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IX. On the Structure and Development of the Skull in the Pig (Sus scrofa).
By W. K. Parker, F.R.S.

Received May 17,—Read June 19, 1873.

My intention for some time past has been to follow up the Morphology of the Fish’s
skull by that of the Mammal; and as amongst the “ Placentalia” the Guineapig (Cavia
aperea) takes a very low place, it was chosen as the type to work out. I have been led
to change my plan, however, and to take a medium type by an unexpected supply of
materials kindly put into my hands, in November 1871, by my friend Mr. CHARLES
Stewart; these were about seventy embryos of the Common Pig, a considerable number
of which were barely two thirds of an inch in length, whilst others measured 6 inches
in a straight line from the snout to the tuberosity of the ischium*.

As the tissues in the earlier stages were only in a nascent condition, the greatest care
has been taken to harden them for slicing into sections and for dissection from without
inwards; and no labour has been spared in this matter the sections being made after
the hardened embryos had been imbedded in solid paraffin. These extremely thin objects
were coloured with an ammoniacal solution of carmine, and then transferred to slides,
on which they were mounted in acid glycerine. The coarser sections of the larger
embryos, to be used as opaque objects, were made without imbedding, after the specimens
had been immersed in a dilute solution of nitric or muriatic acid, to which had been
added some chromic acid}; in the former way I have been able to obtain views of the
tissues of the earliest stage under a magnifying-power of as much as 600 diameters,
although about 50 diameters has been found to be the most useful, showing, as such a
lesser enlargement does, the various parts in relation to each other, and enabling the eye to
follow the granular thickenings which are becoming differentiated into special tissues.

The study of this particular type of Mammalian skull has been facilitated by prepa-
ratory work in many other types of this Class, extending over a period of thirty-three
years; but I have determined not to bring any thing forward relating to special modifi-
cations until this more exhaustive piece of work has seen the light.

The first impulse in this direction was given me by an invaluable work which appeared
long ago; I refer to W. CueseLpen’s ‘ Anatomy of the Human Body’ (London, 1722,
8vo). But my newer stand-point is from the ‘Elements of Comparative Anatomy’
(1864), by Professor Huxtuy (Lecture 7th to the end).

* The actual length of these embryos, measured along the curved line of the spine to the end of the tail, is
about one half more than is given by my practical and easier method of admeasurement.

+ All the finer sections and preparations were made by my son, Mr. T. J. Parker.
MDCCCLXXIV. 2Q

290 MR. W. K. PARKER ON THE STRUCTURE AND

Since the older writer, no native anatomist has arisen more fitted to hold and to
handle this difficult subject than the author of those ** Lectures.”

I shall follow up this matter from point to point in the same manner as that pursued
in the papers already offered to the Society; and my endeavour is to link on paper to
paper so that they may form an organic whole, the idea and purpose being the same in
each, and the special mode of treatment the same.

In the present communication more re/ative anatomy has been given than in the
former papers; I have to steer between the confusion arising from the display of too
many parts, and the baldness of a mere account of skeletal structures.

If the nasal and auditory sense-capsules were as easy of elimination as the eyeball, the
skull and face would present a much less complex problem; but they soon become part
and parcel of a most intricate cranio-facial unity, and everywhere intrude themselves
upon the observer.

A certain convenient subdivision of this especial piece of morphological work can be
made; thus we have—

Ist. The notochordal region of the skull.

2nd. The pronotochordal region of the same.

srd. The facial arches.

Ath. The sense-capsules.

The metamorphosis of the original and, as it were, /arval parts here obtains its highest
degree; the distance which has to be travelled by the morphologist between the starting-
point and the goal may be conceived of if the primary form (Plate XXVIII. fig. 5) be
compared with the finished condition of the skull (Plate XXXVI. fig. 4).

In observing the growth-changes that bring about this result, a large amount of
histological labour is involved; in the present piece of work that part of the research
has been taken pains with as much as if it had been intended to write upon the
tissues, and not upon their massing and arrangement. The determination of homo-
logous parts in this type, as compared with the elements that build up the skull of the
Fish, the Frog, and the Bird, has not been by any means the most difficult part of
my toil; they arrange themselves, and assume their own titles, in a very ready manner ;
for the difficulties of terminology will all melt away as soon as a sufficient number
of types have been traced down to their embryonic “ roots.” Many parts will have to
be re-named; but this will be easy work when the true reason for the change is made
plain.

As the skeletal parts are all composed of the various kinds of ‘* connective tissue,”
and as these kinds are intimately related to, and often pass insensibly into, one another,
it is not easy to keep to a consistent terminology in describing them.

This class of tissues becomes hardened by bone-salts at very different ages; and in any
homologous territory, if ossification is /ate, the tissue becomes hyaline cartilage first; in
other types the like tract may become beny, whilst, as yet, the tissue is extremely soft
and young: in intermediate conditions bone is formed in a tissue which is indifferent ; it

DEVELOPMENT OF THE SKULL IN THE PIG. 291

looks like hyaline cartilage, but the cells are crowded, and it is formed into bone before
the intercellular substance has time to appear*.

In the Mammal, more than in any other type, the original parts are all the more
completely transformed, in that the bony substance formed in the primordial cartilage
becomes very large in relation to its first model; and, moreover, the “ investing bones”
formed in the subcutaneous web become very large indeed, as compared with the small
granular territory, the soft model’ in which they first appeared.

Also in no other type do the primary facial rods become segmented, arrested, and
metamorphosed to the same degree as in this the highest vertebrate Class.

First Stage—Embryo Pig, 74 to 8 lines long.

The primordial skeleton of the most highly specialized Mammal is as simple as that
of the lowest brain-bearing Fish ; the form of the foetal head (Plate XX VIIL fig. 1) may
be aptly compared with that of the Fish and Frog (see my former papers on those types).
In embryos 7} lines in length the three brain-vesicles (C 1", C2, C3) are hollow,
the film of soft brain-substance merely lining the enclosing membranous cranium. The
foremost of the vesicles has budded into the two rudimentary hemispheres above the
primary sac, the “ thalamencephalon ” (Plate XXVIII. figs. 5 & 6,C1,C 1‘); yet at this
stage the cutis does not cover the whole of the third vesicle (C 3) nor the whole of the
auditory sac (au.). ‘The head is bent over upon the thin-walled thorax, and the cervical
region of the spinal chord is very outbent and swollen (fig. 1).

The Visceral Clefts.—After noticing the brain-vesicles and the three pairs of sense-
capsules (0/., é., au.), the foundations of which are already well laid, the eye detects that
peculiar dehiscence of the facial wall, the continuous face being cloven by the formation
of a series of slits or cuts, which pass quite through the substance of the cheek and neck.
By the older embryologists these are counted from behind the mouth; but in my last
paper, especially, I have shown that the mouth itself is a great, double, completed cleft,
and that there is a secondary cleft in front of it, the * palato-trabecular ” or preoral cleft
(cl.1). But the “ first postoral ” is in reality the second cleft; this is the largest in the
embryo pig, with the exception of the mouth. Behind this there are three others; and
the first of these, the ‘‘ second postoral,” is the counterpart of the most anterior of those
through which the water-currents pass in the osseous fish. Below and behind the
clefts the fore limb is seen in rudiment. Here it will be seen that there is a deficiency
in the number of clefts behind, as compared with the gill-bearing vertebrates (see papers
on Frog and Salmon). Only the first ‘ postoral” cleft is persistent and functional, the
three behind soon closing in. I shall describe, anon, what becomes of the persistent
clefts, that in front of and that behind the great mouth-cleft. Between the clefts are
formed the arches; these facial bars have some resemblance to ribs, but are formed
independently of axial parts, whereas the ribs are evident downgrowths from the ver-
tebral portions of the “* Somatomes.”’

* See on this subject, ‘On the Connective Tissues,” by A. Rotzerr, in Srricxer’s ‘Human and Comparative
Histology,’ translated by H. Powxr for the New Sydenham Society. London, 1870, pp. 47-146.

2Q2

292 MR, W. K. PARKER ON THE STRUCTURE AND

Where the facial arches most closely imitate ribs, as in the first and second postoral,
the “capitulum” and the “tuberculum” are applied to a part to which they have no
proper morphological relation—namely, to a sense-capsule. ‘This is one of the many
modifications the morphological elements are subjected to in the cephalic region.

The original pattern of the facial system of a vertebrate is simple in the extreme; the
paired rods are accurately like each other, but their development is not quite synchro-
nous; the secondary preoral pterygo-palatine ( p.pq.) is overshadowed and slow in growth
(see Plate XXVIII. fig. 2, where the arches are drawn as though the object were trans-
parent)*. The facial thickenings between the clefts which contain the arches may be seen
with considerable clearness, especially in front (fig. 3); here in front of (above) the mouth
towards the mid line we see the clubbed ends of the trabecule (¢7.) roofed over by the
nasal sacs. Below and somewhat behind these are the pterygo-palatine arches ( p.pq.),
in the thick outer wall of which the maxillaries and malars will be developed, and the
pith of which will become, by early ossification, the palatine and pterygoid bones,
Below the inferior, transverse, large mouth, the thickenings which contain the first and

second postorals are seen—Meckelian and hyoid. The cleft which is formed between
the trabecular and the pterygo-palatine bars is best seen in the side view (figs. 1 & 2, e/.1);
it opens in the inner canthus of the eye. The two pairs of preoral rods will be best
understood by reference to a palatal view of the skull with the postorals cut away (fig. 4),
and to the diagrammatic view of the skull and face as seen from below (fig. 5). It is
easy to see, by a reference to the palatal view (fig. 4), that we are now standing on the
same level as the “ Dipnoi” amongst the Fishes; the external nostril (¢.7.) and the
internal (é.7.) lie on the same plane ; a free intervening growth of cartilage, binding
the arches together, with no further metamorphosis of the parts, would produce a true
parallel to the skull of those remarkable Fish. The sinuosities of the upturned palate
(fig. 4), its plaits and its crevices, are easily understood by reference to the diagram
(fig. 5).

First Preoral Arch.—The trabecular rods form together an elegantly lyriform struc-
ture; they already have begun their extensive ‘‘ commissure,” being parallel now in
their fore half. Behind, they are like callipers, and the blades are at some distance from
each other; their apices, sharpened off, seem to approach the fore end of the investing
mass (7.v.); but a sectional view (fig. 6, t7.cm., 7.v.) corrects this error, and shows that these
diverse parts lie on a, totally distinct plane and far from each other, a fact I pointed out
long ago in my paper on the Frog (Phil. Trans. 1871, Plate m1. p. 145). ‘These trabe-
cular blades embrace the pituitary body (py.); but their curve does not conform to
its shape, and is altogether independent of it, being the proper ‘ habit” or morpholo-
gical fashion of the arch. After forming the elegant, pyriform, primordial pituitary
space, the trabeculae become thicker, narrower, and lie closely side by side; this is soon
followed by fusion of their edges—the formation of the trabecular commissure (see
Plate XXIX. fig. 4, tr.em.). These two rods do not end as a straight bar, but in front

* In my paper on the Frog (Phil. Trans. 1871, p. 148) the pterygo-palatine arcade is described as a secondary
structure ; in that on the Salmon (bid. 1873, p. 109) it is spoken of as independent. Jt as a secondary arch,

DEVELOPMENT OF THE SKULL IN THE PIG. 293

are bent upon themselves, as the fingers in clutching ; hence the transverse crevice seen in
the palate between the inner nares (fig. 4, ¢.n.c., t7.). This retral growth of the trabecular
““cornua” is not so pronounced in the Frog (Phil. Trans. 1871, Plate v.), but is equal to
the Mammal in the Bird (‘* Fowl’s Skull,” Phil. Trans. 1869, Plate Lxxxt. figs. 1 & 2, ¢r.).
The median part of the upper lip, which is transverse and quite rudimentary in the
youngest embryo (fig. 3, w./.), has developed in a somewhat older specimen (fig. 4, pn.)
into a pointed retral flap. This flap hides an azygous projection of the trabecular com-
missure, the “prenasal cartilage;” this axis of the premaxillaries is a part largely developed
in Birds (see * Fowl’s Skull,” Plates LXxx1.-111. pn.), where it is first retral, then vertical,
and then foreturned, so that it is the principal factor in the exaggerated prognathism of
that Class. Outside this process the trabecular cornua are at present clubbed and bulbous
(Plate XXVIII. figs. 5, 4,&5,¢.¢r.) ; afterwards they each send backwards a recurrent rod *.
The general appearance of the trabecule, as seen from above, is shown in Plate XXIX.
fig. 4; their varying thickness is displayed in sections (Plate X XIX. figs. 1, 2, 3, & 5, é7.).

Second Preoral Arch.—KEyen in the Osseous Fish I found the pterygo-palatine arch
both /ate and feeble in its development ; in the Frog it is a long time before it appears,
and grows very slowly, and is never more than a long conjugational band between the
trabecular and mandibular rod. In the Mammal, as in the Bird, this primarily feeble
rod is ossified hurriedly, as it were, before the cells can acquire any intermediate sub-
stance (see ‘‘ Fowl’s Skull,” Plate nxxxi. figs. 1, 6, & 11); yet in the present instance
the bony plates that arise in and around these small sigmoid granular rods are some of
the most complicated and the most massive in the whole head and face. Even through
the palatal skin the hooked tops of the preoral arches can be seen (fig. 4); but whilst
those of the trabecule grow ‘nwards, those of the pterygo-palatine bars grow upwards
and outwards, persistent in the “hamular process.” The direction of the whole bar
(Plate XXVIII. figs. 4 & 5, p.pg.) is downwards and forwards, and their extremities or
“cornua” approach each other below the trabeculwe: they are at present far apart in
this originally cleft palate (figs. 4& 5); the fold of mucous membrane covering each on
its inner side gradually grows towards its fellow, and they eventually meet and coalesce.
The thick cushion outside each bar is the nidus in which the maxillary and malar are
developed; and the whole maxillo-palatine mass is a mere process or outgrowth of
the first (postoral) arch, and is not an independent morphological region. At present the
arch is subocular; but it does not correspond to the subocular bar of the Tadpole
(‘* Frog’s Skull,” Plate v.), which is formed by the extremely long pier of the mandibular
arch, the arrested conjugational pterygo-palatine lying quite in front of the eyeball.

* The distinctness of these rods from the surrounding tissues is purposely exaggerated in the accompanying
illustrations, for they are imbedded in a gelatinous tissue rich with enclosed granules or young cells, whose
protoplasmic substance takes up the carmine very freely; and the differentiation of these rods is at present a
matter of degree, that part of the blastema which will become hyaline cartilage being the most compact and
crowded with young cells; next to this the nascent perichondrium; and the most gelatinous part outside is the

rudimentary condition of the loose stroma or areolar connective tissue.

294 MR. W. K. PARKER ON THE STRUCTURE AND

In this stage a section of the head (affected as it is by the “ mesocephalic flexure”)
which passes through the first cerebral vesicle and its upgrowth takes the pterygo-
palatine rods almost from end to end, whilst the trabecule are cut directly through
(Plate XXIX. fig. 5, tr. p.pg.). Thus, as compared with the trabecular apices, the pterygo-
palatines descend a little before they send upwards the apical hook.

Third Arch, or First Postoral——Yhis rod, like its immediate successor, is stout,
sigmoid, and strongly inhooked above; it does not at present meet its fellow at the
mid line. This is the primordial mandible, in.; but it remains as the lower Jaw for a
very short time, and is not segmented into an upper and lower piece. ‘There is a stage
in all the oviparous Vertebrata in which this rod is free from segmentation; but, above
the Lamprey, a pier and free arch are formed by subdivision of the bar. The tissue over
it is thick, and in this overlying part the persistent mandible is formed (see Plate
XXVIIL. figs. 1, 4, & 6, and Plate XXIX. figs. 5 & 6, mk.).

The morphological changes that take place in the hooked and inbent apex are of the
greatest interest ; for now we arrive at the point where not only the hyoid arch is arrested
and modified in relation to the outworks of the organ of hearing, but the mandible of
the embryo is also suddenly given up to these secondary correlations. Considered in
relation to their new function, the parts of the mandible of the mammal might, like
those of the upper part of the hyoid arch, be included in the stapedian terminology *.

The Meckelian rod itself is shown in the vertical section near its extremity (Plate
XXVIIL. fig. 6, mz.), and in the palatal view (fig. 4, mk.) near its apex ; near its apex it
is seen on the outside in the lateral view of the sliced head (Plate XXIX. fig. 6, mk.). But
horizontal sections of the head are necessary to show the relation of the apex of this bar
to the first postoral cleft, the rudimentary ear-drum cavity (see Plate X XIX. figs. 7, 8,
9, mk.). ‘These sections show that this very expanded cleft is being divided into two
spaces, one of which (the inner) becomes the tympanic cavity, and the other the “ meatus
auditorius externus.” ‘The septum or diaphragm is formed by the lining skin of the cleft
growing outwards from the side of the ear-sac, and inwards from the outer face; this
latter growth is the most intense, being pushed in by the ingrowth of the apex of the
embryonic mandible, which, growing inwards and backwards, carries the lining skin of
the cleft before it; thus the ‘membrana tympani” is formed. Looking at these
figures, we see at once that the ‘*manubrium mallei” is the hooked apex of the primor-
dial mandibular arch, and that therefore it must correspond with the large bifaceted
backwardly placed head of the Bird’s quadrate bone” f.

The shoulder or tuberculum of this rib-like bar becomes the thick head of the

* See “On the Representatives of the Malleus and the Incus of the Mammalia in the other Vertebrata,” by
Professor Huxtry, Proc. Zool. Soc., May 27, 1869, pp. 391-407.

+ I was under the impression that the ‘internal angular process” of the Bird’s mandible (‘ Fowl’s
Skull,” Plate rxxxt. fig. 13, ¢.a.p.) was the homologue of the manubrium mallei of the mammal; it is not; both
it and the posterior process (p.a.p.) are outgrowths formed lower down, and correspond in nature to the
‘‘opercular knob” of the next or hyoid arch.

DEVELOPMENT OF THE SKULL IN THE PIG. 295

hammer; the solid rod itself develops for a while, but by the time of birth has shrunk
into the feeble, pointed “ processus gracilis.”

Fourth Arch, or Second Postoral.—At present this arch is extremely like the one in
front of it (Plate XXVIII. fig. 5, and Plate XXIX. figs. 5 & 6, hy.); but it is flatter,
and the right and left bars meet more closely and at an obtuse angle; its shoulder,
also, is more upturned. This arch has been cut through in the palatal vertical views
(Plate XXVIII. figs. 4 & 6, hy.); but the form of its tuberculum and capitulum are
best seen in the horizontal section (Plate XXIX. figs. 7-10, hy.), and its shoulder or
tuberculum is exposed in the sliced head (Plate XXIX. fig. 6, hy.). In this latter figure
it is seen that the shoulder stands out like that of a Bird’s rib, the head or capitular
portion thrusting itself as far inwards as it can on to the periotic wall. The /andmarks
exposed in this figure are the portio dura and the top of the jugular vein (Plate XXIX.
fig. 6, hy., 7%, j.v.). In figs. 7, 8, & 10 of the same, Plate, the horizontal sections show
that the head of the hyoid growing towards the auditory mass is exactly like the head
of the mandibular rod. ‘The portio dura nerve is seen both at its entrance into and its
exit from the facial wall in this figure, and it is of the utmost consequence to the morpho-
logist as being a most safe landmark. In the outer lateral view it is seen escaping
behind that part of the hyoid rod which becomes the “ stylohyal” (Plate X XTX. fig. 6
hy., 7).

In one horizontal view (Plate X XIX. fig. 7, hy., 7°) its whole auditory course is seen,

’

on one side its entrance into the wall in front of the first postoral cleft, and its exit
behind the hyoid in the other; the same thing is shown in Plate XXVIII. fig. 8, 77
(see also Plate X XIX. figs. 8-10, 7"). In most of these figures the head and neck of
the hyoid are shown from above (Plate XXIX. figs. 7, 8) and from below (fig. 10, hy.) ;
but in another seen from above (Plate XXIX. fig. 9) the section is through the rods
a little lower down; and here we get a most instructive view, the shoulder evidently
becoming dislocated from the neck, a process which will go on to complete separation
of the parts.

Fifth Arch, or Third Postoral.—In this arch the Mammal has developed merely the
counterpart of the “ hypobranchial” segment of the first branchial arch; it is shown
in a subhorizontal section 7m situ attached to-the larynx (Plate XXIX. fig. 5, th.h., lv.),
and in the diagrammatic figure (Plate XXVIII. fig. 5, th.h.) is seen beneath the audi-
tory sacs. In my paper on the Frog (Plate vit. p. 171) I showed how that the thyrohyals
were the hypobranchial remnants of the first and second branchial arches developed
backwards; those of the Mammal are therefore strictly homologous with those of the
Frog, the latter being formed by retention of a part, which part is alone developed in
the former.

Looking again at the five pairs of facial arches as a whole, we see that the only arch,
at present, which has developed a conjugational keystone piece is the first or trabecular:
this is the “ prenasal rostrum” which figures so largely in my former paper on the
Bird’s Skull. No other keystone appears afterwards in the Pig, save in the last pair;

296 MR. W. K. PARKER ON THE STRUCTURE AND

this becomes the ‘“basihyal” of anthropotomy, but answers to the first “ basibranchial
of the Fish. These and the other “ conjugations” will be shown in the more advanced
stages.

The Notochordal Region and Membranous Cranium.—With the arrest of the soma-
tomic divisions in the cephalic region of the embryo, and the great modification of the
nerves of common sensation and of motion, we have no certain guide as to how much or
how little of the spine the notochordal region corresponds to. ‘The notochord retreating,
relatively, from the fore end of the investing mass and becoming in time the temporary
axis of a single basal bone, the basioccipital, although it gives a vertebral character to
its own territory, is yet placed by its altered conditions in a new category.

In my first stage I take the skull when it has been fully bent upon itself—the
‘“‘mesocephalic flexure ;” and at this time the large notochord (Plate XXVIII. fig. 6, ne.)
bends suddenly upwards, and ends in a free blunted point, exactly opposite that infolding
of the membranous cranium which partially severs the second from the third cerebral
vesicle (C2, C3). The investing mass stops short of the apex of the notochord and
lies beneath its plane. The relation of the two, as seen from above, is given in the hori-
zontal view (Plate XXVIII. fig. 8), and as seen from below, diagrammatically, in fig. 5.
The vertical section (Plate XXVIII. fig. 6) shows the notochord covered above with the
membranous cranium (dura mater and cells of the cutis), and bearing in its hollow
the medulla oblongata (m.0.) and the vesicular cerebellum (C3). The three structures
here seen behind the pituitary body (py.) form the primordial ‘ posterior clinoid wall ;”
and the rounded mass of delicate gelatinous stroma which hes above these three parts, in
the hilus of the kidney-shaped third cerebral vesicle, is the ‘*third or median trabecula”
of Rarike

morphological import*.

a structure quite temporary, as that excellent author ayerred, and of no

Only in the basal region is there at present any developed hyaline cartilage (Plate
XXVIII. figs. 5, 6, 8, and Plate XXIX. figs. 4 & 7, 2.v.), although it does appear in
large tracts afterwards infero-laterally, and even above also in the occipital region. At
present all but the notochordal region of the cranium is a very soft and delicate mem-
brane, inclosing the large blebs into which the great neural axis has developed. After-
wards this membrane will in certain parts split up into three strata—the dura mater
within, the granular territories in which the “investing bones” develop will le on
the outside, and in the middle the hyaline cartilage of the occipital and sphenoidal
regions. At present the skin is represented, but not thickened into distinguishable
dermis, over the third vesicle (Plate XXVIII. figs. 1, 2, & 6,C 5); afterwards this vesicle
will be entirely enringed behind, in the manner of a vertebra, the middle layer of the
membrane chondrifying directly upwards from the investing mass. But in the basi-
sphenoidal region only as much cartilage as was primarily related to the free end of the
notochord (namely, the ‘ postclinoid wall”) has any remnant in it comparable to a

* Raruke erred in supposing the “ paired rafters,” or symmetrical trabecule, to be outgrowths of- the
investing mass of the notochord.

DEVELOPMENT OF THE SKULL IN THE PIG. 297

vertebral structure; and the whole basisphenoidal territory, small as it isin the Pig, is
very compound, having its origin in the two apices of the investing mass, in the apices
and posterior end of the commissure of the trabecular rods, in a chondrified part of the
cranial wall (related to the investing mass merely by coalescence at its postero-inferior
angle), and, lastly, in a secondary growth of cartilage beneath the pituitary body. This
last growth of cartilage is found in Sharks and Batrachians, but not in Teleostean
Fishes nor in Lizards and Birds.

The basisphenoidal territory may be understood by drawing one imaginary line across
the end of the trabecular commissure (Plate XXIX, fig. 4, t7.cm.), and a second across
the apices of the investing mass, leaving a short tract in front of the posterior line; the
figure itself ends at this second line,

The cranial wall in the anterior sphenoidal region is altogether soft and gelatinous
at present (Plate XXIX. fig. 5, a section through the primary cerebral vesicle, thala-
mencephalon, and its two outgrowths, the heméspheres); beneath this part the trabe-
cular bands are now fairly differeutiated (¢7.), and these form the lower half of the
compound presphenoid, as we shall soon see. These are the three proper cranial regions,
corresponding to the cerebral vesicles, but not im any proper morphological sense
answering to the divisions of the body, the somatomes; no other segment can be found,
for the immense outgrowths of the first cerebral vesicle le upon the nasal roofs.

Even the posterior sphenoid loses what little relation it had to the notochord, which
is absorbed by the basioccipital, and is largely formed by borrowing substance from the
first facial arch ; but the anterior sphenoid is a mere chondrification of the middle layer
of the membranous cranium, the two wings mutually sending downwards an azygous
plate which coalesces with the common crest of the trabecular bars.

The Sense-capsules.—The extent of the olfactory region is at present very small;
afterwards the whole labyrinth takes up three fourths of the cranio-facial length. The
squarish septum (Plate XXVIII. fig. 6, s.7.) looks almost directly downwards beneath
the first cerebral vesicle, and the double roof of the labyrinth has the relation of an
eave to the cerebral roof. The most projecting kidney-shaped part of the nasal roof
is the “ala nasi;” and both lateral and front views of the embryonic head show how
this is, as it were, grafted on to the upper surface of the down-bent trabecular bars. A
ereat difficulty is got rid of here, which has cost me much trouble; for the alz nasi
are not formed out of the substance of the trabecule, nor can they be considered, in
the adult, merely the front and portico of the roof of the nasal labyrinth; they com-
pletely coalesce with the trabecular knuckles; and the rooting, ossified snout of the adult
Pig is of a compound nature, principally, however, formed of the genuflection of the
first visceral arch.

The passage from the outer to the inner nostril (Plate XXVIII. fig. 4, e.n., an.) is
already tortuous (Plate XXVIII. fig. 7, a vertical section beyond the septum nasi) ;
for already the mucous membrane has been thrown into baggy folds, into which soft
outgrowths of the roof are entering, afterwards to become a labyrinth of cartilaginous

MDCCCLXXIV. 2k

298 MR. W. K. PARKER ON THE STRUCTURE AND

coils. The bilobate mass directly above the trabecular horn (a/.td., 7.t6., ¢.tr.) has its

anterior lobe developed into the curious * alinasal turbinals” immediately within the
snout, whilst its hinder lobe becomes the long “ inferior turbinal.” The swelling below
the down-turned roof is the rudiment of the ‘nasal turbinal,” scarcely developed in the
adult of this type; and the mass which lies beneath the rudiment of the olfactory crus
(1) becomes the upper and middle turbinal (one mass in the Pig) and the true olfactory
region. Vertical sections* show, most instructively, what could in nowise have been
guessed at—namely, that the nasal labyrinth has its skeletal parts formed by the approxi-
mation and coalescence of two imperfect cylinders open freely below, and by these.
receiving at their junction below the ascending crest formed by the conjugated trabeculie
(Plate XXIX. figs. 1-3, al.s., al.é., tr.). When these trabecular bands continue flat
(as in the embryo, Plate XXIX. figs. 1 & 2, ¢r.), then we have, as in the Frog and the
Crow, a cartilaginous floor to the nasal passages (see memoir on “ Frog’s Skull,” Plate vir.
fig. 6, and Plate x. fig. 3, s.2.d.; and also Proc. Roy. Micr. Soc., Oct. 2, 1872, p. 224,
pl. 38. fig. 1, s.2.). In most Mammals, and in Birds not belonging to the Passerine
group, the trabecule narrow in to form the rounded thickened base of the whole * ethmo-
presphenoidal bar;” this process is seen to be beginning in the section through the
posterior part of the nasal region (Plate XXIX. fig. 3, #7.). The section through the
inner nares (Plate XXIX. fig. 5, én.) also shows the back wall of each nasal passage
(p.n.w.). These large rounded spaces are seen to have the rudiments of the last of the
middle turbinal coils already continuous with the end wall. ‘These posterior walls
correspond to the end of each * sphenoidal sinus ;” this is therefore the presphenoidal
region, and behind the mesoethmnoid; and the pyriform openings above were made
throngh the front of the cranium and through the fore end of the cerebral hemi-
spheres, where they bud-off the olfactory crus (see also Plate XXVIII. fig. 6, C 1% o/.).
This same section has cut through the first cleft (first preoral or lacrymal passage) on
its way to the nasal passage. ‘The anterior extremity of the, as yet, soft palato-pterygoid
rod (p.pg-) is here cut through, where it passes below the inner nostril (¢.7.). The
space between the rudimentary olfactory crus and the budding upper turbinal (Plate
XXVIII. fig. 6, ol., sm.) is composed, at present, of an almost structureless gelatinous
stroma; it is slow to form those cartilaginous bands afterwards, which, creeping between
the olfactory filaments, form the cribriform plate—a secondary morphological structure
almost entirely peculiar to the Mammalian skull.

The eyeball only affects the skull from without, by modifying the facial and cranial
structures to form its safe recess or orbit; but the earball is constructed after the
fashion of the old cottage oven, being built into the side walls of the skull, bulging out
on the outside, and having its nerve-mouth projecting also within.

In my last paper, on the Salmon’s skull, I was able to show the infolding of the

*® These vertical sections of the nasal region were made by the same slicing as the horizontal sections of the
head further back : this depended upon the hooked shape of the head at this stage ; the razor passed at right
angles to the nasal roof, but parallel to the notochord.

DEVELOPMENT OF THE SKULL IN THE PIG. 299

dermal layer to form the ear-sac, the cavity of which was wide open on the outer surface.
In this piece of work “it was my hap to light upon” embryos the youngest of which
were filming over this primordial ‘aqueduct ;” the skin (cutis) is incomplete over
the top (Plate XXVIII. figs. 1 & 2, au.), but the passage itself, leading into the rudi-
mentary labyrinth, is closed by a gelatinous plug. The periotic walls come as near to
cartilage, in their commenced solidification, as the investing mass and facial arches, and
the outline of the sacs can be fairly made out. Their general form can be seen by
referring to the horizontal views (Plate XXVIII. figs. 5 & 8, and Plate XXIX. fig. 7>
au.); but they are well outlined on the external surface (Plate XXVIII. figs. 1 & 2, aw.),
and they are seen to be tuberose bodies, having a straightish inner margin, a sublobular
outer margin, and their broadest end behind. ‘They are separated by the breadth of
the investing mass with its enclosed notochord, and this tract is narrowest in front.
When the upper face is slightly pared off (Plate XXIX. fig. 6, aw.), the opening of the
aqueductus vestibuli is shown; but this is best seen in a horizontal section, viewed from
below (Plate X XIX. fig. 10), where it is seen imbedded in the periotic wall inside the
**tegmen tympani” (¢.ty.); alittle behind it is seen the portio dura, which forms by its
boring the “ aqueductus Fallopii.” In the same figure the opposite side of the section
was made lower down, so that the roof of the tympanum (tegmen) is cut away, and
the tympanic cavity cut through, exposing the head of the second postoral arch and the
“aqueductus ” just above its entrance into the cavity of the ear-sac*.

The reader will observe that this passage has the appearance of being double; TI could
not, however, find more than one perforation. This opening into the auditory sac, which
is large in my first and second stages in the Frog, has closed in the third stage (‘+ Frog’s
Skull,” Plates mr. & tv. av.); in the Salmon (‘*Salmon’s Skull,’ Plate v.) it has not
closed in “ fry” of the first summer.

As for the cavity of the ear-sac, it is at present very rudimentary; the canals are but
beginning to bud out from the postero-superior region, and the cochlea is perfectly
ornithic (compare Plate XXVIII. fig. 8, ¢/., and Plate XXIX. fig. 7, c/., with “ Fowl’s
Skull,” Plate Lxxxu. fig. 1, e/.).

The sections show the larger nerves and vessels, which serve as excellent landmarks,
especially the trigeminal, the portio dura, the glosso-pharyngeal, the vagus, and the
hypoglossal nerves (5, 7%, 8, 8%, 9). The three last nerves all pass through soft stroma
in the angle between the auditory sac and the investing mass; the large vessels also
(‘basilar artery” and “internal carotid”) all he, as dense ensheathed masses of young
blood-corpuscles, in the most difuent stroma, the fluidness and instability of which makes
it an admirable “ soil” for these fast-growing countless * roots.” Before passing to the
next stage I must again refer the reader to the diagrammatic figure (Plate XXVIIT.
fig. 5), that he may compare it with what I have already described in the embryos of
the Fowl, Frog, and Osseous Fish at a similar stage. With the vantage-ground of this

* T have not been able to determine what relation this primary opening bears to the “ aqueductus cochle,”
or whether it is related to it at all.

2R2

300 MR. W. K. PARKER ON THE STRUCTURE AND

simple platform it will be easy to follow the metamorphosis of the primordial parts,
even in the Mammal, where such changes are most of all displayed, and to compare
and harmonize them with the lesser degrees of transformation to be seen in Fowl, Frog,
and Fish.

Second Stage—Embryo Pig, 1 inch long.

Most of my illustrations of the complete embryonic skull will be made from a some-
what more advanced stage than this; but this second stage is of great importance in
illustrating the morphology of the facial arches and auditory sacs *.

In this embryo chondrification has fairly set in, although the cells of the hyaline
cartilage are still close together, quite as close as in the nidus of the vomer in the
next stage, or the tissue in which the rostrum of the parasphenoid is developed in the
embryo bird (* Fowl’s Skull,” Second Stage, Plate Lxxx1. fig. 7, r.st.). Ossification has
commenced also, and can just be seen in the nidus of the vomer, maxillary, and dentary ;
this last is the forwardest of the bony plates (Plate XXX. fig. 2,d.). Beginning at the
snout we see that the ale nasi have chondrified, and that the retral trabecular horns
(Plate XXX. fig. 1, a.n., ¢.tr.) have coalesced with them: the little papular prenasal
cartilage (p.n.) is well seen in this front view; beneath this, a little further back, the
stroma becomes dense on each side and forms the premaxillary territories, and is ready
to ossify. In the deepest and widest part of the ethmoidal region, a vertical section of
which (Plate XXX. fig. 2) shows the commenced ingrowing of the proper turbinal folds,
we see now that the descending nasal roofs and the ascending trabecular crests have
all coalesced together to form the large mesoethmoid (m.eth.). A long scoop-shaped
territory lies immediately under the trabecular base of this septum, and this granular
tract is undergoing endostosis; it is forming the vomer (v.). Far on each side, above a
rudimentary tooth-pulp, is a faint trace of the maxillary (ma.). In this “schizognathous”
stage the root of the tongue is seen at no great distance from the freely exposed vome-
rine region, and the oral cavity (m.) has here steep sides, in the walls of which the
primary palatal bars ( p.pg.) are seen as compressed granular plates. On each side,
below an inferior tooth-rudiment (¢.), a large mass of nascent cartilage is seen, having a
kidney-shaped section ; and inside this a round rod of cartilage is seen, converging towards
its fellow of the other side as it passes forwards. If my observations had ended here,
the thick slab of granular tissue, with its incurved edges, would have merely been noticed
as the proper dentary territory or nidus of the mammalian mandible; it is more than
this, as the next two stages will show: the “rod” is MEcKEL’s cartilage (m/.), the shaft of
the first postoral arch. The dentary bone itself appears in this section, and is of a
rich rose-colour in the preparation, one stained with carmine ; the tissue around the
osseous deposit is becoming colourless, like MEcKEL’s rod, for the carmine scarcely tints
the cartilage. ‘The other postoral bars are shown in this section; the ‘‘ cornu minor”

* From a large number of exquisite sections of this stage I have only made the six illustrations here given ;

for what the rest show is better seen in a somewhat more advanced stage, the morphological level being essen-
tially the same.

DEVELOPMENT OF THE SKULL IN THE PIG. 301

(e.hy.) is cut through near its junction with the long stylohyal, and the “ cornu major ”
(4r. 1) is shown in its whole extent on each side; whilst between we have the basal
piece (4.b7.), not, truly, a basihyal, but answering to the first basibranchial of the Fish.
The larynx (/x.) is below and behind them, and behind it is the cesophagus (@.).

Another section (Plate XXX. fig. 5), taken further back than the last, shows the sphe-
noidal, auditory, and occipital regions as seen from above. ‘The differentiation of parts
has gone on very rapidly, whilst the embryo has merely become longer by one half, and
the difficulties in the way of interpretation are largely removed.

In front the “ anterior clinoid wall” (a.c/.)is seen to be symmetrically divided at the
mid line; this is the junction of the trabecule at the end of their long commissure, in
front of the outbent blades which pass around the pituitary region. The pituitary cup
is deep, wide, narrow above, and has a crescentic form, the concavity of which looks
forwards. Between this actual cavity and the free ascending ends of the notochord and
investing mass there is a large amount of gelatinous tissue, through which the wavy
internal carotids (7.¢.) pass, converging and again diverging. ‘The gelatinous tract, the
base of the so-called “ middle trabecula” (see Plate XXVIII. fig. 6, m.tr.), is widest. close
to the ear-sacs, and narrows to the edge of the pituitary pit; on each side of it is seen
a bulbous mass, the Gasserian ganglion (3). On each side of the extremity of the
notochord and investing mass are seen the well-defined ear-sacs, which are here cut
through in their cochlear region; the coz/s are now well developed. On the left side
the section is behind and below that shown on the right, where the ‘‘ malleus” or head
of the first postoral is cut through, the shaft of the second arch, and the ‘“ meatus
externus” and outer ear. Part of a similar section, taken lower down (fig. 4), displays
the orbito-sphenoids in section (with their upper part cut away); and where they have
coalesced with the trabecular commissure, there the optic nerves (2) are crossing. ‘The
alisphenoids (qa/.s.) are sections seen in their whole extent, but not their connexion
with the basisphenoid, the notochordal region of which is displayed, backwards to
where the basioccipital territory begins.

At a lower level closely packed cells are developing into cartilage, which will form
a secondary floor to the pituitary body, the seat of the ‘sella turcica;” then the poste-
rior sphenoid will be morphologically complete. The connexion of the two great post-
oral bars with the auditory capsule will be better understood by two more sectional
views similar to the large figure (Plate XXX. fig. 3), but of more limited extent and
more highly magnified: all these figures are made from the antero-inferior aspect of the
up-tilted basis cranii, the sections, which in the nasal region were vertical (figs. 1 & 2),
being horizontal behind. Such a section (Plate XXX. fig. 5) through the outer ear or
concha (ca.) and head of the first postoral bar shows how curiously incurved this capitular
portion is, and how that its apex is developed into an orbicular part, like that on the
apex of the next bar. The shoulder, which articulates with the upper part of the
next bar, is very bulbous, and at the root of the neck a conical boss is sent outward ;
the shoulder is the head of the malleus, the boss is the process for attachment of the

302 MR. W. K. PARKER ON THE STRUCTURE AND

tensor tympani muscle, and the rest of the neck with the rounded head is the
‘“‘manubrium mallei” (mé.). The dark jagged space is the tympanic cavity, a development
of the first postoral cleft, and which runs forwards into the mouth-cleft as the Eusta-
chian tube. Now it is easy to see how the membrana tympani is formed; for the
inhooked apex of the mandibular rod, creeping like a tendril toward the auditory sac,
necessarily carries with it the liming membrane of the cleft wrapped over its head.
The shaft is not shown here, because it has been severed with the fore part of the
shoulder or “ tubercular” portion.

On the left side of the larger figure (Plate XXX. fig. 5) the fellow of this is seen, but
cut away further backward. Below the “ manubrium” is seen the shaft of the next arch
(now to be called stylohyal); its direction is downwards and forwards to the root of
the tongue; a good distance must be supposed between this and the section through the
ceratohyal already described (Plate XXX. fig. 2, e.hy.).

The outer ear or concha (ea.) is fast passing into cartilage ; it is curiously folded upon
itself, and runs round the external orifice of the cleft; it is much modified already
from its Batrachian and Plagiostomous prototypes, the “annulus tympanicus” of the
former, the “ principal opercular” of the latter. ‘The interest attached to the vegetative
gemmation of the membrana tympani is more than rivalled in the metamorphic
changes that take place in the succeeding arch and in the neighbouring territory of the
ear-sac. In the first stage we saw that the simply oval primordial ear-pouch was deve-
loping into a lobular form, and that there were three bulgings on the outer side of the
sac (Plate XXVIII. figs. 5 & 8, au.). ‘The middle of these, by a process of gemmation, has
freed itself to a great extent from the wall of the ear-capsule, thus forming a “ fenestra”
in that wall, which, however, is closed by the separated nodule of cartilage. This twin
bud (Plate XXX. fig. 6, st.) (it has two papular elevations which look forward and out-
ward from its free surface) is covered externally by delicate indifferent tissue, ready
to become cartilage. Being in the posterior wall of the first postoral cleft, the second
arch (hyoid), whilst sending its orbicular head inwards, does not become infolded in the
mucous membrane lining the cleft, but is free to creep, tendrilwise, to the surface of
the ear-sac; this it does, and conjugation takes place between its orbicular “ capitulum”
and the freed auditory bud. But in the first stage we saw that a curious kind
of segmentation was taking place through the shoulder of the second postoral bar
(Plate XXIX. fig. 9, hy.); now that process is much more complete, and the simple bar
has undergone a process the exact counterpart of that by which the blade of the orange-
leaf articulates with its petiole: whilst this has been going on, a rounded “ tuberculum,”
distinct as that in the rib of a bird, has been developed on the detached upper segment
(Plate XXX. fig. 6, s.c.7); this is the “ short crus of the incus ;” the neck growing towards
the ear-sac is the ‘‘ long crus” (/.¢.7.); its expanded, conjugating end the nidus of the “ os
orbiculare;” the ha/f-shoulder above is the body of the incus, which articulates with the
shoulder of the arch in front (Plate XXX. fig. 3, 7.,m.); and the bigeminal segment of the
auditory sac is the young stapes (st.). The other half of the shoulder, or tubercular

DEVELOPMENT OF THE SKULL IN THE PIG. 30.

part of the rod, is continuous with the long descending part of the arch (see Plate XXX.
fig. 9, st.h.); it is the head of the stylohyal. Here we see that the second postoral
arch grafts its capitular portion on to the auditory segment, and splits its tubercular
portion into two new condyles, one of which, covered by the squamosal on the outside,
articulates with the tegmen tympani; whilst the other, retreating very sensibly,
coalesces with the ear-sac further backwards and downwards, close in front of the exit
of the portio dura nerve. In the figure these parts are continuous; but the continuity
is kept up at present by new cells, and these younger cells are all soft indifferent tissue
as yet; their morphological differentiation will be explained in the next stage*.

Behindthe stylohyal and some distance outside the promontory (pr.), the portio
dura nerve (7”) is seen in section, an excellent land-mark for the stylohyal; further
backward the compound 8th nerve (8%, 8’) is seen in the “foramen lacerum posterius”
(f-l.p.); the hypoglossal (9) is enclosed in the upgrowing exoccipital cartilage (Plate
MX. figs. 3; 9; ¢.0.).

The relation of the auditory sac to the exoccipital (¢.0) is shown in fig. 7; the whole
arch of the horizontal canal is seen shining through the cartilage, and its ampulla is
obscured by the fibres of the portio mollis nerve (7’); the Gasseran ganglion, and the

compound 8th nerve are also severed (5, 8%, 8’).

Third Stage-—Embryo Pig, Ly inch in length.

Those metamorphic processes which were rapidly proceeding in the last stage have
become very complete in this, where the embryo is one third longer: this stage must be
copiously illustrated and described at length, as it is the best stepping-stone between the
early simple and the later transformed conditions. The sections now to be described
are a series from the end of the snout to the occipital region. Parallel to each other,
yet they do not .keep the same vertical relation to the embryonic head, but become
almost horizontal sections of the occipital region. the whole head at this stage is about
equal in size to a horse-bean.

The first of these slices is through the end of the snout (Plate XXXI. fig. 1), and
shows the coalescence of the alinasal cartilages with the backwardly bent trabecular
cornua (al.n., ¢.tr.). The next (fig. 2) is through the foremost part of the septum nasi
(s.z.) and valvular fold of the nostril—rudiment of alinasal turbinal (q/. tb.): a more
enlarged view of the lower half of the septum (fig. 2%) shows the large and massive
trabecular cornua, and the prenasal part of the trabecular commissure between them.
In the next (figs. 3 & 3") the cornua are now seen to be retral, for here they are
becoming separate from the ‘ prenasal ;” still the base of the septum nasi as well as their

* Thave studied the development of this interhyal tract in the Batrachia Anura and Ophidia, where it
never even chondrifies ; in the Eel (Anguilla), where it is very small and indistinct as cartilage, and fades into
a mere ligament; in the Osseous Fish (Salmo salar) and the Ganoid (Accipenser sturio), where it becomes an
ossified rod of cartilage; and in the embryo of Linota cannabina, where it chondrifies after a time and fuses

together again the incus and stylo-hyal.

304 MR. W. K. PARKER ON THE STRU CTURE AND

own direction is backwards. Further back (fig. 4) the septum is increasing in height,
and the retral processes of the trabecular horns are now much smaller; these slender
laminz I propose to call the “recurrent cartilages”*.

In the fifth and siath sections (figs. 5, 6, 6") there is no longer any distinction between
the rudimentary prenasal cartilage and the completely fused portion of the trabecular
bar, the lower part of the septum nasi; but as this bud-like wedge of cartilage (see
Second Stage, Plate XXX. fig. 1, p.7.) never becomes vertical, having its apex downwards
as in the Chelonians, still less protruded forwards as in its large counterpart in the
Bird, the bony plates that appear as its splints are not superior as in the Bird, nor
anterior as in the Chelonian, but ¢nferior. These plates are the premaxillaries, which
appear in the Mammal below the snout (see also CALLENDER, Philosophical Transactions,
1869, p. 166, Plate xrv. fig. 6, ¢, for its inferior position in Man). Yet in the Mammal
the premaxillaries are related, as splints, more to the retral trabecular cornua themselves
than to the arrested azygous cartilage impacted between them. So much of the alinasal
cartilages as are depicted in the enlarged figure (fig. 6%, a/.n.) is a separate segment—
the “appendix ale nasi.” The next section (fig. 7) is behind the first third of the septum
nasi, where the rudiments of the ‘‘ hard palate” begin in front, the lips of which appear
now on each of the padded bases of the septum, but are here far apart. The long
cushion-like valvular mass in which the aliseptal folds (a/.s.) end and dilate is the early
form of the inferior turbinal, which is not so sharply separate from the alinasal turbinal
(al. tb.) as in the Bird. A sharp process of mucous membrane is seen above this on each
side, where the aliseptal cartilages bend inward; this is the rudiment of the “ nasal
turbinal” (see Huxxey, ‘ Elem. Comp. Anat.’ p. 248), which is but feebly developed in
the Pig. In the thick mass which envelops the base of the septum two flat straps of
cartilage are seen in section ; these are the “ recurrent lamin” (7.¢.c), and they are con-
tinued in this stage back to that part of the septum which, ossifying earlier than that in
front, gets the name of * perpendicular ethmoid” (see fig. 11). On each side of the lower
palatal lip there is a rudimentary tooth-pulp shown in section; and above this, up to the
nasal roof, the tissue is marked off from the skin and subcutaneous tissue; this is the
granular nidus for the posterior margin of the premaxillary and the anterior margin of
the maxillary. The detached piece of this section (fig. 7") is the fore end of the lower
jaw with tooth-pulps appearing, and with a curious result of the great prognathism of
the type, namely, complete fusion of the ends of the primordial mandibular rods—
“ MECKELS cartilages (m/.c.).’ A section made near the middle of the septum (fig. 8),
although answering on the whole to the 7th, shows the tip of the vomer (v.) anda very
near approach of the lips of the hard palate, and, below (fig. 8“), the convergence of
the mandibular rods and the fore end of a bony tract outside them; this is the dentary
(d.); the tongue (¢g.) is here cut across.

The ninth section (fig. 9) takes in part of the frontal wall, with the foremost part of

* The “recurrent cartilages” are of great morphological importance; in future communications I hope to
te} to) } to} }
show their form and meaning in the Ophidians and in Birds, “ Passerines,” “‘ Hemipods,” the Rhea, &e.

DEVELOPMENT OF THE SKULL IN THE PIG. 505

the membranous cranium; here we shall see the * recurrent lamin” (rc.c.) on each side
of the vomer (v.), and a still nearer approach of the edges of the under palatal floor.
The tenth section (fig. 10) is through the most projecting part of the hemispheres, but
in front of the olfactory crus; here, above the inferior turbinal, folds of cartilage are
appearing in the roof, the foremost part of the upper turbinal (w.t.). Here the septum,
now to be called the perpendicular ethmoid (p.e.), is at its highest, and we are now
behind the recurrent processes of cartilage. At this part the palatal bands meet each
other, and in them a new bony centre has appeared, the maxillary (ma.p.); like the
premaxillary, it begins below. ‘The next section (fig. 11) is through the widening
ethmoidal region and the partly separated olfactory crura (1), as well as through the
hemispheres (C 1"). The ¢we/fth section (fig. 12) is through the cavity of the hemisphere,
which is being cut off from that of the olfactory crus (1): it is immediately in front of
the eye, the anterior (inner) canthus being cut through. ‘This section is of great
interest; here we are behind the aliethmoidal cartilages above, and the olfactory bulbs
rest upon the soft mat through which their fibres root down into the nasal cavity.
The walls, both outer and middle, reach further backward than the roof of the nasal
sac; and in the middle wall we see the ribbed condition caused by thickening at the
junction of the trabecular crests with the double keel sent down by the nasal ale.
Here the middle turbinal arises above the inturned nasal wall which ends the inferior
turbinal (m.tb., 7.tb.). This section is behind the new manillary centre, but shows a
large tooth-rudiment on each side of the conjugating palatal flaps; the antagonist teeth
appear in rudiment below on each side of the severed tongue (f7.), above the growing
dentary (d.), whilst inside the dentary is the Meckelian rod (m/-).

The next section (fig. 15) is through the anterior third of the eyeballs (e.) and the
middle of the hemispheres (C 1"), and dehind the perpendicular ethmoid; here the rest
of the septum is almost, if not entirely, of trabecular origin; the section is in front of
the junction of the orbito-sphenoidal cartilages (0.s.) with the basal median part. But
if the mesoethmoid is dying out here, the nasal wall (7.w.) continues much further
backward, bordering the greater part of the so-called presphenoid (p.s.). We are
now behind the upper and lower turbinal regions, and here the ‘middle turbinal ”
(m.tb.) is near its extremity; one interspace is cut through. ‘This narrow, subcranial,
presphenoidal part of the nasal labyrinth, running so far backwards parallel with the
trabecular plate, is the “* sphenoidal sinus ;” and if any osseous centres were to form in
the wall of this narrow region, they would be, as in Man, the * bones of Bertin,” the
hindermost of the ossifications.of the olfactory sacs. Bound strongly beneath the basi-
facial wall is the granular nidus of the vomer (v.), kidney-shaped in section ; and beneath
it the posterior nares are imperfectly floored in this the region of the palatal bone ( pw.),
which is a centre just commencing in granular indifferent tissue less solid and clear
than that of the vomer. Below the mouth this section differs from the last in that the
dentary (d.) is thicker and lies closer to the mandibular rod (m/.).

The fourteenth section (figs. 14 & 14") is through the middle of the eyeball, and
MDCCCLXXIV. 28

506 MR. W. K. PARKER ON THE STRUCTURE AND

gives us the first intimation of the frontal (/.) outside the orbito-sphenoid (0.s.). The
end of the middle turbinal is seen from behind in the sphenoidal sinus (sp.s.); at
this part the nidus of the vomer is most solid, and comes nearest to hyaline cartilage
(fig. 14", v.), a state of things first pointed out to me by my friend Mr. Cas. Srewarr.

The proper territories of each investing bone in the Pig evidently only want time
that they might all become true cartilage ; ossification sets in too soon for the formation
of the intercellular substance, but each tract, before ossification, is a true morphological
clement or organ, as much so as the cartilaginous ** operculars” and “ branchiostegals”
of a Shark.or the “labial cartilages” of a Myxinoid. In illustration of these remarks
I have now to mention a fact new both to Professor HuxLey and myself, namely, that
the substance which ossifies to become the dentary (figs. 14 & 14%, d.) becomes for the
most part very typical solid colourless cartilage, as much so as MuckEL’s cartilage, which
it invests: I shall show this more fully in the next stage.

The fifteenth section (Plate XXXII. fig. 1) is through the fore edge of the optic
foramen; and here we see the nasal wall (2.w.) closing in upon the presphenoid (p.s.),
and joining the end of the sphenoidal sinuses. Part of each optic nerve (2) is seen in
this section, and for that reason the orbito-sphenoid appears distant from the median
cartilage below; its continuity is seen in the vertical section (Plate XX XIII. fig. 4).
Here the frontal (f.) is growing down towards the orbit, to which it will form a ceiling.

The siateenth section (Plate XXXII. fig. 2) is through the largest part of the hemi-
spheres and the underlying thalamencephalon ; the eye is cut through near its posterior
canthus, and the optic chiasma is severed (2). This section is through the lowest part
of the presphenoid, which is still invested below by the vomer (v.); and opposite the
section of the hindermost part of the ascending palatine plate we see the fore part of
the cartilaginous “external pterygoid plates” (e.pq). The orbito-sphenoids (0.s.) are
here at their greatest size, creeping far up the cranial wall and protecting the swelling
hemispheres; the section through the dentary (d.) is close in front of the ‘ coronoid
process.”

The seventeenth section (Plate XXXII. fig. 5) is through the large orbito-sphe-
noidal leaves, where they join the presphenoid behind the optic foramen (sce also
Plate XXXIII. fig. 4, 0.8., ps., 2). This is the last section which shows the vomer (v.),
and here the razor passed through the soft, faintly ossified ‘internal pterygoid plate ”—
pterygoid proper. The fore-turned external pterygoid plates (¢.pg.) are here thick
massive cartilages; and here, also, both the primary (mé.) and secondary (a7.) elements
of the mandible are composed entirely of hyaline cartilage; this part of the permanent
lower jaw is the coronoid and fore part of the articular regions. This section through
the posterior part of the palato-pterygoid bar is of great interest, as it gives the direction
taken by the apex of the second facial bar, namely upwards and outwards, although
the wpward bend is less in the Pig than in many Mammals; it has its fullest develop-
ment in that small Ruminant, Tragulus javanicus.

In the eighteenth section the basisphenoid and its ale (Plate XXXII. fig. 4, .s.,

DEVELOPMENT OF THE SKULL IN THE PIG. 307

al.s.) ave cut through obliquely, so as to show only the floor part of the latter; and the
cartilage beneath the pituitary body is made to appear thicker than it is in reality (see
Plate XXXIII. figs. 2 & 3, py.). On each side of the pituitary body the internal
carotids are seen passing to the “circle of Wiu.is,” and outside these the Gasserian
ganglia. Overlapping the whole are the orbito-sphenoids (0.s.); and on each side of
the flaps of the soft palate (s.pa.) Mucket’s cartilages are severed ; and lower down the
ceratohyals (¢.hy.), thyrohyals (f./y.), and larynx (/v.) are shown.

The nineteenth section (Plate XXXII. fig. 5) is drawn a little more than half across,
and on a larger scale. The curve of the cranio-facial axis makes this and the succeeding
section very oblique; and in this figure the basilar artery (4.a.) is tilted to show the
bulbous end of the notochord (nc.): this thickish section is viewed from behind. ‘The
notochord ends now in the region of the future ‘* spheno-occipital synchondrosis ;” this
narrow part of the basilar plate or investing mass is subcarinate. ‘The razor
has passed through the cochlea (c/.) parallel to the plane of its coils; over this part of
the auditory sac, which is scooped above at the side, lies the great Gasserian ganglion
(5); and inside and above this the fore edge of the large superoccipital lamina (s.0.) is
seen, severed close to the edge, so that there is here a discontinuity between it and the
ear-sac, the reason of which is shown in the dnner lateral view (Plate X XXIII. fig. 5,
au., 8.0.), Where a large rounded notch is seen in front of the occipital cartilage, bulged
out at this part by the lateral sinus. At some little distance from the cochlea the first
postoral (now a veritable “ malleus”) is severed through its head, neck, and shoulders ;
the head is now flattened: this section shows the thin edge of this manubrium, the
thicker part being cut through in the next section (fig. 6, mb.). This view (fig. 5, m.¢.)
well shows the imbedding of the manubrium in the membrana tympani, and the inner
and outer regions of the first postoral cleft, thus divided by the head of the bar.

The twentieth section (Plate XXXII. fig. 6) is a little oblique from side to side; it is
thus practically double ; the left hand shows parts in front of those displayed on the right.
Here, on the left, the manubrium mallei (77.) is cut through at its thickest, posterior part,
and its solid shoulder (m/.) is seen, the part which articulates with the incus. The incus
(z.) is seen on the right side, hiding the manubrium partly, and having its “ short crus”
cut away: the figure shows the dach of the thickish section. On the right side the section
is behind the notch on the base of the fore edge of the superoccipital (s.0.). Below and
outside the tympanic cavity (¢.c.) the stylohyal (s¢.4.) is seen in oblique section as it
passes downwards and forwards, and mesiad of this there is the large jugular vein (7.v.)
with a coiled radicle. The notochord (ne.) is very clearly seen in the substance of the
basioccipital cartilage. On the right side the stapedial bud is seen projecting from the
auditory capsule just above the section of the promontory (s¢., pr.), and to this the orbi-
cular “ capitulum” of the second postoral is applying itself limpet-like. The twenty-
jirst section (fig. 7) is from behind the left side of the last (reversed), and shows on the
whole what is displayed on the right; in both (figs. 6 & 7) we see the opening of the
“aqueduct of the vestibule,” and in this the “aqueduct of Fallopius” containing the

282

308 MR. W. K. PARKER ON THE STRUCTURE AND

portio dura (7*), and mesiad of the jugular vein the glossopharyngeal nerve (8*) is cut
through; outside the nerve, and below the stylohyal (sé./.), a part of the exoccipital
(¢.0.) appears. A similar section to the other side is also shown as a front view (fig. 8) ;
and here the relation of the portio dura (7*) to the hyoid arch is well seen. This figure
does not show the incus, which is removed to display a new segment (/./y.) that has
arisen, the counterpart of the Sauropsidian “ infrastapedial ” (H.) and of the so-called
“ stylohyal” of the Fish (Cuv.); here it will be called the ‘‘interhyal ” (P.), as it really
wants a proper name. In the second stage (Plate XXX. fig. 6) I have displayed the
relation of the segmenting second arch to the very Batrachian stapes (see “‘Frog’s Skull,”
Plate vu. figs. 12-16, sf.); and on the same Plate (fig. 8) I have put for comparison
the state of things in the third stage; both are front views, and the apex of the stapes
is towards the eye. ‘The bigeminal papulie on the younger stapes are now connected by
a bridge of cartilage, and the lateral dimples are the foot-hole of the little stirrup.

The round head of the short crus of the incus is seen articulating with the tegmen
tympani (Plate XXX. fig. 8, ¢.ty., 7.); and below and behind it is the clavate head of the
stylohyal, which is ready to coalesce with the periotic cartilage at the junction of the
epiotic and opisthotic regions (see Plate XXXVL. fig. 2, @., s¢.., op., ep.). The descent
of the dislocated hinder half of the shoulder of this second arch is not so great as in the
Osseous Fish (‘*Salmon’s Skull,” Plate vr. fig. 2), but it is considerable; and this is a
true third stage, as may be seen by comparing fig. 9, Ay., in Plate XXIX. with figs.
6 & 8, Plate XXX. ‘The binding, intervening band of new indifferent tissue which
has grown in the gap of these divided parts has acquired a hardening nucleus of new
cartilage, exactly as we see it in Ganoid and Osseous Fishes, e. g. Accipenser, Anguilla,
Salmo. The portio dura (7*) is seen passing down its aqueduct behind these segments,
and the upturned, inbent, long crus or neck of the rib-like bar ends in an elegant sucker-
shaped disk, its capitulum or apex*.

