, 67) which have been obtained by such modes of preparation it has been conjectured
by various observers that at least in this part the vitreous substance is divided into com-
partments by a number of delicate membranes arranged concentrically and parallel to the
surface ; but the existence of such membranous partitions has not been conclusively
demonstrated. That, however, the vitreous substance does in some way consist of a firmer
material — either in the shape of continuous membranes, or, as II. Virchow states, in the form
of a network of fibres — enclosing in its meshes the more fluid portion, is shown by the fact
that if either the whole or a piece of the vitreous humour be thrown upon a filter, a small
proportion always remains upon the latter ; although by far the larger part drains away, and
may be collected as a clear watery fluid.

THE VITREOUS BODY.

59

In addition to the above-mentioned concentric striation, a radial marking has also been
observed in sections of vitreous humour made transversely to the axis of the eyeball,
but whether there is any pre-existent structure to account for it is not known. It is con-
ceivable that these appearances may be merely produced by the manner in which the
albuminous substance has undergone coagulation by the reagent employed.

It has also been shown by Iwanhoff. Younan and A. Stuart that the periphery of the
vitreous humour near the ciliary body, is considerably strengthened and rendered more consistent
by the presence of an accumulation of fibres which encircle this part of the posterior chamber
of the eye, and are believed to aid in supporting the ciliary body and the attachment of the
suspensory ligament of the lens to that body. The fibrous structure in question appears to
be continuous with the fibres of the zonula of Zinn (see below), which here strengthen the
hyaloid membrane.

There further exists, nearly but not quite in the axis of the eye, a definite
structure in the shape of a distinct canal, about 2 mm. in diameter, filled
with fluid and extending from the papilla optici to the back of the lens-capsule,
where it apparently terminates blindly (fig. 69). This is the canalis hyaloideus or
canal of Stilling. It is best shown in the fresh eye, and may be also injected by
forcing a coloured solution under the pia-matral sheath of the optic nerve (Schwalbe).
The canal widens somewhat towards its posterior part ; its wall is composed of an
extremely delicate homogeneous membrane. It represents the place of passage
of an offset from the central artery of the retina to the capsule of the lens in the
foetus, and from it lymph may pass into the lymphatic spaces of the optic nerve
behind, and perhaps in front round the edge of the lens into the canal of Petit.

Fig. 68. — CELLS OF VITREOUS HUMOURS.

(Schwalbe.)

a and d, without vacuoles ; b, c, e, f, g,
vacuolated.

Scattered about throughout the sub-
stance of the vitreous humour are a
variable number of corpuscles, for the
most part possessed of amoeboid move-
ment. Some of these cellsare remarkable
for the very large vacuoles which they
contain, and which distend the. body
of the corpuscle, pushing the nucleus
to one side ; the cell-processes are often
peculiar in possessing numerous little

secondary bud-like swellings, or they may present a varicose appearance, like strings
of pearls.

Suspensory apparatus of the lens. — The hyaloid membrane invests, as
before mentioned, the whole of the vitreous humour. As the ora serrata it is
apparently split into two layers, one, which must be regarded as the hyaloid
membrane proper, being that which has been already mentioned as demonstrable
over the anterior surface of the vitreous humour. The other layer into which the
hyaloid appears to split adheres to the pars ciliaris retina so closely that when
removed it generally shows some of the pigmented cells of that structure adher-
ing to its outer surface. It forms a fibrous structure much firmer in consistence
than the true hyaloid, and extends over the ciliary body inwards to be attached
to the capsule of the lens, for which it forms a suspensory apparatus, known as
the zonula of Zinn, or zonula ciliaris (fig. 70, z). Its free part, which stretches
from the ciliary body to the lens capsule, is termed the suspensory ligament of
the lens. The posterior part, or hyaloid proper, is exceedingly thin and delicate,
and is readily thrown into folds when detached. Under the microscope it presents no

60

THE EYE.

appearance of structure ; but, flattened against its inner surface, are generally to be
seen a number of granular nucleated corpuscles (leucocytes) which exhibit amoe-
boid movements. The zonula, on the other hand, is composed of or at least con-

1TPITHELIUM
CONJUNCTIV/E"

_ CAMALtS
""SCHLEMMII

MUSCULUS
CILIARIS

OURAU SHEATH

Fig. 69. — RIGHT ADULT HUMAN EYE, DIVIDED HORIZONTALLY THROUGH THE MIDDLE.

(E. A. S.) Magnified 5 times.
The line a 6 passes through the equator, x y through the visual axis of the eye.

tains radiating meridional fibres, stiff in appearance but possessed of considerable
elasticity ; they commence opposite the ora serrata, and are firmly adherent here to
the pars ciliaris retinae. Over the ciliary body the adhesion, as just stated, is firm
to the elevations of that body (ciliary processes), so that when the zonula is torn away

SUSPENSORY APPARATUS OF LENS.

61

Fig. 70. — MERIDIONAL SECTION OP THE CILIARY'
REGION. (Fuchs. ) Moderately magnified.

C, Cornea ; S, sclera ; C/t, choroidea ; R, retina;
PC, its pigmented epithelium ; L, lens ; A-, its capsule;
o. ora serrata ; 0, pars ciliaris retinae, extending over
ciliary process, P, and continuous with the pigment-
layer on the posterior surface of iris (pars iridica
retina?), the two strata of which are accidentally sepa-
rated at v, h : pe,2)c, pigmented and columnar layers of pars ciliaris ; z, zonule of Zinn, continuous over
and between the ciliary processes with the fibres of the suspensory ligament of the lens, 2', i, which
are attached to the lens capsule; ^meridional fibres of the ciliary muscle ; r, radiating or interlacing
fibres of the same ; Mu, Mi'.llerian or circular fibres of the same ; S, canal of Schlemm ; I, iris-corner;
c, c. f, /, folds in anterior surface of iris ; p, edge of pupil ; sp, sphincter pupillae ; ci, anterior ciliary
artery ; a, circular artery in ciliary body ; gl, glandular depressions in ciliary body.

62 THE EYE.

the pigment is often detached from these processes. Over the intervals between
the ciliary processes the zonula is, however, less closely applied to the pars ciliaris
retinas, so that a series of pouches, narrowing posteriorly and widening anteriorly,
where they communicate with the posterior chamber, become left between zonula and
ciliary body (recesses of the posterior chamber, Kulmt). It is into these recesses that
the ciliary glands (see p. 55) open. The recesses are occupied by aqueous humour,
and traversed by fibres belonging to the zonula of Zinn, which serve to attach
the outer surface of that membrane to this portion of the pars ciliaris retinae :
they are also partly subdivided by small subsidiary folds of the ciliary body which
project into the recesses. Opposite the most prominent part of the ciliary body the
zonula gives off bundles of fibres which pass meridionally inwards towards the
margin of the lens, some reaching and extending a short distance over its anterior
surface, others just reaching its posterior surface, and others again occupying inter-
mediate positions at the margin (fig. 70). They are all firmly cemented to the lens-
capsule. Those which pass anteriorly originate mainly from the part of the zonula which
lies in the intervals between the ciliary processes : they form a radially fibrous mem-
Fig. 71. — VlEW FROM BEFORE OF THE CAIsAL OF PETIT INFLATED (from

Sappey).

The anterior parts of the sclerotic, choroid, iris and cornea having been
removed, the remaining parts are viewed from before, and the canal of Petit
has been inflated with air through an artificial opening. 1, front of the
lens ; 2, vitreous body ; 3, outer border of the canal of Petit ; 4, outer part
of the zonule of Zinn ; 5, appearance of sacculated dilatations of the canal of
Petit.

branous layer, but it is not quite complete, for coloured injection can be easily
made to pass from the interstices between the lens capsule and the ciliary body into
the aqueous humour and vice versd. The clefts in it are fine enough, however, to
retain air if blown into this interstice : if this be done after removal of the whole
vitreous body (a removal which can be easily effected in an eye which has been
left for a day or two at the ordinary atmospheric temperature), the interstices which
correspond with the eminences of the ciliary processes are most distended, and the
appearance of a sacculated canal (canal of Petit), encircling the lens, is produced as
in fig, 71.

The canal which is thus artificially produced is bounded behind by the part of
the hyaloid membrane which covers the front of the vitreous humour, and in front
by the imperfect membrane above alluded to as formed by the fibres of the zonula
which are passing to the anterior surface of the lens margin. Since these fibres
spring most abundantly from the part of the zonula which is opposite the intervals
between the ciliary processes, the membrane is as it were tied down at those intervals
and can only be distended between them ; hence the sacculated aspect of the so-called
canal.

Berger states that in the foetus the anterior free surface of the zonula is covered
with a layer of endothelial cells which disappears by birth.

As just stated, in addition to this anterior membranous prolongation of the
zonula, other fibres, more scattered in their disposition, pass at intervals across to
the periphery of the lens, some being attached to the extreme edge, others coming
into continuity with the posterior capsule, and others again occupying intermediate
positions (fig. 70). Those which pass to the posterior surface of the lens capsule
and to the extreme edge of the lens are stated to come for the most part from the
part of the zonula which overlies and is adherent to the most prominent portion of
the ciliary body, and these fibres therefore partially cross in direction those which
are corning from the depressions and passing to the anterior surface.

THE LENS.

THE LENS.

The lens (lens crystallina) is a transparent solid body, of a doubly convex shape,
with the circumference rounded off. It is completely enclosed by a transparent,
highly elastic membrane known as the capsule of the lens. The anterior surface is in

Fig. 72. — 1, FRONT VIEW; 2, HIND VIEW; 3, LATERAL VIEW OF THE FIBROUS STRUCTURE OF THE

ADULT LENS (after Arnold), f

«, anterior ; p, posterior pole. The direction of the superficial fibres is indicated by the curved
lines.

contact with the iris towards the pupil, receding from it slightly at the circumference ;
the posterior is embedded in the vitreous humour. Around the circumference is the
zonula. The capsule is strongest anteriorly (anterior capsule) and thinnest over the

Fig. 73. — DIAGRAM TO ILLUSTRATE THE COURSE OF THE FIBRES IN THE
POSTAL CRYSTALLINE LENS. (Allen Thomson.)

a, anterior ; p, posterior pole.

posterior surface of the lens (posterior capsule). Chemically

the lens-capsule yields neither elastiu nor gelatin, but appears

similar in composition to the sarcolemma of muscle and the

membranae propriae of glands. An indistinct fibrous and

lamellar structure has been described in it. The convexity

of the lens is not alike on the two surfaces, being greater behind ;

moreover, the curvature is less at the centre than towards the

margin. When in its natural position it measures about 8mm.

to 9mm. across, and about 4mm. from before backwards. The radius of curvature

during life of the anterior surface varies with the condition of accommodation from

about 10mm. when the eye is accommodated for distant vision, to Gmm. when

accommodated to the near point of distinct vision. That of the posterior surface is

about Gmm. in distant vision and a little less in near vision. In a fresh Jens,

divested of its capsule, the outer portion is soft and easily detached ; the succeeding

layers are of a firmer consistence ; and in the centre the substance becomes much

harder, constituting the so-called " nucleus." On the anterior and posterior surfaces

are faint white lines directed from the poles towards the circumference ; these in the

64

THE EYE.

adult are somewhat variable and numerous on the surfaces (fig. 72), but in the foetal
lens throughout, and towards the centre of the lens in the adult, they are three in
number, diverging from each other like rays at equal angles of 120° (fig. 73). The
lines which converge to the opposite poles have an alternating position. Thus
of those seen on the posterior surface of the foetal lens, one is directed vertically
upwards, and the other two downwards and to either side, whereas those on the
anterior surface are directed one directly downwards and the other tAvo upwards and
to the sides. These lines are the edges of planes or septa within the lens diverging
from the axis, and receiving the ends of the lens-fibres, which here abut against one

Fig, 74. — LAMINATED STRUC-
TURE OF THE CRYSTAL-
LINE LENS, SHOWN AFTER,
HARDENING IN ALCOHOL

(Arnold), f
1. nucleus ; 2, 2, lamellae.

another. As Tweedy has
pointed out, they may
be seen, by the aid
of the ophthalmoscope,

even during life. The rays seldom meet at a point,
but usually along a somewhat irregular area.

Structure. — When the lens has been hardened
and the capsule removed, a succession of concentric
laminae may be detached from it like the coats from
an onion. They are not continuous, but separate
into parts opposite the radiating lines above de-
scribed (fig. 74). The laminae are composed of
long, riband-shaped, microscopic fibres, 0'005mm.
broad, which adhere together by their edges, the
latter being often finely serrated (fig. 75, A).
The serrations of adjacent fibres abut against
one another so as to leave as in other epithelial

Fig. 75. — FIBRES OF THE CRYSTALLINE LENS. 350 DIAMETERS.

A, longitudinal view of the fibres of tbe lens from the ox,
showing the serrated edges. B, transverse section of the fibres
of the lens from the human eye (from Kolliker). C, longi-
tudinal view of a few of the fibres from the equatorial region
of the human lens (from Henle). Most of the fibres in C are
seen edgeways, and, towards 1 , present the swellings and nuclei
of the "nuclear zone ;" at 2, the flattened sides of two fibres
are seen.

structures fine interfibrillar or intercellular channels for the passage of fluid.
The lens-fibres pass in a curved direction from the intersecting planes of
the anterior half of the lens to those of the posterior half, or vice versa : in this
course no fibre passes from one pole to the other, but those fibres which begin near
the pole or centre of one surface, terminate near the marginal part of a plane on
the opposite surface, and conversely ; the intervening fibres passing to their corre-
sponding places between. The arrangement will be better understood by a reference
to fig. 73, where the course of the fibres in the foetal lens is diagrammatical ly
indicated.

The lens-fibres, as the history of their development shows, are to be looked upon
as greatly elongated cells. In the young state each has a clear oval nucleus, but in

STRUCTURE OF THE LENS.

65

the fully -formed lens the nuclei have disappeared from the fibres which form the
more internal parts of the lens, and only remain in the more superficial layers.

Fig. 76. — SECTION THROUGH THE MARGIN OP THE LENS,

SHOWING THE TRANSITION OP THE EPITHELIUM INTO
THE LENS-FIBRES (Bablichin).

Here they are found, not quite in the middle of
each fibre, but slightly nearer the anterior end,
their situation nearly corresponding in adjacent
fibres, and they form by their juxtaposition the
so-called " nuclear zone " around the lens. The
superficial fibres further differ from the more
deeply seated ones in being softer and larger, and
in possessing a plain, unserrated margin. The
extremities of all the fibres are softer and more
readily acted on by reagents than the middle
parts, and the axial or more internal part of a
fibre more so than the external, but the transi-
tion is gradual from one to the other, and there
is no definite membrane enclosing each fibre.
The lens-fibres when cut across are seen to be
six-sided prisms (fig. 75 B). By reason of this
shape they fit very exactly the one to the other
with but little interfibrillar cementing substance
between. This is met with in rather larger
quantity in the intersecting planes between the
ends of the fibres.

Thin and Ewart have shown that with certain
methods of treatment the superficial lens-fibres show
indications of being1 composed of a number of regular
segments separated by sharply marked lines of inter -
segmental substance (Journal of Anatomy, 1876).

The capsule of the lens is a transparent
structureless membrane ; somewhat brittle and
elastic in character, and when ruptured the
edges roll outwards. The fore part of the capsule,
from about 2*5 mm. from the circumference,
where the anterior part of the suspensory liga-
ment joins it, is much thicker than the back :
at the posterior pole of the lens the capsule is very
thin indeed. In the adult, it, like the lens itself,
is entirely non-vascular, but in the foetus there
is a network of vessels in the superficial part of
the capsule, supplied by the terminal branch of
the central artery of the retina, which passes
from the optic papilla through the canal of
Stilling in the vitreous humour to reach the
back of the capsule, where it divides into radiating branches. After forming
a fine network, these turn round the margin of the lens and extend forwards to
become continuous with the vessels in the pupillary membrane and iris (fig. 42,
p. 34).

VOL. III., FT. 3.

66 THE EYE.

Epithelium of the capsule. — At the back of the lens the fibres are directly in
contact with the inner surface of the capsule, but in front they are separated from
the latter by a single layer of cubical, polygonal, nucleated cells, which covers the
whole anterior surface underneath the capsule. Towards the edge or equator of
the lens the appearance and character of these cells undergo a change : they first
gradually take on a columnar form, and then, becoming more and more elongated,
present every transition to the nucleated lens-fibres of the superficial layers, into
which they are directly continuous (see fig. 76).

After death a small quantity of fluid (liquor Morgagni) frequently collects
between the back of the lens and the capsule : it appears to be derived from the
lens-fibres. There is no epithelium in this situation as in front.

Changes in the lens with age. — In the fcatus, the lens is nearly spherical
(fig. 77, a) : it has a slightly reddish colour, is not perfectly transparent, and is
softer and more readily broken down than at a more advanced age.

i C

^ Fig. 77.— SIDE VIEW OF THE LENS AT DIFFERENT AGES.

«, at birth with the deepest convexity ; b, in adult life with medium
convexity ; c, in old age with considerable flattening of the curvatures.

In the adult, the anterior surface of the lens is distinctly less convex than the
posterior (fig. 77, b) ; and the substance of the lens is firmer, colourless, and
transparent.

In old aye, it is more flattened on both surfaces (c) ; it assumes a yellowish or
amber tinge, and is apt to lose its transparency and gradually to increase in
toughness and specific gravity.

AQUEOUS HUMOUR AND ITS CHAMBER.

The aqueous humour fills the space in the fore part of the eyeball, between the
capsule of the lens with its suspensory ligament and the cornea. The iris, resting
in part upon the lens, divides the aqueous chamber partially into two, named
respectively the anterior and posterior chambers. This subdivision is incomplete in
the adult, but in the foetus before the seventh month it is completed by the mein-
brana pupillaris, which, by its union with the margin of the pupil, closes the
aperture of communication between the two chambers.

The anterior chamber is limited in front by the cornea and behind by the iris,
while opposite the pupil it is bounded by the front of the lens and its capsule.

The posterior chamber lies behind the iris. It js continuous through clefts in
the anterior part of the suspensory ligament of the lens with the triangular space
intervening between the margin of the lens, the anterior surface of the vitreous
humour and the ciliary body (canal of Petit), and it sends prolongations or pouches
between the zonula and the pars ciliaris retinae, as has already been described
(p. 62). The aqueous humour is a clear watery fluid, in which a few leucocytes
can sometimes be found. It is probably secreted mainly by the epithelium of the
ciliary body and its glands, and by the epithelium covering the posterior surface of
the iris. It finds exit through the clefts of the ligamentum pectinatum iridis,
into the spaces of Fontana and thence into the canal of Schlemm and the venous
system of that region, and in part into lymph-spaces in the iris, and thence to the
perichoroideal lymph-space.

RECENT LITERATURE OF THE EYE. 67

RECENT LITERATURE OP THE EYE.

Alexander, A., Ueber die Lymphcapillaren der Chorioidea, Archiv fiir Anatomic u. Phys.,
Anat. Abt., 1889.

Anderson, R. J., The lens in an albino rat, Monthly Int. Journal of Anatomy and Physiology,
x., 1893.

Ang-elucci, Richcrche istoL. entr. epitelio rctinico del vertcbrati, Atti d. R. accad. deiLincei, 1877.

Arnstein u. Agubow, Die Innervation des Ciliarkbrpers, Anat. Anzeiger, 1893.

Baquis, Elia, La retina deUa faina, Anatomischer Anzeiger, Jabrg. v., 1890.

Barabaschew, P., Beitrag zur Anatomic der Linse, Archiv fiir Ophthalmologie, xxxviii., 1892.

Barrett, J. W., The distribution of blood-vessels in the retina; of mammals, Journ. of Physiology,
vol. vii., 1886.

Bayer, J., Bildlichc Darstellung dcs gcsunden und krankcn Auges unserer Ifaustierc, Wien,
1890.

Beauregard, Etude du corps vitre, Journal de 1 Anat. , 1880.

Behrends, G. J., Beitrdge zur Kenntniss der Entwickdung dcs Nervus opticus und des Glas-
kbrpers bei Sdugethicren, Erlangen, 1888.

Berg-er, Emile, Anatomic normale et pathologique de 1'ceil, Paris.

Boden, J. S., and Sprawson, F. C., The pigment cells of the retina, Quarterly Journal of
Microscopical Science, xxxiii. 1892.

Brand, Emil, Die Nervcnendigungcn in der HornJiaut, Archiv fiir Augenheilkunde, Band xix.
1888 ; (Translation in Archives of Ophthalmology, New York, vol. xviii.).

Canfield, W. B., Vcrgl. anatom. Studien u. d. Accommodations-apparat des Vogelauges, Arch.
f. mikr. Anat, xxviii. , 1886.

Chievitz, J. H. , Entivickelung der Fovea centralis retina:; Die Area centralis retinas, Verhandlungen
der anatom. Gesellschaft auf der 2. u. 3. Versammlungen, Anatom. Anzeiger, ii. and iii. 1888, 1889 ;
Untcrsuchungen uber die Area centralis retinae, Arch. f. Anat. u. Physiol., Anat. Abtlg. 1889 ; Ueber
das Vorkommcn der Area centralis retince in den vier hbheren Wirbeltierklassen, Archiv fiir Anatomic
und Physiologic, Anatomische Abteilung, 1891 ; Untersuchungen uber die Entwickelung der Area und
Fovea centralis rctince, Arch. f. Anat. u. Physiol., Anat. Abtlg. ; Die Area und Fovea centralis retina
beim menschlichen Foetus, Internationale Monatsschrift fiir Anatomic und Physiologic, Band iv., 1887.

Ciaccio, G. V., Diuna novissima e notabile particolarita di struttura osservata nella cornea di
un cavallo, Memorie della r. accademia delle scienze di Bologna, v. 1891.

Cirincione, G., Sulla struttura delle vie lacrimali dcWuomo, La riforma medica, vi. 1890.

Claeys, G., De la region ciliaire de la ratine et de la zonule de Zinn, Archives de biologic,
tome viii., 1888.

Collins, E. T., The glands of the ciliary body in the human eye. Transactions of the Ophthal-
mological Society of the United Kingdom, London, 1890—91 ; On the development and abnormalities
of the zonule of Zinn, R. London Ophth. Hosp. Reports, xiii., 1891.

Collins, W. J., The composition of the human lens in health and in cataract, and its bearing
upon operations for the latter, Illustrated Medical News, 1889.

Colucci, Cesare, Alterazioni nella retina d. rana in scguito alia rccisione del nervo ottico,
Riforma medica, 1890.

Cuccati, G., Contributo alV anat. microsc. della retina del bue e del cavallo, Mem. d. r. accad.
d. sci. di Bologna, 1886 ; Sur la structure rayonnee du segment externe des bdtonnets de la rttine,
Arch. ital. de biol., vii. 1886.

Czermak, Wilh., Beitrag zur Kenntniss der sog. cilio-rctinalcn Gefasse, Wiener klinische
Wochenschrift, 1888.

Debierre, Ch., Sur le muscle de Viris de Vhomme, Comptes rendus de la socie'te de Biologic,
v. 1888.

Dimmer, F., Die ophthalmoskopischcn Lichtreflexe dcs Netzhaut nebst Beitrdgen z. normal. Anat.
der Netzhaut, Wien.

Dog-iel, Alexander, Ueber dienervosen Element* in der Netzhaut der Amphibien u. Vogel, Anat.
Anzeiger, iii. ; Ueber das Verhalten der nervosen Elemente in der Retina der Ganoiden, Beptihen,
Vogel und Sdugethiere, Anatora. Anzeiger, iii., 1888 ; Die Nervenendkbrperchen in der Cornea und
Conjunctiva bulbi des Menschen, Archiv fiir mikroskopische Anatomic, xxxvii., 1891 ; Ueber die nervosen
Elemente in der Retina des Menschen, Archiv fiir mikroskopische Anatomic, xxxviii., 1891 ; xl., 1892.

Dog-iel, J., Neue Untersuch. ii. d. pupillenerweiternden Muskdn, &c., Arch. f. mikr. Anat.,
xxvii. 1886 ; Neuroglia der Retina des Menschen, Arch. f. mikr. Anat., 1893.

Dostojewsky, A., Ueber d. Bau des Corpus ciliare u. der Iris von Saugethieren, Arch. f. mikr.
Anat., xxviii. 1886.

Dubois, Raphael, et Renaut, J., Sur la continuite de Vepithelium pigmente de la retine avec
les segments cxterncs des cdnes et dcs bdtonnets, ct la valeur morphotogique de cette disposition chez les
verttbres, Comptes rendus hebdom. de 1'academie des sciences de Paris, tome cix. 1889.

Eng-elmann, T. W., Ue. Bewegungen der Zapfen u. Pigmentzellen unter d. Eivfluss des Lichtes
u. des Nervensy stems, Pfliiger's Archiv, Bd. xxxv., 1885.

Ewing-, A. E. , Ueber ein Bauverhaltniss des Irisumfanges beim Menschen, Archiv fiir Opnthal-
mologie, Bd. xxxiv. 1888.

Falchi, F., Sur Vhistogenese de la retine et du ncrf optique, Archives italiennes de biologic,
tome ix. ; Ueber die Histogenese der Retina und des Nervus opticus, Archiv fiir Opntnalm.,
xxxiv. 1888.

F 2

68 RECENT LITERATURE OF THE EYE.

Fick, Eugren, Untersuchungen iiber die Pigmentwanderuvg in der Netzhaut des Froschcs, Ai'chiv
fur Ophthalmologie, xxxvii., 1891.

Fridenberg-, Percy, Ueber die Sternfigur der Kry stall- Linse, Strassburg, Inaug.Diss. 1891.

v. Gamier, R. , Ueber den normalen und pathologischen Zustand der Zonula Zinnii. Archiv
fiir Augenlieilkunde, xxiv. 1891.

Geberg-, A., Ue. Nerven der Vogel-iris, Monthly Intern. Journ. of Anat., Vol. i.

v. Genderen-Stort, Mouvements des elements de la retine sous Vinfluence de la Ivmiere, Archives
neerland. des sci. med., 1887 ; .Ueber Form- und Ortsvcrdndcrungen der Netzhaut- Elemente unter
Einfluss ron Licht und Dunkel, Archiv fiir Ophthalmologie, Band xxxiii., 1888.

Gilford, H., Ue. d. Lymphstrome des Auges, Arch. f. Augenheilkunde, xvi. 1886 ; Further
experiments, d-c., Arch, of ophthalm., 1892, and Arch. f. Augenheilk., xxvi., 1893.

Golding--Bird, C. H., and Schafer, E. A., On the structure of the fovea centrcdis, Proc.
Physiol. Soc., Journal of Physiol., 1894, and Int. Monthly Journal of Anat. and Physio!., 1894.

Gottschau, Ueber die Entwickl. der Saugethierlinse, Tagebl. d. 59. Versamml. deutsch. Naturf.
u. Aerzte, 1886.

Gradenig-o, Ue. d. Einfluss des Lichtes u. d. Warme an der Retina des Frosches, Allgem. Wiener
Med. Zeitung, 1885.

Grossmann, De I 'ossification dans Vceil, Archives d'ophthalraologie, tome ix. 1889.

Gruenhag-en. A., Ueber die Muskulatur und die BrucKsche Membran der Iris, Anat.
Anz.. iii., 1888.

Gunn, R. Marcus, Researches at the St. Andrews marine laboratory on the embryology of the
retina of Telcosteans, The Annals and Magazine of Natural History, series vi., vol. ii., 1888; On the
nature of light-percipient organs and of light- and colour-perception, The Royal London Ophthalmic
Hospital Reports, 1888 ; Congenital malformations of the eyeball and its appendages, Ophth. Review,
viii. 1889; Growth of new lens-fibres, <kc., Trans, of the Ophthal. Soc., vol. viii., 1889: Article
"Eye" in Morris' Anatomy, 1892.

Gutmann, G., Ueber die Lymphbahnen der Cornea, Archiv fiir mikroskop. Anatomic, xxxii. 1888.

Haase, F., Ueber den Canalis Petiti des Menschen, Inaug. -Dissert. , Rostock, 1889.

Hache, E., Sur la structure et la significance du corps vitre", Compt. rend., cv. 1887 ; Sur
Vhyaloide ct la zone de Zinn, Compt. rend, de la soc. de biol., 1889.

Haensell, P., Recherches sur le corps vitre, Paris, 1886.

Hannover, A., On a spongy formation between the sclerotic and choroid coat in new-born
children, The Lancet, 1886, vol. ii.

Heitzmann, C. , The minute structure of the cornea. The Microscope, Trenton, 1890.

Hirschberg-, J. , Blutgefdssneubildung ini Glaskorper, vor dem Sehnerveneintritt, Centralblatt
fiir praktische Augenheilkunde, Jahrg. 13, 1889.

Hosch, F., Ehrlich's Methylenblaumethode u. ihre Anwendung auf das Auye, Arch. f. Ophth.,
Bd. xxxvii., 1891.

Jessop, "W. H., The intra-ocular muscles of mammals and birds, Abstract of Hunterian lectures,
Ophthalmic Review, vol. vi.

Johnson, G. Lindsay, BemerTcungen iiber die Macula lutea, Archiv fiir Augenheilkunde, xxv,
1892 ; Observations on the Macula luiea, Arch. Ophth., New York, 1892.

Keibel, Franz, Zur EntwicHung des Glaskorpers, Arch. f. Anat. n. Phys., Anatom. Abt., 1886.

Kirschbaumer, Rosa, Ueber Alter sverdnderung en der Urea, Ophbhalmologen-Congress, Heidelberg,
August, 1888 (Arch. f. Ophthalmologie); Ueber Alter sverdnderung en der Uvea, Archiv fiir Ophthal-
mologie, xxxviii., 1892.

Kohl, C., Rudimentdre Wirbelthieraugen, Biblioth. Zool., 1893.

Kollock, The eye of the negro, Trans. Amer. Ophthalm. Assoc., 1892.

Koranyi, A., Beitr. zur Entwicklung der Krystallinse, Intein. Monthly Journal of Anatomy and
Physiology, iii. 1836.

Krause, "W., D'e Retina, Internationale Monatsschrift fiir Anatomic. A series of papers (from
1886 onwards) on the comparative structure of the Retina in the vertebrate classes.

Kuhnt, Ueber die Fovea centralis, Sitzungsb. d. ophthalm. Gesellsch., 1881 ; Histologische
Studien an der menschlichen Netzhaut, Jenaische Zeitschrift fiir Naturwissenschaft, xxiv. 1889.

Landolt, Beitrdge zur Anatomic vom Frosch, Salamander u. Triton, Arch. f. mikr. Anat., vii,
1871.

Lang-, The ciliary processes and the suspensory ligament, Ophthalmolog. Review, December, 1888.

Lang- and Barrett, The refractive character of (he eyes of mammalia, Ophth. Hospital Reports,
xi. 1886.

Lang-e, Otto, Topographische Anatomic des menschlichen Orbitalinhalts, Braunschweig, 1887.

Lang-er, Fritz, Beitrag zur normalen Anatomic des menschlichen Auges, " 1st man berechtigt, den
Per ichor ioidalraum und den Tenon'schen Raum als Lymphrdume aufzufassen ? " Sitzungsber. der
Kais. Akad. d. Wiss. in Wien., Bd. xcix., Abt. iii. 1890.

Lennox, R., Beobacht. u. d. Histologie der Netzhaut, &c.y Arch. f. Ophthalm., xxxii. 1886;
Development of the crystalline lens, Brooklyn Medical Journal, vol. iii. 1889.

Loewenthal, N. , Ue. d. Harder 'sche Druse des J gels, Anat. Anz. vii., 1892 ; Beitr. z. Kcnntn.
d. Harder sche Druse bet. d. Faugethieren, Ibid.

Martin, Paul, Entwickclung der Netzhaut bei der Katze, Zeitschrift fiir vergleichende Augen-
heilkunde, vii. 1891.

Matthiessen, S., Die neueren Fortschrilte in unscrer Kenntniss von dem optischcn Bau des
Auges der Wirbeltiere, Beitrage zur Psychologic und Physiologic der Sinnesorgane, Hermann von Helm-
oltz als Festgruss zu seinem 70. Geburtstage gewidmet, 1891.

RECENT LITERATURE OF THE EYE. 69

Mayerhausen, Der gefiisstose BczirJc der menschlichen Retina, Arch. f. Ophthalm., xxix. .
1883.

Merian, Karl, Vcrsuche ilber die Lymphwege des Auges, Archiv fur Anatoinie und Physiologie,
Anatomische Abteilung, 1891.

Merkel. Fr., Handbuch d. topoyraph. Anat., 1885.

Merkel, Fr., und Orr, Andrew W., Das Auye des Neugeborcnen an einem schematischen
Durchschnitt erlautcrt, Anatomische Hefte, i., 1892.

Meyer, E., De la forme de I' hemisphere antdrieur de Voeil determine par la mensuration des
courburcs de la corne'c et de la sclerotique, Revue gdnerale d'ophthalmologie, annee viii., 1889.

Michel, J., Ueber die Ausstrahlangsweise der Opticusfasern, d-c., Lud wig-Festschrift, 1874.

Morf, J., Exper. Beitr. zur Lekre von den Abflusswegen der vordcren Aunenkammcr, Dissert.
Zurich, 1888.

Motais, Recherche* sur Vanat. humaine et Vanat. comparee de Vappareil moteur de 1'ceil, Arch,
d'ophthalmologie, vi., 1886.

Musgrave, James, The blond-vessels of the retina, The Journal of Anatomy and Physiology,
1892.

Nicati, W., Sur la disposition et le fonctionnement normal et pathologique d'un veritable appareU
glandulaire dans I'ceil des mammifercs, Comptes rendus hebdom. de 1' Academic des sciences, tome
cviii. 1889 ; Note sur la disposition ct le fonctionnement normal d'un apparcil glandulaire dans I'ceil
des mammiferes, Recueil d'ophthalmologie, 1889 ; Physiol. et pathoL de la glande des proces ciliaires,
Compt. rend d. 1. soc. de biol., 1889 ; La glande de Vhumeur aqueuse, glande des proces ciliaires ou
glande uvee, Archives d'ophthalmologie, tome x. 1890.

Nuel, J. P. , De Vendothelium de la chambre anterieure, Archives d'ophthalmologie, x., 1890 ; De la
vascularisation de la choroide et de la nutrition de lei ratine principalement au niveau de la fovea
centralis, Archives d'ophthalmologie, xii. 1892.

Nuel, J. P., et Cornil, F., De Vendothelium de la chambre anterieure de Vceil, particulierement
de celui de la corne'e, Archives de Biologic, tome x. 1890.

Pagret, Stephen, Congenital pig mentation of the sclerotic, Brit. Med. Journ., 1887.

Peltesohn, N., Zur Morphologic der Papilla optica, Centralblatt fur praktische Augenheilkunde,
xii. 1888.

Pollock, C. F., The normal and pathological histology of the human eye and eyelids,
London, 1886.

Probating-, A., Ein Beitrag zur feineren Anatomic des Lides u. der Conjunctiva des Menschenu.
des Affen, Zeitschr. f. vergleich. Augenheilkunde, iv. 1886.

Ramon y Cajal, S., Sur la morphologic et les connexions des tUments de la retine des oiseaux,
Anatomische Anzeiger, Jahrg. iv. 1889 ; .Estruclura de la retina de las aves, Revista trimestral de
Histologia, &c., ano i. ; La retina de los batrachios y reptiles, Trabajos del laboratorio histol. de
Barcelona, 1891; La retina de los Tde6steos, &c., "Madrid, 1892; La, retine des vertebres, La
Cellule, ix., 1893 [contains a general account of the whole subject, including the author's previous
observations].

Rampoldi, R., Sull 'anatomia della regione interna della retina dei mammiferi, Annali di ottal-
mologia, xvii. 1888.

Ranvier, Traite technique d'histologie, 1889.

Retterer, Ed., Note sur la structure de Viris chez les mammiferes, Comptes rendus de la Societe
de biologic, tome v. 1888.

Rieke, A., Ueber Formen und Entiuickelung der Pigmentzellen der Chorioidea, Archiv fiir
Ophthalmologie, xxxvii., 1891.

Ritter, C., Studien uber die Stdbchenschicht der Vogel, Internationale Monatsschrift fur Anatomic
und Physiologie, viii. 1891 ; Zur Histologie der Zapfen der Fischretina, Internationale Monatsschrift
fiir Anatomie und Physiologie, viii. 1891.

Rochon-Durig-neaud, Rechcrches sur Vangle de la chambre anUrieure et du canal de Schlemm,
Paris, 1892 ; and Arch, d'ophthalm., xiii., 1893.

Rudloff, P., Ueber eine Eigcnthumlichkeit der dusseren Korner, Arch. f. Anat. u. Phys., Anat.
Abth., 1886.