On the same Plate the postoral arches of the third stage are shown in a side view
(Plate XXX. fig. 9); and a comparison of the undivided mandibular bar with the displaced
fragments of the hyoid will make things plain to the mind. ‘The apices of the two
bars come very near together; but whilst the first hooks backwards, downwards, and
inwards, it does not graft itself upon the auditory sac; nor does its shoulder send back-
wards a secondary pedicle so distinct as the ** short crus of the incus.” Moreover the shaft
of the bar on the first arch keeps on its way normally, as in the early embryo; but in the
second arch this part has been segmented off, and displaced backwards and downwards,
catching in its descent at the xeck and head of the arch, but travelling still further in
more advanced stages, until it rests and combines with the postero-inferior angle of the
auditory mass. In the new web which grows between the two segments comes the
secondary “ interhyal” segment; this, however, loses all its first relations, and finally

* In both these figures, put together for comparison, the parts of the second arch are coloured, and those of
the auditory capsule are plain, for the sake of distinction, that the eye may learn to separate the “stapes”
from the segments of the hyoid arch,

DEVELOPMENT OF THE SKULL IN THE PIG. 309

coalesces with the neck of the projecting stapes (Plate XXXVI. figs. 2 & 3, i.hy., sf.), and
is half lost, at last, in the tendon of the “stapedius” muscle. The “ cornu minor ” (¢.hy.)
of Man is here seen (Plate XXX. fig. 9, ¢.hy.) below, articulating with the keystone of
the arrested third postoral. This lesser horn answers to the “ hypohyal” (P.) of the
Osseous Fish. The twenty-second section, a front view (Plate XX XIIL. fig. 1), is through
the three semicircular canals; the anterior canal (its arch) is above, near the superocci-
pital cartilage (a.sc., s.o.), whilst the horizontal canal (/.s.c.) is laid bare at its crown
and where its non-ampullar end enters the vestibule (vd.). The posterior canal has the
base of its ampulla laid open, and half the arch is seen shining through the cartilage ;
the lateral cerebellar recess (/.¢.7.) is seen above the aqueductus vestibuli (aq.v.).
The space between the auditory mass and the basi- and exoccipitals is the posterior
foramen lacerum (f./.p.; see also fig. 3); the basilar artery lies on the basioccipital,
and the notochord is within it (.0., 0.a., ne.).

From a series of sections taken horizontally in the nasal region, but which were cut
through the investing mass at a right angle, or nearly so, I have selected two as of most
importance in this demonstration. The first of these (Plate NXXCXIL. fig. 9) is a front view,
and shows the left mandibular rod coming forwards and downwards, its manubrium being
buried in the tissue behind. The portio mollis (7’) is seen lying at the entrance of
the meatus internus. ‘The anterior (superior) canal (¢.s.c.) is cut through near its
ampulla, and the cochlea (c/.) is divided at right angles to the plane of its coils.

On the other side (left of the figure, right side of the head) the portio mollis (7’)
is seen streaming into the labyrinth, and the portio dura (7‘) is cut through close to
the tegmen tympani (¢.fy.). The crown of the anterior canal is here cut through,
and the horizontal canal near its ampulla; here the “tegmen” is seen at its high
anterior part, and the “ short crus” of the incus lies in front of its descending portion,
where the overlying horizontal canal dips before it turns inwards to enter the vestibule.
The “long crus” of the incus (7.) is shown hooking upwards, and expanding into its
orbicular portion on the stapes (s¢.), the apex of which has been cut away, exposing
the hole. The head of the stylohyal (s¢./.) is cut through, and in the angle between
it and the long crus there is a large pisiform “ interhyal” (./.y.). The basioccipital has an
irregularly pentagonal section, shows the notochord in its centre, and is very distinct
from the auditory mass: this distinction is very clear and persistent in the Mammalia.

The plane from which the last section was taken being sliced again, yielded what I
have depicted in fig. 10: this is a ack view, and the left side of the figure corresponds
to the left side of the head. On the right side the occipital arch (s.0.) appears almost
to its crown; on the left its fore edge is just missed.

The left side of this figure corresponds very nearly to the left of the last, but the razor
has passed close behind the auditory nerve and through the promontory, where its
cartilage passes as a narrow band between the fenestrae (f. ovalis and f. rotunda), a tract
which receives osseous matter from the ‘ opisthotic” centre. Here the base of the
stapes is towards the eye, and half of it is seen through the cochlear wall (pro-
montory): the rest is as in the last figure.

510 MR. W. K. PARKER ON THE STRUCTURE AND

But the section of the right side, just a degree further back, is most instructive. The
large superoccipital cartilage is seen embracing and walling in the great sinus (s.0., L.s.),
and the periotic mass is severed at the junction of the anterior and posterior canals, so
that the tube opened here is the ‘common canal” (¢.c.). ‘The posterior non-ampullar
half of the horizontal canal (/.s.¢.) is opened over the hinder part of the tegmen tympani.
The promontory is cut through at the fenestra rotunda (pr., fir), and outside this is
seen the head of the stylohyal; all this long sinuous rod (st.h.) is exposed, and also
the short ceratohyal (¢.hy.) at its base, where it is seen articulating with the three
rudiments of the next arch (base and larger cornua of hyoid of Man).

Reconstruction of the skull at this third stage from the foregoing materials will be
rendered easier by light obtained from longitudinally vertical sections (Plate XXXITI.
figs. 2&5). In these the first is made, in the facial region, a little to the left of the mid
line, so as to give the left face of the septum of the nose ; in the next (fig. 3) the septum is
cut away, and the left face of the right turbinals exposed. In the first (fig. 2), the brain
is sketched in outline én sifu; in fig. 5 it has been removed to display the inner wall
of the cranium. The notochord (zc.) has retired from the posterior clinoid wall, and
has been buried in cartilage; it still lies, however, nearest the upper surface of the in-
vesting mass. This may be compared with the like view in the first stage (Plate XXVIII.
fig. 6). There the basifacial axis scarcely made a right angle with the basicranial ;
here these parts meet at an angle larger by one half: there the notochord mounted
above the investing mass; here it has retired, and lies below the clinoid wall.
The gelatinous space called by Raruke the ‘middle trabecula” is gone, and the
reduplicated lining membrane of the cranium has formed the “tentorum cerebelli”
(fig. 2, t.cb.). The huge expansion of the hemispheres (C1*) has hidden the middle
vesicle (C2), as seen from the outside. Behind the large cerebellum (C3) the occi-
pital cartilage (s.o.) is seen in section ; and below the rounded margin of the basiocci-
pital (d.0.) is shown, the tract becoming thinner forwards, and ther much thicker close
to the pituitary body (py.); it ends above in the overlapping “ posterior .clinoid wall”
(p.cl.). The pituitary depression is not saddle-like, but is a deep cup, floored by a good
plate of cartilage. The anterior clinoid wall (a.c/.) is rounded, and belongs to the
presphenoid; the depression in front of it is for the optic chiasma. The median
plate rises gently in front of the optic depression, and this higher part for a short
distance belongs to the anterior sphenoidal territory: it is formed principally by the
trabecular commissure and crests. The rest of the plate belongs to the perpendicular
ethmoid and septum nasi; the latter is the longest region and the former the highest.
The lateral ethmoid (a/.e.) is scarcely seen in this view (fig. 2). Below the pituitary
body the Eustachian opening (ew.) is seen, in the root of the tongue the ceratohyal
(ty., ¢-hy.), and ia the substance of the lower jaw the commissure of MECKEL’s carti-
lages (mh.).

‘These things and some others are seen in the next figure (fig. 5). Outside the fora-
men magnum (f.72.) is seen the occipital condyle (0.c.); in front of this the “ anterior

DEVELOPMENT OF THE SKULL IN THE PIG. oli

condyloid foramen ” (9), and then the ‘‘ foramen lacerum posterius” (8). Crest-like, above
the foramen magnum and auditory mass, is the superoccipital cartilage (s.o.), ending
in front in a sinuous manner, being notched and bulged out by the lateral sinus
(/.c.). The ear-sac (au.) is an ovoidal flattened body, lying obliquely outwards and °
backwards, with its bored and scooped face on the inner side. The blind recess under
the arch of the anterior canal is for the cerebellar process; the antero-inferior spaces
are for the compound seventh nerve; the meatus internus has a small cartilaginous
bridge in front of it, which passes upwards inside the canal for the portio dura. Between
the ear-sac and the small thick alisphenoid (q/.s.), there is a large shallow fossa for the
Gasserian ganglion (5), and the space for the main part of the fifth nerve is merely the
great chink between these two parts—the alisphenoid and the ear-sac. Hence in the
Pig we see no “foramen ovale,” and the ‘f. rotundum” has no distinctness from the
chink between the orbito- and alisphenoids. Most of the alisphenoid is spent in form-
ing the large “external pterygoid process,” and its cranial part is small; here it is not
the “ala major,” asin Man. On the other hand, the “ale minores” of Man are re-
presented in the Pig by huge wings of cartilage, that spread themselves from the nasal
to the auditory regions. ‘This reversal in size of the anterior and posterior wings is like
what we see in the Lizard, &c.,—unlike the Bird’s skull in this respect, where the orbito-
sphenoids are aborted, the alisphenoids huge. As in the Lizard, the Mammalian
orbito-sphenoid has a postneural band, which encloses the optic nerve (2) in a complete
foramen: this is well developed in the Pig (Plate XXX. fig. 5, 0.8.2). In front of the
optic nerve the base of this orbital wing is continuous with the trabecular commissure
for some extent; the greater part of the so-called presphenoid is, however, trabecular in
nature. The olfactory roof and wall extends backwards behind the septum, which
graduates into the presphenoid; thus a large rounded notch exists on each side, and
the roof of the true olfactory region and floor of the rhinencephalon is soft; through
this delicate tissue the olfactory filaments root downwards to the rudimentary upper
and middle turbinal septa (w.tb., m.tb.). Between the nerve-fibrils cartilage is beginning
to appear, and thus a cribriform plate will be formed of secondary cartilage (fig. 3, cr.p.).
In front of the upper turbinal a rudimentary “ nasal turbinal” (7.¢0.) is formed by bending
inwards of the aliseptal cartilage. Lower down this cartilage turns inwards, and deve-
lops into the inferior or anterior turbinal (7.t0.), attached to which in front is the small

alinasal turbinal (a@/.t0.).

Fourth Stage-—Embryo of the Pig, from 2 inches 4 lines ta 2 inches 6 lines in length.

From dissections and sections of embryos not larger than the grub of the honey-bee
in the first, we come in this stage to specimens as large as a mouse.

This is an excellent stage for morphological comparison, as the skull may well be
placed side by side with that of the adult Osseous and Ganoid Fish, Amphibian and
Reptile, and with that of the ripe chick of the Common Fowl. It also corresponds very
closely in development with an early stage of the skull cf Balena japonica, Lac., <xcel-

312 MR. W. K. PARKER ON THE STRUCTURE AND

lently illustrated by the late Dr. Escuricur (* Ni Tavler til Oplysning af Hvaldyrenes
Bygning, udferte til utrykte Foredrag af afdede Ktatsraad Dr. D. F. Escuricur:” Copen-
hagen, 1869. Edited by Professor Rrinnarpr, plate ii. figs. 1-3).

The well-marked granular territories that at first invested the primordial skull and
face are now largely ossified, and these ossifications are massive in relation to so small a
skull. As in the strong-legged ‘‘ Herbivora” generally, and in the “ Aves precoces,”
the development before birth and before hatching is very rapid, so that they are strong
and in good liking at their first appearance. Moreover, the primordial parts are
undergoing endostosis at many points, and from this time the bony metamorphosis takes
place very rapidly. If this skull (Plate XXXIV. figs. 1-7) be compared with that of
the Bird (** Fowl’s Skull,” Plate Lxxxiv.-Lxxxvu.), it will be seen that the premaxillaries
( px.) do not reach to the end of the snout, instead of projecting beyond it, and they do
not send a nasal process between the nasal bones up to the frontal. Here, in the
Mammal, the maxillary is by far the largest bone, and, with the linking malar and
zygomatic spur of the squamosal, forms a strong subocular arch, one pier of which is
formed by the maxillary and reaches near to the nostril, whilst the other pier is formed
by the supratemporal and stretches over the auditory capsule to the occiput (Plate
XXXIV. fig. 1, m2.,7., 2.sg.). This sigmoid, trilobate femporal (squamosal) bone, besides
creeping over the infero-lateral wall of the cranium by its squamous part, clamping the
outer wall of the ear-capsule by a long falcate process, and perfecting the great facial
yoke (zygoma), also takes in a new relation; it articulates with a well-differentiated
secondary mandible (d). This is distinctively Mammalian ; for in the highest Sauropsida
(the Bird) the primordial and secondary mandibles have an equal development, and are
permanently combined as the free arch of the mandible, the large “pier” of which
is merely the hugely developed head, neck, and shoulder of the first mandibular rod.
In this stage of the Mammalian skull we catch the equivalence of these primary and
investing parts; but the new hinge is formed already, and the primary bar, now at
its highest relative development, shows no sign of segmentation into a pier (quadrate)
anda free arch (articulo-Meckelian). By the time of birth, the whole of the large
succulent rod of cartilage which runs along the inside of the lower jaw (fig. 7, d., mk., m.)
and coalesces largely with its fellow in front will have shrunk up into a delicate fibrous
band, leaving a small bony style (processus gracilis) to the arrested upper part of the
rod*. A bony ring is growing round both the preoral and the first postoral clefts ;
these are the lacrymal (/.) and the tympanic (ty.); the first of these has an outer facial
development, and is not hidden in the orbit as in Man. ‘The nasal, frontal, and parietal
bones (7., f, p.) form a regular double series; they are only equivalent to the énner
fayer of the scutes seen in the same region in Ganoid Fishes; yet they are very thick,
the thickness depending upon the free development of connective (indifferent) tissue
between the cutis and the primordial skull. The fontanelles are still wide open; but

* In the figure (Plate XXXIV, fig. 7, d.mk.) the primary rod is cut through, and the mandible detached

from its new hinge these parts will be described more in detail from the figures of sections.

DEVELOPMENT OF THE SKULL IN THE PIG. 313

the lower edge of the frontal has sent inwards from its eave a plate which reaches the
orbito-sphenoid—the orbital plate. The agreements and the differences seen by com-
paring the Ornithic and Mammalian skulls are made very evident if this palatal view
(Plate XXXIV. fig. 2) be put side by side with the figure of this region in the Ostrich’s
embryo (“ Ostrich’s Skull,” Phil. Trans. 1866, Plate vir. fig. 4); at this stage the con-
formity is more remarkable than the difference.

The dental (d.px.) part of the pig’s premaxillary is broad and filled with tooth-sacs,
which deeply groove it; the palatal processes (pp.v.) ave slender. The approximating
manxillaries (ja.) do not hide the vomer (v.); they are grooved by vessels down the
middle of their palatine plate, whilst their dentary portion is hollow and shell-like,
containing as it does large growing tooth-germs. ‘The palatines ( pa.) are ornithic,
scarcely showing so much of the * hard palate” as a Green Turtle (Chelone mydas).
The pterygoids (pq.) are thin in their ascending part, and are clubbed hooks below ;
they and the palatines both articulate with the great conjugational * basipterygoid,”
which here, as in the Ophidia, mainly arises from the alisphenoid; it is, however,
formed of true cartilage, as in all the Sauropsida in which it occurs. ‘This part,
the ‘external pterygoid plate” (e.pg.), is a pronotochordal secondary structure; it
arises at its root from the side of the apex of the trabecula. These apices of this first
pair of bars do not project outwards and backwards in the Pig as in the Kitten, nor does
the ‘“ basitemporal” appear here in rudiment as the * lingula sphenoidalis ;” both these,
the process and the bone, are exquisitely and most instructively displayed in the Guinea-
pig (Cavia aperea). ‘The ring on which the tympanic diaphragm is stretched (¢y.) is at
present U-shaped, with its crura pointing backwards, and the larger on the outer and
upper side; this crus has a flat flange which looks upwards. The vomer has the same
relative size as in the embryos of the Ostrich and the Whale (* Ostrich’s Skull,” Plate vu.
fig. 4, v, and Escuricur ‘‘ On the Cetacea,” plate ii. fig. 2, V.).

In the endoskeletal parts we have to deal with two tissues at once, hyaline cartilage
and bone, principally endosteal at present, although rapidly gaining the surface and
beginning to affect the perichondrium ; I shall describe it first in the dissections and then
in the sections. In the side view (Plate XXXIV. fig. 1) the tracts that are hardening in
the arch of the occiput are shown; and of these there are five, namely the superoccipital
and two pairs of exoccipitals (see also fig. 5). Moreover the superoccipital is double,
as may be seen in a younger specimen (fig. 4, s.0.), but the two patches run into each
other in a day or so. ‘The ossification of the exoccipital is remarkable ; for within the
substance of the massive condyle an epiphysial centre appears, quite distinct at tirst
from the large rambling growth above (figs. 1 & 3,¢.0.); these two points soon coalesce.
The basioccipital (4.0.) is best studied in a sectional view (fig. 5), but its form is scen
from above and below (figs. 6 & 2); it is spearhead-shaped in outline and thick as to
substance ; it is fast obliterating the notochord. The newer cartilage which underiloors
the pituitary body is rapidly ossifying as basisphenoid (fig. 5, 4.s.); the form of this
centre is seen from below in fig. 2: this is the only bone at present in the posterior

MDCCCLXXIYV. ant

514 MR. W. K. PARKER ON THE STRUCTURE AND

sphenoid. ‘The real harmony between the outstanding bars on each side this bone and
the basipterygoid spurs of the Lizard and Ostrich is here clearly shown; whilst the
“external pterygoid plate” was only studied in Man (where it is said to be merely a
periosteal outgrowth of the “ala major’’), its homology with the “ Sauropsidan” bar
could not be determined; here it is a direct cartilaginous outgrowth of both dase and
wing, and its basal origin is from the side of the trabecular apex. Here it articulates
with both palatine and pterygoid, being so Huge and developed to so great an extent
laterally; there (see ‘‘ Ostrich’s Skull,” Plate vit. fig. 4, pg., ap.) the pterygoid is
wedged in bodily between the basipterygoid spur and the palatine; it is in that memoir
called the ‘anterior pterygoid process” (a@.p.), and by Professor HuxtEy “ basipterygoid”
(On the Classification of Birds,” Proc. Zool. Soc. April 11th, 1867, p. 418). ‘There is
no special ossification in the confluent trabecular base beneath the orbito-sphenoids
(figs. 2 & 5, p.s.), and these large wings have no centre over and behind the optic fora-
men, as in Man (figs. 1, 5, 6, 0.s., 2); from these only the whole mass will be leavened.
These wings have now coalesced with the lateral ethmoid (a/.e.) in front, and overlap
the auditory capsule (av.) behind, exactly as in Escuricut’s figure of the embryo of
Balena japonica (op. cit. plate ii. figs. 1 & 2,4,°mG). The orbito-sphenoids are now at
their highest degree of development (see in third stage, Plate XX XIII. fig. 3, 0.s., and
in the sixth, Plate XXXV. figs. 1, 3, 4, 0.s.). In front of these orbito-sphenoidal
nuclei there is no endosteal deposit, nor is there any for some time to come in the ear-
sacs (au.). ‘The bird’s-eye view (fig. 6) shows how far, as in the Bird, the great septum
of the nasal sacs (‘* mesocthmoid,” continuous perpendicular plate, and septum nasi)
continues backward beyond the primary roof (here compare fig. 6 with primordial stru-
thious skull, op. e7t. Plate vir. fig. 1, al.e., @.g., 0.8.) The cribriform plate is now suff-
ciently advanced on each side of the retral septum of the sacs to be fairly understood ; it
is a delicate comb-shaped lamina of secondary cartilage, with four long “ teeth ” growing
inwards and forwards from its margin or “ back;” the long interspaces admit the olfac-
tory filaments. ‘The common outer band does not fill in all the space which forms the
floor to these huge rhinencephalic fosse, but, as in the embryo of the Ostrich and
Fowl (“ Fowl’s Skull,” Plate txxxt. fig. 4, eth.), the septum is continued backwards to
the verge of the anterior sphenoid, and here, in the Pig, ends in a club-shaped manner.

Between the anterior edge of the orbito-sphenoid (0.s.) and the back of the comb-like
lamina (figs. 5 & 6, er./.) there is a considerable membranous space. The bulgings in
the olfactory roof (q/.e., al.s.) are caused, behind, by the upper and middle turbinals,
now increasing in complexity, and further forwards by the inferior turbinals. Behind
the postneural commissure of the orbito-sphenoid (figs. 5 & 6, 0.8.) the alisphenoids are
obscurely seen (al.s.), overshadowed and obscured by the so-called “ale minores.”
‘They have no foramina in their substance, but the cranial nerves root down in front of
and behind them; on the upper view the whole of the ali and the floor of the “sella
turcica” are far from the eye, the posterior clinoid wall ( p.cl.), the end of the investing

mass, cropping up high into the cranial cavity. The ear-sacs are seen from without,

DEVELOPMENT OF THE SKULL IN THE PIG. 315

within, above, and below (figs. 1, 2, 5, 6, @u.), but as a mass they are not much changed
from the last stage.

Tn the sectional view (fig. 5) the Eustachian tube (ev.) is seen below the basisphenoid
(.s.); below the soft palate the ceratohyal (¢.hy.) is cut through, and along the inside
of the lower jaw the primary mandible is seen. ‘This is better shown when dissected
out (fig. 7); and now its malleal end is ossified (this part is cut through in fig. 1), whilst,
below, the Meckelian commissure is sévered, the bars uniting along their anterior
fourth. I can only find one osseous centre here in the mandible, the dentary (d.); this
is found in the rapidly chondrifying nidus, which, like a huge “ inferior labial,” obliquely
overlaps the primary mandible; in Man, according to CALLENDER, there is an osseous
centre at the chin in MucKEL’s cartilage, and a second splint (splenial) on the inner face
of the dentary (see Phil. Trans. 1869, Plate xu. figs. 6 & 7, p. 170).

A few of the many sections prepared of this stage will now be described, and they
will thoroughly explain the structure of the parts which have above been described
mainly from dissections.

The first is through the snout (Plate XXXIV. fig. 8), and shows the arched cartilages,
united together in front, which were formed by fusion of the ale nasi with the overbent
trabecular horns.

The second (Plate XXXIV. fig. 9) is through the ale nasi (a/.7.), fore part of septum
(s.n.), alinasal turbinal (a/.tb.); and the masses with trilobate outline below are the
recurrent trabecular horns (7¢.¢.).

The third section (Plate XXXIV. fig. 10) shows a curious triradiate cartilage separated
from the “ale nasi;” this is the “ appendix” (a.al.n.); here the trabecular cornua are
becoming slenderer.

The fourth (Plate XXXIV. fig. 11) shows the same parts further back; here the
recurrent process has become a smallish band lying flat on each side of the base of
the septum, which is now becoming high, but has not commenced the inferior turbinal
fold. The four-winged section, on each side, below the septum and recurrent cartilages
is the severed premaxillary (pa., see also fig 2).

The fifth (Plate XXXIV. fig. 12) is through the middle of the inferior turbinal (7.¢0.) ;
the pedate section here shows the upper limb coiled on itself, but not the lower at present.
The recurrent lamin of the trabecular horns are running even past this point backwards ;
they are here vertical, and in close relation with the nidus of the scoop-shaped vomer (v.)*.
In this section the outer stratum of granular tissue overlying the nasal canals is now ossi-
fied as the nasal bones (z.), and the mass of tissue overlying the pterygo-palatine bar has
become the maxillary (m.), with its deep dental groove and pulps and its palatine plate.

The stath (Plate XX XIII. fig. 4) section is through the solid anterior third of the

* The relation of these recurrent developments of the trabecular horns to the splints that belong to the first
facial arch is of intense interest; I am working out this subject in various groups; it is most complicated in
Passerine Birds, ‘ Hgithognathe”’ (H.). They are evidently formed by the fusion of a “labial” with cach

5]

trabecular horn. If we add to this the “appendix ala nasi’ and the secondary mandible, we get thirce pairs
of suctorial cartilages in an ordinary Mammal.

272

516 MR. W. K. PARKER ON THE STRUCTURE AND

frontals ( f.), the true olfactory region, and the zygomatic process of the maxillary (z.m.) ;
above this is the overlapping malar or jugal (j.) The thick frontal slabs send inwards
and downwards an ‘orbital plate,” which clamps the ethmoidal wall; this wall is seen
to be separated by a very large space from the fore top of the septum or perpendicular
ethmoid (p.¢.), on each side of which lie the olfactory crura (1), and above these the
fore part of the hemispheres (C 1‘). Here we see that the comb-like floor of the
olfactory crura (Plate XXXIV. figs. 5, 6, c7.p.) is connected with, and is the top of, a
system of cartilaginous ingrowths, the upper and middle turbinals (w.tb., m.tb.), which,
by repeated splitting, as it were, or rather by a process of foliation, is becoming more
complex day by day. ‘This section is through the most solid part of the vomer (v.),
where it is squared below to rest upon the “ hard palate” over its median suture; here
the palatines are cut through their fore part, where they are thin bony scoops, protecting
the outside of the posterior nostril passage. Large tooth-pulps (¢.p.) are seen above and
below, and the lower are in relation to a large dentary groove, the outer wall of which
is very massive and the inner a smaller rod: both of these sections are parts of a con-
tinuous dentary (d.); below the inner bony bar is the Meckelian rod (ms.), on each side
of the base of the tongue (¢7.).

The seventh section (Plate XXXII. fig. 5) is through the fore part of the eyeballs
(c.) and the sphenoidal sinuses (sp.s.), the hinder part of the backwardly projected nasal
labyrinth. At this point the septum, ‘ perpendicular ethmoid,” ends; and the pyriform
section seen here, at the posterior end of the large ‘‘rhinencephalic fossie”’ (see Plate
XXXIV. fig. 6, o/., crp.), is no longer indebted to the inturmed nasal roofs for its height,
which is due to the upgrowth of the trabecular crests*. ‘This section is through the
most solid part of the palatines (pa.), and their interior edge is thickening and growing
inwards ready to form their part of the hard palate. Only the malar (j.) is seen on
the side and below, and mesiad of it is the coronoid process of the lower jaw (c7.).
MecKeEL’s cartilage (m/'.) is now high up the inside of the jaw, which is here mainly
composed of solid hyaline cartilage, the inner cells of which are rapidly proliferating as
“osteoblasts.” In the root of the tongue (fq.) the ceratohyals are seen articulating with
the basi- and thyrohyals (¢.hy., b.hy., th.h.), now one piece of cartilage.

The eighth section (Plate XXXII. fig. 6) is one of the most instructive; it severs the
orbito-sphenoids (0.s.) where they pass into the presphenoidal trabecular wall close at
the back of the sphenoidal sinuses (see also in third stage, Plate XXXII. fig. 1). ‘This
is the high part immediately in front of the optic foramina (Plate XXXIV. figs. 1, 4,
6,2). ‘Phe orbito-sphenoids are overlapped above by the frontals (f:), and the presphenoid
has the end of the vomer (v.) beneath it. Here the thin ascending plate of the pterygoid,
and its thick **hamular” part, is cut through; the osseous matter is scarcely continuous
in the ascending part, and every now and then a separate ‘* mesopterygoid” is developed.

* If the reader wishes to see an exact counterpart of this structure displayed in the second facial arch or
“ palato-pterygoid,” it is ready at hand in the skull of the Pelican, where both the preoral arches form a long

and solid “commissure,” from which a high crest ascends.

DEVELOPMENT OF THE SKULL IN THE PIG. By UE

The fore part of the curious thick leaf of cartilage which grows out of the ali- and basi-
sphenoid is here cut through; it is the conjugating process between the first and second
preoral arches. Here the zygomatic process of the squamosal (z.s7.) overlaps the jugal
(j.), and here the cartilaginous part of the lower jaw is nearly at its thickest ; in the root
of the tongue the stylohyals are severed at their junction with the ceratohyals (c./y.).

The ninth section (Plate XX XIII. fig. 7) has been made through the orbito-sphenoid
(o.s.) close in front of the osseous nucleus (see Plate XXXIV. fig. 6, 0.s.); it has passed
down through the low part of the presphenoid, where it is crossed by the optic nerve,
and where its territory ends and that of the basisphenoid (d.s.) begins.

Hence in this figure we have the alisphenoids (qa/.s.) cut through beneath the orbital
wings. At this point the hooked coronoid process is severed at its apex (cv.); and
outside this is the “squamosal” (sg.), with its articular cartilage and ‘“ meniscus.”
Below these the articular and angular part of the lower jaw is shown; it is one mass of
hyaline cartilage. Mecket’s cartilage and the stylohyal are also cut through.

Part of this section is shown from the rivht side (Plate XX XIII. fig. 8), magnified
twice as much. Here the three cartilages that form the mandibular hinge are all
secondary, and, like the ‘outer ear, suggest a reversion to the labial and opercular
cartilages of the Shark.

The tenth section (Plate XX XIII. fig. 9) is through the malleal portion of the first
preoral arch (m/.), the front of the tegmen tympani (¢.¢y.), the long, overlapping, pos-
terior angle of the orbito-sphenoid (0.s.), the cochlea (cl.), the stylohyal (s¢.4), and the
“ occipito-sphenoidal synchondrosis” with its enclosed notochord (4.0., 1¢.).

The eleventh section (Plate X XXIII. fig. 10) displays the ampulla of the anterior
canal (a.sc.), the general cavity of the labyrinth (vé., ¢/.), and the tegmen tympani
(t.ty.), with a bony eave formed by the squamosal (sq.) and roofing over the body of
the incus (7). ‘The incus is seen turning up its “long crus” and spreading its orbi-
cular apex over the top of the stapes (st.), which has been cut through from top to
bottom, exposing the foot-hole. Below the stapes is the cartilaginous wall of the pro-
montory (pv'.), and outside this is a continuation of the tympanic cavity, in the outer
wall of which is the stylohyal (ty., st..).

Fifth Stage-—Embryo Pig, 3 inches long.

This is merely introduced to show the ossification of the ‘ alisphenoids” (Plate
XXXII. fig. 11, @/.s.), which had not begun in the last, whilst in the next they are
one solid mass of bone with the basisphenoid (4.s.). Here it will be seen that the
posterior sphenoid is much simpler in the Pig than in Man; in the Sheep at this stage
I find it simpler still, not being able to discover any median centre; but the two alisphe-
noids are to be seen becoming pointed below, and growing towards each other; here,
then, there appears to be no median piece, and thus the postsphenoid is like the ante-
rior region, in which the orbito-spheroids themselves fill in the mid region with bone,
The contrary takes place in the Rodents; and especially in the Guineapig (Cavia aperea)

318 MR. W. K. PARKER ON THE STRUCTURE AND

are the sphenoidal structures complex. As in other Rodents, there is a large presphe-
noid as well as a basisphenoid; the alisphenoids are ossified from two centres on each
side; long “ lingular” pedicles are formed by the apices of the trabecule, and to these
are articulated a pair of long, outstretched falcate bones, the evident counterparts of the
*“‘basitemporals” of the Bird. In this animal also the “ external pterygoid processes ”
are basipterygoids, and the small pterygoid bone is attached to their apex. Even in the
Ruminants these spurs are basa/ in their origin. (For the development of the human
sphenoid, see Huxury, ‘Elem. Comp. Anat.’ p. 144.)

Siath Stage —Lmbryo Pigs, 6 inches long, measured from snout to ischium.

The head in this stage equals in size that of a Squirrel, but its bones are much more
dense. ‘The roof-bones (Plate XX XV. figs. 1-3) are now applied to each other edge
to edge by sutures, and in certain places overlapping as squame. ‘The “anterior fonta-
nelle” ( fo.) is still open, but is much lessened; the parietal and occipital bones now form
a good * lambdoidal suture.” The nasals, frontals, parietals, squamosals, lacrymals, pre-
maxillaries, maxillaries, and malars (7., f., p., 8q., l., pv.,ma., j.) are all so far formed as to
require but little change of size to fit them for their adult relationships. The palatal
region (Plate XXXV. fig. 2) shows a great development of the secondary floor or
“hard palate,” the palatines themselves being now tied together at the mid line below.
The ossification of the cartilaginous skull has advanced greatly; the superoccipital is a
large, strong shell of bone, and it is at present separated by a larger tract of cartilage
from the exoccipitals than in the last stage (s.0., ¢.0.). The latter have now only one
centre, for the epiphysis formed primarily in the substance of the condyle has coalesced
with the outer deposit; this is now creeping far down into the substance of the long
twisted paroccipital process (p.oc.). The basioccipital (.0.) now reaches from the
foramen magnum to the spheno-occipital synchondrosis; and in front of it (fig. 2)
the basisphenoid is now a thick mass of bone (see also fig. 3, d.0., b.s.). The presphe-
noidal region is hidden below by the vomer (fig. 2, v.), but in the section (fig. 3, p.s.) it
is seen to be largely unossified. The alisphenoids (figs, 3 & 4, al.s.) are solidly anchy-
losed to the median piece; they are larger relatively to the orbito-sphenoids, but
are still inferior in size and in place; they largely owe their size, laterally, to the
external pterygoid processes (e.pq.), for their cranial region is small. The whole orbital
wing is much more contracted, relatively (figs. 1, 5, 4, 0.8.); it has become detached
from the ethmoid, and is some distance from the auditory mass. The two centres are
completely anchylosed at the mid line, and quite enring the optic passages (2); below
(fig. 3), they are forming the presphenoid.

The remainder of the facial axis and nasal septum is one sheet of solid cartilage ;
and so also is the complex -nasal labyrinth, now much more complex in its turbinal
growths and cribriform plate (w.tb., Crp):

From the intimate impaction of the auditory mass into the sides of the cranium, its
osseous centres have caused much confusion; this has, however, been greatest in the

DEVELOPMENT OF THE SKULL IN THE PIG. 519

Oviparous Vertebrata, where the fusion of the periotic capsule with the skull proper is
the greatest. Here, in the Pig, the bony deposits are formed much as in Man (see
Huxzey, ‘ Elem. Comp. Anat.’ pp. 147-156). A description such as that quoted above
serves almost equally well for both types. Looking at the inner face of the capsule
(figs. 3 & 4), we see a creeping endosteal patch, which surrounds the ‘ meatus
internus,” runs under the,fore part or apex of the cochlea, and has found its way
supero-posteriorly to the junction of the anterior and posterior canals (@.s¢., p.sc.).
Seen from the outside (fig. 5, pro.) the same bony tract is seen above and in front of
the “ fenestra ovalis” (fov.), below which it forms a sudden hook-like bend, which turns
forwards, passing into the tract seen on the inside of the cochlea: this is the ‘* prootic”
ossification,

On the inside (fig. 5) a small hook of bone is seen in front of the ‘foramen lacerum
posterius” (8); this is a spur sent round the back of the capsule from the outside,
and the plate of which it is a process is seen from that aspect (fig. 5, op.) covering the
most bulbous part of the cochlea, the ‘* promontory” (pv.). ‘This is the “ opisthotic
bone ;” it sends forwards and downwards a long hook, which binds behind the hook of the
prootic, beneath the apex of the cochlea. Another process of the opisthotic runs
between the fenestra ovalis and fenestra rotunda (f.ov., fv.) close in front of the head
of the styloid cartilage (st.h.). Above the head of the styloid, and below the hinder
end of the tegmen tympani, a smaller spatulate scute has appeared; this is the mas-
toid proper, or “ epiotic.” Behind this little bone the auditory mass is much contracted
in the Pig, this part of the capsule being strongly clamped by the squamosal and im-
pinged upon by the exoccipital (e.0.), where it gives off its ‘* paroccipital process ”
(p.oc.). The “ epiotic” centre will, moreover, ossify the true mastoid region; although
it arises in a more forward position, it is less than that of Man (see HuXuey, op. cit. p. 154,
fig. 61, ep.o.). In the vertical section (fig. 11) the prootic and opisthotic centres are cut
through, each at two places, the first (pi'o.) above the stapes (s¢.) and inside the cochlea
(e/.), and the opisthotic appears below the stapes and in the substance of the promon-
tory (pr.). On the outside the semicircular canals are seen (a.8¢., /.sc., p.sc.) imbedded
in solid cartilage. The structures of the “ middle ear” have now acquired their almost
full metamorphosis; these are enclosed in a large imperfect ring of bone, the tympanic
(figs. 1 & 2, ty.). This bone is now becoming very thick, and its breadth has greatly
increased ; butas yet there is no bony meatus stretching outwards beyond the membrana
tympani (i.¢.). It will be seen in the lower view that there is an additional bone
clinging to the inner edge of the tympanic; this wedge and two smaller ossicles which
I shall describe in the next stage are the feeble counterparts of the auditory “bulla” of
the ‘* Felidie” and their congeners *.

* On the subject of the auditory “bulla” of the Carnivora, see Professor W. H. Frowsr’s very valuable
paper “On the Value of the Characters of the Base of the Cranium in the Classification of the Carnivora” &c.,
Proc. Zool. Soc., Jan. 14, 1869, p. 4. Whilst Professor Huxiny’s ‘ Elements’ was going through the press, L
showed him the bulla of the new-born Lion’s whelp, a thin spoon-like lamina of {rue hyaline cartilage growing

outwards from the inferior edge of the opisthotic region. oon after this, Professor Rotrrsron presented me

320 MR. W. K. PARKER ON THE’ STRUCTURE AND

In the Pig the bullar ossifications are found in a very soft stroma of connective tissue,
and not in thin cartilage; yet that stroma is connected with the outer and lower edge of
the opisthotic and prootic regions; it is the membranous floor of this huge air-cell.

The “os bullie” already developed is seen in section, in its fore part (fig. 11, 0.6.), a
little in front of the auditory capsule, at the edge of the lower limb of the tympanic
(ty.). The parts of the facial system of cartilages entering into the structure of the
middle ear are shown in figs. 1 & 12; the “*manubrium mallei” (fig. 1, md.) is now
ossified, and so also is the incus (figs. 12, 7.). The lingual part of the hyoid arch is con-
tinued upwards to the epiotic region (figs. 1 & 5, st.4.), and behind this flattened rod
the portio dura nerve is seen escaping.

The little ceratohyal (e.y.) twms backward to articulate with the basal piece, to
which also is attached the thyrohyals (fig. 1, 0.4., t.hy.); the latter three parts belong
to the “ third postoral arch.”

The ossification of the lower jaw (fig. 1, d.) is almost complete, the unossified cartilage
being principally condylar.

A series of sections selected from a large number now remain to be described; they
will more fully illustrate this stage.

The first of these (Plate XX XV. fig. 6) is through the anterior third of the “ inferior
turbinal ;” the pedate lower edge of the ‘ aliseptal” cartilage here is seen to be coiled
inwards above and below, the common back of the two coils lying towards the septum
(7.¢., s.v.). The sudden inbend of the aliseptal lamina higher up is the rudimentary
“nasal turbinal”’ (7.¢b.); below the septum is the vomer (v.), and below this the palatine
processes of the premaxillaries are seen ( p.p..). The nasals (x.), the side of the pre-
maxillaries, and maxillaries ( pa., a.) show very thick in the section. On each side of
the vomer the “recurrent apices of the trabecular horns” are still present (7¢.c.).

The second section (fig. 7) is through the complex upper and middle turbinal regions
(w.th., m.tb.) and the high part of the perpendicular ethmoid (p.e.). The olfactory
crura (1) are also cut through as they lie on the cribriform plate (e7.p.). This widest
part of the true olfactory region is roofed in by very massive frontals (7); the thin
lower edge of these bones is the orbital plate. The vomer (v.) is here very deep ; on
each side of it the posterior nares are cut through, and these are protected by the
long scoop-shaped processes of the palatines (pa.). A part of the maxillary is seen
on each side of a large molar tooth with its pulp; and above, the outer piece of bone is
the jugal (/.).

The third section (fig. 8) is through the low part of the perpendicular ethmoid and
the end of the cribriform plate, where it overlies the middle turbinal (i.¢b.) only. ‘The
palatines (pa.) are here at their fullest development, their scooped portion underlying
the end of the nasal wall (2.w.), and their subvertical plate sending inwards the palatal
part of the hard palate.

with the head of a new-born Hyrax; and in this I found a large bulla, ossified separately from the true tym-

panic annulus,” and evidently formed in a shell of true cartilage.

21

[Si]

DEVELOPMENT OF THE SKULL IN THE PIG.

The fourth section (fig. 9) instructs us how the olfactory labyrinth ends, as the
sphenoidal sinus, on each side of the presphenoid; and it is seen that the fore edge of
the orbito-sphenoids wall in this region, and underprop the thin descending orbital plate
of the thick arching frontals (0.s., f.). On each side is the eye-socket, and below the
presphenoid is the thin part of the vomer (v.); the palatines ( pa.) are here cut through
behind the hard palate, and opposite them a section of the malar bone and lower jaw
is shown (/., d.).

The fifth section (fig. 10) brings a number of bones into view; the presphenoidal
(trabecular) cartilage is rapidly ossifying from the coalesced orbito-sphenoidal centres
(0.8., p.s.); beneath this is the vomer (v.); and on each side, protecting the hinder
nostrils, we see the thin part of the palatine and pterygoid (pa., py.); outside these is
the fore-bent wing of bone known as the “ external pterygoid plate ” (¢.p7.).

The siath section (fig. 11) is through the postero-external part of the external pterygoid
(e.pq.); it binds strongly against the inner face of the articular (“ glenoid”’) part of the
many-spurred squamosal (sq.). Here the basisphenoid is cut through behind the
“wings,” and the internal carotids mount up here to reach the * circle of WILLis ;” here
the two limbs of the tympanic, the ‘‘os bull,” and the stylohyal (¢y., 0.0., st.h.) are
cut through. The “glenoid hinge”’ is here with its meniscus, and the articular region
of the lower jaw is still largely cartilaginous beyond the head of the articular surface.

The seventh section (fig. 12) is through the lower edge of the parietal (p.), and also
through the upper and lower edges of the squamosal (sq.) above, where it binds upon
the mastoid region, and below, where it flanks the long paroccipital process (p.0c.).
The extremity of the sinuous, creeping tympanic cavity is here seen (¢y.), and outside it
the stylohyal and tympanic (s¢./., ty.) are severed ; below these is a section of the par-
occipital spur. Over the incus (/.) the horizontal canal is seen, and below the stylohyal
the portio dura (7"). Inside the upper and outer portion of the rambling prootic
centre the portio mollis (7’) is seen streaming in; the inner face of the cochlea has
the prootic in its edge, and the outer and lower the opisthotic (pro., op.). ‘The basi-
occipital (4.0.) is seen to have a subcrescentic form in section, and the cartilage at the
edges of this elegant “basilar plate” will have its outer edge ossified by the exoccipitals.

Seventh Stage-—New-born Pigs.

Since the last stage the skull has almost doubled its length, and the process of ossi-
fication has gone on very rapidly; moreover the form of the entire skull has become
much more specialized.

Wishing to limit the illustrations to this paper, I have given but few figures of the
preparations made for my own research; but the head at this stage is most easily
obtained by those interested in these studies. Moreover the semi-adult condition of the
skull, prior to any extensive anchylosis, will be fully illustrated. Besides the finish given
to the general form of the skull by the now complete investing bones, the endoskeletal
parts are well ossified. The whole of the occipital arch and its paroccipital processes,

MDCCCLXXIY. 2U

322 MR. W. K. PARKER ON THE STRUCTURE AND :

and the anterior and posterior sphenoids, are now thoroughly hardened. ‘The “ spheno-
occipital synchondrosis” is of small extent, very thin, and a scarcely thicker tract of
cartilage remains between the posterior and anterior sphenoids; yet these are each a
single bone at this stage. ‘The perpendicular ethmoid and septum nasi are still
unossified ; but the inferior turbinals are almost completely, and the ‘ lateral masses”’
partially, converted into endosteal bone. The cribriform plate is soft, and so is
the snout (Plate XXXVI. fig. 1); but this latter is everywhere burrowed with vessels
prior to hardening.

Beneath the skull we see a most compact building together of the palatal, pterygoid,
external pterygoid, and tympanic bony pieces; the thick, clubbed “ hamular process” of
the internal pterygoid is fixed as an undersetter to the solid nut-like tympanic, and dints
it as an inturned horn dints the frontal in certain varieties of the Cow; this, however,
is only a temporary state of things, and is quite recovered from in the lengthening head
and face.

No “interparietals ” have been found, adding two bones to the growing superoccipital,
as seen in Man; this part, the superoccipital, is now a nearly vertical wall, the parietals
finishing the roof above. The lower jaw is well ossified, and is now entirely free from
the arrested: primordial bar, MecKEL’s cartilage. The three periotic centres have
completely ossified the auditory mass, ‘‘ petrosal” and “ mastoid” (Plate XXXVI. fig. 2);
and a small bilobate ossicle has appeared in the attached (confluent) head of the stylo-
hyal (s¢./.). Further down another centre has appeared in the middle of the long rib-
like bar, taking up nearly the middle third. The upper piece of bone (formed from
two nuclei in the Lamb, and apparently also in the Pig) is called by Professor FLowEr *
the ‘“‘tympano-hyal,”’ a term it may be well to retain. ‘The rudimentary stylohyal
of Man is ossified from the upper centre; for “a centre of ossification appears in the
styloid cartilage, and extending upwards and downwards, gives rise to the pyramid and
styloid process” (Huxtry, ‘Elem.’ p. 160). Hence it will be seen that the tympano-
hyal and the wpper styloid bone are identical; both these bones are largely developed
in the Osseous Fish, the so-called “epi- and “ceratohyals;” they occupy the great flat
‘cornu,’ at the base of which the short ceratohyal proper, with its two bony centres,
is articulated. ‘The unciform ceratohyal (“ cornu minor”) of the Pig is strongly attached
by fibrous tissue to the transverse basal piece (Plate XXXVI. fig. 2, c.h.), now coalesced
with its own rudimentary arch, the “‘cornua majora” of Man; these pieces are ossified
proximally (fig. 2, ¢h.h.), and these centres correspond with the first pair of hypo-
branchials of the Osseous Fish, the median part answering to the first basibranchial.
The “ stylo-mastoid foramen” (fig. 2, s.m.f., 7) is seen transmitting the portio dura
nerve; and this sends upwards and forwards the “ chorda tympani” (7“), to which is
attached the smallest of the three ‘ ossa bull” (0.0'.); the middle-sized piece is seen
in front of the stylohyal (0.0".). The rest of the drum-walls being removed and
the squamosal, the outer face of the periotic mass shows the three semicircular canals

* In his valuable little work ‘On the Osteology of the Mammalia,’ 1870, p. 173.

DEVELOPMENT OF THE SKULL IN THE PIG. 323

above (@.s¢., h.s¢., p.sc.) and the cochlea below (cl.). ‘The hollowed tegmen tympani (¢.ty.)
has in its hinder recess the head of the incus (7.); the recess ends in a round cup-like
facet for the short crus of the incus, with its down-turned rounded head ;_ the “ aceta-
bulum” for this head is finished, externally, by the squamosal, part of which, having
become adherent, is shown in the figure. Below this wall-chamber for the incus is the
fenestra ovalis with the enclosed stapes (f.ov., st.); the long axis of the oval space and
oval base of the stapes is upwards and forwards. ‘The inturned hook of the long crus of
the incus is now coupled to the neat head of the stapes by means of an intermediate
bone, the “ os orbiculare ” (0.0b.), a special centre developed in the primary head of the
second postoral bar, which, limpet-like, applied itself to that periotic “bud” which
became the stapes, by a process similar to that which detaches the axillary buds in Leliwm
tigrinum. In this figure the malleus is not given; it is shown in fig. 5 (ml.). The
processus gracilis ( p.gr.) is reduced to a style, ending in fibrous tissue; the manubrium
(mb.) is flat and slightly arcuate; the “head,” articulated with the incus, is elegantly
notched for this purpose, and fits on to the incus by a synovial joint, the miniature of
that by which the tibia fits on to the astragalus in this same animal. Between the
head and the manubrium the bone is thin, and is scooped externally ; the head sends
inward a rounded process (¢.p.7.), and the manubrium sends backwards an angular snag ;
this latter is for the attachment of the “ tensor tympani” muscle. ‘The little secondary
nucleus of cartilage which we saw developed between the dislocated incus and stylohyal
(Plate XXX. figs. 8 & 9, d.hy.) is now attached to the neck of the stapes by its broad
outer end, whilst its bluntly pointed distal end is buried in the fibres of the tendon of the
“ stapedius’”’ muscle (st.m.). ‘This is the /ast effect of the high degree of metamorphosis
exhibited by the second postoral bar of the Mammal. ‘The fore edge of the exoccipital,
with its paroccipital spur (fig. 2, ¢.0., p.oc.), is strongly clamped upon the auditory capsule ;
this is also made still stronger by the large posterior flange of the overgrowing squamosal,

?

not shown in this figure.

The under surface of the snout is also given at this stage, to show the complete
coalescence of the ale nasi with the recurved trabecular horns, and their continuation
backwards as the ‘recurrent lamine” (rc.c.), also the alinasal external segment or
“appendix.” ‘The solid fore end of the snout, already full of small blood-vessels, is
ready to become the snout-bone for rooting ; this bone is formed in the ossified knees
of the trabeculee: the stunted, recurved prenasal cartilage is now undistinguishable
from the base of the septum nasi, formed by the complete coalescence of a large tract of
the trabecular bars, the long commissure of the foremost facial arch.

Eighth Stage-—The Skull of a Pig 6 months old.

This makes a more convenient /ws?f stage than the adult, as here are still in existence
the greater number of the sutural landmarks, so soon to be largely obliterated, whilst
the change in general form is rather of interest to the zoologist than to the morpho-
logist. The long angular skull (Plate XXXVI. fig. 4, and Plate XX XVII. figs, 1 & 2)

2U2

524 MR. W. K. PARKER ON THE STRUCTURE AND

is an irregular pyramid, with two equal and two unequal sides and an oblique base.
A complete contrast in outward form to the human skull, that of the Pig is straightest
of all the types; it is very angular and strongly built, but its bone-tissue is inferior in
density to that of the Sheep, being intermediate in this respect between the bone of a
tuminant and that of a Cetacean. The flat top of the skull, with its orbits flush with
the top, indicate the semiaquatic habits of its owner; and the immense depth and
squareness of the base of the pyramid is correlative to the high neck and strong
shoulders of this type: leverage is suggested by every ridge and every snag. Coming
back to the morphology of the matter, I may remark that the long straight nasals
(Plate XX XVII. fig. 1, 7.) overlap the snout in front, and only show their edge in the
side view. ‘They are articulated by suture along their outer edge with the upper edge
of the long premaxillary wedge (pa.), and for a less extent with the maxillary (mw.) ;
they terminate in a transverse line half an inch behind their mazil/ary suture. 'The
frontals (f.) together form a somewhat pentagonal plate, divided along the mid line by .
the sagittal suture. The anterior third is deeply grooved, the grooves issuing from the
“infraorbital foramen ;” the posterior half of their outer margin is thick, and some-
what raised as the superorbital ridge. There is a large orbital plate (Plate XXXVIL
fig. 1) which is bounded behind above by the short arrested postorbital process, and
lower down and within by the orbito-sphenoid (0.s.). The upper surface of the parictals
(p.) is of short extent, and divided by the continuation of the sagittal suture ; they are
greatly pinched in to form the large temporal fossa (¢.f.); and behind they are somewhat
impinged upon by the large superoccipital wall (s.0.).

The premaxillaries (Plate XXXVI. fig. 4, and Plate XXXVII. fig. 1, pa.) have a
large facial and a lesser palatine region, the palatine spurs ( p.pa.) being slender and com-
pressed. The huge maxillary (i2.), besides forming most of the fore face and the anterior
root of the zygoma, byits last tooth-socket (a large pupiform cavity), binds behind upon the
external pterygoid plate and descending extremity of the palatine (Plate XXXVIL. fig. 1,
m&.,pa.,e.py.). Below (see Plate XXXVI. fig. 4, me.) it forms three fourths of the elegant
grooved and ribbed hard palate; the double “posterior palatine foramen” (p.p,f-)
is partly in this bone and partly in the palatine. The median suture of the hard
palate (Plate XXXVI. fig. 4) is two thirds the length of the skull and face. The
palatine bones (pw.) by their primary ascending plate articulate with the vomer, and
send forwards a long scoop-like process beneath the lateral ethmoids. After forming
the elegant end of the hard palate they grow downwards as a thick boss, which articu-
lates with the maxillary and external pterygoid process on the outside, and with the
internal pterygoid plate on the inside. ‘Chis latter bone, the “ pterygoid” proper (pq.), is
very thin in its ascending part; and on the right side the uppermost squamous part is
a separate piecc, the mesopterygoid (Plate XXXVL. fig. 4, ms.pg.), a bone not commonly
distinct in the Mammalia; yet in my collection it occurs in the Fox (Canis vulpes),
and is subdistinct in the Hedgehog (Lrinaceus cwropeus); here, in the Pig, it is a small
triangular scale. ‘The inferior part of the pterygoid is thicker and is subfalcate, the

DEVELOPMENT OF THE SKULL IN THE PIG. 325

hooked portion (“ hamular process”) being the apex of the pterygo-palatine arch. The
top of the pterygoid, behind the mesopterygoid, has already coalesced with the pos-
terior sphenoid at the root of the “ala,” and externally also it is almost completely
confluent with the “external plate ” (e.pq.).

The thin dentate end of the vomer (Plate XXXVI. fig. 4, v.) ends at the same trans-
verse line with the mesopterygoids, whilst in front it reaches the fore margin of the
premaxillaries within a barleycorn’s length. The vomerine plate broadens a little to sit
on and articulate with the upturned and dovetailed edge of the palatine plate of the pala-
tine bones, and also with the longer “ harmony suture” of the maxillaries ; its groove
for the trabecular subseptal beam is rather deep. The complex nasal labyrinth is well
ossified, but the septum between the inferior turbinals, supplied by the fifth nerve, is
still soft. Beneath the large lacrymal, the “lamina papyracea” of the ectoethmoid
is Just seen beside the pupiform socket of the developing last molar tooth.

The lacrymal (Plate XX XVII. fig. 1, 7.) is a notable bone on the outer cheek,
with an upper and a lower canal ; it is deeply scooped where it articulates antorbitally
with the orbital plate of the frontal (Plate XNXVIL. fig. 1, /., £.); it forms part of
the anterior root of the zygoma, and is nearly equally developed both within and with-
out the orbit.

The malar or jugal (j.) is a massive bar of bone, strongly set in at the front of the
orbit between the lacrymal and maxillary (Plate NN XVII. fig. 1.7.,7.,7.). It is saddle-
backed in its front thicker part, and its hinder half suddenly becomes only as thick as in
front, so that the squamosal may yoke on to it; its lower surface is arcuate, its inner sur-
face scooped, and its outer surface convex: almost an inch of space intervenes between
the highest part of the malar and the descending postorbital spur of the frontal. The
proper temporal bone, fitting scale-like to the temporal region of the skull, over the
hinder edge of the frontal and the lower part of the parietal, is properly called the
squamosal (sqg.). ‘This temporal part turns suddenly outwards to catch the pyriform
condyle of the lower jaw, and then runs forwards and rides on the upper edge of the
malar, stopping behind the concave portion of that bone. This zygomatic process of the
squamosal rises sharp above the transverse ‘“ glenoid” bridge, which is scooped above
and below, has a convex transverse part in front, and an angular scooping behind: this
part is clothed with articular cartilage, and the mandibular condyle rides freely wader
and wp it, a meniscus intervening.

There is an acute ridge which runs obliquely up to the upper third of the superoccipital
(Plate XX XVII. fig. 1, s7., s.0.); this rising wall closes in the deep temporal fossa.
This ridge of bone, running downwards also, binds strongly upon and coalesces with the
rough rounded uplooking mouth of the “ meatus auditorius externus” (m.e.). Below this
part the squamosal splits into two narrow rough leaves; the hinder of these is the
“posttympanic process,” and the front leaf is the “ postglenoidal.” The latter binds
upon the side of the tympanic (ty.), the former runs down the fore edge of the par-
occipital (paramastoid) process (p.oc.), and scoops its upper third. In front of the

326 MR. W. K. PARKER ON THE STRUCTURE AND

glenoid facet the squamosal is strongly sutured to the alisphenoid (a/.s.) and to its great
expanded wing (é.pq.). ‘Together, the zygomatic elements make a strong, deep, and
convex arch on each side, which starts rather sharply upwards.

‘The tympanic (ty.), now like a large filbert in form and size, although snaggy and
ridged below, is principally a mass of square-chambered diploé. It has a small cavity,
to the produced edge of which the membrana tympani is attached; and its former
“crura” have met, run upwards, and formed the curious, ascending, coral-like meatus.

The flange of the anterior crus is now a squamous process beneath the squamosal, and
close to the inner edge of the glenoidal cartilage. As there are no proper “ foramina
ovalia” in the posterior sphenoid, so there isa continuous “ foramen lacerum” round the
tympanic, and between it and the basis cranii (Plate XXXVI. fig. 4, f.l.p.). Looking
through these large chinks we can see a small part of the periotic mass, which is very
separate from the surrounding parts. ‘The great occipital plane (Plate XX XVII. fig. 2,
8.0., €.0., b.0.) is scooped above (s.o.), and then the bone bends forwards, wedging itself
in between the parietals: the upper element is alate above, and then narrows in and
rests obliquely upon the exoccipitals (¢.0.), forming the keystone of the archway for the
medulla spinalis, the foramen magnum (f:m.). The arch again expands its sides, the
exoccipitals spreading out behind and over the mastoids, which further outwards are
of the squamosal. These lateral

)

plastered over by the “ posttympanic processes’
pieces run downwards as the long paramastoid, or, more correctly, paroccipital spurs ;
whilst their middle region juts out, and forms the diverging, semioval, subpedunculate
articular condyles (0c.c.). Inside the paroccipital process there is a considerable fora-
men for the hypoglossal nerve (Plate XXXVI. fig. 4,9). In front of the paroccipital
process there is a canal, bounded on the outside by the posttympanic spur of the
squamosal, and on the inside by the unciform tympanic. Looking up this canal we
see that its inner half is occupied by a rod of bone, thickest below, where it is flat, the
continuing cartilage being macerated off. This rod is the apex of the stylohyal
“tympano-hyal” (FLOWER), and the open tube is the canal for the portio dura; its
mouth is the *‘ stylo-mastoid foramen.”

The basioccipital (Plate XXXVI. fig. 4, b.0.) is a pentagonal lozenge of bone, joining
the sides of its own arch by suture, and separated from the next basal piece (d.s.) by a
narrow synchondrosis. This basioccipital plate is mammillate at the sides below, and
subcarinate mesially: it is the notochordal bone. Next in front is the basisphenoid
(Plate XXAVI. fig. 4, .s.), now merely the basal part of an inverted arch of bone, the
“posterior sphenoid.” ‘The narrow cartilaginous tract between this and the bar in front
is hidden below by the end of the vomer, and by a sharp ridge which grows mesiad
from each alisphenoid (Plate XXXVI. fig. 4, al.s., 0.s.,v.). The orbito-sphenoids have
met below, ossifying the underlying trabecular bar, which part is ensheathed by the
vomer. ‘These large wings can be seen in the posterior part of the orbit around and
above the optic foramen (Plate XXXVIL. fig. 1, 0.8.2), and also from behind through
the foramen magnum (Plate XXXVII. fig. 2, 0.s.,2). The change which has taken

DEVELOPMENT OF THE SKULL IN THE PIG. ; 3a

place in the little auditory ossicles is too small to require special notice. The mandibular
rami (Plate XX XVIL. fig. 3) are quite distinct from each other at present: they are
large deep bones, with a small notch between the coronoid and articular regions; the
latter is somewhat pyriform, with the narrow end inwards; the angular region is flat,
with a round outline and a thick rugose edge.

Ninth Stage.—The Skull in Adult Pigs.

The further changes that take place in the Pig’s skull are mainly increase of size and
extensive ankylosis. Besides referring the reader to the actual object, I may mention
that a short and useful account of this type of cranium will be found in Professor
Fiowrr’s work, ‘An Introduction to the Osteology of the Mammalia, 1870, p. 172,
and also in Professor Huxtey’s ‘ Anatomy of the Vertebrated Animals,’ 1871, p. 368.

SUMMARY.

The most important results of the present investigation may be stated as follows :—

1. Ina pig embryo, in which the length of the body did not exceed two thirds of an
inch, and four postoral clefts were present, the cranio-facial skeleton was found to
consist of :-—

(a) the notochord, terminating bya rounded end immediately behind the pituitary body.

(2) On each side of the notochord, but below it, a cartilaginous plate, which in front
ends by a rounded extremity on a level with the notochord, whilst behind it widens out
and ends at the free lower margin of ‘the occipital foramen. These two plates, taken
together, constitute the ‘investing mass” of Raruke. In this stage they send up no
prolongations around the occipital foramen ; in other words, the rudiment of the basi-
occipital exists, but not that of the exoccipital nor superoccipital.

(c) The large oval auditory capsules lie on each side of the anterior half of the in-
vesting mass, with which they are but imperfectly united: there is no indication of the
stapes at this stage.

(d) The trabecular or first pair of preoral visceral arches enclose a lyre-shaped pitui-
tary space; they are closely applied together in front of this space, and, coalescing, give
rise to an azygous prenasal rostrum: they are distinct from one another and the
investing mass.

(e) The pterygo-palatine or second pair of visceral arches lie in the maxillo-palatine
processes, and are therefore subocular in position. Each isa sigmoid bar of nascent
cartilage, the incurved anterior end of which lies behind the interior nasal aperture,
while the posterior extremity is curved outwards at about the level of the angle of the
mouth. ‘The pterygo-palatine cartilages are perfectly free and distinct from the first
preoral and the first postoral arch, although developed in a process of the latter, and
are therefore secondary arches.

(f) The mandibular or first pair of postoral visceral arches are stout cartilaginous
rods of cartilage, which lie in the first visceral arch behind the mouth. The ventral or

328 MR. W. K. PARKER ON THE STRUCTURE AND

distal ends of these arches are not yet in contact; the dorsal or proximal end of each is
somewhat pointed and sharply incurved, pushing inwards the membrane which closes
the first visceral cleft and is the rudiment of the membrana tympani.

(y) The hyoid or second pair of postoral arches are in this stage extremely similar to
the first pair, with which they are parallel. They are stout sigmoid rods of cartilage,
which are separated at their distal ends, present an incurved process at their opposite
extremities, and are not segmented.

(1) The thyrohyal ox third postoral arches, which correspond with the first branchial
of branchiate Vertebrata, are represented by two short cartilaginous rods which le on
each side of the larynx.

(‘) The olfactory sacs are surrounded by a cartilaginous capsule, which has coalesced
below with the trabecula of its side; while, within, the mucous membrane lining the
capsule presents clevations which indicate the position of the future turbinal outgrowths
of the capsule.

In this stage the posterior nares are situated at the anterior part of the oral cavity,
as in the Amphibia; and the roof of the mouth is formed by the floor of the skull, the
palatal plates of the maxille and palatine bones being foreshadowed by mere folds.
The outer end of the cleft between the trabecula and the secondary preoral arch appears
to be the rudiment of the lacrymal duct, while its inner end is the hinder nasal aperture.
The gape of the mouth is the cleft between the second preoral and the first postoral arch.
The auditory passage, representing the Eustachian tube, tympanum, and external auditory
meatus, is the cleft between the first and second postoral arches. ,'The proximal end of
the mandibular arch, therefore, lies in the front wall of the auditory passage, and the
hyoid in its hinder wall.

2. In an embryo pig, an inch in length, (7) the notochord is still visible; (d) the
investing mass, the halves of which are completely confluent, has become thoroughly
chondrified, and is continued upwards at each side of the occipital foramen to form an
arch over it.

(c) The auditory capsules are still distinct from the investing mass, and a plug on the
outer cartilaginous wall of each has become marked off as the stapes.

(d) The hinder ends of the trabecular arches have coalesced in front of the pituitary
body, but they are not yet confluent with the imvesting mass.

(e) The pterygo-palatine rods have increased in size; they have not become hyaline
cartilage, but are beginning to ossify in their centre.

(f) In the mandibular arch the proximal end has become somewhat bulbous, and is
recognizable as the head of the malleus, whilst the incurved process, still more prominent
than before, is the manubrium mallei. The rest of the arch is MECKEL’s cartilage; out-
side this a mass of tissue appears, which is converted into cartilage, rapidly ossifies, and
eventually becomes the ramus of the mandible.

(y) The proximal end of the hyoidean arch, similarly enlarging and articulating with
the corresponding part of the mandibular arch, becomes the incus, the incurved process

29

eo

DEVELOPMENT OF THE SKULL IN THE PIG.

attaching itself to the outer surface of the stapes and becoming the long process of the
incus. The incus, thus formed out of the proximal end of the hyoidean arch, becomes
separated from the rest of the arch by conversion of part of the arch into fibrous tissue,
and the moving downwards and backwards of the proper hyoid portion of the arch. A
nodule of cartilage left in the fibrous connecting band becomes a styliform ‘ interhyal ”
cartilage, while the proximal end of the detached arch becomes the stylohyal.

(h) The thyrohyals have merely increased in size and density ; they closely embrace
the larynx by their upper ends.

(‘) The olfactory capsules are well chondrified, and their descending inner edges have
coalesced with each other and with the trabecule below to form the great median
septum: the turbinal outgrowths are apparent.

In this stage the alisphenoids and orbito-sphenoids appear as chondrifications of the
walls of the skull, quite independent of the investing mass and the trabecule.

The floor of the pituitary space chondrifies independently of the trabecule and the
moieties of the investing mass, but serves to unite these four cartilaginous tracts.

3. In an embryo pig 1} inch in length, (a, 6, ¢) the primordial cranium is completely
constituted as a cartilaginous whole, formed by the coalescence of the investing mass
and its exoccipital and superoccipital prolongations, the modified trabecule, the sub-
pituitary cartilage, the auditory capsules, the alisphenoidal and orbito-sphenoidal carti-
lages, and the olfactory capsules. The notochord is still to be seen extending in the
middle line from the hinder wall of the pituitary fossa (now the clinoids of the sella
turcica) to the posterior edge of the occipital region.

(d) The trabecular arches form the sides of the sella turcica, the presphenoid, and
the base of the septum between the olfactory capsules; in front, where they form the
azygous prenasal or ‘“ basitrabecular” element, they are developed backwards as
“yecurrent bands,” elongations of the free recurved cornua.

(ec) The pterygo-palatine arches, still increasing in size, but not chondrifying, now
rapidly ossify; they are half-coiled laminze bounding the posterior nasal passages.

(f) The mandibular arches and the rudimental ramus have become solid cartilage,
and the latter is ossifying as the dentary; the distal part of each mandibular rod unites
with its fellow for some distance.

(y) The hyoid arches are now more fully segmented as incus, with its orbicular
head, interhyal, stylohyal, and ceratohyal.

(h) The thyrohyals are merely larger and denser.

(‘) The olfactory capsules have now the turbinal outgrowths all marked out as ali-
nasal, nasal, upper, middle, and lower turbinals.

4. In pigs of larger size the form and proportions of all the parts of the cranium
become greatly altered, and ossification takes place on an extensive scale, but no new
structure is added.

5. It follows from these facts that the mammalian skull, in an early embryonic con-
dition, is strictly conformable with that of an Osseous Fish, a Frog, or a Bird at a like
period of development, consisting as it does of :—

MDCCCLXXIV. 2X

350 MR. W. K. PARKER ON THE STRUCTURE AND

(«) A cartilaginous basicranial plate embracing the notochord, and stopping, like it,
behind the pituitary body.

(4) Paired cartilaginous arches, of which two are preoral, while the rest are postoral.

(c) A pair of cartilaginous auditory capsules.

(7) A pair of cartilaginous nasal capsules.

Further, that in the Mammalia, as in the other Vertebrata the development of the
skull of which has been examined, the basicranial plate grows up as an arch over
the occipital region of the skull, and coalesces with the auditory capsules, laterally, to
give rise to the primordial skeleton of the occipital, periotic, and basisphenoidal regions
of the skull. The trabeculee become fused together, and, uniting with the olfactory
capsules, give rise to the presphenoidal and ethmoidal parts of the cranium; and the
moieties of the skull thus resulting from the metamorphosis of totally different morpho-
logical elements become united to give rise to the primordial cranium.

As in the Salmon and Fowl, the second pair of preoral arches give rise to the pterygo-
palatine apparatus; in the Frog this arch is late in appearance, and is never distinct
from the trabecular and mandibular bars, serving as a conjugational band between
them. ‘The mandibular arch, which in the Salmon becomes converted into MECKEL’S
cartilage, the os articulare, the os quadratum, and the os metapterygoideum, in the
Frog into MEcKEL’s cartilage and the quadrate cartilage (which early becomes confluent
with the periotic capsule), in the Bird into Mrcxet’s cartilage, the os articulare, and the
os quadratum (which articulates movably with the periotic capsule), in the Pig is meta-
morphosed into the malleus, which is loosely connected with the tegmen tympani, an
outgrowth of the periotic capsule.

MECKEL’s cartilage persists in the Fish and the Amphibia, but disappears early in the
Bird, and still earlier in the Mammal. The permanent ossifications formed outside the
primary mandible are all membrane-bones in Fish, Frog, and Fowl, but in the Mammal
(exceptionally) the ramus has a cartilaginous foundation. In the Fish the hyoidean
arch becomes closely united with the mandibular, and then segmented into the hyo-
mandibular, the stylohyal, ceratohyal, and hypohyal—the hyomandibular or proximal
segment articulating with the outer wall of the periotic, and many of the segments
becoming dislocated.

In the Frog the hyoid also becomes segmented into three pieces. The middle
segment becomes the suprastapedial (hyomandibular) with its extrastapedial process,
and, extending inwards as mediostapedial, ‘articulates with the stapes, developed by
segmentation from the outer wall of the auditory capsule, the proximal part, or inter-
stapedial, intervening. The stylohyal is dislocated and becomes connected with the
auditory capsule below the stapes (opisthotic region).

In the Bird the hyoidean arch remains distinct from the mandibular; whilst in its
primordial condition it coalesces by its incurved apex with the auditory capsule in front
of the promontory, before the stapedial plug is segmented. It then chondrifies as three
distinct cartilages—an incudal, a stylohyal, and, distally, a ceratohyal. The stapes

becomes free from the auditory capsule. but remains united with the cartilaginous part

DEVELOPMENT OF THE SKULL IN THE PIG. 331

of the incus (mediostapedial) ; the ascending part islargely fibrous (suprastapedial), and
the part loosely attached to the mandibular arch is the elongated extrastapedial. ‘The
short stylohyal afterwards coalesces with the body of the upper or incudal segment by
an aftergrowth of cartilage (the “interhyal” tract); a long membranous space inter-
venes between it and the glossal piece (ceratohyal). Thus the “columella” of the
Bird is formed of three hyoidean and one periotic segment.

In the Pig the hyoidean arch is distinct, but articulates closely with the mandibular ;
its upper segment (hyomandibular) is converted into the incus, and becomes connected
with the stapes, its disciform apex being ossified as the ‘os orbiculare.” ‘The stylo-
hyal is dislocated and coalesces with the opisthotic region of the auditory capsule.

The views which have hitherto been entertained respecting the mode of development
of the ossicula auditus of the Mammalia fall under four heads:—-

1. According to Retcuert*, the malleus and incus both result from the metamorphosis
of the cartilaginous skeleton of the mandibular arch, while the stapes proceeds from an
after segment of the hyoidean arch, which becomes separated and imbedded in the outer
wall of the auditory capsule.

The latest writer on the subject, SEMMER?, supports Reicuert’s views in the main,
but is not quite sure about the origin of the stapes.

2. GtytueRyT holds that not only the malleus and the incus, but the stapes as well,
are the product of the metamorphosis of the skeleton of the mandibular arch.

3. Maciror and Rosin 9, on the other hand, maintain that the malleus only takes its
origin from the skeleton of the mandibular arch. ‘They consider the incus and stapes
to arise independently, but do not expressly refer them to the skeleton of the second
postoral visceral arch.

4. Professor Huxtey||, arguing from the anatomy of the mandibular and hyoidean
arches in the lower Vertebrata, has put forward the view that the malleus of the Mam-
malia is the product of the metamorphosis of the proximal end of the cartilaginous
skeleton of the mandibular arch, while the incus proceeds from the proximal end of the
hyoidean arch, and is the homologue of the “ suprastapedial” of the Sawropsida. He
expresses no opinion respecting the origin of the stapes.

* « Ueber die Visceralbogen der Wirbelthiere,’ Mitier’s Archiv, 1837.

y Untersuchungen iiber die Entwickelung der Meckel’schen Knorpels und seiner Nachbargebilde. Dorpat,
1872.

+ Beobachtungen tiber die Entwickelung des Gehérorganes bei Menschen und héheren Siiugethieren. Leipzig,
1842.

§ “ Mémoire sur un organe transitoire de la oie feetale désigné dans le nom cartilage de Mecxer,”’ Annales des
Sciences Naturelles, s¢r. 4, i., xviii. 1862.

|| “On the Representatives of the Malleus and the Incus of the Mammalia in the other Vertebrata,” Pro-
ceedings of the Zoological Society, 1869.

ish)
os
bo

AN.
acl,

ale.

aln.

als.
al.tb.
aq.v.
a.8C.

a.ty.

au.

ba.

b.br.

bh, by.
b.o.

bs.

b.tr.

C.d.

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cr.

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flip:
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h.br.

hise.

hy.

* These may be counted from the lacrymal cr first preoral, or from the tympanic or first postor:

MR. W. K. PARKER ON THE STRUCTURE AND

EXPLANATION OF ABBREVIATIONS,

appendix alee nasi.
anterior clinoid wall.
aliethmoid.

alinasal.

alisphenoid.

alinasal turbinal.
aqueduct of the vestibule.
anterior semicircular canal.
annulus tympanicus.
auditory sac.

basilar artery.
basibranchial.

basihyal.

basioccipital.
basisphenoid.
basitrabecula.

concha auris.

common (auditory) canal.
ceratohyal.

cochlea.

Ist, 2nd, and following visceral clefts*.

coronoid process of mandible.

. cutis.

cornua trabeculae.
thalamencephalon.
hemisphere.

2nd cerebral vesicle.
3rd cerebral vesicle.

. dentary.

dentary part of premaxillary.

. eyeball.

. epiotic.

external nostril.

. exoccipital.

external pterygoid plate.
Sustachian tube.

frontal.

foramen lacerum posterius.
foramen magnum.

fenestra ovalis.

fenestra rotunda.
hypobranchial.

horizontal semicircular canal.

hyoid.

VCs
ihy.
in.
ip.
i.tb.

Ww.

dw.

m.
mb.
ne,
Me.
meth.
mike.
MC.
ml.
mn.
mn.
Vit ob,
MS.pY.
m.th,
mtr.
m.ty.
Mu.
MU pPe
ne
NW.
0.0.
0c.C.
@,

ol.
0.0),
OS.
OU.
p.
pe.
pe.

internal carotid artery.
interhyal.

inner nostril.

internal process of malleus.
inferior turbinal.
investing mass.

jugal.

jugular vein.

lacrymal.

long crus of incus.
lateral cerebellar recess.

. lower lip.
. lip.

lateral sinus.
larynx.

mouth.
manubrium mallei.
meniscus.

meatus externus,
mesethmoid.
Mecker’s cartilage.
Meckelian commissure.
malleus.

mandible.

middle nostril.
medulla oblongata.
mesopterygoid.
middle turbinal.
middle trabecula.
membrana tympani.
maxillary.
maxillo-palatine.
nasal,

nasal wall.

os bulle.

occipital condyle.
cesophagus.
olfactory sac.

os orbiculare.
orbito-sphenoid.
ophthalmic vein.
parietal.

palatine.
perpendicular ethmoid.

1.

PY:
par.

pn

pnw.

p.0e.
pee.
P-pg-
Pp:
ppe.
te
pro.
ps.
pS.
Ry«
770.0.
S.Ct.
s.mf.
Sn.

SO.

S.pd.
Sp.S.

Fig. 1
Fig. 2.
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7.
Fig. 8.
Fig. 1

OG) bo

DEVELOPMENT

pterygoid.

processus gracilis.

prenasal cartilage.
posterior nasal wall.
paroccipital.

posterior palatine foramen.
palato-pterygoid.

palatine floor of palatine.
palatal part of premaxillary.
promontory.

prootic.

presphenoid.

posterior semicircular canal.
pituitary body.

recurrent cartilages.

short crus of incus.
stylo-mastoid foramen.
septum nasi.
supero-occipital.

soft palate.

sphenoidal sinus.

. squamosal.
. sella turcica.
. Stapes.

stylohyal.
stapedius muscle.

OF THE SKULL IN THE PIG.

t.C.

t.ch.

tf.

ty.

th.h.

tp.
Aes

trem.

t.ty.

ty.
ul.
u.th.

tympanic cayity.
tentorium cerebelli.
temporal fossa.
tongue.

thyrohyal.
tooth-pulp.
trabecula.
trabecular commissure.
tegmen tympani.
tympanic.

upper lip.

upper turbinal.

- vomer.

vestibule.
zygomatic process of maxillary.
zygomatic process of squamosal.

. olfactory nerve.

. optic nerve.

. ophthalmic nerve.

5°’, main part of 5th nerve.
. portio dura.

7”. chorda tympani.

. portio mollis,

. glossopharyngeal.

. vagus.

9. hypoglossal.

DESCRIPTION OF THE PLATES.

PLATE XXVIII.
First Stage —Embryo Pig, 3 inch in length.

diameters.

. A vertical section of the head.

x

< 7 diameters.

. A plan of the skull and face, seen from below.
x 10 diameters.

. Side view of upper part of embryo. x 7 diameters.
A plan of the same, with facial arches.
. A front view of the same.
. A palatal view of the same, with the mandible and lower face removed. x 15

7 diameters.

x 10 diameters.

Part of the same, with median part of nasal region removed. X 20 diameters.

Upper view of a horizontal section of the head.

x 10 diameters.

PLATE XXIX.

. Another section through the

. Transversely vertical section of the nose, in front.

1

< 12 diameters.

. A similar section through the middle of the nasal region. X 12 diameters.
posterior nasal region. Xx 12 diameters.

MR. W. K. PARKER ON THE STRUCTURE AND

. 4. Horizontal section below the cranial cavity, exposing first arch, notochord, and

investing mass. X 10 diameters.
A subhorizontal section through the eyes and root of tongue. Xx 10 diameters.

5.
. 6. Part of the head, with outer part of cheek pared away. x 12 diameters.
ls

A section made through the plane of the hinder part of cranium. x 12 dia-
meters.
8. Part of same section. x 20 diameters.

. 9. A similar section. * 26 diameters.

10. Another subhorizontal section through the top of the first postoral cleft. x 20
diameters.

PLATE XXX.

Second Stage-—Lmbryo Pig, 1 inch long.

. |. Section across the end of the snout. x 10 diameters.

. 2. Section through ethmoid region, root of tongue, and larynx. xX 12 diameters.
g. 8. Section nearly in plane of the notochordal region, front view. x 10 diameters.
. 4, A similar section, lower down. x 10 diameters.

i

g. 5. Part of a similar section through apex of mandibular arch, front view. x 15

diameters.

. 6. A similar section through apex of next arch, front view. x 15 diameters.
g. 7. Another similar section through periotic capsule in plane of horizontal canal.

x 10 diameters.

Third Stage—Embryo Pig, 1% inch long. ;

. 8. Part of a section through top of second postoral arch, corresponding with fig. 6

of second stage, front view. x 15 diameters.

g. 9. Side view of the three postoral arches. x 15 diameters.

PLATE XXXT.
Third Stage (continued).

1. Ist section through nasal region. x 7} diameters.

. 2. 2nd section of same. x 74 diameters.
ig. 2%. Part of fig. 2. x 223 diameters.

2

g. 3. drd section of same. x 74 diameters.

27)

. 3, Part of same section. x 224 diameters.
. 4. 4th section of same. x 74 diameters.
. 5. Oth section of same. x 74 diameters.
.. 6. 6th section of same. x 74 diameters.

6*. Part of fig. 6. x 20 diameters.
7. Tth section of nasal region. »x 74 diameters.
Va

. Mandibular portion of same section. x 73 diameters.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Fig. 10.
Fig. 1
Fig. 2
Fig. 3
Fie. 4
Fig. 5
Fig. 6.
Fig. 7
Fig. 8
Pig. 9
Fig. 10.
Fig. 11.

DEVELOPMENT OF THE SKULL IN THE PIG. 339

Fig. 8. 8th section of same. x 73 diameters.

Fig. 8". Mandibular portion of same section. Xx 7} diameters.
Fig. 9. 9th section of nasal region. x 7} diameters.

Fig. 10. 10th section of same. x 7} diameters.

Fig. 11. 11th section of same. x 7} diameters.

Fig. 12. 12th section of same. x 7} diameters.

Fig. 15. 15th section of same, head. > 7} diameters.

Fig. 14. 14th section of same, head. x 74 diameters.

Fig. 14". Part of fig. 14. x 14 diameters.

PLATE XXXII.
Third Stage (continued).

. 15th section of same, head. x 7 diameters.
. 16th section of same, head. x 7 diameters.
. 17th section of same, head. X 7 diameters.
. 18th section of same, head. x 7 diameters.

. 19th section of same (part back view). x 14 diameters.

. 20th section of same, head (back view). x 10 diameters.

. 21st section of same (part back view). x 14 diameters.

. 21st part of section (front view). x 14 diameters.

. Hinder part of a section taken horizontally through the nasal region (front view).

x 10 diameters.
A similar section of same taken further backwards and lower down (back view).
x 10 diameters.

PLATE XXXIIL.
Third Stage (continued).

. 22nd section of the same head (part seen from the front). x 14 diameters.
. Vertical section of head. » 5 diameters.
. The same, with brain and septum nasi removed. Xx 5 diameters.

Fourth Stage-—Embryo Pig, 24 inches long.

. Vertically transverse section through fore part of brain. x 5 diameters.
. A similar section through fore part of orbit (part). x 5 diameters.

A like section through hind part of orbit (part). > 5 diameters.

. A similar section through sphenoid (part). x 5 diameters.
. Part of same section (right side). x 14 diameters.
. A similar section through the fore part of auditory sac. x 7 diameters.

Another section through hinder part of same. x 14 diameters.

Fifth Stage.—Embryo Pig, 3 inches long.

Section through posterior sphenoid. x 54 diameters.

336 ON THE DEVELOPMEMT OF THE SKULL IN THE PIG.

PLATE XXXIV.

Fourth Stage (continued).
Side view of skull. > 535 diameters.
Lower view of same. X 34 diameters.
End view of same. > 34 diameters.
Upper occipital region of a somewhat younger embryo. X 54 diameters.
Section of skull (vertical). x 5} diameters.
Bird’s-eye view of primordial skull. x 5} diameters.

da" ae
or a

gq” 09
[=r)

coc Mco Nc CMce
dq oe
=

Fig. 7. Inner view of compound mandible. x 3} diameters.
Fig. 8. Ist section through nasal region. > 7 diameters.
Fig. 9. 2nd section of same part. x 7 diameters.

Fig. 10. 5rd section through nose. x 7 diameters.

Fig. 11. 4th section of same. x 7 diameters.

Fig. 12. 5th section through inferior turbinal. x 7 diameters.

PLATE XXXYV.
Sixth Stage —Embryo Pig, 6 inches long.

Fig. 1. Side view of skull. x 1) diameter.
Fig. 2. Lower view of same. X 1} diameter.
Fig. 3. Vertical section of same. x 1} diameter.

Fig. 4. Bird's-eye view of primordial skull. > 1} diameter.
. Outer view of occipital and auditory regions. > 2 diameters.

. Another through ethmoids. x 5 diameters.

. Part of section through hinder part of nasal labyrinth. > 35 diameters.
Fig. 9. Section through orbits. x 2 diameters.

Fig. 10. Part of section through anterior sphenoid. »X 3 diameters.

5

Fig. 6. Transversely vertical section through inferior turbinals. x 3 diameters.
if
8

Fig. 11. Section through hinge of lower jaw.» x 2 diameters.
Fig. 12. Section through periotic mass and basioccipital. x 3 diameters.
PLATE XXXVI.
Seventh Stage —Piq at birth.
. Under view of snout-cartilages. x 5 diameters.

Auditory capsule, hyoid, and occiput. Xx 3} diameters.
. Auditory chain of bones. x 5 diameters.

ty
ai
39
oo bo et

Eighth Stage.—Piq, 6 months old.
Fie. 4. Lower view of skull. Natural size.
PLATE XXXVII.

Fie. 1. Side view of same. Natural size.
Fig. 2. End view of same. Natural size.
Fig. 5. Side view of lower jaw. Natural size.

=

Phil. Trans. MDCCCLAAW. Plate Ki
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Phil. Trans M

DCCCLXXAIV. Plate XXIX.

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Phil Trans. MDCCCLXXIV. Plate XXX.

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Phil. Trans MDCCCLEXIV Plate XXXII

W.K P del ad-nat,Geo West hth. . W. West &C° imp.
Pie's es lewd
, Figs. 1-3, 37% Stage. Figs. ¢—10, 4% Stage. Fig. tl. 5% Stage.

Phil Trans MDCCCLXXIV. Plate XXXIV.

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mle pwe

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Phal. Trans MDCCCLXXLV. PlateXXxv-

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a

Parr U.—EDENTATA.
_- Parr IIL—INSECTIVORA.

BY

- WILLIAM KITCHEN PARKER, F.R.S.

_ From the PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY.—Parr I. 1885,

he

2

ON THE ~/ /7

STRUCTURE AND DEVELOPMENT

SKULL IN THE MAMMALIA.

Part IL.—EDENTATA.
Part UL—INSECTIVORA.

BY

WILLIAM KITCHEN PARKER, F.R.S

From the PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY.—Parr I. 1885.

J ; LONDON
: HARRISON AND SONS, PRINTERS IN ORDINARY TO HER MAJESTY,
ST. MARTIN’S LANE.

PHILOSOPHICAL TRANSACTIONS.

I. On the Structure and Development of the Skull in the Mammalia.—
Part Il. Edentata.

By WituiamM Kircoen Parker, F.R.S.
Received May 26,—Read June 19, 1884.
[Piares 1-15.]

INTRODUCTION.

SINCE my first attempt to work out the Mammalian type of skull, the greater part of
my time has been spent upon Cold-blooded Vertebrata--Fishes, Amphibia, and
Reptiles. But between the early part of 1873, when my paper on the skull of the
Pig was presented to the Royal Society, to the beginning of 1882, when I was able
to take up this Class once more, no time or chance was lost as far as materials
for work go; during those nine years a very large collection of embryos and of
early young of the various types of Mammalia was made.

This collection of materials is still going on, and will I trust go on for years to
come. No work lies before me of greater importance; and if the skull, in the Orders of
this, the highest Class, can thus be illustrated, it will give some roundness and shape
to the efforts and labour of the whole life of a never-weary worker.

T am very grateful to the friends that have so kindly and zealously helped me by
presents of specimens ; in this present piece of work I have had the greater part
of my materials from the following well-known Biologists ; viz., Professor W. H.
FLowenr, F.R.S., Dr. GUNTHER, F.R.S., Professor St. GzeorcE Mivart, F.R.S., Dr. P. L.

MDCCCLXXXV. B

2 MR. W. K. PARKER ON THE STRUCTURE AND

Scuater, F.R.S., and H. M. Warp, Esq. (who lost no opportunity during his Botanical
work in Ceylon of procuring valuable specimens for Professor HuxLEy and me).

The order in which these materials are worked depends upon their fulness in any
particular group; the Edentata are worked out, and the Insectivora are almost
finished; then will come the Marsupials; this is not the ‘ order of Nature,” but
of “necessity ;” and those who are interested in these matters must classify the data,
when they have been collected.

Nevertheless, I shall aim at bringing the Monotremata forward as soon as possible ;
thanks to Dr. Bennert, of Sydney, and to Professor MosELry, IT am able to begin at
the Ornithorhynchus and the Echidna. But my hopes, in that quarter, largely rest
upon the results to be obtained by those whom the liberality of the Royal Society
has put into a position for finding such treasures as the early stages of those archaic
forms of Mammalia. ;

As to the “ Order” now under consideration, the Edentata, I have worked out the
skull in one or more embryos, as well as young, in all but the Anteaters;* happily, of
that type I have the young in a very instructive stage.

My richest materials are in the family “ Dasypodide,” or Armadillos. With this
type I shall begin; it is perhaps, on the whole, the best, as it is not so intensely
specialised as the rest, and thus is fittest for comparison with the Insectivora; the
forms that are found on the highway of Mammalian life, and not in a bye-path, like
the Edentata.

The Insectivora will be described in my next, or third, part.

BIBLIOGRAPHY.

a. On the Zoology, Embryology, and Morphology of the Edentata, and of the
Mammalia, generally.

ALBRECHT, P.
1. ‘Mémoire sur le Basiotique.” Bruxelles, 1883.
2. ‘Sur la Fossette Vermienne du Crane des Mammiferes. Avec une planche. Bruxelles,
1884. (Contains Marsupials, Edentates (Dasypus novemeinctus), Sloths, Orycteropus,
Tatusia, Myrmecophaga.) Fig, 1, Halmaturus; fig. 2, Dasypus.
. ‘Sur les os intermaxillaires. Bruxelles, 1885.

He 29

‘Sur la Valeur morphologique de l’Articulation mandibulaire du cartilage de MECKEL et des
osselets de Ouie.’ Bruxelles, 1883.

5. ‘Sur la Valeur morphologique de la Trompe d’Eustache,’ &c. Bruxelles, 1884. (Important

for Mammahan homologies.)

* I have since received from Professor TrEyes an embryo of Cycloturus that has not yet been
worked out. An account of its skull will be given as an Appendix to the present paper.

7

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 3

ALLEN, Harrison, M.D. “Ona Revision of the Ethmoid Bone in the Mammalia.” Bulletin of the
Museum of Comparative Anatomy at Harvard College, Cambridge, Mass., U.S. Nov., 1882;
plates 1-7, pp. 135-164.

Batrour, F.M. ‘A Treatise on Comparative Embryology. Vol. 2. London, 1881.

BERGMANN, C. ‘Einige Beobachtungen und Reflexionen iiber die Skelettsysteme der Wirbelthiere,
deren Beerenzung und Plan.’ Gottingen, 1846. ,

BETZ Hay Uber den Primordialschiidel des Menschen.” ‘ FrorrEP’s Notizen, December, 1848.

Bipper, A. “De cranii conformatione ratione imprimis habitu Jacobsonii de cranio primordiali
ejusque ossificatione sententiz.” Dorpat, 1847.

BLAINVILLE, DE. ‘ Osteographie, 1835-54.

BoEtrcuEr, A.

1. “Bau und Entwicklung der Schnecke.” Denkschriften d. Kaiserl. Leop. Carol. Akad. d.
Wissens., vol. xxxv.

2. Several papers on the structure of the ear in Vircnow’s Archiv., Band xvii. and xix.}
‘ Archiv fiir Anatomie und Physiologie, 1869 ; ‘Archiv fiir Ohrenheilkunde,’ Band vi., 1871.

Born, G. “Die Nasenhéhlen und der Thrinennasengang der Amnioten Wirbelthiere.” ‘ Morpho-
logisches Jahrbuch,’ Bd. ii., 1876; Bd. v., 1879; and Bd. viii, 1882.

Bronn’s “Klassen und Ordnungen des Thierreichs.” Abtheilung Siiugethiere, von C. G. GIEBEL,
1874-79.

Corr, E. D. “On the Foramina Perforating the Posterior part of the Squamosal Bone of the
Mammalia.” Read before the Amer. Phil. Soc., Feb. 6, 1880.

Decker, Frrepricu. “Uber den Primordialschiidel einiger Siiugethiere.” ‘Zeitschrift fiir wissen-
schaftliche Zoologie, 1883, pp. 190-233, plate 9.

Dotto, J. “On the Malleus of the Lacertilia, and the Malar and Quadrate Bones of the Mammaha.”
Quart. Jour. Mier. Sci., xxiii, 1883. This paper contains a complete list of the literature on the
ear, and a tabular arrangement of the views held by previous authors.

Doran,* A. G. H. “Morphology of the Mammalian Ossicula Audittis.” Trans. Linn. Soc., Ser. 2.
Zool. vol. i., pp. 371-497, plates 58-64.

Dursy, E. “Zur Entwicklunesgeschichte des Kopfes des Menschen und der hoheren Wirbelthiere.”
Tiibingen, 1869.

Epwarps, Henri Minne et ALrnonse Mitne. ‘Recherches pour servir 4 l'histoire naturelle des
Mammiféres’ (2 vols.). Paris, 1868-1874.

FLoweEr, W. H.

1. “On the Development and Succession of the Teeth in the Armadillos (Dasypodida).” Proce.
Zool. Soc., 1868, pp. 878-380.

2. ‘An Introduction to the Osteology of the Mammalia, 1885.

3. “On the Mutual Affinities of the Animals composing the Order Ldentata.” Proc. Zool. Soc.,
1882, pp. 358-367.

4. Art. “Mammalia.” Encye. Brit., 9th edition, 1885.

5. “On the Orders and Families of the Mammalia.” Proce. Zool. Soc., April 17, 1883, pp. 178-186.
Fores, W. A. “On some points in the Anatomy of the great Anteater (Afyrmecophaga jubata).”
Proc. Zool. Soc., 1882, pp. 287-302.
Fraser, A. “On the Development of the Ossicula Auditiis in the Higher Mammalia.” Phil.
Trans., 1882, Part IIL, pp. 901-925, Plates 54-58.

* Mr. Doran gives a copious Bibliography of these special parts.

B 2

4 MR. W. K. PARKER ON THE STRUCTURE AND

Garrop, A. H. “Notes on the Anatomy of Volypeutes tricinctus, with remarks on other Armadillos.”
Proc. Zool. Soe., 1878, pp. 222-230.
GEGENBAUR, C.
1. “Ueber primiire und secundiire Knochenbildung, mit besonderer Beziehung auf die Lehre von
dem Primordialeranium.” ‘Jenaische Zeitschrift, vol. ii., 1867.
2. ‘Comparative Anatomy.’ Translated by Professor E. Ray LANKESTER and JEFFERY BELL.
London, 1878.
Gray, J. E.
1. “Revision of the Genera and Species of the Entomophagous Edentata.” Proc. Zool. Soc.,
1865, pp. 859-886.
2. “Notes on the Species of Bradypodide in the British Museum.” Proc. Zool. Soc., 1871,
pp. 428-449, plates 34-37.
HANNovER, A.
1. “Primordial brusken og dens Forbening i det Menneskelige Kraninm fer F¢dselen.”
Kopenhagen, 1880.
2. “On the Formation of Vertebree in the Human Skull.” Transact. Internat. Med. Cong.
London, 1881; ‘ Anatomy,’ vol. i.
Hasse, C. “Die vergleichende Morphologie und Histologie der hiiutigen Gehororgane der Wirbel-
thiere.” Leipzig, 1873.
Hearr, Water. “The Development of the Mole (Zalpa Europea).” Quart. Journ. of Microscop.
Se. for July, 1883.
HENSEN, V.
1. “Zur Morphologie der Schnecke des Menschen und der Siiugethiere.” Zeits. f. wiss. Zool.,
vol. xiii., 1863. .
2. “ Bemerkungen gegen die Cupula terminalis.” ‘Archiv fiir Anatomie und Physiologie, 1878.
Hunt, Davin. “A comparative sketch of the Development of the Ear and Eye in the Pig.” ‘Trans-
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Huscuke. “Ueber die erste Bildungsgeschichte des Auges und Ohres beim bebriiteten Kiichlein.”
‘Tsis, 1831, and MECKEL’s ‘ Archiv,’ vol. vi.
Higxanve I. El
1. “On the Theory of the Vertebrate Skull.”—Croonian Lecture. Proce. Roy. Soc., Nov. 18, 1858.
. ‘Elements of Comparative Anatomy.’ London, 1864.
. ‘A Manual of the Anatomy of Vertebrated Animals.’ London, 1871.
. “On the Representatives of the Malleus and Incus of the Mammalia in the other Vertebrata.”
Proc. Zool. Soc., 1869, pp. 391-407.
. “On the Application of the Laws of Evolution to the Arrangement of the Vertebrata, and
more particularly of the Mammalia.” Proe. Zool. Soc., Dec. 14, 1880, pp. 649-662.
Hiyrtt, J.
1. “ Vergleichend-anatomische Untersuchungen iiber das innere Gehérorgan.” Prag, 1845.

H OF bo

Ol

2. “ Chlamydophorus truncatus.” ‘Denkschriften der Wiener Akademie,’ ix., 1855.
Koiitker, A.
1. “ Mittheilungen der Naturforschenden Gesellschaft in Zurich,” 1847.
2. “Berichte von der Konigl. Zootomischen Anstalt zu Wiirzburg.” 2. Berichte f. d. Schuljahr
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5. “Allgemeine Betrachtungen tiber die Entstehung des knéchernen Schiidels der Wirbelthicre.”
Berichte y. d. Kéniel. Zoot. Anstalt zu Wirzburg, 1849.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 2

4. “Die Theorie des Primordialschiidels.” Berichte v. d. Konigl. Zoot. Anstalt zu Wirzburg,
1850, IL. Bd., p. 281.
5. “Entwicklungsgeschichte der Menschen und der hoheren Thiere.” Zweite Auflage.
Leipzig, 1880.
MECKEL, J. W. “Ueber die osteologischen Differenzen der Igelarten.” Beitrag zur verg]. Anat.,
Heft I., pp. 84-56; 1808.
Meyer, H. “ Der Knorpel und seine Verknocherung.” MULLER’s ‘ Archiv, 1849, p. 292.
Moipennaver, W. “Zur Entwicklung des mittleren und ausseren Ohres.” ‘ Morphologisches
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Parker, W. K., and Berrany, G. T. “The Morphology of the Skull” 1877.
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SALENSKY, W. “ Beitriige zur Entwicklungsgeschichte der knorpeligen Gehorknochelchen bei Siiuge-
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Sponpul, H. “ Uber den Primordialschiidel der Siiugethiere und des Menschen.” Ziirich, 1846.
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2. “Development of the Inferior Maxilla.” Reprinted from Trans. Odont. Soc., 1883.
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WIEDERSHEMM, Rost. “ Lehrbuch der vergleichenden Anatomie der Wirbelthiere.” Jena, 1885.

6 MR. W, K. PARKER ON THE STRUCTURE AND

b. On Jacopson’s Organ.

BaLocu. “Das JAcopson’sche Organ des Schafes.” Sitzunsgber. d. Kais. Akademie der Wiss.
zu Wien, vol. xl, p. 449.
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2. “Ueber die Nasenhohlen und den Thriinennasengang der Amphibien.” ‘Morph. Jahrbuch,’
Bd. ii., 1877, plates 39-41, pp. 577-646.
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Bad. v., 1879, und Bd. viii., 1882,
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KOLLIKER, A.
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Medicin-Fakultiit fiir F. von Riyeckrer,’ Leipzig, 1877.
2. ‘Verhandlungen der physikalisch-medizinischen Gesellschaft zu Wirzburg, xvu. (1883),
pp: 229-257 (four plates),*
Lesouce, H. ‘“ Le Canal naso-palatin chez ?Homme.” ‘ Archives de Biologie,’ vol. i1., 1881.
LeGAaL, E, “ Die Nasenhohlen und der Thrinennasengang der amnioten Wirbelthiere.” ‘Morpho-
logisches Jahrbuch,’ Bd. vii., 1882.
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WIEDERSHEIM, R.
1. “Das Kopfskelet der Urodelen,.” ‘Morphologisches Jahrbuch,’ Bd. IIL, 1877.
2. ‘Die Anatomie der Gymnophionen.’ Jena, 1879,
3. “Die Stammesentwicklung des JAcoBpson’schen Organs.” ‘Tageblatt der 54. Versammlung
deutscher Naturforscher und Aerzte in Salzburg, 1881.

* For an abstract of this important paper, “ On the Development of the Optic and Olfactory Organs
of Human Embryos,” see Jour. Roy. Micros. Soc., 1884, pp. 201-203,

“TI

DEVELOPMENT OF THE SKULL IN THE MAMMALIA.

DaASYPODID®.

First Stage. Embryos of Tutusia hybrida, 13 inch long, measured, in these, and
the rest, from snout to root of tail (see Plate 1, figs. 7, 8).

Second Stage. Embryos of Tatusia hybrida, 2 inches long.

Third Stage. Embryos of Tatusia hybrida, 3 inches long.

Fourth Stage. Embryos of Tatusia peba, 3 inches long.

Fifth Stage. Embryo (ripe) of Tatusia hybrida, 4 inches long. Ripe young of
Dasypus villosus, 3% inches long.

Sixth Stage. Young (new born ?) of Tatusia peba, 44 inches long.

First Stage.—Tatusia hybrida (13 inch long).

In this, the youngest specimen obtained, I shall describe the chondrocranium with
its commencing bony centres and visceral arches, as seen in dissection, and then give
its structure in detail, as illustrated by a series of vertically transverse (transparent)
sections.

Afterwards, in the second stage, the investing bones will be described in their form,
as well as in their relations.

General remarks upon the early skull of the Mammal.

So great is the uniformity of the early chondrocranium in the Eutheria, or Placental
Mammals, that this drawing (Plate 2, fig. 1), made from the skull of an outlying and
low type, might serve as a diagram wherewith to illustrate the skull, at this stage, of
the types of this Order, and of all the Orders above it.

The figure of a chondrocranium like this, but a little less advanced, before the
osseous centres have commenced in it—that of the Mole—will be given in my next
paper ; and such a skull comes very near to that of a Shark or, still better, of a Skate.

The parts, or rather regions, of which it is composed, correspond very exactly with
what is seen in those generalised, but not dow, Fishes; and in this specimen, with
bony centres appearing, the level is obtained which is permanent in the skull of the
Dipnoi, and of such a low Ganoid as the Paddle-fish (Polyudon).*

As in Cartilaginous Fishes and Amphibians, the chondrocranium may be compared
to a basin or a boat, the upper part being unfinished, leaving a membranous fontanelle
of greater or less extent ; this is only partially filled in, at present, by the investing
bones, the frontals and parietals (/,, p.).

The outline of this sectional view is very elegant, and quite similar to that of
a vertical section of a Bird’s skull at a like stage, except that the nasal roof-cartilages

* See Bripge, “ On the Skull of Polyodon folium,” Phil. Trans., 1878, Plates 55-57, pp. 683-733.

5 MR. W. K. PARKER ON THE STRUCTURE AND

run on along the whole extent of the median keeled bar—the intertrabecula ; in the
Bird they stop short, leaving a free cartilaginous rostrum, like that of a Shark or
Skate, which, however, only lasts until it has served as a model on which the huge
premaxillaries of the Bird are formed.

In the sides of this hollow cartilaginous structure, near the hind part, the large
oval auditory capsules (a.s.c., chl.) are seen to have great distinctness; they are, how-
ever, confluent, with the chondrocranium proper, at various points—above, behind, and
below, as the sections will show. These are the only sense-capsules displayed in a
preparation of this kind, for the eye-balls are quite free from the solid cranial
structure (and are, indeed, outside, in such a view as this), and the left nasal
labyrinth has been removed.

Before describing this figure in detail, there is one remark to be made, namely, that
here we have, clearly shown, the true diagnostic mark of a Mammalian skull. This
mark is the rupture of the side walls, due to the pressure of the large lateral masses
of the cerebrum. In front of the auditory capsules there is a large elegantly semi-
circular opening, the crown of the arch looking upwards and forwards.

Only the lower half of the wall has thus broken outwards ; this “ fault” forms the
alisphenoid (a/.s.), whilst the orbitosphenoid (0.s.), the so-called “lesser wing,” is
many times its size, and is continuous, over the archway, with the cartilage that runs
on, backwards, into the supraoccipital region (s.0.)

There is nothing similar to this in that Sautopsidan skull which comes nearest
to that of the Mammal ;—the skull of the Crocodile (see Trans. Zool. Soc., vol. xi.,
plate 65), whilst in Birds the orbitosphenoids are very small even when they are most
developed, as in Struthio (see Phil. Trans., 1866, Plate 7), and in that Class the
alisphenoids almost finish the cranial cavity, being turned inwards towards each other,
on each side of the back part of the orbital septum.

I lay especial stress upon this rupture, outwards, of the alisphenoid, and of the fact
that the nasal roofs utilise the whole of the huge high-crested intertrabecula, because
these are the most distinctive marks of the Mammalian skull, and they arise out of
two things in which the Mammal shows its great superiority to even the highest
Sauropsida, namely, the huge volume of the cerebrum, and the tenfold complexity
of the nasal labyrinth.

A third clear diagnostic is seen in this very figure ; this is the peculiar development
of the antero-inferior part of the oblique auditory capsule, due to the development of
the coils of the cochlea (figs. 1, 6, 8, chl.).

So that, at once, correlated with the sudden expansion, so to speak, of the cerebrum,
we have these new and most important improvements in the organs of smell and of
hearing.

At first sight, seeing how large the median bar (intertrabecula) is, with its inter-
nasal crest (perpendicular ethmoid and septum nasi,—p.e., s.v.), it might be supposed

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. )

that the Mammalian skull was of the high kind, like that seen in many Teleostean
Vishes, in Lizards, and in Birds.

It is not so, however, but belongs to the /ow kind, seen in Selachians and Amphibians ;
and, like theirs, is hinged on to the spine by a pair of occipital condyles.

Hence the eye-balls are kept far apart, instead of coming very near each other as in
most Birds, where, often, nothing but a membranous fenestra is found between the
right and left capsules, and their special rauscular apparatus.

But the face, as well as the skull, of the Mammal shows marks of excellence, such
as are not seen in the Sauropsida, even in the higher kinds, as Crocodiles and Birds.

The great development of the nasal organs is correlated with a most remarkable
growth of the bones of the upper jaw and the palate to form the “ hard palate.”

This is found in rudiment even in the Chelonia and in Birds ; but especially in the
Crocodilia, where, however, its excessive development-—as in certain Edentata,
e.g., Myrmecophaga—is not dependent upon, or correlated with, any great improve-
ment in the organs of smell, but has to do with the peculiar manner in which
these monsters take their prey.

But that great improvement just spoken of as appearing in the organ of hearing in
the Mammal has wrought a change in the hinder face that has two most important
bearings.

From the first promise of an ear-drum in the tailed Amphibia, to its highest fulfil-
ment in the noblest of the Oviparous tribes—the Birds that nestle on high (“ Aves
Altrices ”),—the only element from the visceral arches that is used for carrying the
vibrations of the air inwards to the organ of hearing ig the uppermost part of the
hyoid arch—the “ pharyngobranchial” element of the 2nd postoral arch, to speak
morphologically.

From the Salamandroids to the Singing Birds, all through the Amphibia and Saurop-
sida, the Ist postoral arch—which forms both the upper and lower jaw—is only
segmented once, that is, into an epibranchial and a ceratobranchial element, or
joint.

‘The upper piece is specially termed the “ quadrate,” and the lower the “articulo-
Meckelian;” the one forms the swinging piece, hinge, or pier, to the compound lower
jaw, and the other its axis or pith, the part which becomes covered with more or fewer
“investing bones.”

In these low “ Eutheria,” and also in both the ‘“ Metatheria,” and the “ Prototheria ”
(Marsupials and Monotremes), the modified visceral rod that runs through the drum
cavity has two new elements added to the one (single or variously segmented) element
derived from the hyoid arch.

This is an apparently sudden change, for we have it in the lowest or teatless
Mammals; their ancestry, that should show us the earlier steps of the change are,
unfortunately, all extinct.

MDCCCLXXXYV. Cc

10 MR. W. K. PARKER ON THE STRUCTURE AND

In this dilemma not only Zoology, but Palzeontology also, fails us utterly, but
Embryology comes in with every stage and every link.

I have worked out the early condition of these parts in several kinds of Marsupials,
and in the young of Ornithorhynchus ; but even in the lower Eutheria, the Edentata,
now to be described, and in the large and varied group of the Insectivora, I have
been able to trace every step in the transformation of these parts.

I am now satisfied that the news is the upper element of the first or mandibular
arch ; both Professor SALENSKyY’s and Professor FRasEr’s researches put this, I think,
beyond doubt ; and my own attempts, for a long time, to make the hyoid theory of
this part agree with facts, only kept the subject in hopeless confusion,

The new elements of the ear-chain are, then, the arrested quadrate or incus, and
the arrested and amputated articular region of the articulo-Meckelian rod, or primary
lower jaw. The bony part of the “ramus” is the well-known dentary, with the
coronoid and splenial bones in a sub-distinct state ; the cartilage for the new articu-
lation of the lower jaw is derived from a Jarge superficial slab—a “lower labial ””—the
like of which is not found again until we get as low down as the Chimeeroids.

From this is derived the hinder half of the ramus, by transformation of its substance
into bone; and from this we get the cartilage, both of the condyle and the glenoid

«e : ”
meniscus,

cavity, and also of the intervening
Of course the drum cavity is the “ first cleft ;’

segmented meatus-t ube,—the tympanic bone, the tympanic bulla, and the cartilaginous

)

and the concha auris, with its

lining of the Eustachian tube,—all these are parts of a curiously specialised opercular
growth belonging to the hinder edge of the first visceral fold and arch.

This last assertion has not been made as a stride across the types, from the Mammal
to the Elasmobranch, but is the result of a very slow, step by step process, made

during many years, “ along all the lines” of Vertebrate morphology.

Vertical section of the skull of Tatusia hybrida.—First Stage (embryo, 13 inch long).

The chondrocranium is now at its highest development ; after this it will begin to
decline, for osseous centres are already developing in it; these are the basioccipital,
exoccipital, supraoccipital, basisphenoid, and alisphenoid (Plate 2, fig. 1, b.0., e0.,
S01, O,Sa):

The notochord (nc.) is still to be seen in the basioccipital region, it is hooked
downwards in front. The basioccipital bone (b.0.) occupies the middle half of the
cartilage between the foramen magnum and the posterior clinoid elevation ; this
latter is a moderately high ridge running crosswise.

The cartilage of the base of the skull becomes thicker in front of that ridge, and
rises gently until it reaches the beginning of the great olfactory fossee; the basi-
sphenoid (b.s.) already occupies the hinder half of this more elevated tract of cartilage.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 11

The rest of the base of the skull forms a low triangle whose base is somewhat longer
than the lower part which reaches backwards to the foramen magnum.

The postero-superior side of this triangle is developed into two rounded lobes, the
upper or fore lobe is the larger of the two. The hinder lobe is the top of the
perpendicular ethmoid (p.e.), behind the olfactory fossa with its cribriform plate (see
Plate 5, fig. 1); whilst the front or upper enlargement is the ecrista galli, in solid
cartilage. *

The longer upper side dips down gently to the snout, and is a little concave ; the
triangle does not end in a point, but in a rounded lobe. The Jower part of all this
nasal fore half of the basis cranii is a thick beam of cartilage, carrying a much thinner
crest on its upper edge, which is continuous with it.

Embryologically, the “investing mass” may be said to reach to the posterior clinoid
wall ; but the notochord has retreated relatively from that point; the rest of the
cartilage is “ trabecular.”

But the paired trabeculi, themselves, only reach as far as to the middle of the
proper olfactory region, the septum of which bears the name of “ perpendicular
ethmoid” (p.e.); the filling in between these, behind, and all the rest of the middle
part is formed by an azygous growth, the “ intertrabecula.”

The sides of the cartilaginous basin, whose narrow elongated floor has just been
described, are formed by a very large sheet of cartilage, right and left. This just
reaches the roof, or cover of the basin, in the hinder half, and the sides are imperfect
in two places.

The occipital region, only, forms a complete belt or ring of cartilage.

The postpituitary region of the skull, for two-thirds of its horizontal, and for two-
thirds of its vertical, extent, is occupied by the intruded auditory capsules («.s.c., chl.),
which, above, below, and behind, have coalesced with the cartilage of the proper
chondrocranium,

A more than semicircular space in front of these large capsules is occupied by a
large fenestra whose very accurate arched outline looks forwards and upwards. The
sinuous cartilaginous wall round this space is the orbitosphenoidal region, passing by
a band, equal in width to the fenestra above, into the large supratemporal (or swb-
parietal) tract (s.t.c.), which in turn runs into the crown of the occipital arch.

Half the preauditory fenestra is imperfectly occluded by the alisphenoid (above 0.s.),

* In my paper on the Ostrich’s skull ( Phil. Trans., 1866, Plate 7) the counterpart of this crest is
lettered er.g., or crista galli, and is described as such in the text (p. 118). But in the paper on the
Fowl’s skull (Phil. Trans., 1869, Plate 83) this part is not lettered, for I had been reminded by a friendly
critic that the crista galli of Man is formed by ossification of fibrous tissue in the fore part of the falx
cerebri. It is, however, preformed in cartilage in many Mammals, notably in these Kdentata, and my
lettering in the figures of the Ostrich’s skull is correct. In the same paper (p. 120) the quadrate
cartilage is identified with the incus ; that view of it is, I feel satisfied, now, quite correct.

Cc »)

12 MR. W. K. PARKER ON THE STRUCTURE AND

or free, outstanding wing, not of cartilage now, but of bone. This fan-shaped tract
has its broad part ossified separately, from the lower part or stem (see fig. 6, al.s.).*

At a distance from the basioccipital equal to the width of both the basal and lateral
bony centres, the exoccipitals (¢.0.) have appeared, they form part of the selvedge
round the foramen magnum, Above another equally large space of cartilage we see
the supraoccipital (s.o.): it has a right and left half (see also fig. 6, s0.); each half is
ear-shaped, the broad end being near the mid-line.

A considerable fossa runs between the occipital arch and the auditory capsule ; this
is occupied by the “lateral sinus” (s.c.), which communicates with the outer veins
through a large hole, both above and below.

The foramina for the postauditory nerves are seen in this view; that for the
hypoglossal (XII) in the middle of the space between the exoccipital and_basi-
occipital, and the double space for the vagus and glossopharyngeal (X., LX.) in the
interspace or fissure between the auditory capsule and the front side of the occipital
arch.

The multiperforate ‘meatus internus” for the 7th and 8th nerves (VII., VIII.) has,
beneath and in front of it, the projecting cochlea (chl.) ; and above it the arches of the
anterior and posterior semicircular canals (a.s.¢., p.s.c.), meeting in one common sinus ;
these can be seen shining through the cartilage.

The lower alisphenoidal centre is deeply notched (above b.s.) to form an imperfect
foramen ovale (V*.) for the third branch of the trigeminal; the second and first
branches (V'*.) escape through the sphenoidal fissure—between the bulging
alisphenoid and the concave posterior margin of the stem of the huge orbitosphenoid
(0.5.). The lesser cranial nerves (8rd, 4th, 6th) escape also through this space, but the
optic foramen (II.) is an oval hole pierced through the orbitosphenoidal stem. No
part of the anterior sphenoid is ossitied at present, nor any part of the nasal region.

The turbinal outgrowths of the proper olfactory region shown by the slicing away
of the cartilage (fig. 5, wtb.) are very numerous ; above and behind them, in the huge
recesses for the olfactory lobes, the numerous branches of the Ist nerve are seen to be
escaping through a membranous floor, which is having bands of cartilage formed in it
(cr.p.), that pass round the various fissures through which the nervous bands escape.

The cartilage of the roof of the nasal labyrinth is shown in the main figure (fig. 1)
as cut away from the large partition wall. In front, the alinasal region, behind the
opening and near the mid-line, gives off a curious ‘ recurrent cartilage” (7e.c.) of a
lanceolate shape, and scooped along the outside, except in front, where it forms a tube.

These cartilages (right and left) protect ‘ Jacopson’s organs,” which are partly
encapsuled by them; these parts are related to two small bones and to the vomer, as
I shall show soon. In the figure of this vertical section the frontals and parietals
(f..p.) ave shown, helping to fill in the great fontanelle; the nasals (7.) are seen over

* In Birds, generally, and in many Rodents, the alisphenoid is formed from two osseous centres, but

in a manner very different to what is shown here.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 13

the septum nasi (s.7.); the vomer (v.) under it, and the palatine plates of the maxil-
laries and palatines (m., pa.) are shown as forming the hard floor to the shallow
naso-palatine canal. The “fault” in the skull wall, where the small alisphenoid is
thrust out, is partly filled in externally by the squamosal (sq. ).

First Stage (continued).— Visceral arches of Tatusia hybrida.

This stage, although more advanced than some I have been able to work out in
certain Insectivora, is yet very valuable and instructive ; the two mandibles—the
outer and the inner—are now well developed, but the peculiar Mammalian transforma-
tion of the inner mandible has not yet taken place.

The superficial ramus (Plate 2, fig. 3, d.) is full four times the bulk of the primary
articulo-Meckelian rod (mk.), and reaches backwards nearly to the thick articular
region.

A row of small alveoli is seen in front of the coronoid process (cr.p.), which is
peculiarly long and slender, and forms an acute angle with the condyloid part (cd.p.),
a semi-oval mass of cartilage. The tip of the coronoid process is also cartilaginous,
and so is the edge of the feebly developed angular process (ag.p.).

MecKEv’s cartilage—the inner or primary mandible—is a very uniform terete rod,
lying all along the inner face of the ramus, near its lower edge ; it follows the sinuosi-
ties of the ramus up to the “ mentum,” where it is confluent with its fellow (fig. 2, mh.).

At this confluence there is developed a tongue-shaped non-segmented rudiment of a
basimandibular element (b.mn.); this is more distinct in the Insectivora than in the
Armadillos. There is no appearance, at this stage, of a distinct splenial, or of a
distinct coronoid, bone inside the ramus, in this type. There is, however, here, as
everywhere in the Mammalia, a very large tract of cartilage on which the hinder
half of the dentary is formed, and out of which the new articular facet, that on the
lower edge of the squamosal, the “ glenoid” facet, is also developed.

This subcutaneous slab of cartilage is manifestly the homologue of the lower labial
of cartilaginous Fishes, as much as the bone itself corresponds with the antero-
external splint of MreckEt’s cartilage in Ganoids and Teleostei, the Amphibia and

6c

the Sauropsida—the well-known “ dentary.”

A preparation of the whole auditory and articular region of the skull shows many
things in their proper relations (fig. 4). Part of the squamosal (sq.), with its glenoid
facet (gl.f.), is figured, and the condylar (ed.p.) and angular part of the ramus or lower
jaw, with its solidly cartilaginous hinder margin.

MECKEL’s cartilage, large and solid, is seen running along a groove on the inner face
of the ramus, and in the other direction shows itself as a large pars articulare, with
its sinuous condyloid face for articulation with a remarkable form of quadrate—now,
evidently, the “incus,” before ossification.

c

As in the Fowl! and many other Birds, there is a lone ‘‘ internal aneular process ” to
ay > g g I

J4 MR. W. K. PARKER ON THE STRUCTURE AND

the articular region, and a rudiment of the well-known avian “ posterior angular

process ;” in Mammals the former is called the

ce

manubrium of the malleus.” Under
the proximal part of Mercket’s cartilage, where it becomes the massive articular
region, there is an ectosteal deposit—the well-known bony tract which develops into
the articulare in oviparous types, often having an endosteal centre added to it; it is

ce

the “articulare externum” (Plate 2, fig. 4). Here it forms the outer rudiment of the

ce

bony malleus ; it 1s partly hidden by the “ annulus” (a.ty.).

In comparing the next or proximal segment of the first visceral arch with that of
the Bird—the quadratum—there are two things to be noticed; first, that the “ orbital
process ” is suppressed ; and secondly, the head of the segment is articulated with the
cranium further forwards than in most Birds.*

There is a neat head to the upper crus of this cartilage, called in human anatomy
the “short crus of the incus” (s.c..), and this fits into a neat cup in the cartilage of
the ear capsule, above, just between the ampullze of the anterior and horizontal canals
(a.s.c.,h.s.c.). Below and behind the saddle-shaped condyle, the body of this segment
narrows into the “ long crus” (/.¢.7.), and this part acquires an inturned “neck,” very
slender, which carries a discoid head—the pars orbiculare.