Rumschewitsch, Conrad, Ueber die Anastomosen der hinteren Ciliargefdsse mit denen des
Opticus und der Retina, Klinische Monatsblatter fiir Augenheilkunde, Jahrg. xxvii. 1889 ; Zur
Morphographie der Papilla nervi optici, Centralblatt fiir praktische Augenheilkunde, xiii. 1!

Samuelsohn, Zur Topographic d. Faserverlaufs im mcnschlichen Sehnerven, Centralbl. f. d.
med. Wissensch., 1880.

Sardemann, E., Beitrdge zur Anatomie der Thranendruse, Berichte der naturforschencien
Gesellschaft zu Freiburg i. B., Band iii. 1888.

Schaper, A., Zur Histologie der menschlichen Retina, A. f. mikr. Anat., Bd. xh., 1}

Scherl, J., Unters. u. d. Pigment des Auges, Arch. f. Ophth., Bd. xxxix., 1893.

Schiefferdecker, P., Studien zur vergleichenden Histologie der Retina, Arch. f. mikr. Anat.,
Bd. xxviii., 1886.

Schloesser, Ueber die Lymphbahnen der Linse, Miincheuer medicinische Wochenschrift, Jahrg.
xxxvi., 1889.

Schoen, Zonula u. Grenzhaut des Glaskorpers, Arch. f. Ophth., xxxii. 1886 ; Die Ronkamtat des
vorderen Zonablattes nach vorn, Archiv fiir Augenheilkunde, Band xxi. 1889-90.

Schwalbe, G., Lehrbuch der Anatomie der Sinnesorgane, Erlangen, 1887.

Smith, Priestley, On the size of the cornea in relation to age, sex, refraction and primary
glaucoma, The Lancet, 1889, also Brit. Med. Journ,, 1889 ; On the escape of fluid from the aqueous
and vitreous chambers, Ophth. Review, 1888.

70 RECENT LITERATURE OF THE EYE.

Solg-er, Schnitte durch die normale Netzhaut, Verhandlungen deranatom. Gesellschaft, Anat. Anz.,
iv. 1889.

Staderini, Carlo, Ueber die Abflusswege des Humor aqueus, Archiv fiir Ophthalmologie, xxxvii.,
1891.

Stieda, Ludwigr, Ueber die Caruncula lacrymalis des Menschen, Archiv fiir mikroskopische
Anatomie, Band xxxvi. , 1890.

Stohr, Philipp, Ueber die Netzhaut, Sitzungsberichte der physikalisch-medicin. Gesellschaft zu
Wiirzburg, Jahrg. 1883.

Straub, M., Notiz uber das Ligamentum pectinatum und die Endigung der Membrana Descemeti,
Archiv f. Ophthalmologie, Band xxxiii., 1888 ; Die Lymphbahnen der Hornhaut, Archiv fur Anatomie
und Physiologic, Anatom. Abt. , 1887 ; Beitr. zur Kenntniss des Glaskorpergewebes, Arch. f. Ophthalm.,
Band xxxiv., 1888; Ueber das Gleichctcwicht der Gewebs- u. Fiiissigkeitsspanungen im Auge, Ibid.,
Bd. xxxv., 1889.

Stuart, T. P. Anderson. On a membrane lining the fossa patellarls of the corpus vitreum,
Proceedings of the Royal Society, xlix., 1891 ; On the connexion between the suspensory ligament
of the crystalline lens and the lens capsule, Proceedings of the Royal Society, xlix., 1891 ; A mode
of demonstrating the gross structure of the eye-ball, Journal of Anat. and Physiol., 1891.

Tartuferi, P., SuWanatomia della retina, Ai'chivio per le scierize mediche, anno xi., 1887 ;
SulV anatomia della retina, Internationale Monatsschrift fiir Anatomie und Physiologie, Bandiv., 1887 ;
Sulla strata dei granuli interni della retina, Giornale della r. accademia di medicina di Torino,
vol. 1.

Topolanski, A., Ueber den Bau der Zonula und Umgebung nebst Bemerkungen uber das
albinotische Augc, Archiv fiir Ophthalmologie, xxxvii., 1891.

TJcke, Alexander, Zur Entwickelung des Pigmentepithels der Retina, Inaug.-Diss., Dorpat,
1891.

TJlrich, Richard, Neue Untersuchungen uber die Lymphstromung im Auge, Archiv fiir Augen-
heilkunde, Band xx., 1889.

Virchow, Hans, Ueber d. GlasTcorpergewebe u. s. w., Ber. der ophthalm. Gesellschaft, 1885 ;
Ue. d. Form u. Fatten des Corpus ciliare, Morph. Jahbr., xi., 1885 ; Ue. d. verschiedenen Formen d.
Ligam. pect. iridis, Arch. f. Anat. u. Phys., Phys. Abth., 1885 ; Ueber Augengefdsse der Carnivoren,
Verhandl. der physiol. Gesellschaft zu Berlin, Jahrg. 1887.

Voll, Adam, Ueber die Entwickelung der Membrana vasculosa retinee, Festschrift fiir A. v
Koelliker, gewidmet vom anat. Institut zu Wiirzburg, 1892.

Vossius, Ein Fall von beidenseitigen centralen Skotom, <bc., Arch. f. Ophthal., xxviii., 1883.

Weiss, Anatomie der Eintrittsstelle der Sehnerven, Miinchener medicinische Wochenschrift,
1889.

Wertheim, Th., Ueber die Zahl der Seheinheiten im mittleren Teile der Netzhaut, Archiv fiir
Ophthalmologie, Bd. xxxiii., 1888.

Wiener kiewicz, B., Beitrdge zur Kenntniss der persistierenden Pupillarmembran, Archiv fiir
Ophthalmologie, Band xxxiv., 1888.

Wurding-er, Ue. d. vergl. Anatomie des Ciliarmuskels, Zeitschr. f. vergl. Augenheilkunde, 1886.

Zaluskowski, K., Bemerkungen uber den Bau der Bindehaut, Archiv fiir mikroskopische
Anatomie, Band xxx.

Ziem, Ueber das SchweUgeivebe des Auges, Archiv fiir pathologische Anatomie, 1891.

THE EAR.

71

THE EAR.

THE organ of hearing is divisible into three parts : the external ear (fig. 78,
1, 2), the tympanum or middle ear (3), and the labyrinth or internal ear (G). The
•
Fig. 78. — DIAGRAMMATIC VIKW FROM

BEFORE OF THE PARTS COMPOSING
THE ORGAN OF HEARING OF THE

LEFT SIDE (after Arnold).

The temporal bone of the left side,
with the accompanying soft parts, has
been detached from the head, and a
section has been carried obliquely
through it so as to remove the front
of the meatus externus, half the
tympanic membrane, and the upper
and anterior wall of the tympanum
and Eustachian tube. The meatus
internus has also been opened, and
the bony labyrinth exposed by the
removal of the surrounding parts of
the petrous bone. 1, the pinna and
lobule ; 2 to 2', meatus externus ; 2',
membrana tympani ; 3, cavity of the
tympanum ; above 3, the chain of
small bones ; 3', opening into the
mastoid cells ; 4, Eustachian tube ;
5, meatus internus, containing the
facial (uppermost) and auditory
nerves ; 6, placed on the vestibule of
the labyrinth above the feuestra
pvalis ; a, apex of the petrous bone ; b, internal carotid artery ; c, styloid process ; d, facial nerve
issuing from the stylo-mastoid foramen ; e. mastoid process ; /, squarnous part of the bone.

first two of these are to be considered as accessories to the third, which is the
portion of the organ to which the fibres of the eighth or auditory nerve are
distributed.

THE EXTERNAL EAR.

In the external ear are included the pinna — the part of the outer ear which
projects from the side of the head — and the meatus or passage which leads thence
to the tympanum, and which is closed at its inner extremity by a membrane inter-
posed between it and the middle ear.

THE PINNA.

The general form of the pinna or auricle, as seen from the outside, is concave,
to fit it for collecting and concentrating the undulations of sound, but it is thrown
into various elevations and hollows, to which distinct names have been given
(fig. 79). The largest and deepest concavity is called the concha ; it surrounds the
entrance to the meatus, and is interrupted at its upper and anterior part by a ridge,
which is the beginning of the helix. In front of the concha, and projecting back-
wards over the meatus, is a conical prominence, the trayus (fig. 79), covered
usually with hairs. Its upper part sometimes forms a rounded prominence (tuber-
culum supratragicum, His). Behind the tragus, and separated from it by a deep notch,
is another smaller elevation, the antitragus. Below the antitragus, and forming the
lower end of the auricle, is the lobule, which is devoid of the firmness and
elasticity that characterise the rest of the pinna. The thinner and larger portion of

THE EAR.

the pinna is bounded by a prominent and incurved margin, the helix, which,
springing above and rather within the tragus, from the hollow of the concha,
surrounds the upper and posterior margin of the auricle, and gradually loses itself
in the back part of the lobule. Within the helix is another curved ridge, the
anthelix, which, beginning below at the antitragus, sweeps round the hollow of
the concha, forming the posterior boundary of that concavity, diverging above it
into two ridges. Between the helix and the anthelix is a narrow curved groove,
the fossa of the helix (fossa scaphoidea) ; and in the fork of the anthelix is a
somewhat triangular depression, the fossa of the anthelir (fossa triangular is).

car-point (when present]

crus anthelicis sup.

Mix

fossa triangularis
crus anthelicis inf.

tragus

I,. _ __ antitragus

incisura intertragica

lobulus

Fig. 79. — OUTER SURFACE OF THE RIGHT AURICLE. (After Arnold.)

Ear-point ; Tubercle of Darwin. — Slight projections are occasionally observed
in the human subject at the margin of the helix. One of these to which Darwin's
attention was drawn by Mr. Woolner, the sculptor, is of interest as representing the
much more distinct pointed extremity met with in the expanded ears of quadrupeds
(Darwin, " The Descent of Man "). The point in question is represented in the
sketch given in fig. 79 B. It is constant in the embryo of about the 6th month,
where it presents a relative extent of development which is permanent in certain
monkeys (Schwalbe).

Considerable variation is met with in the size and shape of the pinna,1 in its amount of
projection from the side of the head, in the extent of folding which it exhibits, and in the
size of the lobule, and this is not only in individuals of different races, but even in those
belonging to the same family. Attempts have been made to use these variations as a basis of
classification in criminal anthropology, but with results of very doubtful value. The lobule
is usually regarded as a human characteristic, but it is sometimes found fairly well developed
in anthropoids, and is often very little developed in man.

Structure. — The pinna consists mainly of yellow fibro-cartilage and integument,
with a certain amount of adipose tissue. It has several ligaments and small muscles
of minor importance.

The sJcin covering it is thin, closely adherent to the cartilage, especially on the
concave aspect, and is covered with hairs which are .provided with large sebaceous
follicles. It also contains sweat glands on the convex aspect, but few or none on

1 The relation of the transverse to the longitudinal measurement of the pinna is known as the ear-
index ( _ J and is employed in anthropometry.

STRUCTURE OF THE PINNA.

73

the concave side. In the external auditory meatus these reappear in a modified
form as the ceruminous glands. The hairs of the pinna are most numerous and
longest on the tragus and antitragus. The hairs on the margin and convex aspect
of the ear are arranged with a general tendency to point towards the tubercle of
Darwin, where the converging series may even form a distinct tuft, thus furnishing
an additional argument in favour of the view regarding the meaning of that promi-
nence which was taken by Darwin.

crus helicis

helix

fossa scaphoidea _

spina helicis -

anthelix —i

free edge of trar/u* _-,

incisura Santorhn J

tragus plate —

end of cartilage of -
meatus

Fig. 80. — EAR-CARTILAGE, ANTERIOR ASPECT. (Arnold.)

The cartilage (figs. 80 to 82) forms a plate 1 mm. to 3 mm. thick, with all the
inequalities already described as apparent on the outer surface of the pinna, and on its

antitragus
a

processus caudalis
b

-. spina helicis

— incisura Santorini

Fig. 81. — EAR-CARTILAGE, LATERAL ASPECT. (Schwalbe.)

In the natural position of the parts the corner of the tragus plate ** fits into the angle marked * at
the anterior part of the helix. Between a and b, the isthmus separating the auricle-cartilage from the
cartilage of the meatus.

cranial surface having prominences the reverse of the concha and the fossa of the helix,
while between these is a depression in the situation of the anthelix. The cartilage
is not confined to the pinna, but enters likewise into the construction of the outer
part of the external auditory canal. When dissected from other structures, it is

THE EAR.

seen to be attached by fibrous tissue to the rough and prominent margin of the
external auditory meatus of the temporal bone. The tubular part is cleft in front
between the tragus and fore-part of the helix inwards to the bone, the deficiency
being filled with fibrous membrane. The whole cartilage may be looked upon as an
elongated plate, the lower part of which is folded round in front so as to bring it
nearly into contact with the upper part. There is no cartilage in the lobule except
at its base, where the caudal process of the ear-cartilage passes into it : otherwise
it contains only fat and tough connective tissue.

Behind the prominence of cartilage which forms the antitragus is a deep notch,
separating it from the helix. Behind and below this the ear-cartilage forms a tail-like
process descending towards the lobule (caudal process). At the fore part of the pinna,
opposite the first bend of the helix, is a small conical projection of the cartilage,
called the spine of the helix, to which the anterior ligament is attached. Behind this
process is a short vertical slit in the helix ; and on the surface of the tragus is a
similar but somewhat longer fissure. A deep fissure (incisura terminalis, Schwalbe)
passes back between the commencement of the helix and the tube of the ear, and

cminentia fosscc
triangularis

cinincntia
scaphce

i

sulcus anthelicis
transversus

incisura Santorini

fossa anthelicis
eminentia conch ce

i_ sulcus cruris kelicis

ponticulus (insertion of
post- auricular musde}

processus posterior
processus caudalis

processus
triangularis

Fig. 82. — EAR-CARTILAGE, MESIAL ASPECT. (Schwalbe.)

another passing outwards and backwards from the deep end of the longitudinal cleft
separates the part forming the tragus from the rest of the tube, so that the tube is
continuous with the pinna only by means of a narrow isthmus. Other irregular gaps
or fissures partially divide the cartilaginous tube transversely. These deficiencies are
termed fissures of Santorini. They are usually two in number. These and the other
named recesses and prominences of the ear-cartilage are shown in the accompanying
figures, and do not require to be further described. The substance of the cartilage
is very pliable, and is covered by a firm fibrous perichondrium. Near its attachment
to the bone it becomes hyaline.

Ligaments. — Of the ligaments of the pinna, the most important are two, which
assist in attaching it to the side of the head. The anterior ligament, broad and
strong, extends from the spine of the helix to the root of the zygoma. The
posterior ligament fixes the back of the auricle (opposite the concha) to the outer
surface of the mastoid process of the temporal bone. A few fibres attach the tragus
also to the root of the zygoma. Ligamentous fibres are likewise placed across the
fissures and intervals left in the cartilage (intrinsic ligaments).

MTSG'LES OF THE PINNA. 75

Muscles.— Of the muscles of the pinna, those which are attached by one end to
the side of the head, and move the pinna as a whole, have been already described
(Vol. II.) : there remain to be examined several smaller muscles, composed of thin
layers of pale-looking fibres, which extend from one part of the pinna to another,
and may be named the, special muscles of the organ. Six such small muscles are
distinguished ; four being placed on the outer and two on the inner or deep surface
of the pinna.

The smaller muscle of the helix (fig. 83, 1) is a small bundle of oblique fibres,
lying over, and firmly attached to, that portion of the helix which springs from the
bottom of the concha. Like the other of these muscles, its fibres are, in part,
attached to the skin.

The greater muscle of the helix (2) lies vertically along the anterior margin of the
pinna. By its lower end it is attached to the spine of the helix ; and above, its
fibres terminate opposite the point at which the ridge of the helix turns backwards.
The anterior auricular muscle is sometimes continued partly into this muscle.

Fig. 83, A and B. — OUTER AND INNER SURFACES OF THE RIGHT PINNA, EXPOSED TO SHOW THE SMALL

MUSCLES (from Arnold).

1, musculus helicis minor; 2, m. helicis major ; 3, tvagicus ; 4, antitragicus ; 5, musculus transversus
auriculae ; 6, musculus obliquus auriculae.

The muscle of the tragus (3) is a flat bundle of short fibres covering the outer
surface of the tragus : its direction is nearly vertical. Occasionally a slender bundle
of muscular fibres is seen prolonging this muscle across the cleft in the cartilage
between the tragus and fore part of the helix to be attached to the spine of the helix
(m. pyramidalis, Jung). Another muscle (dilatator conchce, Theile) of less constant
occurrence lies upon the anterior face of the tragus, bridging over the greater fissure
of Santorini, which is there present.

The muscle of the antitragus (4) is placed obliquely over the antitragus and
behind the lower part of the anthelix. It is fixed at one end to the antitragus,
from which point its fibres ascend somewhat to be inserted into the caudate process
of the helix, above and behind the lobule.

The transverse muscle (5) lies on the inner or cranial surface of the pinna, and
consists of radiating fibres which extend from the back of the concha to the promi-
nence which corresponds with the groove of the helix.

The oUique muscle (Tod) (6) consists of a few fibres stretching from the back
of the concha to the convexity directly above it, across the back of the inferior
branch of the anthelix, and near the fibres of the transverse muscle.

The muscles of the tragus and antitragus tend to contract the entrance to the meatus
when stimulated by electricity (Duchenne), the muscles of the helix having a contrary ten-
dency. They are none of them under the influence of the will, but it is possible they may act
slightly in a reflex manner. All the ear- muscles are supplied by the facial nerve.

76

THE EAR.

Vessels of the pinna (fig. 84). — The auricular branch of the posterior auricular
artery, a branch from the external carotid, is distributed chiefly on the mesial surface,
but some of its branches turn over the folded margin to reach the external surface
of the helix : others pierce the cartilage and ramify on the external surface of the
anthelix, concha and lobule. Besides this artery, the auricle receives the anterior
auricular branches from the superficial temporal. These chiefly supply the anterior
part of the lobule, the tragus, and the anterior part of the helix.

The veins for the most part accompany the arteries. They join the posterior
auricular and temporal veins, but some enter the mastoid emissary vein of the
lateral sinus (see Vol. II., p. 526). The lymphatics of the pinna pass partly
forwards from the concha to join a gland in front of the tragus ; partly downwards
and backwards from the upper and posterior part of the pinna towards the mastoid
glands ; and partly downwards from the lobule towards the parotid lymphatic
glands.

Nerves. — The great auricular nerve, from the cervical plexus, supplies the
integument of the greater part of the inner surface of the auricle, and sends small
filaments with the posterior auricular artery to the outer surface of the lobule and

attrahens
aurem 8 7

rctrahens
6 aurem

\ \

3 10 1 2

Fig. 84. — ARTERIES SUPPLYING THE AURICLE. (Testut.)

10

1, external carotid ; 2, internal maxillary ; 3, superficial temporal ; 4, transverse facial ; 5, middle
temporal ; 6, orbital branch of temporal ; 7, anterior terminal branch ; 8, posterior terminal branch ;
9, anterior auricular branches ; 10, posterior auricular artery ; 11, its mastoid branch ; 12, perforating
branches.

the part of the ear above it. The auricular branch of the posterior auricular nerve,
derived from the facial, after communicating with the auricular "branch of the
pneumogastric, ramifies on the back of the ear, supplying the small muscles. The
auricula-temporal branch of the third division of the fifth nerve gives filaments
chiefly to the outer surface of the pinna. A branch of the small occipital supplies
the upper part of the inner surface. Filaments from the temporal branches of the
facial supply the external muscles.

THE EXTEBNAL AUDITORY CANAL.

The external auditory canal, meatus auditorius externus (85, 2, 2), extends
from the bottom of the concha to the membrane of the tympanum and serves to
convey the vibrations of sound to the middle chamber of the ear. The canal is

VESSELS AND NERVES OF THE PINNA.

77

about 25 mm. long, but the superior and posterior boundaries are considerably
shorter than the inferior and anterior. If the part of the concha which is
bounded anteriorly and externally by the tragus is reckoned in with the canal,

Fig. 85, — DIAGRAMMATIC VIEW FROM

BEFORE OF THE PARTS COMPOSING
THE ORGAN OF HEARING OF THE

LEFT SIDE. (After Arnold. )

The temporal bone of the left side,
with the accompanying soft parts, has
been detached from the head, and a
section has been carried obliquely
through it so as to remove the front
of the meatus externus, half the
tympanic membrane, and the upper
and anterior wall of the tympanum
and Eustachian tube. The meatus
internus has also been opened, and
the bony labyrinth exposed by the
removal of the surrounding parts of
the petrous bone. 1, the pinna and
lobe ; 2 to 2', meatus externus ; 2',
membrana tympani ; 3, cavity of the
tympanum ; above 3, the chain of
small bones ; 3', opening into the
mastoid cells ; 4, Eustar.hian tube ;
5, meatus internus, containing the
facial (uppermost) and auditory
nerves ; 6. placed on the vestibule
of the labyrinth above the fenestra
ovalis ; a, apex of the petrous bone ; 6, internal carotid artery ; c, styloid process ; d, facial nerve
issuing from the stylo-mastoid foramen ; e, mastoid process ; /, squamous part of the bone.

its length must be given as considerably more (35 mm ). In its inward course it is
inclined at first somewhat forwards and very slightly ascends (external portion) : it
then turns pretty sharply backwards and is nearly horizontal (middle portion), and

fossa scaphoidca

fossa i liter crur alls
concha proper (upper part) —

impression of membrana —
flaccida

bend of mcalus concha proper (lower part)
Fig. 86.— CAST OF THE EXTERNAL AUDITORY MEATDS. (Bezold.)

is finally directed slightly forwards and decidedly downwards (internal portion)
(fig. 85). The calibre of the passage is smallest in the osseous part of the canal a
few millimeters from the membrana tympani : it is also somewhat contracted near
the end of the cartilaginous portion. Its form and dimensions have been studied
by v. Bezold, chiefly by means of casts of the cavity : the results of the transverse

.

78

THE EAR.

measurements at certain points are given in the accompanying diagram. At the
inner extremity the tube is terminated by the membrana tympani, which is placed
obliquely, being inclined downwards, forwards, and towards the median plane ; and
thus, as shown in fig. 85, the floor of the meatus is longer than its roof.

JT

WT

DIAGRAM SHOWING THE FORM
AND MEASUREMENTS OP
SECTIONS ACROSS THE
EXTERNAL AUDITOKY MKA-
TUS. (Bezold.) Natural
size.

J., at commencement of
cartilaginous portion ; II. ,
near end of cartilaginous por-
tion : ///., near beginning
of osseous portion ; IV., near
end of osseous portion.

Structure. — The wall of the meatus is composed partly of cartilage, and partly
of bone, and is lined by a prolongation of the skin.

The cartilaginous part occupies somewhat less than half the length of the passage.
It is formed, as already mentioned, by an inflection of the deep part of the cartilage
of the pinna, but the cartilage does not form a complete boundary ; the tube being
deficient at the upper and posterior part where it is completed by fibrous membrane.

The osseous portion is a little longer and on the whole rather narrower than the
cartilaginous part. At its inner end is a narrow groove (sulcus tympanicus), which

Fig. 87. — VIEW OF THE LOWER HALF OF THE AURICLE AND MEATUS IN THE LEFT EAR, DIVIDED BY A
NEARLY HORIZONTAL SECTION (after Rudinger).

1, posterior wall : 2, anterior wall of the cartilaginous meatus ; 3, posterior wall of the bony meatus ;
4 to 5, membrane of the tympanum, with the handle of the malleus cut ; 6, stapes, to the right of 6,
section of the cochlea ; 7, stapedius muscle ; 8, section of facial nerve ; 9, tensor tympani muscle ;
10, branches of the auditory nerve to the cochlea, saccule, and utricle, 11.

extends round the sides and floor of the meatus, but is deficient above ; into this
the margin of the membrana tympani is inserted.

The sltin of the meatus is continuous with that covering the pinna, but is very
thin in the osseous part, especially at the bottom of the passage. Here it adheres
very closely to the periosteum, and has no hairs or glands, but is provided with
vascular papillae (ridges, according to Kaufmann). At the end of the tube the
skin is prolonged over the surface of the membrana tympani, forming the outer
layer of that structure. Towards the outer part of the roof of the osseous portion
and throughout the cartilaginous portion the skin possesses fine hairs and sebaceous

EXTERNAL AUDITORY CANAL.

79

glands ; and in the thick subdermic tissue are small oval convoluted tubular glands
of a brownish-yellow colour, agreeing in form and structure with the sweat glands,
but larger in part or entirely, and in sufficient number at some parts, especially
where cartilage is deficient, to form an almost complete layer in the subcutaneous
tissue. The cerumen or ear-wax is secreted by these glands (glandulm ceruminosce),
and their fine ducts may be seen to perforate the skin of the meatus close to or
into the mouths of the hair follicles. According to Schwalbe the fatty part of the
ear-wax is formed by the sebaceous glands. This may be partly the case, but the
secretion of the ceruminous glands is certainly also of a fatty nature (fig. 88).

Vessels and nerves. — The external auditory meatus is supplied with arteries
from the posterior auricular, internal maxillary, and temporal arteries. The principal

Fig. 88. — SECTION OP SKIN OP

AUDITORY MEATUS, INCLUDING
TWO CERUMINOUS GLANDS.

(Griiber.)

root of hair -i

'V
I ;

hair

sebaceous
yland

&««• Wide

branches of the arteries
course along the upper and
back wall of the canal. The
veins and lymphatics take
the same course on leaving
the meatus as do the corre-
sponding vessels of the
pinna. The nerves are
derived from the auriculo- root-sheath -ffi
temporal branch of the fifth
and the auricular branch of „„„, „/*„„•„ 3$
the vagus. The latter sup-
plies the skin of the osseous
part of the canal and that
which covers the lower part
of the tympanic membrane.
State in the infant.
—The auditory passage is
only in part formed of bone
and cartilage in the infant.
The osseous part is formed
at birth by a small ring
of bone (tympanic bone)
which is deficient antero-
superiorly, where it is completed by uniting with the squamous portion of the
temporal bone, and this part of the temporal overhangs the meatus and con-
stitutes the chief part of its superior boundary. The floor is mainly formed by
fibrous tissue which unites the tympanic ring of bone with the fibro-cartilage
of the pinna and external part of the meatus. This is the fibrous tympanic
plate of Symington, and into it the tympanic bone gradually grows after birth.
This growth takes place chiefly from two points (Zuckerkandl) outwards into
the fibrous plate in question and usually in such a manner that a gap is left for
some time in the antero-inferior part of the bony meatus which sometimes persists
throughout life. The membrane of the drum is more inclined away from the
vertical in the foetus and new-born infant than in the adult, being in fact in the
same plane as the roof and overlying the fibrous floor of the inner part of the

cerumiiunts
glands

80

THE EAR.

meatus. The meatus of the foetus is for the most part closed by apposition of
its upper and lower walls, but towards the end of foetal life it becomes occupied with
epithelial scales and ear-wax. The cartilage of the external ear and meatus appears
to be formed in two or three pieces, the fissures of Santorini marking the junctions
of these component portions (Burkner).

THE MIDDLE EAR OR TYMPANUM.

The tympanum or drum, the middle chamber of the ear, is a narrow irregular
cavity in the substance of the temporal bone, placed between the membrane occlud-
ing the inner end of the external auditory canal and the outer bony wall of the

Fig. 89.— THE RIGHT TEMPORAL BONE SAWN IN A CORONAL PLANE THROUGH THE TYMPANUM, VESTIBULE,

AND AUDITORY MEATUS, THE POSTERIOR PART OF THE SAWN BONE HAVING BEEN TURNED ROUND

so AS TO DISPLAY BOTH SURFACES OF THE SECTION. Natural size. (Testut.)
A, Anterior aspect ; B, posterior aspect.

labyrinth. Its width between these boundaries varies from about 2 mm. to 4 mm.,
being narrowest opposite the middle of the membrane, and narrower below and in
front than above and behind. It measures about 15 mm. from above down and
about the same from before back.

The vertical measurement includes the so-called reccssus epitympanicvg or anfJifus ad
antrum, which lodges the head of the malleus and the greater part of the incus : this, by
Bezold and some other authors is excluded from the tympanum proper, which without
it measures about 9 mm. In other words, the entrance to the mastoid antrum and mastoid
cells is about 9 mm. above the bottom of the tympanic cavity. The orifice of the Eustachian
tube is about 4 mm. above the lowest part of the floor.

The tympanum contains a chain of small bones (by means of which the vibra-
tions communicated from without to the membrana tympani are conveyed across
the cavity to the internal ear) and also certain minute muscles and ligaments, which
belong to the bones referred to, as well as nerves, some of which end within the
cavity, whilst others merely pass through it to other parts. The cavity is otherwise
filled with air, for it communicates with the atmosphere through the Eustachian
tube, which leads into the pharynx. The bony walls of the cavity are by no means

THE TYMPANUM. 81

everywhere smooth, but marked in many situations with depressions, some deeper
others shallower, which are lined by a prolongation of the mucous membrane of the
cavity and also contain air. These depressions are known as the tympanic cells. A
roof and floor, an outer and inner wall, and an anterior and posterior boundary are
commonly described.

The roof of the tympanum is formed by a thin plate of bone (tec/men tympani),
which may be easily broken through so as to obtain a view of the tympanic cavity
from above ; it is situated on the upper anterior surface of the petrous portion of
the temporal bone near the angle of union with the squamous portion, the petro-
squamous fissure passing just external to it. The tegmen tympani also roofs over
the canal of the Eustachian tube and tensor tympani muscle. It is not unfrequently
partly deficient (compare Vol. II., p. 42). The floor is narrow, in consequence
of the outer and inner boundaries being inclined towards each other. It passes
without any sharp demarcation into the anterior and posterior boundaries. It
is separated by a thin plate of bone, which in rare cases is found to be incomplete,
from the lateral part of the jugular fossa, and exhibits a small aperture through
which the tympanic nerve reaches the inner wall.

The outer wall is formed, to a small extent, by bone, but mainly by the
membrane (uwmbrana lympani) already mentioned as closing the inner end of the

Fig. 90. — VlKW OK THK LKKT .MK.MI5KANA TYMI'AM
AXD AUDITORY OSSICLES FROM THE INNER SIDE,
AND SOMEWHAT FROM ABOVE (E. A. S. ). f

?/i, malleus ; /, incus ; *£, stapes ; py, pyramid
from which the tendon of the stapedius muscle is
seen emerging ; t t, tendon of the tensor tympani
cut short near its insertion ; I a, anterior ligament
of the malleus : the processus gracilis is concealed
by the lower fibres of this ligament ; I s, superior
ligament of the malleus ; I. i, ligament of the incus ;
ch, chorda tympani nerve passing across the outer
wall of the tympanum.

external auditory meatus. Immediately

in front of the ring of bone into which

the membrana tympani is inserted, is the

inner extremity of the fissure of Glaser

(petro -tympanic fissure). Close to the

inner end of this fissure is the opening

of a small canal (iter chordcv anterius),

through which the chorda tympani nerve

passes out from the tympanum. The margin of the tympanic ring is inter-

rupted above by a notch (incisura Ririni) which is bounded in front and behind

by prominent angles, the anterior and posterior tympanic spines. The outer wall

of the recessus epitympanicus is formed by the thickened part of the squamosal

which lies behind the root of the zygoma : it may contain, according to Kirchner,

cells communicating with those of the mastoid process. This recess overhangs the

inner end of the external auditory meatus.

The membrana tympani is an ellipsoidal disc, the longer axis of which i
directed from behind and above, forwards and downwards, and is about 10 mm. in
length : the shorter axis being about 0 mm. It is nearly as large at birth as in the
adult. It is inserted into the groove already noticed at the end of the meatus
externus, and so obliquely that the membrane inclines towards the anterior and lower
part of the canal at an angle of about 55° (fig. 102). It is said to be more vertical in
musicians and more horizontal in the congenitally deaf. In the foetus and even
at or near birth it is as already stated nearly horizontal. The handle of the malleus.

VOL. 111.. J'T.

THE EAR.

one of the small bones of the tympanum, descends in contact with the inner
surface of the membrane, covered by mucous membrane, to a little below the
centre, where it is firmly fixed ; and, as this process of the bone is directed inwards,
the outer surface of the membrane is thereby depressed in a conical form (fig. 102).
The membrana tympanitis about O'l mm. thick, but at its insertion into
the sulcus tympanicus it becomes thickened and firmly attached to the bone by a
considerable accumulation of fibres (annulus fibrosus), and this thickened margin is
prolonged from the spines of the tympanic ring as two ligamentous bands which
pass to the short process of the malleus, constituting the so-called anterior and
posterior tympano-malleolar folds or ligaments ("fig. 92), and forming the lower boundary
of the membrana tiaccida (see below). Covering it externally is a prolongation of the
skin of the external meatus ; internally is a prolongation of the mucous membrane
lining the cavity of the tympanum ; and between the two is the proper substance
of the membrane, composed of fibrous tissue. The greater number of the fibres
radiate from the attachment of the handle of the malleus (fig. 91), but there are
also circular fibres (fig. 90) which are situated within or mesially to the radial, and
near the circumference of the membrane, form a dense, almost ligamentous
thickening. Besides these two sets of fibres there are others met with, especially

Fig. 91. — VIEW OF THE OUTER SURFACE OF THE LEFT MEM-
BRANA TYMPANI, AFTER REMOVAL OF THE CUTANEOUS
LATER (E. A. S. ) *

The handle of the malleus is distinctly seen, and the long
process of the incus appears as a faint light band parallel with
and a little behind the handle of the malleus. The other
light band nearly at right angles to the malleus is caused by
the chorda tympani nerve. The notch of Bivinus is seen above
the handle of the malleus.

in the posterior half of the membrane, which are
irregularly disposed and form at places prominent
fibrous bands in and upon the mesial surface of the
membrane (covered of course by the mucous mem-
brane), and even extend here and there across part
of the cavity of the tympanum. At the inser-
tion of the malleus the membrane, especially its

integumental layer, is thickened. The fibrous tunica propria here becomes con-
tinuous with the periosteum of the malleus, but along the line of contact of the
bone with the membrane there is generally a streak of cartilage forming the actual
uniting tissue : a similar thin layer of cartilage may also be found along the opposite
(free) border of the manubrium mallei, and also forming a complete cap to the end
of the manubrium. In the thickening of the integumental layer above mentioned
vessels and nerves to the membrane are seen in section. The epidermal layer is
stratified, as elsewhere in the external auditory meatus : it is also somewhat thickened
along the malleolar line, and here small papillse of the cutis project into it. The
radial fibres are not straight, but are slightly bowed outwards, so that between the
most depressed point or umbo, and the attached border, the membrane is slightly
convex outwardly. This shape is maintained by the annular fibres.

At the upper and anterior part, the annular fibres stretch, as just related, across
the mouth of a small notch in the bony ring to which the membrane is attached
(notch of Bivinus). The notch is occupied by a lax membrane (membrana flaccida,
Shrapnell) (fig. 92), consisting of loose connective tissue, with vessels and nerves, and
covered by skin and mucous membrane. It occasionally happens that a fissure or
perforation is to be detected at this place.

The membrane is supplied with blood-vessels, but they are chiefly confined to the

INNER WALL OF TYMPANUM. 83

skin and mucous membrane covering the surfaces : a few are, however, found in the
proper fibrous membrane, and form a communication between the two systems on
the surfaces. Those of the skin are mostly supplied by a small artery, derived from
the deep auricular branch of the internal maxillary, which passes from above
parallel to and along the handle of the malleus. The nerves for the most part
accompany the blood-vessels, first supplying these and then forming a plexus both
in the cutis and in the mucosa. They are derived, for the upper and greater part of
the membrane, from the auriculo-temporal ; for the lowermost part, according to
Sappey, from the auricular branch of the vagus. For the mucosa they come from
the plexus tympanicus. Lymphatic vessels are, according to Kessel, tolerably
abundant in all three layers.

The inner wall of the tympanum (fig. 1);3, A & B), which separates it from the
internal ear, is very uneven. Near its upper part is an ovoid, or nearly kidney-

membrana flaccida posterior ligament

anterior ligament

— long process of incus

end of manubrium of malleus

Fig. 92. — MEMBRANA TYMPANI, AS SEEN WITH THE OTOSCOPE. (Hensiuan.)

shaped opening— -fenestra ovalis, which leads into the cavity of the vestibule. This
opening, which is elongated from before backwards, with a slight inclination down-
wards in front, is occupied in the recent state by the base of the stapes and the
annular ligament connected with that plate of bone. It measures 3 mm. by 1 \ mm.,
and lies at the bottom of a depression (fossula ovalis), which is bounded by the bony
prominences immediately to be mentioned. Above the fenestra ovalis, and between
it and the roof of the tympanum, a ridge indicates the position of the aqueduct of
Fallopius (aF), as it passes backwards, containing the facial nerve. Below is a
larger and more rounded elevation, caused by the projection outwards of the first
turn of the cochlea, and named the promontory, or tuber cochtece ; its surface is
marked by grooves, in which lie the nerves of the tympanic plexus.