This is another and new, or Mamnialian, character; here the top of the first visceral
arch keeps outside the top of the second, as in Fishes, generally, and amongst
the Sauropsida in the Chameleon (see Trans. Zool. Soc., vol. xi., plate 16, figs. 4
and 7); whereas in many Amphibia and Sauropsida the topmost hyoid element—the
columella—rides over the quadrate.

The great specialisation which these parts have undergone, which they show so
early in the embryo, is seen in the tilted position of the semicircular canals (a.s.c.,
h.s.c., p.s.c.) ; for in relation to the axis of the skull, the horizontal canal is almost
vertical, and the two vertical canals are quite oblique in position. Thus the hinder
part of the ‘“tegmen tympani” (¢,t7.) forms a recess for the stapes (s¢t.) and its muscle
(st.m.) ; this is quite like the recess formed by the paroccipital wing in the Bird’s
skull.

The form of the stapes (which will be shown in the next stage) is quite normal;
it is a short, flat, perforated column, the oval base of which fits accurately into the
fenestra ovalis. In this figure it lies in the shade, within the incus, and the stapedius
muscle (sf.m.) is seen arising, tendinous, from its neck, and enlarging, backwards, to
be inserted, fleshy, in the bottom of the recess at the back of the tympanic cavity.

As the parts in this early stage were newly, but completely, chondrified, I had a
good chance for seeing the exact relations of the parts of the hyoid arch.

The stapes, as the counterpart of the Skate’s hyomandibular, chondrifies separately ;
it is the only pharyngobranchial element developed in the walls of the Mammalian

* Tlay stress upon further forwards; no one has ever dreamed of putting the Bird’s quadrate into

the hyoid category, notwithstanding that its articulation with the occipital arch is partly behind the

auditory capsule.

DEVELOPMENT OF THE SKULL IN THE MAMMALITA. t5
throat. In the Skate (Pristiwrus, see Trans. Zool. Soc., vol. x., plate 35, fig. 4) all
the pharyngobranchials are developed (chondrified) independently of the rest of the
arches to which they belong, which for the most part undergo secondary segmentation
into more or fewer joints.

Here the segmentation of that part of the arch which in Fishes carries the gills
is more than normal; the feebly developed epihyal (¢.hy.) is in two imperfectly
divided joints, and the strong ceratohyal (c.iy.), which is imperfectly segmented
from the lower epihyal, is completely cut across at its lower third.

Below this part there is the normal (ichthyic) hypohyal (/.hy.), the shortest of the
segments. *

The basal part is a trifoliate basi-hyobranchial (b./.b7.), to the fore angles of which
the hypohyals are articulated, and which gives off a pair of hypobranchial rudiments,
and a free retral rudiment of the long, seemented bastbranchial bar of Fishes.

I found only one inner segment of the opercular growth round the first cleft; the
“ concha auris” becomes tubular in the meatus externus, and partly segmented ; the
innermost segment in this case forms an imperfect ring, and its softish cartilage is
rapidly becoming ossified to form the normal annulus tympanicus (a.ty ), in a groove
of which Mecxev’s cartilage lies at its proximal end. The upper end is most ossified,
the membrana tympani (7.ty.) 1s inserted into its inner face, and the radiating fibres
of this membrane start from the internal angular process of the primary mandible
(the manubrium mallei). The tensor tympani muscle (¢.¢.7.) is manifestly the counter-
part of one of the “adductor muscles” of the hinder part of the mandible of a
Reptile or Bird.

This muscle, and the “ stapedius,” want tracing downwards; they are the accurate
muscular correlates of the curiously specialised skeletal elements of this part of the

skull.
Vertically-transverse sections of the head of Tatusia hybrida.—First Stage.

The figures given in Plates 3, 4, and the following descriptions must be compared
with the figures and descriptions of the bisected and dissected chondrocranium ; the
latter is of a later stage (Plate 5, fig. 1).

Before going into details, I may remark that the huge nasal capsules that take up
half the sections selected to be figured lie under the fore part of the skull, so that the
floor on which the olfactory lobes le is the roof of the hinder and more important
part of the nasal labyrinth. The septum between the two halves of this labyrinth is
mainly formed of the intertrabecula, but the thicker part of the septum, where it is
becoming lower behind, has the cornua trabeculze confluent with the azygous bar.

,

* Tn this, as in my former papers, the “hyomandibular,” in all its modifications, is treated of as part
of the hyoid arch. In ancestral forms it may have been a distinct arch (see Anton Doury’s ‘ Studien,’

1885).

16 MR. W. K. PARKER ON THE STRUCTURE AND

There is no complete nasal floor, except close behind the external nostrils, in front,
and in the blind end of each capsule, behind, where the presphenoid lies between each
space: the cavities, there, right and left, being the embryonic form of the “sphenoidal
sinuses.”

To make these numerous and complex figures more intelligible, the related parts
are merely indicated; the skeletal structures are the parts to be brought into pro-
minence.*

1st Section (Plate 3, fig. 1).—This section is through the end of the snout at the
opening of the nostrils and in front of the lower jaws. The broad upper part passes
sinuously into a narrower lower part, which has a concave outline below. The
septum nasi (s.7.) is complete, and has two narrow wings below, that belong to the
floor (n.f.), and wide arched wings above (a/.n.), bifid at their lower edge. The section
of the prenarial cavity (n.p.) is lunate, for there is here the beginning of the thick
valvular cushion of the nostril.

2nd Section (Plate 3, fig. 2).—This section is from behind the nostrils, but close
to them; here the palatal hollow begins.

The septum (s.n.) is thin in the middle at this part, and the alinasal roof-tracts
are sharp at their lower edge. The two dilatations of cartilage below the septum are
confluent here, and right and left of the solid foot there is a large pouch-shaped recess
to the nostril (m.7.); this arial recess runs through several sections, showing that it,
is of considerable width. At the top, the septum is beginning to dilate, and a
valvular wing of the lining membrane is seen in this dilatation.

The narial valve (n.v.) is very large here, and contains a section of a finger-shaped
process of the alanasi. In the following sections this passes into the general cartilage,
so that it is not a separate segment.

The nasal bones (n.) come into view as far forwards as this section (see also Plate 2,
fig. 1), for they run well over the snout.

3rd Section (Plate 3, fig. 3).—This is through the whole fore face, for it takes in
the top of the tongue (ty.) and the beginning of the lower jaws, where MECKEL’s
cartilages (b.mn.) are confluent. The septum nasi (s.7.)is very thin in the middle, but
is expanded above ; below, it stretches into a limited floor, flat below, and not far from
the wide proximinal part of the valvular process, which supports the many-lobed valve
(.v.). The nasal bones (7.) only are seen in this section.

4th Section (Plate 3, fig. 4)—In this section the Meckelian rods (mk.) are
separate, the dentaries (d.) are cut across, and a tooth-socket (¢.) is seen above each
bone ; above, the nasals (n.) are seen. The septum nasi still thin below, is winged
above, and these wings are the skeleton of a large upper narial lobe. The lower valve
is smaller, but the whole passage is narrowed by folded thickenings of the lining

* These sections, and the rest of the thin transparent stained preparations of this kind, were made for
me by one of my Sons, and the camera drawings of them by another; about one-sixth of the 163
sections made of this one head were drawn; only three-fifths of each drawing has been engraved.

DEVELOPMENT OF THE SKULL IN THE MAMMALITA. 17

skin. The valvular process of cartilage is seen here to be merely a part of the wall,
and there is but a small space between this and the oblique floor-tract attached to the
bottom of the septum. Two of the foremost of a series of glandular crypts (gl.c.) are
cut across, the larger of these is lodged between the side and floor.

5th Section (Plate 3, fig. 5).— About six of the sections made at this part show a
complete double nasal tube, for here the wall, valvular process, floor, and septum, are
all confluent. Here the septum (s.n.) is much thicker throughout; it still retains the
winged growth above, and the valvular folds of the lining skin are very numerous.
Here the thickened septum is of less vertical extent, and the thick ends of the floor
drop from their point of union with the septum. There is a erypt (g/.c.) here under
the valvular process, and another at the upper third of the wall, between it and the
lining membrane. The nasals (7.) are wider here.

6th Section (Plate 3, fig. 6).—At this part the floor of the alinasal fold has again
become free from the base of the septum (s.7.), which is of small vertical extent, but
thick—thickest in the middle The upper alate enlargement is gone, but the fold of
skin is still large, and runs out transversely. This is the last section showing the
fold in the narial valve (7.v.), and there is a wide and hollowed space between it and
the part forming the inner floor. That part is now tubular, the top of the tube (re.c.)
being sharp and fitting against the base of the septum. Besides the two pairs of
elandular erypts (g/.c.), there is, in each tube of cartilage, an apparently glandular
body; this is ‘‘ Jacopson’s organ” (j.0.), a structure which will appear in several of
these selected sections.”

Small points of bone are now apparent beneath the nasal canal, right and left,
these are the premaxillaries ( pz.) ; the nasals (7.) are still seen above.

7th Section (Plate 3, fig. 7) —This section is behind the alinasal, in the fore part of
the aliseptal region. The thickening which showed itself in the middle of the septum
in the last section is now at the base; it is due to the fact that the intertrabecula is
essentially a roundish and somewhat compressed bar of cartilage, which has shot up
into a thick crest to join the roofs of the nasal capsule (a/.sp.). The middle valvular
fold has now sunk down so as to be opposite the base of the septum; between it and the

* For accounts of the structure and meaning of this part the reader is referred to the ‘ Bibliographical
List.” In my earlier papers on the skull my attention had not been directed to this part, and I was not
then aware of the curious modification of the fore part of the skull caused by it. In the paper on the
Pig’s skull (Phil. Trans., 1874, Plates 28-37) the supporting cartilage is figured and described as the
“recurrent cartilage’—a name I shall retain. In the more recent papers on the skull of the Snake
(Phil. Trans., 1878, Plates 27-33), and in that on the skull of the Lizard (Phil. Trans., 1879, Plates
37-45), I have called the pair of Jaconson’s organs by Ratakn’s term, namely, “nasal glands ;” this,
however, is a misleading term, as they have nothing to do with the nasal glands of Birds. In the Snake
and Lizard these parts are protected by cartilage derived from the alinasal region, but they are actually
encapsuled in a pair of curious bones; these are the paired vomers, which form the “dish” and the
septomaxillaries that form its “cover.” The anterior paired vomers are very constant in Mammals ;

but I have not yet found the septomaxillaries in any member of this Class.

MDCCCLXXXV, D

18 MR. W. K. PARKER ON THE STRUCTURE AND

outer fold the nasal canal is deep. The outer fold is not the same as in the last
section; it is not a valvular fold of the external nostril, but the beginning of the
‘inferior turbinal” (7.tb.), and is formed as a pedate enlargement of the upturned
wall. The cartilages protecting ‘“‘ Jacopson’s organs” (j.0.) are no longer tubular,
but form half a tube, open externally, the organ lying in the outer hollow. But the
cartilages themselves have an osseous counterpart protecting them on the inner side,

ce

and having their shape and direction; these are the “ anterior paired vomers ” (v’.),
bones well known for their large development in the Ophidia and Lacertilia; they
do not represent a divided “ vomer,” proper, which in nearly all Mammalia is well
developed also, and begins above these bones, as the next section well shows. Two
pairs of “crypts” are seen still, in section, and besides the large section of the nasal
bones (n.), we have the hinder edge of the premaxillaries (see Plate 2, figs. 6 and 8, pz.).

The palatal vault is very high here, it is partly occluded by the tongue (¢g.),
below which the lower jaws are seen each with its Meckelian rod (mk.), its dentary
bone (d.), and its tooth socket (¢.).

8th Section (Plate 3, fig. 8).—This is through the angle of the mouth and the middle
of the inferior turbinal. The septum nasi is here one-third deeper than in the last,
and is more definitely bulbous below. The roof passes into a deep wall which ends
in the inferior turbinal ; this is two-lobed, now, and each lobe is convex in its inner
and upper face ; the wall of the nose is sharp below the turbinals.

The recurrent cartilage (7c.c.) is largest at this part, and so are the small anterior
paired vomers, but JAcopson’s organ has the same diameter, nearly, as in the last
section. Here the bifid fore end of the true vomer is cut across, close beneath the
intertrabecular cartilage. The crypts (g/.c.) still appear, so that there are two rows of
them on each side. Here the section of the nasal (.) is large, and the fore part of
the maxillary (m.) is cut across on each side ; this bone appears in two parts ; this is
because of the beginning of the alveolar groove, which runs between the lateral and
palatine portions of the bone (see Plate 2, fig. 6).

The section of the tongue (tg.) is large here, and the dentary bone (d.) outside
MeEcKEL’s cartilages (mk.) is in several lamine.

9th Section (Plate 3, fig. 9).—This section, of which more than half is figured, and
drawn on a smaller scale than the first eight, brings us into an increased complexity of
the nasal labyrinth. ‘The septum (s.7.) is like that of the last section, but the roof
of the labyrinth is much flatter, and besides the more developed inferior turbinal,
there is now the nasal turbinal (7.¢b.), which runs obliquely from the roof to the side
wall, enclosing a long oval space. In the main channel, inside this space, there is a
free section of cartilage, it is triangular, and has its apex looking upwards, this is a
‘‘precurrent process” of the middle turbinal (see also fig. 94, pe.c.) ; it is equally
developed in these types, and in the Insectivorous Hedgehog—its largest growth is
seen in the Aard-Vark (Orycteropus, Plate 15).

This section is near the end of JAcoBson’s organ and its related cartilages ; but the

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 19

proper vomer (v.) is now a large trough of bone composed of several laminee. The
nasals and the maxillaries (mz.) are still seen in section, and below we have the
dentary with its increasing lamine, and MrecKer’s cartilage (mk.).

10th Section (Plate 3, for fig. 94. read 10)—This is from a very slight distance
behind the last, it is given to show how soon the nasal turbinal (7.tb.) becomes free
below. In both this and fig. 9 the glandular crypts (gl.c.) are seen to be increasing in
number, and to be crowding between the Schneiderian membrane and the cartilage.

11th Section (Plate 3, fig. 11).—Here we see that the most complex part of the nasal
labyrinth lies beneath the cribriform plate; the olfactory fibres (I.) are here seen
‘rhinencephala” (CY). The septum here is the

«

entering from the olfactory lobes or
perpendicular ethmoid (p.e.); it is thinuish above, and very bulbous below ; the crest
above is the “crista galli.”

The floor of the fore part of the cranium is here only perfect near the septum ; but
the cartilage increases, laterally, so that the olfactory nerves then pass through holes,
and not through chinks as at present (see Plate 2, fig. 5). Here the upper part of
the labyrinth answers to the upper turbinal in Man, and the lower part to his middle
turbinal. The cartilage at this part encloses a large oblique oval cavity, round which
a perfect ring of glandular crypts are packed. The inner process of cartilage, which
runs free from that ring, is the hinder or proximal part of the free precurrent cartilage
seen in the last two figures (see fig. 9, pe.c.).

Here we see that, behind, the recurrent cartilage (7c.c.) protecting JACOBSON’s organ
overlaps this curious fore-growth of the middle turbinal, for its section is still seen
above the edge of the vomer (v.).

The bones seen above the labyrinth are no longer the nasals, but the frontals (see
Plate 2, fig. 7, f.), which are very large plates in this type, whilst the nasals are
rather short. The maxillaries (mx.) are very large, and have many laminz at this
part, and the palatine plates (above m.) nearly meet at the mid-line. But between
the frontals and maxillaries there is the huge lacrymal (/.; see also Plate 2, fig. 8),
which has a facial as well as an orbital plate.

MECKEL' cartilages (mk.) are seen below, with their protecting dentaries (d.) which
are developing a considerable amount of diploé, here, at the middle of the ramus (see
Plate 2, figs. 3 and 8, d.).

12th Section (Plate 3, fig. 12).—This is through the fore part of the hemispheres
(Cl) and of the eye-balls (e). The nasal roof is cut through behind the cribriform
plate (see Plate 5, fig. 1), and this part of the nasal labyrinth is sub-cranial, and the
proper cranial walls are above, and external, to this part of the turbinals which are
reduced to two folds. The outer of these folds of the middle turbinal (m.tb.) is fixed,
both above and below, the inner is free, above; they are both turned inwards and
upwards. This part of the capsule has, in some degree, coalesced with the septum
(p.e.) both above and below; its very bulbous form at the base is well shown ; this is
the last figured section that shows only the intertrabecula. Indeed, even here, it is

m 2

20 MR. W. K. PARKER ON THE STRUCTURE AND

possible that the foremost part of the paired trabeculee may have helped to thicken
the bulbous part.

At a short distance from the nasal wall the fore part of the orbitosphenoid is shown
in section; but further forwards (see Plate 5, fig. 1, 0.s.) that wing is continuous with
the nasal wall. Over these parts the frontal shows itself twice, above, where it lies
over the flattish hemispheres (C'.), and laterally, where the orbital plate protects the
orbitosphenoid over the eye-ball (e.).

The nasal channels are almost reduced to two sub-oval naso-palatine canals, for
here the skin covering the vomer (v.) les very near the skin covering the halves of the
hard palate.

Four bony sections are seen here ; the two small upper pieces are the hinder forks of
the vomer (v.), the outer and larger plates are the palatine bones (pa.), which extend
round the passage, above and below. Below, these bones soon meet at the mid-line,
like the maxillaries, carrying on the hard palate (see Plate 2, fig. 6, mx., pa.) ; above,
they nearly touch the forks of the vomer. Under each eye-ball there is a bony section,
flattish and upturned externally ; this is the jugal (j.). Nearer the mid-line the
large high dentary (d.) is seen, and inside its lower part MecKkeEv’s cartilage (mk.).

13th Section (Plate 4, fig. 1).--This partial figure shows a very long part of the
frontal bone (f:) and a larger amount of orbitosphenoidal cartilage (0.s.), confluent,
here, with the outside of the narrowing nasal labyrinth, but at a distance from its own
root, the presphenoid. The median cartilage is still the perpendicular ethmoid (p.e.),
and its shape here is very instructive ; the extension of the cartilage below the nasal
labyrinth is due to the addition, right and left, of a wedge-shaped tract—the cornu
trabeculee to each side of the bulbous, crested intertrabecula.*

The cavity of the nasal labyrinth is now reduced to three small recesses, the cuter
nearly obsolete ; and the folds of the middle turbinal (m.tb.) are confluent with both
wall and floor, and look inwards and upwards. Here the top of the intertrabecula has
lost the crest (crista galli); the cartilage here, behind the cribriform plate, is lowering
towards the presphenoidal region.

In the last section the upper part of the mucous membrane lining the naso-palatine
canals almost rested upon the lower so as to divide them imperfectly. Here these
folds are more separated in the middle, and the canal (7.p.c.) is single, shallow in the
middle and deeper at each end. Outside this common canal the pterygoid bone (py.)
is seen merely hooking round the passage in a crescentic form,

The high coronoid region of the mandible (d.) is here cut across, and MrEcKeEt’s
cartilage (mk.) is seen lying on the inturned lower edge; the jugal (7.) still comes
into section under the eye-socket.

14th Section (Plate 4, fig. 2).—This is through the widest part of the orbito-

* This part is explained by what is seen in the early chondrocranium of the Turtle and the Crocodile

(see ‘Challenger Reports,’ Zoology, vol. 1, plate 5; and Trans. Zool. Soc., vol. 11, plate 64, fig. 5;

and plate 65, figs. 2, 3, 7).

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 21

sphenoid (0.s.), which appears in the figure to be cut off from its base; this is due,
however, to the fact that this section is through the sphenoidal fissure. Here the
basal part (p.s.) is spindle-shaped in section ; this is due to the fact that the trabecule
are here adding their thickness to the solid intertrabecula, and that they are giving
off the orbitosphenoids, which, here, are not continuous with their root. The
frontal (f) is broad, and curls round the orbitosphenoid, intu the orbit. Here the
pterygoids (pg.) are very solid, and protect a transversely elliptical space, the naso-
palatine canal (7.p.c.). Above and outside each pterygoid, a small \V-shaped section
of bone is seen; this is the foremost part of the lower alisphenoidal centre (see Plate 2,
fig. 6, al.s.). The jugal (j.), dentary (d.), and Meckelian rod (aik.), are very similar in
this to the last section.

15th Section (Plate 4, fig. 3).—Here the presphenoid (p.s.) is far separated from
the large upper band of the orbitosphenoid (see Plate 2, fig. 1, 0.s.) ; its triple form
answers to its compound nature, formed as it is from a bulbous middle, and two
wedge-shaped, lateral, pieces—the intertrabecula and the trabecule. The Mammalian
type of skull is seen here, for the alisphenoid (a/.s.) overlaps the lower part of the
orbitosphenoidal region, and lies a good distance outside it. There is a thick core of
cartilage at this part, with an ectosteal deposit on its upper edge, the foremost part
of which was seen in the last section, The naso-palatine canal (7.p.c) is kidney-
shaped in section here, the ‘ hilus” being above. On each side of this passage the
pterygoids (pg.) are seen to be very thick in this their hinder part. Laterally, the
point of the zygomatic process of the squamosal (sq.) is seen riding over the hind
part of the jugal (j.), and, inside this, the ramus of the mandible is seen to be
composed of a mass of hyaline cartilage, besides the bony dentary (d.) which protects
MecxeEv’s rod (mk.).

16th Section (Plate 5, fig. 4).—We are here in the widest part of the hemispheres,
and the fore part of the pituitary body (py.) is cut through. Beneath, the basal
cartilage is composed of the beginning of the trabeculz (¢r.), and it is seen to be
double not triple.*

This prepituitary part of the basisphenoid (b.s.) is cut across close in front of the
narrow pedicle of the alisphenoid (see Plate 5, fig. 1, al.s., b.s.), in the innermost part
of the sphenoidal fissure, so that the cartilage appears in two pieces on each side of
the basal mass. The alisphenoid is not merely calcifying; it is being rapidly
converted into bone, within, and, externally, has two thick ectosteal plates on it, an
upper and a lower alisphenoidal bone (see Plate 2, fig. 6, and Plate 5, fig. 1, al.s.’,
al.s.). The parts of the mandible and face are like what are seen in the last section ;
but the naso-palatine canal (7.p.c.) has now opened into the fauces. The upper band of

* In these decalcified sections the lime-salts were removed, but the cartilage cells were becoming
calcified (see Plate 2, fig. 1, b.s.) as the basisphenoidal bone. In the 19th and 20th Sections (Plate 4,

figs. 8, 9) the same is true of the middle of the basioccipital region.

22 MR. W. K. PARKER ON THE STRUCTURE AND

cartilage (0.s.) running froin the orbitosphenoid to the auditory capsules still retains
its breadth, and is protected by the frontal bone (/.).

17th Section (Plate 4, fig. 5).—This section is through some very notable parts of
the skull and its contents. The hemispheres are here at their widest part, and, below,
the pituitary body (py.) is eut through. Here is the wide spheno-auditory fissure
(see Plate 2, fig. 6, and Plate 5), over which the large Gasserian ganglion (V.) lies.

The frontal (f) still protects the posterior band of the orbitosphenoid (0.s.), and
below this an infero-lateral bone comes into section, namely, the squamosal (sq.), just
where it is forming a broad part for the hinge of the lower jaw (cd.p.). Here this bone
helps to form the cranial wall, in the re-entering angle between the frontal and
parietal (see Plate 2, fir. 8; f,p.). The dentary bone (d.) and MEcKEt’s cartilage
(mk.) are seen below that mass of superficial cartilage. The dentary (d.) at its angular
part here comes close to the pyriform cavity exposed at this part—the tympanic
eavity (c.ty.); the broad end of this open section is below, and the narrow upper end
turns a little outwards.

Below this space the epihyal cartilage (e.hy.) is cut across. Here the faucial
passage is very narrow below; above it, the basis cranii is near the basioccipital
region close behind the postclinoid elevation. The notochord (nc.) lies below, in the
primary chink between the two parachordal tracts ; and its end is hooked downwards
(see also Plate 3, fig. 13, c.), a state of things first shown by Banrour in the Shark
(* Elasmobranchs,’ p. 209, Plate 14, figs. 9A and 164); and then by me in the Green
Turtle (‘ Challenger’ Reports, Zoology, vol. 1., plate 8, figs. 6 and 6a).*

The interauditory part of the basis cranii is, bere, twice as wide as it is thick ; it is
hollow above, and convex below ; the latter part being split, and having the notochord
in the fissure. The bulbous end of the cochlear part of the auditory capsule (see fig.
6, chl.) is here cut across, just exposing the spiral cavity, and showing the apiculated
fore end.

18th Section (Plate 4, fig. 6)—The hemispheres (C'.), the mid-brain (C*.) ; the
infundibulum, and the pituitary body (py.) are still seen (for the sections are a
little oblique, and they incline downwards and backwards), but the basis cranii is
cut through close behind the postpituitary wall or elevation. The hinder part of
the Gasserian ganglion (V.) is cut through, and under this the cochlea (ch/.) has its
cavity exposed; the notochord (nc.) is seen in the chink below, in the solid basi-
occipital cartilage (b.0.).

The backward extension of the orbitosphenoid (s.q.c.) is still seen, overlapped here
by the parietal (p.). The squamosal (sq.) is eut across behind the glenoid cavity, and
below and within this part, at a moderate distance, MecKEL’s cartilage (mk-) is still
seen in section. Under and inside it there is a small crescentic tract of bone; this

* Whatever theory may turn out to be true as to the nature of the prepituitary part of the skull—the
trabecule and intertrabecula—we have here a most valuable landmark, for the down-turned end of the
notochord is certainly the cephalic termination of the axis of the yertebrated creature.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 2e

is the “articulare externum”—-here the rudiment of the bony malleus (ml.). Opposite
these parts the outer skin is somewhat enfolded ; this is the beginning, or fore margin,
of the external auditory meatus (m.a.e.). The tympanic cavity (e.ty.) broadens
towards Mecker’s cartilage, and has a concave upper border ; it is very large at this
part, and has the epibyal (e.hy.) below its lower, inturned recess.

19th Section (Plate 4, fig. 7).—This is from a short distance behind the last, and is
through the posterior clinoid wall, which is low and indistinct. The cochlea (chi.) is
Jaid open at its anterior third, and the cartilaginous capsule ts perforated above, and
notched laterally, for the facial nerve (VII). Through the obliquity of the section the
pituitary body (py.) is still seen from behind; the internal carotid arteries (v.c.) are
entering, right and left.

The basis cranii is here at its narrowest part; this is the region of occipito-sphenoidal
synchondrosis. The wall-cartilage is here of great depth; this may be called the
supra-auditory tract of the chondrocranium (s.a.c.) between the hinder orbito-

sphenoidal band and the completed occipital roof (Plate 5, fig. 1). The squamosal
(sq.) and the parietal (p.) are here seen cut through; the latter also reappears opposite
the involution of the skin forming the outer ear. MecKEL’s cartilage is here seen
where it is giving off the “manubrium mallei,” and the bulbous form it has at this part
gives the section the appearance of discontinuity between the head and the handle ;
this is corrected by the figure of the dissection (Plate 2, fig. 4).

This internal angular process of the lower element of the first arch is seen to push
the lining of the drum cavity before it, in its geowth downwards and inwards. Under
and outside the cavity patches of cartilage are seen ; these are parts of the annulated
meatus, and the inner ring, on which the “os tympanicum” or annulus is forming.

Below the cavity, the epihyal is seen cut across ; below it the chorda tympani
branch of the facial nerve was seen in section, and from the manubrium mallei the
tensor tympanic muscle (¢.f/.) is seen passing inwards and upwards.

20th Section (Plate 4, fig. 8).—The supra-auditory cartilage is not continuous, here,
with the capsule; this tract is protected by the parietal (p.), and below the parietal
a part of the squamosal (see fig. 7, sq.) is cut across. The large lateral lobes of the
hemispheres are seen to cover the mid-brain; below this the basilar artery (b.a.) is
seen, and right and left of the basis cranii the internal carotids (7.c.) are entering.
Here the basioccipital cartilage (b.0.) is like a thick warped plank whose convexity is
below. The space between the capsule and the basal part, which was slight in the last
section, is widened here, and will become considerably wider where the 9th and 10th
herves emerge.

On this left side the cochlea (ch/.) is cut through at its widest or proximal part, and
the tegmen tympani growing out from it covers the emerging facial nerve (VIL).
Here the malleus (ml.) is sectioned so as to show a continuous growth of cartilage from
the head down to the end of the manubrium, the inturned end of which lies on that
part of the infolded skin which becomes the membrana tympani. Under the crescentic

24 MR. W. K. PARKER ON THE STRUCTURE AND

cavum tympani the meatus (m.«.e.), at its proximal part, is cut through and is carti-
laginous and partly bony; this is the “annulus ;” below this is the epihyal (e.hy.),
and below this the chorda tympani.

21st Section (Plate 4, fig. 9).—In this section the inner wall of the capsule is broken
up into three tracts, for here the related nerves (VII., VIIT.) enter.

On its inner face the capsule appears very solid, this is partly due to the obliquity
of the section, here, as we are at the proximal part of the cochlea, where it opens into
the general vestibule (v).), The outer face of the capsule is very broken up here, and
there are several small tracts of cartilage to be accounted for. Below the narrowed
end of the inner wall of the capsule the tympanic cavity (c.ty.) is seen as a large oval
space, enlarged a little upwards; below this the annulus is still seen, and outside that
one of the imperfect rings of the meatus (i.a,e.) ; further outwards at the edge of the
section the folds of the outer skin, at the passage of the ear, are shown.

Two fenestrae are cut through in the infero-external wall of the capsule, these are
the fenestra rotunda (/f7.) below, and the fenestra ovalis (f5.0.) above ; the latter is
partly occluded by a cartilaginous plate, the stapes (st.), which, being perforated
by the stapedial artery (s¢.@.), appears in two pieces, these are the base and neck
of the stapes; to the latter a short nucleus of cartilage is seen to be articulated,
and a joint cavity exists between the two. Here we have the inturned, orbicular
part of the Jong crus of the incus (/.¢.7.)

Under the lessened tegmen tympani (¢.ty.) we see a round tract of cartilage ; this
is the short crus of the incus (s.c.7.).

22nd Section (Plate 4, fig, 10).—This is from a part close behind the last section,
and the description just given may serve, on the whole, for this. The head of the
malleus is hidden by the short crus of the incus, and the cartilage is deficient in some
degree. The facial nerve (VII.) is seen passing into its canal beneath the tegmen.
The cartilaginous matrix of the “annulus” is shown for half its extent, and part of
what seems to be another annulus belonging to the meatus is seen, both are lettered
as meatus-cartilages (m.c.e.).

The three main openings of the capsule are still seen, namely, the meatus internus
for the 7th and 8th nerves (VII., VIIL), the fenestra ovalis (fs.o.) with part of the
base and one of the crura of the stapes (sf.) in it; and, below, the fenestra rotunda
(fr.). Only the top of the incus (s.c.7.) is seen on the outside of the capsule, and over
the stapes the facial nerve (VIL) is passing out. The flattening basioccipital cartilage
(b.0.) is coalescing with the capsule on this side,

23rd Section (Plate 4, fig. 11).—This is a very instructive section, showing
the relation of the visceral cartilages to the auditory capsule. That capsule is laid
open in the fore part of the internal meatus, and the facial nerve (VIL) is seen
from behind as it enters the capsule, burrowing through it, and then reappearing
over the incus (7.) under the tegmen tympani. Its chorda tympani, or mandibular
branch (VII.'), is seen below the epihyal before it crosses over (outside) it to join the

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 25

third branch of the trigeminal. On the inside the capsule and basioccipital cartilage
are largely confluent at this part, but this is only for a short distance, between the
ingoing of the internal carotid and the outgoing of the 9th and 10th nerves. The
huge, swelling cochlea (see Plate 2, fig. 6, ch/.) causes part of the floor of the capsule
to appear, in this section, to be seen below the junction of the capsule with the base.
Outside this part the fenestra rotunda (fr.) is cut across, and then, above it, the
fenestra ovalis (/%.0.), plugged with the base of the stapes which is cut through, so as
to show the stapedial artery (sf.a.) in its hole. Here the incus (7.) is severed through
its body and long crus, so as to show it entire. The annulus and a large part of the
meatus (i.c.e.) are seen here as cartilaginous bands. The tympanic cavity (c.ty.) is
lessening. (This section is in front of the last two (figs. 9 and 10) for the supra-auditory
cartilage (s.a.c.) is separate from the capsule; it should have been described before
them).

24th Section (Plate 4, fig. 12).—Here we are behind the cavum tympani, in the
hinder part of the junction of the capsule with the basioccipital, for the 9th and 10th
nerves are here cut through (but not lettered). Under the ascending cartilaginous
wall, where the cartilage has thickened into the wall of the capsule, the anterior sem1-
circular canal (@.s.c.) is cut across,

A large, irregular, open space is seen, the vestibule (v).), and in the wall behind it,
on the outside and below, the facial nerve (VII.) is seen emerging behind the epilyal,
which is seen here in its union with the capsule. The front face of this section has
been drawn ; the small recess, here, is the back of the tympanic cavity, and the inser-
tion of the stapedius muscle is seen below the hole for the escaping facial nerve (VIL).

Part of the meatus externus (7.a.e.) is laid open, and in the wall of that tube one
of the imperfect rings of cartilage is shown. The parietal (p.) and the squamosal
(sq.) are cut through laterally, and, below, the fore edge of the atlas (vt.) comes imto
view, where it is overlapping the basis-cranii.

25th Section (Plate 4, fig. 13).—This section is somewhat oblique, both laterally and
vertically. The mid and hind brain are cut through; the razor has passed close
behind the basioccipital below, and in front of the supraoccipital above ; hence the
chondrocranium appears as two distinct tracts, right and left.

The supra-auditory cartilage (s.a.c.) is very deep here, and below its thick base
we see the arch of the anterior canal (a.s.c.). This canal is also seen on the inner side
of the capsule where it joins the posterior canal to form the common sinus ; on the left
side the horizontal canal (h.s.c.) is also cut across, and below it the ampulla of the
posterior canal (p.s.c.; see also Plate 2, fig. 1). The foramen for the two larger post-
auditory nerves shows part of the glosso pharyngeal (IX.), and of the vagus (X.)
in situ, and that for the hypoglossal (XII.) does the same; the meatus-cartilage
is cut across. :

In my first Paper on the Mammalian skull—that of the Pig (Phil. Trans., 1874,
Plates 28-37), the lateral internal view of the chondrocranium of the 3rd Stage

MDCCCLXXXV. EK

26 MR. W. K. PARKER ON THE STRUCTURE AND

(Plate 33, fig. 8) shows the hugh orbitosphenoid as separate from the auditory
capsule. It is so, afterwards, and in the 4th Stage (Plate 34, figs. 5, 6) I have given
perfectly correct figures. In the 3rd Stage the sections show the continuity of these
tracts (Plate 32, fig. 6), but this upper tract was considered by me as part of the
supraoccipital roof. On the left side of the figure referred to, the cartilage (s.o.) should
have been lettered s.a.c.—‘supra-auditory cartilage ;” on the right that tract also
lettered s.o. shows where the cartilaginous wall is passing into the occipital roof. My
views as to the morphological meaning of some of the parts will be seen in this Paper
to have undergone some change ; I give here my last deductions.

I have not cumbered my description with mere details, although the actual sections
tempted me to give a much more detailed account of the structures displayed in them.
A comparison of the figured sections with the figured dissections will make everything
plain, as every part may be identified and compared in the two sets of figures.

Dissection of the skull of Tatusia hybrida.—Second Stage (embryos, 2 in.,and 24 in. long).

This skull was dissected so as to leave all the investing bones in sitw (Plate 2,
figs. 6-8) ; part of it is shown as dislocated to display the hinder end of the mandible
and the tympanic region (Plate 6, fig. 8). The endrocranium may be considered as
altered very little since the last stage ; the embryos, dissected, measured, not including
their tail, the one 2 inches, and the other 24 inches in length.

This somewhat more advanced stage is very valuable, however, with regard to the
endocranium, for the bony centres formed in the cartilage are more perfect—not mere
calcified tracts.

The lower view (Plate 2, fig. 6) shows the peculiar position of the outer nostrils
(e.n.), namely, quite on the ventral aspect of the face; the Armadillos are terricolous
in their habits. Behind and between the coiled valvular processes (al.n.,7.v.) the basal
part is bilobate ; from the back part of the double tract the protecting cartilages of
JACOBSON’S organ (fig, 1, 7¢.c.) arise. In this figure they are hidden to some extent
by two small bones lying one on each side of the mid line (v’.; see also Plate 3,
figs. 7, 8). These are the anterior paired vomers ; they are thin, long shells of bone,
concave within and above. Outside these the small premaxillaries (px.) are seen ;
they are notched below, and have no palatine process.

These parts lie in an angular space formed by the fore part of the huge maxillaries
(fig. 6, ma.); these latter bones have several well-marked regions ; they extend from
the premaxillaries to the zygomatic arch (j.), and then fork, behind, so as to enclose the
fore margin of the open orbital floor. A long suture unites the two bones at the mid
line, and outside this there are two parts of bone divided by a furrow which runs
almost parallel with the median suture. Thus the palatine part is sub-distinct from
the flange that grows from the alveolar region, with its double wall, its intervening
imperfect tooth-sockets, and developing teeth. The maxillaries are scarcely seen from

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 27

above (fig. 7), and, lying prone on the under part of the face, the infero-anterior orbital
foramen, through which a large branch of the maxillary nerve (V®.) passes, is well seen
in the lower view.

The palatine bones (pa,) are well developed, and they form two-fifths of the hard
palate ; their suture continues that of the maxillaries up to the front edge of the basi-
sphenoidal region.

In general form they, together, suggest the shape of the human thorax as seen from
the front, and are overlapped by the maxillaries that form their shoulder. In front,
they interdigitate with those bones, and then have each a foramen in their front
fourth ; their “‘ waist” is succeeded by a pair of small “ haunches -” these are the
pterygoids (pg.), smallish, thick shells of bone, which partly floor the naso-palatine
canal, but do not meet in the middle. The ascending processes of the palatines and
pterygoids are not seen in this view, but they have been described in the sections
(1st Stage).

The orbital plates of the frontals (7) are seen in this view, and also the bones that
form the zygomatic arch ; these are the moderately large, but simple, jugal (j.), and
the squamosal (sq.).

Besides showing the crescentic, hollow glenoid facet (gl.f:), this view gives us a good
idea of the secondary, splint-like character of the latter bone, stretching from the
jugal nearly to the occipital arch ; it is beginning to be scooped out where it overlies
the tegmen tympani (t.ty.). The hinder half of the endocranium is well shown in this
view, obscured by no investing bones. In the openings of the orbits, below, we see
the lateral ethmoidal masses containing the turbinals, and behind these the orbito-
sphenoidal cartilage (0.s.), perforated by the large optic nerve (II.). Overlapping
that wing, and itself overlapped above and outside, we see the alisphenoid (a/.s.), a
half-opened fan of thick cellular bone, the handle of which is separately ossified.
Between the handle and the orbitosphenoid we see the sphenoidal fissure through
which pass the orbital and maxillary branches of the 5th nerve (V'*.), and the 3rd,
Ath, and 5th orbital nerves.

In the hinder margin, behind the suture of the two centres of ossification, there is
a large notch, becoming a foramen; this is for the 3rd branch of the 5th nerve
(V*.), and will be the foramen ovale.

The basis cranii is winged here, for the lower bone, forming the handle of the
fan-shaped alisphenoid, does not ossify close up to the median beam ; in that part,
a little further backwards, a median bony centre, small and transverse, is seen ; this
is the basisphenoid (0.s.) ; it is below and in front of the postclinoid wall (see fig. 1).

The organs of hearing are highly developed in the Armadillos ; here, right and left
of the basis cranii, we see the huge cartilaginous capsules, with the special cochlear
enlargement (chi.), larger, relatively, than I remember to have seen it in any Mammal
of a moderate size ; of course it is, relatively, very large in the smaller kinds of Bats.

In this view the cochlear bulbs (ch/.), the tegmen tympani (t.ty.) outside each, and

2

28 MR. W. K. PARKER ON THE STRUCTURE AND

the lesser bulb forming the mastoid (opisthotic) region (op.) are all displayed ; in the
latter, the ampulla of the posterior, and the end of the horizontal canals (p.s.c., the
latter is not lettered ; it is in fig. 4) shine through the cartilage.

In the interspaces between these large ear-balls and the hind skull, the vagus and
glossopharyngeal nerves (X., IX.) emerge, partly through the fissures, and partly in
enclosing cartilage. The internal carotids enter the cranium between the cochlez
and the basisphenoidal beam (b.s.). Under the tegmen the facial nerve (VII.) makes
its first exit, and then burrows the cartilage again, over and behind the junction of the
epihyal (e.y.) with the capsule. Postero-externally, the auditory capsule shows
two large perforations, the foremost of these lies inside the hind part of the tegmen,
and opens into the vestibule ; this is the fenestra ovalis (fs.0.) ; the other, the fenestra
rotunda (/-7.), opens into the cochlea (ch/.) in the postero-lateral face of the first turn
of the three-coiled “ helix.”

The basis cranii for the rest of the skull is half cartilage, spheno-occipital, and half
bone, basioccipital (b.0.) ; this “ centre” is oval, but truncated in front. Outside it, at
a distance equal to its width, right and left, the hypoglossal nerve (XIL.) burrows the
solid cartilage of the base of the exoccipital wall. Behind this, at a like distance, the
semi-oval condyles are seen (0c.c.), margining the huge sub-circular foramen magnum
(f-m.), at its antero-inferior edge. The paroccipital thickenings outside the condyles
are not large ; the exoccipitals (e.0.) are beginning to harden the walls ; and over the
foramen magnum two tracts of bone are seen, the two supraoccipitals (s.0.).

In the upper view (Plate 2, fig. 7) the parts seen are mainly superficial ; the huge
occipital roof, with its two ear-shaped bony centres (b.0.) are seen behind the great
fontanelle (fo.). In front, the roof of the alinasal region (al.n.) is but little shown, on
account of the very forward position of the nasal bones (n.). These bones are nearly
oblong, they project at the mid-line,in front, and are cut away, equally, behind; then
they widen slightly. This region of the skull is like the narrow end of a gourd, and
the rest may be likened to its bulbous part.

The frontals (f-), together, give a broad-waisted outline, being gently pinched in
over the orbits; the parts there marked off are each as large as the parietals (p.),
behind. Outside, the maxillaries, jugals, and squamosals (mz., j., sq.) are just seen ;
the lacrymal (/.) also slightly. The fontanelle (/v.) is still large and cruciform; it is
pointed in front, and dilated behind.

But the side wew (Plate 2, fig. 8) brings out the form and relations of the investing
bones best ; it also displays more of the inner skull; and with it the arches of the
face are given. In front the alinasal cartilage and external nostril (al.n., en.) are
seen ; between the frontal and maxillary, the wall of the upper turbinal (v.¢b.), and
inside the orbit, at the bottom, in front, the wall of the middle turbinal (m.tb.).

Below the squamosal we see part of the capsule of the ear (ch/.) where the tympanic
should be; behind the squamosal, the opisthotic region with the enclosed posterior

DEVELOPMENT OF THE SKULL IN THE MAMMALIA, 29

canal (p.s.c.) shining through ; below and behind it the occipital condyle (oc.c.) ; and
above that the occipital arch and one of the supraoccipital bones (s.0.).

In this view the peculiar forward position of the nasals (n.) ; the small infero-lateral
premaxillary (pz.); the large maxillary (mz.), with its long nasal suture, its deficient
upper facial plate, and its notched jugal process, are seen. The infraorbital foramen
(V?.) is very low down; at a moderate distance above it is the large, shell-like
lacrymal (/.), with an antorbital and a facial region, and the canal (/.c.) between.
Here, as well as in the upper view, we see what a large amount of space is covered
by the frontals (f.). The preorbital part of each bone is swelling, to fit over the huge,
complex nasal capsule, and then, behind the supraorbital ‘ waist,” the bone swells
again to cover the hemispheres. The orbital plate is also very large, and hides most
of the large orbitosphenoidal plate; the optic nerve (II.) can just be seen emerging
from its stem. The parietals (p.) are roundish shells, like the halves of a “ bivalve ;”
they nearly reach the frontals in front, and rest upon the squamosals (sg.) below.
These latter bones are nearly as large as the parietals, but of a very different shape.
They reach nearly as far back, and much further forwards, but are not so deep. A
large triradiate space separates the three main bones, here, below which the temporal
fossa passes directly into the wide, gaping orbit. The zygomatic process of the
squamosal is strong, and is clamped by the straight, thickish jugal (j.), behind which
we see the edge of the glenoid cavity. The postglenoid process is hollow, and of a
triangular form ; the posttemporal process is rounded.

The lower jaw is very elegant, with its arcuate general ramus (d.) and its slender
coronoid process separated by a narrow notch from the articular condyle, and the
latter by a smaller notch from the angular process (ag.p.); much solid cartilage still
remains in these parts.

The endoskeletal part of this arch (Plate 2, fig, 8; and Plate 5, fig. 4) is of great
interest. MEcKEL’s cartilage (mk.) is full-sized, a long and solid rod, passing inwards
and forwards to melt into its fellow in front. Behind the massive condyloid cartilage
(Plate 5, fig. 4, cd.p.) the bony plate of the malleus is seen, under the dilating part of
this primary jaw. The head of the malleus (ml.) has a very deeply scooped saddle-
shaped condyloid surface for articulation with the incus (?.) ; below this, the cartilage
grows in a right angle to the main bar, and then forms the manubrium (m.mb.) by
growing forwards again, as a slender terete rod. This is the “internal angular
process” of the Ovipara; but the posterior process (p.ag.) is also to be seen as a
tubercle above and behind the elbow of this long process. On the inside, one-third
the way up, we see the tensor tympani muscle (¢.tm.). The incus (7.) has no ectostosis
at present ; its articular surface is a deep, oblique saddle ; its short crus (s.c7.) is a
solid cone, and its long crus (/.¢.7.) is large, long, somewhat constricted proximally,
and supplied with a large inturned discoid facet for articulation with the head of the
stapes (sf.).

That top piece of the hyoid arch (Plate 5, fig. 4, st.) is a solid little “ stirrup,” with

30 MR. W. K. PARKER ON THE STRUCTURE AND

a small round hole, a large face above for the incudal facet, and a thick dilated base ;
the neck, with the stapedius muscle (st.m,), and interhyal (z.hy.) attached to it, is short.

Two changes have appeared in the arch of the hyoid; one is the complete fusion of
the epihyal with the auditory capsule (see, also, Plate 2, figs, 4 and 8, e.hy.); and
the other is the degeneration of the lower sub-segmented part of the epihyal
into a ligamentous tract. The fused upper part has thickened; over it the chorda
tympani (VII'.) passes from the facial nerve (VII.), behind.

The ceratohyal (chy.) has a larger upper, and a shorter lower, segment; then
comes the thick ovoidal hypohyal (h.hy.), articulated to the trifoliate basihyo-
branchial (b.4.br.) ; the median lobe, here, is a rudiment of the long basibranchial
series of the Ichthyopsida ; the lateral processes are the ‘“ thyrohyals ” (¢.Ay.).

The annulus tympanicus (Plate 5, fig. 4, a.ty.) 1s forming out of a ligulate,
U-shaped tract of softish cartilage,

Endocranium of Tatusia hybrida.—Third Stage (embryo, 3 inches long).

Although this embryo is one-third longer than the last, it has altered but little
except in the size of the parts; yet some new osseous centres have appeared, and the
others are more perfect. The endocranium, as seen from above (Plate 5, fig. 1), is a
remarkable and a very complex structure. The basal line is occupied for the front
two-thirds, by the huge nasal labyrinth; a large space, right and left of the remaining
third, is taken up by the organs of hearing; the eye-balls occupy a considerable space,
but they have dominated the cranial growths but little ; the sockets are very imper-
fectly marked out.

The nasal labyrinth, with its right and left galleries confluent with the great
median middle wall, is naturally divisible into three regions—the alinasal, aliseptal,
and aliethmoidal (fig. 1, a/.n., al.sp., al.e.). The first two of these regions are supplied
with the ophthalmic (orbitonasal) branch of the 5th nerve; the hinder region with
the olfactory or 1st nerve. So that, although these parts run into each other, there is
an important difference between them; of course the alinasal region is merely
vestibular.

The alinasal region (aé.7.) is but little seen from above (compare figs. 1 and 5);
there it runs across in front of the symmetrical, imperfect cylinders of the aliseptal
region (a/.sp.) as a narrow arched band, The last fourth of the long convex roofs of
the labyrinth belong to the aliethmoidal region (al.c.), and have the inner part of the
upper turbinals (w.tb.) growing within, and from them. Where this region begins,
there the whole capsule spreads out, suddenly, into two widely divaricating, ovoidal
masses, marked with the backs of the bifurcating turbinal outgrowths.

A large valley, in shape like a Butterfly, with its head backwards, lies between
the large upper turbinal masses; the “ body” between the “ wings” is the top of the

perpendicular ethmoid ().¢.), whose highest, crested part is the cartilaginous crista

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 31

galli (crg.). The diverging rows of spots, right and left, are the holes of the unossified
cribriform plate (cr.p.), which extends some distance under the lateral masses. A
much lesser region, shaped like a Butterfly, but with the head forwards, is seen
behind the cribriform plate; its body or septum is low and thick, and the markings
on each side, caused by the folds of the middle turbinal (m.tb.), diverge backwards
and outwards, like the rows of the nerve passages. The septum, there, is the end of
the perpendicular ethmoid (p.e.); thence the presphenoid (p.s.) begins ; it is hollow
along the mid-line, for the roots of the huge, leafy wings are bulbous. Yet these
swollen parts belong to the basal region, which, however, has no median bone in these
types; they are formed by the trabecule cranii. All these winged parts may be aptly
compared to Insects; here, the orbitosphenoids, growing outwards and forwards
behind the nasal labyrinth, and the alisphenoids, growing out behind them, have a
similar general form.

Where the swollen trabecular bars have grown up into wings, there the width
lessens a little ; it then increases, gently, and then suddenly becomes a large, dilated
band, confluent with the aliethmoid in front, and continuous with the supra-auditory
and supraoccipital cartilage (0.s., s.a.c., s.0.) behind. This tract has lessened very
little since the first stage (Plate 2, fig. 1). The narrowish stem of the great lateral
cranial band is ossified in its upper half, and this bone—the orbitosphenoid (0.s.)—-
runs along the front part of the root ; the optic foramen (IL.) lies on the lower edge of
this new bony centre, midway between the two margins

The next dipterous growth has a bony median body—the body of the posterior
sphenoid (b.s.). This ossification fits in between the swellings of the presphenoid,
and is convex in front; it is short at present, and has a concave hinder margin
reaching to the slightly elevated postclinoid wall. The proximal part of each wing
is ossified by the basisphenoid ; and the alisphenoid (al.s.) is double on each side,
for the rounded, outer free part is separately ossified from the narrow inner portion.
This narrow part is concave at its lower margin, to enlarge the sphenoidal fissure,
through which the Ist and 2nd branches of the 5th nerve pass (V'., V*.), besides the
3rd, 4th and 6th nerves. The inner bone is also notched at its outer part behind,
and the bony matter is beginning to convert the notch for the 8rd branch of the 5th
nerve (V°.) into the foramen ovale.

The cartilage formed by the moieties of the investing mass (parachordals) becomes
very narrow behind the postclinoid wall, between the large cochleze (ch/.), and then
it expands again as the threshold of the great occipital passage (fm.). The sub-
pentagonal basioccipital (b.0.) reaches halfway to the basisphenoid (b.s.) leaving a
long synchondrosis. The basioccipital is notched in front, and has a concave hind
margin, of less extent than its oblique sides. The sinuous margins of the proximal
part of the exoccipital region have their larger concavity in the front, to let out
the glossopharyngeal and vagus nerves (IX., X.); and behind and outside these
passages the thick square tract of cartilage is perforated for the hypoglossal (XII.).

B2 MR. W. K. PARKER ON THE STRUCTURE AND

Then comes a short exoccipital bone (e.0.) right and left, and then a considerable tract
of cartilage between these and the supraoccipital bones (s.0.) above. The cartilage in
which these latter centres lie is continuous with the broad, sinuous supra-auditory and
orbitosphenoidal belt (s.c.c., 0.s.). Seen from above, the huge auditory capsules, with
their apiculated helical cochlez (ch/.) are seen to be confluent with the proper chondro-
cranium both in front of and behind the passage for the 9th and 10th nerves. A
notch separates each cochlea from the upper mass of the capsule, and a well-formed
archway is formed by the proximal coil of the cochlea over and in front of the com-
pound meatus internus (VII,, VIIL.).

The end view of the chondrocranium (fig. 2) shows what a large occiput these types
possess. The supraoccipital centres (s.0.) are still distinct, and meet over the foramen
magnum (f.m.), which is ovoidal in form, with the narrow end above; they occupy
less than half their own region, at present. The exoccipitals (e.0.) are largely hidden
in this view by the ear-shaped condyles (oc.c.); in front of these, the cochlea (chl.)
can be seen, below, and in the distance. The paroccipital elevations outside the
condyles are but little developed ; the cartilage is nearly convex. A lozenge-shaped
tract of the ear-capsule is seen above their convexities, right and left, and all the three
canals (a.s.¢., h.s.c., p.s.¢.) can be seen shining through it, so great is the obliquity of
the capsule in its cranial setting ; the /arge inner (LX., X.) and the Jesser outer (XII)
nerves are also seen (the dotted line is wrong).

The tympanic region, from the outside, has been separately worked out and figured
(fig. 3) on a larger scale. The annulus (a.ty.) is fast becoming bony, especially in the
end of the upper crus, where it is partly bifid, above, to form a rest for the processus
gracilis of the malleus (i/.). That element is still a perfect mandible in itself; the
stem (mk.) is drawn as cut across, in the figure.

The depth of the sinuous selliform condyle for the incus (7.) explains why the
malleus shows @ hole at this part in the section (Plate 4, fig. 7). The styliform
ectostosis is now expanding and embracing the under face of the head of this
bar; below and inside this bony tract the tensor tympani muscle (¢.tm.) can be
seen arising by a narrow and short tendon, and then passing upwards and inwards,
solid and fleshy. The posterior angular process behind the internal, or manubrium,
is very indistinct ; the latter is nearly parallel with the main bar. The sinuosities of
the condyle of the well-formed but unossified incus (?.) correspond with those of the
inalleus ; the short crus (s.c.2.) is thick, and fits into a neat cup in the auditory
capsule, close over the ampulla of the horizontal canal (/.s.c.). The thick, long crus
is almost parallel with the elbowed part of tie malleus; it has a well-formed
orbicular facet on its inturned end. The unossified stapes (s¢.) is also large and well
formed ; here it is figured looking outwards, inside the incus ; its ovoidal base has the
narrow end looking upwards and forwards, according to the shape of the fenestra
ovalis (fs.0.). The tendon of the stapedius muscle (st.m.) shows in its substance a
considerable nucleus of cartilage, the interhyal (¢.hy.) or infrastapedial. The slice of

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 33

cartilage here drawn as taken off the auditory capsule shows the horizontal and most
of the posterior canal (h.s.c., p.s.c.) exposed in the tube of cartilage. Winding round
the inside of the incus, where it has been cut off from its proximal part in the cranial
wall, we see the facial nerve (VII.) forming an elegant arch nearly parallel with that
of the horizontal canal. In front of its imbedded part in the figure there is an oblong
tract of cartilage, this is the part where the epihyal (e.y.) has coalesced with the
capsule, and from this it has been cut away in this slice. Below this the facial nerve
is seen to send upwards a fork, suddenly ; this is considerably smaller than the stem of
the nerve, and in the uninjured skull rides over the epibyal to get inside the manu-
brium mallei; this is the “chorda tympani” nerve (VII’.), forking over the visceral
cleft to join the hindmost division of the 5th nerve.

Dissection of the Skull of Tatusia peba.—Fourth Stage (embryo, 3 inches long).

The dissected skull of Tutusia peba shows some differences from that of 7. hybrida
that are specific, yet most of the changes now to be described are due simply to
advanced growth.

Here the ale nasi, nostrils, and narial valves (Plate 5, fig. 5, al.n., e.n., 2.v.) are like
what I have just described, but the bones just behind these cartilages are larger than
we should find them in a species of 7. hybrida of the same age; these are the pre-
maxillaries (px.) and the foremost paired vomers (v’,). Still they are all distinct and
characteristic, the premaxillaries being small, oblique, notched, lateral shells of bone,
with no palatine portion, only with their lower edge curled in. The front paired
vomers (v’.) are twice as large as in the last, and are long shells of bone, with their
oblique hollow face turned outwards, towards “ J ACOBSON’s organ.”

Interdigitating with these four bones we see the two maxillaries (mz.), large,
inferiorly placed tracts of bone, showing the infraorbital foramina (V*.) on their under
surface, halfway from their swollen shoulder to their suborbital notch.

I find several alveoli, with their teeth, on the hinder two-thirds of their lower
margin, and then a flange from the inner alveolar wall growing intv the palatal region,
as wide as the rest of the hard palate, but separated from it by a very distinct multi-
perforate groove. The jugal process is wide, and is clamped by the angular fore part
of the jugal (7.) which widens, inwards, at its middle part, and then becomes narrow
where the zygomatic process of the squamosa] rides upon it.

A very long sutural line runs along the palate from the alze nasi (a/.n.) to the
presphenoid (p.s.) ; in front this is formed by the front paired vomers ; in the middle by
the maxillaries ; and behind by the palatines (pa.). Their mutual suture is two-fifths
the length ot that formed by the palatine plates of the maxillaries ; the palato-maxillary
suture is arched forwards. The palatines do not narrow in so much behind, as in
the last (Plate 2, fig. 6), and they also are grooved to, and beyond, their foramen.
The thick half-coiled pterygoids (pg.) also do not run so far under the skull, and they

MDCCCLXXXV. F

34 MR. W. K. PARKER ON THE STRUCTURE AND

form a more gaping space for the “ posterior nares;” they are notched behind, and
have the “ hamular process ” suppressed.

The squamosal (sy.) with its crescentic glenoid facet (g/.f.) is seen to run from its
overlapping jugal part on the jugal to the hinder face of the opisthotic region (op.).
The postjugal elevation is followed by a pneumatic foramen (pn.f.) which opens into a
definite air cavity. The semiosseous annulus tympanicus (a.ty. ; see also fig. 7) is left
on one side ; on the other the capsule is exposed.

Along the middle, behind the posterior nares, the presphenoidal region (p.s.) is a
thick roundish beam, quite free from bony deposit. But, laterally, in the fundas of
the orbit, the roots of the orbitosphenoids (0.s.) are ossified, and the optic nerves (II.)
are seen emerging. Behind the pterygoid, and opposite the last coil of the cochlez
(chl.) the basisphenoid (b.s.) is seen to be a short broad tract ; the cartilage between
it and the basioccipital (b.0.) is half the extent of the basisphenoidal bone. Outside
the pterygoids, the alisphenoid (al.s.) can be seen ; in front of these is the sphenoidal
fissure (V'*.), and at their junction, near the hind margin of the wing, is the foramen
ovale for the 3rd branch of the trigeminal nerve (V*.).

On one side the malleus (i/.) is seen stretching the membrana tympani (m.ty.),
radiating to the annulus, and on the other the cochlea (ch/.) and tegmen tympani
(t.ty.) are seen ; also the two fenestree (fs.0. and the large hole behind it). On both
sides the epihyal and the facial nerve (e.hy., III. read VII.) are shown, and also the
passage for the 9th and 10th nerves (IX., X.).

The occipital arch has a good bony threshold, now, the six-sided basioccipital (b.0.),
which has one side in the foramen magnum (f:m.). The large trilobate condyles (0c.c.)
have the exoccipital bony centres (e.0.) creeping round them ; they are still a long way
from the basal bone, and the cartilage near them is perforated by the 12th nerve (XII),
and over this passage there is now one large supraoccipital centre (s.0.).

The end view (fig. 7) shows how large this bone is, now that the two centres are
fused together (see in the younger specimen—TZ. hybrida, fig. 2). The occipital
cincture, in its upper part, is a large shield of bone and cartilage overlapping the
opisthotic part of the auditory capsules (op.), with their inctuded posterior canals
(p.s.c.) seen endwise ; the skull is roofed-in by the parietals (p.), and Hanked by the
squamosals (sq.).

The sectional view of this older specimen (Plate 5, fig. 6) shows what changes have
taken place since the first stage (Plate 2, fig. 1); during this time the young have not
doubled their size.

The arched line formed by the lower edge of the basis cranii is but little elevated ;
the main part of the internasal septum has almost a straight base. The prepituitary
part is three and a half times as long as the postpituitary; the thickening of the
great middle wall (p.e., 7.tr.), just in front of the presphenoid, has been caused by the
flattened and pressed cornua trabeculee ; the rest of the thickening, below, is due to
the intertrabecula, which is there seen to be a long prochordal tract.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 35

The snout is turned downwards, so that its lower angle projects but little beyond
its upper; from that angle the scooped recurrent cartilages (/.s.c., read re.c.) are seen
to arise. The highest part of the partition—the crista galli (c7.g.)—is nearly mid-way
between the bottom of the sella turcica (b.s.) and the projecting end of the snout.
From the septum, in front of that crest, the nasal roof has been cut away ; behind,
for some distance, the cribriform plate (cr.p.) grew from the sloping crest near its
top. The lowermg median cartilage becomes presphenoidal ; it is quite unossified at
present ; the basisphenoid (b.s.) and the basioccipital (b.0.) are seen, in section, with
the lowish, thick postclinoid wall between them; the former is twice as thick and
half as long as the latter. The large side-wall of cartilage reaching from the nasal
capsule to the supraoccipital roof (0.s., s.a.c.) has lessened since the first stage (Plate 2,
fig. 1) to one-half its relative size. Yet the band, even over the protruding alisphenoid,
is still of considerable thickness. The fore corner of the orbitosphenoid is becom-
ing free, outside the cribriform plate; its main part is only ossified in the narrow
stem below ; the upper outline is sinuous. The fontanelle between the frontals and
parietals (f., p.) is nearly filled in by these bones, and the retreating cartilage
exposes the squamosal (sq.) somewhat, at the base of the coronal suture. The ali-
sphenoid (above b.s.) is now a single bone, and the foramen ovale (V*.) is finished by
bony growths behind.

The supratemporal cartilage (s.a.c.) is still two-thirds the width of the tilted
auditory capsule, which is continuous with the band for some distance, hiding the fore
part of the great sinus canal (s.c.). Below, and in front of that canal, the elevation for
the anterior and posterior semicircular canals (q.s.c., p.s.c.) is not great, and the
hollow for the ‘‘flocculus” is shallow. There is a difference of size in the whole
capsule, and especially in the cochlea, as compared with what we have just seen in an
embryo of 7. hybrida of the same size (fig. 1), that is verv remarkable. This species
also either has a smaller ernbryo, or its bones develop much earlier than im the other.

The whole capsule has a well defined, definite outline, often widened into a chink,
marking it out from the rest of the endocranium. There is a large porch over the
actual openings of the meatus internus (VIL, VIII.); and in front of these the cochlea
swells up into the cavity of the skull. The occipital cincture is narrower than
the oblique capsule, and has a very large keystone piece, the supraoccipital (s.0.).
The exoccipital (e¢.0.) is nearly twice the depth of each interspace of cartilage ; it is
notched for the hypoglossal (XJT.), and has a concave face against the emerging vagus
and glossopharyngeal (X., LX.).

Besides the large frontal and parietal (/, p.), and the angle of the squamosal
(sq.), the nasal (7.), the palatine plate of the maxillary and palatine, and the small
pterygoid (mx., pa., pg.) are all seen edgewise. In this section, detached from the
skull, the lower jaw and its related parts are shown from the inside; it has the
same elegant shape as the other species ; its processes are still cartilaginous at their
extremities. MECKEL’s cartilage (mk.), fused with its fellow, is still complete along

FY

36 MR. W. K. PARKER ON THE STRUCTURE AND

the inner face of the ramus (d.); but the malleus (m/.) and incus (7.) are now three-
fourths of them bony ; their shape is very similar to that of the other kind (fig. 3), but
the head of the malleus (fig. 8, m/.) is heavier, and its handle smaller. A similar
difference may be seen in the incus (7.). The stapes also (st.) differs in having a larger
hole, a longer neck, and a larger nucleus of cartilage—the interhyal (or infrastapedial ;
v.hy.) in the tendon of the stapedius muscle. These differences are partly due to
age and are partly specific.”

Dissection of the skull of Tatusia hybrida.—Fifth Stage (ripe embryo, 4 inches long).

My most mature skulls of this type were those of ripe young; they are all that
is needful, now, for the interpretation of the highly anchylosed skull of the adult.

The outer parts of the skull, as seen in a dissection of this specimen (Plate 6,
fies. 1-4), give a good idea of the peculiarities of the Dasypodian type. The lower
view (fig. 1) still shows the nostrils and als nasi (e.n., adn.) on the under surface, but
the bones have encroached on the cartilage, here. The premaxillaries (px.) are larger
and they have, now, a definite palatine tract; they fit, now, well into the notches of
the maxillaries (m.).

The palatine part is not alike on the two sides, being more notched, and hooked on
the left than on the right.

These parts do not meet in the middle, but space enough is left to expose the over-
lying front paired vomers (v’.) The palatine portion of the maxillaries (m.) only
forms a narrow tract, gently widening backwards.

The alveolar region has teeth on all but the front fourth. In front of this tract
the bone is notched for the premaxillary, and, behind, it bends round the palatine (pa.).
The flange from the alveolar region is on a higher plane than the submesial part of
the hard palate ; these two tracts are separated by a perforated sulcus, and the inner
and higher bony tract is marked by the transverse ridges of the palatal skin. Outside
these parts the maxillaries spread into large shells of bone, the under and inner part
of which forms a tunnel for the infraorbital nerve (V*.). Behind the short floor of this
tunnel the whole bone has a notched outline, the rounded concavity of which makes
the fore and inner border of the imperfect orbit. The jugal process is broad and
notched for the jugal or malar bone (j.). Inside these parts the penthouse formed by
the orbital plates of the frontals (f:) can be seen. The rest of the hard palate is about
half as long as that formed by the maxillaries ; it is mainly made by the palatines (pa.).

* The remarkable differences just shown between these two closely allied specimens of the sub-genus
Tatusia (or 9-banded Armadillos) suggest the great importance of careful zoological (Taxonomic) work.
Forms that to the eye of an observer not well trained in zoological work might easily be mistaken for
unimportant varieties, may, to the eye of an expert, show very important modifications. Moreover,
any really important external specific character is almost sure to be correlated with some curious and

instructive modification of deep-lying structures.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 37

They, together, look like the opened shells of a Bivalve, their fore margin is rounded
and the hind part somewhat cut away ; their sides are pinched in,

Behind them come the pterygoids (pg.); these bones have grown considerably on
to the palute since the early stage (see Plate 2, fig. 6).*

This addition to the hard palate is rare in Mammals, even; and in this small
degree is instructive, linking on these types to the Anteaters, where it takes place
to the greatest degree. Their thickness also is worthy of note, for in another
Neotropical Family of Edentata—the Sloths—the pterygoids are often curiously
enlarged,

Behind the short, thick, jugal (7.) the squamosals (sqg.) are seen to be of great
length, reaching as far to the back as the occipital condyles.

They strongly clamp the auditory capsules over the tegmen, and opposite the
manubrium mallei (i.m/.) they show the pneumatic foramen, leading into their air-
cell. A pair of superficial bones are seen at their inner border ; these are the “ annul,”
finished crescents of bone, now; they are more than semicircular, hollow within, and
convex on their outside. Yet at present they do not ossify any part of the tube of the
meatus externus, but when that segmented cartilaginous tube is removed, the mem-
brana tympani (m.ty.) is well exposed in this surface view. The endocranium is
largely exposed behind the hard palate, and the bony centres of the posterior sphenoid
and occipital arch are seen, as well as some parts of the auditory capsule. A very
small part of the orbitosphenoid (0.s.) is seen, where the optic nerve (I].) emerges.
Behind these parts the alisphenoid is seen as one centre, right and left, confluent with
the basal piece (al.s., b.0., read b.s.). Vhe sphenoidal fissure and foramen ovale
(V1, 2., V%.) are not well seen. There is a considerable synchondrosis between the
basisphenoid and the six-sided basioccipital (b.0.), and also between that bone and the
exoccipitals (e.0.) below, and between them and the large shield-shaped supraoccipital
(s.0.), above. The emerging post-auditory nerves ([X., X , XIL) have their passages
exposed, and the facial (VII.) is seen escaping from the stylo-mastoid foramen, behind
the epihyal (e.hy.). The tympanic annulus fails to cover the inner side of the
cochlea (chl.), which is partly ossified.

The peculiar form of the Armadillo’s skull is shown in the upper view (fig. 2). Three
pairs of investing bones, the nasals, frontals, and parietals (n., f, p.) cover nearly the
whole of the top of the skull; the maxillaries, lacrymals, jugals, and squamosals
(mz., 1, j., sq.) are just seen at the sides; at the end, the convex top of the supra-
occipital is seen, and in front, a small tract of the alee nasi (al.n.). The nasals form,

* T am now satisfied that my oldest (ripe) young of this kind of Armadillo belonged, like the smaller
specimens, to the species hybrida. For my second stage (Plate 2, fig. 6) shows the pterygoids with a
larger palatine tract than is seen in 7’, peba, one third longer (Plate 5, fig. 5). That skull is also longer
and slenderer, whilst that of the older is like the skull of my second stage (Plate 2, fig. 6); both these
are very broad in relation to their length. I feel sure that this ripe young is really 7. hybrida, although

given to me as 7’. peba.

38 MR. W. K. PARKER ON THE STRUCTURE AND

in the outline of the top of the skull, a small neck to a large flask ; they are half
the length and one-fourth the greatest width of the frontals. These latter bones
swell over the huge turbinals, and are eleyantly concave at the middle of the orbit.
The parietals are about the size, now, of the hinder, dilated two-thirds of the frontals.

The side view (Plate 6, fig. 8) displays many parts, and corrects the visual
appearance of the other aspects.

There is considerable deflexion of the snout, the nasals reach nearly to the end,
above, and the nostrils look downwards.

The premaxillaries now form a squarish tract, followed by the maxillaries which
overlap them; these latter bones are half as long as the skull, they rise high,
midway between the orbit and the end of the snout, have their infraorbital foramen
(V*.) very low, and their jugal process notched to let in the jugal. The large
lacrymal (/.) has a roughly triangular outline, externally, the orbital margin, where it
has its hole (/.c.), and its antorbital flange, is concave. It covers in the upper turbinal
region, which was exposed in the second stage (Plate 2, fig. 8); its upper suture, with
the frontal, and its lower, with the maxillary, are nearly equal ; both of those margins
of the lacrymal are gently convex. The frontal (f{) swells over the lacrymal ; it is
then somewhat notched where it runs inwards as the orbital plate, which hides nearly
all the orbitosphenoid ; the whole bone is rounded where the roof passes into the
orbital wall.

The large rounded parietal (p.) helps but little towards forming the temporal fossa ;
it has a sheht concavity, besides, near its hind border, where it just overlaps the supra-
occipital (s.0.). From that part, behind, but not quite so far back, the squamosal (sq.)
reaches to the orbitosphenoid in front. Its three regions, the post-temporal, post-
orbital, and jugal are all nearly of equal length; the last of these is stout, and the
pre- and postglenoid processes are well marked, the latter being the larger of the two.

In the postorbital region it forms a large triradiate suture with the frontal and
parietal ; these bones so united do nothing towards enclosing the orbital space, which
is only marked out well in its antero-inferior half. Part of the palatine, pterygoid,
and alisphenoid can be seen in this view, and also the annulus (a.ty.), the manubrium
mallei (m.ml., line directed wrong), the epihyal (e.hy.), the facial nerve (VII.), the
opisthotic region and the parts of the occipital arch (s.0., €.0., 0c.¢.).

The lower jaw (fiys. 3 and 34) has retained its elegant shape; it has still some
cartilage on its projections, especially for the condyle (cd.p.). The splenial and coro-
noid regions hang well over MrecKeEv’s cartilage (mk.), which is still perfect. The
malleus (figs. 34 and 6, ml.) and incus (7.) are almost ossified, and the stapes (s¢.) now
a slenderer and more elegant “stirrup,” has the lower part of its crura, and the centre
of its base, bony. The little module of cartilage in the stapedius (st.m.) is now a mere
projection on the neck of the stapes. The upper ceratohyal (fig. 5, e.hy.) has a small
ring of bone near its base; the rest of the hyoid arch is still cartilaginous, and is
little altered since the last stage.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 39

The end view of the skull (fig. 4) shows a very large orbicular supraoccipital (s.0.),
divided vertically by two shallow sulci into three convexities. The lateral elevations
have a large selvedge of cartilage, half their breadth, which has to be ossified by this
large post-cranial shield of bone.

The paroccipital ridges are very obscurely marked off from the mastoid region (op.);
but the exoccipitals (e.0.) are getting near to the upper centre (s.0.), over the large
convex condyles (ac.c.); these latter are wide apart, and show the basioccipital (b.0.)
between them. The parietals, squamosals, and tympanics (p., sq., @.ty.) can be seen,
end-wise, in this view, as also the epihyal and facial nerve (e.hy., VIL).

The auditory capsules were removed and figured separately on a larger scale (Plate
6, figs. 7, 8).

The inner view (fig. 7) shows a very large squarish part above the bulbous cochlea
(chl.), and having in it the canals, only the anterior and posterior marking this aspect,
where they meet in one common sinus,

The antero-superior part runs forwards as a curved process, which is, indeed, the
anterior part of the tegmen tympani (see also fig, 11). The meatus internus,
with its various foramina (VII., VIIL), is very large; another small hole is seen
under the arch of the anterior canal (a.s.c.), which has no recess for the “ flocculus,”
but only a gentle scooping at this part, Another larger passage is seen, postero-
inferiorly, inside the stylomastoid foramen (see fig, 8).

In the outer view (fig. 8) the large square top of the capsule has a sinuous outline
postero-superiorly and antero-superiorly ; but the mastoid margin, which contains most
of the posterior canal (p.s.c.), is straight, It is deeply notched below for the facial
nerve (VII), the notch is the stylomastoid foramen, whose lower border is the
epihyal spur (¢./y.), now separated from the ceratohyal.

Within and in front of these parts we see the fenestra rotunda (/r.), and at a
distance equal to its width, the fenestra ovalis (/s.o.). Over these openings the
tegmen tympani forms an arch, continued forwards in the free spur; over the tegmen
the horizontal canal (h.s.c.) is seen shining through the cartilage. The ossification of
the capsule is very low and generalised as in certain anurous Amphibia, eg., Pseudis
(see Phil. Trans., 1881, Plates 2, 10, 11, 12). The bony matter, wh'ch is formed
endosteally, is showing itself everywhere on the convexity of the cochlea, on the spur

of the tegmen, along the sinus of the anterior and posterior canals (fig. 7), and on

t=)
part of their arches and their interspace.

Endocranium of Tatusia peba.—Sixth Stage (young specimen, apparently new-born,

4} inches long).

These drawings (Plate 6, figs. 9-11) were made from dissections ofa large ripe
embryo or new-born young of Tutusia peba; this, and that figured in Plate 5,
figs. 5-8, were the only long-headed specimens in my collection; I am satisfied that all

40 MR. W. K. PARKER ON THE STRUCTURE AND

the rest belonged to 7. hybrida, for their skulls were all much wider and more bulbous
in form, they had much larger cochlew, and were far less ossified in proportion to
their size.

In a figure of the lower view of the endocranium, with the auditory capsules
removed, and the vomers kept 7m situ, we get things that are very instructive (fig. 9).

The als nasi (a/.n.) are seen folding over the external nostrils (e.n.), which are
inferior in aspect. The base of the septum, in this fore part, is alate and lobed where
it gives off the recurrent cartilages (7c.c.); over them the aliseptal walls (a/.sp.) are
seen. Below, and overlapping the recurrent cartilages, we see the inferior turbinals
(7.tb.), now, endosteally ossified. The rest of the nasal labyrinth (al.e., Ul.tb., n.tb., read
u.th., m.tb.) shows no bony deposit, externally, although the turbinals are beginning to
harden within; these enfoldings are seen on the outer wall. The vomerine series ot
bones is half as long as the entire skull, the principal vomer (v.) being very large—a
trough in which the solid intertrabecular beam rests. In front, that bone half overlies
the anterior paired vomers (v’.), which are only one-fourth of its length and of its
width, and are like miniature Razor shells (Solen), wide open ; their concavity is above.
Widening backwards, the main vomer send off a short snag, right and left, at its
hinder third; its hinder fourth is in two sharp forks, that expose the perpendicular
ethmoid, and the presphenoid (p.e., p.s.) in their angle. From the side spur to nearly

the end of the fork, there is, on each side, a lanceolate scale of bone, one-fourth Jarger
than the anterior vomers (v”.), these are the posterior paired vomers (v’, the line, by
inistake, is carried to the left inferior turbinal), bones that help, afterwards, to bind
the middle vomer to the ossifying ethmoidal masses.

Just overlying the forks of the vomer we see the forepart of the base of each
orbitosphenoid (0.s.) ; the base of each of these bones is nearly equal to the extent of
the basisphenoid (b.s.) behind; but there is no presphenoid between them, only the
hind part of the great median cartilaginous beam.

These wings are now lesser than those behind them, the alisphenoids (a/.s.) ; they
are only two-thirds their breadth, and reach out, laterally, not quite so far. They are
free, and emarginate above, the whole of that large cartilaginous band seen in young
embryos having disappeared. The orbitosphenoids run forwards, as well as outwards,
binding, obliquely, upon the great turbinal masses (m.tb.). Besides the upper notch,
their whole hind margin is sinuous; and their base is thick, and perforated. The
anterior margin, below, is carinate up to the outer fourth ; behind this ridge, midway
outwards, we see the optic foramen (II).

The thick alisphenoids (a/.s.) have their wide roof perforated, and the fore part of it
binds upon the thick base of the corresponding orbitosphenoid. The basal part of
each wing is confluent with, but does not reach back so far as, the basisphenoid (b.s.).
The anterior margin is concave, and the outer convex; the posterior margin
projects backwards as an upper and a lower tooth—the latter being a process
from the thick ribbed part behind the larger foramen ovale (V*.), which is, now, in

DEVELOPMENT OF THE SKULL IN THE MAMMALITA. 41

the middle of this plate. The thick basisphenoid (b.s.) is almost as long as wide ; it 1s
emarginate, a little, both before and behind.

The synchondrosis has only half the extent shown in the last stage (fig. 1), and the
basioccipital (b.0.) is now a large six-sided bone, having lessened cartilaginous inter-
spaces between it and the exoccipitals (e.0.). These large centres of ossification are
concave on the inner, and lobate on their outer, side; they are notched, below, by the
hypoglossal nerve (XIL.), and above are separated by a definite cartilaginous tract
from the large shield-shaped supraoccipital (v.s., read s.o.). The broadly reniform
condyles (0c.c.) are now mere caps of cartilage on the exoccipitals.

In the detached hyoid arch (fig. 10) the upper and lower ceratohyals and the
thyrohyals (c.hy., t.hy.) are rapidly becoming ossitied.

The auditory region (fig. 11), removed from the rest of the skull, and seen from the
outside, shows a great increase of the bony deposit, which now runs round the large,
squarish mass, and is especially developed over the tegmen tympani. The ossicula
are now ossified; the processus gracilis of the malleus (pr.g.) is a large spatula,
with no Mrcket’s cartilage left, and lies in a groove in the upper crus of the well-
developed shell-like annulus tympanicus («.ty.). The stout incus (7.) is shown 7 svtv,
with the head of the stapes seen inside; that bone is also shown, detached, and it is
now high, and narrow, and has a tubercle on its neck in the tendon of the stapedius.
The epihyal (e.hy.) still shows a point of cartilage in front of the facial nerve (VIT.) ;
it is fibrous below.

Dissection of the Skull of a ripe embryo of Dasypus villosus (43 inches long).—
Fifth Stage (continued).

This was the largest, but not the oldest, of my specimens of young and embryo
Armadillos ; its centres of ossification were not, however, so much developed as in the
specimen of Tatusia peba, which forms my fourth stage (Plate 5, figs. 5-8).*

This is a much more massive kind of skull than that of a Tatusia, and the upper
parts do not so completely overlie the lower; it is more generally outspread; evidently
the genus Tatusia comes nearer to Myrmecophaga than does the genus Dasypus.

The lower view (Plate 7, fig. 1) shows a very wide and very short snout, with the
nostrils (e.7.) almost obliquely below. The base of the septum at this part is alate,
and the valves of the openings (7.v.) very large, and coiled upon themselves. The
whole space occupied by these cartilaginous growths is transversely oval, and is neatly
rimmed with bone. The nasals are only just hidden in this view by the cartilage
(see fig. 2, n., al.n.); two-thirds of the rim is formed by the premaxillaries (p-.),
which are twice as large as in Tutusia. Much of the facial plate of these bones can

* These three kinds are all I have been able to obtain in their early stages; yet they show a most
extraordinary amount of variation, and suggest to me, that it would be well worth while to work out
the various stages of every species in the Family.

MDCCCLX XXV. G

42 MR. W. K. PARKER ON THE STRUCTURE AND

be seen in this view, for they converge in a very curious manner to form the fore end
of the hard palate.

This fore part of the hard palate is semi-oval, and forms the beginning of the very
elegant palatal roof which, altogether, would be a long ellipse if the pterygoids had
closed in instead of keeping at the sides. The toothless dentary margin is curiously
drawn inwards; and the higher palatal tract of each bone is concave, and has a large
semicircular notch where it should meet its fellow; thus the even suture is cut
into two short tracts. The suture between these bones and the maxillaries is sinuous,
the latter pushing forwards externally and in the middle.

In the subcireular space between the premaxillaries the front paired vomers (v’.)
are seen; they are convexo-concave styles as in Tatusia.

The broad hard palate (mz.) with its convex sides and teeth running up to the pre-
maxillaries, and back beyond the palatine suture, is much more normal than what we
see in Tutusia, and the alveolar region is thicker. The teeth, six on each side, are still
in one groove, and they give it a moniliform appearance. Inside this arcuate cavity the
bone is thick and cross-grooved by the palatal skin; a row of holes, instead of a
chink or fissure, separates the sides from the inner higher part of the hard palate.
The great pinching-in of the fore part of the bone seen in the nine-banded kinds is
not seen here, yet the infraorbital foramen (V*.) is inferior, not lateral; its floor is
much larger.

The jugal process instead of going beyond the alveolar region does not reach so far,
and is smaller. The palatal region of the palatine bone (pa.), instead of being very
unlike that of the maxillaries, is very much like that tract. The two bones have a
W-shaped hind margin, in front of which the bones are thick and rough as at the
sides, just contrary to what the other kinds show; the palatines are widest where the
pterygoid bones fit on to them ; these latter bones (pg.) fit obliquely to the outer half
of the palatine edge, leaving its median notch free; they then run outwards and
forwards.

They have a thick, ascending, or cranial part, and a retral inferior hamular process,
which has a concave outer and a convex inner margin, and a slight inclination to the mid-
line. Each bone is tipped with true cartilage as in the Hedgehog and Mole (as I shall
show in my next part). Yet, notwithstanding the merely lateral position of the ptery-
goids, the hard palate hides the presphenoidal cartilage, which it does not in a Tatusia
of the same age (Plate 6, fig. 1), and this great bony floor occupies the foremost two-thirds
of the basal part of the skull. The jugals (j.) are altogether larger than in the other
genus, and they are much further apart, through the width of the skull. The squamosal
(sq.) carries a much larger glenoidal cartilage (g/.f.), and it lies at the beginning of the
hindmost fourth, instead of the hindmost third of the skull’s length. Also the annulus
tympanicus (a.ty.) does not cover, in this aspect, the inner part of the squamosal, as in
Tatusia; in this type that part is very large. Behind the condyloid lunule the bone
forms a thick obtuse process with a pneumatic foramen in its postglenoid process.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 43

Inside the glenoid condyle the squamosal runs across and forwards, binding strongly
on the solid alisphenoids (q/.s.); with their help, an oblique thick ridge of bone is
formed, which runs, with a concave outline, outwards and backwards, from the ptery-
goid to the opisthotic corner of the ear-capsule (op.). There the broad thick basis
cranii also has a concave margin which runs outwards and backwards, and thus a large,
oblique, oval space is left in the floor of the cranium ; this is filled in by the auditory
capsule, mainly by its cochlear region (ch/.). On the inside the fissure is filled with
fibrous tissue until we come to the opening for the vagus and glossopharyngeal nerves
(X., [X.). In the front of this fissure the internal carotid artery enters. Outside we
see the higher part of the outer lamina of the squamosal helping to enlarge the tegmen
tympani, and, in front, the facial nerve (VIIL.) escapes from the skull, and gains the
hollow of the tegmen. It then runs along that arched way, and before escaping
through the stylomastoid foramen burrows through the cartilage formed by the fusion
of the auditory capsule with the epihyal (¢.hy.).

Near this tunnel, on the side of the capsule, we see the fenestra ovalis (/s.0.), and at
the fenestra rotunda (fr.) the outside of the proximal coil of the cochlea (ch/.). The
optic nerve (II.) can be seen emerging from the orbitosphenoid, and behind it an
oblique tract of the alisphenoid is seen; it is very thick, has the foramen ovale
(V3.) in its middle, and a suture appears right and left of this hole, due, I have no
doubt, to a primary division of the bony deposit as in Tutusia, but with the suture
more oblique.

Like the other structures, the parachordal region is much more outspread ; the
basisphenoid (b.s.) has a rounded outline, and does not yet reach the edges of the
great cartilaginous beam. The basioccipital (b.0.), also, lies in a large tract of
cartilage, reaching the sides nowhere ; it is oval, with the long diameter median, A
widish tract of cartilage exists between the basal and lateral bones—the exoccipitals
(e.0.), on the edge of which, in front, the hole for the hypoglossal (XII) is seen. The
unossified capsules, in their opisthotic region (op.), run almost directly inwards, with
scarcely any paroccipital elevation between them and the condyles (oc.c.). Instead
of being in front of the general lower face of the skull, the large ovato-reniform
condyles are behind it, and instead of the supraoccipital tract (s.0.) being largely seen
in this view, it is only apparent at the hinder outline of the foramen magnum (/m.).

Hence the setting on of the head in these two types 1s very different ; here, it is
much more terminal than in Tatusia, where it is almost as much under the head as in
the Primates. On one side of my dissection the ear-drum was left én situ. The
annulus (a.ty.) is only half as broad as in the other kind, although quite ossified ; a
considerable space, filled with fibrous tissue, exists between the annulus and the basis
cranii. The malleus, MecKenr’s cartilage, and the membrana tympani (ml., mk., m.ty.)
are shown in this view, these will be better understood by reference to other figures
(figs. 34 and 6).

The upper view (Plate 7, fig. 2) shows the great breadth and shield-like form of

G 2

44 MR. W. K. PARKER ON THE STRUCTURE AND

the skull, with its more outspread zygomatic arches, and its more definite orbital waist.
The premaxillaries, maxillaries, lacrymals, jugals, and squamosals (px., mx., l., j., sq.)
are all fairly in view in this aspect. Right and left of the median suture the
three main roof bones, nasal, frontal, and parietal (n., f., p.), finish the roof ; here, as in
Tatusia, there is no interparietal, so large in the Insectivora. Both the nasals and
the parietals are relatively about one-third larger in this kind, so that the frontals do
not cover so large a proportion of the roof, nor are they specially swollen over the
iateral ethmoids. Postero-laterally, the temporal fossee, which open freely into the
orbit, are well seen from above, and the squamosals form a rounded angle, behind,
over the opisthotic cartilage (see fig. 1, op.). Mesiad of those elbows, the hind margin
of the skull forms a neatish quadrant, the inner half of which is the ossified supra-
occipital (s.0.), which turns over the roof to an extent equal to half the sagittal suture;
the lambdoidal suture is gently sinuous, the convexity of the line looking forwards in
the middle and backwards at the sides.

If the sede view be compared with that of the other kind (Plate 7, fig. 3; and Plate 6,
fig. 3) the general likeness and the special differences of the two kinds will be seen.

Here, the premaxillaries (px.) are twice as large, and the lacrymals (/.) only half
the size of those of Tautusia; then the frontals (f) being flatter, the maxillaries (mz.)
are larger behind ; their infraorbital foramen (V*.) is higher up and more exposed.
The smaller lozenge-shaped lacrymal (/.) has its canal (/.c.) nearly in the middle of the
facial part, and this bone, with the jugal (j.) and frontal (f-) form a more rounded and
neater orbital rim, two-thirds round the space. But the orbit and the temporal fossa
do but form one general valley, reaching from the lacrymal to a point over the head
of the malleus (m/.).

The coronal suture is formed by the sinuous line of union of the thick edged
frontals and parietals ; it ends, below, on the squamosal, at its front third, opposite
the end of the jugal, which bone (7.) is flat, thick, and especially enlarged both before
and behind, where it rests on the maxillary, and where the jugal process of the
squamosal rests on it. If the squamosal (sqg.) shows more in the upper, it shows less
in the side view ; its pre- and postglenoid processes are small, but the post-temporal
part grows well down over the hinder tympanic recess.

Looking under the jugal, we see a small part of the orbitosphenoid, with its optic
foramen (see fig. 1, 2), the chink for the Ist and 2nd branches of the 5th nerve (V"*.),
and the alisphenoid, with its foramen ovale and the suture across it (V*.). Beneath

these parts the palatal elements—maxillary, palatine, pterygoid (mz., pa., pg.)—are
seen. The hamular process of the pterygoid is seen to look downwards, and to be
capped with cartilage. The tympanic region is well seen in this side view of the
skull; the annulus, Mecken’s cartilage, malleus, incus, and membrana tympani (a.ty.,
mk., ml., m.ml.,i.) are all seen, and above them a considerable tract of the squamosal.
The epihyal (e.4y.) is still continuous with the opisthotic cartilage (op.), and behind it
the facial nerve (VII.) is emerging; these parts are very near the end of the skull,

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 45

and between them and the condyle (0c.c.) there is a very inconspicuous paroccipital
tract. The exoccipital and supraoccipital (e.0., s.o.) are seen in the midst of large
tracts of solid cartilage.

It is impossible to look at the end view (fig. 4) without being reminded of low
Ichthyopsidan types of skull ; the cartilage is as solid as in them, and the osseous
centres are mere patches in it. The general form of the occipital end-wall is trans-
versely oval ; it overhangs a little above (see fig. 3), and then curls over, above, where
the bony centre (s.0.)—single now, but undoubtedly double once—is somewhat
trilobate. This supraoccipital centre is thus like a sessile leaf with a trilobate upper
outline, and a concave petiolar attachment ; this is the lower margin over the foramen
magnum (fim.). What looks in the side view (fig. 3) like a large epiotic swelling is,
in reality, seen here to be the thick convex edge, right and left, of the great supra-
occipital shield. Here we see the whole line of demarcation between the auditory
capsule and the back wall of the skull proper, converted into an arcuate chink, which
becomes a triangular recess, below Outside this, the epiotic and opisthotic regions
(op.)—to the latter of which the epihyal (e.hy.) is fused, and through which the
facial nerve (VII.) passes—is but a narrowish convex, lateral tract, thinning out helow,
where it flanks a very indefinite paroccipital tract (p.oc.). Inside that tract, and over
and within the condyle (oc.c.), we see the orbicular, exoccipital (¢.0.), only one-tenth
the size of the once double upper bony tract (s,0.),

Like the rest of the skull the occipital basal margin and condyles are a very wide
structure, the bony basioccipital does not reach the foramen magnum ; this passage is
lower than in Tatusia (Plate 6, fig. 4), it inclines upwards and backwards (see figs. 1
and 3), The parietals (p.) and squamosals (sq.) are hardly seen in this view.

The mandible (figs. 3, 34) has the same general shape as in Tatusva, but it is heavily
built, and not at all like the elegantly slight structure seen in the other kind; the
teeth also run further forwards, and are larger. Altogether this type is further from
the Anteaters than the others, and on the whole less modified from the average
Mammalian type.

A little cartilage is still seen in the coronoid and angular processes as well as in
the articular; MecKkev’s cartilage (mk.) is still quite perfect. The malleus (figs. 34
and 6, ml.) is unlike that of Tatusia, the head is more solid, and the pesterior angular
process is more distinct, but high up, almost close to the articular condyle. The
manubrium forms an acute angle with the main bar instead of being parallel with it,

“elbow ” low down; it is also longer, and is dilated at its end.

and having its

The small, hooked ectosteal plate has only just begun to graft itself on the under
face of the malleus. The incus (7.), which is quite unossified, is like that of Tatusva,
and so is the stapes (s¢.) ; it also shows a small “interhyal” (7.4y.) in the tendon of the
stapedius muscle (st.m.). The hyoid arch is quite normally Mammalian, and not like
that of Tatusia; the epihyal (figs. 4 and 5, e.hy.) lingers on as part of the general

arch, which is thus tied to the skull; the partly ossified upper ceratohyal (c.hy.), not

46 MR. W. K. PARKER ON THE STRUCTURE AND

yet seomented from it, thickens downwards, then comes the shorter ceratohyal (c.hy.)
not ossified, and the hypohyal (h.hy.) the same. The body (b.4.b7r.) has no retral
process, and is unossified at present; the thyrohyals (¢.hy.) are partly ossified, and
are in this type segmented off from the body.

In these things Dasypus shows itself more as a normal Mammal, whilst Tatusia is
very low and abnornal,

BRADYPODID.

This second and only other group of Neotropical Edentata with imperfect teeth is in
as great a contrast with the first as can be well imagined, and yet I quite agree with
Professor FrowEr in looking upon all the Edentata from that region, toothed or
toothless, as being suckers from one common root-stock (see Proc. Zool. Soc., 1882,
pp. 858-367 ; and Art. “ Mammalia,” Encye. Brit., 9th edit., vol. 15, p. 384). I shall
describe the South American forms first, and then take up the Palzeotropical kinds ;
in both the extreme diversity of the existing forms, and in some cases their almost
extinct condition—just one or two species of an extremely isolated type—suggest,
powerfully, the great losses this group has suffered since its evolution.

If any one doubts that the short-faced Sloths are intrinsically of the same stock as
the long-faced Anteaters of the same region, I would refer him to my figures and
descriptions of the scapula in these curiously dissimilar forms (‘Shoulder-girdle and
Sternum,’ Plates 21-23, pp. 199-207).

My materials for working out the skull in this group were as follows :—

First Stage. Embryo of Unau (Cholopus didactylus),* 34 inches long (Plate 1,
figs. 1, 2.)

Second Stage. Embryo of Ai (Bradypus) (Arctopithecus),(

Third Stage. Young of Unau (Cholopus Hoffmannz), 8 inches long.

Fourth Stage. Young, half-grown, of Ai (Bradypus tridactylus, Linn.).

? sp.) 5 inches long.

I have just given reasons for supposing that the Tatous (Zutusia) are less typical
than the species of the genus Dasypus, so I shall now give reasons for considering the
Bradypodidie, generally, as inferior to the Dasypodidee, as a whole. Cuvirr’s insight
was never better shown than when he classed the heterogeneous Edentata together—
both the Old and New World forms ; and the same instinct, which led him to put the
Monotremes with them, was not so far out as seems at first sight. I am satisfied that
the Edentata in becoming “ Eutheria” never utilized the Metatherian stage, but

passed rapidly—at a bound, so to speak—from the Prototherian stage, into the basal
region of the highest group. There, however, they have stayed; they are just equi-
valent, in their fullest development, to the lowest and most generalized of the In-
sectivora, some of which, very probably, are modified and improved “ Metatheria,” or

Marsupials.

* This Embryo has seven cervical vertebra ; C. Hoffmanni has only siz.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. A7

Skull of embryo of Cholopus didactylus (34 inches long).—First Stage.

In this type the nostrils, as seen in the lower view (Plate 8, fig. 1, e.n.), are not
inferior, but lateral ; and the alinasal floor (a/.n.) shows but a small distance in front
of the premaxillaries (px.); the basal alee reach to these openings, as the roofs do,
above (fig. 2, al.n.). The premaxillaries are as small as in Tatusia, but they have each
a well-formed palatine process, nearly as large as the narrow, anterior, or dentary
tract. The pointed ends of these submesial spurs do not reach the inner part of the
maxillary palatine plates (muw.), for these retreat considerably, leaving a considerable
angle of membrane exposed ; this, and the two round notches between the inner and
marginal parts of the premaxillaries, form a cordiform tract, in the anterior lobes of
which we see the openings of Jacosson’s organs (j.0.). In this early embryo,
about one-third ripe, the palatine plates of the maxillaries (mx.) are only just
approximating even in the middle ; in the hind part, as in front, there is a considerable
angular space, enclosed by these ingrowths of bone. The whole of this double tract
is nearly square; the breadth across the foremost alveoli is greater than the length
in the middle; at the sides, the last pair of alveoli overlap the palatines (pa.), and
there make the side measurement the longer of the two. Already the foremost
alveoli, with their teeth, project most, whilst the last pair project least ; there is room
for two sockets, with their teeth; between the first and second, a shallow groove is seen
along this edentulous space. The inter-alveolar flange is separated from the inner
part of the bone by a less distinct groove than that seen in Tatusia ; behind, it forms,
at its palatine end, a definite and widish space. In this view, the facial part of the
maxillaries is seen, as a right and left wing ; in this space the infraorbital foramen (V*.),
is well shown ; its bridge, or floor, is narrow. The rest of the palate is very peculiar,
it is quite a rough, generalized structure, the palatines (pa.) themselves being not so
much developed in this region as the pterygoids are in Tutusia hybrida, at a somewhat
later stage. There is an angular space between the palatine plates of these bones,
in front, and behind ; they do not meet at the mid line. They then, like the pterygoids
of Tutusia hybrida, diverge, so as to leave a semi-oval space, in which the broad
basis cranii is seen, or all its presphenoidal region (p.s.). The ascending or cranial part
of the palatines is very limited; the wall formed by the bone is extremely thick and
rough, and behind the Jast tooth socket each bone forms a rounded boss, from which
the rest of the bone diverges gently.

But all this roughness is seen in a double degree in the pterygoids (pg.), which
have a very reptilian simplicity of form, and independence of the basis cranii, to which
their attachment is very limited. Each bone is like a rough nut, in miniature ; it is
somewhat scooped postero-laterally, and at its end has a cupped cavity, filled with
hyaline cartilage ; the remnant of the Ichthyopsidan cartilaginous “ upper jaw.”

The whole palate is very generalized, and therefore very instructive ; it improves
afterwards (see Plate 9, fig. 1), and yet in the large young of this genus the palatine

48 MR. W. K. PARKER ON THE STRUCTURE AND

plate of the palatines is as arrested as in the very open palate of a Rabbit, or the
most closed (‘desmognathous”) palate seen in Birds, namely, in Podargus (see Trans.
Linn. Soe., ser. 2, Zool., vol. 1, Tab. 23, figs 6-8).*

In the distance, the large orbital plates of the frontal are seen, and laterally, on the
level of the palate, the jugals and squamosals (j., sq.) ; these lateral parts have a pecu-
liar independence of each other. Such is not seen again until we are down among the
Lizards and Serpents. Here the large jugal (j.) is articulated to the maxillary in
front, but has its bifurcated hind part free. Answering to this structure, the zygomatic
process of the squamosal (sq.) is aborted, and the large crescentic glenoid saddle (g/.f-)
lies between two thick ridges of bone, its concavity looking forwards. These ridges
meet behind the facet as a low, arched postglenoid tract, and then the rest of the
bone, as seen in this aspect, runs outside the tegmen tympani (¢.ty.), largely helping
by its concavity to increase the size of the chamber in which the ossicula auditds
(m.ml., m.k.) lie, and along which the facial nerve (VIT.) runs. A very small tract of
skull-wall is seen between the pterygoids and the glenoid region, right and left, but
the basis cranii is seen up the fore end of the presphenoidal region (p.s.),

That is all cartilaginous, and in this marvellously stout little skull the whole beam
has twice the thickness it has in Tutus’a, The basisphenoidal region is more than
equal to the presphenoidal in extent, but its middle two-thirds only is ossified ; this
basisphenoidal bone (b.s.) has all its four subequal sides concave ; its outer sides are
pressed upon by the pterygoids. Then comes a tract of cartilage which is louger than
the bone, but narrows, backwards, for its hind margin is between the most bulging
part of the large cochleze. The basioccipital (b.0.) is lozenge-shaped, with the front
und hind angle truncated; it is larger than the basisphenoid, and, like it, reaches
the edges of the basal cartilage. The occipital arch is less by far than the auditory

region, and the paroccipital region is but little marked—as in the Dasypodidee. The
large condyles (0c.c.) are partly under the skull, yet they are well seen behind (fig. 4) ;
they are obliquely reniform and enclose a large, subcircular foramen magnum (/-m.).
The exoccipitals (e.0.) are separated by a tract equal, nearly, to their own width from
the other occipital centres (b.0., s.o.) ; the hypoglossal (XII.) notches the bone in its
lower or anterior edge on the right side, nearer to the auditory capsule than to the
condyle. Still further forwards the 9th and 10th nerves (IX., X.) pass out, the basal
cartilage being notched for them behind the capsules.

These latter parts are very large, and wholly cartilaginous, at present ; the cochlea
has the appearance of being composed of only two coils, for the proximal part is one
large curved convexity, the distal or hemispherical mass lying in its concavity. Both
the fenestra (fs.o., fr.) are seen in this view, and also the facial nerve (VII.), both
along the tegmen, and at its exit behind the thick epihyal (e.hy.), which it notches.

*The Unau comes very near the extinct Cwlodon in the structure of its palate ; compare these figures

(Plate 8, fig. 1, Plate 9, fig. 1) with Rutuarpr’s admirable illustrations of that type (“ Kempedovendyr-

sleeten Cornopon.” Copenhagen, 1878).

DEVELOPMENT OF THE SKULL IN THE MAMMALTA. 49

This somewhat Jemurine skull, seen from above (Plate 8, fig. 2), shows in this early
stage some promise of the stony solidity of the skull of the adult. The roof-bones
are forming rapidly, and only a lozenge-shaped fontanelle ( fo.) remains in the vertex.
The premaxillaries (px.) are scarcely seen in this aspect; but the facial plate of the
maxillaries (mx.), and the great front alveoli, come into view; between them the
nasals (n.), behind the short snout (a/.n.), are seen as short, wide bones, only one-third
longer than broad, and having their fore edge cut away on the inside. The maxillaries
and nasals form a convex margin to unite with the concave fore margin of the
trontals (f). Outside their narrow fore end the smallish lacrymals rest on the jugal
process of the maxillaries, and behind these the jugals (j.) come into view. Even
now, in their narrow fore part, the frontals show that pitting which is a sure sign of a
dense and solid bone in its early stage. The remainder of these bones is radially
fibrous, like the parietals (p.), and these plates are about equal, the fore part of the
frontals being left out of consideration.

The supraorbital rim is better formed than in the Armadillos; its terminal or
postorbital process is well defined. From it, forwards, the edge of the bone has a
gently concave outline, so that, although the frontals narrow in, forwards, they form
everywhere a large roof over the fore brain. The postorbital part of the frontals is
one-third the extent of the whole, and it nearly reaches as far outwards as the large
convex parietals (p.). In their re-entering angle, behind, we get a view of the upper
half of the occipital arch (s.0.), which is ossified very early and very rapidly ; much
more so than in the Dasypodide, although in neither of these types is there any
“interparietal ” or additional membrane bone, or bones.*

This cartilage bone shows the pitting, which is seen in the fore part of the frontals.
The occipital condyles (see, also, fig. 1, oc.c.) can just be seen from above.

In the side view (fig. 3) we get a display of parts, the figure of which might serve
as an elementary diagram of a Mammalian skull. The short, depressed snout shows

* There is something which has to be accounted for, here; the interparietal, which is formed nearly
always from two primary centres, and which figures so largely in Marsupials and Insectivores, and in the
Eutheria above them, is totally absent in the Neotropical Edentates, and in the Pangolins of the Old
World. In Orycteropus it is as large as in the Insectivorous Rhyncocyon from the neighbouring region—
(Zanzibar, Hast Coast)
able to show of Orycteropus in this; for the Cape Anteater lies somewhere between the Armadillos and

a type, the skull of which I shall compare, in my next paper, with what Iam

that most perplexing, most generalized Insectivore. Looking at the Mammalia, generally, and bearing in
mind that Birds with the largest skulls (Crows and Songsters) have no interparietal, it seems evident
that that bone comes in to help the parietals in roofing in the enlarging brain of the Mammal. Ina
young Ornithorhynchus, the size of a new born kitten, with the hairs just appearing, the parietals form
one thick continuous mass, as in the Ophidia, and the large bilobate ossification of the supraoccipital
eartilage, is fast growing to its hind margin. I see, also, the same thing in the Hchidna at a little later
stage. Some things, no doubt, in the Edentata are due to degeneration, or suppression, but I feel sure
that they were never higher in the scale of the Mammalia, on the whole, than they are now, and strongly
suspect that they are a sort of metamorphosed Monotremes, in which the Marsupial stage was got
through rapidly.

MDCCCLXXXYV. H

50 MR. W. K. PARKER ON THE STRUCTURE AND

the nostrils with a rounded rim, and a small valvular process ; they open laterally.
The premaxillaries (pa.) can be seen in this view, on their outer edge, without any
ascending or facial plate, looking no larger than the Ist maxillary tooth.

The maxillaries (ma.) are small relatively to the skull, generally, and they have
their infraorbital foramen (V®, see fig. 1) rather inferior than lateral; there is a small
hole in front of the main passage ; the bone generally is curiously ribbed and wrinkled.

Over it we see the edge of the nasal (n.), and under the contiguous parts of the
nasal, frontal, and maxillary, the smallish, thick, perforated lacrymal (/.) comes in to
form the foremost part of the orbital margin ; the canal (/.c.) opens on its edge. The
jugal (j.) has as well-formed an orbital margin as the frontal, above, and they with
the lacrymal make a rim about the eye-socket for all but its hinder fourth. Even
there the postorbital process of each bone is thick and tends to cover in this part ;
we shall see that this nascent perfection of the orbital rim is only temporary (see
Plate 9, fig. 3), so that the early skull, only, can be said to look towards that of
a Lemur; here, it is evident, we find signs of degeneracy, or retreat, from the more
normal Mammalian type of skull. That the great peculiarity of the jugal bone is not

something new in the existing, dwarfed Bradypodide is evident, for in this species

2,
this early stage shows its great peculiarities best ; they are softened down after-
wards. *

Below the neat orbital rim of the jugal, the bone is obliquely attached to the
maxillary ; thence it is free, and ends in a postorbital, a zygomatic, and an infrajugal
process ; together, these processes give a great depth to the bone ; behind the middle
and lower snags we see the coronoid process of the mandible.

Over the orbit the frontal rises—until at the vertex it is very high—as the roof of
avery large skull cavity. The orbital plate of the frontal is large, but is imperfect
below at present. The parietal (p.) is larger than would seem from the upper view, for
it runs well down behind the auditory capsule, between it and the supraoccipital.
The lower margin forms a sinuous line over the inside of the huge, open temporal
fossa, and only at its middle, most projecting part does it reach the top of the
squamosal (sg.). Besides the fontanelle at the vertex (fo.) there is another on
each side, where the frontals and parietals diverge behind the orbits. This is, at
present, several times as large as the upper open space, and as far as superficial bones
are concerned, it reaches from that divergence above, and the junction of the
squamosal and parietal behind, forwards, to the bottom of the orbit in front. In
its fore half it exposes the large orbitosphenoid (0.s.), and in its hinder half the
long band of cartilage (s.a.c.), which runs on to join the top of the auditory capsule,

* If this figure of the skull of the early embryo of the Unau be compared with Reruarp’s splendid
plates of Calodon (Copenhagen, 1878), and Gryptotherium (Copenhagen, 1879), it will be seen how
remarkably the jugals correspond. In the latter (plate 1) there is the appearance of a small hole
above and in front of the infraorbital foramen, which evidently corresponds with what I have figured
in the embryo of the Unau; this small hole is also to be seen in the half-grown Ai.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. ol

is seen passing upwards and backwards along the middle of this hinder membranous
tract.

We shall see, afterwards (Plate 9), how completely this space is filled in by the
frontal and squamosal; the latter is now a large ear-shaped scale of bone with a thick
horizontal part, capped with the glenoid facet (see fig. 1). The temporal fossa,
widely opening into the orbit, is but slightly walled in externally by the projecting
articular part, and its small zygomatic process. The inner plate of the squamosal
reaches further forwards than the outer; behind, the bone ends in a round post-
temporal lobe, which overlaps the massive ear-capsule up to the junction of the anterior
and posterior semicircular canals (a.s.c., p.s.c.). The occipital piane is very wide and
transverse (see fig. 4); here, in the side view, little save the edge of the arch, with
its ossifications (s.0., e.0.), and the condyle (oc.c.), are seen. At present, the mandibular
ramus (d.) is very slender, not much stouter than that of Tutusia ; the absence of
teeth makes the fore part narrow (Plate 8, fig. 3; and Plate 9, fig. 9). But the coro-
noid, articular, and angular processes are large, and largely cartilaginous ; the first
of these is long and distinct, the next solid and wide, the next a large rounded
lobe.

The annulus tympanicus (a ty.), although narrow and simple, is quite ossified
already ; MecKEL’s cartilage (mk.) is seen in front of it; the head and manubrium of
the malleus (m,ml.), are seen between its obliquely placed crura; and behind the
head of the malleus the cartilaginous junction of the ear-capsule with the epihyal
is seen, behind which the facial nerve (VII.) is emerging. The hyoid arch is short,
and the segmentation below what is normal even for a branchial arch; not only
is the ceratohyal (c.hy.) not re-segmented, but it is continuous with the epihyal.
The hypohyal (A.hy ) is a longish curved tongue-shaped piece, pointed in front, where
it nearly meets its fellow, and articulated loosely with the fore parts of the U-shaped
basal piece (b.h.b7.), for.the thyrohyals (t.hy.) are not segmented off from it. The
only bony deposit is a sheath to the main part of the ceratohyal.

The end view (Plate 9, fig. 4) is roughly oval, the long diameter being across, and
the lower margin least convex and with several sinuosities. The upper view (fig. 2),
which fails to show the full size of the parietals (p.), is corrected by the side and end
views (figs. 3 and 4). Here they are seen with gently sinuous margins, and meeting
at a right angle to overlap the upper margin of the occipital arch and the hind part
of the auditory capsules. Below these, right and left, just the thin slightly inturned
hind edge of the squamosal (sq. )} comes into view, binding over the place where, within,
the ampullee of the anterior and horizontal canals lie. For so early an embryo the
supraoccipital (s.0.) is a very large osseous centre ; it has, recently, become one by the
union in most of its lower half of two centres of bony deposit ; much of the suture is
seen above, and a little of it below. The part next the two parietals is nearly a right-
angled triangle; on each side the lower angles lie on the auditory capsules. Below
them the bone, keeping to its own proper chondrocranial field, has a short concave

H 2

52 MR. W. K. PARKER ON THE STRUCTURE AND

edge, touching the top of the two united canals (tig. 4, p.s.c.). The angle between
this short oblique side and the concave line of the base of the bone dips somewhat into
the oblique deep fossa, which at this part divides each capsule from the proper occipital
cartilage. The projecting points of each bone, on each side of the lower remnant of
the suture, come within a short distance of the neatly circular, large foramen magnum
(f.m.). Between the convex, ear-shaped condyles (oc.c.), below, the basioccipital is seen
(b.0.), and over, and outside the condyles, the squarish exoccipitals (see fig. 1, e.0.) are
seen, creeping upwards towards the supraoccipital and outwards into the quite incon-
spicuous paroccipital region. Outside that tract the epihyals and facial nerves (e.hy.,
VII.) are shown, and above thein the oblique, massive, unossified auditory capsule,
swelling with the large canals (op., p.s.c.). Already, so rapid is the ossification, the
broadest part of the supraoccipital bone (s.0.) is marked by an arched ridge for mus-
cular attachment right and left of the mid-line; these ridges are parallel with the
lower margin of the bone.

A vertically longitudinal section of this most instructive skull (Plate 15, fig. 5) shows
the height of the skull cavity, whilst the embryo is still very immature, and the
continuity of the marginal part of the cartilaginous skull-basin is still complete. As
in the side view, the frontals, parietals, and squamosals (f, p., sq.) are seen, just
meeting in their most projecting parts, but they fail to wall-in the skull. Already, in
front, the frontals are very thick, and the nasals (n.) also; the middle vomer (v.) is
short and stout, and the anterior paired vomers (v’.) are small, thin, curved, clavate
bones.

The septum nasi and perpendicular ethmoid (from a./.n. to p.e.), together, form but
a small, low, triangular wall, whose blunt apex is a little behind the middle, and
scarcely rises into a cartilaginous crista galli. Altogether, this part of the skull
is less developed than in the Armadillos. Between the partition of the snout and
the proper septum nasi, there is a small oval fenestra (nf), with its long axis
lengthwise.

The thick hind margin of the vertical ethmoid (p.e.) is grooved for the olfactory
nerves, but the cribriform plate (cr.p.) is but little seen in this view ; between it and
the orbitosphenoidal band (0.s.) there is a semicircular fenestra. The roof-cartilage is
cut away (a/.n. to al.e.), and also the alinasal (al.n.) itself, but its thickness is
shown ; the base of the whole septum is thickened below by the great intertrabecula,
This is shown as cut away from the presphenoidal region (p.e., to b.s.), for in the hind
half the section is in the middle, but in the fore half the basal part is left complete.

Where thie alinasal region ends, there the cartilage gives off a curious spoon-shaped
retral process, the recurrent cartilage (rc.c.); this is concave outside and convex
towards the septum nasi; it protects JAcoBsoN’s organ, and so, also, does the little
additional vomer (v’.) seen on each side in this region. These parts are better seen
below (Plate 15, fig. 6), which shows the broad, symmetrical floor of the snout and
the lateral nostrils (7.f, e.n.). The floor is elegantly alate behind, and from each

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 3

ala, on its inner edge, arises a recurrent cartilage. Together, in this view, these
look like a lanceolate leaf, with convex halves, like that of Magnolia grandiflora.
The walls are developed into the inferior turbinals (7.tb. ; see also Plate 8, fig. 9, in
Bradypus) ; the inner part of the floor is developed behind them. Between the
halves of the nasal floor the middle vomer (v.) is seen ; it is short, notched behind,
carinate, and has its fore end, which is blunt, hidden by the recurrent cartilages ;
behind the vomer, the widening basis cranii is seen where the vertical ethmoid passes
into the presphenoid (p.c., p.s.), This latter region (fig. 5) is still unossified ; it
passes insensibly into the perpendicular ethmoid in front, and on each side grows into
a large wing, the orbitosphenoid (0.s.), which is perforated at its base by the optic
nerve (II.). In this stage the cartilage ascends and becomes a large plate, continuous
by its fore corner with the margin of the rhinencephalic fossa, floored by the cribriform
plate (cr.p.), Below that junction there is a crescentic fenestra between the two
regions, then the orbitosphenoid rises inside the orbital plate of the frontal (f),
and then dips again heneath the hind lobe of that bony plate, Across its widest part
the orbitosphenoid is nearly equal to the great internasal partition. After a little
irregularity of margin the cartilage runs on, rising upwards again as a narrow band,
and then loses itself in the wide supratemporal lamina, which, in its turn, passes into
the supraoccipital (s.a.¢., s.o.); the upper edge of the supratemporal tract is crenate,
and so is its front margin, where it forms the postero-superior margin of the huge
oval lateral fontanelle. That space is as wide as the auditory capsule, and wider than
the orbitosphenoid ; it is covered in, externally, all but its anterior and upper margin,
by the alisphenoid (a/.s.) below, and the squamosal (sq.), still further outwards, above.

That peculiarly Mammalian character, the out-thrust of the alisphenoid, is well
seen here ; this “ala” is now ossified as a thick bilobate mass, which leans backwards
on to the tilted auditory capsule; it is still separate from the basisphenoid (b.s.) ;
this bony deposit does not reach the low, transverse postclinoid wall, At present, I
see no proper foramina in the alisphenoid (qa/.s.), but the branches of the Sth nerve
(V'., V°.) evidently pass through mere fissures. Over the notched top of the ali-
sphenoid we see part of the squamosal (sq.), and the 3rd branch of the 5th nerve
(V*.) escapes, at present between that bone and the alisphenoid (@/.s.), in the chink
between its lobes, whilst the Ist and 2nd branches (V"*.) emerge through the sphenoidal
fissure ; this bone is very rudimentary at present.

The rest of the endocranium, proper, is well distinguished from the auditory capsule,
which is tilted back at an acute angle to the basis cranii. The whole capsule is one-
third larger in outline than the fenestra in front of it ; the cochlear portion is jammed
in between the basal beam and the infero-lateral walls (see also Plate 8, fig. 1), whilst
the upper and hinder margin is ribbed all round by the thickening outside the anterior
and posterior canals (a.s.c., p.s.c.) ; this thickening is mereased and turned downwards
where the two canals are fused into one “sinus.” Behind the ampullar region of the
anterior canal there is a notable aperture, seemingly for the facial nerve (VIT.), but

o4 MR. W. K. PARKER ON THE STRUCTURE AND

it is in front of the great archway for the branches of the facial and the auditory
nerve (VII., VIII.). There is a lesser aperture under the anterior canal, where the
concavity is shallow, as in the Dasypodide, and not deep, as in the Insectivora and
many other Eutheria; hence the “ flocculus” must be but little developed in these
Edentata. The endocranial “setting” of the capsule is about two-thirds the breadth
of the imbedded sense-organ which bulges, inwardly, and is, although confluent with
the capsule here and there, yet everywhere well marked off from it,

The relation of the three osseous centres—the basi-, ex-, and supraoccipital
(b.0., €.0., 8.0.) 18 well seen; the basal piece is one-third longer than the cartilage in
front of it, twice the length of the basisphenoid (b.s.) in front of that. There are four
holes in the short exoccipital ; the largest of these, behind, is evidently the posterior
condyloid foramen, the rest would appear to let out the hypoglossal (XII.) in three
strands ; externally (Plate 8, fig. 1), it only has one passage for its exit. The deep
oblique passage for the larger post-auditory nerves (IX., X.) is shown in this figure.

The tnner view of the double mandible (Plate 9, fig. 9) shows some extremely
important morphological points. The primary mandible runs from a point near the
fore end of the secondary ramus to a point considerably behind it; it is therefore the
longer of the two; moreover, it is in two parts, a short proximal, and a long distal,
segment. The true swinging point of the primary mandible—the “pedicle” or
“orbital process,” such as we see in the Ovipara—is suppressed in the Mammal ; hence
the ‘ucus (or quadrate) has merely the secondary or hinder point of attachment, above,
the short crus (s.c./.) or ‘ otic process,” The line of segmentation or condyloid face is
sinuous or saddle-shaped, and the specially Mammalian process—the long crus (l.c.7.),
with its inturned neck and flat orbicular head for articulation with the topmost
segment of the hyoid arch—is well developed. The solid condyloid region of the main
or distal segment, the head of the malleus, overlies the scooped tract that gives off the
blunt “ posterior,” (p.ag.), and long foreturned “internal angular process” (manubrium
mallei, mail.) ; this latter part is slender, pinched in the middle and pointed at its end.
The main shaft or Mxcket’s cartilage (mk.) is pinched on its inner face proximally and
then runs its course, gently arching downwards, and thickening in the middle as a
strong terete rod. Where it joins its fellow, there a small basal rod (b,mn.) is given
off which lies in the symphysis of the superficial rami. The outside part (d.) has
already been described as seen from its outer side (Plate 8, fig. 3) ; here, in front of
the dentary canal, a flange of bone is given off from the alveolar wall, which overlies
MeEcKEL’s cartilage ; this tract is the continuous counterpart of the distinct splenial
and coronoid of the Ovipara.

The stapes (Plate 9, fig, 9, st.) or topmost segment of the hyoid arch is shown as
dissected away with the double mandible ; its oval proximal head is seen sideways
as a thick rim to this short flat rod. The length of the rod (not a stapes but a
“columella”) is equal to the breadth of this proximal plate; its hind margin is
concave, and its front convex. here is a short distal neck, with a circular flat head,

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 55

for articulation with the incus, and in the tendon of origin of the stapedius muscle
(st.m.) there is a round ‘ interbyal” (infrastapedial) nucleus of cartilage (c.hy.).
Besides the superficial dentary bone (d.), with its splenial and coronoid tract, there
is only one other osseous centre shown in this figure; that is the first rudiment of
the malleus (ml.)
of the Ovipara,

as a bone “ articulare externum ”

and it is the homologue of the

Skull ofan embryo of Bradypus (Arctopithecus) 2 sp.(5 inches long).—Second Stage.