Below and behind the promontory, and somewhat hidden by it, is another
aperture named fenestra rotunda, T5 mm. to 2 mm. in diameter, which lies within
a funnel-shaped depression (fossula rotunda). In the macerated and dried bone the
fenestra rotunda opens into the scala tympani of the cochlea ; but, in the recent
state, it is closed by a thin membrane.

The membrane closing the fenestra rotunda — secondary membrane of the tympanum
(Scarpa) — is rather concave towards the tympanic cavity and convex to the scala
tympani, and, like the membrana tympani, is composed of three structures, the
middle being fibrous, and the outer and inner derived from the membranes lining
the cavities between which it interposed, viz., the tympanum and the cochlea. The

G 2

84

THE EAK.

membrane is not quite circular but is prolonged superiorly and posteriorly into a
somewhat triangular extension, which lies parallel and close to the lamina spiralis
cochlese, and forms an angle with the principal part of the membrane ; the latter
looks somewhat backwards and downwards, as well as outwards.

Another fossa is seen on the inner wall, behind the promontory and between the
fossula ovalis and fossula rotunda, from each of which it is separated by a bony
prominence, while behind it is the base of the pyramid (see below). This fossa,
which has been named the sinus tympiuii, is about 4 mm. in diameter and 3 mm.

<mtrti.m niastoidcum

surface for attachment
a f short process of incus

cvchleariform process for
tendon of tensor tympani

canal for tensor tynipctni

sums posterior

carotid canal

grooi-e for Eusta-
chian tu'jc

canal for

tympanic

nerve

p rot ub.
stt/loidca

Fig. 93 A. — SECTION OF THE RIGHT PETROUS BONE PASSING THROUGH THE MIDDLE OF THE TYMPANIC

CAVITY SO AS TO EXPOSE THE INNER WALL OF THAT CAVITY AND TO EXHIBIT ITS CONNEXION

WITH NEIGHBOURING SPACES WITHIN THE BONE. (E. A. S.) About twice the natural size.

tiyep. The ampulla of the posterior semicircular canal lies close to its floor, and it
is marked by one or two small apertures for vessels (Stein briigge).

The posterior wall of the tympanum has at its upper part a large opening
which leads into a considerable air-space (antrum mastoideum, figs. 93, A and B)
behind and above the proper tympanic cavity. From this antrum numerous irregular
cavities, the mastoid cells, pass into the substance of the mastoid portion of the
temporal bone. These cells communicate for the most part freely with one another,
and are lined by a thin mucous membrane continuous with that of the tympanum.
In the foetus and new-born child the mastoid cells are not developed (corresponding
with the slight development of the mastoid process), but the antrum mastoideum is
formed at birth. The petroso-squamosal fissure passes through the antrum. The

THIO TYMPANUM.

85

masfcoid cells are very variable in development : when large they approach close to
the free surface of the bone, and may come into proximity with the lateral sinus,
when small there is a considerable thickness of bone between them and the surface.
Sometimes they are undeveloped, and their place is occupied by spongy bony
substance (diploe). At the lower margin of the orifice of the antrum is a depressed
surface for the attachment of the lower ligament of the incus.

-20

-

V

Fig. 93 B. — PART OF THE SECTION SHOWN IN FIG. 93 A, MORE MAGNIFIED, SHOWING THE VARIOUS

NAMED PARTS IN AND CONNECTED WITH THE INNER WALL OF THE TYMPANUM. (E. A. S. )

1, tympanic crest ; 2, entrance to raastoicl cells ; 3, mastoicl antrum ; 4, prominence due to external
semicircular canal ; 5, prominence over aqueduct of Fallopius (a bristle, 13, 13, has been passed through
this canal) ; 6, fenestra ovalis ; 7, pyramid ; 8, posterior sinus ; 9, sinus tympani ; 10, styloid protu-
berance ; ll,subiculum promontorii ; 12, fenestra rotunda ; 14, bristle gassed through the canal for the
tympanic nerve ; 15, jugular fossa ; 16, tympanic cells ; 17, canal for Eustachian tube ; 18, promontory ;
19, 20, 21, grooves for nerves on promontory emerging from the end of the canal for the tympanic
nerve, 19 being for the carotico-tympanic, 20 for the small deep petrosal, and 21 for the small super-
ficial petrosal ; 22, trochlear end of the canal for the tensor tympani muscle ; 23, bridge of bone uniting
the promontory with the pyramid.

Below the orifice of the antrum and behind the fenestra ovalis is a small
conical eminence (1 m. to r~> m. high), called the pyramid, or eminentui papillaris
(fig. 90, pij ; fig. 93, 7). Its apex is pierced by a foramen, through which the
tendon of the stapedius muscle emerges. The muscle is contained within a canal

86

THE EAR.

which when traced back is found to turn downwards in the posterior wall of the
tympanum, sometimes opening at the base of the cranium by a small aperture just
in front of the stylo-mastoid foramen, and connected at one or two places with the
descending part of the aqueduct of Fallopius. A small bony spiculum often connects
the end of the pyramid with the upper part of the promontory (see fig. 93 B, 23).

Anterior boundary. Canal for the tensor tympani. — The anterior
extremity of the tympanum is narrowed by the gradual descent of the roof,
and is continued into the inner orifice of the Eustachian tube (fig. 85).
Above the commencement of this is the small (2 mm. diameter) canal which
lodges the tensor tympani muscle. This canal, which is lined by a fibrous
membrane, is about half an inch (12 mm.) long, and it opens immediately in front

external

pterygoid

plate

internal

pterygoid

plate

Eustachian
cartilage

Eustachian
cartilage

carotid
foramen

jugular
foramen

posterior
condylar
foramen

palate bone

f"- nasal fossa?

scaphoid
fossce

foramen
ovale

foramen
lacerum

occipital
condyle

foramen
magnum

Fig. 94. — BASE OF THE SKULL, SHOWING THE POSITION OP THE EUSTACHIAN CARTILAGE.
(Modified from Testut.) (E. A. S.)

of the fenestra ovalis, surrounded by the expanded and everted end of the
cochleariform process, which separates it from the Enstachian canal. The bony
septum between the two canals is often incomplete, so that in the macerated bone
they may appear as a single large canal partly subdivided by a thin osseous
partition.

In the recent state the fibrous sheath of the tendon is expanded over the end of the canal,
so as to impart to it a conical shape (see fig-. 101 . tf).

The Eustachian tube (sdlpinx) (fig. 85, 4) is a canal about 86 mm.
(1'5 inches) long and from 2 mm. to 4 or 5 mm. diameter, bounded partly by bone,
partly by cartilage and fibrous membrane, which leads from the cavity of the
tympanum to the upper part < of the pharynx. From the opening into the
tympanum (ostium tympanicum) it is directed forwards and inwards, at an angle of
about 45 degrees with the sagittal plane, with an inclination of about 30 degrees
downwards from the horizontal ; the downward inclination is slightly greater in the

THE EUSTACHIAN TUBE.

87

cartilaginous part than in the osseous. The posterior or osseous division of the
tube, about half an inch long, is placed at the angle of junction of the petrous
portion of the temporal bone with the squamous portion. It is funnel shaped,
diminishing somewhat rapidly in size from behind forwards, to the junction with
the cartilaginous part ; here the tube is narrowest (isthmus tubce). The carotid
canal lies mesially to the osseous portion of the tube, and is occasionally found to
communicate with it owing to deficiencies in the bony septum between them.

The mucous membrane lining the osseous portion of the tube is thin and closely
attached to the bone except along the floor of the canal, where it is separated from the
periosteum by a venous plexus. It is lined by ciliated epithelium, and has no glands
opening into it. The anterior part of the tube, about an inch in length, is formed of a
triangular piece of elastic fibro-cartilage, the edges of which are slightly curled
round towards each other, leaving an interval at the under and outer side, in which the
wall of the canal is completed by dense but pliable fibrous membrane (fascia salpingo-
pharyngea), and by a muscular band connected with the tensor palati and termed by

Fig. 95. — SECTION ACROSS THE CARTILA-
GINOUS PART OF THE EUSTACHIAN
TUBE. (Riidinger.)

1, 2, bent cartilaginous plate; 3,
muse, dilatator ttibse ; to the left of 4,
part of the attachment of the levator palati
muscle ; 5, tissue uniting the tube to the
base of the skull ; 6, and 7, mucous
glands ; 8, 10, fat ; 9 to 11, lumen of the
tube ; 12, connective tissue on the lateral
aspect of the tube.

Riidinger the dilatator tula. The
cartilaginous plate is hook-shaped
in transverse section (fig. 95), the
larger part of the plate being on
the mesial side, and only a small
part on the lateral border. The
cartilage is largest near the ostium
pharyngeum, where it measures
12 mm. from above down, and is

7 mm. thick. It here occupies the whole mesial wall of the tube, but gradually
diminishes in size as it approaches the bony canal. It is often partially or entirely
broken up by fissures, or there may be accessory pieces of cartilage in various
situations in the wall of the tube. The cartilaginous part of the tube is trumpet-
shaped, being narrow behind, and gradually expanding to a greater width in
front (fig. 1)4) ; the anterior part is compressed from side to side, and is fixed
to the inner pterygoid plate of the sphenoid bone. The anterior opening (ostium
pharyngeum) is of a compressed oval, somewhat triangular form, and is placed
obliquely at the side and upper part of the pharynx, into which its prominent
margin projects behind the lower turbinate process of the nose and above the level
of the hard palate (fig. 96). The aperture is bounded above and posteriorly by a
projection, which is caused by the end of the curved plate of cartilage (covered,
of course, by mucous membrane), which separates it behind from a longitudinal
depression of the pharyngeal wall, known as the lateral recess of the pharynx or
fossa of Rosenmiiller. The projection in question is continued into the salpingo-
pharyngeal fold. Below it is limited by a thickening, increased when the
levator palati contracts, continued from a fold (salpingo-palatine), which also
assists in forming the anterior boundary of the orifice. The opening is placed

THE KAIL

relatively to the palate somewhat lower in the child than in the adult. Through
this aperture the mucous membrane of the pharynx is continuous with that which
lines the tympanum, and under certain conditions air passes into and out of that
cavity. Mucous glands open on the inner surface of the cartilaginous part of
the tube : they are most numerous near the pharyngeal orifice. There is also a

Fig. 96. — VIEW OF THE RIGHT NASAL FOSSA AS SEEN IN A SECTION THROUGH THE SKULL TAKEX

TO THE RIGHT OF THE SEPTUM. (E. A. S.)

1, incisor canal ; 2, bone of hard palate ; 3, 4, 5, parts of the cartilage of the aperture : 6,
cartilage of the septum ; 7, atrium leading to middle meatus ; 8, agger nasi ; 9, frontal sinus ; 10,
inferior ethmoidal concha ; 11, superior ethmoidal concha ; 12, spheno-ethmoidal recess ; 13, entrance
to sphenoidal sinus ; 14, pituitary fossa ; 15, sphenoidal sinus ; 16, inferior turbinal ; 17, rod passed
into Eustachian txibe ; J8, salpingo-pharyngeal fold, immediately behind this is the lateral recess of
the pharynx, not specially indicated in the drawing ; 19; soft palate ; 20, uvula ; 21, tongue.

considerable amount of lymphoid tissue especially in young subjects, and near the
pharyngeal end of the tube.

Vessels and Nerves. — The arteries of the tube are derived on the one hand from
the pharyngeal branch of the external carotid, and on the other from the middle
meningeal and vidian branches of the internal maxillary. The nerves arise from
the tympanic plexus and pharyngeal twigs of the vidian nerve.

Muscles. — Besides the middle part of the tensor palati muscle, which takes
origin along the whole length of the lateral plate of the hooked cartilage of the tube
(fig. 95), the levator palati also has an attachment to the commencement of the

THE Al'DITOKV OSSK'I.KS. SO

lateral plate, and from the adjacent membranous part of the floor of the tube,
parallel to which its fibres course towards their insertion into the soft palate.
When the muscle contracts the membranous floor of the tube is tightened, and is
also raised near the ostium pharyngeum by the thickening of the muscular fibres
which run just below it, and this helps to open the lower orifice during swallowing.

Lastly, some muscular bundles, forming the salpingo-pharyngeus of Santorini,
arise from the lower and fore part of the mesial plate of cartilage, and passing down
immediately beneath the mucous membrane, join the palato-pharyngeus (Vol. II.,
p. 308). This muscle tends to drag the mesial plate backwards and downwards,
and thus assists in opening the tube during deglutition.

The anterior wall of the tympanum, below the orifice of the Eustachian
tube, is formed by a bony plate forming part of the petrous portion of the temporal
bone, which is hollowed out by air-cells, and here separates the tympanic cavity
from the vertical part of the carotid canal. Rarely there are one or more deficiencies
in this wall.

SMALL BONES OF THE EAR.— Three small bones (ossicula auditns) are
contained in the upper part of the tympanum : of these, the outermost (malkus)
is attached to the membrana tympani ; the innermost (stapes) is fixed in the
fenestra ovalis ; and the third (incus), placed between the other two, is connected to
them by articular surfaces. They form together an angular and jointed connecting
rod between the membrana tympani and the fenestra ovalis.

The malleus or hammer-bone (fig. 1)7), (18 mm. to 10 mm. long, weight
24 milligr.), consists of an upper thicker portion, with a tapering lower portion, and

m

Fig. 97 A.— THE LEFT MALLEUS OF THE ADULT VIEWED FROM THE OUTER SIDE. Magnified four times.

(After Helmholtz. )

c, capitulum ; a i, grooved articular surface for the incus; c, its prominent lower margin ; d, cervix,
in, end of the manubrium ; b, processus brevis ; pr.gr, processus gracilis, here represented only by a
short stump, the rest of the process having been converted into ligament ; a, ridge to which the external
ligament is attached.

Fig. 97 B. — LEFT MALLEUS OF A CHILD VIEWED FROM BEFORE. Magnified four times. (E. A. S.)

The lettering is the same as in the previous figure. The processus gracilis is here complete. The
angle which the manubrium forms with the rest of the bone is seen in this view.

two processes. The upper end is formed by the rounded head (capitulum) (c),
on the posterior surface of which is an elliptical depressed surface (a.i) with
prominent margins, which passes obliquely downwards and inwards, and serves for
articulation with the incus. The articular surface shows two principal facets,
nearly at right angles to one another. They are separated by a constriction and by
an obliquely crossing crest or edge. These facets look respectively, the upper and
larger one backwards, the lower one inwards ; and each principal facet is subdivided

90 THE EAE.

by a longitudinal groove into secondary facets. The inferior margin of the articular
surface is very prominent opposite the constriction, and forms here, in fact, the
lower end of the ridge above mentioned (spur of the malleus}. Below the head
is a constricted neck (d) ; and beneath this another slight enlargement of the bone,
to which the processes are attached. The handle (manubrium) (m), the lower
tapering point of the malleus, is slightly twisted, and is compressed from before
backwards to near its point, where it is flattened laterally. It forms a rounded
obtuse angle with the head of the bone (fig. 97 B), and passes downwards with an
inclination forwards and inwards, on the inner side of the membrana tympani, to
which it is closely attached both by its periosteal covering and. also by a layer of
cartilage extending its whole length, and especially marked at the attachment of the
processus brevis. The point of insertion of the tendon of the tensor tympani muscle
is sometimes marked by a slight projection on the inner side of the manubrium near
its upper end. The long process (processus gracilis vel Folianus) (fig. 97 B, pr. (jr.)
is a very slender spiculum of bone, which in the adult is usually converted, except
a small stump, into ligamentous tissue, and even where it still exists as bone is often
broken off in its removal from the tympanum ; it projects at nearly a right angle
from the front of the neck of the malleus, and extends thence obliquely downwards
and forwards to the Glaserian fissure. Its end is flattened and expanded, and is
connected by ligamentous fibres or bone to the sides of the fissure. In the foetus
this process is directly continued into Meckel's cartilage (see Vol. I, Part I, p. 168).
The short process (processus brevis vel obtusus) (b) is a low conical eminence situated
at the root of the manubrium, beneath the cervix, and projecting outwards towards
the upper part of the membrana tympani, to which it is attached.

The incus (fig. 98), as its name implies, has been compared to an anvil ; but it
resembles perhaps more nearly a tooth with two fangs widely separated. It consists

Fig. 98. — LEFT INCUS, VIEWED FROM THE INNER SIDE AND SOMEWHAT
FROM BEFORE. Magnified four times. (GK D. Thane.)

b, body ; a m. ridged articular surface for the malleus ; pr. br,
processus brevis ; I. ?', rough surface near its extremity for the
, attachment of the ligament of the incus ; pr. I, processus longus,

terminating below in a small projection which comes off from it at a
right angle, and is capped by a convex tubercle, processus lenticularis,
p7*o CB) pv- v, for articulation with the stapes.

of a body and two processes. The body has a deep saddle-shaped articular surface
in front (a.m\ which fits over the articular surface on the head of the malleus, and
which consists, like that of the malleus, of two chief facets, each subdivided to form
two secondary facets. The lower margin of the articulation is excavated to receive
the spur-like prominence of the malleus, and in front of this excavation is very
prominent, where it also forms a spur, against which that of the malleus catches in
inward movements of the manubrium. The shorter process (cms breve) (pr.br.) of
the incus projects backwards. Its extremity is tipped with cartilage, and is
moveably articulated by ligamentous fibres with the posterior and partly with the
outer wall of the tympanum near the entrance to the mastoid cells. The place
where the ligamentous fibres are attached to the wall of the tympanum is somewhat
depressed, and has a covering of cartilage. The long process (crus longum)
(pr.l.) tapers rather more gradually, and passes downwards and inwards parallel
to the handle of the malleus, and about 1| mm. mesial to and behind it. At
its extremity it is bent inwards at an angle which varies considerably in different
bones, and is suddenly narrowed into a short neck ; and upon this is set a flattened
tubercle (pj'ocessus orbicular is seu lenticularis) (pr. o.), tipped with cartilage. This
tubercle, which articulates with the head of the stapes, was formerly, under the name.

THE AUDITORY OSSICLES. 91

of os orbicular* seu lenticulare, described as a separate bone, which indeed it
originally is in the foetus up to the sixth month.

The length of the short process is about 3 to 3J mm., of the long process about
4J mm. The weight of the incus is very nearly the same as that of the malleus
(Blake).

At the joints between the incus and malleus on the one hand and the incus and stapes on
the other the articular surfaces are tipped with cartilage and enclosed by a synovial membrane.
Riidinger describes both in this joint and in the articulation of the incus with the stapes an
iiiterarticular fibro- cartilage which subdivides the joint into two parts ; but according to
Brunner neither are synovial joints but are symphyses, the articular cartilages being united
by fibrous tissue. At all events the existence of an interarticular cartilage at the joint between
incus and stapes is doubtful, although most authorities admit its presence at the joint between
the malleus and incus. Some anatomists describe a synovial joint at the articulation of the
short process of the incus with the bone at the entrance to the mastoid cells.

The stapes (figs. 00, 100), the third and innermost bone of the ear, is in shape
remarkably like a stirrup, and is composed of a head, a base, and two crura. The
whole bone measures 3 to 4 mm. in length and about 2J mm. in breadth. Its
weight is from 2 to 4 milligrams. The head (h) is directed outwards, and has
on its end a slight depression, covered with cartilage, which articulates with
the lenticular process of the incus. The lase (£) is a plate of bone fitting into

Fig. 99.— LEFT STAPES, VIEWED FROM BELOW. Magnified four times. (E. A. S.)

A, outer extremity or head of the bone, with a shallow concavity for articulation
with the orbicular process of the incus ; c, constricted part or cervix. This is not
always so well-marked as in the present specimen, cr a, anterior crus ; cr p,
posterior crus ; b, base ; a, arch of the stapes. The bony .groove which bounds the
arch is shown in front and below ; above and behind it is concealed from view.

the fenestra ovalis, but not quite closely, so that a slight amount of movement is
allowed. Its form is irregularly oval, the upper margin being curved, while the
lower is nearly straight (fig. 00, st). Its border is encircled by hyaline cartilage,
which also covers its vestibular surface. The margin of the fenestra ovalis has also
a covering of the same tissue (Toynbee), and the opposed cartilaginous surfaces are
closely connected by a network of elastic fibres passing between them, and forming
an especially dense ligamentous band near the tympanic and vestibular cavities
(Riidinger). The crura of the stapes diverge from a constricted part (neck,
fig. 00, c) of the bone, situated close to the head, and are attached to the outer
surface of the base near its extremities. The anterior crus (cr. a) is the shorter and
straighter of the two. The crura, with the base of the stapes, encircle a small
triangle or arched space (#), across which in the recent state a thin membrane is
stretched. A shallow groove runs round the opposed surfaces of the arch, and into
this the membrane is received.

The formation and morphological relations of the auditory ossicles have already been
noticed in the Embryology (Vol. I., p. 167, et seq."). Suffice it here to recall the fact that
the incus and malleus are originally laid down as one piece of cartilage, which is continued
forwards as Meckel's cartilage along the first visceral arch, and that the stapes is formed by
ossification in cartilage which develops around an artery (stapedial or mandibular — Fraser,
Salensky), which arises from the internal carotid, and passing into the tympanum through the
wall of the carotid canal, ascends over the promontory and anastomoses with branches of the
stylo-mastoid, 'middle meningeal, and ascending pharyngeal arteries. In rare instances this
artery remains, but it has usually disappeared before birth. In some animals (Cheiroptera,
Insectivora, Rodentia) it persists in the adult. In these cartilaginous foundations of the
auditory ossicles the formation of the individual bones occurs in the following manner : the
separation and articulation between the malleus and incus appears in the third month of
embryonic life ; the cartilaginous continuity between the malleus and Meckel's cartilage
disappears somewhat later, and its place is taken partly by ligamentous tissue (forming the

THE EAR.

anterior ligament of the malleus and the accessory mesial ligament of the mandibular
articulation) and partly by a thin slip of membrane bone which develops in the perichondrium.
and becomes the processus gracilis of the malleus. Besides this the malleus has two ossifica-
tion centres, one in the head, the other in the manubrium. which appear at the end of the
third or the beginning of the fourth month. About the same time an ossification centre
appears in the body of the incus, and from this the whole of the bone is formed, except the

Fig. 100. — SECTION* THROUGH STAPES AND FEXESTRA OVALTS. (Brunner.)

lenticular process, which appears as an epiphysis. The stapes ossifies somewhat later than the
other ossicles, and from four centres — one for the head, one for each cms. and one for the base.

Ligaments. — In the articulations of the small bones of the ear with one another
the connection is strengthened by ligamentous fibres.

Their attachment to the walls of the tympanum is effected chiefly by the
following ligaments, as well as by the reflections of the mucous membrane lining
that cavity.

The anterior ligament of the malleus (figs. 00, I. a, and 101, La. m) is a
comparatively strong and broad band of fibres, which connects the base of the
processus gracilis and the anterior part of the malleus above this process with
the anterior wall of the tympanum close to the Glaserian fissure. The part
of the ligament which passes out of the Glaserian fissure was long thought to
be muscular (laxator tympani auct.), but most observers agree in denying the

THE AUDITORY OSSICLES. 93

existence of muscular tissue in this situation. Many of the fibres of the anterior
Hiram ent take origin from a bony prominence which projects from the margin of
the external meatus into the tympanum, and forms the anterior boundary of the
notch of Rivinus. This prominence is known as the anterior spinous process of the
tympanum (spina tympanica anterior) (fig. 101, sp) to distinguish it from another
smaller bony prominence or spine at the posterior extremity of the notch (see p. 81 ).

Arri'xxort/ tintcr'nir lit/iDiH'nt. — A comparatively stout sheath surrounds the tendon of the
tensor tympani as it passes from the end of the cochlearifonn process to the malleus, and a
flat ligamentous band with a thickened margin (fig. 101. /). which lies along1 the anterior
border of this sheath, stretching- between the anterior wall of the tympanum and the upper

Fig. 101. — VlK\V OF THE CAVITY OK THE

JO'f O ?/ S(

TY.Ml'AM M. OPENED FROM ABOVE.

(Magnified four times.) (E. A. S.)

m, head of the malleus ; sp, spina
tympanica anterior ; I. a. m, anterior
ligament of the malleus ; Lc.ni, external
ligament of the malleus ; Ji, gap between
the two ligaments leading to the mem-
brana flaccida and notch of Rivinus ; i,
body of the incus ; I. i, posterior ligament
of the incus ; pr. o, processus orbicularis
of the incus seen in the depth of the
cavity, articulated with the head of the
stapes, at ; st', tendon of the stapedius
muscle emerging from the pyramid ; tt,
tendon of the tensor tympani, emerging

from the conical end of its canal ; I, thickened edge of a flattened band of ligamentous fibres which lies
in the fold of the mucous membrane, m.m., and assists in fixing the malleus ; ». I. m, superior ligament of
the malleus, cut short ; n, chorda tympani nerve.

part of the manubrium and neck of the malleus, may be regarded as assisting in the fixation
of the malleus anteriorly. Toynbee described the sheath in question as acting as an accessory
ligament (tensor ligament).

The external ligament of the malleus (fig. 101, l.e^n.), is a fan-shaped ligamentous
structure, the fibres of which arise from the margin of the notch of Rivinus, and
converge to the short process and adjacent part of the malleus.

The posterior bundle of fibres of this ligament, together with the anterior bundle of the
anterior ligament are termed by Helmholtz the "axis-ligament of the malleus," since they are
attached nearly in the axis of rotation of that bone.

The superior ligament of the malleus (figs. 101, loi, s.l.m.) consists of a
small bundle of fibres, which passes downwards and outwards from the roof of
the tympanum to the head of the malleus, and serves to check the outward move-
ments of the manubrium and membrona tympani.

Inferior liija iiu-nt of tin- titnUetat. — A small bundle of ligamentous fibres is occasionally found
passing from near the extremity of the handle of the malleus upwards and backwards behind
the long process of the incus, to be attached to the outer wall of the tympanum. This liga-
ment assists the external ligament in resisting a too violent action of the tensor tympani
muscle, and it serves also to restrict any rotating action which that muscle may tend to exert
upon the malleus.

The ligament of the incus (figs. 90, 101, Li.) extends from near the point of the
short crus backwards towards the posterior wall of the tympanum, but some of its
fibres spread also outwards and inwards. It is attached below the entrance to the
mastoid cells.

Muscles. — There are only two well-determined muscles of the tympanum.
Sormnerring described four, and some authors have mentioned a larger number ; but

94 THE EAE.

their descriptions have not been confirmed by later research. Of the two muscles
generally recognised, one is attached to the malleus, and the other to the stapes.

The tensor tympani is the larger of these muscles. It consists of a tapering
fleshy part, about half an inch in length, and a slender tendon. The muscular
fibres arise from the cartilaginous end of the Eustachian tube and the adjoining
surface of the sphenoid bone, and from the sides of the canal in which the muscle
lies and in which it is conducted backwards to the cavity of the tympanum.
Immediately in front of the fenestra ovalis the tendon of the muscle bends at nearly
a right angle over the end of the processus cochleariformis as round a pulley, and,
contained in a fibrous sheath, passes outwards, to be inserted into the inner part of

Fig. 102. — PROFILE VIEW OP THE LEFT MEMBRANA TYMPANI AND AUDITORY OSSICLES FROM BEFORE
AND SOMEWHAT FROM ABOVE. Magnified four times. (E. A. S. )

The anterior half of the membrane has been cut away by an oblique slice, m, head of the malleus ;
sp, spur-like projection of the lower border of its articular sin-face ; pr. br, its short process ; pr. gr, root of
processus gracilis, cut; s.l.m, suspensory ligamentof the malleus ; l.e.m, its external ligament; t.t, tendon of
the tensor tympani, cut ; i, incus, its long process ; st, stapes in fenestra ovalis ; e.au.m, external auditory
rneatus ; p.R, notch of Kivinus ; m.t, membrana tympani ; u, its most depressed pointer umbo ; d, de-
clivity at the extremity of the external meatus : i.au.m, internal auditory meatus ; a and b, its upper
and lower divisions for the corresponding parts of the auditory nerve ; n.p, canal for the nerve to the
ampulla of the posterior semicircular canal ; s.s.c, ampullary end of the superior canal ; p, ampullary
opening of the posterior canal ; c. common aperture of the superior and posterior canals ; e.s.c, ampul-
lary, and e'.s.c, non-ampullary end of the external canal ; s.t.c, scala tympani cochleae; /.?•, fenestra
rotunda, closed by its membrane ; a. Fy aqueduct of Fallopius.

the handle of the malleus, close to its root (figs. 101, 102, tt). The tensor tympani
is supplied by a branch of the fifth pair through the otic ganglion. Its nerve is
furnished with a small ganglion (Dastre and Morat).

The stapedins is a very distinct muscle, but is hidden within the bone, being
lodged in a canal in front of the descending part of the aqueductus Fallopii and in
the hollow of the pyramid. The tendon issues from the aperture at the apex of that
little elevation (fig. DO), and passing forwards, surrounded by a fibrous sheath, is
inserted into the neck of the stapes posteriorly, close to the articulation of that bone
with the lenticular process of the incus (figs. 90, 101).

A very slender spine of bone has been found occasionally in the tendon of the
stapedius in man ; and a similar piece of bone, though of a rounder shape, exists
constantly in the horse, the ox, and other animals.

MOVEMENTS OF AUDITORY OSSICLES.

95

Movements of the auditory ossicles. — The malleus and incus move together
round an axis extending backwards from the attachment of the malleus by its anterior
ligament to the attachment of the short process of the incus posteriorly. The
handle of the malleus follows all the movements of the membrana tympani, and
when the membrane is impelled inwards, the incus, moving inwards along with the
malleus, pushes the stapes inwards towards the internal ear. In this movement the
head of the stapes is slightly raised as well as pressed inwards, and the upper margin
of its base moves more than the lower. But the cavity of the inner ear is full of
liquid ; and its walls are unyielding, except at the fenestra rotunda ; when, there-
fore, the stapes is pushed inwards, the secondary membrane of the tympanum, which
blocks up the fenestra rotunda, must be bulged outwards. When the membrana
tympani returns to its original condition these movements are reversed. That the
movement inwards of the incus must closely accompany that of the malleus, is
necessitated by the fact that the lower margin of its articular surface has a well

Fig. 103. — FIGURE TO SHOW THE

INTERLOCKING OP THE MALLEUS

AND INCUS. (Helmholtz.)

The line a I indicates the axis of
rotation of the two bones, the line
x y z joins this axis with the two
ends of the crank lever which these
bones form.

body of incus head of malleus

tooth of incus
interlocking

with tooth —
of malleus

processus
yraciliis

end of long process of incus

marked projection which
catches against the prominent
border of the articular surface
of the malleus (fig. 102, sp,
and fig. 103). If, however,
in consequence of increase of
tension of the air in the tym-
panum, the malleus should be
moved too freely outwards, the
incus need not follow that
movement to its full extent,
but may merely glide over the

smooth adjoining surface of the malleus, and thus the danger that there would
otherwise be of forcibly dragging out the stapes from the fenestra ovalis is avoided
(Helmholtz).

The tensor tympani muscle, being attached near the base of the manubrium of
the malleus, draws the whole bone and the membrane inwards, tightening the latter.
Its action is opposed by the strong external ligament of the malleus. The tensor
tympani exerts but little rotating action upon the malleus. The action of the stape-
dius muscle is obviously to draw the head of the stapes backwards, in doing which
the hinder end of the base of that bone will be pressed against the margin of the
fenestra ovalis, while the fore part will be withdrawn from the fenestra.

The lining membrane of the tympanum. — The mucous membrane of the
tympanum is continuous with that of the pharynx through the Eustachian tube, and
is further prolonged from the tympanum backwards into the mastoid cells. The
malleus and incus are invested by the lining membrane of the outer wall of the
cavity. The membrane forms also folds extending down from the roof in front of
and behind the conjoined heads of the incus and malleus, and another passing down
to the chorda tympani nerve or even below it ; these folds wholly or partially
separate off small pouch-like portions of the tympanic cavity which will be further

96 THE EAR.

noticed below. Another well-marked fold has been already noticed in connection
with the tendon of the tensor tympani, and various other smaller folds are met
with. They often contain strands of fibrous tissue and sometimes osseous spicules.
All these folds are, however, very variable in their development.

The mucous membrane which lines the cartilaginous part of the Eustachian tube
resembles much the membrane of the pharynx, with which it is immediately con-
tinuous ; it is thick and vascular, is covered by ciliated epithelium, and is provided
with many simple mucous glands which pour out a thick secretion : in the osseous
part of the tube, however, the membrane becomes gradually thinner. In the tym-
panum and the mastoid cells the mucous membrane is paler, thinner, and less
vascular, and secretes a small amount of less viscid, yellowish fluid. Accord-
ing to most observers no glands are normally met with in the tympanum, but
Krause has described and figured simple glands in parts, and Troltsch describes an
acinous gland on the external wall, anteriorly. Between the mucous membrane and
the periosteum is a network of fibrous bundles, which are here and there raised
above the general surface, causing corresponding projections of the mucous mem-
brane. In various places on the interlacing bundles, peculiar swellings occur of
various sizes, w^hich appear to be caused by the superaddition of concentrically
arranged fibres upon the smaller bundles, producing an appearance similar to that
of miniature Pacinian corpuscles (Politzer, Kessel). The epithelium in the
tympanic cavity is in part columnar and ciliated, with small cells between the
bases of the ciliated cells, but the promontory, the ossicula, and the membrana, are
covered with a simple layer of flattened non-ciliated cells (Kolliker) ; and a similar
non-ciliated epithelium is said to line the mastoid antrum and cells.

Recesses or pouches of the tympanum. — The ossicula, as well as the
ligaments which unite them with the wTall of the tympanum, and the chorda
tympani nerve, are all invested by folds of the lining mucous membrane, which in
many cases also pass across the spaces between the several ligaments and bony
projections. These uniting folds and the prominences which they cover and connect
thus mark off in certain places pouch-like portions of the general cavity. There is
a good deal of variation in the extent of development of these folds and pouches,
but some are fairly constant in their occurrence, and one pouch in particular,
between the heads of the malleus and incus and the external wall is nearly shut off
from the rest of the cavity by well marked folds, which pass down from the roof of
the tympanum in front of and behind the suspensory ligament of the malleus.
This pouch may be termed the superior external pouch. Immediately below it and
partly separated from it by the anterior and external ligaments of the malleus and a
fold of membrane which unites them, is another smaller pouch, described by
Prussak, which may be termed the infer o-external. It is bounded above by the
ligaments and folds just mentioned, externally by the membrana flaccida, below and
internally by the processus brevis mallei. In front it ends blindly, but behind it
opens into the general cavity of the tympanum. This pouch is of considerable
importance clinically and pathologically because fluid (e.g., pus) may accumulate in
it, especially since its opening into the rest of the posterior pouch is placed
somewhat above its floor. It is into this pouch that perforations of the membrana
flaccida occur.

The fold which passes down from the roof of the cavity towards the mesial part
of the neck of the malleus, and which incloses in or near its free border the chorda
tympani nerve, also separates off twro pouches, one in front of and the other behind
the manubrium mallei, and both bounded externally by the membrana tympani.
These pouches are the anterior and posterior pouches of Troltsch. For a detailed
description of the various folds and pouches, the student is referred to certain of
the memoirs cited in the Bibliography.

VESSELS AND NERVES OF TYMPANUM.

07

In the foetus the mucous membrane of the tympanum consists of a swollen gela-
tinous embryonic tissue which fills the cavity, leaving only an irregular cleft between
its folds. Towards the end of intrauterine life the membrane becomes gradually
thinner and less gelatinous and the cleft enlarges, fluid accumulating within it.
After birth this fluid becomes replaced by air, and the mucous membrane speedily
acquires the thin fibrous character which it exhibits throughout life.

superior ligament of malleus head of malleus

superior external pouch .^||

external ligament of malleus
inferior external pouch (of Prussak) ,
processus brevis mallei '''•

external auditory meatus J

tendon of tensor
t/jmpani

manubrium mallei
end of manubrium

Fig. 104. — SECTION THROUGH THE MALLEUS AND MEMBRANA TYMPANI, SHOWING SOMK OF THE POUCHES
OR RECESSES OP THE TYMPANIC CAVITY. (After Merkel.)

Vessels and nerves of tympanum. — The arteries of the tympanum, though
very small, are numerous, and are derived from branches of the external carotid,
and from the internal carotid.

The fore part of the cavity is supplied chiefly by the tympanic branch of the
internal maxillary, which enters by the fissure of Glaser. The back part of the
cavity including the mastoid cells, receives its arteries from the stijlo-mastoid branch
of the posterior auricular artery, which is conducted to the tympanum by the aque-
duct of Fallopius. These two arteries form by their anastomosis a vascular circle
round the margin of the membrana tympani. The smaller arteries of the tympanum
are, the petrosal branch of the middle meningeal, which enters through the hiatus
Fallopii, and branches through the bone from the internal caroiid artery, furnished
from that vessel whilst in the carotid canal.

The veins of the tympanum empty their contents into the superior petrosal
sinus arid the temporo-maxillary vein.

Nerves. — The tympanum contains numerous nerves ; for, besides those which
supply the parts of the middle ear itself, there are several which serve merely to
connect nerves of different origin.

The lining membrane of the tympanum is supplied by filaments from the
tympanic plexus, which occupies the shallow grooves on the inner wall of the cavity,
particularly on the surface of the promontory (fig. 93).

This plexus (fig. 105) is formed by 1st, the nerve of Jacobson from the petrosal
ganglion of the glosso-pharyngeal ; 2nd, the small deep petrosal nerve, a filament
connecting the nerve of Jacobson with the carotid plexus of the sympathetic ; 3rd,
a branch which joins the great superficial petrosal nerve ; 4th and lastly, the small
superficial petrosal nerve, passing to the otic ganglion.

Numerous ganglion cells are found both in the uniting cords and also at the
points of junction of the plexus.

VOL. III., PT. 3. H

98

THE EAR.

The nerve of Jacobson or tympanic nerve enters the tympanum by a small
foramen near its floor, which forms the upper end of a short canal in the petrous
portion of the temporal bone, beginning at the base of the skull between the carotid
foramen and the jugular fossa. The nerve connecting it with the carotid plexus is
above and in front, and passes through the bone directly from the carotid canal.
The branch to the great superficial petrosal nerve is lodged in a canal which opens
on the inner wall of the tympanum in front of the fenestra ovalis. The small
superficial petrosal nerve also leaves at the fore part of the cavity beneath the canal
for the tensor tympani.

The tensor tympani muscle obtains its nerve from the internal pterygoid of the
fifth through the otic ganglion ; as already mentioned its nerve is provided with a
small ganglion. The stapedius receives filaments from the facial nerve.

The chorda tympani, arising from the facial near the lower end of the aqueduct
of Fallopius, takes a recurrent course to the tympanum, which it enters by an

Fig. 105. — THE FACIAL NERVE IN ITS CANAL,

WITH ITS CONNECTING BRANCHES, &C.

(From Sappey, after Hirschfeld and Le-
veille.) 2

The mastoid and a part of the petrous bone
have been divided nearly vertically, and the
canal of the facial nerve opened in its whole
extent from the internal meatus to the stylo-
mastoid foramen ; the Vidian canal has also been
opened from the outer side : 1, facial nerve in
the first horizontal part of its course ; 2, its
second part turning backwards ; 3, its vertical
portion ; 4, the nerve at its exit from the stylo-
mastoid foramen ; 5, geniculate ganglion ; 6,
large superficial petrosal nerve ; 7, spheno-
palatine ganglion ; 8, small superficial petrosal
nerve; 9, chorda tympani ; 10, posterior auricu-
lar branch cut short ; 11, branch to the digastric
muscle ; 12, branch to the stylo-hyoid muscle ;
13, twig uniting with the glosso-pharyngeal nerve (14 and 15).

aperture in the posterior wall (iter chordce posterius) just below the level of the
pyramid. From this place it passes with a slight curve across the cavity near the
outer boundary, and crossing successively the posterior part of the membrana
tympani, the handle of the malleus near its neck, and the processus gracilis of the
same bone, finally enters a small canaljj (iter chordce anterius) in the bone close to
the Glaserian fissure (fig. 90, ch). It is invested by the fold of the lining-
membrane already mentioned.

THE INTERNAL EAR, OR LABYRINTH.

The inner, essential part of the organ of hearing, is contained in the petrous
portion of the temporal bone. It consists of a complex cavity — the osseous laby-
rinth— hollowed out of the bone, and containing the membranous labyrinth.

The osseous labyrinth is incompletely divided into three parts, named the vesti-
bule, the semicircular canals, and the cochlea. They are lined throughout by a thin
periosteal membrane, within which there is a clear fluid named perilymph, or liquor
Cotunnii.

The membranous labyrinth being distinctly smaller than the bony labyrinth, a
space is left between the two, occupied by the perilymph just referred to. The
membranous structure is lined throughout by epithelium, and at certain parts
receives branches of the auditory nerve. It contains a fluid named the endolymph,
and consists of several parts, viz. : the ntricle, saccule, semicircular canals, and
membranous cochlea.

THE OSSEOUS LABYRINTH.

99

THE OSSEOUS LABYRINTH.

The vestibule forms a central chamber of the labyrinth, which communicates
in front with the cochlea, and behind with the semicircular canals. It is irregularly
ovoidal in shape, measuring about 5mm. from above down and from before back but
slightly less from without inwards.

The outer wall, which separates it from the cavity of the tympanum, is perforated
by the fenestra ovalis, which in the recent state is closed by the base of the stapes.

At the fore part of the inner wall is a small round pit, the fovea hemwpherica
(fig. 108, 2 ; fig. Ill), pierced with many minute holes, which serve to transmit
branches of the auditory nerve from the internal auditory meatus to the saccule.
This fossa is limited behind by a vertical ridge named crista vestibuli, the anterior

C. tympkl Pi:

Fig. 106. — THE RIGHT TEMPORAL BONE SAWN ACROSS IN A CORONAL PLANE ; THE CUT PASSING THROUGH
THE FENESTRA OVALIS. Natural size. (Testut.)

A, anterior, B, posterior segment, showing the cut surfaces.

m.e., meatus externus ; m.tymp., groove for membrana tympani ; c.ti/mp., tympanic cavity;
antr.mast., antrum mastoideum ; pr., promontory ; or.Eu.t., orifice of Eustachian tube ; /.o., fenestra
ovalis ; /.?*., fenestra rotunda ; cock. , commencement of cochlea ; m.i., meatus audit, internus ; art.car.,
carotid artery.

extremity of which has been termed the pyramid of the vestibule, and merges on to
the roof. The crista passes backwards and downwards and bifurcates behind the
fovea hemispherica ; the fork encloses a small fossa, which was termed recessus
cochlearis by Reichert : it receives the beginning of the ductus cochlearis and is
pierced with a number of holes for the passage of nerve-fibres (fig. Ill, fossa
cochlearis}. Behind the lower part of the crest is the small oblique groove which
deepens into a fine canal, the aqueduct of tJie vestibule (fig. 108, 4). This extends
to the posterior surface of the petrous bone and transmits the ductus endo-
lymphaticus (p. 105) and a small vein.

In the roof is an oval depression, placed somewhat transversely, fovea hemi-
elliptica (fig. 108, 1 ; fig. ] 11), which is separated by the crest from the hemispherical
fossa. The crest and pyramid close to this fossa are pierced with fine holes for the
passage of nerve-fibres, those in the crest itself being destined for the utricle : those
in the pyramid for the ampullae of the superior and external semicircular canals.

At the back part of the vestibule are five round apertures, leading into the semi-
: ::: : ; ; ^ "•" "% ,%:;;*" H 2

100

THE EAR.

circular canals : and at the lower and fore part of the cavity is a larger opening,
which communicates with the scala vestibuli of the cochlea.

The semicircular canals are three tubes, situated above and behind the vesti-
bule, into which they open by five apertures, the contiguous ends of two of the
canals being joined. They are unequal in length, but each tube is bent so as to
form about two-thirds of an ellipse ; and is moreover dilated at one end, the
enlargement being known as the ampulla. The canals are compressed laterally, and
measure 1mm. to l'5mm. across ; but the ampulla has a diameter of about 2mm.

The canals differ from one another in direction, in length, and in position with
regard to the vestibule. The superior semicircular canal (fig. 108, 3, fig. 109, 5).
19 mm. long, is nearly vertical and lies transversely to the bony axis of the petrous

s.c.e. s.c.s-p.

amp

amp

aq. Fall.

pyr.
sin.tymp.

pr. -

amp.c.
aq.Fall.

, o.Eu.t.

Fig. 107. — PORTIONS OF THE PREVIOUS FIGURE ENLARGED. (Testut.)

A., anterior ; B., posterior segment, amp.e., amp.s. and amp. p., ampullary orifices of external,
superior and posterior semicircular canals ; s.c.e., non-ampullary orifice of the external canal ; s.c.s-p.,
conjoint non-ampullary orifice of the superior and posterior canals ; aq.Fall., aqueductus Fallopii ; f.o.,
fenestra ovalis ; f.r., fenestra rotunda ; aq.cochl., aqueductus cochleae ; sc.vest., commencement of scala
vestibuli : that of the scala tympani is just below it ; lam.sp., spiral lamina ; n. VII., orifice for facial
nerve ; n. VIII. s., orifices for superior or vestibular division of auditory nerve ; tr.sp.for., orifices for
cochlear nerve ; f.s., foramen singulare ; pyr., pyramid ; pr., promontory ; sin.tymp., sinus tym-
pani ; o.Eu.t., orifice of osseous Enstachian tube.

bone, forming an angle of about 45° with the coronal plane ; it rises higher than any
other part of the labyrinth, and its place is indicated by a smooth arched projection
on the upper surface of the petrous bone. The ampullary end of this canal is the
external and anterior, and opens by a distinct orifice into the upper part of the
vestibule (fig. 107, s) ; whilst the opposite extremity joins the non-dilated end of
the posterior semicircular canal, and opens by a common aperture with it into the
back part of the vestibule (fig. 107, s.c.s-p. ; fig. 109, 3). The posterior semi-
circular canal (fig. 108, 5, fig. 109, 6), is also nearly vertical, and lies in a plane
which is almost parallel with the superior canal of the other side (Crum Brown).
The posterior and superior canals of the same side incline towards one another at
their inner ends. The posterior is the longest of the three (22 mm.) : its ampullary
end is at the lower and back part of the vestibule (fig. 107, amp.p) ; and the
opposite end terminates in the common canal above described (s.c.s-p.}. The

THE OSSEOUS LABYRINTH.

101

external semicircular canal (fig. 108, 4 ; fig. 109. 7) arches horizontally outwards,
and opens by two distinct orifices into the upper and back part of the vestibule
(fig. 107, amp.e. and s.c.e.). The canal is shorter than either of the other two
(15 mm.) : its ampulla is at the oucer end, above the fenestra ovalis.

Fig. 108. — RIGHT BONY LABYRINTH, VIEWED FROM THE OUTER SIDE (after Soramerring).

Magnified 2£ times.

The specimen here represented is prepared by separating piecemeal the looser substance of the

petrous bone from the dense walls which immediately enclose the labyrinth. 1, the vestibule :

2, fenestra ovalis ; 3, superior semicircular canal ; 4, horizontal or external canal ; 5, posterior canal ;

*, ampullae of the semicircular canals ; 6, first turn of the cochlea ; 7, second turn ; 8, apex ;

9, fenestra rotunda. The smaller figure in outline below shows the natural size.

Fig. 109. — VIEW OP THE INTERIOR OP THE LEFT LABYRINTH. (From Sommerring.) &

The bony wall of the labyrinth is removed superiorly and externally. 1, fovea hemi-elliptica ;
2, fovea hemispherica ; 3, common opening of the superior and posterior semicircular canals ; 4, opening
of the aqueduct of the vestibule ; 5, the superior ; 6, the posterior, and 7, the external semicircular
canals ; 8, spiral tube of the cochlea (scala tympani) ; 9, opening of the aqueduct of the cochlea ;

10, placed on the lamina spiralis in the scala vestibuli.

The cochlea (figs. 108 to 116), when cleared of the surrounding less dense bony
substance in which it lies embedded, appears in the form of a blunt cone, the base
of which is turned towards the internal auditory meatus, whilst the apex is directed

Fig. 110. — VIEWS OF A. CAST OF THE INTERIOR OF THE LABYRINTH. (From Henle.) f

Such casts may easily be made in fusible metal, and give a very correct view of the form of the
different parts of the labyrinthic cavity. A, view of the left labyrinth from the outer side ; B, the
right labyrinth from the inner side ; C, the left labyrinth from above ; s, the superior, p, the posterior,
nnd e, the external semicircular canals ; a, their several ampullae ; r e, fovea hemi-elliptica of the
vestibule ; r s, fovea hemispherica ; a v, aqueduct of the vestibule ; f o, fenestra ovalis ; f r, fenestra
rotunda ; c, the coiled tube of the cochlea ; c', the tractus spiralis foraminulentus.

outwards, with an inclination forwards and downwards, and is close to the canal for
the tensor tympani muscle. It measures about 5mm. from base to apex, and 0 mm.
in breadth at the base. It consists of a gradually tapering spiral tube, the inner
\vall of which is formed by a central column, or modiohis (fig. 113), around which

102

THE EAR.

it winds. It is partially divided along its whole extent by a spiral lamina,
projecting into it from the modiolus. From this osseous spiral lamina membranous
structures are in the recent condition stretched across to the outer wall of the tube,
and thus completely separate two passages or scalw, one on each side of the spiral
lamina, which communicate one with the other only by a small opening, named
helicotrema, placed at the apex of the cochlea.

SceUAtynpani, ScoUa.

Fig. 111. — THE COCHLEA AND VESTIBULE EXPOSED BY REMOVING THE ROOF OF THE BONY LABYRINTH

WITH THE SAW, SO AS TO VIEW THE PARTS FROM ABOVE. Magnified. (Testllt. )

That the cochlea is justly to be considered as an elongated tube, coiled spirally on the
modiolus, is illustrated by the simple pouch-like form of the rudimentary cochlea of birds
(fig. 112) as well as by the history of its development.

The spiral osseous canal is about 33mm. long, and about 2mm. in diameter at
the commencement, where it is widest. From this point the canal makes nearly 2J
turns round the central pillar (from left* to right in the right ear, and in the opposite
direction in the left ear, supposing the cochlea viewed from the base), and ends by
an arched and closed extremity called the cupola, which forms the summit of the

Fig. 112. — OSSEOUS LABYRINTH OF THE BARN OWL (STRIX FLAMMEA). (From

Breschet.) ±

1, semicircular canals ; 2, vestibule ; 3, cochlea in the form of a short straight
tube.

cochlea. The first coil, having by far the most extensive curve
and being the largest portion of the tube, nearly hides the second
from view ; and, bulging somewhat into the tympanum, forms
the round elevation on the inner wall of that cavity called the
promontory. The last half-coil is somewhat flattened from above
down and its extremity is partly embedded in the coil next below it.
The modiolus (columella cochleae), the central pillar or axis of the cochlea, is
much the thickest within the first turn of the tube, rapidly diminishing in size in
the succeeding parts. Its central part is spongy as far as the last half-coil, and is
pierced by many small canals, for the passage of the nerves and vessels to the spiral
lamina ; one of these canals, larger than the rest, central canal of the modiolus, runs
from the base through the centre of the modiolus (fig. 114). The base of the
modiolus appears in the internal auditory meatus as the fossula cochlese containing
the foramen centrale and the tractus spiralis foraminulentus : the latter transmit-

THE OSSEOUS LABYRINTH.

103

ting the nerve-fibres of 1| turns of the cochlear tube, the former being continued
into the central canal of the modiolus and transmitting the nerve-fibres for the
uppermost turn.

The osseous spiral lamina is a thin, flat plate, growing from the modiolus, and

vcfitibidi helic'trcma

lamina spiralis scala tympani
membranacca

expansion of cochlear nerve
Fig. 113. — DIAGRAMMATIC VIEW OF THE OSSEOUS COCHLEA LAID OPEN. (Arnold.)

projecting into the spiral tube, so as to divide it partly into two. It does not reach
farther than about half-way towards the outer wall of the spiral tube. Close to the

scala vcstibuli

v. . ...

scala tympani lamina spiralis ossea tncatus auditorius inttrnus (fovea cochlea?)

Fig. 114. — VIEW OF THE OSSEOUS COCHLEA DIVIDED THROUGH THE MIDDLE. (Arnold.)

npex of the cochlea, it ends in a hooklike process (hamulus), which partly bounds
the helicotrema. Opposite the lamina spiralis at the commencement or base of the
cochlear tube is another bony lamina (secondary spiral lamina) which nearly meets
the spiral lamina, so that there is here only a narrow cleft between the two.

The lamina is dense at its free edge ; but nearer the modiolus its internal

104 THE EAR.

structure is more open and spongy, and contains numerous small canals for
vessels and nerves, continuous with, but running at right angles to, the canals in
the modiolus. Winding round the modiolus, in the base of the spiral lamina, is a
small canal, named the spiral canal of the modiolus.

The scala tympani (fig. Ill ; fig. 113, 3), the portion of the tube on the basal
side of the lamina spiralis, commences at the fenestra rotunda, where in the recent
state it is separated from the tympanum by the secondary membrane of the tympa-
num. Close to its commencement is the orifice of a small canal (aqueductus cochlece),
which extends downwards and inwards to the lower border of the petrous bone,
where it opens into a depression immediately in front of the jugular fossa, It
transmits a small vein which joins the inferior petrosal sinus. There is also a
communication along the aqueductus cochleae between the subarachnoid space and
the perilymph in the scala tympani. The scala vestibuU (figs. Ill, 113, 4) is rather
narrower than the scala tympani in the first turn of the cochlea, but in the
succeeding turns is larger ; it commences from the cavity of the vestibule, and com-
municates, as already described, with the scala tympani at the apex of the modiolus.

THE MEMBRANOUS LABYRINTH.

Within the osseous labyrinth, and separated in most parts from its lining mem-
brane by the perilymph, membranous structures exist in which the ultimate ramifi-
cations of the auditory nerve are spread. In the vestibule and semicircular canals

Fig. 115. — PLAN OF THE RIGHT MEMBRANOUS LABYRINTH

VIEWED FROM THE MESIAL ASPECT. (E. A. S.)

u, utricle, with its macula and the three semicircular
canals with their ampullae ; s, saccule ; s.e. saccus endo-
lymphaticus ; c.r. canalis reuniens ; c.c. canal of the cochlea.

these structures have a general resemblance in
form to the complicated cavity in which they
are contained. They do not, however, lie loose
within the osseous cavity, but along the convex
border of the canals, and at the places of
entrance of the nerves into the vestibule and

ampullae are fixed to its wall. In the cochlea the membranous structures complete
the septum between the scalas already mentioned, and enclose an intermediate
passage, the membranous canal of the cochlea. As before stated, the liquid contained
within the membranous labyrinth is distinguished as endolymph.

The cavity which, contains the perilymph communicates through the sheath, of the auditory
nerve with both the subdural and subarachnoid spaces.

Within the osseous vestibule are two membranous sacs, the one of which, termed
the utricle, is connected with the semicircular canals, whilst the other, the saccule,
is connected with the cochlea. These two sacs although in close contact do not
open directly into one another although they are in indirect communication, in a
manner presently to be explained.

The larger of the two sacs, the common sinus or utricle (fig. 115, u ; fig. 116),
is of a very irregular oblong form, measuring in all G mm. to 7 mm. in length, and
averaging 5 mm. in breadth, slightly flattened from behind forwards. It is lodged
in the upper and back part of the vestibule, occupying the fovea hemi-elliptica and
the space immediately below this. The part which lies in the fovea is termed the
recessus utriculi (fig. 116, rec. utr.). This forms a distinct blind forward projection,
some 3 mm. in length, into which, opposite the crista vestibuli, several small
branches of the auditory nerve enter from the foramina in the bone ; and here the

THE MEMBRANOUS LABYRINTH. 105

wall of the utricle is thickened, the thickening having a concave surface towards
the interior of the utricle, and being covered by auditory epithelium (macula
acusttca utriculi}. A small mass of calcareous particles (otoliths or oioconia) lies

Fig. 116.— OTOLITHS. (From Schwalbe.)

within the sac, attached to the macula. These
otoliths are crystals of carbonate of lime, rhombic,
octahedral, or six-sided, often pointed at their ex- 0
tremities (fig. 118).

The ends of all the membranous semicircular
canals open into the utricle in the situations shown
in the diagrams, and a fine canal (canalis utriculo-
saccularis) passes from the antero-mesial wall of the

utricle, which joins with another one from the saccule to form the ducius endo-
lymphaticus (fig, 11G, d.e) (see below).

The ampulla; of the superior and external canals open into the roof of the recessus
utriculi. The part of the utricle where the ampulla of the posterior semicircular canal opens
is termed by GL Retzius si nits posterior, and the conjoined limbs of the superior and external
canals form the .v/'^w.s- Kiijin-tor of that author. In all vertebrates below mammals the utricle
has a second macula acustica in its lower part near the sinus posterior {macula, ncgleeta of
Retzius).

The smaller vesicle, the saccule (fig. 115, s ; fig. 117), is an irregularly oval
vesicle about 3 mm. long and nearly 2 mm. broad, and is somewhat flattened from
within out. The saccule is situated in the lower and fore part of the cavity of the
osseous vestibule, close to the opening from the scala vestibuli of the cochlea, and
is received into the hollow of the fovea hemispherica, from the bottom of which
many branches of nerve enter it, and here there is a similar broad and concave
macula in its wall, which is covered by a small mass of otoliths. The upper end of
the saccule bends round towards the recessus utriculi, with which it comes in
contact, without direct communication (fig. 117).

The saccule gradually narrows below into a short funnel-shaped duct (1 mm.
long, 0*5 mm. wide), the canalis reuniens of Hensen (fig. 115, c. r. ; fig. 117, 19),
which passes downwards and outwards to open directly into the epithelial canal of
the cochlea a short distance from its blind lower extremity. There is also, as
already mentioned, a canal, lined with epithelium, which passes from the posterior
wall of the saccule along the aqueductus vestibuli to end blindly in a dilated
extremity (saccus endo-lymphaticus, fig. 115, s.e.) on the posterior surface of the
petrous bone just below the orifice of the aqueduct and lying in the tissue of the
dura mater (Cotugno). This canal is joined near its origin by a minute tube from
the utricle (fig. 117, 7), so that in this way the cavity of the saccule is brought into
communication with that of the utricle (Boettcher).

The membranous semicircular canals are from one-third to one-fifth the
diameter of the osseous tubes in which they are lodged, and are dilated into ampullae
within the ampullary enlargements of those tubes. In section they are oval or some-
what elliptical (fig. 119). The ampullae measure from '2 mm. to 2*5 mm. in length ;
they are thicker and less translucent than the rest of the canals, and nearly fill
their bony cases, the (membranous) ampullae being nearly three times the diameter
of the canals. That part of each which is towards the concavity of the semicircle
of the canal is free ; whilst the opposite portion is fixed to the wall of the bony
canal ; in the ampulla this part is flattened and receives branches of nerves and
blood-vessels, and on its inner surface is a transverse projection (septum transversum)
which partly divides the cavity into two, and broadens out somewhat at either end.
The most prominent part of the septum, which is surmounted by the auditory

106

THE EAR.

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Fig. 117.

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Fig. 118.

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THE MEMBRANOUS LABYRINTH.

107

Fig. 117. — RIGHT HUMAN MEMBRANOUS LABYRINTH, REMOVED FROM ITS BONV ENCLOSURE, AND VIEWED

FROM THE ANTERO-LATERAL ASPECT. (Gr. RetZUlS.)

Fig. 118. — THE SAME FROM THE POSTERO- MESIAL ASPECT. (Gf. Retzius.) £

1, external semicircular canal ; 1', its ampulla ; 2, posterior canal ; 2', its ampulla ; 3, superior
canal ; 3', its ampulla ; 4, conjoined limb of superior and posterior canals (sinus utriculi superior) ;
5, utricle ; 5', recessus utriculi ; 5", sinus utriculi posterior ; 6, ductus endolymphaticus ; 7, canalis
utriculo-saccularis ; 8, nerve to ampulla of superior canal ; 9, nerve to ampulla of external canal ; 10,
nerve to recessus utriculi (in fig. 117, the three branches appear conjoined) ; 10', ending of nerve in
recessus utriculi ; 11, facial nerve ; 12, lagena cochleae ; 13, nerve of cochlea within spiral lamina ;
14, basilar membrane ; lo, nerve fibres to macula of saccule ; 16, nerve to ampulla of posterior canal ;
17, saccule ; 18, secondary membrane of tympanum ; 19, canalis reunions ; 20, blind ending of cochlear
canal in vestibule; 21, outer wall of cochlea; 22, spiral ligament ; 23, section of the seventh and
eighth nerves within internal auditory meatus (the separation between them is not apparent in the
section).

epithelium, is termed the crista acustica. Seen from above (i.e., through the roof of
the ampulla), the septum is somewhat fiddle-shaped, the ends being broader than

Fig. 119.— VIEWS OF THE EXTERNAL SEMICIRCULAR CANAL, HUMAN. Magnified. (Gr. Retzius.)

A, The whole of the external canal attached to the utricle, the anterior and posterior canals having
been cut away. Amp.cxt., ampulla of the external canal ; Amp.ant., ampulla of the anterior canal :
Or., crista acustica of the same ; R.utr., recessus utriculi ; S.utr.s., sinus utriculi superior, cut short ;
S.utr.p.j sinus utriculi posterior, ditto ; C.utr.sac., canalis utriculo-saccularis ; M.utr,, fibres passing
to macula recessus utriculi ; M.ittr.', the same passing round the wall of the utricle.

B, Lateral view of the external ampulla ; n, nerve bundle entering crista.

C, View of external ampulla, showing the free surface of the crista acustica, Cr.

D, Transverse sectional view of the external ampulla, showing the transverse extent of the
crista, Cr. ; n, nerve fibres.

108

THE EAR.

the middle ; and beyond each rounded end of the crista is a crescent-shaped
edge (covered by columnar epithelium) which has been termed planum semi-
hmatum (fig. 119, C. D.).

Branches of the eighth nerve. — Within the internal auditory meatus the
eighth nerve divides into two branches, which, broken up into minute filaments,
pass through perforations in the plate of bone which separates the meatus from the
internal ear, and are distributed respectively to the cochlea and vestibule. In both
branches, as well as in the trunk, there are numerous nerve-cells. The superior
division (fig. 118, 8, 9, 10), which is at first also anterior in position (ramus anterior
of Retzius), and is separated by a crest of bone from the other division below it, gives
off three branches, which proceed respectively to the utricle and the ampullae of the
superior and external semicircular canals, entering the vestibular cavity in a group

falciform orifice for orifices for vestibular division
ridge facial nerve of eighth nerve

\^$$/fi*

i^/turfc

apex of petrous

cent. orif. foram. vest, scala fossa

canal for sing,
foram. of mo- nerve of
diolus saccule

tymp. ovalis

Fig. 120. — THE PETROSAL SAWN THROUGH IN TWO PLANES, so AS TO SHO\V THE EXTREMITY OF THE

INTERNAL AUDITORY MEATUS AND THE VESTIBULE. (Testllt. )

along the crista vestibuli. This superior division has a ganglion upon it whilst still
within the internal auditory meatus (ganglion of Scarpa) and the ganglion- cells
also extend for some distance along the branches within the canals in the bone.
The inferior division on the other hand (ramus posterior of Retzius) (Q, which is at
first behind as well as below the vestibular division, gives off, besides the cochlear
branch which enters the cochlea by the tractus foraminulentus, a branch for the
saccule — which enters the vestibule by a small group of foramina, opening at the
bottom of the fovea hemispherica — and a branch for the posterior semicircular
canal ; this is long and slender, and traverses a small passage in the bone (foramen
singulars} behind the foramina for the nerve of the saccule. The part of the
inferior division which gives the branches to the saccule and posterior canal is
distinguished by Schwalbe as the ramus medius. The branch to the saccule also
has a ganglion upon it within the meatus and that to the posterior semicircular
canal a ganglion near its ending in the ampulla (ganglion of Corti), whereas the

VESSELS OF THE LABYRINTH.

109

ganglion of the cochlear branch lies within the modiolus, at the base of the spiral
lamina (ganglion spirale). All the cells of these several ganglia are bipolar. The
nerves of the ampullse enter the flattened or least prominent side of the ampullse,
where they each form a forked swelling, which corresponds with the crista acustica,
in the interior of the dilatation.

Vessels of the labyrinth. — The internal auditory artery, a branch of the
basilar, accompanies the auditory nerve in the internal auditory meatus, and divides
into branches for the vestibule and cochlea. Those of the vestibule supply the
membranous labyrinth and the endosteum, and small vessels ensheathed by tibrous
tissue pass across the cavity containing the perilymph. The blood is chiefly
collected into the internal auditory veins which accompany the artery and open
into the inferior petrosal sinus, but some is conveyed to the inferior petrosal sinus
by fine veins in the aqueductus vestibuli and aqueductus cochleae. Small arterial
branches from the vessels of the dura mater and also from the stylo-mastoid artery,
and from vessels of the middle ear, supply the bony walls of the labyrinth, but do
not appear to anastomose with the arteries of the membranous labyrinth.

Structure of the utricle, saccule, and semicircular canals. — Three
layers can be distinguished in the membranous walls of the semicircular canals, an

Fig. 121. — SECTION OF ONE OF

THE HUMAN SEMICIRCULAR

CANALS. (Riidinger.) Mag-
nified.
1, osseous wall ; 2, fibrous

bands with included blood-vessels,

united at 3 with the periosteum ;

4, membranous canal with its

three layers ; 5, short fibrous

bands (with intervening spaces)

uniting the membranous canal

firmly to the periosteum ; 6,

union of its outermost layer with

the periosteum.

outer fibrous stratum, an

inner epithelial lining, and

between the two a tunica

propria. These layers are

not of equal thickness

throughout, for along the

side which is in contact

with and supported by the

bone (fig. 122, 6), they are

thinner than at the rest of

the circumference, where

they lie free and are bathed by the perilymph. The difference in thickness affects

the fibrous layer and the tunica propria only, for the epithelium forms throughout a

lining of simple flattened cells.

The Jilrous layer (fig. 122, 1), which contains some irregular pigment-cells, is
apparently composed of ordinary fibrous tissue, similar to that of the periosteum,
with which it becomes continuous at the parts where the two structures are in con-
tact. It is especially developed at the ends of the oval section, whence well-marked
bands of fibrous tissue pass to the periosteum (fig. 122, 7). More delicate bands of
fibrous tissue traverse the perilymph to become connected with the periosteum of the
opposite wall of the canal (fig. 121, 2). Both along these bands and also more
directly from the contiguous periosteum, numerous small blood-vessels pass into the

110

THE EAR.

fibrous layer and there break up into a coarse capillary network, the branches of
which do not, in man, pass into the tunica propria.

The tunica propria is a clear membranous structure continuous around the whole
tube, although thinning off very much opposite the part where the membranous
canal is in contact with the bone (fig. 122, 5). Externally it is not very distinctly
marked off from the fibrous coat : internally it has a number of papilliform emi-
nences (fig. 122, 6,) which project into the interior of the canal except at the thin-
nest part (Rudinger).

The epithelial lining takes the form of a complete layer of flattened cells, which
in the human semicircular canals are of the same nature throughout, except along

Fig. 122.— SECTION OF MEMBRANOUS SEMICIRCULAR CANAL, MUCH MAGNIFIED. (Rudinger.)

1, outer fibrous layer ; 2, tunica propria ; 3, 6, papilliform projections with epithelial covering ;
f>, fixed side of the canal, with very thin tunica propria without papillae ; 7, fibrous bands passing to
periosteum.

the outer part of the lumen, where there is a longitudinal tract of cells which are
more elongated than the rest. This line is sometimes termed the raphe of the
canal.

In many of the lower animals — birds and fishes — some of these lining- cells are columnar,
while in one species of fish (Salmo hucho), as described by Rudinger, a tract along- the
whole length of each canal becomes developed into two rows of rounded cells, from each
of which a long filament extends to the wall of the canal in a direction transverse to the
axis.

The ampullae, as well as the saccule and utricle, agree generally in structure
with the semicircular canals : but at the part where they are connected with the
osseous wall the fibrous outer layer is looser, and the tunica propria is much
thickened, and in the ampullae projects into the cavity as the septum transversum
surmounted by the crista acustica, before mentioned (fig. 119). Through the
substance of this thickening the nerve-fibres pass to the edge of the ridge, and over
it the epithelium is of an elongated columnar form (figs. 123 to 126), and is sur-
mounted by long, conical, gradually tapering filaments (auditory hairs (h), ), which
project stiffly into the cavity, and are about 0'03 mm. in length. These hairs are
borne by the columnar epithelium-cells (fig. 126), a single hair projecting from each
cell, but under the influence of reagents they are apt to become broken near the
base, and thus split up into fine fibrils which appear as a bunch of cilium-like
filaments attached to the free border of the cell. The columnar cells, or hair-cells,
do not extend down to the basement membrane, but terminate short of this in a

VESSELS OF THE LABYRINTH.

Ill

rounded extremity. They are surrounded by the branching axis-cylinders of the
nerve-fibres which penetrate into the epithelium ; the medullary sheath disappears

Fig. 123. — LONGITUDINAL SECTION OF AN AMPULLA ' THROUGH THE GKISTA ACUSTICA.

SEMI-DIAGRAMMATIC (E.A.S.).

'.amp, cavity of the ampulla; sc. c, semicircular canal opening out of it; c, connective tissue
attached to the wall of the membranous ainpulla and traversing the perilymph ; e e, flattened epithelium
of ampulla ; h, auditory hairs projecting from the columnar cells of the auditory epithelium into the
cupula, cup. term. ; v, limit of the auditory epithelium on the crista ; n, nerve-fibres entering the base
of the crista and passing into the columnar cells.

as the fibres enter the epithelial layer, and the axis-cylinders ramify amongst the
cells, but there does not appear to be any actual continuity between the terminal
arborizations of the nerve fibres (fig. 125) and the hair-cells.

••_ -
•J.

Fig. 124. — SECTION OF THE MACULA ACUSTICA OF THE RECESSUS UTRICULI, HUMAN.
(GK Retzius.) Magnified.

n.utr., bundles of the utricular branch of the eighth nerve ; A, hair-cells ; p.l.s., perifymphatic
space.

Between and beneath the columnar cells other cells are met with of a different
character. They take the form of long and comparatively rigid fibres (fibre-cells of
Retzius) which extend through the whole thickness of the epithelium, and are pro-
vided at one part of their course with a nucleated enlargement. This is always

THE EAR.

placed below the columnar cells, and in many ifc is close to the central end of the
fibre. The fibres, which are probably sustentacular in function, like the fibres

Fig. 125. — NERVE TERMINATIONS IN

MACULA ACUSTICA, SHOWN BY
GrOLGl's METHOD. (Gf. Retzius.)

of Miiller in the retina and the
cells of Deiters in the cochlea,
expand slightly as they ap-
proach the free surface, and
appear to become attached to
a cuticular structure which en-
closes the ends of the hair-cells
and is thus comparable to the
reticular lamina of the cochlea
(Urban Pritchard). On the other
hand the fibres are set by their
central ends upon a limiting
membrane which bounds the
epithelium next to the tunica
propria, and which appears in section as a fine but well-marked line.

Fig. 126.-

-SECTION OF EPITHELIUM OF AMPULLA OF LACEUTA
VIRIDIS. (Gr. Retzius.) Magnified.

The limit of the auditory epithelium at the sides of
the crest is sometimes marked, at least in the human
ampullae, by a prominent vessel (fig-. 123. r).

The auditory hairs were first noticed by Max Schultze,
who described them as being- connected with the elongated
cells and not with those of a columnar shape. Their true
relations were pointed out by Retzius. and in this matter
my own observations, in the fish and in man, coincide
with his. When the cells are isolated after preservation
in osmic acid, the separated columnar cells are alone
surmounted by auditory hairs, whereas the elongated
intermediate cells are not provided with auditory fila-
ments. It is worthy of note that the auditory hairs do
not in sections made from hardened specimens appear to
project freely into the endolymph of the ampulla, but
into a soft material which takes a dome-like shape (cvpula
frrittina?!*. Lang), and appears to possess an indistinctly
fibrillar structure. If this material is pre-existent (and
not merely, as some have supposed, produced by a swelling
and alteration of the auditory hairs after death), it is not
possible to imagine that the hairs can be set in vibration
singly, but whatever movements are communicated to
the endolymph, must affect the whole cupula and all the
hairs embedded in it.

The foregoing description of the characters of the
epithelium and mode of nerve-distribution in the cristae
acusticae of the ampullae, is equally applicable to the
maculae acusticae of the saccule and utricle. The nerves

which are supplied to the maculae seem, however, to spread out more than those to the
ampullae. The auditory hairs are somewhat shorter than those of the ampullae. As before
mentioned, both saccule and utricle contain in their cavity and lying in contact with the
nerve-epithelium a little mass of otoliths. which, however, do not float free in the fluid, but
appear imbedded in a soft matrix which is perhaps enclosed in a delicate cuticular investment.
Otoliths are also found scattered here and there in the ampullae and semicircular canals.