We must in these comparisons keep in view the fact that we are dealing with
modifications of growth in the individual, and also with specific, and even generic
differences ; these latter are not very great, and can easily be allowed for.

This skull of an embryo, almost twice as advanced as the last, looks more embryonic
than it, for the face is shorter, and the cranium swells up above, giving it an almost
Simian character (Plate 8, figs. 5 and 6).

The lower view (Plate 8, fig. 5) is curiously like, and yet in several things unlike,
that of the earlier embryo of the Unau (Plate 8, fig. 1). The nostrils and alinasal
region (e.7., al.n.) are quite similar in both, but behind them the premaxillaries (p2.)
are smaller, but have longer palatine processes. The anterior palatine foramina,
exposing the openings of Jacopsoy’s organs (j.0.), are better enclosed as two lanceo-
late spaces, for the maxillaries (mz.) have closed in, in front, and bind on both the
palatine processes behind, and the feeble dentary tract of the premaxillaries.

The hard palate is not a squared oblong tract here, but is elegantly wrceolate, for
the fore half forms an outline of more than half a regular ellipse, then it narrows
gently, and then widens again, to grow out into handles or horns, where the palatine
bones (pa.) take their part in its formation.

The whole maxillary region is well flattened out; a pair of middle palatine foramina
end the submedian grooves, which bend outwards near their fore end. One-fourth
further back the palatine plates are cut away, in asemi-oval manner, to make room for
two wedges of bone, the fore part of the palatines. The rounded end of the alveolar
tract of each maxillary rests against the thick outer part of the palatine, and the
sockets, with their teeth, scarcely enlarge from the fifth, forwards, to the third; the
second is the largest tooth, and swells the bone out there to its greatest convexity.
The first tooth is less than a fourth the size of the second, and lies midway between
it and the front convergence of the bone.

Outside the second and third teeth the maxillary enlarges outwards, so as to hide
the infraorbital foramen in this aspect; this squarish outgrowth gives a horned
appearance to this part of the skull, so viewed. The hind part of this tract articu-
lates with the jugal (j.), being rugged where that bone fits in, and then there is a
rounded notch between this short jugal process, and the outer alveolar wall. Each
large jugal (j.) stretches outwards and backwards to its free but notched end; the

a6 MR. W. K. PARKER ON THE STRUCTURE AND

right is larger than the left. Longitudinally, in the hard palate, the palatines (pa.)
are half as long as the maxillaries, but their semicircular hind margin is but a short
distance from the end of the alveolar tract of the maxillary. The thick outer part,
forming a wall to the naso-palatine passage, projects outwards, and is notched behind
for articulation with the pterygoid (pg.). The upper transverse flange of the palatine,
which articulates with the presphenoidal cartilage (p.s.), is followed by a similar plate,
belonging to the pterygoid, which binds upon the bony basisphenoid. The descend-
ing part of the pterygoid is nearly parallel with its fellow ; the two continue the
naso-palatine wall, but are not so solid—cn this species—as the corresponding tract of
the palatines ; the hook or ‘ hamular process” is blunt, free, and capped with hyaline
cartilage.

Through the badly-enclosed orbital space the orbital plate of the frontal can be
seen, but much less than in the Unau embryo (Plate 8, fig. 1). Outside, the large
squamosals (sg.) flank the greater part of the hind skull; they have a considerable
temporal tract binding on the alisphenoids (a/.s.), outside which there is a large
glenoid facet (g/.f:), protected externally by a thickish zygomatic process, which projects
forwards more, and is sharper than that of the other kind (Plate 8, fig. 1). Behind
the glenoid region the squamosal bulges outwards, greatly increasing the strength of
the auditory region; it reaches, behind, to a point over the stylomastoid foramen
(VIL). Abuttin

wardly-turned horns of the large annulus tympanicus (a.ty.), a bone which, even now,
8 ry MOY ,

g against this posterior tract of the squamosal are seen the two back-
is a broadish shell, with a dentated inner margin. Both really and relatively, these
“rings” are much larger than in the other kind; in both they are large, relatively to
the size of the skull; but in this kind they cover the cochlea (ch/.) much better.
Much of the endocranium is visible in this aspect. In the fundus of the orbit the
unossified top of the orbitosphenoid and the optic nerve (o0.s., II.) are shown, then
the sphenoidal fissure (V!*.), followed by the large, thick, ossified alisphenoid, notched,
above, for the third branch of the 5th nerve (V°.). In the middle, the broad basisphe-
noid (b.s.), notched in front and concave behind, lies behind a tract of cartilage, which
narrows forwards ; this is the presphenoid (p.s.).. The synchondrosis is less than half
the extent of the basisphenoid ; then comes the basioccipital (b.0.), one-third larger
than that bone, imperfect im front, and alate and sub-triangular behind. The apex of
the triangle is notched, for there the bone forms a small part of the outline of the
foramen magnum (f:m.). The rest of the occipital arch is but little seen in this
aspect ; but the large condyles (0c.c.), the postauditory and condyloid foramina (IX.,
X., XII.), the interspace of cartilage between the basioccipital and the exoccipitals
(b.0., ¢.0.), as large as these centres, right and left, and the edge of the supraoccipital
cartilage (s.o.), behind the foramen magnum, are clearly shown.

A widish crescentic tract of cartilage, the inner face of the cochlea (chl.), is seen
inside each “annulus ;” and, opposite the fore end of the basioccipital, the Eustachian
opening (ev.), a lipped, crescentie slit in the inner and front face of the tympanic

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. on

cavity, is also shown. Mecket’s cartilage (mk.) is cut off where it is ready to enter
the Glaserian fissure, and obliquely across the membrana tympani the manubrium
mnallei (i.2/.) runs inwards and forwards, stretching the drum parchment.

The side view (Plate 6, fig. 6) shows a skull still more in contrast with that of the
long-faced Edentata than that of the Unau (fig. 3). The stmean shortness of the
face, as compared with the bulk of the swelling skull, is very noteworthy ; for the Ai
has gone off on one way, as far as the Ant-bear on another.*

The small snout, with its rounded lateral external nostril (e.7.), surrounded by a
valvular vrowth, is followed, in this view, by the maxillary below, and the nasal above
(mzx., n.), for the premaxillary is too small to be seen laterally.

The short broad nasals (7.) just overlie the facial plate of the short but broad
maxillary (mzx.) ; at the postero-superior angle, however, the frontal (/) comes in, and
below its angle the lacrymal (/.) lies in a notch on the maxillary ; it is a small seed-
like bone perforated on its most projecting part (/.c.). A little below the lacrymal,
another notch in the hind margin of the maxillary receives the large falcate Jugal, which
forms the lower margin of the orbit. This bone sends downwards a spur behind its
middle, where it broadens considerably ; the free hind part ends opposite the lower
angle of the parietal (p.). The bone on the right side (fig. 7) is larger than that on
the left (fig. 6), and has a deeper and wider descending process ; its postero-superior
part is also notched in a shallow manner. Even on this side the descending process
is not equal to that of the embryo Unau (fig. 3, 7.).

Measured along the lower border, the frontal is found to be one-fourth shorter
than the parietal (f, p.), but the depth of the frontal exceeds that of the parietal on
account of the large size of its concave orbital plate. The upper fontanelle is not
quite covered, the lateral membranous space seen in the embryo Unau (fig. 3) is in this
covered by the meeting together of the frontal, parietal, and squamosal (s7.).
is sinuous,

The large roof-bones are very convex above, their suture—the coronal
the frontal margin being convex above and below and concave in the middle, and the
parietal the coutrary to this. The squamosal, beginning even now to form its large
air-cavity, forms a roughly oval, convex shell of bone. It has a stout zygomatic
process, behind and within which is the glenoid facet (gl.f., see also fig. 5); the
cranial plate runs further forwards than the zygomatic spur, which latter part is
some distance from the end of the jugal.

The upper margin of the syuamosal, in the large open temporal fossa, is convex, the
lower is sinuous, dips downwards, and is somewhat notched, behind, where it overlaps

* If Nature, who “ innovateth gently,” can show us such results as these—can in process of time grow
the Ai and the Ant-bear from one common ‘ root-stock ’’—we need have no misgivings about the diver-
gence of any primary radical type, whatever. As to sudden variations which may develop into important
modifications, divaricating this way or that, I shall be able, when I come to the Insectivora, to show

polymorphic types that suggest possibilities of all sorts.

MDCCCLXXXYV. I

58 MR. W. K. PARKER ON THE STRUCTURE AND

the opisthotie region (op.). An oblique view is had, also, of the annulus tympanicus
(a.ty.) with its related parts.

The mandible (fig. 6) is shorter and stouter than in the embryo Unau (fig. 3),
the coronoid process (c7.p.) is not so sharply divided from the articular or condyloid
process (cd.p.), and the angular (ag.p.) is much deeper, further forwards, and has a
larger crescentic notch between it and the condyloid part; the middle of these pro-
cesses, only, is still capped with cartilage.

Of the parts of the endocranium to be seen in this view, the snout (a/.n.) has already
been described. Inside the orbit, the orbitosphenoid (0.s.) is partly seen, with the
optic nerve (II.) emerging ; the upper border of this plate is indicated by dots along the
orbital plate of the frontal. MxcKket’s cartilage and the manubrium of the malleus
(mk.) are seen, and behind the large investing bones the massive occipital arch.
The large supraoccipital (s.o.) looks like a continuation of the roof plates ; below it, the
tract of cartilage is large, for the exoccipitals (e.0.) are small at present, they are
creeping round the outside of the projecting condyles (o0c.c.). Where the epihyal
passes off from the opisthotic region (op.) there some bony deposit has begun ; then
the bar suddenly lessens and ossifies as the ceratohyal (¢c./y.), which is short, one-
jointed, and is articulated to a shortish, thick, unciform hypohyal (h.hy). That
segment is attached by its narrow distal end to the front of the U-shaped unossified
basal pair; the thyrohyals (t.hy.) are mere spurs, the crura, of the U-shaped piece, as
in the Unau,

The end view of the skull (Plate 13, fig. 10) is much like that of the younger
embryo of the Unau (Plate 8, fig. 4), and as in the latter the ossification is nearly as
far advanced as in this much older embryo, it follows that the ossification is more
rapid and intense in the other kind—the Unau.

Signs of median subdivision are still evident in this large, roughly semicircular
centre (s.0.), which has thoroughly ossified all the upper part of the large occipital plane.
The lower angles are cut away, as it were, the shortened outline then running inwards
and downwards ; thence the lower outline, sharply marked off from the cartilage, has a
small median and two large lateral concavities. Here the foramen magnum (/:m.) is
pyriform, the narrow part being above; the condyles (0e.c.) project well, and are
flanked by the small exoccipitals (e.0.) ;

>

a very smal] tract of the basioccipital (b.0.) is
seen in the fore margin of the great opening. The epihyals (e.y.), as they pass
inwards and forwards, cover part of the shallow and narrow paroccipital region ;
above, and outside them, the opisthotic region (p.s.c., .s.c.) is seen from behind.
Covering the whole top and sides we see the parietals and squamosals (p., sy.).

Part of a vertical section, taken left of the great septum (Plate 8, fig. 8, p.e.),
shows this wall as a short low triangle, shorter than in the Unau, but higher (Plate

15, fig. 5.). A small fenestra (7.n,f)—-very common in low Eutheria—appears near the
end of the snout, dividing the septum nasi, proper, from the septum of the snout, where

the alinasal tract (al.n.) ends below; thence the cartilage grows backwards as the

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 59

spatulate recurrent cartilage (re.c.), right and left ; it is hollow on its outside, convex
within, and hides the fore part of the short median vomer (v.). The whole septum
(p.e.) is moderately thick, and has the roof (al.sp., al.e.) cut away. Behind, the outline
of the septum is arched, but there is no special crista galli. Further back, and
below, the presphenoidal cartilage (p.s.) passes into the basisphenoidal (b.s.), which
is ossified. The naso-palatine canal is rather deep, and is divided along the mid-
line for some extent into two channels by the vomer (v.) About this time the small
hinder lateral vomer appears right and left of the forks cf the vomer: it was not
noticed in this specimen. Part of the frontal, nasal, maxillary, palatine, and pterygoid
are seen in this view. The small front paired vomers (see in the Unau, Plate 15,
fig. 5, v'.) are probably already fused with the palatine processes of the premaxillaries.
A large tract of the other half of this vertical section (Plate 8, fig. 9), with the orbito-
temporal wall-bones —frontal, parietal, and squamosal (f., p., sq.), partly drawn, shows,
also, the inside of the nasal labyrinth, with the lower, nasal, middle, and upper turbinal
folds (7.tb. line wrong, n.tb., m.tb., u.tb.). The orbitosphenoid (0.s.) has lost its front
and hinder fastening bands (see Plate 15, fig. 5), but it is still much larger than the
alisphenoid (above b.s.), its angles, from which the bands have been absorbed, are
rounded, and the upper margin is concave. Less than the antero-inferior fourth of
this tract is ossified, and this centre lies in front of the optic foramen (II.), which is
bounded behind by a very narrow tract of cartilage, soon to be absorbed! The lesser
alisphenoid, and also its base (b.s.), is quite ossified ; it is a roughish, thick bilobate
wing of bone, the hinder narrow lobe being separated from the broad front part by
a deepish notch, under which is a small foramen; the notch is the beginning of the
foramen ovale (V*.), not finished on its outer side (see the Unau, also Plate 15, fig. 5).
The internal carotid artery enters in at the notch between the alisphenoid and its
base, and the 1st and 2nd branches of the 5th nerve (V'*.), pass out of the sphenoidal
fissure between the two “ale ;” afterwards a bar of bone divides the passage for the
second branch of the 5th nerve from the sphenoidal fissure, thus anticipating the
human foramen rotundum,—a very inconstant passage in the Mammalia, generally.
The solidity of the bones at this part 1s shown by a transverse section of the alli-
sphenoid, basisphenoid, and pterygoid (Plate 13, fig. 11, al.s., b.s., p.g.).

An inner view of the double mandible instructively follows that already described
in the Unau (Plate 9, figs. 8 and 9). Here the superficial “ramus” (fig. 8, d.),
shows a great difference between the two types, as already described; but the
endoskeletal or more archaic parts are not so much unlike ; part of the ditterence here,
namely, the lessening of MecKet’s cartilage (mk.), and the ossification of the
“ogsicula,” is due to age. The splenio-coronoid region of the ramus has thrust
Meckev’s cartilage down to the lower edge of the mandible, and bent it into
a curiously sinuous rod. The basal rod (b.mn.) is large and quite perfect yet.
The mallear portion (ml.) has a less lobular head, and a more dilated manubrium
(m.ml.) than in the other kind, for there is well seen, from the inner side, a consider-

r 2

60 MR. W. K. PARKER ON THE STRUCTURE AND

able flange or crest to the thick lower edge of this “internal angular process.” The
incus (z.) and the stapes (sf.) are much alike in both species; the latter is seen
edgewise in this, and flat in the other. There is a definite cartilaginous nucleuas—the
interhyal (7.hy.), in the beginning of the tendon of the stapedius muscle (st.m.).*

Skull of young Unau (Cholopus Hoffmanni), 8 inches long.—Third Stage.

Taking such materials as come to hand, I now get a third stage in a very young
Unau of the species that has only six cervical vertebrae. In interpreting the adult
skull of this type, this stage alone is of great importance, the ankylosis of that massive
skull being so intense.t

A lower view (Plate 9, fig. 1) of this strongly built skull, already very solid,
shows, in front, a very small tract of the snout, with its lateral openings (a/.n., e.n.).
Behind it, the two wings of bone, meeting in front at a very obtuse angle,
are the edentulous dentary regions of the premaxillaries (px.); they are quite
inferior (see fig. 8) in position. They slightly overlap the maxillaries (m.), and close
to the mid-line send backwards a small styloid palatine process; between the two
there is a rounded notch, and this forms the front border of the anterior palatine
foramen, with the aperture of JAcopson’s organ (j.0.) seen in it; each maxillary is
cut away, as it were, obliquely, to form the hind margin of this space ; the two
foramina open into each other, behind.

The whole of the bony palate, solid from side to side in the first three-fifths, and
then strongly enclosed, right and left, but exposing a spatulate tract of the endocranial
base, is a most remarkable architectural growth. The huge first tooth—a doubtful
“canine ”—is fixed in a large swelling socket; thus this part of the face and palate is
greatly widened. There is then a rounded interspace, large enough for another tooth
equal to those that follow ; there are four of these, the second is the largest, and the
Jast the smallest of the series. These curious mammillate teeth, resembling the
degenerate teeth of the Walrus, but devoid of enamel, make their outer alveolar wall
sinuous; it draws in, backwards. The alveolar ‘ flange” in the hard palate is one-
third wider than the submesial part of each bony plate; the ragged groove, right and
left, is nearly straight, and the two are almost parallel.

The zygomatic process of the maxillary, opposite the second tooth, projects further
outwards than the socket of the first, an oblique suture with few “teeth” is seen
running backwards and inwards, between this process and the jugal bone (j.). The
palatines (pa.) scarcely form a tenth part of the hard palate; they run in, behind

* If these two mandibles, belonging to such closely related types, be compared with those of the
Dasypodide, already described, and with that of the lesser Ant-eater (Plate 10), and of its huge relative
the Ant-bear, then the most easy passage is seen from type to type; during growth, the mandibles of
the two sorts of Sloth approximate very considerably (see Plate 9, figs. 5, 8, and 9).

+ I owe this specimen, and many others, to my lamented friend, Mr. W. A. Forbes.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 61

and between the palatine plates of the maxillaries, which together have a convex
margin outside and a concave margin at the middle, answering to the curved line of

the fore edge of the palatines. The notch bounding the naso-palatine canal—as seen in
the skull—is rounded, but each palatine projects a littie where it meets its fellow.
Outside, the palatines do not form a third of the wall, which is finished by the
pterygoids (py.); both of these bones are dilated into a subcranial flange above.
The pterygoids look like short clubs ; they are, in reality, rough shells of bone, and
open in front into the naso-palatine canal. Being so large, they hide much of the
alisphenoids, which are clamped by them up to their antero-inferior margin, and are,
themselves, notched to let the 3rd branch of the 5th nerve (V*.) pass out of the foramen
ovale. Behind that passage they unite by suture with the squainosal, inside and in front
of the glenoid facet (g/.f). Along this line of junction with the squamosals the
pterygoids are grooved; inside that groove they swell into a large bilobate mass, which
reaches further backwards than the fore edge of the basioccipital (b.0.), close in front
of the Eustachian openings (ev.).

Outside the hard palate, in the distance, we see the orbital plates of the frontals
(7), and nearer the eye, the jugals(j.). These latter bones are large shells, convex
infero-externally, and concave above ; the inferior margin is cut away in its hinder
two-fifths, and ends as a free rounded lobe some distance in front of the aborted jugal
process of the squamosal (sqg.) ; the right Jugal reaches much further backwards than
the left. This want of facial symmetry I have already described in the Az, also
(Plate 8, figs. 6, 7,7.). The great extension of the squamosals, fore and aft, is seen in
this figure, as well as in the side view (fig. 3.) ; for these bones bulge forwards, under
the parietals, close to the back of the orbit. Hence a considerable tract of each bone
is seen inside in front of the large uncinate, reniform glenoid facet (g/.f-), with its
protecting stump of a zygomatic process. Binding obliquely against the side of
the hinder half of the skull, each bone forms an eave over the tegmen tympani,
between which and the top of the ear-drum there is a large fissure, the postglenoid
passage into the pneumatic cavity of the bone (see also fig. 3, sg.). The imperfect
annulus (a.ty.) surrounding the exposed drum-membrane is fastened, like a horse-shoe,
under this eave of the temporal bone ; it is less developed than in the A?, but is a strong
bone notwithstanding.* :

Outside the palatine, the exposed part of the orbitosphenoid (0.s.) can be seen with
the optic nerve (II) emerging. Then the alisphenoid, with its special Mammalian
out-thrust is seen behind the orbital wing and the sphenoidal fissure (V'.) ; close to the
edge, the foramen rotundum (V®*.) can be seen. Then this thick outstanding wing

* Many and most instructive parts of the endocranium come into yiew here, and this skull, so lke
that of the extinct Megatheroids (see Reinwarpr, op. cit.), can be seen to have a most remarkable con-
formity with that of the great Ant-eater—the little Cycloturus serving as an interpreter between these
two skulls, whose outward form is so dissimilar. No one, however, who is familiar with the structure of

Birds—especially the Ratitw, and the Carinate Gralle—will be surprised at this.

62 MR. W. K. PARKER ON THE STRUCTURE AND

binds down upon the fore part of the squamosal, and its oval hole (V*.) can be seen,
where the pterygoid also underlies the alisphenoid. Between the palatines and
pterygoids the basal parts of the two sphenoids are shown. At their base the orbito-
sphenoids (0.s.) are fast meeting each other, presenting each to each a convex edge ;
there is no bony presphenoid. The interspace of cartilage here enlarges into a
roundish tract, bounded, behind, by the basisphenoid (b.s.), the descending ribbed
margins of which touch the orbitosphenoidal bones by their fore ends. The suture
between the alisphenoids and their basal piece can be seen outside these crests.

From the presphenoidal cartilage (p.s.) to the foramen magnum (fm.) the basis
cranil is scooped, or concave, and widens, gradually, to the end. The basisphenoid
(b.s.) is one-third longer than wide, and is notched in a rounded manner at both ends.
The cartilage between it and the basioccipital (b.¢.) is a transversely oval tract, and
the two bones nearly touch by their outer margins. The rudimentary crests growing
down from the edges of the basisphenoid are the homologues of the wings, so familiar to
us in the Insectivora, that assist in the formation of the ear-drum. The much larger,
thick, diverging ridges that grow from the edges of the basioccipital, are the exact
counterparts of the ridges to which the elongated pterygoids are attached in the
Ant-eaters (see in Cycloturus, Plate 10). Here the shortness of the palatines, and the
arrest of the dilated pterygoids in front of the basioccipital, makes all the real
difference there is in these parts between this Sloth and an Ant-eater (Myrmecophaga,
Cycloturus). These outgrowths of the basioccipital of the Unau might have served
the same purpose as the tympannic wings of the basioccipital in the Insectivora, or
the alisphenoidal outgrowths in the Marsupial.* Here they serve no auditory purpose,
but are used as strong points of attachment to muscular bands. Narrowing, again,
from the ends of these ribbed edges, the basioccipital runs now nearly to the convex
condyles (oc.c.), and has a deeply emarginate hind margin against the foramen
magnum (fm.). In front of the reniform condyle there is an oval mass of carti-
lage, and beyond it the exoccipital, pierced by the 12th nerve (XII.), and forming a
low paroccipital ridge (p.oc.) against the auditory capsule. As the occipital plane
leans forward, above, the supraoccipital (s.0.) is only seen at its lower edge, bounding
the foramen magnum, behind. Right and left of the basioccipital the auditory capsule
is seen here and there, hidden largely by the drum-ring and membrane. Here the
ossified manubrium (7,7/.) is seen, and opposite it is found the long-lipped Eustachian
opening (euv.). ‘The opisothotic region (op.) is seen outside the paroccipital, and
running from, and through it, the epihyal, and facial nerve (e.hy., VIL).

The upper view (Plate 9, fig. 2) shows a strong, smooth, oval roof, composed mainly
of three pairs of bones that lessen, forwards: these are tie nasals, frontals, and
parietals (n., f, p.). Together, the nasals have somewhat of an hour-glass shape, but
they are pointed in front and spread out behind, at their frontal suture. The

* The root of the “tympanic wing” in the Marsupial is a direct outgrowth of the alisphenoid; the

‘

hinder part is the ‘Sos bull,” anchylosed to that root.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 63

frontals begin wider than the nasals at the suture, and then are cut away gently in
an arcuate manner over the orbits. This crescentic rim is rounded, and beyond it
there is, towards the frontal suture, a gentle crescentic hollowing of the surface. The
postorbital process is rounded and short, and the last third of the bone behind it
widens up to the parietal. Longer than the nasal suture, the frontal and saggital
sutures are nearly equal, and the wide swelling parietals (p.) gently dip towards the
temporal and supraoccipital regions. In the latter place, from above, the endoskeletal
keystone of the back skull (s.0.), is just seen as a transversely spindle-shaped tract.
Laterally, the squamosals (sg.) can just be seen flanking the parietals.

In front the alinasal porches (a/.n.) can be seen, more than from below ; and, in the
distance, the top of the dentary region of the premaxillaries (px.) comes into view.
But behind, and outside these parts, the maxillaries and nasals (ma., 7.) meet with no
premaxillary process intervening ; thus there is a deep triangular notch right and
left. Outside that notch is the swelling first tooth-socket, then a deep rounded
indentation, and then a hinder swelling of the maxillary, where it binds upon the
small burrowed lacrymal (J., U.c.) ; these strong round knuckles of the maxillaries give
the skull a remarkable form, Behind these parts, in the distance, the jugals (j.) show
their scooped upper or suborbital face, with their thickened outer edge.

The side view (Plate 10, fig. 3) shows many parts with their relations not well seen
in the other aspects. The circular narial cartilage and hole (a/.n., e.n.) is seen in front of
the recess caused by the suppression of the facial process of the premaxillary (px.), which
is just seen, below. The nasals are seen, now, to be, not one-fourth shorter than the
frontals (fig. 2, n., f), but only one-seventh ; the outer and hinder lobe of the bone,
also, shows well, wedging in between the frontal and maxillary, over the lacrymal (/.)
of which we have got, here, the best view. It is not so small as the other aspects
suggest, but has a good oblong facial tract, thus forming a thick perforated rim to the
orbit, and it runs inwards as a small antorbital plate. Then, the maxillary (mz.)
below, also, takes a good piece from the fore edge of the scooped orbital plate of the
frontal by running up inside the fore rim, and joining the small antorbital plate of
the lacrymal. This tract appears to me to be a very unusual antorbital growth of
the maxillary, preventing any appearance of the lateral ethmoid as a “ pars plana.”

The outer part of the maxillary is a large high plate, worked well in to the lateral notch
of the nasal, and carrying on its scooped descending hind edge the lacrymal and jugal.
Its last tooth-socket and tooth can be seen, here, inside the notched jugal ; three more
teeth are seen, in their convex sockets, and then a gap before we come to the swelling
socket of the large tusk. About two-thirds of the orbit is rimmed with bone, and
the lower half of the rim is formed by the free-ended notched jugal (j.). Over its
margin is seen the orbital plate of the frontal, under the short thick supraorbital eave ;
it is notched twice, below, and the ophthalmic nerve (V!.) takes its remarkable course
under the front notch, below which some unossified orbitosphenoid (0.s.) is still to
be seen. Under and in the other notch that plate is ossified, and deep in, under the

O4 MR. W. K. PARKER ON THE STRUCTURE AND

Jugal, the optic hole (II.) can be seen, The temporal region of the frontal is gently
marked off from the orbital, and here a large triradiate suture can be seen; it is formed
by the squamosal runuing backwards and forwards from the coronal suture ; both of
these are very long seams.

The coronal suture rans downwards and forwards, and the squamosal backwards
and downwards; these plates of bone, thus stitched together, swell towards the
temporal space aud muscle, and that space is but little enclosed, outwards, by the
stunted zygomatic process of the squamosal. Over those parts the parietal forms
a larger front, and a lesser hind, convexity, and ends against the supraoccipital in
a straightish line—halt the lambdoidal suture (see fig. 4). The squamosal is two-
thirds the size of the parietal ; it is a roughly oval plate, narrowing backwards.

Before and behind its edge is fretted away, or toothed, below ; between its ends
the bone grows outwards, swelling behind into an air-cavity of unusual size, in front
it grows out into the condyle and small zygomatic spur (gl.f.).

Under the notched fore edge we see the alisphenoid standing out from the
orbitosphenoid, and between the two sphenoidal fissure (V!.). Close under and
behind this notch the enclosed foramen rotundum (V*.) is seen, and peeping out
between the lower edge of the squamosal and the upper edge of the pterygoid (pgq.)
the foramen ovale (V*.).

Between the latter rough, hollow bone, and the last tooth-socket (m.), we see the
edge and ascending part of the limited palatine (pa.).

The annulus, manubrium, and membrana tympant (a.ty., m.ml.) come into view
under the postglenoid part of the squamosal, and under its hinder toothed part, the
opisthotie region (op.) with the confluent epihyal (e.Ay.), unossified, and under and
behind the junction, the facial nerve (VII.). Just the edge of the occipital arch with
its condyles (s.0., @.0., oc.c.) are seen in this aspect.

The external view of the mandible (fig. 3, d.) shows what development has taken
place since the first stage (tig. 9, d.). I spoke of the first tooth or tusk as doubtfully
canine ; in the upper jaw, in the first stage (Plate 8, fig. 1), it is the first tooth, but in
the lower jaw there is one in front of the rudimentary lower tusk—five in all ; it is
very small, prematurely developed, and early lost (see Plate 9, figs. 3 and 9). Thus
the tusk, at most, can only represent the first premolar of the normal Mammalian
dentition.

The coronoid process (cr.p.) is now separated by a large semicircular notch from the
condyle (ed.p.), and that by a shallow notch from the angular (ag.p.), which is not
very deep in this genus.

The fore end of the mandibles is narrow (figs. 3 and 5) and the sutural symphysis
of a considerable extent ; seen from below, the mandibles are as curiously swollen to
form the socket of the tusk, as the face is above; the sockets of the hinder teeth are
directed strongly inwards. Here we see how soon the dentition attects the form of the
mandible (figs. 3 and 9), and the loss of teeth is taking place, here, before one’s eyes.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 65

The end view of the skull (Plate 10, fig. 4), shows the strength of the wide and
high occipital arch. The foramen magnum (fm., see also fig. 1) is round above,
notched below or in front, and it widens out over the condyles.

The supraoccipital (s.0.) is roughly semicircular and extends, without an “ inter-
parietal” over it, from the well-arched parietals to the foramen magnum. A. hook-
shaped wedge of cartilage still separates it from the exoccipitals (¢.0.). The muscular
impressions in the main piece are well marked; the outer and lower edge of the bone
is flanked by the squamosals (sq.), and the lowest corner is pierced bya vessel. The ex-
occipitals (e.0.) are roundish, and in this aspect are separated by a considerable band
of cartilage from the opisthotic bone out of which we see the facial nerve (VII.) pro-
ceeding, and to which the epihyal (e.y.) has grown. Below, the annuli (a.ty.) are seen
in the distance. The proper or anterior condyloid foramen (fig. 1, XII.) must be seen
from below ; here, the posterior condyloid foramen ( p.c,f.) is seen outside each condyle.

An inner view of the ossicula audittis, removed, and freed from the remains of
MECKEL’s cartilage (fig. 6), and an outer view (fig. 7) of those parts attached to the
capsule, and with the tympanic remnant of the primary bar, show some very instructive
things.

The main part of MEcKeEr’s cartilage has been used up—partly ossitied and lost in
the ramus, and partly absorbed. The head of the malleus, the osseous matter of
which runs forwards as the styliform “ processus gracilis” (p.gr.), has, in front of it,
yet, a large tract of the primary mandible. — This thick semiosseous hook (ik.) curves
itself, after it becomes detached from the rest of the main bar, round the front of the
tympanic cavity. The distal third is still unossified ; this bony tract is, essentially, a
second “articulare internum,” such as is seen in the Holostean Ganoids, Lepidosteus
and Amia; (see Brrpck “On the Skull of Améa,” Journ. of Anat. and Phys.,
Vol. 11, Plate 23), and the writer’s paper “On the Development of the Skull in
Lepidosteus,”’ Phil. Trans., 1882.

But this tract has a greater interest for the morphologist even than this, for such
a further remnant of the normal mandible is often present in adult Marsupials (see
Doran, ‘ Ossicula Auditts,’ plate 64), and for a time—during the first autumn—the
Mole has a similar malleus, as I shall show in my next Part.

More than that—in a similar malleus of a young Koala (Phascolarctos cinereus) of
the same size, nearly, as this young Unau—lI find two smallish, but well-defined mem-
brane bones in this premalleal tract; these are seen at once to be the same as the
“supra-angulare ” and the “angulare” of the Oviparous types. One such bone is seen
in this case, the angulare (Plate 9, fig. 7, ag.), an oblong splint, pointed at both ends.

When this temporary mass is removed (fig. 6) then the processus gracilis (p.gr.) is
seen to be no larger than the manubrium (7.m/.) and parallel with it, but pointed and
grooved, above, instead of being terete like that process. There is an evident elbow,
or posterior angular process (p.ag.), to this masked and arrested proximal end of the
mandible. The lamina uniting the manubrium to the head of the bone is thin and

MDCCCLXXXYV. K

66 MR. W. K. PARKER ON THE STRUCTURE AND

splintery, and hollow on the inside (fig. 6). Over this plate the head of the malleus
grows like the hood of the Monkshood flower, a remarkable semioval growth of
bone. The sinuous, saddle-shaped condyloid facets of the malleus and incus form, as
the figures show, a very strong joint, and the latter bone is equal in size to the head
of the former.

Both the crura of the incus are short, but well formed, the short crus (s.c.7.) has an
oval facet for articulation with the cupped space in the tegmen tympani, and the
long crus (/.¢.7.) has a nearly circular and flat facet for the head of the stapes (st.).
This latter bone is shown 7n sitw from the outside (fig. 7), and, detached and dislo-
cated, from the inside (fig. 6). The little nucleus of cartilage representing the inter-
hyal (7.hy., see fig. 9) is now a small spur on the neck of the short columella ; now
by absorption of the centre of the flat stem, a veritable stapes. Here again we are on
the Metatherian level; the Marsupials have a “ pharyngohyal” which, in ditferent
types, oscillates between the columella and the stapes (see Doran, ‘ Ossicula Auditits,’
plate 64). The secondary perforation of the “columella,” making it into a sort of
stapes, is seen also in Birds (see Doran, plate 64, figs. 44-46). In this figure
(fig. 7), little except the cochlear part of the auditory capsule is drawn, with the
fenestra ovalis (fs.0.) occupied by the stapes, and the fenestra rotunda (f7.). This well
ossified mass must be considered as a thick section, cut off from the part that contains
the canals, and from the opisthotie angle, behind (figs. 1, 3, 4, op.).

T am satisfied that in the Sloths the periotic bony deposit is generalized, as in
the Armadillos—and in certain anurous Amphibia.

The epihyal (fig. 8, e.hy) is still cartilaginous, and is followed by a single ossified
ceratohyal segment (c.hy.), and then by an unusually long hypohyal (h.hy.), now
largely ossified. The U-shaped basal piece (b.4.br.) is also getting a bony centre in
each thyrohyal horn (t.hy).

Skull of half-grown Common Three-toed Sloth (Bradypus tridactylus, Linn.).—Fourth
Stage.

A dry skull of the half-grown young of this species has served to make many things
plain to me in this type.

The side view, with the olfactory, auditory, and most of the occipital, region
removed (Plate 13, fig. 5), shows the roof bones (x., f, p.), the nasals, frontals, and
parietals, supported behind by the large supraoccipital (s.o.), and below by the
sphenoids (V!. to V°.) and the superficial squamosal (sq.). The nasals (7.) are short,
the frontals (f) have but an indefinite supraorbital rim, and the parietals have a
sinuously swelling general surface. The squamosals (sq.) are less produced forwards
and backwards than in the Unau (Plate 9, fig. 3, sq.), but have a more well-marked
postglenoid process ; the zyomatic process also is longer.

The thick short palatine ( pa.) and the long swollen pterygoid (pg.) are seen in

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 67

situ; over them, the orbitosphenoid and alisphenoid (V'. to V*.) are partly seen.
Many nerve passages are shown in this part, namely, the optic (II.), which opens into
the sphenoidal fissure, through which, besides the orbital nerves, the ophthalmic or
Ist branch of the 5th nerve (V'.) passes. This also enters the skull again by one of
the more marked orbital foramina (V!.), in the anterior angle of the orbital plate of the
frontal (f). Behind the palatine (pa.), the foramen rotundum (V*.) is seen close to
the sphenoidal fissure, and where the alisphenoid, squamosal, and pterygoid meet, the
foramen ovale (V°.) is seen.

This latter is really a foramen; in this disarticulated skull, a thin, narrow, post-
neural lamina of the alisphenoid lies on the top of the hind part of the pterygoid ;
the 2nd branch of the 5th nerve burrows the alisphenoid in front of the foramen
ovale for the 3rd branch, runs over the top of the pterygoidal sinus or “antrum,” and
then escapes through its very forwardly placed foramen rotundum. As far as I
can see, this is the behaviour of the branches of the 5th nerve in this type; but
this is not all. I mentioned that the optic foramen (II.), opened into the sphenoidal
fissure ; this is clearly shown in the hinder end view of this preparation (Plate 13,
fig. 7, 0.s.). In this aspect the orbitosphenoids are seen to be quite ossified, and
nearly confluent ; but the post-neural band of cartilage (Plate 8, fig. 9, 0.s.), still larger
in the much younger embryo of the Unau (Plate 15, fig. 5), has not been ossified, but
has been absorbed.

Here, again, we are on the level, so to speak, of the Marsupials; this is a third
Metatherian character; and it is acquired by osseous degeneration, correlated with
degeneration and loss of the dental series.

The alisphenoids (qa/.s.) are seen in this end view, bulging out beyond the orbital
plates; the end view of the basisphenoid ().s.), shows a middle part, faced with the
cartilage of the spheno-occipital synchondrosis, and, outside this, the rough ends of the
ridged sides of the bone, notched for the internal carotid artery (7.c.) on their outside.

In the distance, below, the two palatines (pa.) are seen to meet at the mid-line ;
and outside these, nearer the eye, the swollen pterygoids (pg.). Outside and above
these the squamosals (sg.) show their large pneumatic opening.

The under view (fig. 6) shows the lower face of the nasals (v.), and the frontals (/)
with their approximating orbital plates resting upon the ascending process of each
palatine (pa., see also fig. 5). A very small tract of the parietals comes into view
here in the postorbital region, but these bones (p.) and their “ lambdoidal” suture
with the huge supraoccipital (s.o.) are seen behind. Externally, the squamosals (sq.),
with their pneumatic foramen, hollow glenoid facet, and short zygomatic process, are
seen. In the middle we have, at a distance from the eye, the fused orbitosphenoids
forming a presphenoidal region (p.s.) by their confluence.

This part is underfloored and flanked by the ascending parts of the palatines (pa.),
in front, and by the like parts of the pterygoids (py.), behind. The proximal region of
each alisphenoid (V!.-V*.), is hidden in this view by the pterygoid, but the base (b.s.)

eal D2
Kes

68 MR. W. K. PARKER ON THE STRUCTURE AND

ean be seen with its thickened sides, growing backwards as rudimentary “ tympanic
wings,” and wedging forwards under the uniting orbitosphenoids. | The distal part
of the alisphenoids comes into view outside the pterygoids, and the foramen ovale,
foramen rotundum, and common passage for the orbital and optic nerves (V*., V*.,
V:., IL) can all be distinguished in this aspect of the skull.

Here the large unique pneumatic pterygoids show their communicating passage
with the great ‘naso-palatine canal, and therefore, also, with the whole system of
air-galleries in the nasal labyrinth.

I have mentioned the parallelism of the Unau and the Mole in the peculiar
temporary pretympanie process of the malleus ; here in the Ai (Plate 13, figs. 8, 9),
the outer and inner aspects of the tympanic annulus are almost precisely like those
of the Hedgehog, and of the young Mole; they have a considerable concavity, a large
amount of ossified floor, and strong, incurved cornua, the front horn being deeply and
obliquely notched for the processus gracilis.

MyYRMECOPHAGID.E.

Young of Cycloturus didactylus; one with head 14 inch long, and another 4} inches
long from snout to root of tail, and head 14 inch long.

I shall treat these as one stage ; they correspond well with the larger specimens of
the Armadillos, and with the third stage of the Sloth. This small arboreal Anteater
comes in well after the Sloths ; the difficulty of comparison of these two Families is
lessened considerably in this case.

Once well understood, the same stage in each type— Sloth and Anteater—can be
put side by side, and then the special adaptive modifications may be accounted for and
the true radical kinship of these two, apparently so diverse, forms, can be demon-
strated. I have found that by putting them alongside of each other, and carefully
removing their special “ marks,” the evidence for a common descent is very great. We
have a similar comparison to make between the toothed and toothless Anteaters of the
Old W orld—Orycteropus and Manis

with its horny “sueccedanea” for teeth, and the absolutely edentulous Hchidna.

and also, indeed, between the Ornithorhynchus

Nowhere can the modifications produced by the gradual abortion, and the complete
suppression, of teeth in the higher Vertebrata be better seen than in the Edentata or
Bruta. In the Chelonia the massive horn-covered jaws are less modified than might
have been expected ; the strong shears that serve as a makeshift for teeth, ask for as
strong a setting as the normal teeth of a Reptile.

So also in Birds, to a greater or less degree, as may be seen by comparing the skulls
of the toothed Birds (so ably described and exquisitely figured by Dr. Mars) with
those of the existing toothless types.

But, in the Mammalia, we are so familiar with the huge dental apparatus seen in
this or that high Eutherian—jaws answering to teeth, and teeth to jaws—that any

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 69

perfectly toothless type of Mammal seems to be a monster; and to be sans teeth is to
be sans everything.

In the Snapping Turtle or the Macaw the massiveness of the face makes no
difference in the morphology of the type ; here also, in this little toothless arboreal
Anteater, the bird-likeness of the face is a very thin mask to its true nature as a low
Eutherian Mammal; the whole result is but a faint and feeble imitation of the face
of the feathered and winged Edentate.

Yet the result of this slow secular “drawing” of the teeth is very curious and
instructive (see Plate 10), and the result in this quasi-senile creature is to form a skull
like a small gourd or a flask. But this lageniform skull is flat on one side, and bent
downwards towards that flattened side. That is the wnder surface (Plate 10, fig. 1) ;
here we see a small, short snout, with lateral nostrils (a@/.n., e.n.), quite like that of
the Sloths, but more slender.

The basal part of the premaxillaries (pz.) is a small subtriangular tract ; the right
and left bones are separated by the width of the base of the nasal septum (fig. 7, s.7.).
Where they diverge, behind, there the maxillaries (ma.) begin to converge ; in the fore
part of their palatine plate there is then left a lozenge-shaped interspace, and here we
see the two front paired vomers, small pyriform ossicles (fig. 10, v’.), lying parallel
with their pointed end forwards. The hard palate is very much sculptured and
perforated, two-thirds of it belongs to the maxillaries, and one-third to the pala-
tines (pa.) This under region widens a little backwards, and narrows again towards
the end of the perfect floor, That perfect part runs to the middle of the skull, the
rest is indeed well marked off and hedged in with solid bone, but the floor is merely a
strong “ aponeurosis,” and not a bony tract right across, as in the large Myrmeco-
phagide; the naso-palatine canal, however, is quite perfect in this little kind, and
opens close under the junction of the head and neck.

The sharp-edged, toothless alveolar region of the maxillary (m.) sends inwards the
usual flange, and this only leaves a small tract for the higher submesial part ; the two
tracts are separated by a deepish groove. About three-fifths of the underview of
the maxillaries is palatine, the rest belongs to the facial walls, which spread out
on each side of the znferior infraorbital foramina (V*.) into an ear-shaped lobe, and
then the bone contracts suddenly, and runs inwards to bind on to the middle of the
side of the rest of the hard palate. This part answers to the socket of the upper
* wisdom tooth ” in man.

Fine threads of bone are seen extending backwards into the jugal region from the
outer lobe of the maxillaries ; these are the starved, abortive jugals (7. ).

The orbits are less enclosed than ever in this type; in this aspect the inturned
orbital plate of the frontals (f.), and the antero-inferior cornu of the parietals (p.) can
be seen, folded over the two pairs of wings of the ‘“sphenoid bone.” The palatine
hinder third of the hard palate is quite like the part in front of it, and at the line of
junction of the two palatines, behind, this floor is emarginate, angularly.

70 MR. W. K. PARKER ON THE STRUCTURE AND

This takes up three-fifths of the large palatines, the remaining part merely helps
to wall in the great naso-palatine canal. Each bone diverges backwards and leaves
an interspace wider than each bar, at the top of which, on the inner side of each, the
palatine bone is seen to clamp the basis cranii by a dilated plate.

Then the pterygoids (pg.) begin ; they run forward, a little, inside the palatines,
and these, in turn, run backwards outside them, fastening together, obliquely.

Each bone has, away from the eye in this view, an upper plate embracing the
skull, a flange, as in the palatines—which runs on to the last fourth of the basi-
occipital (b.0.). Up to the spheno-occipital synchondrosis (b.s., b.0.), the two ptery-
goids form the margin to a lanceolate space, the sides diverging and then converging ;
but in their last third the pterygoids diverge again, and then their upper plate is well
seen. At their middle these bones spread out, sloubling their breadth and becoming
rugged and notched ; they thus form an angle which wedges strongly in between the
innermost part of the squamosal and the foremost part of the annulus tympanicus
(sq., a.ty.). In the angle, here, the foramen ovale (figs. 1 and 9, V*.) is seen. At
their rounded ends, which are cut away somewhat, externally, the pterygoids are
capped with cartilage, as in the embryos of most of the lower Eutheria, which have
this sign or remembrance of the great pterygo-quadrate bar, or endoskeletal upper Jaw
of the Ichthyopsida.

The double sphenoidal region is largely displayed in this view ; outside the
unfloored part of the palatines, the orbitosphenoids and optic nerves (0.s., I.) are
seen, and behind these a large, lozenge-shaped tract of each alisphenoid (al.s.), behind
the sphenoidal fissure, through which both the Ist and 2nd branches of the 5th
nerve (V'*.) pass. Opposite the junction of the pterygoids and palatines there is a
semi-oval tract of cartilage, separating the presphenoidal region from the basi-
sphenoidal bone (p.s., b.s.), for here the orbitosphenoids (0.s.) meet and coalesce, and
the cartilage has, necessarily, a convex form at their junction. In front, where it
runs on over the hard palate, it becomes the unossified perpendicular ethmoid (fig. 7,
p.e.). The large, and unusually long basisphenoid (b.s.) has a small pituitary hole
at its front third, and is longer, contrary to rule, than the basioccipital, that is,
measured along the mid-line.*

This is correlated with the great length of the pterygoid bones (pg.), which are one-
third the length of the bony cranio-facial base, and even in the Unau (Plate 9, fig. 1)
are only one-fourth, with its relatively much shorter skull. The external descending
ridges of the basisphenoid (b.s.), like those in the Unau (Plate 9, fig. 1), are hidden
by the junction with those of the backwardly extended pterygoids. Only the pre-
pituitary part of the basis cranii is convex along the middle, in the notochordal region ;

* In the Unau at the same stage (Plate 9, fig. 1) the basisphenoid is one-third shorter than the
basioccipital ; here the bony basal tracts, measured along the middle in my younger specimen, are as

follows :—presphenoidal region 2 millims.; basisphenoidal 4°5 millims.; basioccipital 4 millims

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 71

behind the middle of the basisphenoid, it is gently concave, as the roof of the hind
part of the very long naso-palatine canal.

The rest of the basal region, formed by the basioccipital (b.0.) is very large, and
between pentagonal and orbicular in shape; and like that of the Unau (Plate 9, fig. 1)
has a very Sauropsidan form and size, but still more so than in the Sloth. As in
that type, the bone has strong “ basipterygoid processes” (figs. 4 and 9, b.pg.), which
functionally correspond to the parts so named in the Sauropsida, but are, here, the
outgrowths of a hinder bone. Here they reach within a short distance of the rim of
the foramen magnum (figs. 1, 4), and are, indeed, as strong and well-developed as any
of their analogues in Reptiles or Birds.*

In the sides of the hind skull, as seen in this under aspect, the parietals (p.) come
into view, outside the squamosals (sqy.), a rare character, and one that can only occur
in such a curious gourd-shaped skull as this, or in the similar skull of the Pangolin—
next to be described. Inside them, the abnormally small squamosals (figs. 1 and 9)
make a better figure in this under face of the skull than they do as seen from the
outside (fig. 3). The zygomatic process is very stunted, and behind it we see the
small pyriform gently concave glenoid facet (g/.f:), with its narrow end forwards and a
little turned outwards.

The postglenoidal part of the bone curls inwards, but is notched in the middle,
iust in front of the tegmen tympani and ossicula audittis, and where the hollow bone
has its pneumatic passage opening into the cavum tympani. A large sinuous under
and inner flange runs from the convex outer part of the squamosal, and strongly
undergirds the alisphenoid; it almost reaches the basicranial plate of the pterygoid
(pg.), and is, in turn, itself undergirt by the fore horn of the large bony annulus
(a.ty.), and also by the large spatulate processus gracilis of the malleus (fig. 9, p.gr.).

A small vascular foramen is seen at the posterior angle of the squamosal (see also
fig. 3, sq.).

The tympanic annuli (a.ty.) are quite comparable to those of the embryo of the Ai
(Plate 8, fig. 5), as to their large, relative, size. The side view (fig. 3) shows them,
but not so well as this; their aperture is wide, and obliquely turned outwards and
forwards, and is occupied by the manubrium and ear-drum skin (m.ml., m.ty.). The
part round the rim of the opening is smooth, convex, and is taking on the well-
marked bulliform character seen in the adult. All round the horns and convexity,
externally, they are notched, or toothed, in a remarkable manner. Behind these
bones, the ossified auditory capsule (op.) comes into view, with the opening for the
9th and 10th nerves (IX., X.). This skull is somewhat more advanced as to its

* The quasi-embryonte arrest of the hinder hard palate in this kind is very instructive ; a little more
energy of growth would have given this dwarfed, arrested, Anteater, with its long pretensile tail for the
service of its timid, arboreal life, a palate equal to that of its larger congeners (compare fig. 1 with
Professor FLower’s figure of the basal view of the skull in the Ant-bear; ‘Osteol. of Mammalia,’ fig. 65,
p. 206).

72 MR. W. K. PARKER ON THE STRUCTURE AND

lower arches than that of the young Unau (Plate 9), for the fixed part of the hyoid
arch (epihyal, ey.) has formed a “ tympanohyal” ossification (fig. 9, between fr.
and IX., X.) in front of the stylomastoid foramen (VIL.), separate from the opisthotic
(op.); the rest of the arch (fig. 6) has become free.

The occipital arch, the base of which has already been described, is here seen, show-
ing a semi-inferior, almost cireular foramen magnum (f.m.), convex sub-reniform con-
dyles (0c.c.), exoccipitals with a low par-occipital ridge, and the lower edge of the
large supraoccipital (s.o.). All the bones, here, are separated by a moderate tract
of cartilage ; in front of that which runs sinuously inwards and forwards, between the
basal and side pieces, we see the hole for the hypoglossal nerve (fig. 9, XII.) lying in a
notch of the exoccipital (e.0.).

The upper view (Plate 10, fig. 2) shows the form of the skull best, in its resemblance
to a small gourd, the nasal labyrinth merely forming the neck to the bulbous cranium,

Here an unossified endoskeletal tract of the snout («/.n.) finishes the upper end,
and an ossified tract, the wide superoccipital (s.0.), finishes the lower ; all the rest, as
seen in this view, is composed of paired investing bones.

The emarginate space in front of the nasals shows a considerable amount of the
double narial tube, ending near the fore end in the lateral nostrils (e.n.).

The nasals (n., line too short), notched in front, widen, wing-like, at their frontal
end, and are somewhat pinched at their sides. Just the top of the feeble facial plate
of the premaxillaries (pw.) can be seen here, followed by the ascending part of the
maxillaries (mx.), into which is set the small perforated lacrymal (/., /.c.), and from
which grow the feeble threads that remain of the jugals (/.).

The frontals (f/) are notched at their fore angle by the lacrymal wedge ; they then
expand a little, and contract again, to finish the “neck” of the “ gourd.”

From this neck, or waist, at the front third of the badly enclosed orbits, the whole
cranium swells into its bulb, with but little injury to its neatly oval form, until we
come to the gentle median projection of the supraoccipital.

There is but little difference in the length of the frontal and sagittal sutures (see
also fig. 3, f, p.); but these bones are not finished where they should pass into each
other ; there the sutural teeth are large enough for a very much larger type, just as
we find in the Caducibranchiate Salamandrians (see. Trans. Linn. Soc., ser. 2, vol. 2,
plate 18, Cynops; plate 21, Spelerpes and Desmognathus). Here, in this dwarfed
arboreal type, the fontanelle (fo.) is bilobate, and fills in slowly, reminding the
observer of the numerous dwarfed arboreal kinds of Anura (Tree-frogs) that abound
in the same primzeval forests, the companions of this very type.

But the side view (fig. 3) shows some of the most remarkable things in this
arrested type of skull; this may be compared with the similar figure given of the
embryo Unau (Plate 8, fig. 3); such a comparison will show a likeness between the
two that is very remarkable.

One thing may be stated here, namely, that the length of the basifacial axis, from

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 73

the front of the presphenoidal region to the end of the snout, and of the basicranial,
from the former point to the foramen magnum, are nearly equal ; so they are in the
embryo, and in the new-born, Unau.

But in the great Ant-bear the front measurement is about three times the length
of the hinder; hence I call this little skull quasi-embryonic—the Myrmecophagine
specialization of the face is arrested, and it is, very probably, the descendant of a
much larger type, with a much longer face.

The fore part of the face is bent downwards in a manner that is abnormal for this
advanced stage, although it would be quite normal for an early embryo. The snout
(al.n.) is compressed and the nostrils (e.n.) lateral; the premaxillaries (pw.) are very
small angulated bones just touching the nasals above, and followed by the maxillaries,
which for them, have a starved appearance ; they are wrinkled, and hollow externally,
without much convexity in the alveolar region. The infraorbital foramen is oval, and
the bone over this passage swells somewhat, but has a notched upper margin where
the lacrymal (/.) rests upon it. The maxillary is notched again, twice, in its sub-
orbital region, and then ends in an ear-shaped jugal process, with fine threads of bone
attached to it.

The lacrymal (/.) is a thin shell of bone, perforated for the duct (/.c.), and hollow

—remnants of the jugal (7.)

towards the eye-ball; it has both a facial and an antorbital region, The frontals
are almost Ophidian; together they nearly form a cincture by the large develop-
ment of their orbital plates, which leave no space for any “pars plana” of the
ethmoid, or allow more than a small patch of the low orbitosphenoids (0.s., see fig. 7)
to be seen in the base of the orbital region.

These orbital plates come down to rest upon the palatines (figs. 1 and 3, pa.), and
form a moderately concave wall to the very indefinite orbit. The supraorbital region
is marked by a convexity having the shape of an hour-glass, the ‘“ waist” of which is
part of the general constriction of the skull round the enclosed ethmoids.

The greatest concavity of the deep orbital plate is just below the second supra-
orbital swelling; it is then a little convex, and then hollows out backwards and
downwards, the hollow ending in the principal orbital foramen, for the ophthalmic
(orbitonasal) nerve (V'.). There the orbitosphenoid (0.s.) is exposed, and in it the
optic passage (II.) is seen.

Behind the sinuous imperfect coronal suture the parietal (p.) stretches backwards
to the occipital arch, and, below, comes down towards the floor of the skull nearly as
well as in the Snake.

Thus the temporal fossa is merely a part of the general face of the skull, infero-
laterally, the parietal being scarcely at all hollowed to form it; here, at the lowest
front angle, the parietal sends forwards a large round lobe that binds down upon
both the wings of the sphenoid just over the sphenoidal fissure (V+ *).

Looking towards the mid-line, below, we see the undergirders of the skull—the
palatines and pterygoids (pa., pg.) ; they show, from this aspect, their ribbed edge, and

MDCCCLXXXV. L

74 MR. W. K. PARKER ON THE STRUCTURE AND

the manner in which the infero-lateral parts of the endocranium are built upon them.
Over their junction, and over the exposed part of the pterygoid, the alisphenoid is
seen, partially, with its foramen ovale (V*.) in its middle, far forwards from the primary
normal place for the escape of the hinder division of the trigeminal nerve.*

The squamosal (fig. 3, sg.) is a very narrow, low-lying scale, a lateral or temporal
scute, differmg but little from that of the Frog, but specialized in another manner.
In that Amphibian the outer or obliquely descending process binds upon a massive
quadrate region, the hind part of the endoskeletal upper jaw. In this case, that of
the Mammal, the outer process binds over the much arrested quadrate (=incus) at its
proximal part, but the free end acquires a cartilaginous facet for articulation with the
detached fore part of a compound mandible. The upper edge of the squamosal is
gently convex, there is a small notch near the end, and the bone then forms a small]
angular process which fits in between the parietal and opisthotic (op.).

Below that junction, in front of its squared end, the bone is perforated for a vessel ;
it is then lobate, then notched over the front crus of the tympanic (a.ty.), and, in front,
on the inside of the short Jugal process and glenoid hollow, it ends as a rounded angle
behind the descending lobe of the parietal (see also figs. 1 and 9). The obliquity of
the annulus (a.ty.) is well seen here, and the large size of the drum-membrane and
the manubrium (m.ty., m.ml.). A convex, roughly pentagonal mastoid region (op.)
is displayed in this side view, and over it the edge of the huge supraoccipital (s.0.),
dovetailed by the lateral occipital (0.), behind which the condyle (o0c.c.) is hardly
visible. The projection of the crown of the occipital arch is well shown in this view ;
the general relation and direction of these parts is very similar to what is seen in the
early embryo of the Unau (Plate 8, fig. 3), whose squamosal (sq.) is probably very
much like that of the little Anteater at the same stage. In the latter the parietal
overgrows the squamosal; in the Unau (Plate 8, fig. 3; Plate 10, fig. 3) it is the
squamosal that becomes so greatly developed, becoming half the size of the parietal,
whereas in this case it is about one-tenth the size.t

In the Unau, whilst the teeth are thin caps of dentine on small rudimentary pulps
(Plate 8, fig. 3), the mandibular ramus is not more unlike that of this edentulous type
(Plate 10, figs. 8, 34) than it is to that which it will become in the ripe embryo
(Plate 9, fig. 3), The edge of the ramus is curiously denticulated where the outer and
inner laminze should form the alveolar walls. This is very similar to what is seen in

* The position of the foramen ovale in the Mammalia is correlated with many remarkable specializa-
tions that are diagnostic of the skull in this class; one of these is the extreme obliquity, or tilting, of
the auditory capsules, and another is the out-thrust of the alisphenoids, themselves, which now in the
Mammal, for the first time, are pushed clean outwards from the general endoskeletal wall.
could be

+ Iam satisfied that if a perfect series of embryonic Unaus and Anteaters—small or large
obtained, we should find that these two extremely specialized forms of low Eutheria would be found to
approximate more and more when thus studied downwards and backwards; thus they would be seen to

repeat, in their prental state, their secular birth and growth.

sein

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 75

other edentulous types, as for instance in a remarkable Neotropical Passerine Bird--
Phytotoma rara (Trans. Zool. Soc., vol. 10, plate 46, figs. 8-10); and in a gigantic
Toad (Bufo agua, Phil. Trans., 1881, Plate 36, fig. 2) from the same region, whose
palatines (normally edentulous in existing Anura) show signs of an old tooth-surface
in the form of sharp osseous denticulations.*

In this slender mandible, decurved like the snout end of the upper jaw, the coronoid
process (cr.p.) is a good wide hook, separated from the round condyloid process (cd.p.),
with its clearly marked neck, by a large semicircular notch; a shallow notch separates the
latter from the less marked angular process (g.p.), which is slightly incurved. The
inner face of the ramus (fig. 834) shows tracts or regions of bone that correspond most
accurately with the coronoid and splenial bones of the Oviparous Vertebrata; the
rapid ossification of the ramus from the main bone, or dentary, does not allow of
distinct centres for these parts ; at least, as far as I have seen, they are only partially
distinct.