The membranous cochlea, which occupies the spirally-wound tube of the
osseous cochlea consists like this of about two and three-quarter turns, which

THE MEMBRANOUS COCHLEA. 131

may be termed respectively the basal, middle, and apical, the last-named being
incomplete. The total length of the tube is about 35 mm. In structure it
resembles the membranous semicircular canals just described in consisting of a tube,
lined by epithelium and containing endolymph, partly surrounded by a clear space
containing perilymph, but it differs from them both in shape and in the modifica-
tions presented by its epithelial lining. In macerated specimens, the two parts
into which the osseous tube of the cochlea is divided are, it will be remembered,
only imperfectly separated by the osseous spiral lamina which projects from the
columella ; but in the fresh specimen the tube is separated completely into three
distinct parts by means of two membranes, which extend along its whole length
(figs. 127 to 129). In the first place the lamina spiralis is directly prolonged by a
comparatively strong, well-marked membrane, the basilar membrane, which stretches
straight across to the outer wall of the cochlea, and is here connected to an inward

-cc

Fig. 127. — LEFT COCHLEA OF A CHILD SOME WEEKS OLD (Reichert). £

The drawing was taken from a specimen which had been preserved in alcohol, and was afterwards
dried ; a section is made so as to show the lamina spiralis, scalse, and cochlear canal in each of the
three coils : the membranous spiral lamina is preserved, but the appearances connected with the organ
of Corti, &c., have been lost from drying, f r, fossula of the fenestra rotunda. The secondary
membrane of the tympanum is seen at the bottom of the fossula attached below to a bony projection
of the lower wall (crista semilunaris, to the right of d) ; s t, scala tympani ; s v, scala vestibuli. In
the lowermost turn the scala tympani is seen to be the larger : in the higher turns the proportions are
reversed ; I s, lamina spiralis ; h, hamulus ; c c, canalis cochleae ; d, opening of the aqueductus
cochleae.

Fig. 128. — VERTICAL SECTION OP THE COCHLEA OP A FCETAL CALF (Kb'lliker). 2

In this specimen the external wall was ossified, but the modiolus and spiral lamina was still
cartilaginous ; the section shows in each part of the cochlear tube the two scalse with the intermediate
canalis cochleae and lamina spiralis.

projection of the lining periosteum and sub-periosteal tissue known as the spiral
ligament. The basilar membrane thus helps to complete the upper * limit of
the scala tympani but does not, properly speaking, enter into the lower boundary
of the scala vestibuli, for a second, much more delicate membrane, known as
the membrane of Reissner, passes from the upper part of the lamina a little
distance from its end, and stretches obliquely upwards and outwards, also to
become connected with the lining periosteum. The oblique direction of the
membrane of Eeissner causes a triangular space to be shut off between it and
the basilar membrane, which is bounded externally by the outer osseous wall of the
cochlea lined by periosteum ; and this space, extending throughout the whole length
of the osseous tube, and lined throughout by an epithelium variously modified in
different parts, is known distinctively as the canal of the cochlea, canalis membranaceus ,

1 To avoid repetition it may here be stated that for convenience sake the cochlea is considered in
the present description as having its larger part or base lowermost, and the domed extremity uppermost,
although of course this is far from being the relative position of the parts whilst within the body.
Moreover, parts nearer the columella are spoken of as inner ; parts nearer the external wall as outer.

VOL. III. PT. 3. I

114

THE EAR.

or ductus cochlearis (fig. 127, cc ; figs. 128, 129). It terminates in a blind extremity
at the apex (lagena),1 and another at the base. That at the apex, extending

membrana scala
tectoria restibuli

membrana scala

ganglion spirale Reissneri vestibuli

/neat us
auditorius
internus
fovea cochleae)

membrana
basilaris

ganglion
spirale

scala
tympani

membrana
basilaris
Fig. 129.— SECTION THROUGH THE MIDDLE OP THE COCHLEA, DIAGRAMMATIC. (E. A. S.)

beyond the hamulus, is fixed to the wall of the cupola, and partly bounds the helico-
trema ; that at the base fits into the angle at the commencement of the osseous

stria vascular is T,. , 0 -.

Fig. 130. — APEX OP COCHLEAR

CANAL. (Retzius.)

spiral lamina in front of the
floor of the vestibule. Near
to this blind extremity the
canal of the cochlea receives a
small canal, lined with epithe-
lium, cmialis reuniens (Hen-
sen), which is continued from
the saccule of the vestibule
like a neck of a flask, and
enters the canal of the cochlea
abruptly nearly at a right
angle (figs. 117, 118, ID).
The cavity of the canal of the

cochlea is thus rendered continuous with that of the saccule. The structures which
are found upon the floor of this spirally- wound triangular canal of the cochlea
claim more particular attention, for it is to them that the branches of the cochlear
nerve are distributed, and upon them the function of the cochlea as a part of the
auditory apparatus appears more especially dependent.

1 In monotreraes and in birds, reptiles, amphibia, and fishes, there is a specially modified patch of
auditory epithelium at the lagena, similar to the maculae of utricle and saccule, and provided with
otoliths. In fishes this is the only nerve-terminal apparatus in the cochlea, which is also otherwise quite
rudimentary.

lagena

hamulus bundles of

cochlear nerve

organ of Corti.

THE MEMBRANOUS COCHLEA.

115

The floor itself of the cochlear canal is formed of a narrow portion of the spiral
lamina external to the membrane of Reissner, and of the basilar membrane. In the
macerated specimen this part of the lamina thins off gradually to a fine edge like the
blade cf a knife, but in the recent condition (fig. 129) it retains its thickness for
some distance (or even exhibits a slight increase), and then abruptly terminates with
a border which in section is C-shaped, with the lower limb of the C (labium
tympanicwri) much more prolonged and tapering than the upper (labium vesti-
bulare). The lower limb is in fact the section of the end of the osseous lamina,
together with a thin membranous layer which covers it, and which is directly
prolonged into the basilar membrane. This membrane, as well as the whole
thickened upper part of the edge of the spiral lamina, not being ossified, disappears
in the process of maceration. The thickened part (fig. 131, l\ with its somewhat

s.v

Fig. 131. — SECTION ACROSS THE BASAL TURN OP THE HUMAN COCHLEA. (G-. Retzius.) Magnified.

D.C, ductus cochleae ; s.v, scala vestibuli ; s.t, scala tympani ; II, membrana Reissneri ; Mt, mem-
brana tectoria ; b.m, membrana basilaris ; str.v, stria vascularis ; l.sp, ligamentum spirale ; 1, limbus ;
s.sp, sulcus spiralis ; t. C, tunnel of Corti ; n, nerve fibres ; sp.l, spiral lamina.

overhanging, crest-like edge, is known as the limbus of the spiral lamina, and the
groove which it overhangs, and which in section is represented by the bay of the C,
is known as the spiral groove (fig. 131, s.sp.).

The tissue of which the limbus is composed seems to be a peculiar form of con-
nective tissue. Towards the under and inner part there are numerous corpuscles, and
the texture is fibrous, but above and near the crest few or no connective tissue cor-
puscles are met with, but the tissue has a columnar aspect with somewhat regularly-
arranged nuclei. The fibrillated tissue is prolonged, as just intimated, beyond the
osseous lamina, into the basilar membrane. Near its termination, close to the
junction with the basilar membrane, it is perforated with a number of regularly-
arranged, elongated apertures (fig. 132,^?), about 4,000 in number, which serve for
the transmission of bundles of the nerve-fibres. The latter, in their course from
the spiral ganglion to the auditory epithelium, are lodged, as far as this, in canals in
the lower osseous part of the spiral lamina. Their arrangement will be afterwards
more fully described.

i 2

116

THE EAU.

When the limbus is viewed from above, the vestibular edge is seen to present a
succession of tooth-like projections (fig. 132, Or), about 7,000 in number alto-
gether, which give it a jagged aspect. These projections are continued as flattened
eminences a short distance on the upper surface of the limbus, which is, therefore,
not smooth, at least near the edge, but marked in this way with eminences and
intervening furrows. Nearer the line of origin of the membrane of Reissner, it
becomes smoother, and here, too, its epithelial covering, which is directly continuous
with that of the under surface of Reissner's membrane, is evenly distributed ;
whereas at the crest itself the epithelial cells are columnar in the furrows, but
flattened out over the teeth, so as to be invisible here with ordinary methods of
preparation. Their outlines can, however, according to G. Retzius, be brought to
view by the employment of the silver method. Immediately below the overhanging
projections, the epithelium again forms a well-defined layer of cubical or short
columnar cells which lines the spiral groove, and is continuous externally with the
specialized cells, presently to be described as forming the organ of Corti.

The basilar membrane stretches, as before mentioned, straight between the
osseous lamina and the spiral ligament, and separates the canal of the cochlea from the

Fig. 132. — SEMI-DIAGRAMMATIC VIEW OP PART OP THE BASILAR MEMBRANE AND TUNNEL OF CORTI OF

THE RABBIT, FROM ABOVE AND THE SIDE. Much magnified. (E.A.S.)

I, limbus ; Cr, labium vestibulare or crest of limbus with tooth-like projections ; b b, basilar mem-
brane ; sp.l, spiral lamina with, p, perforations for transmission of nerve fibres. In the lower half of
the part of the spiral lamina here represented the nerve fibres are left, and are supposed to be seen
through the upper layer of that lamina, converging to three of the perforations ; below, in the section of
the lamina, they are shown occupying a canal, or cleft, in the osseous substance ; i.r, fifteen of the
inner rods of Corti ; h.i, their flattened heads seen from above ; e.r, nine outer rods of Corti ; h.e, their
heads, with the phalangeal processes extending outward from them and forming, with the two rows of
phalanges, the lamina reticularis, I.r. On the left of the figure the connective tissue fibres and nuclei
of the undermost layer of the ba,silar membrane are seen through the upper layers. Portions of the
basilar processes of the outer hair-cells remain attached here and there to the membrane at this part.

scala tympani. It increases in breadth, at first rapidly but afterwards more gradu-
ally, from the base to the apex of the cochlea, while the breadth of the osseous spiral
lamina diminishes. At the lowest part of the cochlea, where this membrane occupies
the naiTow cleft between the lamina spiralis ossea and the lamina secundaria, the
breadth is only about 0*041 mm. ; but towards the apex of the cochlea it increases
at the expense of the bony lamina, until, near the helicotrema, the membranous part
is left almost unsupported by any plate of bone, measuring as much as 0'495 mm.,
or about twelve times as much as at the base (Hensen). The average measurements
given by Retzius are, for the first or basal turn 0'21 mm. ; for the middle turn
0'34 mm. ; and for the apical turn 0*36 mm. Its total breadth averages, according

THE BASILAR MEMBRANE,

117

to Retzius, 33'5 mm. The basilar membrane is usually described as showing two
zones, viz., the zona arcuata, which is the part upon which the rods of Corti stand,
and the zona pectinata, extending from the feet of the outer rods to the spiral liga-

Fig. 133. — BASILAR MEMBRANE AND LIMBUS VIEWED
FROM ABOVE. Magnified. (GK Retzius.)

ment, the latter zone being somewhat thicker
and much more distinctly fibrous. The proper
substance of the membrane appears to be
formed of a homogeneous ground-substance
containing nuclei embedded in it here and
there, and having straight fibres (running
radially from the spiral lamina to the external
spiral ligament) embedded in it, so that the
membrane, especially its outer part, presents
a marked striation when viewed on the sur-
face (fig. 133). Externally, at its attachment
to the spiral ligament, it breaks up into
diverging fibres, which spread into that pro-
jection. In a section of the membrane across
the direction of its fibres the latter appear as
fine points enclosed by the homogeneous

^Ucurwrbcb

Fig. 134. — TANGENTIAL SECTION ACROSS THE ZONA

PECTINATA OP THE BASILAR MEMBRANE OF THE

GUINEA-PIG. (Schwalbe. ) Highly magnified.

ground-substance (fig. 134). In chemical
nature they resemble elastic fibres but are
rather less resistant to alkalies and most other
reagents. It has been calculated by Retzius
that there are altogether as many as 24,000 of
these fibres in the human membranabasilaris,
but they do not all run singly, some being
top-ether. On the unner surface of the

To go opposite p. 116.]

In the description of fig. 132 the words "In the lower half- in the osseous substance,"

are to be omitted ; and in the last line of the description the words " cells of Deiters " are
to be substituted for "outer hair-cells "

of the membrane), the fibres of which have a
direction parallel with the spiral, and across
that of the fibres of the membrane proper.
There are numerous intermixed spindle-
shaped corpuscles in this tissue, which is in
continuity with the lining periosteum of the
scala tympani (fig. 134). Small blood-vessels

are found in it, but as a rule extending only over the inner part of the membrane.
They are usually terminated by a rather larger longitudinally running vessel,
situated opposite the outer rods o!' Corti, and known as the vas spirals (fig. 136).

118

THE EAR.

The membrane of Reissner (fig. 129, 131, E), separates the scala vestibuli
from the canal of the cochlea. It is composed of an exceedingly delicate layer of
connective tissue continuous with the lining periosteum of the scala vestibuli, and is
covered on the surface, which is turned to the cochlear canal with a simple pavement
epithelium which is in continuity below with the epithelium of the limbus and
above with that lining the outer wall of the canal. The cells have each a circular
flattened nucleus, and not unfrequently contain fat-droplets. The vestibular side of
the membrane of Reissner is quite smooth, and is covered with an epithelial layer of
flattened connective-tissue cells, distinguishable from the epithelial cells on the other
side by their greater delicacy of outline,and their larger size. A few blood-capillaries are
continued into the adjacent part of the membrane from the neighbouring periosteum.
Outer wall of the cochlear canal. — The periosteum which lines the scala
vestibuli and scala tympani, consists of ordinary connective tissue. There is no COll-

wall of cochlea

spiral ligamen t IB

attachment of
Eeissner's membrane

stria vascularis

vas prommerts

; — epithelium cells
•— basilar membrane

Fig. 135. — SECTION SHOWING THE STRUCTURE OP THE LTGAMENTUM SPIRALE AND ADJACENT PARTS,
FROM THE GUINEA-PIG'S COCHLEA. (Sch \valbe.) Ap

tinuous lining of flattened cells on the free surface, such as covers the surface of
serous membranes. On the other hand the periosteum which bounds the canal of

OKGAN OF CORTI.

119

the cochlea externally, is much thickened by a development of re ti form, connective
tissue, and is covered by the epithelium of that tube, which here forms .a single layer
of columnar cells, which contain pigment, and are prolonged by forked or arborescent
processes into the subjacent connective tissue. There is usually a slight inward
projection a little above the spiral ligament, containing a prominent blood-vessel
(figs. 131, 135). In the tract between this prominence and the membrane of
lleissner, the substance of the periosteum is also frequently pigmented, and from
containing large and numerous blood-vessels, the capillary loops of which may even
project between the bases of the epithelium-cells, is termed stria vascularis. Imme-
diately beneath the epithelium of the outer wall is a basement membrane, through
which, in section, the cell-processes above mentioned may be seen passing from the
epithelium into the subjacent connective tissue.

The spiral ligament (fig. 131 l.sp., fig. 135) appears in section as a triangular
prominence attached to the outer wall of the cochlea, with the basilar membrane
prolonged from its apex. It is composed of a retiform connective tissue, many of
the cells of which have an elongated shape and radiate from the point of attachment
of the basilar membrane. They have been considered by some to be muscular, but
there is no distinct proof of their contractile nature.

Organ of Corti. — The epithelium which covers the basilar membrane includes

limbus

membrana tectoria

outer hair-cells

.- « :
©•

:<&«>

nerve fibres

inner rod vas
spimh

basilar
membrane

outer cells of Deilers
rod

Fig. 136. — SECTION THROUGH THE ORGAN OP CORTI OF THE MIDDLE TURN OP THE HUMAN COCHLEA.

(G. Retzius.) Highly magnified.

the highly-specialised structures which are known by the name of the organ of
Corti (fig. 136). The central part of this apparatus is formed by two sets of stiff,
rod-like bodies— the inner and outer rods of Corti (fig. 132) — which stand upon the
basilar membrane, the outer series (e.r.), at some little distance from the inner (i.r.),
and are inclined towards each other, coming in contact above. In this way each
pair of rods forms a pointed arch with slanting sides (fig. 137), and since the rods
of each series are in lateral juxtaposition, the double row of inclined columns forms
a tunnel (fig. 132) along the whole extent of the cochlear canal.

On the inner side of the inner series of rods is a row of epithelial cells (fig. 136),
which are surmounted by a brush of fine, short, stiff hairlets, and external to the
outer rods are three or four successive rows of similar but more elongated cells.
These cells are termed respectively the inner and outer hair-celts. The hairlets of
the outer hair-cells project through apertures in a curiously formed cuticular mem-
brane, termed the reticular lamina (fig. 132, /.r., 140), which covers this part of

120

THE EAR.

the organ of Corti like a wire net. The hairlets of the inner hair-cells are 1 J times
as long as those on the outer hair- cells (Retzius). On either side of the two sets
of hair-cells, the epithelium, becoming gradually shorter, passes continuously into
the simple layer of cubical cells which is found in the spiral groove and on the
lateral part of the basilar membrane.

The whole organ is further covered by a thick, fibrillated membrane — the factorial
membrane (fig. 131, Mt) — which is attached at one edge to the upper surface of the
limbus, falls over the crest, and rests on the rods of Corti and the hair-cells, thus
converting the spiral groove into a canal. It will be necessary to describe more
minutely these several parts of the organ of Corti.

Bods of Corti. — The inner and outer ] rods of Corti differ from one another in
shape, although agreeing, for the most part, as regards the details of their structure.

Fig. 137. A PAIR OF RODS OF CORTI, FROM THE

RABBIT'S COCHLEA, SIDE VIEW. (E.A.S.)
Highly magnified.

6 b, basilar membrane ; i.r, inner rod ; e.r,
outer rod. The nucleated protoplasmic masses
at the feet are also shown.

Each inner rod may be best compared in shape to a human ulna, the upper end of
the rod being pretty accurately represented by the upper extremity of that bone, the

Fig. 138.— TEASED PREPARATION SHOWING AN INNER AND AN OUTER ROD IN CONNECTION WITH THREE

HAIR-CELLS, AND PART OF THE LAMINA RETICULARIS (FROM THE GUINEA-PIG). (E.A.S.) Very

highly magnified.

i.r, inner rod ; e.r, outer rod ; hv A2f 7<3, hair-cells of first, second, and third rows respectively.
They appear, especially the second and third, narrow in the middle, the thin edge of the riband-shaped
cell being here seen, but below have become accidentally twisted so that the flattened side is brought
into view. A nucleus is visible in h}, but none is seen in hz, A3, probably owing to its being contained
in the part of the cell the edge of which is turned towards the observer. The lower ends of all three
have become broken in the preparation of the specimen ; s, one of the succeeding epithelial cells
(cell of Hensen) ; c, cuticular thread attached to lamina reticularis, belonging to a cell of Deiters \
p, phalangeal process of outer rod ; jp2, jp3, phalanges of lamina reticularis seen in section.

shape of the olecranon and coronoid processes, as well as the concave articular surface
between, being readily recognisable. The upper end of each of the outer rods, on the

ORGAN OF CORTI. 121

other hand, somewhat resembles the outline of a swan's head ; the rounded part,
which represents the back of the head, fitting into the concave surface on the head
of the corresponding inner rod or rods, while the part which represents the bill
projects outwards and is connected with the reticular lamina, aiding to form the
first series of rings for the transmission of the auditory hairlets. Both inner and
outer rods are more slender about the middle of their length and expand again
below, so as to rest upon the basilar membrane by a somewhat widened foot. They
are distinctly striated throughout their length (fig. 138).

In the head of the outer rod is an oval part free from fibres, and staining with
carmine more deeply than the remainder of the rod (pseudo-nucleus). A similar,
but smaller clear body, staining deeply with carmine, is seen in the head of the inner
rod, and the substance of the rod in its neighbourhood has a somewhat granular
appearance (fig. 1 38).

The inner rods are more numerous than the outer ; l they are also more closely
set and touch one another along their whole length, whereas the outer rods are only
in contact laterally by their heads ; finally the outer rods are in all parts longer
than the inner, and in the upper turns of the cochlea considerably so.

How the two sets of rods are jointed together is not very clear. It is certain that
the individual rods have little, if any, independent movement ; they are securely
fixed below to the basilar membrane, and the heads of adjacent rods are in close
contact.

Basilar cells. — In connection with both inner and outer rods, there is seen a
protoplasmic cell occupying the angle which the rod makes with the plane of the
basilar membrane (figs. 136, 137). Sometimes these cells extend along the membrane
until they come into contact, and they may, especially in young subjects, be seen to
rise up and partly envelope each rod. They are usually regarded as the cells by
and from which the rods have been formed.

Hair-cells and cells of Deiters. — The inner hair-cells, some 3,500 in number
in all, are closely applied against two or three of the corresponding rods, the cells
being considerably larger in diameter than the rods. Seen from above they are
oval and marked by a curved line, which is the line along which the hairlets are
attached (fig. 140, i.h.) They are very like somewhat short, columnar epithelium-
cells, and are prolonged below into a process (which may be branched) by which
they are connected with the upper surface of the spiral lamina. Beneath them, and
extending also under the gradually decreasing columnar epithelium of the spiral
groove, is a layer of protoplasmic cells with large round nuclei, amongst which fine
nerve-fibres appear to run in a spiral direction. Around the top of each inner hair-
cell is a sort of ring of cuticular substance, which is connected with slight projections
on the flattened heads of the inner rods, and perhaps represents the reticular lamina
in this place.

The outer hair-cells are peculiar in shape. They are cylindrical at the upper
end, where they fit into the rings of the reticular lamina and bear the hairlets, but
lower down they are flattened from within out, so that, in profile, they look narrow,
but broader when seen on the flat (fig. 138). These cells end below with a rounded
extremity (fig. 136), extending about as far as to the narrowing part of Deiters' cells.
The hairlets, as with the inner cells, are about 20 in number on each cell, and spring
also from a curved line on the upper surface of the cell. Beneath the hair-cells and
resting by a broad base upon the basilar membrane, certain other cells are found
which are known as the cells of Deiters (fig. 136). These, which are of a cylindrico-

1 According to Retzius there are altogether in the human cochlea about 5,600 of the inner rods
and nearly 4,000 of the outer ones.

122 THE EAR.

conical shape, rest by their bases upon the basilar membrane, and each one encloses
in its substance a cuticular filament which is fixed below to that membrane. This
filament is prolonged above in the tapering apex of the cell, between the hair-cells
and in close contact with one of them, and is attached above to, or rather expands
to form, one of the so-called phalanges of the reticular lamina : it is known as the
phalangeal process of Deiters' cell. This cuticular filament may probably be regarded
as the equivalent of the rod of Corti, the cell of Deiters to which it belongs being
looked upon as representing the protoplasmic cell which lies at the foot of each rod
of Corti, and in the young subject encloses the rod.

Hensen has described a clear oval capsule with a spiral fibre wound around it, occupying
the part of the hair-cell next to the free extremity.

Fig. 139. — FOUR CELLS OF DEITERS, FROM THE RABBIT. (Modified
from Gr. Retzius.) Highly magnified.

The phalangeal processes are shown, each expanding to form a
phalanx of the reticular lamina. The varicose lines are spirally
running nerve-fibrils.

In most animals there are three series of outer hair-
cells, but in man there are four series except in the
lowermost turn (fig. 136, ?i) and even five and six in the
upper turns of the cochlea (Pritchard) ; but where they
are more numerous they tend to be somewhat irregularly
placed and intermittent. There are about 12,000 outer
hair-cells and 20 hairlets to each cell in the human
cochlea (Retzius). The columnar cells outside the hair-
cells are much elongated and obliquely disposed, but

become gradually shorter and more vertical as they pass into the simple cubical

epithelium on the outer part of the basilar membrane.

Spaces filled with endolymph are seen both in the inner and outer hair- cell region and
communicate between the rods of Corti with the tunnel-space. The largest of these secondary
spaces lies between the outer rods and the first row of outer hair-cells (Nuel). (See fig. 136.)

The cells which immediately succeed the hair-cells form in some animals a distinct
swelling or arch outside the hair-cell region, from which and from the basilar membrane they
may be separated by a considerable space occupied by endolymph. In the guinea-pig they
contain a considerable number of fat globules in the upper turns of the cochlea. They are
sometimes known as the (i cells of Hensen," whilst those which follow them and rest on the
lateral half of the basilar membrane have been termed " cells of Claudius/'

Lamina reticularis (figs. 132, 140). — The net-like membrane which overlies
the outer hair-cell region of the organ of Corti is composed of at least two rows of
elongated fiddle-shaped structures termed " phalanges " which are united to one
another and to the phalangeal processes of the outer rods in such a manner as to
leave between them oblong apertures through which the free ends of the hair-cells
with their semicircular rows of auditory hairs project. The phalanges, although
they seem like rings, are in reality thin plates with thickened margins, and are to
all appearance of a cuticular nature : the most external row of phalanges is in con-
tinuity with a cuticular tissue which lies between the external epithelium cells.
Attached to the phalanges below are the phalangeal processes of the cells of Deiters
(fig. 139). The lamina varies in extent with the number of rows of hair-cells.
Where there are four or more of these, a corresponding increase in the number of
rows of cells of Deiters and of phalanges is observed. The phalanges serve to
isolate the hair-bearing ends of the auditory cells.

ORGAN OF CORTT.

123

The tectorial membrane is the last special structure which remains to be
described in connection with the organ of Corti. It arises, as before stated, on
the limbus, not far from the line of origin of Reissner's membrane (fig. 131).
It overlies the projecting teeth at the edge of the limbus, and also the epithelium
between them : all this part of the membrane is thin and delicate, imperceptibly

//.

Fig. 140. — VIEW OF A SMALL PART OF THE ORGAN

OF CORTI OF THE HUMAN COCHLEA FROM ABOVE,
SHOWING THE LAMINA RETICULARIS. Much

magnified. (Gf. Retzius. )

i.h, inner hair-cells, the hairlets being seen in
section ; i.r.h, heads of inner rods ; o.r.h, heads
of outer rods ; i.r.p, " olecranon " processes of inner
rods ; pk.pr, phalangeal processes of outer rods ;
phl, pk2, phz, first, second, and third series of
phalanges ; A1, A*, h3, A4, first, second, third, and
fourth series of outer hair-cells : //, cells of Hensen.

Fig. 141. — SURFACE VIEW OF A SMALL PIECE OF

THE MEMBRANA TECTORIA OF THE HUMAN

COCHLEA. (Gr. Retzius. )

7.~., limbus-zone of the membrane, showing
markings caused by the cells covering the limbus ;
0.2., 0.2., outer zone, showing a well-marked fibrous
structure ; II., stria described by Hensen in the
middle of the outer zone ; /. , reticular free border.

shading off towards the inner edge of attachment. As the membrane projects over
the crest of the limbus, it swells out below into a pad-like projection (fig. 136)
which covers in and partly fills up the spiral groove, and rests below upon the rods
of Corti and contiguous structures. Towards its external edge the membrane again
thins out, and overlies the outer hair-cell region as a delicate film presenting a
somewhat reticular appearance, as if impressed by or moulded on the subjacent
structures. The thickened part of the membrane is distinctly fibrous in appearance
(the fibrillation extending obliquely from within out) (fig. 141), and after immersion
in weak solutions of omic acid, chromic acid, or bichromate of potash, it appears to
possess considerable toughness and elasticity. From its position the hairlets borne
by the hair-cells must necessarily be in contact with the under surface of this

124

THE EAR.

membrane. In its situation relative to the auditory epithelium it corresponds to
the otolithic accumulations of the maculae.

Nerves of the cochlea. — The branch of the auditory nerve which goes to the
cochlea is given off in common with those to the saccule and the posterior ampulla,

Fig. 142. — GENERAL VIEW OF THE MODE OF DIS-
TRIBUTION OF THE COCHLEAR NERVE, ALL THE
OTHER PARTS HAVING BEEN REMOVED. (Arnold.)

It is shorter, flatter, and broader than any
of the other branches. It perforates the
bone by groups of minute foramina at the
bottom of the internal meatus, below the
opening of the Fallopian aqueduct. These
groups are arranged in a shallow spiral
furrow (tractus spiralis foraminulentus) in
the centre of the base of the cochlea ; and
they lead into small bony canals, which
first follow the direction of the axis of the

cochlea, through the modiolus, and then radiate outwards, between the plates of the
the bony spiral lamina (fig. 129). In the centre of the spiral tract is a larger foramen
which leads to the central canal of the modiolus. Through this foramen and canal the

Fig. 143. — DISTRIBUTION OF THE COCH

LEAR NERVES IN THE SPIRAL LAMINA.

(After Henle.)

This figure shows part of the modiolus
and spiral lamina, viewed from the base,
showing the plexiform arrangement of the
cochlear nerves ; 1, filaments of the nerve
issuing from the tractus spiralis foraminu-
leiitus ; 2, branches of the nerve entering
the central canal of the modiolus ; 3, wide
plexus in the bony lamina spiralis j 4,
close plexus at its border.

Fig. 144. — PART OF THE NERVES EX-
TRACTED AND MORK HIGHLY MAGNI-
FIED.

2, twigs of the nerve from the
modiolus close to the lamina spiralis
ossea ; ys, spiral ganglion ; /•?, nerve-
fibres running spirally along the outer
part of the ganglionic swelling 3, wide
plexus ; 4, close plexus of nerve-fibres as
in fig. 143.

filaments for the last half- turn of
the spiral lamina are conducted ;
whilst the first two turns are
supplied by the filaments which

occupy the smaller foramina and bent canals. 3Tear the root of the spiral lamina
the nerve-fibres pass outwards through a spirally wound ganglionic cord (ganglion
spirals), situated in the special bony canal (spiral canal of the modiolus) already
mentioned. The cells of this ganglion are bipolar and each nerve-fibre appears
to have one of the cells interpolated in its course. From the outer side of the
ganglion, the fibres, having resumed their medullary sheath, pass onwards with a
plexiform arrangement, at first in distinct but anastomosing cords (fig. 144, 3),

NERVES OF COCHLEA.

125

contained in separate canals in the bony lamina, but afterwards spreading out
into a stratum of intermingling fibres, to be again gathered up, near the edge

limbvs

membrana tectoria

outer hair- cells
I

nerve fibres

inner rod t'as basilar outer cells of Deiters
spirale membrane rod

Fig. 145.— SECTION THROUGH THE ORGAN OF CORTI OP THE MIDDLE TURN OP THE HUMAN COCHLEA.

(GK Retzius.) Highly magnified.

of the osseous lamina, into conical bundles which turn abruptly upwards, and
passing through the elongated apertures previously described (p. 112 and fig. 132,

Fig. 146. — ENDING OP NERVE-FIBRES IN THE

COCHLEA, SHOWN BY Q-OLGl's METHOD. (Gr.

Retzius. ) Much magnified.

g, a cell of the spiral ganglion ; i. h., inner
hair-cells ; o.A., outer hair-cells, \vith the
nerve-fibres running spirally between the cells.

lose their medullary sheath, and enter
the epithelium in the region of the
inner hair-cells (fig. 145). Some of
the nerve-fibres appear to end here by
ramifying with a spiral course amongst
the bases of the inner hair-cells, but
others are continued as fine threads
between the inner rods, and form a
second spiral band close to the outer
side of these and in contact with the
protoplasmic cell which ensheaths them.
Other fibres may be seen in sections to
pass across the tunnel of Corti between
the rods and to enter the region of the
outer hair-cells. Here the fibres, which
now again branch and alter their direc-
tion, run spirally parallel with the
successive series of hair-cells. They
rest against the corresponding cells of
Deiters, and in man form a bunch
of spirally-running fibres immediately
below the expanded part of each hair-cell (fig. 145). They form, therefore, altogether
five or six spiral strands of fibrils, which lie between the epithelium-cells of the organ

126

THE EAR.

of Corfci. In most animals they are less grouped together and more distributed
along the length of each cell of Deiters (fig. 139), but with the same spiral arrange-
ment and in the same relative position.

Vessels of the cochlea. — The branches of the internal auditory artery to the
cochlea, twelve or fourteen in number, arising at the bottom of the internal auditory
meatus, traverse small canals in the modiolus and bony lamina spiralis, and also pass
to the outer wall of the cochlea, forming at the root of the septum, between the
turns of the cochlear tube a spirally-arranged glomerulus-like arterial plexus,
which sends vessels to the subjacent stria vascularis and to the periosteum lining
the adjacent scalse (Schwalbe). From this plexus offsets are distributed in the
form of a fine network on the periosteum, but the vessels do not anastomose across
the membrana basilaris. The bony cochlea also receives through the fenestra rotunda
a twig from the stylomastoid branch of the occipital artery.

The veins of the cochlea issue from the grooves of the cochlear axis, and join the
veins of the vestibule and semicircular canals at the base of the modiolus. A small
sinus-like vein passes through the aqueductus cochleae, from the lowermost turn of
the cochlear tube, and joins the commencement of the internal jugular vein.

Development of the organ of Corti. — The organ of Corti is at first com-
posed of columnar epithelium-cells forming part of the layer of epithelium which

membrana, inner

tectoria hair-cell outer hair-cells

duct of cochlea
inner hair-cell outer hair-cells

inner rod vas spirale outer rod

Figs. 147 and 148. — Two STAGES IN THE DEVELOPMENT OF THE ORGAN OP CORTI OF THE CAT.

(GL Retains.)

In the preparation represented in fig. 147 the hair-cells are differentiated ; in that shown in fig. 148
the rods of Corti are also beginning to be formed, and the nerve-fibres have reached the organ of Corti,
and are already running spirally below the hair-cells.

lines the whole of the membranous labyrinth. After a time certain of these cells
begin to be differentiated and become distinguishable from the rest as the inner and

DEVELOPMENT OF THE ORGAN OF CORTI.

outer hair-cells. Subsequently the rods of Corti become formed by a transformation
of the protoplasm of other of these columnar cells, and the cells of Deiters also
begin to appear. In the meantime the epithelium of the vascular stria which was
at first similar to that of the rest of the canal becomes pigmented and vascularized,
and the remaining epithelium of the cochlear canal is also gradually acquiring the
form and character by which its various parts are distinguished.

The membrana tectoria appears to be formed as a cuticular deposit or secretion
from the epithelial cells of the limbus, upon which, even at a comparatively early
stage of development, it may be seen to lie.

Measurements of some of the parts of the cochlea. — The following
numbers (from Eetzius) show the average dimensions of various parts of the
human cochlea, and represent the size in micromillimeters.

Cochlear canal, breadth, basal turn 0'45

„ „ „ middle „ ... 0*77

apical „ . . . . 0-80

„ extreme length 35-00

Reissner's membrane, breadth, basal turn . . . . 0*81

„ middle „ 0'88

„ „ „ apical „ . . 0-85

Limbus laminse spiralis, breadth, basal turn .... 0*24

„ • „ „ „ middle „ . . 0'23

„ „ » „ apical „ . 0-22

Rods of Corti, space between attachment of feet, basal turn . 0*048

„ middle „ . 0-081
» apical „ . 0-09

„ „ height of arch, basal turn . . ... 0*028

„ „ „ middle „ .... 0-045

„ „ „ apical „ . . . . 0-049

„ length of inner rods . . .0-048—0'07

„ „ length of outer rods . . . . 0*06 — 0*1

Hair-cells, length of inner 0*018—0-024

„ „ length of outer 0*03—0-04

„ ,, length of hairlets .... . 0-005

Membrana tectoria, breadth ... . 0'28 — 0'34

„ „ extreme thickness . . 0'025

Basilar membrane, breadth from habenula perforata to lig.

spirale, basal turn 0'21
» middle „ 0-34
,. apical ,, 0-36
breadth from habenula perforata to feet

of outer rods, basal turn 0*075
„ -. middle,, 0-12
„ „ apical „ 0-126

RECENT LITERATURE OP THE EAR.

Altzheimer, A., Ueber die Okrenschmakdrusen, WUrzburg, 1888,

Ayers Howard, Die Membrana tectoria— ioas sie ist, und die Membrana basilans—was sic
verrichtet, Anatomischer Anzeiger, vi. 1891 ; Ueber das peripherische, Verhalten dcr Miornerven,
Anat. Anz., 1893. ... .

Bag-insky, G-., Zur EntwicU. der Gehorsehuecke, Arch. f. mikr. Anat., xxvin. 11

Barth, A., Beitraffe zur Anatomic des Ohres, Zeitschrift fur Ohrenheilkunde Band xvn. ; Ueber
die Darstdlung des h&utvjen Labyrinthes, Archiv fur Anatomie und Physiologie, Physiol. Abt., Jahrg.
1889 ; Beitrag zur Anatomie der Schnecke, Anatomischer Anzeiger, iv. 1889.

1£8 RECENT LITERATURE OF THE EAR.

Beauregard, H., Rccherclies sur Vappareil auditif chez les mammiferes, Journal de 1'anat., 1893.

Bertelli, D., Contribution d la structure de la couche moyenne de la membrane tympanique chez
le cobaye, Archives italiennes cle biologie, xvi. 1891.

Binder, Das Morelsche Ohr, Eine psijchiatrisch-anthropologische Studie, Archiv fur Psychiatric,
Band xx.

Bistrzycki, A., und von Kostanecki, K., Das Gewicht menschlicher Gchorknochelchen,
Monatsschrift fiir Ohrenheilkunde, xxv. 1891.

Boettcher, Riickblicke auf die neueren Untersuchungen il. d. Bail der Schnecke, im Anschluss an
eigene Beobachtungen, Arch. f. Ohrenheilkunde, xxiv. 1886.

Bryant, ~W. S., Observations on the topography of the normal human tympanum, Arch. Otol.,
New York, 1 890.

Bulle, Hermann, Beitrdye zur Anatomic des Ohres, Archiv fiir mikroskop. Anatomic, Band xxix.

Biirkner, Kurd, Atlas von Beleuchtungsbildern des Trommels fells, 1890.

CMarugi, GK, II tubercolo di Darwin e la dirczione del peli nel padiylione delV orecchio umano,
Bollett. d. r. ace. d. fisiocrit. di Siena, anno vi. 1888.

Cog-gi, Alexander, Ueber die soy. Kalksdckchen an den Spinalganglien des Frosches und ihre
Beziehungen zum Ductus endoli/mphaticus, Anatomischer Anzeiger, v. 1890.

Draispul, Zur Entwickelungsgeschichte des Hammer- Ambos- G 'elenkcs ; Ueber die Membrana
propria des Trommelfelles, Verhandlungen des x. internationalen meclicinischen Kongresses zu Berlin,
1890.

Dreyfuss, Beitr. z. Entwicklungsgesch, des Mittelohrcs u. des Trommelfelles, Morph. Arbeiten,
Bd. ii., 1893.

Eichler, Oswald, Anatomische Untersuchungen ubcr die Wege des Blutstromes im menschlichen
Ohrlabyrinth, Abhandl. d. math.-phys. Kl. d. kgl. Sachs. Ges. d. Wiss., No. v. 1892.

Ellis, H. H., The ear in criminals, The Lancet, 1890.

Eng-elmann, Th. W., Ueber die Function der Otolithen, Zoolog. Anzeiger, Jahrg. x., Nr. 258.

Fick, A., Betrachtungen ilber den Mechanismus des Paukenfells, Archiv fiir Ohrenheilkunde,
Band xxiv. ; and Wurzb. Verhandl. xx. 1886.

Fischer, Ferdinand, Ueber das Epithel und die Driisen der Ohrtrompcte und Paukenhohle,
Inaug. -Dissert., Rostock, 1889.

Gradenig-o, Die Entwickelung der Ohrmuschel beim Memchen und bei den Sduyethieren, Zeit-
sehrift fiir Ohrenheilkunde, Band xix. ; Die Formentwickelung der Ohrmuschel mit Rucksicht auf die
Morphologic und Teratologie derselben, Centralblatt fiir die medicin. Wissenschaften, 1888 ; Beitrag
zur Morphologic des Anthelix der menschlichen Ohrmuschel, Zeitschrif t f iir Ohrenheilkunde, Band xxi.,
1891 ; A contribution to the morphology of the human auricle, New York, 1891 ; Missbildungen der
Ohrmuschel, Arch. f. Ohrenheilkunde, Bd. xxxiv., 1893.

Hasse, C., Ue. d. Gefdsse in d. lamina spiral-is membranacea des Gehororgancs, Anat. Anzeiger, i.
1886.

His, Wilhelm, Zur Anatomic des Ohrlappchens, Archiv f. Anat. u. Physiol., Anat. Ahtlg.,
1889.

Kaiser, Otto, Das Epithel der Cristae und Maculae acusticae, Archiv fiir Ohrenheilkunde, xxii.,
1891.

Katz, Ii., Beitrag zur Frage iiber die Verbindung der Corti'schen und Deiterschen Zcllen des
Corli'schen Organcs und dcren Gestalt, Monatsschrift fiir Ohrenheilkunde, Jahrg. 1888 ; Ueber die
Epithelgebilde des Corti'schen Organes, Archiv fiir Ohrenheilkunde, Band xxvii. ; Ueber die Endigung
des Ncrvus Cochleae im Corti'schen Organ, Zeitschrift fiir Ohrenheilkunde, Band xxix, 1889-90 ;
Histologisches ueber den SchncckenTcanal, speziell die Stria vascular is, mit Demonstration mikro-
skopische Prdparate, Verhandlungen des x. internationalen medicinischeii Kongresses zu Berlin,
1890 ; and Archiv fiir Ohrenheilkunde, Band xxxi., 1890 ; Ueber einige Streitpunkte in der Histologie
des Gehorganges, Verhandlungen des x. internat. medic. Kongresses, Berlin, 1890 ; Mikrophoto-
graphischcr Atlas der normalen und pathologischen Anatomic des Ohrcs, Berlin, 1891, 1892.

Kirchner, W., Ueber Divertikelbildung in der Tuba Eustachii des Menschen, Festschrift zu von
Kolliker's 70. Greburtstage.

Kostanecki, C., Die pharyngeale Tubenmiindung und ihr Verhdltniss zum Nasenrachenraum,
Archiv fiir mikroskopische Anatomic, Band xxix.

Larson, P. C., Ein anatomisch-physiologisclier Beitrag zur Lehre von den Ossicula auditus,
Anatomischer Anzeiger, v. 1890.

Lenhossek, M., Die Nervenendigungen im Gehororgans, Verhandl. d. anat. Gesellschaft, Anat.
Anz., viii., 1893 ; Die Nervenendigunyen in den Maculce u. Cristce acusticce, Anat. Hefte. ix., 1893.

Linsmayer, L., Ein Fall von Verknocherung der Ohrmuscheln, Wiener klinische Wochenschrift,
1889.

Niemack, J., Maculce u. Cristce acusticae mit Ehrlich^s Methylcnblaumethodey Anatom. Hefte,
1892.

Prenant, A., Recherches sur la paroi externc du limacon des mammiferes et specialement sur la
strie vasculaire, Internationale Monatsschrift fiir Anatomie und Physiologie, ix. 1892.

Randall, B. A., and Morse, H. L., Photographic illustrations of the anatomy of the human
ear, together with pathological conditions of the drum membrane and descriptive text, Philadelphia,
1887.

Rauber, Ueber d. Bau des Gehorlabyrinthes, Sitzungsb. d. natiirf. Gesellsch. z. Leipzig, xii.
1886.

Retzius, G., Das Gehororgan der Wirbelthierc, Stockholm, 1884 ; and in Biolog. Unters., vols.
iii. & v., 1892 & 1893.

RECENT LITERATURE OF THE EAR. 129

Riiding-er, N., Ueber die Abflusskandle der Endolymphe dcs inneren Ohres, Sitzungsber. d. k.
bayer. Akacl., 1887 ; Zur Anatomic und Entwickd/uny dcs inneren Ohres, Monatsschrift fiir
Ohrenbeilkunde, xxii. 1888 ; Ueber die Beziehuny der Ncuroepithclstellen der beiden Sdckchen zu
den Schall-leitunyswegcn im Labyrinth, Miinchener metlizin. Wochenschrift, xxxv. 1888 ; Zur
Entwickeluny der hdutiycn Bogengdnge dcs inneren Ohres, Sitzungsbericbte der matbem.-physikal.
Klasse der k. b. Akademie der Wissensch. zu Miinchen, 1888 ; Ueber die Deckmembran der Maculae
acusticae der Sackchcn dcs hautiycn Labyrinths, Sitzungsberichte der Gesellschaft fiir Morphologie u.
Physiologie in Miinchen, v. 1889.

Schaeffer, O., Ueb. d. foe talc Ohrcntwickeluny, &c., Arch. f. Anthrop., xxi., 1892.

Schwalbe, G., E'uiBeitragzur Kenntnissd. Circulationsverhdltnisse in der Gehorschnecke, Lud wig-
Festschrift, 1886 ; Lehrbuch der Anatomic der Sinnesoryane, Erlangen, 1887 ; Ueber die vergleichende
Anatomic u. Entwickclunysycschichte dcs Ohrknorpels, Deutsche medicinische Wochenschrift, Jahrg. xv.
1889 ; Inu-icfcrn 1st die menschlichc Ohrmuschcl ein rudimcntares Organ 1 Archiv f. Anatomic u.
Physiol., Anatom. Abt., 1889 ; Das Darwin'sche Spitzohr, &c., Anat. Anzeiger, iv., 1889 ; and Arch,
f. Psychiatric, xxi., 1889 ; Ueber Auricularhocker bei Reptilien, ein Beitrag zur Phylogenie des
dussercn Ohres, Anatomischer Anzeiger, vi. 1891 ; Beitrdge zur Anthropologie des Ohres, Festschrift f.
Virchow, I>d. i.

Schroeder, J. K., Untcrs. u. d. Blutyefass-system des dusseren Ohres, Jena, 1893.

Siebenmann, Friedrich, Die Korrosions- Anatomic des knochernen Labyrinthes des menschlichen
Ohrcs, Wiesbaden.

Steinbriig-g-e, H., On the Cupula -formations in the human labyrinth, Arch, of Otology, New
York, xvi. 1887 ; Ueber d. Verhaltcn d. menschl. Ductus cochlcaris im Verhofblindsack, Anat. Hefte,
1893.

Syming-ton, J., The external auditory meatus in the child, Journal of Anatomy, xix., 1885 ;
Demonstration of auditory air-passages, Journal of Anatomy, vol. xxiii. 1888.

Tartaroff, Dimitry, Ueber die Muskeln der Ohrmuschel und einige Besonderheiten des Ohr-
knvrpcls, Archiv fiir Anatomic u. Physiologic, Anatom. Abt., 1887.

Voltolini, Uc. d. 'ichdrzahne der Schnecke dcs Menschen u. der Sduyethicrc u. deren Gefassc,
Arch. f. path. Anat., Bd. civ., 1886.

Zuckerkandl, E., Beitr. zur veryl. Anatomie d. Ohrtrompete, Arch. f. Ohrenheilkunde, xxiii.
1886.

VOL. in., PT. 3.

THE NOSE.

THE nose is the special organ of the sense of smell. It has also other functions
to fulfil : — for, communicating freely with the cavities of the mouth and lungs, it is
concerned in respiration, voice, and taste ; and by means of its muscles it assists in
expression.

The nose forms a prominence composed of bone and hyaline cartilage with
certain muscles, and a general covering of integument. At its lower extremity or
base the nostrils (anterior nares) open downwards. Its upper end is the root, the
rounded or flattened ridge along its middle is termed the dorsum, and this ends
below in the point of the nose. The upper or bony part of the dorsum is often
spoken of as the bridge; it frequently forms an angle with the cartilaginous part
(aquiline type). The root springs from below the glabella of the frontal bone,
with which it usually forms a more or less marked angle, so that the nose appears
to spring from a well-marked groove : if this groove is absent, and the line of the
dorsum is continuous with the plane of the forehead, the Grecian type of nose is
produced. The sides of the nose, which form an open angle (naso-facial angle]
with the general anterior surface of the face, diverge from the dorsum at an
increasing angle as we trace them down from the root ; the nose is therefore
broadest below at the nostrils. This lowest part of the lateral wall is slightly bulged
outwards, and is separated from the rest by a slight groove ; it is known as the ala
of the nose, and is mobile, its form being capable of alteration by the action of
certain muscles, which thereby dilate or contract the nostrils. A median parti-
tion (septum nasi) divides the interior of the nose into two approximately equal
parts, the right and left nasal fossw. These open above and behind into the
pharynx by the posterior nares (choanse), and below on to the exterior by the
anterior nares. The septum is composed of bone and cartilage in the greater part
of its extent, but at its lower end it is formed only of integument and connective
tissue (septum mobile, or columna nasi). This part of the septum forms the mesial
boundary or sej a ration between the anterior nares ; in the rest of their extent they
are bounded by the curved free margin of the alge.

From the development and complexity of the nasal fossae and olfactory lobes of the
cerebrum mammals are divided by Turner into the three subdivisions of macroxmatics.
including1 rodents, carnivora, marsupials, and most mammals ; microfmatics, including man
and most primates, monotremes, and some cetacea ; and anosmatics, including certain cetacea
(e.g., porpoise).

The nasal fossse communicate with hollows in the neighbouring bones (ethmoid,
sphenoid, frontal, and superior maxillary). The skin of the nose is studded,
particularly in the grooves of the alse or outer walls of the nostrils, with numerous
small openings, which lead to sebaceous follicles. Within the margin of the nostrils
are a number of short, stiff, and slightly curved hairs — vibrissce — which grow from
the inner surface of the alee and septum nasi.

As is well known the nose presents great variety in size and shape in different
individuals. Into most of these it is unnecessary here to enter, but there is
one kind of variation which is of considerable anthropological importance, viz.,
the extent of lateral expansion of the anterior nares as compared with the

CARTILAGES OF THE NOSE. 131

total length of the organ. This relationship is expressed by the cephalometric nasal

• i / greatest breadth x 100 \ , . /. -, ,, . . ,, , ..
index ( . It is found that m the white races of man-

Men gth measured vertically/

kind the nasal index is below 70 ; in the black races (African, Australasian) it is
85 and upwards : in the yellow races (Asiatic, American-Indians, Eskimo) from 70
to 85 (Topinard).

The blood-vessels of the outer nose are branches of the ophthalmic and facial.
The lymphatics pass to the submaxillary lymphatic glands. The sensory nerves
are branches of the first and second divisions of the fifth, and the motor nerves are
derived from the facial. All of these have been already noticed in previous parts of
this work.

CARTILAGES OF THE NOSE.

These are the chief support of the outer part of the organ. They occupy the
triangular interval seen in front of the nasal cavity in the dried skull (anterior

nasal bone

cartilage of aperture,
lateral crus

cartilage of aperture,
mesial crus

upper lateral cartilage

-i minor cartilages

\
\- — subcutaneous tissue of ala

Fig. 149. — LATERAL VIEW OF THE CARTILAGES OF THE NOSE. (Modified from Arnold.)

nasal aperture), and assist in forming the septum between the nasal fossae. There
are two large cartilages, one on each side, partly enclosing the aperture of the
anterior nares, and known as the cartilages of the aperture or loicer lateral cartilages,
and one winged median cartilage which forms part of the septum nasi, and spreads
externally and superiorly into two large flattened expansions which are commonly
known as the upper lateral cartilages, and may conveniently be described separately,
although part of the cartilage of the septum.

The upper lateral cartilages (figs. 149 and 150) are situated in the middle part
of the projecting portion of the ncse, immediately below the. free margin of the
nasal bones. Each is flattened and triangular in shape, with one surface looking
outwards, and the other inwards towards the nasal cavity. The anterior margin,

K 2

132

THE NOSE.

thicker than the posterior, is united with the edge of the cartilage of the septum
above, but is separated therefrom by a small fissure below. The posterior edge is
closely attached to the free margins of the upper maxilla and of the nasal bone,
and the inferior margin is connected by fibrous membrane with the lower lateral

Fig. 150. — FRONT VIEW OF THE

CARTILAGES OF THE NOSE. (Modified

from Arnold.)

cartilage ; and there are often
small portions of cartilage
(cartilagines epactiles] lying in
the fibrous tissue in this situa-
tion.

The lower lateral cartilages
or cartilages of the aperture
(figs. 141), 150, 151) are
thinner than the preceding,
below which they are placed,
and are characterised by their
peculiar curved form. Each
consists of an elongated plate,
so bent upon itself as to pass
in front and on each side of
the nostril to which it belongs,
and by this arrangement serve
to keep it open. The outer
portion is somewhat oval and
flattened, or irregularly con-
vex externally. Behind, it is
attached to the margin of the upper maxilla by tough fibrous membrane, enclosed
in which there is usually to be met with either a prolongation backwards of the
posterior angle of the cartilage, or two or three separate cartilaginous nodules
(cartilag. minores vel quadrate) (figs. 149, 150) ; above, it is fixed, also by fibrous
membrane, to the upper lateral cartilage, and to the lower and fore part of the

nasal bone

cartilage of sept inn

upper lateral cartilages

-f-. .. minor cartilages
•&$--- — cartilaae of aner,

cartilage of aperture
— - subcutaneous tissue of ala

cartilage of aperture

minor cartilage

cartilage of septum

minor cartilage

cartilage of Jacobson

subcutaneous tissue

Fig. 151. — VlEW OF THE CARTILAGES OF THE

NOSE FROM BELOW. (Modified from
Arnold. )

cartilage of the septum. Towards
the middle line it is curved back-
wards (fig. 151), bounding a deep
median groove, at the bottom of
which it meets with its fellow of
the opposite side, and continues to
pass backwards, lying in the upper
part of the columna nasi, below the
level of the cartilage of the septum. This inner part of the cartilage of the aperture
is thick and narrow, curls outwards, and ends in a free rounded margin which
projects outwards. The ala of the nose, like the lobule of the ear, is formed of
thickened skin with subjacent tissue, and is unsupported by cartilage.

The cartilage of. the septum (fig. 152) is quadrilateral in form, and is thicker
at the edges than near the centre. It is placed nearly vertically in the median plane
of the nose, but often with an inclination to one or other side, and completes, at the

CARTILAGES OF THE NOSE.

133

fore part, the separation between the nasal fossae. The anterior margin of the
cartilage, thickest above, is firmly attached to the back of the nasal bones near
their line of junction ; and below this it lies successively between the upper and t In-
lower lateral cartilages, united with the former, which constitute its alae, and
connected loosely by fibrous tissue with the latter. The posterior margin is fixed
to the lower and fore part of the central plate of the ethmoid bone (e) ; and the
lower margin is received into the groove of the vomer (v), and rests anteriorly on the
incisor crest of the superior maxillae.

This cartilage is the persistent anterior extremity of the primordial cartilaginous

sinus of
sphenoid ;'

»'»,•
proc. post, \<

cart, septi '1C

cthmovomerine suture pendicularlt

vomer
2ialate-bone

cartlhtffc of
septum

cartilage of

aperture
cartilage of
Jacobson

Fig. 152. — OSSEOUS AND CARTILAGINOUS SEPTUM OF THE NOSE, SEEN FROM THE SIDE. (Arnold.)

cranium. In young subjects it is prolonged back to the body of the pre-sphenoid
bone ; and in many adults an irregular thin band remains between the vomer and
the central plate of the ethmoid (processus posterior s. sphenoidalis, fig. 152). The
vomerine cartilages (Huschke) or cartilages of Jacobson, are two small longitudinal
strips of cartilage which lie along the lower border of the cartilage of the septum,
attached to the vomer. They are not always distinct from the cartilage of the
septum and are relatively better developed in the embryo and in many of the lower
mammals conformably with the greater extent of development o£ the organ of
Jacobson (see p. 143), which, in some animals, they partly enclose.

NA8AL FOSSJE.

The nasal fossae are, as already stated, the cavities which occupy the interior of
the nose and effect a communication between the exterior and the pharynx. They
have been described in Vol. II. as they exist in the skeleton, but they are much
narrower in the living condition owing to the thickness and vascularity of the
lining membrane, which also covers over many of the apertures seen in the macerated

134

THE NOSE.

bone. These differences are well exemplified by comparing fig. 153, which
represents the lateral wall of the left nasal fossa in the macerated condition with
fig. 154, which shows the right nasal fossa as it appears when still covered by
mucous membrane. In (coronal) section each nasal fossa is irregularly triangular
in shape, -the apex of the triangle being formed by the roof of the fossa, and the
base by the floor. Towards the apex the triangle is quite narrow, but about
halfway towards its base, i.e., immediately below the free edge of the middle
turbinal (see below), each fossa expands, so that this lower part is nearly quadri-
lateral in coronal section (fig. 156) ; this is the respiratory part : the upper narrow
part is the olfactory part of the fossa or olfactory cleft. The mesial wall and floor
of each fossa is smooth, but the lateral wall is complicated by a series of lamellar

os frontale

concha sup. ^£— ]

sin. sphenoid. -

setta turcica -

os valati

— sulcus sup.

— agger nasi

sulcus med.

concha inf.

— proc. pal.

foramen

incisivus

Fig. 153. — VIEW OF THE LATERAL WALL OF THE LEFT NASAL FOSSA AS IT APPEARS IN THE MACERATED

SKELETON. (Modified from Arnold.)

prominences running in a sagittal direction and projecting into the cavity ; these
prominences, which are formed by the turbinate processes of the ethmoid bone
and by the inferior turbinate bone covered by mucous membrane, may be termed
the turbinate fiodws, or simply turMnals (concha}.

The following are the average dimensions of the nasal fossaa (Thane) : —

Greatest vertical measurement (at fore part of cribriform plate) . . 44 mm.
Greatest sagittal measurement (along floor, from posterior margin of

hard palate to anterior extremity of roof) . . . . . . 73 mm.

Sagittal measurement of osseous part of floor 44 mm.

Least sagittal measurement (close below cribriform plate) . . . 35 mm.
Greatest coronal measurement (near floor) . . . . . .16 mm.

Least coronal measurement (near roof) . . . . . . . 2'5 mm.

THE NASAL FOSSAE. 135

The turbinals on the lateral wall of each fossa are .usually described as three in
number, viz., two on the lateral mass of the ethmoid, which are known as the
superior and middle turbinals (superior and inferior ethmoidal conchse), and one,
the inferior turbinal, on the superior maxillary bone (maxillary concha). Each
concha overhangs and partially separates from the general cavity of the fossa a
groove-like space, which is known as the corresponding meatus (superior, middle, or

9 ~

Fig. 154. — VIEW OF THE RIGHT NASAL FOSSA AS SEEN IN A SECTION THROUGH THE SKULL, TAKEN JUST

TO THE RIGHT OF THE SEPTUM. (E. A. S.)

1, incisor canal ; 2, bone of hard palate ; 8 and 4, parts of the mesial crus of the cartilage of the
aperture ; 5, anterior part of the same cartilage ; 6, cartilage of the septum ; 7, groove leading to
middle meatus ; 8, agger nasi ; 9, frontal sinus ; 10, inferior ethmoidal concha ; 11, superior ethmoidal
concha; 12, recess of upper meatus above superior concha; ]3, entrance to sphenoidal sinus; 14,
pituitary fossa ; 15, sphenoidal sinus ; 16, inferior turbinal (maxillary concha) ; 17, rod passed into
Eustachian tube ; 18, salpingo-pharyngeal fold : immediately behind this is the lateral recess of the
pharynx, not specially indicated in the drawing ; 19, soft palate ; 20, uvula ; 21, tongue.

inferior, as the case may be). The groove of the superior meatus between the
superior and middle conchse is also termed the ethmoidal fissure. This meatus is
relatively small, corresponding with the small size and extent of its overhanging
concha : into it the posterior ethmoidal cells open by one or two apertures (fig. 155).
The middle turbinal or concha is large, and overhangs a correspondingly large
middle meatus, which'can only be properly seen on cutting away the concha (fig. 155).
It is .then found that the meatus extends under the anterior part of the turbinal
into a gradually narrowing funnel-shaped diverticulum (wfundilulum) which leads

136

THE NOSE.

directly upwards into the frontal smiix, and that the lateral wall of this meatus is
farther marked by a deep curvilinear depression (hiatus semilunaris, Zuckerkandl),
extending from behind and below upwards and forwards towards the infundibulum.
Into the deepest part of this depression the anterior ethmoidal cells and the maxillary
antrubi open, often by a common orifice ; sometimes the antrum has a second orifice
rather lower down in the hiatus. Immediately above and behind the hiatus serni-

?ig. 155. — SKETCH SHOWING THE POSITION OP THE ORIFICES OF THE AIR-CELLS AND OF OTHKR

PASSAGES LEADING INTO THE NASAL FOSSJ5 (E. A. S. ).

The middle and inferior turbinals are cut away as much as is necessary to expose the orifices.

sph.ethm., probe passed from the spheno-ethmoidal recess into the sphenoidal sinus, sph.sln. ;
post.ethm., apertures of the posterior ethmoidal cells beneath the superior ethmoidal concha ; mid.ctkm.
apertures of the middle ethmoidal cells beneath the midddle (inferior ethmoidal) concha, and just above
the ethmoidal bulla, ethm.b. ; ant.cthm., aperture of the anterior ethmoidal cells in the hiatus serni-
lunaris, h.s., immediately below the ethmoidal bulla ; antr., aperture of the maxillary anti-urn also in
the hiatus, and close to those of the anterior ethmoidal cells but concealed by the uncinate process,
pr.nnc. ; antr.', an accessory orifice to the antrum, sometimes present in the lower part of the hiatus
semilunaris ; infund., infundibulum leading to the aperture of the frontal sinus, fr.sin. (through which
a probe is passed) ; n.d., orifice of nasal duct, beneath the inferior turbinal ; ay.n., agger nasi ; Eu.t.,
Eustachian tube ; f.R., lateral recess of pharynx (fossa of Rosenmiiller).

lunaris and below the attachment of the concha is an oval prominence of the lateral
wall which is often very strongly marked. This is the eihmoidal lulla of Zucker-
kandl, and above or upon it are the apertures of the middle ethmoidal cells (fig. 155).

The ethmoidal bulla has been held to be a rudiment of an additional ethmoidal concha
which is well developed in macrosmatic mammals ; but this opinion, although it seemed a
probable one, is not supported by the most recent researches.

Zuckerkandl has shown that there is frequently present, especially in the foetus and child,
a second ethmoidal fissure parallel to and above the principal fissure. This second fissure
separates off the lower part of the superior ethmoidal concha as a middle <>t1i»ioidal concha.

THE NASA.L

137

There may also be found a third parallel fissure above the second fissure, effecting a further
separation of the upper concha, so that in these cases there are four distinct conchae on the
ethmoid bone alone, viz., suprema, superior, media, and inferior (besides the lowermost or
maxillary concha). This condition represents one which is met with in macrosmatic mam-
mals in a much more developed form. The most common condition, however, in man,
according- to Zuckerkandl, is that with three ethmoidal conchaa, but the middle one, when
present, is frequently hidden beneath the superior concha, and thus often escapes observation.
Hence the usual description of the ethmoidal conchse as superior and inferior only, the
inferior being the one which is spoken of above as the middle turbinal.

Fig. 156. — CORONAL SECTION OP THE NASAL FOSS.E SEEN FROM BEHIND.

THROUGH THE LAST MOLAR TEETH. (Testut.)

THE SECTION PASSES

1, septum nasi ; 2, superior turbinal ; 3, middle turbinal ; 4, inferior turbinal ; 5, posterior
ethmoidal cells opening at 5' (on the right side) into the superior meatus ; 6, maxillary antrum,
opening at 6' into the middle meatus : the head of the arrow is in the hiatus sermlunaris ; 7, bulla
ethmoldalis ; 8, frontal sinuses ; 9, crista galli ; 9', falx cerebri ; 10, cerebral hemispheres; 11, right
orbit containing the globe of the eye (surrounded by orbital fat) and its muscles ; 12, great wing of
sphenoid ; 13, spheno-maxillary fissure ; 14, fatty tissue of zygomatic fossa ; 15, buccinator muscle ;
16, last molar tooth ; 17, vault of palate ; 18, zygoma ; 19, left orbit.

Besides the ethmoidal fissures which separate the conchse from one another, the superior
turbinal is often marked by a distinct groove at its posterior part, which leads backwards into
the spheno- ethmoidal recess (fig. 154).

The superior and middle turbinals are conjoined in front and may be said
to spring from the cribriform plate, through which pass the branches of the
olfactory nerve. Their free edges slope downwards and backwards, that of the
middle turbinal gradually becoming nearly horizontal. The lower margins of both,
covered by thick raucous membrane, are free and overhang respectively the superior
and middle meatus ; the middle turbinal has also a nearly vertical free border
anteriorly, which, together with the adjoining part of the concha, forms an
operculum covering the corresponding part of the middle meatus, and concealing

138 THE NOSE.

the bulla ethraoidalis, the hiatus semilunaris, and the apertures of the air-cells
which open into this meatus.

The middle meatus, which lies beneath the middle turbinal, is roughly triangular
in shape, with the base of the triangle directed forwards. It expands in front of
the middle turbinal into a nearly smooth-walled chamber which communicates
through the vestibule with the anterior nares ; this chamber is known as the atrium
of the middle meatus. On the outer wall above the atrium a low ridge (figs. 154,
155) may usually be detected passing downwards and forwards from the anterior
attachment of the middle turbinal. This ridge (agger nasi of H. Meyer), which
is seen also in the macerated bone (fig. 153), is the rudiment of a well-developed
turbinal (nasoturbinal), which is met with in most mammals (Schwalbe). It is
usually better marked in the foetus and new-born child, in which it is seen to be
continued below and behind into the imcinate process of the ethmoid, which forms the
lower and anterior boundary of the hiatus semilunaris (Seydel). The groove above
the agger nasi leads to the olfactory part of the nose, and is termed sulcus olfactorius.

In the lower meatus, which lies between the inferior turbinal and the floor of the
fossa, is the inferior orifice of the nasal duct which is defended by one or two folds of
membrane : when there are two, the folds are often adapted so accurately together
as to prevent air from passing up from the cavity of the nose to the lachrymal sac.

The roof of the nasal fossa is divided into three parts, viz. : nasal, in front ;
efhmoidal, in the middle, and sphenoidal, behind, corresponding with the bones of
the same name. The roof is at the front formed only by the conjunction of the
septum and lateral walls, and is quite narrow, but it is broader near the choanae.
Above and behind the upper turbinal is a diverticulum of the nasal fossa, the
spheno-ethmoidal recess, which communicates posteriorly with the sphenoidal sinus
(fig. 154). The floor of the fossa is broader than the roof. In it in front is the
incisor foramen, but this is in the recent state generally closed (fig. 154). Some-
times, however, a narrow funnel-shaped tube of mucous membrane (nasopalatine
canal, canal of Stensen, or canalis incisivus) passes obliquely downwards from each
nasal fossa for a short distance towards the front of the hard palate. Yesalius,
Stensen, and Santorini believed that these tubes of membrane opened generally into
the roof of the mouth by small apertures close behind the central incisor teeth.
Haller, Scarpa, and Jacobson found the canals in man usually closed, and often
difficult of detection, and these statements have been confirmed by most modern
investigators. The canal is a remnant of the wide communication between the
nasal and buccal cavities found at an early period of foetal life, being in man usually
obliterated, at least in its lower part, before birth, although persistent in many
animals. It is long represented below by a solid column of epithelium cells
continuous with the epithelium of the palate, and above by a narrow tube lined
with ciliated epithelium, opening into the floor of the nasal fossa but closed below.

The part of the inferior meatus which lies behind the incisor canal, together
with the space immediately behind the posterior end of the superior and middle
turbinals as far back as the orifice of the Eustachian tube, belongs to the primitive
buccal cavity of the foetus, having become separated from the permanent mouth by
the growth of the palate (see Yol. I., p. 97). It is known as the naso-pharyngeal
part (ductus naso-pharyngeus), and its mucous membrane is marked off behind from
that of the pharynx by a prominence which is termed the naso-pharyngeal fold.

The anterior and lowermost part of the nasal cavity is termed the vestibule
(fig. 157). This is bounded laterally by and corresponds in extent with the ala and
the cartilage of the aperture. It is lined by skin and is furnished with hairs and
with sebaceous and sudoriferous glands. The hairs are large and numerous just
within the orifice of the anterior nares (vibrissae), but over the rest of the. vestibule.

MUCOUS MEMBRANE OF THE NASAL FOSSAE.

139

they are small and thinly scattered, and both the hairs and glands are absent near
the posterior limit of the vestibule, which is marked off by a curved prominence
(limen restibuli) from the nasal fossae proper. At this line the stratified epithelium
of the vestibule passes into the ciliated epithelium of the fossae, and the cutaneous
glands are replaced by compound mucous glands. At the front of the vestibule,
enclosed by the curved cartilage of the aperture, is a shallow cul-de-sac known as the
ventricle of the nares.

MUCOUS MEMBRANE.

The pituitary or Schneiderian membrane, which lines the cavities of the nose, is
a highly vascular mucous membrane, inseparably united with the periosteum and
perichondrium over which it lies. It is continuous with the skin through the
nostrils ; with the mucous membrane of the pharynx through the posterior nares ;
with the conjunctiva through the nasal duct and lachrymal canaliculi ; and with
the lining membrane of the several sinuses which communicate with the nasal fossae.

upper
lateral

cartilage

of
cartilage aperture

sphenoidal antrum

ost. border of septum

Eustachian aperture
salpingo-phar. fold

soft palate

nasal septui

Fig. 157. — VlBW OF THE SEPTUM NASI FROM THE RIGHT SIDE.

vestibule

The pituitary membrane, however, varies much in thickness and vascularity in
different parts. It is thickest and most vascular over the turbinate bones
(particularly the inferior) and on the septum nasi it is also very thick and spongy ;
but in the intervals between the turbiiiate bones, and over the floor of the nasal
fossae, it is considerably thinner. In the maxillary, frontal, and sphenoidal sinuses,
and in the ethmoidal cells, the lining mucous membrane is very thin and pale, and
contrasts strongly with that which lines the nasal fossae.

The character of the epithelium varies in different parts, and by this, in a general
way, three regions of the nasal fossae may be distinguished. Thus, the region of
the external nostrils (the vestibule) is lined with stratified squamous epithelium ;

140

THE NOSE.

and the remainder is divisible into two parts, viz., the upper or olfactory region in
which the epithelium is non-ciliated and columnar, and the lower or respiratory
region in which, as also in the sinuses, it is ciliated and columnar. The membrane
in the respiratory part covers the middle and inferior turbinals and all the lower
portions of the fossae, and is studded with racemose glands, which open by orifices
apparent on the surface. They are most numerous about the middle and hinder
parts of the nasal fossae, and are largest at the back of the septum near the floor of
the nasal cavity. Glands which are much smaller and less numerous are stated to
open into the several cavities which communicate with the nasal fossae, but many
observers have failed to find them. Besides the glands the mucous membrane of
the fossae contains a variable amount of lymphoid tissue, occasionally accumulated
into " nodules." In some parts large venous plexuses are found, encircled, as well
as the alveoli of the glands amongst which they lie, by bundles of plain muscular
fibres (Klein), thus forming a sort of cavernous tissue.

Olfactory mucous membrane. — The olfactory region, or that in which the
olfactory nerve is distributed, includes in man only the uppermost part of the fossae

Fig. 158. — SECTION OP THE OLFACTORY MUCOUS MEMBRANE. (Cadiat.;
a, epithelium ; 6, glands of Bowman ; c, nerve-bundles.

(superior turbinal and corresponding part of the septum). It is extremely vascular,
a close plexus of large capillary vessels being found under the lining membrane
throughout its whole extent. Its mucous membrane is covered by a very thick
non-ciliated epithelium, and it is more delicate in consistence than that of the
ciliated region, being indeed soft and pulpy. It has a distinct yellow colour in
man (locus luteus) ; brown in some animals ; the colour may extend however
beyond the true olfactory part of the mucous membrane. The glands of this
region (glands of Bowmati) are numerous, and are of a more simple structure
than those in the lower part of the fossae. They open by fine ducts lined with
flattened cells which extend to the surface between the olfactory epithelium cells
(fig. 158). In the mucous membrane itself, the gland-tube is somewhat convoluted
and enlarged, and it may have one or two branches. It is limited throughout by a
basement membrane, and lined and almost filled with columnar or polyhedral
secreting cells. These are of the "serous" type in man, but in some mammals
there are " mucous " cells intermingled with the serous (Paulsen). The gland-cells
contain yellowish brown pigment. In man the gland-ducts frequently open into a
small sub-epithelial receptacle lined with flattened epithelium, from which a fine
tube passes to the surface between the epithelium cells. Occasionally the opening

OLFACTORY EPITHELIUM.

is into a ciliated crypfc. Here and there the epithelium of the surface, as shown by
Max Schultze, is ciliated and not olfactory ; where this is the case, the ordinary
racemose glands are found (Klein). On the other hand, Bowman's glands are not
entirely confined to the olfactory mucous membrane, but may extend a short
distance beyond it into the respiratory part of the fossa.

The columnar cells on the surface of the olfactory mucous membrane (fig. 159, a)
are prolonged at their deep extremities into a process which is generally somewhat

Fig. 159. — CELLS OF THE OLFACTORY REGION. (M. Bchultze.)
Highly magnified.