The end view of this skull (fig. 4) is as important as the other aspects, which have
to be corrected, visually, by this. The fundus of this flask-shaped skull is subcircular
and gently convex ; the’ perfect semicircle, above, is finished in its outline by the
deep parietals (p.); the rest of the outline is made more irregular than it would be by
the appearance, in the distance, of the hinder swellings of the tympanics (@.ty.). The
supraoccipital (s.0.) is reniform, with a concentric muscular ridge, but the lower edge,
besides its “ hilus” over the large, nearly circular foramen magnum (/m.), is notched,
right and left, by the squared upper end of the exoccipitals (¢.0.) ; the upper and
outer junction of these bones is sinuous, the outer and lower margin fitting against
the opisthotic (op.) is rounded. A notch separates the outer lobe, with its thick par-
occipital edge, from the reniform condyle, and between the right and left condyles
the basioccipital comes into view. Here we see the extraordinary development of the
“ basipterygoids” of the basioccipital (b.py.) like those of the Unau (Plate 9, fig. 1),
but larger, and carrying the ends of each pterygoid bone (pg.). The lower face of each
pterygoid is flat, but oblique, the outside being the deeper part; the interspace
between the two bones is not greater than the width of each; this is floored by a strong
membrane, and thus the circular hind part of the naso-palatine canal (7.p.c.) is

completed, a little in front of the foramen magnum. A membranous interspace is seen

()
oO
between each tympanic and the opisthotic («.ty., [X., X.); outside the broad outer
opisthotic part we see the hind margin of the narrow squamosal (sq.), and over the

tympanic the epihyal (e./y.), and right and left in this region the nerve passages for

the facial, glossopharyngeal, vagus, and hypoglossal (WII., IX., X., XII).
The external views (figs. 1-3) were taken from the smaller dry skull, with the help
of the larger sprrit-specimen ; the sectional views (figs. 7 and 8), the hyoid (fig. 6), and

* The embryology of the Myrmecophagidx and of the Manidee would possibly show us rudimentary
teeth in both families.

L 2

76 MR. W. K. PARKER ON THE STRUCTURE AND

the vomerine bones and cartilages (fig. 10) are from dissections of the latter, more
developed, young; this will account for some differences of form in the parts.

The complete /ongitudinally vertical section, made a little to the left of the
mid-line, shows almost perfect ossification of the endoskeletal part of the skull, proper,
with no appearance of bone in the internasal region. That region is very short in
proportion to the long cranial cavity, which, itself, is remarkable for the large
development of the supraoccipital (s.o.) and for the peculiarly low position of the
whole of the double sphenoid, reminding the observer of the skull of Serpents. The
delicate decurved snout has the familiar fenestra (7.7,f) in the fore part of the septum
nasi (s.7.) between the external nostrils. The JAcopson’s, or recurrent, cartilage
(re.c.)* is cut across on the left, but that of the right side is seen under the septum nasi
(see also fig. 10). The whole septum (p.e., s.v.) is rather high in proportion to its length ;
its thick intertrabecular base has an arched or concave outline, but the top of the crest
or partition is convex for some distance, and then drops rather suddenly towards the
snout. The descending margin of the middle ethmoid (p.e.) is somewhat crested (the
crista galli) and grooved by the olfactory filaments; the cribriform plate (below c7.p.)
cannot be seen in this view; the partition hides it. Here” the presphenoidal bony
tract (p.s.) is now almost complete through the fusion of the orbitosphenoids, which
have long ago lost their large upper cartilaginous tract joining on to the supratemporal
crest, and the supraoceipital.

The upper part of the orbitosphenoid only can be seen, and half the optic foramen
(II.); that wing has its margin first descending and then rising into a short lobe in
front of the sphenoidal fissure (V'*)). The alisphenoidal (a/., vead al.s.) lies still further
out of sight, being thrust outwards as well as downwards (see fig. 1); its upper edge
is notched gently, here, and the foramen ovale (V*.) is below the angular process that
divides the notches (see also fig. 9).

The cartilage between the pre- and basisphenoids (p.s., b.s.) is longer than that
between the basisphenoid and basioccipital (b.0.) ; and the latter tract is high, being
part of the postclinoid wall. This is thick now, being composed of part of two bones
and the intervening cartilage, but in the adult the “sella” becomes more scooped, and
the postelinoid wall is thin and curls forwards. The shorter presphenoidal tract
of bone is twice as thick as the basal pieces behind ; the basisphenoid is the longest
of the three. The internal carotid artery (/.c.) enters the skull nearer to the mid-line
than in Eutheria, generally, but its entrance is normal; its internal continuation,
forwards, is large, and lies in a very definite groove over the junction of the base
and ala.

The exoccipitals (¢.0.) have a considerable parting of cartilage, yet, between them
and the basal plate (b.0.); the latter is notched in a crescentic manner, twice, first for
the cochlea, and then for the exoccipital. A definite tract of cartilage still separates

* The line from 7e.c. is wrongly directed to the premaxillary ; the anterior vomer (see fig. 10, v’.) is

not lettered.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 77

the latter bone from the great keystone piece (s.0.), which is notched in a triangular
manner for the upper angle of the exoccipital.
le of the great supraoccipital is not in

e, rather obtuse ang

The rounded, projectin
the middle, but below it, for the bony section along the top is one-fourth longer than
that which leans over towards the spine, behind. Here, as in the Monotremes, the
hind brain lies in a great hollow recess, formed by the ossified chondrocranium, and
does not simply lean against a moderately concave wall. If the fore angle of the
supraoccipital had been sharply pointed, and the frontals more developed backwards,
we might have had what is seen in the highest physoclystie Teleostei, namely, lateral
parietals, and the supraoccipital meeting the frontals. Here, the cut edge of the
occipital “ tegmen” is longer than the inner edge of the parietal, where it meets its
fellow to form the sagittal suture.

The tilting of the auditory capsules has been so great that their hind border
lies almost flat upon the exoccipitals and basioccipital. The capsule is rather small,
well ossified, and from the smallness of the space, and its immaturity, the form or
the exquisite labyrinth within has been retained in the bony capsule. The anterior
eanal, with its ampulla (a.s.c.), 1s seen arching over a very definite recess for the
flocculus ; and also its junction with the posterior canal (p.s.c.). Over both these
canals the bony capsule becomes angular, to fit into the interspace of the neigh-
bouring bones. Across, below the swelling of the vestibule, where the ampullee open,
the archway of the meatus internus shows the normal passages (VII., VIII.) and,
antero-inferiorly, below these, the coils of the cochlea.

A part of the exposed lower surface (fig. 9, ch.) shows a very tumid proximal coil, with
no definite mark of the further turns of the helix. This figure clearly shows how the
squamosal, where it opens into the air cavity of the drum, helps the ‘“ tegmen,”
forming an eave over it, and that under this eave the top of the Ist and 2nd visceral
arches are sheltered. The secondary fenestra ovalis, and the primary fenestra rotunda
(inside st., and f:r.)* are here shown, the former closed by the proximal part of the
hyoid arch, or stapes (st.). The sub-proximal part of that arch, the epihyal (¢.hy.),
is confluent with the opisthotic region (op.), and has formed the bony “ tympano-
hyal” of FLrower—the proximal endoskeletal part of the so-called ‘ stylohyal.”

The remainder of the hyoid arch is shown separately (fig. 6); the ceratohyal (c./y.),
as in the Sloth, is undivided, and is followed by a longish hypohyal (A.hy.); this
is pointed at its distal end, and joined, lightly, to the basal piece; it is slightly
ossified. The ceratohyal is largely ossified ; flattened above, and united, there, by
fibrous tissue to the epihyal ; below it is thick, and presents a flat face to the flat face
of the hypohyal, where there is a joint cavity.

The basihyobranchial (b.h.b7.) is U-shaped ; the median part is a thick wedge of
cartilage, the diverging horns are solid, round, bony rods, tipped with cartilage—the
thyrohyals (t.hy.).

* According to the excellent researches of Professor ALEXANDER FRASER.

78 MR. W. K. PARKER ON THE STRUCTURE AND

The structures seen under the tegmen (fig. 9) are the incus, malleus, and stapes
(see also fig. 5), where they are shown as detached, and from the outside, the stapes
dislocated from the incus. The malleus has a large manubrium (m.i/.), with a strong
elbow (posterior angular process, p.ag.), turned towards the membrana tympani. The

oht angle ;

ic

whole of the process is set on to the head of the malleus at more than a ri
but, from the round bulbous fore part of the head, the processus gracilis (p.g7.) is con-
tinued straight forwards; that part is a long spatula, dilating forwards as it runs
towards the Glaserian fissure. It has been much larger, | have no doubt (see in the
Unau, Plate 9); afterwards it is absorbed up to its root (see Doran, plate 64, fig. 13).

The mutual sinuosities of the two bones at their junction give the hinge of the
malleus with the incus an angular appearance (fig. 5, 7, ml.) ; a good face of cartilage
remains at this part. The top of the short process and the disk of the long process of
the incus (s.c.7., 1.¢.7.), are still unossified ; the long process is well elbowed before it
turns inwards, near its dilated end; this part is quite normally Mammalian.

But the stapes (sf.) is not normal; the hole is absent ; this element is a short. flat
“columella,” with apex and base still unossified; afterwards (DoRAN, op., cit.) a
feeble vertical fossa forms along the shaft where a groove isshown, Now and then this

‘

bone becomes almost a “stapes.” Here we are on the level, or height, so to speak, of

the Metatheria. There is a small interhyal (7./y.) on the neck of the stapes.

Returning to the large vertical section (fig. 7) and its partial counterpart (fig. 8) we

see that the nasal labyrinth is quite normal and not badly developed; the nasal,
inferior, middle, and upper turbinals (fig. 8, 7.th., 7.tb., m.tb., u.tb.) are all well formed,
although the complication of the last two regions—parts of the true olfactory region
—is not great ; these coils of cartilage are quite unossified, so that my largest specimen
must have been very young.

In the main section (fig. 7) the roof bones (i, f, p.) are shown to be rather solid ;
the nasals overlap the frontals, which cover the olfactory region by their fore part (see
also fig. 2). But the orbital region of the frontal, and the temporal region of the
parietal bones are developed downwards in an almost Ophidian manner, so that a little

further ingrowth of the former would have given us a perfect frontal cincture—a
state of things not absent from some of the high Eutheria. The parietal comes down
and lies on the low alisphenoid (a/.s.) by a broad emarginate process, behind which a
small oval intereranial tract of the squamosal (sg.) is seen; as small as in the average
Bird. The right jointed palatine beam is seen reaching from the back of the snout to

>

the front of the foramen magnum, the series forming this many-pieced “balk” of
bones is as follows: the premaxillary, maxillary, palatine, and pterygoid (pw., mx., pa.,
pa. read py.); these form the floor of a continuous canal, which opens freely into that
of the other side, all along.

There is a small bone, the front paired vomer (figs. 7 and 10, v’.), right and left
over the fore part of the double channel—the naso-palatine canal, and behind it a

erooved bone, the vomer (v.), as long as the palatine plate of the maxillary ; might

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. ie

and left of the hind part of the vomer there is a bony plate; these are hind paired
vomers (fig. 10,v.”) ; they serve to unite the vomer, proper, with the ossifying ethmoidal
masses, afterwards ; the principal or proper vomer is not carinate below either in this
type, in the Armadillo, or in the Sloth (see Plate 2, fig. 1; Plate 3, fig. 9; Plate 5,
fir. 6; Plate 6, fig. 9; Plate 8, fig. 8.).

When it is carinate below, the vomer, resting upon the hard palate, keeps up the
subdivision of the nasal passages, so far back; whereas in these Neotropical
Edentates these passages open into each other close behind the snout. Now this state
of things is not seen in the Palzotropical kinds, as I shall soon show, and as these
latter agree in this respect with the Insectivora, and also, as in one of their Old
World forms, the Aard-Vark, we have the exceptional “ interparietal ”-—so large and
universal in the Insectivora---it seems reasonable to suppose that we have in the Old
and New World Edentata two “ suckers” from some old ‘ root-stock,” that separated
from each other long since, diverging and breaking up, each into its own special sub-
division, of which sub-division we have only two genera, representing two, families in
the Old World, and many genera and several families—especially if we take in the
extinct kinds—in the New World.*

MANID&.

My materials for working out the skull in this family were as follows :—

First Stage. Embryo of Munis,——? sp. ; 2% inches long, snout to root of tail ;
tail itself 3 inch long (Plate 1, figs. 3, 4).+

Second Stage. Embryo of Manis brevicaudata (from Ceylon ; procured for me by
Mr. Warp); 43 inches long, snout to root of tail; head 13 inch long; tail
24 inches (Plate 1, figs. 5, 6).

Third Stage. New-born young of Manis Temminckii; head 2+ inches long.

Fourth Stage. Adult Pangolin’s skull, Manis,——? sp.

First Stage-—Embryo of Manis,—-—? sp. ; 24 inches long (Plate 1, figs. 3, 4).

The skull of this very immature embryo (Plate 11, figs. 1-6) differs very greatly
from anything I have as yet seen in the Mammalia; it has its endocranial parts as
abortive as its ectocranial.

* In the present state of my slow work I scarcely can hint at the relation of these Old and New
World Edentata to the groups below and around them; I feel sure, however, that the Aard-Vark is
the nearest to the Insectivora, of any in the Order; and that the New World kinds, generally, and the
Old World Pangolins, also, are nearer to the Monotremes than to the Marsupials.

t The youngest Tatou (Tatusia hybrida) was only 12 inch long from snout to root of tail (Plate 1],
fies. 7, 8), but its development was twice as much advanced as this; the Pangolins, like the Aard-Vark,
are very large at the time of birth. This embryo of the Pangolin, for which I am indebted to Dr.
Gintuer, is therefore my proper starting-point in tne study of the skull in the Hdentata. In the
Tnsectivora, Marsupialia, &c., I shall describe much earlier stages than this. But if time and materials
serve, I hope, some day, to add an appendix to the present paper, giving earlier stages.

80 MR. W. K. PARKER ON THE STRUCTURE AND

I have been able to compare it with the early skull—twice as advanced, and yet
with a very perfect chondrocranium—in the Armadillo and the Unau, amongst the
Kdentata,

But in types that have yet to be described, especially the Marsupials and
Insectivores, I find early crania differing in various ways, but quite normal, and with
a well-developed chondrocranium.

In the Monotremes I have the most important, because most radical, types for
comparison ; but in both genera

Ornithorhynchus and Eechidna—in young two or
three times as advanced as this embryo, the chondrocranium is most massive and
well developed—almost Dipnoan.

Both in the early skull of the Marsupialia and of the Insectivora I shall be able to
show how gentle the modification is of a Mammalian skull at this stage, from that of
the embryo Crocodile. Even if that good, practically fundamental type of skull of a
well-developed Amuniote (see Trans. Zool. Soe., vol. xi, plate 65), be compared with
those of the Tatou and Unau just described (Plates 2 and 8), it will be evident that we
have in the chrondrocranium of that Reptile everything we want, in a generalized form,
out of which to frame (mentally) the much more specialized skull of a normal Mammal.

But there are other Sauropsida whose skulls have undergone, in various ways, the
uttermost degree of specialization—I refer to the Ophidia and Carinate Birds.

In explaining this early skull of the Pangolin and also its latter stages—even that
of the adult—I shall have to show a parallelism in several things between the skull of
this low Eutherian, and of those two extreme forms of the Oviparous Amniotes—
the Snake and the Flying Bird.

The earliest skull, worked out by me, of the Ostrich (Phil. Trans., 1866, Plate 7),
being at the same stage, is very profitable for comparison ; yet, when all is done, and
the likeness of this skull to any or all of these Sauropsidan types has been shown,
there will still remain all that is strictly and absolutely Mammalian, the result of a
transformation of various parts that suggests a true historic metamorphosis which
once lifted up the Mammal, when just emerging from its low /arval form, far above the
platform of the other Amniota—the Sauropsida,—whether scaly or feathered.

The lower view of the skull (Plate 11, fig. 1) shows that the nostrils (e..) are large,
and obliquely inferior in position ; they are roofed over by dilated alinasals (al.n.),
which have a wide base (7,/:).

All the beginnings of the ectoskeletal tracts are fine bony films, and are very far
from investing the parts they are intended to cover.

The premaxillaries (pwx.) are small, V-shaped bones, with their rounded angle fore-
most ; their proper dentary tract is no larger than their palatine process, which is short
at present ; afterwards (fig. 8) it is long, having received the addition of the small
corresponding anterior paired vomer (fig. 1, v’.).

Each maxillary (m.), as seen from below, is a leafy lanceolate bone, with a
notched hinder end and an inferior ridge. This ridge is the closed alveolar region ; it

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 81

is arched outwards, and runs from end to end of the bone, its hind part being continued
into the inner fork of the bone. From this ridge a scooped plate runs inwards as a
palatine flange to the main bone ; its outline, on the inside, is symmetrical with that of
the alveolar ridge. The right and left lanceolate palatine plates are separated by a
space nearly their own individual width ; the first third of this space is taken up by
the palatine processes of the premaxillaries and the front paired vomers, the hinder
two-thirds is occupied by the vomer, proper (v.), the outer edges of which rest upon the
corresponding palatine plates of the maxillaries. The vomer is split in front, keeled all
along, and somewhat trilobate behind ; it is a stout, shortish bone. The nasal capsules
are seen inside and around these bones—side, septum, and terminal recesses (q/.s.p.,
al.e.); the septum is first seen where it begins to run over the fore part of the vomer,
and the proper olfactory region, after swelling outwards beyond the maxillaries, runs
inwards over the sharp forks of those bones, to end right and left of the presphenoidal
region (p.s.).

As far as the maxillaries are concerned, this skull is now perfectly “schizognathous;”
so it is as regards the palatines (pa.), which are in a very primitive, quasi-reptilian
condition. Each bone is falcate, and arched inwards; it is thicker forwards than
behind, is a sharp wedge in front, binding obliquely on to the inside of the inner
sharp process of the maxillary, whilst, behind, it runs outwards as a fine point of bone,
binding over the pterygoid (pg.). Behind the vomer (v.), the palatines are, at their
nearest, nearly their own width apart, whilst, further back, they expose the whole
width of the basicranial beam.

The palatal series is completed by the pterygoids (pg.) ; these bones are only two-
thirds the length of the palatines, of the same thickness, on the whole, and are wider
apart, for at their middle they elbow out, like two pieces of ‘ knee-timber.” The
fore end of each bone is sharp, and runs obliquely inside the palatine, the hind
converging part is rounded, and is capped by a truly cartilaginous remnant of its
mother-tissue. This cartilaginous hamular process is common in the embryos of low
Eutheria. It isa slight re-appearance of the old “pterygo-quadrate” of the Ichthyopsida.
The rest of the superficial bones seen in this view are the frontals (/.), and the
squamosals (sg.) ; the former are turned in under the suborbital ridge, and over the
orbit, and the latter are applied to the endocranium opposite the pterygoids. The
frontals are very partial, however, in this region, and only partially invest the arrested
orbitosphenoids (0.s.). Behind these endo- and exo-skeletal laminz there is a large
lateral fontanelle, which takes up most of the posterior region of the orbital space
(see also fig. 3). The squamosals are distinguishable from those of a Chick by the
presence of a small, flattish, pyriform tract of cartilage attached to their jugal process ;
in the Chick this process serves for muscular attachment merely ; here, in this low
Mammal, we have the “ glenoid” facet for the special Mammalian mandible, at its
lowest state of development.

The floor and sides of the chondrocranium are largely seen in this view; I have

MDCCCLXXXYV. M

82 MR. W. K. PARKER ON THE STRUCTURE AND

already spoken of its nasal or olfactory territories. The hind part of the perpendicular
ethmoid (p.e.), and all the rest of the basis cranii, is displayed ; but the edges of the
bar, in front, are hidden by the inbent palatines ; just in front of their middle, the
presphenoid (p.s.) begins, and this is halfway, exactly, between the end of the snout
and the front edge of the foramen magnum (fim.). If the postelinoid wall could be
seen, it would be found to be half way from the end of the former to the foramen
magnum ; the open pituitary space ( py.) is a little in front of it.

A little in front of that primary opening, the basicranial beam is composed of three
bars melted into one; the lateral bars are the trabeculee, and they end between the
widest parts of the ethmoidal swellings and the middle of the vomer; thence the
basiseptal mass is formed of the azygous intertrabecula,

The orbitosphenoids are trabecular crests, as the great internasal partition is an
upgrowth of the intertrabecula.

In the Crocodile and Alligator (see Trans. Zool. Soc., vol. 11, plate 64, fig. 2,
tr’., 0.8.) the orbitosphenoids, are seen growing directly upwards and outwards, from the
paired trabecule. After the great intertrabecular crest is well developed, and the
trabeculee become thinned out on its sides, right and left, some transverse sections
show a discontinuity between the orbitosphenoids, perched at the top of the crest,
and the flattened trabeculz from which they sprung (7bid., plate 67, figs. 2, 3).

In Serpents (Phil. Trans., 1878, Plates 28-31) there is no intertrabecula, and
the nasal roofs dip down, and coalesce with the trabeculee, which become fused in the
internasal region. But in the interorbital region the trabeculze persist as free terete
rods of cartilage, and both the orbitosphenoids and alisphenoids arise in the wall of
the membrano-cranium as small, free patches of cartilage. This is a curiously
abortive and arrested condition of these parts.

Here in this little skull, which is abortively developed, both within and without, the
very feeble orbitosphenoids, small and with very imperfect angular extensions,
above (compare figs. 1 and 3 with the skull of the embryo of Tatusia, Plate 2, fig. 1),
are articulated to, or distinct from, the proximal part, ending above it in a bilobate
process. There is, however, evidence here that this is the abortive development of a
type above the Marsupials, for the optic nerve (TI.) passes through a ring of cartilage,
and not through a common optico-sphenoidal fissure, as in them.

The rest of the sphenoid, excluding the abortively developed orbitosphenoids, is a
remarkable structure. The basal beam is very wide, and has, for a Mammal, an
unusually large and almost Sauropsidan pituitary hole; opposite that unfinished
space the base grows out into a pair of thick rounded ears of cartilage, thicker and a
little wider than the lateral processes of the presphenoid, which are perforated for the
optic nerve. A rounded notch is seen both in front of and behind these small auriform
alisphenoids (a/.s.), and these notches are actual foramina, through the membrano-
eranium ; the foremost is the sphenoidal fissure (V*.), and the hinder is the foramen
ovale (V®.), only a foramen as it respects the membrane, not the cartilage. But the

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 83

hinder of these passages is a great distance from the mid-line, and has a considerable
(proximal) part of the alisphenoid between it and the proper basis cranii. The
breadth of the investing mass or parachordal tract behind the pituitary opening is
nearly equal to that of the cochlez (chl.)—those diverticula of the huge auditory
capsules. The notch for the foramen ovale (V*.) is against the inner third of the
cochlea, the squamosal reaches the outer third, and then increases the size of the
tegmen tympani (¢.ty.), the incus is shown in that space overlapped by the squa-
mosal. The bulbous cochlez (ch/.) have the appearance in this view of being only
composed of two coils, for the proximal coil is very large, and the distal is not marked
off from the second. The outline, even in the inner face, is evident, but the cartilage
of the capsule has for some distance coalesced with the basal plate (b.0.), that is, along
its inner edge, from the foramen ovale (V*.) to the opening for the internal carotid
artery, and then again on to the fissure for the 9th and 10th nerves (for X., XL, read
IX., X.). The stapes (see also figs. 3 and 6) has been removed from the fenestra ovalis
and from the incus (7.), and from the latter the primary mandible or malleus (m/ ) has
been removed. Thus in this figure the pier of the primary mandibular arch, the
quadrate —or, speaking specially of it as a Mammalian element, the incus—is seen
inside the posterior radiations of the squama temporis (sq.). Its position here in this
very simple kind of Mammalian skull is well worthy of consideration.

If we take the short crus of the incus as the equivalent of the “ otic process” of the
quadrate, and the long crus as a special Mammalian modification of the incus for
articulation with the head of the stapes (=extra stapedial process of the columella, see
in Chameleon, Trans. Zool. Soc., vol. xi., plate 16), and remember that in the
Mammal the “ orbital process” is suppressed, we shall see clearly what these things
mean. In all essentials, everything is the same, here, as in the Fow! (Phil. Trans.,
1869, Plate 81).

The body of the incus, which articulates with the primary mandible, is opposite the
middle of the cochlea; the long crus runs inwards to join the stapes—or columella in
this case (see fig. 6)—and the short crus or otic process runs backwards over the stapes
and fenestra ovalis, so as to get behind the ampulla of the horizontal canal (see fig. 3,
h.s.c.; and in the Fowl, op. cit., Plate 81, fig. 5, q., h.s.c.). The fenestra rotunda, in this
figure, is hidden from sight by the small rounded epihyal (e./y.) which is already
confluent with the capsule ; behind it the facial nerve (VIL) escapes through the stylo-
mastoid foramen, giving off in its escape the chorda tympani to join the 3rd branch
of the 5th nerve inside the primary mandible. In spite of the intrusion of the auditory
capsules, and their tilted position, the cranial nerves make their escape in a very
orderly manner. Here the facial nerve (VIT.) although thrust far outwards—having to
bore its way through the forepart of the capsule, from the meatus internus, and then
travel backwards, under the tegmen tympani, yet manages to escape into the face
a considerable distance in front of the 9th and 10th nerves ([X., X.).

The opisthotic region (op.) behind and outside the cochlea is very large, and the

M 2

84 MR. W. K. PARKER ON THE STRUCTURE AND

Q

canals (see also figs. 3 and 4), are very conspicuous, shining through the hyaline
cartilage. Outside the innermost lobe of the capsule, the ampulla and ascending part
of the arch of the posterior semicircular canal (p.s.c.) is seen, and in front of it, more
outward, the hind part of the horizontal canal (/.s.c.), which arches over the incus.

At present, the hind skull is a funnel-shaped structure, as though it were a
detached and enlarged part of the spinal column. Along its wide floor, the basi-
occipital region (.0.), the notochord (7c.) still persists, and runs more than half way
to the pituitary hole (py.); it enlarges somewhat whilst in the parachordal channel,
and then ends ina point. Right and left of its hind part, at a moderate distance from
each other, the occipital condyles (0c.c.) are seen to be sub-crescentic thickenings of the
infero-lateral margins of the chondrocranium ; above and behind them, the roof (s.o.),
imperfect behind, is ossified by a median osseous centre.*

The lateral occipital region (e.0.) is but little raised as a paroccipital ridge ; it
is notched for the 9th and 10th nerves (IX., X.)—the foramen being in the inter-
space of the arch and the auditory capsule—and perforated a little further backwards
and inwards for the 12th nerve (XIL.). This would have been a pure chondrocranium
but for the premature, single supraoccipital centre (s.0.).

The upper view (fig. 2) shows the wide alinasal region (a/.n.) followed by the more
contracted double tube of the aliseptal territory (a/.sp.), and this gradually widening
into the aliethmoidal (al.c.), which swells on each side of the face in front of the orbits,
and contains the upper and middle turbinals. The pyriform cranium has the broad, partly
ossified supraoccipital (s.o.) for its base, and shows the deficient chondrification (s.0.n.)
over the foramen magnum (see also fig. 4). The fore margin of this convex wall is sinuous,
concave right and left of the middle, but with a convex margin, there, on each side.
The ethmoidal and supraorbital regions are covered with bony films; and also the right
and left third of the most swollen part in front of the supraoccipital. Three pairs of
these centres are visible from this aspect, the nasals, frontals, and parietals (7, f., p.).

The very small, short, nasals, are both in form, position, and relative size like those of
a Bird, being deeply notched in front. But, in a Bird, these forks embrace the upper
part of the external nostril, and between the nasals the premaxillaries send, each, a
long lathy process—the nasal process (see in the Fowl, Phil. Trans. 1869, Plate 86,
fig. 15). The Mammal has that process arrested, and the premaxillaries run under the
outer edge of the nasals, and only have that extra-nasal process, large in certain types,
e.g., the Hare and Rabbit.

The frontals (fig. 2, £) here lie over the orbital region, looking like the dislocated
valves of a Bivalve ; they do not meet in the middle, above and in front ; beyond their

* A rare character—normal in Reptiles, but as rare in Birds as in Mammals; I have only, as yet,
found it in one genus of Birds, namely, Turdus—the Thrushes (see Monthly Microscopical Journal, 1873,
plate 9, pp. 102-107).

In this figure of the skull of the embryo Pangolin (Plate 11, fig. 1, s.o.) the roof with its bony tract is
figured as it appeared in the flattened preparation; figs. 2-4 correct this.

—,.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 85

middle they diverge rapidly, so do the parietals (p.) behind them, but they are
separated by a much wider space, almost equal to their own width, Hence the
fontanelle ( fo.) is very large, has a narrow median limb in front, and a postorbital, and
a supraoccipital pair of transverse limbs ; above, the median part is, over the vertex,
dilated as a wide lozenge-shaped space.

But these things are seen also in an instructive manner in the side view (fig. 3),
The narrowish snout is but little turned downwards, it very suddenly passes from its
short aliseptal region into the swelling ethmoids (a/.c.). In front (a/.e.) the alinasals
form a crescentic portico over the sub-inferior nostrils (e.7.). Behind these parts—the
snout, proper—the swelling caused by the inferior turbinal at the side, arches upwards
and outwards from the semicylindrical upper tract (a/.sp.), which contains the nasal
turbinal; behind this is the bulbous olfactory region (a/.c.), the narrow end of which
(m.tb.) can be seen in the fore part of the orbit, below. The small forked nasal (7.) is
seen to be a long way behind the external nostril (¢.7.), and a good distance from the
ascending toothed edge of the maxillary “scale” (m.), in front of which is the
narrow, oblique, ascending part of the premaxillary (p..).

The frontal (£) is moulding itself upon the orbital recess, and has a neat, super-
orbital edge ; the bone is pinched in in front of that part. The toothed edges of
these osseous scales—the frontals and parietals—nearly touch in the postorbital
region. Under the inturned part of the frontal, the cartilage (0.s.’) lines the orbit,
and just shows itself beyond, at the edge of the temporal region. Below, in the
postero-inferior recess of the orbit, the optic nerve (II.) can be seen emerging through
its ring of cartilage (0.s.); it rests upon the thickish palatine bone (pa.). A large
lozenge-shaped space is seen between the frontal, parietal, and squamosal (/., p., sq.)
the latter hardly reaches the parietal in the temporal region, and is altogether a very
jagged plate. Its jugal process runs outwards and forwards and shows its small
pyriform glenoid facet (g/.f.) ; its posterior part runs, splintery, over the face of the
auditory capsule, hiding the ampulle of the anterior and horizontal canals (cess,
h.s.c.). But the hinder part of the latter, and the junction of the anterior and
posterior canals (p.s.c.)—the latter displaying its ampulla—all these are clearly seen in
this view, and also that the capsule itself is not much tilted, at present. The cochlea
(chl.), with its coils, and the pterygoid (pg.) with its cartilaginous cap, are seen under
the squamosal. Behind the swelling capsule, the large occipital arch shows au
unusual amount of its surface in this aspect ; it is a short, wide tube.

Above, the bony supraoccipital (s.0.) is partly seen ; laterally, this broad arch shows
its sinuous edge behind the parietal, coming down to unite with the capsule above the
junction of the two upper canals (a.s.c., p.s.c.). The two parts of cartilage are con-
fluent along the hind margin of the capsule, and here the exoccipital region (¢.0.) is
thickened obliquely, upwards and backwards, into a low paroccipital ridge; the
condyle (0e.c.) is here seen in its upper part.

The incus (7.) is seen just peeping from under the postero-inferior corner of the

86 MR. W. K. PARKER ON THE STRUCTURE AND

squamosal ; the malleus (m/.) has been dislocated from it, and also the new ramus
from its zygomatic or glenoid facet (figs. 3 and 6 ; in the former these parts are seen
from the outside, in the latter more magnified figure, from within). The superficial
secondary mandible (d.) is lesser than the deep primary rod (mé.) ; it is applying itself
to the upper and outer face of that rod, and in front is composed of two delicate
tracts of bone, the inner and lower of which (sp., line too short) corresponds to the
separate splenial of the Ovipara. But the main part of the ramus is a thickish
lanceolate tract of hyaline cartilage; an “ inferior labial,” part of which tract has
already become segmented off to form the glenoid facet.

MeckEv’s cartilage (mk.) has united with its fellow in front, and the two have an
azygous rod in front of them, a basimandibular (b.mn.). The whole rod is sinuous,
and thickens gradually backwards ; the last fifth is behind the “ramus,” and is the
part which becomes the malleus (ml.). Then the rod is arched upwards, and thence
swells into a head, or articular portion, with a saddle-shaped condyle ; from the head
there arises a long and a short process—internal and posterior angular processes,
which become the manubrium mallei (m.m/.). The long process forms an acute angle
with the main rod, and ends in a slight dilatation in the middle of the developing
membrana tympani (7.ty.), in the fore margin of which a slight are of bony cells is
seen, the annulus (a.ty.). Under the proximal part of the rod a fine tract of
membrane-bone is seen, the first appearance of bone to form the malleus (= the
ectosteal “articulare” of the Ovipara).

The quadrate or incus (7.) is a quadrilobate segment of cartilage, binding against
the malleus by the two front lobes, articulated to the tegmen tympani by the postero-
superior, and applying its inturned postero-inferior lobe, which has an orbicular facet at
its end, to the head of the stapes. The latter part (s¢.) is oval in its base or proximal
part, and then its short so/id stem dilates in an orbicular manner to articulate with
the incus.

That is the pharyngohyal ; the epihyal is seen from below as a small lobe of car-
tilage, confluent with the ear-capsule, and forming a small bridge for the facial nerve
to pass over (fig. 1, edy., VIL). The next segment is the ceratohyal (fig. 5, e.hy.), it
is fibrous above, and instead of having an extra segment, above, and a hypohyal,
below, as in most Mammals, there is but one piece altogether. The basal piece
(b.h.br.) is also very rudimentary, being a bent U-shaped rod, with very short
continuous crura (t./7.).

Now in such an aberrant and feebly developed face as this, we can the better com-
pare the Mammal with the Bird. In the latter the epihyal (=stylohyal) cartilage is
also short ; it does not, however, form an adhesion with the auditory capsule, but
with a slender outgrowth from the neck of the columella (=stapes) (see “ Bird’s
Skull,” Part IL, Trans. Linn. Soc., ser. 2: Zool. vol. i., Plate 20, figs. 7, and 8-11).
That outgrowth—the infrastapedial band—is represented in Fishes by the interhyal,
a segment which re-appears in the Mammal, and becomes wrapped up amongst the

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 87

fibres of the tendon of the stapedius muscle. In the Bird the stapes, or columella,
has not a flat head, but a tongue-like process (extrastapedial), which sends upwards
ati its base a forked spike (suprastapedial).

The ceratohyal is not distinct, in the Bird (as in Manis), from the hypohyal, but this
feeble distal rod does not end abruptly and articulate with a transverse basal piece ; it
runs forwards into the substance of the tongue, meeting its fellow, there, at an acute
angle; whilst the basal piece is longitudinal, and fits into the sharp re-entering angle
formed by the two ceratohyals. The long basal piece is divided into what represents
two basibranchials ; and where the two segments meet, there is given off a large,
segmented, gill-less Ist branchial arch.

In the Bird the distal basibranchial forms the support for the thyroid cartilage ; in
the Mammal it is supported by, and articulated to, the paired hypobranchials of the
aborted 3rd arch (=1st branchial).

The end view of this skull (Plate 11, fig. 4) is suborbicular—sinuous below—
gently convex, and Jeans forwards above where the supraoccipital joins the parietals
(s.0., p.). These latter are just seen, above, and so also are the squamosals (sq.) at
_the sides. The foramen magnum ( fm.) is large and oval, with the long diameter
vertical; it has a small deficiency in its upper outline, which leads to a circular
membranous space—“ the median occipital fontanelle” so familiar in certain Birds,
e.g., Pigeon, Owl, &c. (see Trans. Zool. Soc., vol. v., plate 34, fig. 2; plate 35, fig. 1; and
plate 37, fig. 6, m.of{). Over this, from edge to edge, the cartilage has become
ossified, by the azygous supraocctpital (s.0.), which is two-winged above, and forked
below, the forks holding the fontanelle, like pincers. The rest of the occipital cartilage
(e.0., b.o.) is free from bony deposit; in the middle of the basal plate, under the
foramen magnum (fm.), the notochord (ne.) can be seen lying on the upper part of the
thickness of the floor. The exoccipital region is very slightly raised into a par-
occipital ridge, right and left, and is well marked off from the auditory capsules, in
which are seen the posterior and horizontal canals (p.s.c., h.s.c.). Underneath, in the
distance, the cochleze (ch/.) swell the bottom of the skull, right and left.

Second Stage.—Embryo of Manis brevicaudata; 42 inches long, from snout to root
of tail (see Plate 1, figs. 5, 6).

The under view of the skull at this stage (Plate 11, fig. 8), which is twice as
advanced as the last, shows a great approach to the permanent condition.

The inferior nostrils (e.n.) are protected by a rounded but quite simple alinasal
fold, and they approach each other more closely now, right and left of the alate
floor. Part of the aliseptal region can be seen right and left of the front bones
of the face—the premaxillaries (pw.). These bones (px.) are very feeble, and are
composed of an outer and an inner stalk; in the rounded re-entering angle, formed by
the two stalks, the opening of “ JAcopson’s organs” (j.0.) can be seen. The narrow

88 MR. W. K. PARKER ON THE STRUCTURE AND

fore part of the bone in its toothless alveolar region runs with its fellow close up to
the alate alisnasal floor; it broadens to send upwards and backwards (see also
fig. 7, px.) its faleate facial plate. The palatine processes, once very short (fig. 1),
are now extremely long, they have evidently made their hind part from the paired
front vomers (fig. 1, v.). Two-fifths of the palatine plate of each maxillary (mz.)
comes short of the mid-line, and exposes the long styles running backwards from the
premaxillaries. The rest of these plates is complete, the termination of them
behind is in sharp wedges that run between the palatines (pc.). The region between
the thick edentate margins of the palate is elegantly lanceolate, and is more than a
third of the general width of the face as seen from below ; it is also high or arched,
for the fore palate im this type is very hollow. The arched alveolar ridges turn
inwards to clamp the fore part of the palatines ( pa.), and outside the ridges the bone is
seen, right and left, expanding in a roughly convex manner to form the large facial
plate (see also fig. 7, mx.). That plate swells suddenly over the lateral ethmoidal
masses, and in the widest part is burrowed below for the 2nd branch of the 5th
nerve (V*.). The ridge from the infraorbital opening of that burrow runs backwards
and outwards, and ends in a short, free, blunt zygomatie process, on which, in this
stage, I find no trace of a jugal bone. The palatines (pa.), as seen from this aspect,
are as long as the palatine region of the maxillaries. A considerable right-angled
space divides the two bones behind, and a more acute-angled gap receives the
maxillaries in front.

They are somewhat pinched in, laterally, are slightly bevelled, externally, in front,
and form a low ridge outside; each bone is gently hollowed towards its fellow ; the
two unite and carry on the median suture of the hard palate, which is half the
length of the basis cranii, including the snout. This view only gives half the
extent of the palatine bones (see fig. 7, pa.) which have a large orbital develop-
ment. The pterygoids (pg.) have only the average development, their external
outline is concave as in the case of the palatines; their lower edge is thick, and they
have a free hamular process, capped, still, with cartilage; they are two-thirds the
length of the palatines ; they still overlap the cochlez (ch/.). Two large bony tracts
can be seen on each side, the orbital plates of the frontals (f-), and the zygomatic
and postglenoid regions of the squamosals (sqg.). The hind part of the nasal capsules
(m.tb.) are still uncovered in the inner part of the orbital floor, the infraorbital
nerve (V*.) is seen running under this tract right and left. The pyriform glenoid
facet (g/.f-) in the back of the zygomatic stump of the squamosal (sq.) is now large,
and the bone, after swelling to enclose the facet, contracts into a neck, and then,
hollow within, overarches the auditory capsule ; the bony eave reaches back beyond
the stylomastoid foramen (VII.) Inside the orbital plate of the frontal a large
exposed part of the osseous orbitosphenoid (0.s.) is shown as a rounded wing right
and left. The optic nerve (II.) is escaping from its inner part, and its edge in
front is notched for the re-entering orbitonasal nerve, which emerges from the

tel

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 89

skull at the sphenoidal fissure with the 2nd branch of the 5th (V',*.). The pre-
sphenoidal region (p.s.) is still unossified; it can be seen between the diverging
palatines. The posterior sphenoid stretches across the whole inter-glenoidal region,
outside and inside the pterygoids. The basisphenoid (0.s.) has ossified three-fourths
of its proper territory; it is emarginate both before and behind. Nearer the eye
than the orbital wing (0.s.), each alisphenoid (V1, *. to V*.) reaches the squamosal in
front, and is then deeply notched for the 3rd branch of the 5th nerve (V*.). This
notch is protected by bone behind, which runs between the nerve and the auditory
capsule (ch/.) ; on the outside the foramen ovale is finished by other parts, it merely
notches the outer edge of the alisphenoid bone. In this figure the left annulus and its
related parts are shown; whilst on the right side of the head—left of the figure—
the lower face of the capsule is exposed.

The annulus (a.ty.) is a wide U-shaped tract, thickened at the end of its inturned
cornua; the foremost of these is notched to let Mercker’s cartilage (mk.) pass.
This is drawn as cut across. The narrow annulus leaves a wide and exposed drum
membrane (m.ty.), in which we see a long manubrium mallei proceeding from
the head of the malleus (m/.), which articulates with the incus (7.) under the double
teomen formed by the squamosal (sq.) outside and the capsule within. The cochlea
is exposed on the inner side of the annulus, and where the pterygoid (pg.) overlaps
these parts, there the Eustachian aperture opens into the throat. The cochlea and
vestibule (ch/., op.) are large and normal; they are quite unossified ; the fenestra
ovalis (f%.0.) is large; outside it is the passage for the 7th nerve (VII.), which escapes
through the stylomastoid foramen behind the small epihyal (e.y.); the rounded
part behind that opening (op.) contains the ampulla of the posterior canal. A band
of cartilage separates the fenestra ovalis (fs.0.) from the fenestra rotunda (/7.), which
is seen behind the first or proximal coil of the cochlea (ch/.). A deep groove runs
between the occipital arch and the capsule, and on the inner side of the vestibule
both parts are notched to make a common passage for the 9th and 10th nerves (IX,
X.). Behind and within this is another passage or hole in the occipital arch within
the exoccipital bone (e.0.), which is creeping forwards ; this is for the large hypoglossal
nerve (XII.). Thence to the edge this part is ossified; and the bony matter runs
right and left, up to and over the convex arcuate condyles (¢c.oc). But a very wide
band of cartilage is seen continuous with, and in front of the condyles, margining the
foramen magnum (f.m.), and ending in a concave margin, where the basioccipital
bone (b.0.) has broadened out to twice its interauditory region. That bone is rather
pinched in towards its fore end, where it is notched, and has a fine tubular process
in the notch which runs much of the distance between this bone and the basi-
sphenoid (b.s.); that process is the ossified sheath of the fore part of the cramial
notochord (nc.)

The upper view (Plate 12, fig. 1) shows how greatly the investing bones have
developed since the early stage (Plate 11, fig. 2). The facial region is very small

MDCCCLXXXYV. N

90 MR. W. K. PARKER ON THE STRUCTURE AND

compared with the cranial; the whole outline is pyriform. The nasal capsule is still
considerably exposed, the whole alinasal, half the aliseptal, and part of the alieth-
moidal parts (al.n., al.s.p., ale.) still being visible. But the forked, ornithoid nasals
(n.) have more than doubled their size, and outside them the premaxillaries and
maxillaries (px., mx.) just show their upper edge.

The nasals and frontals (v., f°) now fairly meet in the middle, and the frontal suture is
now of considerable extent; behind it the lessening fontanelle (fo.) is a four-rayed lozenge
of membrane. The postorbital part of the frontal and the contiguous part of the
parietal (p.) are too convex to allow the squamosal to be seen in this view, yet it is
a large bone (see Plate 11, fig. 7, sq). There is a fontanelle in the lambdoidal region,
three-rayed, and half the size of the other ; the parietals then meet for about half their
inner margin to make the sagittal suture. The hind skull lessens one-third to form
the occipital cincture (s.0.) which is largely ossified in its upper part—more than half of
the part exposed in this aspect ; about a third in reality (Plate 12, fig. 2, s.0.).

The side view (Plate 11, fig. 7) has gained a more normal form than that of the
early stage (fig. 3), the greater development both of the deep and of the superficial
parts has brought this about.

The large, nearly inferior, circular nostril (e.7.) is seen covered by a crescentic roof
(al.n.) and the beginning of the roof and side of the great nasal tube (a/.sp.) is seen in
front of the oblique falcate facial plate of the premaxillary (px.) which is pedate in front,
where it forms the aborted alveolar region. The nasal is seen over the olfactory capsule
just reaching the frontal (#1) and the arched top of the facial plate of the maxillary
(mx.), which thickens below to form the edge of the jaw, and sends backwards a free
zygomatic process, the root of which is perforated by the 2nd branch of the 5th nerve
(V*.). The top of the maxillary does not reach the frontal, but the nasal wall (q/.e.)
outside the upper turbinal (w.tb.) is exposed for some extent there, and in the antorbital
region, showing there an unossified “ pars plana” (m.tb.). There is no lacrymal bone, a
rare character ina Mammal, as far as my experience goes. The well formed upper and
orbital plates of the frontal (f) give form to the upper half of the orbit, in which this
bone forms roof and wall, the latter is a large rounded tract. The upper region of the
frontal has a very large postorbital extension, and the large membranous tract seen
there in the immature embryo (fig. 3), is here covered by the frontal and squamosal,
the parietal in this type being kept well out of the temporal fossa. Thus in this side
view the parietal (p.) looks scarcely larger than the squamosal (sg.) which reaches
nearly as far backwards, and much further forwards, than the great upper plate.*

The squamosal is notched behind the orbit to give form to that space, and is
scooped over the hinge for the mandible; the rest of the bone is evenly convex ; it
ends behind, like the parietal, in a rounded outline. Under the orbit the large

* J fail to understand this modification, the opposite of what is seen in the Little Anteater (Plate
10), which has a far more perfect lower jaw than the Pangolin.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 91

ascending plate of the palatine (pu.) is seen; it helps the maxillary to form the ant-
orbital bony wall.

The hind skull now leans backwards, above ; it is very convex, and has its upper
and middle part ossified (s.0., e.0.); the exoccipital, a broad band, runs across and then
downwards behind the crescentic convexity of the opisthotic—which encloses the pos-
terior canal (p.s.c.)—and the reniform occipital condyle (oc.c.). The articulated
mandible and the ear-drum hide parts seen in the other side view (fig. 3); the
annulus (a.ty.) runs inwards and downwards.

The outer and inner mandibles (here seen from the outside, but shown in their inner
aspect and more enlarged in Plate 12, fig. 4) are very instructive in this type, at this
stage.

Even now the superficial ramus is a very small sinuous bar, with a considerable
amount of cartilage in its hinder fourth, into which the dentary (d.) runs, ending in
a point. The condyle (cd.p.) is a convex pyriform tract, lying lengthwise, and with
the narrow end forwards, it is quite similar to that of the Echidna, but the ramus
itself (= dentary) is less developed than in that type, although stouter; it has now
no rudiments, even, of the coronoid and angular processes.

In this figure (Plate 11, fig. 7) the parts are shown in situ that correspond with
what we see in the embryo Sauropsidan, the incus or small quadrate (7.) is just seen
in front of the epihyal (best seen in fig. 8, e.hy.), ander the tegmen tympani; also
the long internal angular process (m.ml.), with a rudiment of the posterior spur,
running along the membrana tympani, and Mercket’s cartilage running under and
within the dentary, which, however, has been made largely out of cartilage.*

MEcKEL’s cartilage (Plate 12, fig. 4, mk.) is slenderer, relatively, its thickest part,
now, being near the symphysis; there, meeting with its fellow, it forms a considerable
basimandibular (figs. 4 and 5, b.mn.).

As in the Green Turtle (Chelone viridis) the ectosteal articulare (=superficial bony
centre of malleus), appears first, and the endosteal centre afterwards—in that Reptile
several years afterwards. The head of the malleal end of the Meckelian rod is solid
and convex ; the manubrium (m.m/.) is slender and more arcuate than in the early
embryo (Plate 11, fig. 6), and the lesser posterior process is more indistinct. The
large incus (7.) and the short, columelliform stapes (s¢.) are unossified, as yet ; the

* T have never found an “inferior labial’’ cartilage in a Reptile; in Birds, however, it has turned up ;
in 1843 I found and figured a tract of this kind, of an oblong shape, over the middle of the mandible in
the Coot (Fulica atra), and twenty years afterwards I dissected out the same thing in another of the
Rallide, namely, Gallinula chloropus. Now one thing is noticeable in this comparison, and that is that in
the Sauropsida, as far as I have seen, Mrecket’s cartilage simply shrinks and dies out in the main part
of the mandible in front of the “articulare,’”’ and does not ossify and become a direct addition to the
jaw. Nor can I find any actual endosteal ossification of Mucxet’s cartilage in the distal part in the
Edentates, although the part that is ultimately absorbed directly in front of the malleus (= articulare)
is separately ossified in the Unau (Plate 9, fig. 7); but in the Insectivora, and even in Man, a large tract
of Mecket’s cartilage ossifies, and then unites with the ramus.

N 2

92 MR. W. K. PARKER ON THE STRUCTURE AND

interhyal has not appeared, up to this time; but abortively developed parts are often
late. The inturned neck of the incus is curiously alate. The base of the stapes is
very thick.

The distal parts of the hyoid arch (Plate 12, fig. 3) have undergone little change
except as to size and solidity (see Plate 11, fig. 5); but the thyrohyals (t.hy.) are
more incurved, for clasping the larynx.

The end view (Plate 12, fig. 2), as compared with the same aspect of the skull in
the early stage (Plate 11, fig. 4), shows considerable progress in development.

The thick parietals (p.) almost meet to finish, with the supraoccipital, the
lambdoidal suture. The squamosals (sqg.) now show considerably from the end; they
have gained much substance, and are large convex plates.

The upper half of the face of the great occipital arch has its middle third occupied
by a supraoccipital bone (s.0.), shaped roughly like an hour-glass; it does not yet
reach the foramen magnum (f-m.), but the fenestra (or fontanelle) over that doorway
is now a mere notch in the lower edge of the cartilage.

Nearly half the space from the lower edge of the bony supraoccipital to the
occipital condyles (0¢.c.) is occupied, below, by the large spreading exoccipitals (e.0.).
Their upper margin is sinuous, their outer rounded, and the large outer margin runs
over the opisthotie convexity. Below, each bone runs in as an uncinate tract,
between the opisthotic and the condyle; the thickish, convex, outer edge of the tract
is the low, indistinct paroccipital process. The opisthotic tract, which has taken the
form of the enclosed posterior canal, must be conceived of as lying some distance from
the eye (see also Plate 11, fig. 8), and the bulbous cochleze (ch/.) as still further off.

This stage is further illustrated by a vertically longitudinal section, made a little to
the left of the mid-line in the fore half (Plate 13, fig. 12).

We see at once in this figure what is also seen in the side view (Plate 11,
fig. 7), namely, that the snout and fore part of the nasal capsule is considerably
curved downwards. I only see that in this stage and in this species, and am not sure
whether there is some specific modification in this case; at any rate, this skull thus
repeats a character seen well in Cycloturus (Plate 10, fig. 7).*

The ethmoseptal or front half of this skull is one-fourth longer than the proper
basiscrann or spheno-occipital region. In the early stages they were equal.

Nowhere is the intertrabecula, or thick base of the great partition (p.e., s.v.), more
distinct and massive than in this; but for its crest, it would be almost Cetacean.t

* These lesser modifications, both as seen in species and in stages, are almost endless, and yet none of
them is without signification. The two nine-banded Armadillos differ in this respect, for Tatusia peba
(Plate 5, fig. 6) has a very straight snout, whilst the closely related Tatusia hybridw has it considerably
decurved (Plate 2, figs. 1 and 8, and Plate 6, fig. 3).

} See Hscnricut’s figure of the skull of an embryo of Balena japonica in a posthumus paper published
by the late Professor Brinnarpr: “Ni Tavler til Oplysning af Hvaldyrenes Bygning,” tab. ii., Copen-

hagen, L860.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 93

The alinasal fold (ad.n.) rans well round the end of the septum (s.7.), which
shows the usual fenestra at this part (7.n,f); behind the snout the ale nasi give off
from their base the usual spoon-like recurrent cartilage (rc.c.) for the protection of
“¢ JACOBSON’S organ.”

Two bones protect most of the top, but, below, the middle part, only, is supported by
bone. The upper are the nasals (n.), and frontals (f-), the lower the vomer (v.) ; I did
not find the “ postero-lateral vomers” developed in this stage; when they do appear
they do not remain distinct, for long : the antero-lateral vomers had evidently already
coalesced with the premaxillaries (Plate 11, fig. 8). The floor of the deep olfactory
recess, or cribriform plate (cr.p.) has been cut across; but it will be seen that this
section leaves a large triangle of cartilage above and behind, making the recesses
appear much deeper than they otherwise would do; this forms a large cartilaginous
“cristi galli” or proximal solid part of the falx cerebri (see also in Tatusia hybrida,
Plate 2, fig. 1, er.g., where, however, it is not so large as in this type.)*

The hemispheres are lodged in a strong box, already ; the fontanelle (fo.), and the
triradiate suture between the frontal, parietal, and squamosal (/, p., sq.) are clearly
seen, and the growing thickness of the bones, especially of the parietal, where it forms
an attachment for the “tentorium cerebelli” in front of the anterior semicircular
canal (a.s.c.). The faleate cartilage over the low bony orbito-sphenoid (0.s.’, 0.s.) still
shows its distinctness and is still a considerable distance behind the cribriform plate,
below. The bony orbitosphenoids (0.s.) are obliquely oblong and are turned forwards
and outwards ; the large optic foramen (II.), well surrounded by bone, lies low down ;
the basal bar (p.s.) is not ossified. A considerable fenestra (or fontanelle) still exists
over the sphenoidal fissure (V" *.), not yet covered over by the frontal and squamosal.
Under the latter the alisphenoid (a/.s.) lies outwards, and leans forwards, letting the
nerve of the lower jaw (V*.) pass over its edge at the hinder fourth ; a snag of bone
protects the nerve behind, but above, it escapes through a notch. The basisphenoid
(b.s.) is separately ossified, and has taken up much of the cartilage of its own
territory ; then comes a tract of cartilage three-fourths as long, and then a tract of
bone, the basioccipital (b-0.).

The latter bone comes far short of the foramen magnum (see Plate 11, fig. 8). The

fore part of the spheno-occipital synchondrosis is thick, forming the low postclinoid

>

wall. In the large “foramen lacerum” between it, the alisphenoid, the squamosal,
and the round end of the large cochlea, the internal carotid artery enters. The large
auditory capsule is separated, above, from the supraoccipital (s.o.) by a deep groove
that contains the “ lateral sinus,” and is partly overlapped by the posterior (tentorial)
edge of the parietal, and lower down by the posterior edge of the squamosal.

* Tf the presphenoid (p.s.) were crested, like this part, in front, then we should have a cartilaginous
septum to the orbits, as in the Bird (see Phil. Trans., 1869, Plate 81, figs. 3, 4, 5); in that case the
cartilaginous crista galli would be an additional crest on the antero-saperior edge of this vertical orbital

septum.

94 MR. W. K. PARKER ON THE STRUCTURE AND

Thus the swelling cochlea (ch/.) has made itself a very accurate “nest” in the
inferolateral region of the skull, and the posterior canal (p.s.c.) rising up from its
junction with the anterior (a.s.c.) pushes itself into the antero-internal face of the
exoccipital (e.0.). The whole arch of the anterior canal is seen, and the fore part of
the space under it is well scooped for the “ flocculus.” The great multiperforate
“meatus internus” (VII., VIII.) is arched over by a convex tract of cartilage ; below,
the entrance is floored by the swelling cochlea.

The whole capsule is large and normal, both as to the parts shown, and also, as to
the degree of tilting it has undergone during growth.

The hind part of the wall formed by the occipital arch, is as large as the large
preauditory region, walled in by the parietal and squamosal. In this internal side view
the supraoccipital bone (s.0.) looks less than it is, but the band of cartilage below it
shows its full breadth. The middle third of the wall—nearer the bottom than the
top—is formed by the exoccipital (¢.0.) which is somewhat of an hour-glass shape. It
is notched, below, for the large 12th nerve (XII.), and in front of and below it the
common nick for the 9th and 10th nerve (IX., X.) is seen. The cartilage between
the basioccipital and exoccipital (b.0., s.0.) is narrower than the tract above, but
widens out behind, to lose itself in the large convex condyle (oc.c.).

Third Stage.—Newly-born Pangolin (Manis Temminckii), South Africa ;

head 24 inches long.

This young Pangolin was born in captivity in its native country, and died the next
day (see Proc. Zool. Soc., 1878, pp. 632, 633). I am indebted to Dr. Sctarer for
this very valuable specimen.

This type, like its neighbour the Aard-Vark (Orycteropus, next to be described),
becomes very large and well developed before birth, and the skull promises, even then,
the strength it ultimately attains to.

The lower view (Plate 12, fig. 6) shows the sutures and synchondroses very clearly,
and the remarkable shape of this toothless skull.

The alinasal region (a/.n.) in front of the premaxillaries (pz.) is short, and but little
seen in this aspect; the nostrils (e.v.) are now more lateral. The premaxillaries
have recovered some strength and size, now; their marginal and palatine parts are
stronger; between these the notch for the opening of JAcopson’s organ is rounded.
The maxillaries (mx.) soon expand into broad shoulders, laterally, after which the
general convexity of the outline of the skull only lessens slightly, a little behind the
Junction of the maxillaries with the frontals (f.), and, again, behind the auditory
capsules, where the occipital cincture retains its great similarity to the skeletal
segments that follow it. The alveolar ridge is now a sharp balk between the general
convexity of the upper face, and the general concavity of the hard palate, which is imper-
fectly developed, but in a manner very different from what we see in Marsupials and

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 95

Insectivores, where this floor fills in well, at first, and then suffers large absorption in
the part where the maxillaries and palatines join. If we compare this with the two
previous stages, and with the adult, we shall see that there is a steady attempt to pass
from the normal primary schizognathous condition to the normal secondary desmog-
nathous state, and that in this curious toothless type the latter is never attained to—
it comes short of the mark of the high and perfect Mammalian hard palate.*

Only in the hinder third do the concave palatine plates of the maxillaries approxi-
mate, and then not perfectly ; in the front third they fail to hide the palatine spikes
of the premaxillaries which run, as a wedge, far into the angle formed by those bones.
In the middle third they are divided by the protruding ridge on the fore part of the
vomer. The scooped part of the maxillaries inside the sharp alveolar edge is twice
as large as the second and still more scooped part near the mid-line; where the bones
nearly meet behind their thin edge is thickened. That thickened edge ends in a
point, and the corresponding palatine sends its pointed fore end between that point
and the outer flange of the bone which runs backwards and outwards. The outline of
the maxillary is then notched, then bulbous, and is then obliquely cut away, where
it articulates with the frontal ; the infraorbital foramen (V*.) has but a small bridge
under it, but from it there runs a considerable fossa upwards and forwards. Behind
the bridge the jugal process is very stunted.

On each side of the vomer, the maxillaries are most concave; that bone (v.) is thick
and split at its fore end. This exposed part is of great interest to the morphologist ;
it corresponds with the enlarged dentigerous fore end of the bone in osseous Fishes,
which in their extreme specialization have acquired a median vomer; and also with
the flat infero-anterior part of the vomer of the Green Turtle (Chelone viridis) (« Chal-
lenger Series,’ vol. 1, Zool., plates 10 and 11); and of certain Birds, e.g., Fulco, Dicho-
lophus (Trans. Linn. Soe., ser. 2, Zool., vol. i., plate 24). Odd enough, one of the
strongest and most perfectly specialized of the skulls of the Eutheria—that of the
Cat—shows a trace of this very plate, where the maxillaries fail to meet in the hard
palate.

The palatines (pa.) form a squarish tract ; they make about one-third of the hard
palate, which ends with them; and, indeed, they fail to produce the plate in their
hinder fourth, and the hind margin of the hard palate is cut away in a crescentic
manner. The submarginal groove of the maxillary palatine plate runs on under the
palatine, but soon turns outwards and is lost. The palatines form one-third of the
wall of the great nasopalatine canal behind, and the pterygoids (pg.) two-thirds ; these
bones, like the palatines, have a broad basicranial flange, and this upper dilatation of
these vertical bones overlaps the basioccipital. The wall or vertical part is deeply
notched behind, and thus the hamular process (see also fig. 8, pg.) is large and free.