1, from the frog ; 2, from man ; a, epithelial cell, extending deeply
into a ramified process ; 6, olfactory cells ; c, their peripheral pro-
cesses ; e, their extremities, seen in 1 to be prolonged into fine hairs ;
d, their central filaments.

branched towards its deeper end. The nuclei of these
cells are oval in shape and lie all at about the same level
(zone of oral nuclei), i.e., in the deeper part of the
columnar portion of each cell. The protoplasm of the
columnar cells contains granules of yellowish-brown pig-
ment. Amongst the branching central ends of these
columnar cells there are a large number of peculiar
spindle-shaped cells (fig. 159, #), each consisting of a
large, clear, nearly spherical, nucleus surrounded by a
relatively small amount of granular protoplasm. From
each cell proceeds a superficial and a deep process. The
superficial process (c) is a cylindrical or slightly tapering-
thread passing directly to the surface, and terminating
abruptly at about the same level as the free surface of
the epithelial cells between which it lies, or a little
beyond ; the deep process (d) is more slender, and passes vertically inwards. This
last usually presents a beaded appearance similar to that observed in fine nerve-

Fig. 160. — AN OLFACTORY CELL, HUMAN. (v. BlTinn.)

n, central process prolonged as an olfactory nerve fibril ; b, body of cell with nucleus ;
p, peripheral process passing towards free surface ; c, knob-like clear termination of
peripheral process ; A, bunch of olfactory hairs.

filaments. These cells were termed by Max Schultze, olfactory cells,
to distinguish them from the columnar epithelium cells, which are much
fewer in number, and which are entirely surrounded with the fine
rod-like peripheral processes of the smaller cells. The nucleated bodies
of the olfactory cells are several rows deep, and form a layer of
considerable thickness beneath the columnar cells (zone of round nuclei).

In the rabbit and guinea-pig Klein, in confirmation of a statement
by Sidky, describes a lowermost layer of conical vertical cells resting
by their bases upon the membrana propria.

The total thickness of the olfactory epithelium in man is 0'06 mm.,
whereas in macrosmatic mammals it is O'l mm. or more (v. Brunn).

The olfactory (but not the columnar) cells are said to project
through apertures in a cuticular lamina which bounds the mucous
membrane superficially (external limiting membrane, v. Brunn). The
existence of this cuticle has been, however, called in question by other
observers.

The peripheral process of the olfactory cell was observed by Schultze to be

142

THE NOSE.

surmounted by a short projection (fig. 159, 2, e) ; according to v. Brunn, this
appears in well-preserved specimens to be surmounted by a bunch of fine short
hairlets, which are termed the olfactory hairs (fig. 160). Long and fine hair-like
processes have long been known to exist on the olfactory cells of amphibia, reptiles,
and birds (fig. 159, 1, e).

In amphibia and fishes the olfactory cells are grouped together in the form ot
bud-like organs resembling the taste-buds of the tongue.

It has been shown by various observers, by aid of the methyl- blue and silver-
chromate methods, that the fine varicose central processes of these cells are directly
continuous with the fibres of the olfactory nerve, and terminate centrally by

Fig. 161. — DIAGRAM OF THE CONNECTIONS OF CELLS AND FIBRES IN THE OLFACTORY BULB.

(E. A. S.)

olf.c.. cells of the olfactory mucous membrane ; olf.n., deepest layer of the bulb composed of the
olfactory nerve-fibres, which are prolonged from the olfactory cells ; gl., olfactory glomeruli, containing
arborisations of the olfactory nerve-fibres and of the dendrons of the mitral cells ; m.c., mitral cells ;
«, their axis-cylinder processes passing towards the nerve-fibre layer, n.tr., of the bulb to become
continuous with fibres of the olfactory tract : these axis-cylinder processes are seen to give off collaterals,
some of which pass again into the deeper layers of the bulb ; n', a nerve-fibre from the olfactory tract
ramifying in the grey matter of the bulb.

dendritic ramifications in the glomeruli of the olfactory bulb (see fig. 161, and
Vol. III., Part 1, p. 175).

Olfactory Nerve. — The filaments of this nerve, lodged at first in grooves on
the surface of the bones, enter the substance of the Schneiderian membrane
obliquely. The nerves of the septum (fig. 162) are rather larger than those of the
outer wall of the nasal fossae ; they extend over the upper third of the septum,
becoming very indistinct as they descend. The nerves of the outer wall (fig. 163)
are divided into two groups — the posterior being distributed over the surface of
the upper turbinal, and the anterior over the anterior part of the olfactory groove.
In the embryo the extent of distribution of the olfactory nerves is relatively
greater, but it becomes more limited as development proceeds, and ultimately the
actual distribution of olfactory nerve-fibres, to judge by the character of the
epithelium covering the membrane, becomes limited to a relatively small tract
embracing little but the superior turbinal and a corresponding extent of the septum
(v. Brunn).

OKGAN OF JACOBSOX.

143

The nerves ramify so as to form flattened tufts, the filaments of which, spreading
out laterally and communicating freely with similar offsets on each side, form a
close plexus, with elongated and narrow meshes.

Fig. 162. — NERVES OF THE SEPTUM NASI, SEEN PROM THK RIGHT SIDE.

Hirschfeld and Leveille.) §

(From Sappey, after

I, the olfactory bulb ; 1, the olfactory nerves passing through the foramina of the cribriform plate,
and descending to be distributed on the septum ; 2, the internal or septal twig of the nasal branch of
the ophthalmic nerve ; 3, naso-palatine nerves.

In their structure the olfactory nerve-fibres differ much from the ordinary
dark-bordered fibres of the cerebral and spinal nerves : they possess no medullary

Fig. 163. — NERVES OF THE OUTER WALL OF THE NASAL
FOSS.E. (From Sappey, after Hirschfeld and
Leveille. ) f

1, network of the branches of the olfactory nerve,
descending upon the region of the superior and middle
turbinated bones ; 2, external twig of the nasal nerve ;
3, spheno -palatine ganglion ; 4, ramification of the
large palatine nerve ; 5, small, and 6, external palatine
nerves ; 7, branch to the region of the inferior tur-
binated bone ; 8, branch to the region of the superior
and middle turbinated bones ; 9, naso-palatine branch
to the septum cut short.

sheath, but are axis-cylinders provided with
a distinct nucleated sheath, much more
distinct than that of the fibres of Eemak
and with nuclei at less frequent intervals
(fig. 164).

The greater part of the mucous mem-
brane of the nasal fossae is provided also

with nerves of common sensibility, derived from branches of the fifth pair : the
distribution of these has already been described. They appear to end amongst the
epithelium cells in arborisations which have been noticed by several observers in
preparations made by the silver chromate method.

The Organ of Jacobson. — In the anterior and lower part of the nasal septum
a small aperture may sometimes be seen opening obliquely on to the surface of the
mucous membrane slightly above and in front of the orifice of the nasopalatine canal
(see fig. 157). This aperture leads into a minute canal which passes backwards for
a short distance along the septum to terminate blindly a few millimeters from the
orifice. The canal, which is lined with epithelium continuous with that of the

144

THE NOSE.

nasal cavity and has numerous glands opening into it, is the homologue of a much
more extensively developed tubular organ which opens in a similar position m many
quadrupeds, and is encircled by a special curved plate of cartilage which lies below
the septal cartilage on either side and is known as the cartilage of Jacobson. This
is only represented in man by a narrow shred of cartilage (the vomerine cartilage
of Huschke), which lies wholly below the rudimentary organ of Jacobson. In the
rabbit and guinea-pig as shown by Klein, arid probably in other animals in which
the organ is in a well-developed condition, the epithelium which lines the inner or
mesial side of the canal is much thicker than that on the outer side. It is throughout
similar in structure to that lining the olfactory part of the Schneiderian membrane.
Moreover it receives considerable branches of the olfactory nerve, and in these
animals is no doubt of high functional importance as an accessory to the proper
organ of smell. In man the epithelium on the mesial wall of the canal is thick like
the olfactory epithelium, but contains no true olfactory cells. Most of the cells are
of the columnar (sustentacular) type, and although there are some more slender
spindle-cells between these, probably homologous with the olfactory cells, they do
not reach the surface, nor are they connected with nerve-fibres. Moreover,
calcareous concretions are frequent amongst the epithelium cells, so that it is
highly probable that the function of the organ in man is entirely in abeyance. In

Fig. 164. — NERVE-FIBRES FROM THE OLFACTORY MUCOUS MEMBRANE. (Max Schultze.)
Magnified between 400 and 500 diameters.

From a branch of the olfactory nerve of the sheep ; at a, a, two dark-bordered or medullated fibres,
from the fifth pair, associated with the pale olfactory fibres.

the embryo, up to eight weeks this epithelium is relatively far better developed, but
after this time it appears to undergo retrograde changes.

Blood-vessels and lymphatics of the nasal fossae. — The spheno-palatine
branch of the internal maxillary artery enters the cavity by the spheno-palatine
foramen and divides into external branches (posterior nasal) to the meatuses and
turbinals, sending offsets also to the ethmoidal cells and to the maxillary and frontal
sinuses, and an internal branch (naso-palatine, artery of the septum} along the
septum to the incisor foramen. The branches of the naso-palatine communicate
freely with the anterior and posterior ethmoidal of the ophthalmic.

The descending palatine branch of the internal maxillary artery gives small offsets
to the hinder part of the inferior turbinal and meatus.

The anterior ethmoidal branch of the ophthalmic artery enters the cavity with
the nasal nerve and is distributed to the mucous membrane of the fore part of the
septum and outer wall.

The posterior ethmoidal branch of the same artery sends small twigs to the
posterior ethmoidal cells, to the roof, and to the upper part of the septum.

Lastly a branch from the superior coronary of the facial and the lateral nasal
artery supply the part near the anterior nares. The several arteries anastomose
freely together in the mucous membrane, and are distributed to three sets of
capillaries, viz., a periosteal, glandular, and sub-epithelial.

BLOOD-VESSELS AND LYMPHATICS.

145

The veins form a dense plexus in the mucous membrane, those in the deeper
parts of the membrane being especially large and closely arranged so as almost to
approach the structure of a cavernous tissue. This is most largely developed over
the whole lower turbinal, the lower and hinder border of the middle turbiual, and
the hinder end of the upper turbinal as well as on the lower and hinder part of
the septum. A similar dense venous plexus, continuous with that of the nasal
fossae, extends around the nasal duct, as far upwards as the lachrymal sac. The
trunks leaving the cavity accompany the arteries, the spheno-palatine vein emptying

eptal branch of ant. ethmoidal

communicating
branch between
post, nasal and
post, ethmoidal

naso-palatinc, artery

1
post, nasal artery

branches of post, nasal branch for inferior concha
for the inf. mcatus

Fig. 165. — ARTERIAL SUPPLY TO THE MUCOUS MEMBRANE OP THE LATERAL WALL OF THE NASAL FOSSA.

(AfterZuckerkancll.)

itself into the pterygoid plexus ; the ethmoidal veins joining the ophthalmic vein
and the veins of the dura mater, and also sending a branch to join the veins of the
orbital part of the frontal lobe of the brain (Zuckerkandl), and small veins passing
out at the margin of the nares to join the venous plexus of the upper lip. Some
small veins also pierce the nasal bone and the ascending process of the superior
maxilla to join the commencement of the facial vein.

The lymphatics are abundant and large. They form a close plexus in the
mucous membrane, the branches extending almost to the surface, and a more open
plexus of valved vessels nearer the bone. These are in communication with the
lymphatic spaces which enclose the branches of the olfactory nerve, and these spaces
again communicate with the subdural and subarachnoid spaces of the cranium, so
that the lymphatics of the nasal mucous membrane can be injected from the cranial

VOL. III., PT. 3. L

146

THE NOSE.

cavity (Schwalbe, Key and Retzius). Lymphatic nodules are here and there
present in the mucous membrane.

septal branch of ant. ethmoidal

septal

branch

of ant."

ethmoidal

artery of

septum

narium

from

superior

coronary

septal branches of

posterior ethmoidal

artery of sepium, upper branch
\

I i

anastomosis of na so -palatine veins with palatine artery of septum,

lower branch

Fig. 166. — ARTERIAL SUPPLY TO THE SEPTUM NASI. (After Zuckerkandl. )

BECENT LITERATURE OP THE OLFACTORY ORGAN.

Allen, Harrison, The anatomy of the nasal chambers, The New York Med. Journ., 1889.

Beard, J., Morphological Studies, No. 4, The nose and Jacobson s organ, Zoologische Jahrbiicher,
Abt. f. Anatomic, Band iii., 1889.

Bovier-Lapierre, Ernile, De la vascularite dc Vepithelium olfactif, Comptes rendus hebdom. de
la Societe de biologic, 1888.

v. Brunn, Ueber die Ausbrcitung der menscJdichen Riechschleimhaut, Rostoeker Zeitung, 1891 ;
Die Nervenendigung im Riechepithel, Rostocker Zeitung, 1891 ; Beitr. zur mikr. Anat. der Nasenhohlc,
Arch. f. mikr. Anat., Bd. xxxix., 1892 ; Die Endigungen d. Olfactoriusfasern im Jacobson' schen
Organe des Schafes, Arch. f. mikr. Anat. xxxix., 1892.

Cajal, B,. y, Termin. del nervio olfact. en la mucosa nasal, Barcelona, 1889 ; Origen y termin.
d. 1. fibras nerviosas olfatorias, Gac. med., Catalona, 1890.

Cozzolino, V., Deviazioni del setto nasale, &c., II Morgagni, xxviii., 1886.

Disse, J., Die Ausbildung der Nasenhohle nach der Geburt, Archiv f. Anatomic u. Phys.,
Anatom. Abt., 1889.

Frankel, B., Gefricrdurchschnitt zur Anatomic der Nasenhohle, Berlin, 1890.

van Q-enuchten, A., Contributions a V etude dc la muqueuse olfactive chez Us mamm\feres, La
Cellule, vi., 1890.

Grassi, B., und Castronovo, A., Beitrag zur Kenntniss des Geruchsorganes des ffundes, Archiv
fur inikroskopische Anatomic, xxxiv., 1889.

Hartmann, A., Atlas der normalen und pathologischen Anatomie der Nase, Berlin, 1891.

Herzfeld, J., Beitrdge zur Anatomie des Schwellkorpers der Nasenschleimhaut, Archiv fiir
mikroskopische Anatomie, xxxiv., 1889.

Herzfeld, P., Ueber das Jacobson sche Organ des menschen u. der Saugethiere, Zool. Jahrb., iii.,
1888.

RECENT LITERATURE OK THE OLFACTORY ORGAN. 147

Hovorcka, O., Die dusserc Nase. Sine anatomisch-anthropologischc Studie, Wien, 1893.

Hubert, K. W., Uber die Verkriimmungen dcr Nasenschcidcivand, Diss., Heidelberg, 1886.

Kaufmann, Ucbcr die Bedcutung der Ricch- und EpithclialzeUen der Itegio olfactoria, Mittheilungen
aus clem embryolog. Institute der k. k. Universitat. Wien, 1887.

Keibel, F., Zur Entwicklunysgesch. u. vergleichcndc Anat. der Nasc, &c., Anat. Anz., 1893.

Klein, E., The Organ of Jacobson, Quarterly Journ. of Micr. Science, 1881.

v. Lenhossek, M., Die Ncrvenursprunge und Endigungen im Jacobson' schen Organ des
Kaninchcns. Anatomischer Anzeiger, 1892.

Lowe, L., Zur Anatomic der Nase und ncbenhohle, Leipzig, 1883.

I/ustig-, A. , Des cellules epitheliales dans la region off active des cmbryons, Archives italiennes de
Biologic, tome x., 1888.

Merkel, F., Jacobson1 'sches Organ u. Papilla pcdatina, Anat. Hefte, i., 1892.

Moreno, J., Sobre las terminaciones nerviosas pcrifericas en la mucosa olfatoria de los Peccs,
Anales d. sociedad espan. d. histor. natur., tomo xvii.

Onodi, A., Die Nasenhohle u. ihre Ncbenhohlcn, Wien, 1893.

Pilliet, A. H. , Note sur le tissu erectile des fosses nasalcs, Bulletins de la societe anatomique de
Paris, 1891.

Pog-ojeff, L., Vebcr die feincre Struktur des Geruchsorgans des Neunauges, Archiv fiir mikro-
skopische Anatomic, xxxi.

Preobraschensky, S. S., Zur Kcnntniss des Baues der Regio olfactoria, Wiener klinische
Wochenschrift, iv., 1891.

Retzius, G., Biol. Untersuchungcn, iii., Stockholm, 1889.

Hose, C., Ueber das rudimentdre Jacobson 'sche Organ der Crocodil u. des Menschen, Anat.
Anz., 1893.

Roux, Deviation de la cloison du nez, Revue med. de la Suisse romande, vi., 1886.

Schmidt, M., Die seitliche Divertikel des Nasenrachenraumes, Arch. f. Laryngol. u. Rhinol. i.,
1893.

Seydel, Otto, Ueber die Nasenhofde der hoheren Sdugethicre und des Menschen, Morphologisches
Jahrbuch, xvii., 1891.

Spurgat, F., Die regdmassige Formen der Nasenknorpel des Menschen, <$'c., Anat. Anzeiger,
viii., 1893.

Suchannek, Hermann, Beitrag zur Frage dcr Spezificitat der Zellen in der tierischen und
menschlichen Mechschleimhaut , Anatomischer Anzeiger, 1891 ; Beitrdge zur feineren normalen
Anatomic des menschlichen Geruchsorganes, Archiv fiir mikroskopische Anatomic, xxxvi., 1890 ;
Beitrdge zur normalen und pathologischcn Histologie der Nasenschleimhaut, Auatom. Anzeiger, vii.
1892, and in Arch. f. Ohrenheilkunde, xxxiv., 1893.

Zuckerkandl, E., Das peripherc Gcruchsorgan der Sdugcthierc, Eine veryleichcnd-anatome
Studie, Stuttgart ; Ueber d. Cirndationsapparat in der Nasenschleimhaut. Wiener Denkschriften,
xlix., 1885; Das adcnoide Gewebe der Nasenschleimhaut, Medic. Jahrb., Neue Folge, i. 1886 ;
Die Siebbcinmuscheln des Menschen, Anatom. Anzeiger, vii. 1892 ; Normale und paihologisch
Anatomic der Nasenhohle und ihrcr pneumatischen Anhdngc, 1892.

148

THE ORGANS OF TASTE.

THE ORGANS OF TASTE.

THE gustatory organs are represented by certain patches or groups of peculiarly
modified epithelium cells which are lodged in the thickness of the stratified epithe-
lium of certain parts of the tongue and pharynx. These groups of cells have in
mammals a bud-like arrangement and have therefore been termed taste-buds. They
occur in man at the sides of the papillae vallatse of the tongue, forming a zone around
the papillae and also upon the opposed wall of the vallum. They are also found on

Fig. 167. — PAPILLARY SURFACE OP THE TONGUE, WITH THE FAUCES AND TONSILS. (Sappey.)

1, 2, circumvallate papillae ; 3, fungiform papillse ; 4, 5, filiform and conical papillae : 6 glands
and glandular recesses ; 7, tonsils ; 8, tip of the epiglottis ; 9, frsenum epiglottidis.

the fungiform papillse of the back and sides of the tongue, extending to the lip, and
here and there in the epithelium covering the general surface of the same parts of
that organ. They are especially numerous over a small area just in front of the
anterior pillar of the fauces (fimlria lingua). This area usually displays four or
five longitudinal folds or elevations of the mucous membrane and appears to
represent a much better defined oval laminated structure which is found in a similar
situation in the tongue of some mammals (e.g., rabbit), and which is known as the

TASTE-BUDS.

papilla foliata (fig. 161)). Taste-buds are also found over the anterior surface of
the soft palate, and are very numerous over the posterior surface of the epiglottis.

Fig. lb'8. — VERTICAL SECTION OF CIRCUMVALLATE PAPILLA, FROM THE CALF. (Engelnmnn. ) -^

A, papilla ; B, vallum ; >/, bundles of nerve-fibres entering papilla ; d, duct of a serous gland
opening into fossa around papilla.

According to W. Krause they follow the distribution of the glosso-pharyngeal
nerve.

Flask-shaped organs similar to taste-buds were discovered by Leydig in fishes in

Fig. 169. — VIEW FROM ABOVE OF THE RABBIT'S TONGUE SHOWING THE PAPILLA FOLIATE. (E. A. S.)

certain parts of the skin, and they also occur in the mucous membrane of the mouth
and throat in those animals. In amphibia the taste-organs take the form of patches

Fig. 170. — VERTICAL SECTION OF A FOLIATE PAPILLA OF THE RABBIT, PASSING ACROSS THE FOLIA.

(Ranvier. )

p, central lamina of folium ; v, vein ; p', lateral lamina of folium ; g, taste-bud ; w, sections of
nerve-bundles ; a, serous gland.

of modified epithelium-cells set on the surface of certain papillse of the tongue. The
structure of the taste-buds is most easily studied in sections of the papilla foliata of
the rabbit (figs. 170, 171).

150

THE ORGANS OF TASTE.

Taste-buds have been compared in general form and appearance to the leaf-buds
of a plant. They are flask-shaped bodies, the base of the flask resting upon
the corium of the mucous membrane and the apex projecting towards the free
surface of the epithelium, and emerging between the ordinary flattened surface-

Fig. 171. — SECTION THROUGH ONE OF THE TASTE-BUDS OF THE PAPILLA FOLIATA OF THE RABBIT.

(Ranvier.) Highly magnified.

p, gustatory pore ; «. gustatory cell ; ?•, sustentacular cell ; m, leucocyte containing granules ;
c, superficial epithelium cells ; n, nerve-fibres.

cells of the stratified epithelium. The cells of the stratified epithelium are adapted
and applied to the outer surface of the taste-bud and form a sort of adventitious
capsule for it. The most superficial cells may even be perforated to allow of the
access of the apex of the taste-bud to the free surface. In any case the apex does
not quite reach the surface, but is approached from the surface by a small opening,
the gustatory pore. Into this a bunch of fine hairlets, prolonged from the gustatory
cells of the taste-bud, is seen to project.

Every taste-bud contains two kinds of cells termed respectively the sustentactdar
and the gustatory cells. The snstentacular cells (fig. 172, b) are long and
spindle-shaped, tapering to either end. They form a complete envelope to the
taste-bud, being fitted together like the staves of a barrel : these surface cells are
flattened from within out. Other sustentacular cells lie within the taste-bud
amongst the gustatory cells, extending from apex to base of the taste-bud.

The gustatory cells (fig. 172, a] closely resemble in general appearance the
olfactory cells of Max Schultze (see p. 141). From the nucleated body of the cell

Fig. 172. — CELLS FROM TASTE-BUDS OF RABBIT. (Engelmann.)
«, four gustatory cells ; b, two gustatory and one sustentacular cell ; c, three sustentacular cells.

RECENT LITERATURE OF GUSTATORY ORGANS.

151

which is somewhat bulged, two processes extend. One, the peripheral, is nearly
straight, and passes to the gustatory pore where it ends in a cilium-like projection,
the taste-Mir. The other process, the central one, passes towards the base of the
flask : it may be fine and varicose, and is often bifurcated or even further branched,
and, according to G. Retzius and Lenhossek, it ends in a free extremity or
extremities, and not, as was formerly thought, in continuity with the nerve-fibrils
which pass to the taste-bud.

Each taste-bud receives a small bundle of nerve-fibres, derived, at least in the
case of those of the papilla? vallatae, from the glosso-pharyngeal nerve. The nerve-
Fig. 173. — ENDING OP NERVE FIBRES IN AND AROUND TASTE-BUDS OF

RABBIT : GOLGI PREPARATION. (Gr. RetzillS. )

fibres lose their medullary sheath as they enter the organ
and are continued as axis-cylinders which end by ramify-
ing amongst the gustatory cells (intrabulbar ramification,
fig. 173, t) without, as has been just stated, coming into
actual continuity with these cells. A number of nerve-
fibrils also pass into the enclosing capsule of stratified
epithelium and end by ramifying between the cells of
that epithelium (peribulbar ramification, fig. 173, p).
These peribulbar nerves are believed to be nerves of
general sensibility and not gustatory.

Section of the glosso-pharyngeal nerves in young
animals is followed by atrophy of the taste-buds after
some time. The taste-buds of the anterior part of the
tongue appear to be supplied by the chorda tympani
nerve.

RECENT LITERATURE OF THE GUSTATORY ORGANS.

Arnstein, C., Die Nervenendigungen in den SchmecTcbechern der Sauger., Arch. f. mikr.
Anat., xxxi., 1893.

Drasch, O., Untersuchungen iiber die PapiUce foliates und circumvallatce der KanincJien und
Feldhasen, Leipzig, 1887,

G-melin, Zur Morphologic der Papilla vallata und foliata, Archiv flir mikroskopische Anatomie,
xl., 1892.

Hermann, Friedrich, Studien iiber den feineren Bau des Geschmackorgans, Erlangen, 1887 ;
Sitzungsberichte der math.-physik. Klasse d. k. b. Akad. d. Wissensch., Mlinchen, 1888.

Hb'nig-schmied, J., Kleine Beitrdge, betreffend die Anordnung der Geschmacksknospen bei den
Sciugcthiercn, Zeitschrift fiir wissenschaftl. Zoologie, Band xlvii., 1888.

.Lenhossek, M. v. , Der feinere Bau u. d. Nervcnendigungen der Geschmacksknospen, Anat.
Anzeiger, viii. 1893.

Niemack, J., Der nervose Apparat in den Endscheiben der Frosch-zunge, Anat. Hefte, 1892.

Tuckerman, Frederick, Note on the papilla foliata and other taste areas of the pig, Ana-torn.
Anzeiger, iii. , 1888 ; Anatomy of the papilla foliata of the human infant, Journ. of Anat., vol. xxii.,
1888 ; Observations on the structure of the gustatory organs of the bat, Journal of Morphology, 1888 ;
On the gustatory organs of some Edentata, Internationale Monatsschrift fiir Anatomie und Physiologic,
Band vii., 1890 ; The development of the gustatory organs in Man, Journal of Anatomy, 1889 ;
Americ. Journal of Psychology, vol. iii., 1890 ; On the gustatory organs of some of the Mammalia,
Journal of Morphology, vol. iv., 1890 ; Observations on some mammalian taste-organs, Journ. of
Anat. and Physiol., 1891.

152

COMPARISON OF SENSE-ORGANS.

COMPABISON OP THE MODES OF ARRANGEMENT OP SENSORY CELLS AND NERVE
FIBRES IN THE DIFFERENT ORGANS OF SPECIAL SENSE.

All the organs of special sense contain specially modified cells or the processes of such cells.
the so-called nerve-epithelium cells or sense-epithelium cells which serve to receive the
physical impressions upon which the sensation depends, and to transmute these impressions
into nerve-impulses which are then conducted by nerve-fibres to a nerve-centre. The skin
appears at first sight to present an exception to this general rule, but the ganglion-cells on
the posterior roots, which send their peripheral processes in the form of nerve-fibres to
end by ramifying in the skin, either in a special tactile organ or between the cells of the

Fig. 174.— DIAGRAM OP THE NERVOUS SYSTEM OP THE EARTHWORM. (E. A. g., after Lenhossek and

Retzius. )

m, motor cells ; .<?, sensory fibres emanating from s't sensory cells in the epidermis ; i, median
intercalated cell.

epidermis, do in fact represent the sense-epithelium cells such as we find in the olfactory
organ and in the retina of the eye. This becomes plain from a comparison of the arrange-
ments of the sensory nerves of Annelids with those of Vertebrates. Thus in the earthworm
(Lumbricus) the whole epidermis is pervaded by cells (fig. 174, .s-') which resemble in nearly
every particular the olfactory cells of Vertebrates. They are spindle-shaped cells, having two
processes, one unbranched and extending straight to the free surface, the other branching,
and with one of its branches prolonged as a nerve-fibre to the central nervous system and
ending in a forked termination which comes into relation with branches of the nerve-cells
there present. As in the olfactory organ the sense-cells are supported by columnar epithelium
cells which are not connected with the nerve centre. In other Annelids (e.g., Nereis) the
sense-cells are no longer situated between the other cells of the epidermis, but occupy a
deeper position and send their peripheral process, which is still unbranched, to penetrate
between the cells of the epidermis, and thus to reach the surface, whilst the central process

COMPARISON OF SENSE-ORGANS.

153

is prolonged towards the central nervous system, where it terminates as in Lumbricus
(fig-. 175). Here, in Nereis, the body of the sense-cell, which, since it gives origin to a nerve-
fibre or fibres, may be termed the sensory nerve-cell, is beginning to move away from the
periphery. In Vertebrata, the only essential difference is that the same cell is further
removed from the periphery, and is nearer the central nervous system, viz., in the ganglion
of the posterior root. In all vertebrate embryos and in some Vertebrata throughout life,
the sensory nerve-cell is a spindle-shaped cell, with a peripheral process extending as the
sensory nerve-fibre towards the integument, and a central process, passing by the posterior
root into the grey matter of the nerve-centre. In most Vertebrata. the spindle-shaped
bipolar character of these sensory nerve-cells becomes lost, owing to the fact that as develop-
ment proceeds the two processes shift towards one another at their attachment to the cell
and ultimately come off from it by a common stem, but this is a mere secondary modification
and does not affect the validity of the comparison. In most other sense organs, the sensory
cells remain at or near the periphery, and the most important differences between them
consist in the relative extent of development of the centrally directed prolongation. In the
auditory organ (fig. 170), which is an involuted portion of the iiitegumental surface, the sense-
cells are represented by the hair-cells of the maculae and of the organ of Corti. Here a central
process is absent, and the connection with the central nervous system is effected by the
endings of the auditory nerve enveloping the cell-bodies by a close terminal ramification.
These hair-cells of the auditory organ are not in the same category of sensory cells with the

Lumbricus

Nereis

Vertebrata

Fig. 175. — DIAGRAMS SHOWING THE RELATIVE POSITION OF THE SENSORY CELL IN LUMBRICUS, NEREIS,
AND VERTEBRATA. (After G. Retzius.)

olfactory cells of the nasal membrane or the visual cells of the retina. For they are destitute
of a central or nerve-fibre process, and it may be doubted whether they transmute the auditory
vibrations into nervous impulses. On the other hand the manner in which the terminations
of the auditory nerve-fibres surround or abut against the enlarged deeper ends of these cells
suggests the possibility of a mechanical excitation of the nerve-terminations by a direct trans-
mission of the vibrations of the endolymph through the cells in question. If this view be
taken, viz.. that the hair-cells of the auditory organ are not true nerve-epithelium cells, but
only ordinary epithelium cells somewhat modified for the transmission of mechanical impulses,
then it will follow that the terminal sensory cells are to be looked for in the cells of the spiral
ganglion of the cochlea and in the cells in the vestibular branch of the auditory nerve. These
are bipolar cells having a peripheral process ending as we have seen in contact with the hair-
cells, and a central process (auditory nerve fibre) ramifying in the grey matter of the nerve-
centre. There will thus be a close analogy as regards nerve-ending between the auditory and
tactile organs. With regard to the gustatory organ our knowledge is still imperfect. It has
usually been supposed hitherto that the central processes of the gustatory cells are prolonged
into nerve-fibres, and if this were the case, these cells would come into the same category with
the olfactory cells of the nasal mucous membrane. But according to the most recent observa-

VOL. III., PT. 3. M

154

COMPARISON OF SENSE-ORGANS.

tions the central process of the gustatory cell is not continuous with a fibre of the glosso-
pharyngeal nerve, and the connection of the gustatory cells with the fibres of that nerve is

auditory

gustatory

tactile

Fig. 176. — DIAGRAM SHOWING THE MODE OP TERMINATION OF SENSORY NERVE FIBRES IN THE

AUDITORY, GUSTATORY, AND TACTILE STRUCTURES OF YERTEBRATA. (After G. RetziuS.)

indirect and not by continuity. If this is so. the arrangement in the gustatory organ would
appear to be somewhat similar to that which obtains in the general integument and in the
auditory organ (fig. 176).

Fig. 177. —DIAGRAM OF THE CONNEXIONS OF THE RETINAL
ELEMENTS. (After (r. Retzius.)

gr.i., inner granules ; m.i., inner molecular layer ; </, ganglion
cell ; n, its nerve fibre process or neuron ramifying in the nerve
centre.

The retina of the eye, as its development shows, is
rather to be regarded as an extension of the central nervous
system than a peripheral organ. It is composed of nerve-
elements (nerve -cells) which are arranged in three tiers
(fig. 177). Those which are placed most peripherally are
the visual cells or rod- and cone-cells, which resemble the
general type of sensory cells in consisting of a nucleated
enlargement or cell-body (outer granule) with a specially
modified peripheral process (rod or cone), and a centrally
directed ramified (nerve-fibre) process (rod- or cone-fibre).
In the case of the cone-elements the peripheral process has
been shown to be contractile, since it shortens under the
excitation of light (see p. 50). It is usually believed that in
these peripheral processes the nerve-impulses are produced
and that the impulses are thence conducted centrally by the
central or nerve-fibre process (rod- or cone-fibre), and by it
transmitted to the next tier of cells. The second tier of
nervous elements is afforded by the layer of inner granules.
Here there are bipolar nerve-cells, the peripheral processes
of which interlace with the central processes of the rod-
and cone-cells, but one peripheral fibre (fibre of Landolt)
extends in most vertebrates beyond the rest and comes to lie between the bodies of the
rod- and cone-cells. The central processes of the' bipolars interlace with the peripheral
processes of the cells of the next tier.

COMPARISON OF SENSE-ORGANS.

155

Lastly, the third tier of nervous elements is formed by the ganglion-cells of the retina
whose peripheral dendritic processes interlace with the central processes of the inner granules
and whose centrally directed processes are fibres of the nerve and have their central optic
terminations in the grey matter of the general nerve-centres.

The comparison of the elements of the retina with those of the other sense organs is not
<;asy. If we compare the retina with the olfactory organ, we are at a loss to say whether we
are to place the rod- and cone-cells along with the olfactory cells, as in making this com-
parison is most frequently done, or whether we should not rather look upon the bipolar inner
granules as the homologues of those elements. In the latter case we should be led to
suppose that the nervous impulses originate in the peripheral process of the inner granules.

Fig. 178.— DIAGRAM OF THE ARRANGEMENT OF THE SENSORY NERVE-FIBRKS

IN THE OLFACTORY ORGAN AND BULB. (After Gr. RetzillS.)

being there set up by a stimulation received from the rod-
and cone-cells. And it is further open to us to suppose this
stimulation to be a mechanical one caused by the contraction of
the rod- and cone-elements under the influence of light. If on
the other hand we regard the rod- and cone-elements as representing
the olfactory cells, there appears to be no structure in the olfactory
apparatus homologous with the tier of inner granules of the retina.
A comparison of the retina with the remaining sense-organs is also
easier on the assumption that the inner granules represent the
actual sensory cells in which nervous impulses originate in response
to stimulation set up through the rod- and cone-elements.

The connections of the olfactory cells (fig. 17H) more nearly
resemble the primitive arrangement of sensory structures which
occurs in Lumbricus, than is the case in any other of the sense
organs. For here, as in the epidermis of Lumbricus, the sensory
nerve-cells are at the free surface, lying between and supported by
columnar epithelium cells. And the sensory nerve-fibres are a
direct prolongation of the fixed ends of the olfactory cells, passing
to the nerve centre and there becoming interlaced with the
processes of the nerve-cells of the centre. The nature of the

olfactory excitation, whether mechanical, chemical, or otherwise, is not known, but whatever
it be, we must assume that its result is to set up nervous impulses within the olfactory
cells, and that these impulses are then propagated along the fibres of the olfactory nerve to
the olfactory bulb : where, within the olfactory glomeruli, they are somehow transmitted to
the dendritic processes of the mitral cells, through the nerve-fibre processes of which they
are again passed on to other parts of the brain.

It will therefore be seen that all the sense-organs have this in common, viz., a bipolar
sensory nerve-cell having (1) a peripheral process extending towards the surface and
penetrating between more or less modified epithelium-cells which cover that surface, and
(2) a central process which is in all cases recognizable as a nerve-fibre and the terminal
ramification of which interlaces with ramifications of nerve-cells within a nerve-centre. The
chief differences occur in the greater or less special modification of the epithelium-cells between
which the peripheral processes penetrate, such modification being very considerable in the
visual organ, less in the auditory and gustatory organs, very slight in the olfactory organ, -
and absent in the case of the general integument.

INDEX AND GLOSSAKY TO VOL. III., PT. III.

ADITUS ad antrum (approach to antrum), 80

Adventitia oculi, 1 1

Agger (mound) nasi, 138

Ala (wing) of nose, 130, 132

Amacrine (o priv. /j.a.Kp6s, long ; is, tVos, fibre)

cells, 41, 44, 52, 57
Amphibia, retinal cells of, 44

end-knobs of retina of, 46

lagena of, 114

olfactory cells of, 142

rods and cones of, 49

taste-organs of, 149
Ampulla (flask-shaped vessel) of semicircular

canals, 100, 105, 108, no
Anderson, on dilatator iridis, 33
Angle, of eye, i

naso-facial, 130

Annelids, sensory cells and nerves of, 152
Annular ligament, 83
Annulus fibrosus, 82
Anosmatics (o priv. 001*0.01*0.1, smell), 130
Anterior chamber of eye, 21, 22, 66

homogeneous lamina of cornea, 19
hyaline layer of iris, 33
limiting layer of iris, 33
Anthelix (O.VTI, opposite to ; helix), 72
Antitragus, 71

muscle of, 75
Antrum (cave), mastoid, 80, 84

maxillary, 136, 139
Aqueduct of cochlea, 104
Fallopius, 83
vestibule, 99, 105

Aqueous humour (humor, liquid), 11, 55, 66
Arch, tarsal, 5
Arcus senilis, 19
Area centralis retinse, 54
Arteria centralis retinas, 38, 55, 59, 65
Arteries or Artery, auditory, internal, 109

auricular, 76, 79, 83

central of retina, 38, 55, 59, 65

of choroid coat, 36, 55

ciliary, 13, 15, 16, 26, 29, 33

of cochlea, 126

of conjunctiva, 5, 16

of cornea, 22

ethmoidal, 144

of Eustachian tube, 88

of eyelids, 5

of external auditory canal, 79

of iris, 33

of labyrinth, 109

of lens, 65

of lachrymal gland, 8

mandibular, 91

of membrana tympani, 82

nasal, 144

of nasal duct, 10
fossae, 144

naso-palatine, 144

of nose, 131

VOL. III., PT. 3.

Arteries— continued.

of optic nerve, 16, 55

palatine, 144

palpebral, 5, 16

papillary, 55

of pinna, 76

of retina, 36, 55

of sclerotic coat, 16, 55

of septum nasi, 144

spheno-palatine, 144

stapedial, 91

of tympanic membrane. 97

of tympanum, 97

Atrium (hall) of middle meatus, 1 38
Auditory artery, internal, 109

canal, external. See CANAL.

epithelium, 105

hairs, no, 112

meatus, external. See CANAL.
internal, 102, 124

nerve, 99, 104, 108, 124, 152

ossicles, 89, 96

movements of, 95
Auricle, 71
Auricular artery, 76, 79, 83

nerve, 76, 79, 83

Auriculo-temporal nerve, 76, 79, 83
Axis of eye, 1 1
Axis-ligament of malleus, 93

BACILLARY layer of retina, 38, 46

Ball of eye. See GLOBE.

Basal cells, 45

Basilar membrane, 113, 116, 119, 127

cells, 121

Berger on zonula of Zinn, 62
v. Bezold on external auditory canal, 77
Bibliography. See LITERATURE.
Bipolar cells, 41, 45, 52, 109, 124, 153, 154, 155
Birds, bipolar cells of retina of, 44

ciliary muscle of, 30

cochlea of, 102

dilatator iridis of, 33

end-knobs of retina of. 46

epithelium of semicircular canals of, no

fovea centralis of, 54

lagena of, 1 14

olfactory cells of, 142

retinal cones of, 49

Blood-vessels. Sec ARTERIES ; VEINS.
Body, ciliary, 15, 29, 62, 66

vitreous, n, 38, 58
Bones or bone, small, of ear, 89

of stapedius muscle, 94

tympanic, 79
Bowman, corneal tubes of, 18

glands of, 140

membrane of, 19
Brnch, membrane of, 29
v. Brunn, on olfactory cells, 142

158

INDEX AND GLOSSARY TO VOLUME III. PART III.

Bninner, on articulations of auditory ossicles, 91
Bulla (boss) ethmoidalis, 136
Bundle, ciliary, 2

CAJAL, on amacrine cells, 45

bipolar cells of retina, 43
ganglionic layer of retina, 41
horizontal cells, 15
Canal or canals, carotid, 87, 89

central, of modiolus, 102, 124

of chorda tympani, 98

of cochlea, 113, 118, 127

Eustachian, 86

external auditory, 76, 81
of infant, 79
nerves of, 79
structure of, 78
vessels of, 79

of Jacobson's nerve, 98

lachrymal, 7, 8, 10

membranous of cochlea, 104

membranous semicircular, 105

nasopalatine, 138

of Petit, 59, 62, 66

of Recklinghausen, 18

of Schlemm, 21, 34, 66

semicircular, 98, 99, 100, 105, 109

spiral of cochlea, 102

of modiolus, 104, 124

of Stensen, 138

of Stilling, 38, 59

of tensor tympani muscle, 86, 94
Canaliculus lacrimalis, I
Canalis hyaloideus, 59

incisivus, 138

membranacens, 113

reuniens, 105, 114

utriculo-saccularis, 105
Canthus (tire of wheel), I

Capitulurn (dim. of caput, head) of malleus, 89
Capsule of lens, 34, 59, 62, 63, 65

of Tenon, n
Carotid canal, 87, 89
Cartilage of Eustachian tube, 87

of external auditory canal, 78, 80

of Jacobson, 133, 144

lateral, of nose, 131

of nasal aperture, 131, 132

of Meckel, 90, 91

of pinna, 73, 80

of septum nasi, 132

tarsal, 2. See also TARSUS.

vomerine, 133, 144
Cartilagines epactiles (eira.KT&s, intercalary), 132

minores vel quadratffi, 132
Caruncula (dim. of caro, flesh) lacrimalis, 2, 10
Cat, dilatator iridis of, 33
Caudal process, 74
Cells, basilar, 121

of Claudius, 122

of Deiters, 121, 127

ethmoidal, 135, 136, 139

gustatory, 150, 153

of Hensen, 122

niastoid, 84, 96

nerve-epithelium. 152

olfactory, 141, 154

sense-epithelium, 152

tympanic, 81

visual, 46, 154

Central artery of retina, 38, 55, 59

canal of modiolus, 102, 124
Cerumen (cera aurium, wax of ears), 79
Ceruminous glands. 73, 79
Chamber, anterior, of eye, 21. 22, 66

posterior of eye, 66
Chievitz, on fovea centralis, 54
Choanae (xodvrj, funnel), 130
Chorda (string) tympani nerve, 81, 96, 98, 151
Choroid (correctly chorioid, from x°VtoJ/» mem-
brane) coat, n, 13, 14, 16, 23, 30, 53

structure of, 24

nerves of, 34

Cilia (cilium, eyelid, eyelash), 4
Ciliary arteries, 26, 29, 33

body, 15, 24, 29, 62, 66

bundle, 2

glands, 29, 55, 62, 66

ligament, 30

muscle, 20, 30
circular, 30

nerves, 13, 15, 16, 26, 29, 55

processes, 23, 24, 29, 54, 60

vessels, 13, 15, 16, 26, 29, 55
Circular ciliary muscle, 30
Circulus major, 33, 34

minor, 33

Zinnii, 16

Claudius, cells of, 122
Cleft, olfactory, 134
Coat, choroid, n, 13, 14, 16, 23, 30, 53

sclerotic, n, 13, 14, 30

vascular, of eye, 23
Cochlea (snail), 83, 98, 101, 108

canal of, 113, 118, 127

measurements of, 127

membranous, 98, 104, 112

vessels of, 126

Cochlear nerve, 108. 114, 124
Cochleariform (cochleare, spoon ; forma, shape)

process, 86, 94

Colliculus (dim. of collis, hill) nervi optici, 36
Colosanti, on Meibomian glands, 4
Columella (dim. of columna, pillar) cochleae, 102
Columna nasi, 130, 132
Comparison of different sensory nerves and cells,

J52

Concha (mussel shell) of ear, 71
Conchse, ethmoidal, 135, 136
Cone-bipolar cells, 43
Cone-fibre, 46,53, 57, 154
Cone-foot, 47
Cone-granules, 46

Cones of retina, 46, 47, 50, 52, 54, 57, 154
Conjunctiva (conjungit palpcbras cam oculo}, I,
4, 10, ii

arteries of, 16

bulbi, 4, 1 6

palpebrarum, 4, n

veins of, 17
Cornea (eorneus, horny), 11, 13, 14, 17

structure of, 17

vessels and nerves of, 22
Corneal corpuscles, 18, 23

tubes, 1 8

Corpus ciliare, 15, 24, 29, 62, 66
Corpuscles of cornea. 18, 23

vitreous body, 59
Crista (crest) acustica, 107, no

vestibuli, 99

Crura (cms, leg) of incus, 90
of stapes, 91

INDEX AND GLOSSARY TO VOLUME III. PART III.

159

Crystalline lens. Sec LENS.

Cupola, 102

Cupula (vault) terminalis, 112

DARWIN, tubercle of. 72
Deiters, cells of, 121, 127
Demours, membrane of, 19
Denissenko, on retina of eel, 46
Descemet, membrane of, 19, 22
Diameters of cornea, 1 7
of eyeball, 14
Dilatator conclue, 75

pupilne, 32

tubae, 87

Dimensions. See MEASUREMENTS.
Disc, optic, 38

Divisions of auditory nerve, 108
Dog, orifice of nasal duct of, 10
Dogiel, on spongioblasts, 44
Drum of ear, 80
Duct, nasal, 7, 9, 138, 140
Ductus cochlearis, 113

endolymphaticus, 99, 105

naso-pharyngeus, 138

EAR, 71

external, 71
index of, 72
internal, 98
literature of, 127
middle, 80
ossicles of, 89
Ear-point, 72

Earthworm, sensory cells and nerves of, 152
Eel, vessels of retina of, 46
Eighth nerve. See AUDITORY NERVE.
Elastic lamina, posterior, 17, 19
Ellipsoid, 49
Eminentia papillaris, 85
End-bulbs of conjunctiva! nerves, 16
End- knob, 46

Endolymph, 98, 104, 113, 152
Eiidotheliuin of cornea, 17, 20, 22

lamina suprachoroidea, 25
ligamentmn pectinatum, 21
sclerotic coat, 16
Tenon's capsule, n
zonula of Zinn, 62
Epiglottis, 149
Episcleral (lirl, upon ; sclerotic) plexus of veins,

17

Epithelium, of ampullae, no
auditory, 105
of conjunctiva, 16
of cornea, 17, 22
of Eustachian tube, 87, 96
of iris, 31, 66
of lens capsule, 66
oflimbus, 116
of mastoid cells, 96
of membrane of Keissner, 1 18
of membranous cochlea, 113
of nasal fossae, 139

nerve , 152

olfactory, 140, 141

of organ of Corti, 117, 119, 126

of organ of Jacobson, 144

of retina, 46, 50, 54

of semicircular canals, 109, no

Epithelium — continued.

sense , 152

of tympanum, 96
Ethmoidal arteries, 144
bulla, 136
cells. 135, 136, 139
conchse, 135, 136
fissure, 135, 136
Eustachian canal, 86

cartilage, 87, 96
tube, 80, 81, 86, 94, 96
muscles of, 88
vessels and nerves of, 83
Ewart, on lens fibres, 65
External auditory canal. See CANAL.
ear, 71

palpebral arteries, 5
Eye, i

axes of, 1 1

chambers of, 21, 22, 66
choroid coat of, 23
coverings of, I

globe of, 10
ms of, 63

literature of, 67

measurements of, 14, 17, 63

retina of, 35

sclerotic coat of, 13

suspensory ligament of, 12

vitreous humour of, 58
Eyelashes, 4
Eyelids, i, 2, 10

lymphatics of, 6

nerves of. 7

smooth muscle of, 4

structure of, 2

vessels of, 5

FALLOPIUS, aqueduct of, 83
Fascia (band), palpebral, 2, 3

salpingo-pharyngea, 87
Fat, orbital, 10, n
Fenestra (window) ovalis, 83, 91, 95, 99

rotunda, 83, 95, 104
Fibre-cells, in
Fibres of lens, 64

of Miiller, 39, 41, 50, 54

radial, 50

Fibril of Landolt, 44, 57, 154
Fibrous tympanic plate, 79
Fimbria (fringe) liiigiife, 148
Fingered cells, 17

Fishes, epithelium of semicircular canals of,
no

lagena of, 114

olfactory cells of, 142

rods and cones of, 49

taste-organs of, 149
Fissure, ethmoidal, 135, 136

of Glaser, 81, 90

petroso-squamosal, 84

petro-tympanic, 81
Fissures of Santorini, 74, 80
Fold, naso-pharyngeal, 138

salpingo-palatine, 87

salpingo-pharyngeal, 87
Folds, tympano-malleolar, 82
Fon tan a, spaces of, 21, 66
Foramen centrale, 102

incisor, 138

singulare (solitary), 108

N 2

160

INDEX AND GLOSSARY TO VOLUME III. PART 111.

Fornix (arch, vault) conjunctiva?, I, 8
Fossa (ditch) of anthelix, 72

of helix, 72

nasal, 130, 133

raucous membrane of, 139

patellaris (patella, small dish), 58

of Rosenmiiller. 87

scaphoidea, 72

triangularis, 72
Fossula (dim. of fossa) cochleje, 102

ovalis, 83

rotunda, 83
Fovea (pit) centralis retinae, 15, 35, 40, 44, 52,

55

extern a, 53

hernielliptica, 99, 104

hemispherica, 99, 105, 108
Frog, bipolar cells of retina of, 44

retinal cones of, 50

retinal rods of, 49
Frontal sinus, 136, 139
Fundamental nerve-plexus of cornea, 22
Fungiform papillse, 148
Funiculus (dim. offunis, cord) sclerse, 17

GANGLION of Corti, 108

nervi optici, 38, 40, 57

of nerve of tensor tyrnpani, 94, 98

retinpe, 38, 4i, 154

of Scarpa, 108

spirale, 109, 124, 152
Ganglionic layer of retina, 40, 52, 54, 57
Ganoidei, retinal cones of, 49
Giacomini on plica semilunaris of negro, 2
Giant-cells of retina, 41
Glands of Bowman, 140

ceruminous, 73, 79

ciliary, 29, 55, 62, 66

Harderian, 5

lachrymal, 7, 8
inferior, 7

Meibomian, 2, 3

of Moll, 4

of nasal duct, 10

tarsal, 3

posterior, 4

of tympanum, 96
Glandula lacrimalis inferior, 7
Glandulse ceruminosre, 79
Glaser, fissure of, 81, 90
Globe of eye, I, 10

diameters of, 14, 15

dimensions of, I, 10, 14
Glomeruli, olfactory, 142
Granules, inner, 41, 52, 57, 154

myeloid, 50

outer, 46, 52, 154

pigment, of retina, 50
Groove, spiral, 115
Guinea-pig, cells of Hensen of, 122

olfactory epithelium of, 141

organ of Jacobson of, 144
Gustatory cells, 150, 153

organs, 148

literature of, 151

pore, 150

HAIRS, auditory, no, 112

olfactory, 142
Hair-cells, no, 119, 121, 127, 152

Hamulus (small hook), 103

Handle of malleus, 82, 90

Hannover on funiculus sclene, 17

Harderian gland, 5

Helicotrema (e'Ai£, spiral ; rpr^a, hole), 102

Helix, 72

muscles of, 75

spine of, 74
Henle on bacillary layer of retina, 50

on smooth muscle of eyelid, 4
Hensen, cells of, 122

on hair-cells, 122

Hexagonal cells of retina, 24, 35, 38, 50
Hiatus (opening, from Mo, open) Fallopii, 97

semilunaris, 136, 138
Homogeneous lamina of cornea, 19
Horizontal cells, 45, 57
Humour (humor, liquid) aqueous, n, 54, 66

vitreous, n, 38
Hyaline layers of iris, 33
Hyaloid membrane, 53, 58, 59

INCISOR foramen, 138
Incisura (notch) Rivini, 81, 82

terminalis, 74
Incus (anvil), 80, 89, 90, 91, 95

ligaments of, 85, 93
Index, of ear, 72

nasal, 131

Infundibulum (funnel), 135
Internal auditory meatus, 102, 124
ear, 71, 98
palpebral artery, 5
Intrabulbar nerves, 151
Intrinsic ligaments of pinna, 74

muscles of pinna, 75
Iris (rainbow), n, 15, 20, 23, 31
muscular tissue of, 32
nerves of, 34
pillars of, 21
vessels of, 33
Isthmus tubre, 87
Iter chordte anterius, 84, 98
posterius, 98

JACOBSON, cartilages of, 133, 144
nerve of, 97
organ of, 133, 143

KKAUSE on glands of tympanum, 96

LABIUM tympanicum, 115

vestibulare, 115
Labyrinth, 71, 98

membranous, 98, 104

osseous, 98, 99
Lachrymal (lacrima, tear) apparatus, 7

canals, 7, 8, 10

gland, 7, 8

inferior, 7

reservoir, I

sac, 7, 9

Lacus (reservoir) lacrimalis, I
Lagena (flagon), 114

INDEX AND GLOSSARY TO VOLUME III. PART III.

161

Lamellae (dim. of lamina, plate) of cornea, 18
Lamina, anterior homogeneous, of cornea, 19
cribrosa (cribrum, sieve), 15

fusca (dark), 13, 16

posterior elastic, of cornea, 17, 19

reticularis, 119, 12 1, 122

spiralis, 102, 103, 113, 124
secondary, 103

suprachoroidea, 24, 53
Laminaj of lens, 64
Landolt, fibril of, 44, 57, 154
Langley on dilatator iridis, 33
Lateral recess of pharynxx 87

sinus, 85

Laxator tympani muscle, 92
Layer, of horizontal cells, 45

outer fibrous, of retina, 53
Layers of retina, 38, 52, 54, 56
Leber on canal of Sclilemm, 22
Lenhossek on gustatory cells, 151
Lens, n, 14, 31, 63

capsule of, 34, 59, 62, 63, 65

changes with age of, 66

fibres of, 64

structure of, 64

suspensory ligament of, 59
Levator palati muscle, 88

palpebrae muscle, i, 2, 3
Leydig on taste-organs of fishes, 149
Lid of eye. See EYELID.
Ligaments or ligament, annular, 83

of auditory ossicles, 92

of capsule of Tenon, 1 1

ciliary, 30

of incus, 85, 93

of malleus, 92

palpebral, 2, 3

of pinna, 74

spiral, 113, 117, 119

suspensory of eye, 12

of lens, 24, 31, 59

tarsal, 2, 3, 10

tympano-malleolar, 82

Ligamentum pectinatum (pecten, comb), 21,
30, 66

suspensorium oculi, 12
Limbus (sill, border) luteus, 35

of spiral lamina, 115, 127
Limen (threshold) vestibuli, 139
Limiting layers of iris, 33
Liquor Cotunuii, 98

Morgagni, 66
Literature of ear, 127

of eye, 67

of gustatory organs, 151

of nose, 146
Lobule, 71, 74

Lockwood on capsule of Tenon, 12
Locus luteus, 140
Long ciliary arteries, 33
Lumbricus, sensory cells and nerves of, 152
Lymphatics of conjunctiva, 16

of cornea, 22

of external auditory canal, 76, 81

of eyelid, 6

of nasal fossae, 145

of nose, 131

of pinna, 76

of tympanic membrane, 83
Lymph-spaces of olfactory nerves, 145

of optic nerve, 56, 59

perichoroidal, 13, 25, 66

Ly m ph- spaces — continued.

perivascular, 26, 56

of retina, 56

of Tenon's capsule, n, 25
Lizard, bipolar cells of retina of, 44

MACROSMATICS (na.Kp6s. large ; oo>i&>/xaj, smell),

130, 137, 141
Macula (spot) acustica utriculi, 105, 112

lutea (yellow), 35, 40, 47, 52, 55

neglecta, 105
I Maier, sinus of, 9
j Malleus (hammer), 80, 81, 82, 89, 91, 92, 94,

i 95,98

ligaments of, 92
Mammals, end-knobs of retina of, 46

rod-ellipsoid of, 49
Mandibular artery, 91
Manubrium (handle) mallei, 82, 90
Marginal fasciculus, 2

plexus, 7

Marsupials, retinal cones of, 49
Mastoid antrum, 80, 84

cells, 84, 96
Maxillary antrum, 136, 139

concha, 135
Measurements of coats of eye, 14

of cochlea, 127

of cornea, 14, 17

of globe of eye, 14

of lens, 63

of nasal fossae, 1 34

of tympanum, 80

Meatus (passage ), auditory, external. See CANAL.
internal, 102, 124

of nose, 135, 138
Meckel, cartilage of, 90, 91
Meibomian glands, 2, 3
Membrana fenestrata, 45

flaccida, 82, 96

limitans of pituitary membrane, 141
of retina, 38, 51, 52

nictitans (nicto, wink), 2

tympani, 78, 79, 81, 90, 93, 95, 96, 98
Membrane, basilar, 113, 116, 119, 127

of Bowman, 19

of Bruch, 29

of Demours, 19

of Descemet, 19, 22

hyaloid, 53, 58, 59

papillary, 34, 66

pituitary, 139

ofReissner, 113, 118, 127

Schneiderian, 139

secondary, of tympanum, 83, 95, 104

tectorial, 120, 123. 127
Membranous cochlea, 98, 104, 112

labyrinth, 98, 104

semicircular canals, 105
Microsmatics (fj.iKp6s, little ; o0yt«to/««, smell),

130

Middle ear, 71, 80

Modiolus (nave of wheel), 101, 102, 124
Molecular layer, inner, 38, 41, 43, 44, 52, 54 57

outer, 38, 43, 45> 47, S2. 57
Moll, glands of, 4
Monotremes, lagena of, 114
Mtiller on bacillary layer, 50

fibres of, 39, 41, 50, 54

on spheno-maxillary muscle, 4

162

INDEX AND GLOSSARY TO VOLUME III. PART III.

Muscles or Muscle, of antitragus, 75

ciliary, 20. 30

circular, 30

dilatator concha?, 75
pupillre, 32
tuba?, 87

of Eustachian tube, 88

of eyelid, 2, 3, 4, 9, 10

of helix, 75

laxator tympani, 92

levator palati, 88

of pinna, 75

pyramidalis, 75

of Riolan, 2

salpingo-pharyngeus, 89

smooth, of iris, 32

of capsule of Tenon, 1 1

spheno-maxillary, 4

sphincter pupillre, 32

stapedius, 85, 94, 95, 98

tensor choroideie, 30

tensor palati, 87, 88

tensor tarsi, 9, 10

tensor tympani, 81, 86, 93, 94, 95,

of tragus, 75

transverse, of pinna, 75

of tympanum, 93
Myeloid granules, 50

NARES, anterior and posterior, 130

ventricle of, 139
Nasal arteries, 144

duct, 7, 9, 10. 138, 145

fossae, 130, 133

measurements of, 134.
mucous membrane of, 134
vessels of, 144

index, 131

Naso-facial angle, 130
Naso-palatine artery, 144

canal, 138

Naso-pharyngeal fold, 138
Naso-turbinal, 138
Negro, plica semilunaris of, 2
Nereis, sensory cells and nerves of, 152
Nerve- epithelium cells, 151
Nerve-fibre layer of retina, 38, 52, 54, 57
Nerves or nerve, auditory, 99, 104, 108, 124, 152

auricular, 76

chorda tympani, 81, 96, 98, 151

of choroid, 31, 34

ciliary, 13, 15, 17, 22, 34

of cochlea, 108, 114, 124

of conjunctiva, 16

of cornea, 22

of Eustachian tube, 88

of external auditory canal, 79

of eyelid, 7

intrabulbar, 151

of iris, 34

of Jacobson, 97

of lachrymal gland, 8

of nasal duct, 10
fossae, 143

of nose, 131

olfactory, 140, 142

optic, 10, u, 15, 16, 35, 39, 47, 55, 56, 57

peribulbar, 151

petrosal, 97

of pinna, 76

of retina, 39

Nerves — continued.
of saccule, 108
of sclerotic, 17
of taste-buds, 151
of tympanum, 81, 83, 97

Neuroglia- cells, 40

Neurospongium, 41

Nose, 130

cartilages of, 131
literature of, 146
septum of, 130, 142, 145
vessels and nerves of, 131

Notch of Rivinus, 81, 82, 93

Nuclear layer, inner, 38, 41, 54, 57
outer, 38, 46, 53, 54
zone of lens, 65

Nucleus of lens, 63

OBLIQUE muscle of pinna, 75
Ocular conjunctiva, 5
Oil-globule of retinal cones, 49
Olfactory cells, 141, 154

cleft, 134

epithelium, 140, 141

glomeruli, 142

hairs, 142

mucous membrane, 140

nerves, 140, 142

organs, 131

literature of, 146
Optic disc, 38

nerve, 10, 11, 15, 16, 35, 47, 55, 56, 57

papilla, 55, 59

vesicle, primary. 50
Ora serrata (notched edge), 35, 54
Orbicularis palpebrarum muscle, 2, 3, 9, 10
Organ of Corti, 119, 126

of Jacobson, 133, 143
Os orbiculare s. lenticulare, 91
Osseous labyrinth, 98, 99
Ossicula auditus, 89, 96

movements of, 95

Ostium (entrance) pharyngeum, 87
tympanicum, 86

Otoconia (o5s, urSs, ear ; nov(u, dust), 105
Otoliths (ur6s ; \(8os, stone), 105, 112
Otter, dilatator iridis of, 33
Outer fibrous layer of retina, 53
Ox, ligamenturn pectinatum of, 21

PALATE, soft, 149
Palatine artery, 144
Palpebrae (eyelids), I
Palpebral arteries, 5, 16
conjunctiva, 4
fascia, 2, 3
ligament, 2, 3
Papilla (nipple) foliata, 149

fungiform. 148
lacrimalis, i, 9
optici, 55, 59

vallatse (vallum, rampart),
Papillary arteries, 55
Pars choroidalis iridis, 31

ciliaris retinae, 35, 54, 60
iridica retinae, 31, 35, 54
lacrimalis, 9
retinalis iridis, 31
Peribulbar nerves, 151

INDEX AND GLOSSARY TO VOLUME III. PART III.

163

Perilymph, 98, 104, 113
Perivascular lymph-space, 26, 56
Petit, canal of, 59, 62, 66
Petrosal artery, 97

nerves, 97

Petroso-squamosal fissure, 84
Pctro-ty in panic fissure, 81
Phalangeal process, 122
Phalanges, 122
Pharynx, 148

lateral recess of, 87
Pigment granules, 50

Pigmentary layer of retina, 38, 50, 52, 53, 54
Pillars of iris, 21
Pinna, 71

ligaments of, 74

muscles of, 75

nerves of, 76

structure of, 72

vessels of, 76

Pituitary (pituita, phlegm or mucus) mem-
brane, 139

Planum semilunatum, 108
Plate, fibrous tympanic, 79
Plexiform layer of retina, 41
Plexus annularis, 22

episcleral venous, 17

fundamental nervous, of cornea, 22

marginal, 7

subepithelial nervous, of cornea, 22

tympanic, 83, 97

venous, of nasal fossne, 140, 145
Plica (fold) semilunaris, 2, 10
Pore, gustatory, 150
Porus (passage) opticus, 36
Post-tarsal veins, 6
Posterior chamber of eye, 66

elastic lamina, 19

hyaline layer of iris, 33

limiting layer of iris, 33

tarsal glands, 4
Pouches of tympanum, 96
Pretarsal veins, 6
Primary optic vesicle, 50
Process, caudal, 74

phalangeal, 122
Processes, ciliary, 23, 24, 29, 54, 60

of incus, 90

of malleus, 90
Processus brevis, 90

cochleariformis, 86, 94

Folianus, 90

gracilis (slender), 90, 92

lenticularis (dim. of lens), 90

obtusus, 90

orbicularis, 90

sphenoidalis, 133
Promontory, 83, 96, 102
Pseudo-nucleus, 51, 121
Punctum (small hole) lacrimale, I, 8
Pupil (pupa, small image ; referring to reflected
image seen on looking into eye), 31

dilatator muscle of, 32

sphincter muscle of, 32
Pupillary membrane, 34. 66
Purple, visual, 35, 48, 50
Pyramid of tympanum, 85, 94

of vestibule, 99

QUADRATE cartilages, 132

RABBIT, olfactory epithelium of, 141

organ of Jacobson of, 144

papilla foliata of, 149
Radial fibres, 50
Radii of eyeball, 15

of lens, 63

Rami of auditory nerve, 108
Raphe (^o^, seam) of semicircular canal,

no
Recess, lateral of pharynx, 87

spheno-ethmoidal, 138
Recesses of posterior chamber, 62

of tympanum, 96
Recessus cochlearis, 99

epitympanicus, 80, 81

utriculi, 104

Recklinghausen, canals of, 18
Reissner, membrane of, 113, 118, 127
Reptiles, bipolar cells of retina of, 44

ellipsoid of, 49

lagena of, 114

olfactory cells of, 142

retinal cones of, 49
Reticular lamina, 119, 121, 122
Retina (rete, net), n, 14, 35, 154

epithelium of, 46

hexagonal cells of, 24, 35

intercommunications of elements of, 56

layers of, 38, 52

lymph-spaces of, 56

structure of, 38

sustentacular tissue of, 50
Retzius 011 gustatory cells, 151
Rhodopsin (f>o5ov, rose ; fyis, appearance), 35,

48

Riolan, muscle of, 2
Rivinus, notch of, 81, 82, 93
Rod-bipolar cells, 43

-ellipsoid, 49

-fibre, 46, 57, 154

-granules, 46

Rods of Corti, 119, 120, 127
Rods, retinal, 46, 47, 50, 52, 54, 57, 154
Rosenmiiller, fossa of, 87

Riidinger on articulation of auditory ossicles,
91

SAC, lachrymal. 7, 9 '

Saccule, 98, 104, 105, 109, 112, 114

nerve of, 108

Saccus endolymphaticus, 105
Salpingo-palatine fold, 87
Salpingo-pharyngeal fold, 87
Salpingo-pharyngcus muscle, 89
Salpinx (ad\-irtv£, trumpet), 86
Santorini, fissures of, 74, 80
Sappey on ligament of Tenon's capsule, 1 1
Scala (staircase) tympani, 83, 102, 104

vestibuli, 99, 102, 104
Scarpa, ganglion of, 108
Schlemm, canal of, 21, 34, 66
Schneiderian membrane, 139
Schultze on fovea centralis, 52
Schwalbe on bacillary layer, 50

on canal of Schlemm, 22

on funiculus sclerse, 17
Sclerotic (a-KXrjpos, tough) coat, II, 13, 16, 21,

30

Semicircular canals, 98, 99, 100, 105, 109
Sense-epithelium cells, 151

164

INDEX AND GLOSSARY TO VOLUME III. PART III.

Septum mobile, 130

misi, 130, 142, 145
artery of, 144
cartilage of, 132

orbitale, 3

transversum of ampullte, 105, 1 10
Sheath, perivascular, 26, 55
Sheep, ligamentum pectinatum of, 21
Sinus (hollow, bay) circulus iridis, 21

frontal, 136, 139

lateral, 85

of Maier, 9

of membranous labyrinth, 104

sphenoidal, 139

tympanic, 84

of utricle, 105
Spaces of Fontana, 21, 66
Spheno-ethmoidal recess, 138
Sphenoidal sinus, 139
Spheno-maxillary muscle, 4
Spheno-palatine artery, 144
Sphincter (<r<f>tyy<a, bind) pupillte, 32
Spider-cells, 40
Spina tympanica, 93
Spine of helix, 74
Spines, tympanic, 81, 82, 93
Spiral canal of cochlea, 102

ofmodiolus, 104, 124

ganglion, 109, 124, 152

groove, 115

lamina of cochlea, 102, 103, 124

ligament, 113, 117, 119
Spongioblasts, 44, 45
Spot, yellow, 35, 40
Spur of malleus, 90
Stapedial artery, 91
Stapedius muscle, 85, 94, 95, 98

bone of, 94

Stapes (stirrup), 83, 89, 91, 94, 95
Stensen, canal of, 138
Stilling, canal of, 38, 59
Stomata (<rr<J;ua, mouth) of iris, 31
Stratum bacillorum (bacillum, small staff) 8,

46, 47, 54
granularum externum, 38, 46, 52, 53, 54

internum, 38, 41, 52, 54, 57
of horizontal cells, 45
nigrum, 38, 50, 52, 53, 54
opticum, 38, 52, 54
reticulare internum, 38, 41, 43, 44, 52, 54,

57

externum, 38, 43, 45, 47, 52, 57
Stria (flute of column) vascularis, 119
Stroma iridis, 31
Stuart, on hyaloid membrane, 58
Substantia propria of cornea, 1 7
Sulcus (furrow) olfactorius, 138
sclerse, 10, 17
spiralis, 115
tympanicus, 78
Suspensory ligament of eye, 12

of lens, 24, 31, 59
Sustentacular cells of taste-buds, 150

fibres of ampullary epithelium,

112

tissue of retina, 50

TAPETUM, 25
Tarsal arches, 5

cartilage, I, 2, 12

glands, 3

Tarsal — continued.

ligament, 2, 3, 10
posterior, 4

Tarsus (rapa-os, wing), I, 2, 12
Taste-buds, 148, 149, 150
Taste-hair, 151
Taste-organs, 148

literature of, 151
i Tectorial (tectorium, cover) membrane, 120, 123,

127

Tegmen (cover) tympani, 81
Teleostei, cone-fibres of, 47

end-knobs of retina of, 46
Tenon, capsule of, n
Tensor choroidese, 30
palati, 87, 88
tarsi, 9, 10

tympani, 81, 86, 93, 94, 95, 98
Thin on lens-fibres, 65
Tongue, 148

Tractus spiralis foraminulentus, 102, 108, 124
Tragus, 71

muscle of, 75

Transverse muscle of pinna, 75
Tube. Eustachian, 80, 81, 86, 94, 96
muscles of, 88
vessels and nerves of, 88
Tuber cochlea, 83
Tubercle of Darwin, 72
Tuberculum supra tragic um, 71
Tubes, corneal, 18
Tunica choroidea, 23

propria of semicircular canals, no
Kuyschiana s. chorio-capillaris, 27
sclera, u

uvea s. vasculosa, n, 23
vaginalis oculi, 1 1
Tunnel of Corti, 119, 125
Turbinate bodies or Turbinals (turbo, whirl,

twist), 134, 137, 142, 145
Turner on olfactory organs of mammals, 130
Tutamina (tutamcn, means of protection)

oculi, i

Tympanic artery, 97
bone, 79
cells, 8 1
membrane, 78, 79, 81, 90, 93, 95,

96,98
nerve, 81
plate, fibrous, 79
plexus, 83, 97
spines, 81, 82, 93
sulcus, 78
Tympano-inalleolar folds, 82

ligaments, 82
Tympanum (drum), 71, 80. See also TYM-

PANIC.

glands of, 96
mucous membrane of, 95
muscles of, 93
nerves of, 97

recesses or pouches of, 96
secondary membrane of, 83, 104
vessels of, 97

UMBO (boss of shield), 82

Utricle, 98, 99, 104, 108, 109, 112

Uvea (Lat. rendering of ^ayoeiS^s %n -d)v = tunica
uviformis, choroid and iris together being
compared to the skin of a grape, uva), 35

INDEX AND GLOSSARY TO VOLUME III. PAKT III.

165

VAS spirale, 117
Vasa vorticosa (whorled), 26
Vascular coat of eye, 23
Veins of choroid coat, 26

of ciliary processes, 30

of cochlea, 126

of cornea, 22

of eyelids, 6

of external auditory canal 79

of iris, 34

of labyrinth, 109

of lachrymal gland, 8

of nasal duct, 10
fossae, 145

of pinna, 76

post-tarsal, 6

pretarsal, 6

of retina, 55

of sclerotic coat, 1 7

of tympanum, 97
Venae vorticosse, 15
Ventricle of nares, 139
Vertebrates, sensory cells and fibres of, 152
Vesicle, primary optic, 50
Vessels. See ARTERIES, VEINS, LYMPHATICS.
Vestibule, aqueduct of, 99

Vestibule — continued.

of labyrinth, 83, 98, 99

of nasal fossre, 138
Vibrissai, 130, 138
Visual cells, 46, 154

purple, 35, 48, 50
Vitreous body or humour (humor liquid), II,

38, 58
Vomerine cartilage, 133, 144

WAX of ear, 79, 80

YELLOW spot, 35, 40, 47, 52, 55

Jf, zonula (dim. of zona, belt) of, 59
Zona arcuata, 117

pectinata. 117
Zone, nuclear, of lens, 65

of oval nuclei, 141

of round nuclei, 141
Zonula ciliaris, 59

of Zinn, 59
Zuckerkaudl on ethmoidal fissures, 136

END OF PART III.

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