* To me this seems to suggest that whilst the Pangolin has suffered degeneration and relapse, as
it were, as rezards the teeth, and with the teeth the size and fulness of the jaws, yet that this abor-
tion and suppression began when the type itself was very low, and only very imperfectly desmognathous.

96 MR. W. K. PARKER ON THE STRUCTURE AND

The whole series of palatine bones in this scarcely perfect hard palate is a narrow,
oblong tract, with the sides gently bowed out, and the ends gently converging.
Opposite the end of the hard palate the fronto-squamosal suture, which is very large
(see fig. 8), runs across, and the strong, concave orbital plate of the frontal takes up
all the orbital space here, except at the inner edge.

There we see part of the orbitosphenoid (0.s.) notched at its anterior margin where
the ophthalmic nerve (V1) is re-entering the skull through the orbital foramen. The
optic passage (IT.) is out of sight; but the sphenoidal fissure (V' *.) comes into view,
followed by the deeply notched, oblong alisphenoid (qJ.s.), notched deeply in the
middle of its outer margin by the 8rd branch of the 5th nerve (V%.); it does not finish
the foramen ovale, and emerges far in front of the auditory capsule (chl.). Those
wings and these capsules are both walled in, externally, by the huge squamosals (sq.)
that have pushed the parietals away from their frontal attachment, below (see fig. 8),
and continue the general ovoidal convexity of the skull up to the paroccipital promi-
nence (¢.0.). Each bone has a pneumatic cavity opening behind the stunted zygomatic
process (see also Plate 13, fig. 1—for x 2, read x 3), with its oval glenoid facet, which
reaches, in this specimen, nearly to the fore end of this arrested process. Then the
whole lower part of the bone in the postglenoid region is hollowed out to form an upper
chamber to the ‘ cavum tympani ;” hence the great convexity of the squamosal in its
hinder half (see also fig. 8). The whole line of junction of this great bony scale with
the infero-lateral parts of the hind skull is well worthy of remark (Plate 12, fig. 6,
and Plate 13, fig. 1). A strong flange from the glenoid region, inside the postglenoid
pneumatic foramen (p.n.f-), binds on to the outer edge of the alisphenoid, running in
with an angular process to complete the imperfect foramen ovale (V*.) and then, after
leaving the hinder half of the alisphenoid, clamping the antero-external margin of
the auditory capsule (ch/.). Here this “ flange ” becomes scooped and runs upwards
until it ends in the general hollowing of the bone above the tympanic cavity. In its
hinder part the bone strongly closes in under its own pneumatic cavity and interdigi-
tates with the rough, grooved opisthotic, and the small epihyal bridge (op., e.hy.).*

Since the last stage (Plate 11, fig. 8, p.s.) the presphenoidal region has become bony
and the bar (Plate 12, fig. 6, p.s.) looks like that next behind it (b.s.), but I strongly
question the independence of it, as an ossification ; it was most probably formed by the
confluence of the orbitosphenoids in the middle cartilage.

The next basal piece, the basisphenoid (b.s.) is an independent centre; it is oblong,
nearly as long as the broad (reptilian) basioccipital, and is separated by a moderate
tract of cartilage from the other two basal bony plates. In this species there is, now,
a small pituitary hole (py.) at the front third of this flat bone. The huge oval
basioccipital, behind it, is everywhere surrounded by cartilage except where it binds

* I am satisfied that anyone wishful to compare the skull of an adult Pangolin with that of any
high normal Mammal, will not complain of these details, nor make light of the pains I have taken to pull
this puzzle to pieces to get at its meaning.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 97

against the cochlez (ch/.), and behind; there it has thick-ribbed edges, which make
the middle part of the bone concave ; this is like what is seen in the Unau (Plate 9,
fig. 1) ; this is shown still more where these ridges are functiona/, as in the Anteater
(Plate 10, fig. 1).*

The oval basioccipital (b.0.) is notched a little where it forms the front boundary of
the foramen magnum (fim.); on each side of that end the large occipital condyles
are seen (oc.c.); their direction is infero-posterior. The exoccipitals (c.o.) run well
outwards to the grooved and rough opisthotie (op.), which is wedged in between the
squamosal and the gently convex paroccipital ridge.

The large hypoglossal (condyloid) foramen (XII) is partly finished inside by
cartilage, and the exoccipital bone only partially surrounds that nerve and the
9th and 10th (IX., X.) at their exit; the cartilage here is half as broad as the bone
outside it. The bony tracts seen in the distance behind the foramen magnum are not
parts of the supraoccipital but an extension of the lateral bones (see also fig. 9, ¢.0.,
s.o.) The moderately broad annulus tympanicus has been left in situ on the left
side (Plate 12, fig. 6, a.ty.); on the right side of the skull this bone and the
ossicules were removed (see also Plate 13, fig. 1). This imperfect ring has doubled
its breadth since the last stage (Plate 11, fig. 8), but it fails to run along the meatus
externus, and leaves the large membrana tympani exposed in this view.

The well and roughly ossified auditory capsule (Plate 12, fig. 6; and Plate 13,
fig. 1, ch/., op.) runs obliquely inwards and forwards, warty, as it were, and riddled
with holes and passages. The facial nerve (VII.) runs through a bony canal, and
appears on the roof of the tegmen tympani to escape again through the stylo-
mastoid foramen, which is bridged over by the small confluent epihyal (e.hy.) (see
also Plate 11, fig. 8, e.hy., VIL), which has become confluent at its once free end with
the highly ossified capsule, behind the obliquely seen fenestra rotunda (/-7.). Another
small bridge of bone at right angles with the inner end of the epihyal bridge
separates the fenestra rotunda from the fenestra ovalis (f%.0.). In front, the ossified
wall of the cochlea (ch/.) fits into digitations of the alisphenoid (a/.s.) by knobs of bone ;
and, behind the stylomastoid foramen (VII.), the opisthotic region, is divided into
two rough convexities by a considerable groove. On the inner face, where the cochlear
and opisthotic regions unite, there the bony mass is notched twice, to let out the 9th
and 10th cranial nerves (IX., X.).

The pyriform shape is well seen in the upper view of the skull (Plate 12, fig. 7).
The snout (al.n.) is twice as much seen here as in the lower view (fig. 6). The only
additional parts that come into view as compared with the last stage (fig. 1) are
the squamosals (sq.) that can be just seen flanking the parietals (p.). The pre-
maxillaries ( pw.) are seen in front, and the maxillaries (iz.) can also be seen flanking
the frontals (/:); the partly ossified supraoccipital (s.o.) finishes the structure behind,
The still-notched, but improved, nasals (7.) run well back between the frontals,

* This character reappears in normal tooth-bearing Mammals, e.g., in the Marmot (Aretomys monax).
MDCCCLXXXYV. oO

98 MR. W. K. PARKER ON THE STRUCTURE AND

which pinch in very little over the orbits, and cover as much surface above as
the parietals (p.), for what they lack in breadth they gain in length. The sutures
are now well finished and dentate, the lambdoidal takes an arcuate turn forwards,
in the middle, and retreats at the sides, where the parietals are only flanked by the
unossified margins of the supraoccipital plane.

The side view (Plate 12, fig. 8) shows well the feebleness of the short straight face,
and the fruit-like roundness and general convexity of the skull, proper, to which
no thick-bellied muscles are attached, and over which a strong horny helmet has grown.

A thin wedge of bone, the facial part of the premaxillary (pz.), runs its point between
the nasal (7.) and the maxillary (mz.), above; this is bounded in front by the snout, with
its cresentic fold over the almost lateral nostril (e.7.). The square-topped maxillary
takes up much of the outer edge of the nasal, and then runs downwards and back-
wards, where the lacrymal should be, and barely covers the nasal capsule. The antor-
bital, as well as the lower edge, is thick, and the infraorbital foramen and fossa (V*.)
are seen in front of the round, stunted rough zygomatic process in which, in this
specimen, I can find no distinct rudiment of a jugal bone. A small vascular
foramen is seen above the main passage (V*.) in the hind margin of the fossa. The
supraorbital part of the frontal ends below in an arcuate line, which is roughly semi-
circular, and straightish in the middle; the orbital plate is most hollow, almost angular,
where it runs downwards to the orbital foramen for the re-entrance of the Ist branch of
the 5th nerve (V'.). The lower edge of the orbital plate ends in a line parallel with
its upper edge ; in the notch the orbitosphenoid (0.s.) is seen, and the oblique, but large,
optic hole (II.). Below the frontal, and behind the maxillary, the palatine (pa.) is seen
edgewise as it runs upwards to form its basicranial flange, and forwards to assist the
maxillaries and frontals to finish the antorbital wall. This is done imperfectly, and a
considerable lanceolate cartilaginous “pars plana” is to be seen between the max-
illary and the palatine. At the fore end of that tract I have looked in vain to find a
lacrymal foramen. The 2nd branch of the 5th nerve (V*.) strongly grooves the outer
face of the palatine on its journey from the sphenoidal fissure to the infraorbital canal.

Most of the hind-skull, as seen in this view, is composed of two nearly equal
tracts of bone, the parietal and squamosal (p., sq.). The coronal suture ends on the
highest angle of the squamosal, which is not scooped out to form any definite temporal
fossa, all the space answering to that valley is to be seen in that part of the squa-
mosal which has caught the notched hinder margin of the frontal. This is made into
a small space for the temporal muscle by the ridge which runs down to form the
stunted zygomatic process, in the infero-internal face of which the glenoid facet lies.
Behind this ridge is the pneumatic foramen (pn.f), then a gentle hollow, and then the
general convexity over the large air cavity that forms the chamber over the cavum
tympani, The hamular process of the pterygoid (pg.) and the annulus (a.ty.) are just
to be seen, away from the eye, below, and the margin of the occipital plane, behind. A
gentle concavity is seen between the external or paroccipital edge of the exocci-

——

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. SS)

pital (¢.0.), and the thickened rim formed by it to the foramen magnum, The bony and
cartilaginous parts of the supraoccipital are just seen, and also the condyle (0c.c.), below.

The lower jaw (Plate 12, figs. 8, 10, 11, d.) is a mere sinuous bar of bone, capped
at its posterior-superior part by a condyloid facet, in front of which a slight elevation
is all that appears of the coronoid process (cr.p.), and under which there is no angular
process, whatever. The symphysial face is oval and rough, and the dentary edge is
sharp and roughly dentated ; between that part and the aborted coronoid process
the upper outline sinks into a gentle curve, answering to the convex outline below.
Inside the hind part of the ramus the bone is scooped away for MecKEtr’s cartilage
and the burrowing nerve (V*.), and vessels. The secondary mandible is now one-
fourth larger than the primary, for the fore part of MecKEt’s cartilage (mk.) is lost,
and the rest is a sinuous rod partly in front of and partly behind the persistent
ramus. ‘This sub-proximal part of the primary rod is only attached to the ramus in
front of the bony processus gracilis, behind, by ligamentous fibres. The proximal
part, now the ossified malleus (m/.), is quite normal, with the curved manubrium (m.m.)
and is equal to the processus gracilis. The incus (/.) is now quite ossified, and its
short crus is relatively larger. The stapes (figs. 11 and 12, sf.) is still merely a
columella, with a ragged hinder margin to its flat rugous stem, and a small inter-
hyal in the tendon of the stapedius muscle (7./y., st.2.).

In this species, at this stage, there is a small second upper ceratohyal (fig. 13, ¢.hy.),
and the rest of the bar (¢.4y.) is ossified in its middle part; the basal bar, with its
horns (b.h.br., t.hy.) is still unossified ; its shape has not changed since the last stage.

The occipital rigion, as seen from behind (Plate 12, fig. 9), shows great progress in
ossification since the last stage (fig. 2); and in this more finished ovoid the superficial
bones (sq., p.) come more into view in this aspect. The notch above the foramen
magnum (s.0.7.) 18 as large here, as in the smallest specimen (Plate 11, fig. 4), the lateral
cartilaginous tracts failing here for some distance. The three bones that are forming
this face of the skull (s.0., ¢0.) are still separated by a considerable amount. of
cartilage. The basal bone (b.0.) just comes into view. The paroccipital margin
(p.oc.) of the lateral bones (e.0.) forms a definite ridge on each side, separated from the
condyle (oc.c.) by a gentle vacuity.

Fourth Stage.—Skull of adult Pangolin. (Manis

? sp.).

Some things worthy of notice appear in the skull as it becomes adult. In the
lower view of the adult skull, with the hinder part removed (Plate 13, fig. 2), we see
the strength of the roof-bones, and that they are strongly marked, inside, by the
brain; these digital impressions of the inner table are very clear. So also is the
bony tentorium (f.tm.) strong, and strongly fixed to the supraoceipital (s.0.) as its
key-stone ; outside that ingrowth the great tympanic recess in the squamosal (sq.) is
laid bare. In front of this the postglenoid pneumatic foramen (pn.f’) is seen, and in

02

100 MR. W. K. PARKER ON THE STRUCTURE AND

front of it the strong stunted zygomatic process with its small oval, glenoid facet
(g/.f:) on its inner face in front. The basisphenoid (b.s.) was cut across near its
front margin, and only part of the alisphenoids are shown—just to the notch for the
3rd branch of the 5th nerve (V*.). Then we see the sphenoidal fissure between the
two wings (V!*.); the optic foramen (II.), the orbital foramen (V!.), and the orbital
tunnel (V*.).

The palate is much like that of the newly born specimen (Plate 12, fig. 6), but the
palatines (pa.) are relatively longer, the palatal portion of the hard palate being nearly
as long as that of the maxillary (m«.), which is very imperfect in front, and shows the
long (borrowed) palatine processes of the premaxillaries (pa.), and the forked antero-
inferior part of the vomer (v.). The alveolar flange of the maxillary (mz.) is perforated
in two or three places, and the right palatine has lost its bony floor in one place, just
as in Marsupials and some Insectivores, but not tothe same extent. A small seed-like
jugal (j.) is now to be seen on the angle of the maxillary—its jugal process—but there
is no lacrymal, and the place where that bone and the bony “pars plana” should be
seen is merely an enlargement of the very open suture—like a ‘mere crack—which
runs, above, between the frontal and maxillary, and then, below, between these two
bones and the palatine, where it rises into the floor of the orbit, in front.

The hind view of the fore skull (Plate 13, fig. 3) shows the strength of the frontal
cincture, the concavities (‘digital impressions”) of the inner table, the enormous size
of the ethmoid with its cribriform plate (c7.p.), and the strength and depth of the
“crista galli” (cr.g.). The optic foramina (II.) are surrounded by bone, and the
whole anterior sphenoid (0.s.) is about equal to that of Man—relatively to its size.
The sphenoidal fissures (V1 *.) are large oval passages, and the nasopalatine canal (7.p.c.)
is large and subcircular. The manner in which the squamosal grow downwards to
form the hollow zygomatic processes is also seen in this view, and the thinness of
the floor of the sella turcica (/.s., read b.s.). The pterygoids (pg.) are anchylosed,
to a great degree, to the posterior sphenoid.

A front view of the nasal end of the dry skull shows that the septum nasi (fig. 4,
sv.) in front of the vertical ethmoid is unossified, but that the nasal and inferior
turbinals (7.tb., 7.tb.) are quite bony, and anchylosed to the nasals (7.), in one case,
and to the maxillaries (i.), in the other.

ORYCTEROPODIDA.
Nearly ripe embryo of Aard-Vark, Orycteropus capensis (Plates 14, 15).

Here, if anywhere, we have a generalized type, evidently very archaic. Figures
of the adult suggest the idea that this is an ancient, primordial, unarmed Armadillo.*

55

* The figures (Plate 1, fies. 9-11) given of the head in this nearly ripe embryo (belonging to the

Museum of the Royal College of Surgeons) are suggestive of the new-born young of several types of

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 101

I have, moreover, to begin the description of this type of skull under an impression,
which I believe is not prejudiced, that Orycteropus comes nearer the Marsupials and
the lower Insectivores, and is further from the Monotremes, than the other Old
World Edentates—the Pangolins. The whole of the New World Edentates, whether
toothless, or with an imperfect dentition, appear to be like the Pangolins, upgrowths
from the Monotremes.

Unfortunately, I cannot bring the evidence for these views forward, now; but the
papers on the skull of the Insectivora and Marsupialia will follow, next, upon the
present.

The complex structure displayed in the lower view (Plate 14, fig. 1), if traced out
point by point, will show how much unlikeness there is between the only two remaining
types of Old World Edentates. The face is long, the measurement, even now, of the
base shows the tract in front of the fore margin of the presphenoidal territory to be
twice the extent of the tract behind that point. Here the development of the jaws
hardly suggests any change from that of the ordinary typical Mammals, with their
well-developed sets of teeth, all round. ‘The alinasal cartilages and nostrils
(al.n., en.) ave very peculiar, and quite unlike what I have lately been describing.

Here the nostrils are anterior, and the intervening ale, after spreading out into
projecting folds and processes, suddenly narrow in, and then project again right and
left, the projection being caused by a peculiar and large narial valve (7.v.). A deep
fissure—not a solution of continuity of the cartilage—runs across, below, arching
backwards a little in front of the premaxillaries (px.); and a median groove runs
forward from this part to the end of the snout, the converging folds of the floor in this
front part being elegantly crescentic—back to back. The part behind the transverse
arched groove soon opens out, right and left, where it gives off the recurrent cartilages
(fig. 5, 7c.c.) ; I shall describe these parts soon.

In this developing skull there is a palatal character seen at once, which is perma-
nent in the curiously arrested skull of the Pangolin, this is the imperfect desmognathism
of the palate, in front, exposing the vomer (v.). As to the character of the bones
covering the endocranium, they are very unlike those of Armadillos, Sloths and
Pangolins, not thick and cellular, but thin and fibrous, very much like those of the
Insectivora. The premaxillaries (px.) have retained their normal size, notwithstanding
their loss of teeth ; the alveolar edge is a thick tract, with a lanceolate outline, and

higher Mammalia, e.g., Lamb, Calf, &c.; but on my first, and very casual, look at the British Museum
spirit-specimen, of the same age as this, I mistook it for the young, from the pouch, of some large kind
of Kangaroo.

The head, only, of this single stage, as worked out here, will be fruitful of suggestions of relationship,
which point to quite other quarters than those just mentioned, which are, manifestly, somewhat fanciful.

There are two species of this isolated, unique genus, namely, O. capensis and O. ethiopicus (see Proc.
Zool. Soc., 1869, p. 431, and 1870, p. 669; also “ List” of the animals of Zool. Soc. 1883, p. 192, fig. 35,
and p. 193, fig. 86). The differences between these two, external and internal, are not great, but are
worthy of note.

102 MR. W. K. PARKER ON THE STRUCTURE AND

it is separated from the palatine process by a deepish concavity ; the two processes
reach backwards about the same extent. The re-entering angle between the two
processes is rounded for the opening of JAcoBson’s organ (see also fig. 5, j.0.), and the
wedge-like end of the maxillary (m.) reaches up to this passage.

The maxillaries are nearly half as long as the whole basal line, from the fore end of
the snout to the foramen magnum, and their alveolar tract is really large, behind,
where the two last teeth, with their subdivided pulps, take on somewhat of a
Zeuglodontic character.

he first of the simpler front teeth—there are five, in all, at this stage—would
answer to the second or third premolar, of a Hedgehog or a Mole; all those that
should be in front of this part are suppressed, and yet the jaw-bones have suffered but
little by this suppression.

The palatine plates of the maxillaries certainly do resemble those of the Armadillos
(see Plate 2, fig. 2), for inside the steep alveolar wall the great palatine flange, at first
scooped, rises into a ridge, and is then separated by another concave and grooved tract
from the lesser submesial tract of bone. This tract is deficient, both before and
behind ; in front it lets us see the fore part of the main vomer (v.) and the small
front paired vomers (v.’, see also fig. 5). The main part of the maxillaries ends a little
in front of the palatine end (pa.) of the hard palate, but at present the last alveolus
is not walled in. The shoulder of the maxillary, its jugal region, extends outwards
nearly as far as any part of the skull, the only wider part is the glenoid region (gl,f.).
The infraorbital canal (V*.) is one-fourth the length of the maxillary, and its opening
in front is infero-lateral.

The total length of the palatines (pa.) is half that of the maxillaries, but they
form less than one-third of the hard palate ; that tract runs in between that of the
maxillaries, leaving those bones only a narrow flange, there, inside the inner alveolar
wall. The two plates do not meet well together, especially in front, and each forms,
in this part, a rounded leafy plate of bone, fitting against a large, rounded notch on
the inner angle of each maxillary plate.

The margin of each palatine, behind, is rounded, and has a strong rim, which is
distinct from the thickened outer rim of the bone at its articulation with the end of
the maxillary. Under that outer rim, which forms a bridge, there is a large oblique
oval passage, or subway, and from it, in front, a groove runs forwards, along the outer
third of the flat plate. The unfloored part of each palatine is only two-thirds as long
as that which helps to form the hard palate; it is thick-edged below, and that edge
does not project so far outwards as the hinder rim of the completer part ; above, it is
oblique, with a shortened upper margin, to which there is scarcely any basicranial
flange.

The pterygoids (behind pa.) continue the wall to the nasopalatine canal, they are as
long as the palatines, and have a broader basicranial flange, which runs backwards, and
is emarginate in front of the Eustachean opening (ew.). The short thick hamular

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 105

process is but little free at its end (see also fig. 3., pg.) ; the fore part of each bone,
above, runs inwards over the palatines and the two bones are toothed where their thin
edges touch.

Outside these bones, we see, in the distance, the orbital plate of the frontal (#1) with
its large vascular hole, and at the margin of this space the jugal (j.), a considerable
bone, broadened out where it overlaps the maxillary. It is, in turn, overlapped by the
squamosal (sq.), whose jugal process passes a short distance beyond the jugal, and
then, on its inside, at its root, we see the rather large glenoid facet (g/.f.) which is oval,
the long axis forwards, but the fore part emarginate, having there a deep rounded
notch.

The squamosal can be seen a little in front of the glenoid cartilage ; laterally, it
runs from its Jugal process, backwards, until we see it, after forming four gentle con-
vexities and slightly converging, lie over the auditory capsule, ending beyond the
stylomastoid foramen (VIL).

The thickened postglenoid edge is separated from the beginning of the hollow, and
somewhat pneumatic, part that covers the tegmen tympani. The inner margin is
scooped, thin, and then thickens again before it ends as a scaly tract over the swelling
in the ear capsule caused by the horizontal semicircular canal (see fig. 3, h.s.c.).

Another superficial bone is seen inside the squamosal; this is the tympanic (@.ty.),
it is a thinnish U-shaped tract, with a foot-shaped flange, in front, for protection of
the processus gracilis of the malleus. This imperfect ring leaves a large space of the
auditory capsule only covered by membrane on its inner side, and the rim of the bone
lies a good distance behind the Eustachian opening (ew.). The membrana tympani
(m.ty.) is much exposed, and the unossified manubrium (72.77/.) is seen running obliquely
across it.

The proximal, ossified part of the orbitosphenoid (0.s.), can be seen in the fundus of
the orbit, with the optic nerve (IL.) running through, and the maxillary nerve (V*.)
behind, it. A considerable tract of each alisphenoid (a/.s.) is seen between the ptery-
goid and squamosal (sq.), and the large inferior branch of the 5th nerve (V*.) passes
through a very large foramen ovale, which lies in the centre of the plate, but which
is not quite bound in with bone on the outside.

The large median beam, with the presphenoidal region unossitied, the basisphenoidal
centre (b.s.), the basioccipital, and the whole occipital cincture will be described soon,
as parts of the separated endocranium (Plate 15, figs. 1, 2). There is in this
figure a small scale of bone seen in front of the stylo-mastoid foramen, and on the
proximal part of the epihyal cartilage (e.hy.); this is the proper parosteal stylo-
hyal bone (s¢./.), answering to that of Man, and of the Rabbit.*

I have not found this superficial ossicle in any other kind of Edentate, and

* Prorgessor FLowsr’s “ tympano-hyal”’ answers in a general way to this bone, but it lies deeper, and

soon forms the ectosteal plate of a small patch of bone which is added to the “ opisthotic,” but belongs
to the proximal part of the hyoid arch, where it has become confluent with the capsule.

104 MR. W. kK. PARKER ON THE STRUCTURE AND

therefore must add it to the list of characters in which this type comes nearer to the
normal Mammal than its congeners.

The upper view of the cranium (Plate 14, fig. 2) shows, in front, the remarkable
form of the snout, the roof of which suddenly pinches in, in front, after dilating as
suddenly on emerging from beneath the nasal bones (v.). The roof (al.n.) ends in
front, like the nib of a pen, and the sides are swollen, and then scooped away in a
crescentic manner, making the nostrils look forward. Close beneath this expanded
front lies the root of the curious long twisted narial valve (n.v., fig. 3) which projects
in front, right and left of the contracted fore end of the snout.

The difference between the general outline of this skull, and that of a nearly ripe
Tatusia hybrida, is considerable ; moreover, although larger relatively at the time of
birth, it is not nearly so much developed (compare Plate 14 with Plate 6).

The Edentate diminution of the jaws is much less than in the Tatou; indeed, the
skull is fairly intermediate between the skull of that kind of Armadillo and that of a
large and important Insectivore from the East Coast of Africa, namely, Rhyncoeyon—
a type to be described in my next paper.

In both these nearly mature embryos the basifacial length is twice that of the
basicranial, the point taken being that where the vertical ethmoidal and the
presphenoidal regions meet. But the Aard-Vark’s head is much the longer and
narrower of the two—more like that of an Anteater, in this respect, and yet more
like the skull of an Insectivore than that of any of the Myrmecophagide. Looking
at the main roof bones the nasals are now only one-tenth shorter than the frontals
and are one-tenth longer than the parietals (n., f, p.). This is a very different propor-
tion to what we see in Zutusia, and yet the general form is very similar, for the
frontals have to swell and broaden over huge ethmoidal masses in both cases (Plate 15,
figs. 1,2; and Plate 5, fig. 1). Thus, in both cases, the antorbital and postorbital
regions are of equal breadth, except in so far as the latter is widened by the
squamosals in the glenoid region. The general frontal convexity seen in Tutusia
(Plate 6, fig. 2), and still more in Dusypus (Plate 7, fig. 2), is exchanged in Orycteropus
for a considerable median hollowing of the roof, which affects even the hinder part of
the nasal bones. So that, as we shall see in the next figure (3), there is a very
peculiar “ beetling” of the brow in this type, the convexity of the frontals being only
lateral and not general. But the skull rises well in the coronal region ; yet there, at
present, it is unfinished, a large diamond-shaped fontanelle ( fo.) still persisting. Here
we gain that which the Armadillos are deficient in, namely, a good postorbital process
to the frontal bone, as the end of a good, clean, well arched supraorbital rim. That
ridge and process is very short and abortive even in the Unau (Plate 9), which has
also some suprafrontal hollowing, but in Cycloturus, Tutusia, Dasypus, and Manis, all
this is absent.*

* We shall see this Bchidnine feebleness of the skull in many of the Insectivora, also, so that this
imperfection of the orbit must not be taken as a necessary correlate of the suppression or abortive

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 105

Here the nasals (v.), narrowing steadily forwards, have their edge cut away from
without, inwards, and not notched as in Manis. The upper part of the facial plate of
the premaxillaries and maxillaries (px., mx.) can just be seen, and also the lacrymal ;
(see fig. 3, 7.) under and outside the well-formed orbital rim, the jugal (j.) can be
seen, and behind it the most projecting part of each squamosal (sq.).

The front two-thirds of the frontal suture, and the hinder third of the sagittal,
are complete; behind the latter, the temporal fossa is evidently gaining somewhat
upon the postero-external part of each parietal. The lambdoidal suture is in two
limbs, as it were, in front, running forwards in the middle, and backwards, behind,
between the two parietals and the one large, wide, bracket-shaped intraparietal (7.p.) ;
and behind, having a similar curve, and separating the intraparietal from the pro-
jecting endoskeletal supraoccipital (s.o.). Outside the latter this plane is unossitied,
and part of the projection is opisthotic, the swelling caused by the posterior canal
being just caught by the eye.

The side view (Plate 14, fig. 3) shows many things well, that are only partly visible
in the other aspects.

In front, the curious snout, with its alee, valve, and opening (a/.n., 1.v., e.n.), are
shown, and these are followed by the oval face-plate of the premaxillary (p..) with
its pedate lateral enlargement, below. The remaining three-fourths of the alveolar
edge belongs to the maxillary (m.), but the foremost third is edentulous. Surmounted
by the long nasal (v.) this bone forms most of the side of the large, long face ; its
upper margin ascends, at first gently, and then suddenly, its lower edge descends
gently and sinuously back to the jugal (j.). The highest part contributes to the bony
investment of the swelling ethmoidal mass (q/.e.) which it fails to cover, not meet-
ing the frontal (f#) at that part.

The hinder half of that preorbital tract is, however, covered by bone, but not by
either of these ; the lacrymal (/.) comes in here as an antorbital wedge. It is a pyriform
bone about the size of the face-plate of the premaxillary, has a straightish edge above,
against the frontal, but dips into the maxillary below. The large canal is behind
this rounded lobe ; then the bone flattens inwards to form a small orbital plate, and
thickens, below, where it places a solid foot upon the fore part of the jugal.

The hind part of the maxillary, the direction of which is forwards and upwards, is
scooped for the broad overlapping fore end of the jugal (/j.), so that the zygomatic
part of the maxillary is almost half its hind border; this is burrowed by the upper
maxillary nerve, which comes out at a moderate distance from the jugal, at the infra-
orbital foramen (V®.). Thence, forwards, the face-plate of the maxillary is grooved
twice—under the great swelling, and just above the alveolar margin; a vascular
foramen is seen in front of the great nerve passage, in this lower groove.

development of the teeth. Rhynocoyon and Orycteropus come very near each other in this character; the
former, indeed, lies, in this respect, between the Shrews and Moles on the one hand, and the almost
Lemurine Tupaia on the other,

MDCCCLXXXV. P

106 MR. W. K. PARKER ON THE STRUCTURE AND

Here the form of the frontal is well seen, and can be compared with the same
view in the Zatow (Plate 6, fig. 3). Here the swelling in front of and above the
orbit makes the skull at this part almost as bulky as it is in the region of the upper
fontanelle (fo.), and in this side view the frontal seems to be made of two parts,
separated by a deep, oblique valley. The supraorbital ridge does not extend so far
backwards as the wall-plate of the bone, which runs back there, and notches the fore
edge of the parietal, on the lower part of the coronal suture. Thus the parietal is of
a more normal size, and the squamosal does not dominate this part of the skull as in
Pangolins and Sloths.

Below the notch, the parietal (p.) forms a round lobe which rests upon both the cartila-
ginous top of the orbitosphenoid (0.s.), and the wholly ossified alisphenoid (aJ.s.), and
further back it forms the upper part of the temporal fossa, its whole lower edge being
somewhat concave, and the outline both there and behind is somewhat emarginate, to
receive the arched margin of the squamosal and intraparietal (7.p.). The latter bone
is about one-third the size of the parietal, and it reaches back over the outer edge of
the unossified part of the occipital plane.

The squamosal (sg.) is quite normal, it is much smaller than that of a Sloth or
Pangolin, and much larger than that of Cycloturus.

The temporal squama has an arched upper edge; the hind margin of the bone is
broad and emarginate ; the outer face is moderately convex for a moderate pneumatic
cavity over the drum cavity, and both there, where the glenoid cartilage (g/.f-)
has grown on to it, the margin is notched ; the zygomatic spur is well developed.

From the peculiar manner in which the overlappings, or imbrications, of the parts that
form the inner wall of the orbit are developed, the mind at once refers to the skull of
the Insectivora. The orbital plate of the frontal (/-) is a thin hollow shell of bone,
the hind margin of which is one large crescentic notch, inside which a semicircular
tract of the semiosseous orbitosphenoid is exposed; the optic nerve (II.) escapes
through the proximal part of the bony base of this tract, and the ophthalmic nerve
(V!.) re-enters the skull near the junction of the bone and cartilage in that plate.
The rounded corners of both the frontal and parietal bones overlap the cartilage
postero-superiorly, and, behind, its cartilaginous part is notched in the same crescentic
manner as the orbital plate of the frontal, and is then overlapped by the semicircular
fore edge of the alisphenoid (a/.s.), which round edge is nearly parallel with the hind
margin of the orbital plate of the frontal. This outstanding fore edge of the ali-
sphenoid forms the hinder boundary of the sphenoidal fissure (V" *.) ; its camer boundary
is formed by the orbitosphenoid (o0.s.). The palatine (pa.) crops up in the antero-
inferior part of the orbit; the pterygoid (pg.) can be seen below the jugal arch.
Below the tegminal notch of the squamosal the tympanic (a.ty.) and manubrium
can just be seen. The supraoccipital bone (s.o.) bends down behind the intraparietals,
behind which the thick wide convex unossified part is seen. Behind the lower lobe
of the end of the squamosal a small convexity is seen; this is formed by the hori-

bore.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 107

zontal canal (h.s.c.); behind this the larger crescentic swelling is due to the posterior
eanal (p.s.c.). The exoccipitals (e.0.) margin the foramen magnum (see also fig. 4,
e.0.); below, the occipital condyle (oc.c.) is shown, and outside this the low par-
occipital ridge (p.oc.).

The facial nerve (WII.) is seen escaping below the horizontal and posterior canals
where they meet, and in front of the nerve the epihyal (e./y.), with its obliquely
oblong splint, the stylohyal (st./.). The cartilaginous bar is elbowed and enlarged ;
it then runs downwards and forwards into the upper ceratohyal (c.4y.) without
segmentation. Then comes the lower ceratohyal half as long as the main bar, and
then, less than half as long as the lower ceratohyal, the hypohyal (h.hy.). That
little hillock of cartilage dilates to articulate with the fore part of the U-shaped
basal bar (0.h.b7.), a very regular semi-ellipse. The sides (or horns) of which are the
continuous thyrohyals (t.hy.).

When the hyoid bar becomes segmented from the cranial part, then this will be
quite a normal hyoid arch, except that the thyrohyals are continuous. But in the
Edentata the hyoid arch is most variable, and that not only as to Families, but the
genera Dasypus and Tatusia do not agree in the structure of this arch.

The smallness and imperfection of the teeth has given rise to a great reduction in
the size and bulk of the fore part of the mandible; this is a much larger “ramus”’
than that of Tutusia (Plate 6, fig. 3), for the hind part is very large, the coronoid
process (cr.p.) being of great extent and rather wide. The articular or condyloid
part (ed.p.), with its oval condyle. rans downwards and forwards till it meets the over-
lapping thick part where the vessels and nerves enter. That thickening corre-
sponds to the distinct coronoid bone of the Ovipara, and the gently convex inner wall
of the ramus to the splenial bone. Below the foramen, the ramus forms a second
lobe similar to the rounded angular process (ag.p.) behind.

The end view (Plate 14, fig. 4) shows the occipital plane, still largely unossified.
The investing bones (7.p., p., sq.) can be seen overlapping the whole of this hind wall,
and the auditory capsules (op.), swollen here with the posterior canal (p.s.c.), are seen
planted into a deep oblique notch, right and left ; below these the facial nerve (VII.)
and the epihyal (e.iy.) come into view. The rest is occipital, and here we see, as a
correlate of the development of the large intraparietal, a decrease in the size of the
subcircular supraoccipital (s.0.); see also in Totusia (Plate 6, fig. 4). By this we
know that we are further from the Monotremes, and from the rest of the Edentata.
A large sinuously transverse muscular ridge runs across this bone already, so that here,
as in the temporal region and lower jaw, we see that we have to do with a strong and
muscular animal. The subcircular foramen magnum (fim.) has the outer part of
its arch and upper half occupied by the rounded exoccipitals (e.0.) ; their depth, the
depth of the cartilage between them and the supraoccipital centre, and the depth of
the occipital condyles (oc.c.), are all nearly equal. Outside the condyles, the arch
projects as a quite distinct, though not large, paroccipital ridge and process (p.oc.): a

P22

108 MR. W. K. PARKER ON THE STRUCTURE AND

good normal Mammalian character. The concave hind margin of the basioccipital (b.0.)
is seen in the distance.

The ossicula audittis (Plate 15, fig. 4) are, like those of the Armadillos (Plate 6,
fig. 6 and 11; and Plate 7, fig. 6), intermediate between those of the more aberrant
Edentates and those of ordinary Eutheria.

Already in this relatively, and really very large, embryo, these parts are well formed,
and the rest of the primary jaw is gone. The inner view (Plate 15, fig. 4) shows a
reniform sinuous condyle, on a large head, which is convex externally, and scooped on
the inside. The large styliform processus gracilis (p.gr.) is a little longer than the
styliform manubrium (m.ml.), which is still cartilaginous. Doray’s figure (op. cit.,
Plate 64, fig. 14) shows a still smaller manubrium and a still larger processus gracilis,
even in the adult.

The quite normal incus (7.) is ossified, but the stapes (st.) has it facet and neck
still cartilaginous ; in the adult (Doran, op. cit.) the long crus of the incus has become
slenderer and the hole through the high stapes somewhat larger, and more circular.
I see no interhyal nucleus in the tendon of the stapedius muscle (st.m.). One more
point may be noticed, namely, that the base of the stapes is convex, and projects
inwards beyond the rim, as in the Mole (Talpa europea), but not to the same
extent.

In the lower view of the peeled inner skull (Plate 15, fig. 1), the eye is almost con-
fused with the number of parts to be described. If these figures be compared with
figures already given by me in other papers of the endocranium,—of Selachians
(Trans. Zool. Soc., vol. x., plates 34-42), and of the larvee of the Urodela and Anura
(Phil. Trans., 1877, Plates 21-29; Phil. Trans., 1876, Plates 54-62 ; and «hid., 1881,
Plates 1-44 ; Linn. Trans., ser. 2., Zool., vol. i, plates 14-21)-—it will be seen that
the interpretation of the Mammalian skull is no easy task. But there lie, obliquely
between this marvellously specialized skull and the skull of the Ichthyopsida, the
various kinds of skulls to be seen in the oviparous “ Amniota,” or Sauropsida.

To see the meaning of what les before me, here, in the skull of this somewhat
abnormal, low Eutherian, I find it necessary to remember the structure of the skull
in every division of the great groups just mentioned, that is in Serpents, Lizards,
Tortoises, Crocodiles, and Birds.

But the best of all these is the Crocodile, an ancient type, and one on which the
loss of parts by degenerative specialization, is much less than in the other Sauropsida,
for the living members of those other groups are manifestly more modified than the
Crocodile.*

This lower view (Plate 15, fig. 1) shows, behind the exposed part of the snout

* Now, and for the future, I must avoid the use of the term Reptilian, qualifying it by the prefix qguasi,—
for what islow in a Mammalian skull; if some Paleontologist were to stumble upon a fossil Hypotherian
it would be a great gift of fortune, then one could use that term as an adjective. That such a type

once existed I feel certain—as certainas that T myself have had a series of ancestors.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 109

(al.n., e.n.) already described, that the double nasal canal, after narrowing in a little,
enlarges only gradually in the aliseptal region (a/.sp.). But in the aliethmoidal («l.e.)
or proper olfactory territory it widens out rapidly, and forms a large bulbous structure
which reaches backwards to the anterior sphenoid (0.s., p.s.). This broad end of the
pyriform labyrinth is not finished by cartilage below, and the internasal desmos which
binds side to side is the main vomer (v.). But the septal region, above the front
half of the hard palate, and which is supplied by the ophthalmic or orbitonasal
branch of the 5th nerve, is open, now that the lower bony floor has been removed.
The thick base of the alinasal region behind the crescentic groove soon opens out,
right and left, like curtains folded back, and the aliseptal wall behind the snout, for
an extent which is half the length of the whole labyrinth, turns inwards very little
below. This open part is divided into two lanceolate spaces by the septum nasi (above
v’.), and its grooved bony rest—the vomer (v., see also Plate 14, tig. 5).

But the nasal canals are not open towards the hard palate more than by narrow
chinks ; for there are two pairs of folded eartilages in this general open space—two on
each side—one, the internal, half the size of the other, the external, fold.

From above the inner part of the selvedge of the closed floor of the snout, close
to the septum nasi, right and left, a rod of cartilage—the recurrent cartilage or the
cartilage of JACcOBSON’s organ—grows backwards, and before it passes inside the
opening of that organ (j.0.) it sends a curling process half way round the front of the
passage. The narrow stem, beyond the opening of the organ, soon expands, and then
the cartilage becomes lanceolate, and ends opposite the middle of the outer coil, or
inferior turbinal (7.tb.). Below, the recurrent cartilage is convex ; seen from the side
(Plate 15, fig. 3, 7¢.c.), it is seen to be scooped on its supero-external face, The inferior
turbinal arises opposite the thickening part of the lesser tract ; it also has the same
lanceolate form with a convex under face, like the other, but is twice as large. This
“maxillary,” or “inferior, turbinal ” is not fixed by its fore end ; its root is from the side ;
it is an ingrowth of the aliseptal wall (a/.sp.). The thin lamina which grows inwards
is concave below, it runs half-way across the gap in the floor towards the vomer,
and then forms an upper and a lower secondary fold, These are coiled over from their
common free face, like the leaflets of Cycas revoluta, but to a greater extent,

The nasal turbinals cannot be seen in this figure; they are similar in all the
Edentata, and dip down from the cartilage that underlies the nasal bones, just as the
inferior turbinals grow in from the cartilage that lines the maxillaries (see in
Tatusia, Plate 3, figs. 9 and 10, n.tb.). In the figures just referred to, and in
figures, soon to be described, of these parts in the Hedgehog, a free section of cartilage
is seen right and left of the septum nasi (s.7., pe.c.). They are a little displaced by
the razor, and should lie nearer the base of the septum. This dissection of the nasal
labyrinth of the Aard-Vark gave me the interpretation of those sections of the
nose of Tutusia and Erinaceus.

The lanceolate form of the gap right and left of the septum (Plate 14, fig. 5, and

5

110 MR. W. K. PARKER ON THE STRUCTURE AND

Plate 15, fig. 1) is finished on the inside in its hinder half, by a precurrent cartilage,
which overlaps the recurrent tract (pe.c., re.c.). This stoutish rod, which ends in
a point in front, is a direct ongrowth from the inner edge of the nasal floor, over
which floor the copious folds of the so-called “middle turbinal” are to be found.
Behind these precurrent spikes, the proper olfactory floor, formed by a large ingrowth of
the aliethmoidal fold (a/.e.), is a wide sinuous tract, convex towards the inside, and at
the outside, but convave along the middle. This wide part is divided, by a renewal of
the concavity, into two lobes, the inner of which lies on a lower plane than the outer,
and reaches a little further back. The inner part of the inner lobe is hollowed out,
the nasal floor running upwards, in a concave manner, to reach the vomer. The outer
and higher lobe is rather uncinate, hooking a little towards the orbitosphenoidal
region ; it is the lower face of the great lateral ethmoidal mass, seen from above in
fig. 2.

The main median investing bone, the vomer (v.), and the small paired anterior bones
(v’.), were not peeled off with the rest of the superficial bones, when the preparation,
here figured, was made. The large parosteal tract (v.) has been dominated by two very
distinct endoskeletal structures, namely, the intertrabecula, and the floor of the
double nasal labyrinth. This large, long vomer reaches by its hind forks as far as
the labyrinth, whose halves it unites, below ; in front, it runs nearly as far as to
JAcopson’s organ. It is cleft, behind, up to its middle, the cloven part having the
keel divided, which has run back from the fore half. In the foremost part the bone is
simply rounded, running thence to its grooved upper face, on which the front partition
wall rests.

This very remarkable foliacious vomer (Plate 14, fig. 5; Plate 15, figs. 1 and 3, v.)
is roughly pointed in front ; then at the beginning of its second third it gives off a
narrow wing, right and left, and these wings widen up to the median slit; a little
behind it they end. Overlapping them, another pair of wings arise, right and left,
twice as wide, and then another pair wider still, which run on to the diverging end
of the forks, behind ; the left middle wing is perforated,

The vomer is pinched in under the first and last wing, which are thinnish, as is
usual in the edges of the Mammalian vomer (Plate 15, fig. 3, séde view) ; but the
middle wing is a solid mass with an oval outline.

This lobe or wing did not peel away easily, like the other, as is usual with a paros-
tosis in its relation to the underlying cartilage, but had to be broken away, there
being no line sharply dividing the bone-cells from the cartilage-cells. Thus the
vomer is here grafted on to each moiety of the cartilaginous nasal capsule at the inner
edges of its floor, as in Passerine Birds.*

* See Nirzscu, article “ Passerine,” in Exscn and Griiper’s ‘ Encyclopeedie,’ 1840; “‘ Ueber die Familie
der Passerinen,” Zeits. fiir die gesammten Naturwiss., 1862; Huxiny, Proc. Zool. Soc., April 11, 1867, pp:
450-454; and my papers on the Aigithognathous type of skull, Trans. Zool. Soc., vol. 9, plates 54-62,
and vol. 10, plates 46-54: Trans. Linn. Soc., ser. 2, Zool. vol. i., plates 20, 21; and Monthly Micros.

Journ., 1872, plates 34-39 ; and, ibid., 1873, plates 8-10.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 111

I may have missed this peculiar structure in some of my dissections ; this is the
last skull at which I have worked—if so this character will not easily escape me
again. It appears to me to be a new and rare thing, and one of many remarkable
cases of the conformity of the Mammalian skull with what is to be found in the
Oviparous types—high and low.

Afterwards, I have no doubt, the bony matter transforms still more cartilage, that
bone soon becoming anchylosed with the ossified tracts of the rest of the lateral
ethmoids. Whether “posterior paired vomers ” appear or not I cannot say, possibly
the hindmost lobes or wings of the main bone become distinct for a time, and then
unite with the bone forming within, so as to complete the compound desmognathisni of
the Mammalian upper face.

The anterior paired vomers (v’.) are very small in this type ; they are club-shaped,
convex below and towards the septum, and hollow towards JAcopson’s organs, of
which they are the bony correlates. They lie right and left, a little in front of the
main vomer.

The skull proper is composed, now, of about equal] parts of unossified and ossified
cartilage. The anterior sphenoid shows no basal piece below ; the whole of the thick
beam, from the basisphenoid (Plate 15, fig. 3, p.s., p.e, sn.) to the end of the
snout, being cartilaginous.

That beam shows lateral wings where it passes into the alisphenoids, but for the rest
of its extent, as seen from below, it is simply convex, lessening forwards (Plate 15,
figs. 1 and 3, p.s., s.7.).

In this large embryo the orbitosphenoids (0.s.) have lost their ethmoidal and supra-
auditory attachments, but the wide outer half is still unossified. Their rounded fore
edge comes short of the retiring margin of the lateral ethmoids, only membrane
flooring the front part of the cranial cavity there. The ear-shaped upper part of each
orbitosphenoid runs backwards inside the alisphenoids (fig. 2), but the two broad
wings of bone at the proximal part are in front of the alisphenoids, and these form
the front boundary of the sphenoidal fissure, through which the 1st and 2nd branches
of the 5th nerve (V'*.) escape. The orbitosphenoidal bones are thick, below, fore
and aft of the optic foramen (II.), and the front thickening nearly touches the vomerine
fork on one side—the right in the figure—and overlaps it on the left, the concave
margin of the bone fitting against the rounded inner lobe of the great nasal capsule.
The hinder thickening of the bone, below, rests upon the ossified angle of the proximal
part of the alisphenoid (ad.s.).

The posterior sphenoid is about equal now to the anterior, which it imbricates,
behind, clearing itself well, outwards, from the rest of the skull wall.

The bony basisphenoid (b.s.) occupies about three-fourths of its own territory ;
the whole of this subpituitary part is thick and convex, showing no sign of the
primary deficiency in the cartilaginous floor, The sides (al.s.) have united, already,
with their keystone piece, but a groove below marks the old line of division

112 MR. W. K. PARKER ON THE STRUCTURE AND

of the bony centres. The als are not ossified up to their root in front, but the
bone reaches the front of the unfinished basisphenoid bone (b.s.); behind, they overlap
it. The hollow under the junction of the base and ale is the place where the
pterygoids clamped the skull (Plate 14, fig. 1); here the alisphenoids are bevelled ;
beyond that part they are strongly convex, as they grow first outwards, and
then upwards. All their three free edges are crescentically emarginate ; the notch
in front forms part of the wide sphenoidal fissure (V1 *.) ; on the outside a suture is seen
running from the concave edge to the large foramen ovale (V*.). The ale being
measured fore and aft, is in the middle of the bone, but it comes near the outer
edge. Here, again, we have that remarkable character of the alisphenoid which
we have just seen in the Sloth, Pangolins, and in the genus Dasypus (Plate 7, fig. 1),
but not in Tutusia (Plate 5, fig. 1), where the alisphenoid, freed from the general
cranial wall of the chondrocranium, is slow in developing—see especially in Manis
(Plate 11, fig. 1, als.)
branch over the edge of the ala. Normally, the 3rd branch of the 5th notches this
hind margin of the ale (see in Tatusia, Plate 5, fig. 1, V*.), the ‘foramen ovale”

and thus the huge trigeminal nerve sends its hindmost

being completed afterwards by a postneural bar of bone. But in the Mole (Zalpa
europea) it perforates the primary cartilage, and the 2nd branch does the same,
so that in that type the ‘foramen rotundum” is also a primary foramen of the
chondrocranium, and not a notch completed afterwards by a bony bar.*

The large outer and hinder lobe of the alisphenoid binds in front of the “ tympanic
recess” of the squamosal, and then the hind margin rapidly running forwards, this
bene closes upon that great auditory outgrowth, the cochlea (chl.). Between the
cochlese the basal beam keeps on widening backwards, behind the bony basisphenoid
(b.s.). There is a tract of this widening cartilage three-fourths the extent of the bone ;
behind this the basioccipital is twice as long as the cartilage, and reaches to the front
(or lower) edge of the foramen magnum (/.7.).

This latter bone (b.0.) is six-sided, has a straight front margin, a concave side margin
lying against the convex cochlez, a slightly concave margin followed by cartilage,
postero-laterally, and its emarginate end is at the foramen magnum. The condyles
(oc.c.) are short, convex, and ear-shaped ; the small exoccipital bones (e.0.) are close
in front of them, and end against the hypoglossal (or condyloid) foramen (XII.). The
fore part of the foramen magnum has the bone and cartilage raised into a protecting

* If we lose patience over these details we shall miss the best things in this minute morphology.
In the normal freedom and out-thrust of the Mammalian alisphenoid, and in the very varied manner
of escape of this inferior maxillary nerve—through, or over, or behind the ale—we have specializations
that must be compared with the modification of this part of the general cranial wall to be seen in
Serpents, Lizards, and Tortoises, where what is one continuous growth in Sharks, Frogs, &e., is in
one case a little patch, in the next a narrow “ upright,” and in the third case, the Chelonian, it has
suffered complete suppression. (See Trans. Zool. Soc., vol. x., plate 38, fig. 2; Phil. Trans., 1881,
Plates 1-44; ibid., 1878, Plates 27-83; zbid., 1879, Plates 37-45; and ‘Challenger Reports,’ vol. i.,

Zoology, plates 1-13.)

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 113

rim. Outside the condyles a definite low convex paroccipital ridge is seen (po.c.),
outside this the cartilage is opisthotic (op.). Beyond and behind the condyles, there
is a narrowish tract of cartilage, and there the lower edge of the bony supraoccipital
(s.o.) is seen bulging backwards.

The ovoidal cochlear region of the auditory capsule (ch/.) lies each in its own
oblique, well-made socket; the rest of the capsule seen in this aspect is the tegmen
tympani outside, and the opisthotic region (op.) postero-externally. Outside the
tegmen the large pneumatic foramen of the squamosal (¢7.c.) is drawn in outline,
and under the tegmen the facial nerve (VII.) is seen passing to its place of exit,
the stylomastoid foramen. In front of the nerve the small stylohyal bone (st.h.)
is seen, and inside it the epihyal cartilage (e.y.) Further inwards, in the enlarged
occipito-auditory “foramen lacerum posterius,” the 9th and 10th nerves (IX., X.)
are emerging a little in front of the 12th (XII). In front of this semicircular
chink, the fenestra ovalis and fenestra rotunda (f%.0., 7.) are shown in the
fundus of the nut-shaped cochlea (ch/.), the proximal or hinder part of which is
more convex than the rest.

The upper view (Plate 15, fig. 2) of the endocranium shows what a long tract there
is of the nasal labyrinth before we come to the dilated, and most complex, true
olfactory region ; the cartilage roofing and walling all the regions in may still retain
the old terms of alinasal, aliseptal, and aliethmoidal (a/.n, a/.sp., al.e.). The whole
structure, as seen in this aspect, is more like the parts of « flower than the fore end of a
skull; the vestibular flitted part is very elegant, with its two pairs of semicylindrical
tracts, gradually enlarging backwards, and then appearing to end, in each, in a point.
Between these pointed ends, of which the submesial go furthest back, the roof (q/.e.)
is sinuously and gently concave, and then ends in a perforated triangular tongue—
as in Birds—that tongue-like growth being the top of the moderately developed
cartilaginous “ crista galli” (c7.g.).

Right and left of the crista galli—which is the concave free, posterior, mediastinal
edge of the perpendicular ethmoid (see also fig. 3, p.e., cr.g.), the large, hollow,
burrowing olfactory fossee are seen floored by the multiperforate cribriform plate (c7r.p.).
This porous roof over the “middle turbinals” is itself the floor of the fore skull, and
these two pre-cranial ovens are themselves roofed in front and at their sides by the
arched edges of the upper turbinal regions of the olfactory capsule. The copious growths
of the upper turbinal (v.tb.) are indicated right and left in the great pillow-shaped
lobes of the ethmoid. On the inner edge of each of these there is a small angular tag
of cartilage, and at a moderate distance behind the round swelling end of these upper
turbinal masses, the round fore end of the cartilaginous, outer part of the orbito-
sphenoid (0.s.) is seen; the tag is the remnant of the bond that did hold the much
larger orbitosphenoid to the olfactory capsule.

The cribriform plate is margined behind by a thick rim of cartilage—very thick
inside and below the tag; but nearer the middle the cartilage is still more solid, form-

MDCCCLXX XV. Q

114 MR. W. K. PARKER ON THE STRUCTURE AND

ing a remarkable structure right and left of the axial crest, which is hollow between
these two sessile berries of cartilage, and then thickens as it passes into the presphe-
noidal region (p.s.).

We must cross over into the territory of another group of the “ Amniota ’ to get
an explanation of these parts, which appear to be rather for ornament than use, but
which are really most important in their morphological signification.

In the chondrocranium of the Crocodile and Alligator (see Trans. Zool. Soc., vol. xi.,
plates 63-67, and especially plate 67, fig. 1, i.tv., ¢.tr.) we have the explanation of
this right and left berry-shaped swelling of the hind part of the ethmoidal region.
They are the swollen ends of the paired trabeculze
familiar to us in the Ichthyopsida.*

the “cornua trabecule,” so

A large unciform lobe of the orbitosphenoidal cartilage (0.s.) is seen lying upon the
bony alisphenoid (q/.s.), but it is now two-thirds its own length from the front edge of
the large superauditory (or pterotic) cartilage (s.a.c.), with which it was once continuous.
The hind margin of the still large orbitosphenoid is a great semicircular notch, the
fore margin is wavy, up to the rounded front and outer margin. The first and largest
rounded notch of the orbitosphenoid fits against the berry-like cornu trabeculz (e.t7.),
and the inner angle of the bone is separated from the same part of the other side by
cartilage, the hindmost part of the perpendicular ethmoid (p.e.). Nearly in the
middle of the inner margin of the bony part the oblique optic passage (IT.) is seen well
margined by bone behind (see also fig. 1), but in this aspect this margin of bone is
pressed upon by a mass of cartilage. Between the two bony tracts—orbitosphenoids
(0.s.)—there is a short, thickish wedge of bone with notched sides ; this is the presphe-
noid (p.s.), it is doubtfully independent, but is well marked off by a right and left
groove, t

The cartilaginous tract between the pre- and basisphenoidal ossifications is also
elevated into a sort of double berry ; here with no stem between. Here we have the
trabeculee behind the intertrabecula, with the thickening at their origin, showing here
most on the upper side, whereas this is seen most on the lower in the Crocodilia (op.
cit., Plate 65, figs. 1-8). The large bony ale (al.s.) lie down low and are well scooped ;
they have a sharp raised ridge on their inside, and this is separated from the now
confluent basisphenoid by a groove which is open at both ends; in the hinder space
the internal carotid artery (7.c.) enters, and then runs along the groove. In front, the
basisphenoid projects between the roots of the trabecule ; behind, it is notched thrice

* The reader is also referred to the sections of the skull of the embryo Turtle (Chelone viridis)
(‘ Challenger Reports,’ Zool., vol. i., plate 5, especially fig. 7,7.tr., tr.). Tf these figures be compared with
those of the like sections of the skull of the embryo of Struthio camelus (Phil. Trans., 1866,
Plate 10, figs. 2-5, s.n.), and of the skull of the Chick (Phil. Trans., 1869, Plate 81, fig. 6, s.n., and
ibid., Plate 83, fig. 4, s.v.l.), the meaning of these things will be evident.

{ The presphenoid is very rarely an independent ossification ; it attains to that special condition most

perfectly in the Marsupials and Rodents; but in that remarkable Insectivore, Rhyncocyon, the pre-
sphenoid has evidently had its own longitudinal centre of ossification.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 115

to receive the thiee convexities of the parachordal tract. The bone is gently hollow
for the pituitary body, and this “sella turcica” is finished behind by the triple rising,
very slight, of the postpituitary wall, the fore part of the cartilaginous tract in which
the basisphenoid and basioccipital (b.0.) will ultimately meet. The three convexities
of the cartilage are due to the manner in which the thick parachordal tracts met, and
united, over the narrowing cranial end of the notochord.

Below (fig. 1), the investing mass, or parachordal cartilage, was finished into bone
right and left, by the basioccipital (b.0.); above, the sharp edges that lie against
the nut-shaped cochlev (ch/.) are unfinished, the rest corresponds with what is seen
below.

The cochleze (ch/.) look broader in this aspect than from below; they overlap the
out-thrust alisphenoids, somewhat ; their arched inner porch or meatus internus (VIL,
VIII.) is seen in this view, and also the widened chinks for the 9th and 10th nerves
(IX., X.). The bulging supraoccipital centre (s.o.) has the outer third, on each side,
occupied with a large convex inturned crest of cartilage, which runs forwards in front
of the hinder angle of the alisphenoid; that foremost part is the remnant of the
great continuous band that did run into the orbitosphenoid. It is mainly the hinder
third of the sides of the “tegmen cranii,” and is supraoccipital behind, and “ pterotic ”
at the sides.*

This “demonstration” will be finished when I have described the great septum of
the nasal labyrinth in its lateral aspect (Plate 15, fig. 3). The whole of the large crest
of the intertrabecula is rather low, its basal or primary part is very round and solid.
A large oval fenestra (7.2.1) lies in front of the crest, surrounded by the alinasal
growths (al.n.).

These are figured as cut away, but from the lower part there is given off the
recurrent or JACOBSON’s cartilage (7c.c.), a long, hollow-faced spatula, with a small
vomerine bone (v’.) above its dilating part, in front. The aliseptal fold (al.sp.) is thin,
but where the hinder part of the roof is cut through the aliethmoid (al.e.), there the
cartilage is very solid. Behind it the cartilaginous crista galli (c7.g.) stands like a
reversed “rostrum.” The margin of the septum then forms one large, nearly semi-
circular notch along the thin end of the intertrabecular septum (p.e.). Concentrically
with this, a little lower down, the thick, cribriform plate (c7.p.) is cut through. Behind
the fosse, the stem of the cornu trabecule (see fig. 2, ¢.tr.) is cut through, and then
comes the orbito-presphenoidal bone (p.s.) grooved laterally in the attempt to form
a distinct median centre. Much cartilage is still unused, below and behind; then
the basisphenoid (b.s.) shows itself through the thickness of the basal beam. The

* This lateral tract is ossified separately in the Osseous Fishes as the “ pterotic” (see ‘ Salmon’s
skull,” Phil. Trans., 1873, Plates 5-8). In the Mole and Shrew the ossification of this part (as I shall
presently show) takes placeina remarkable manner. The opisthotic rapidly ossifies nearly all the walls
of the labyrinth, but the prootic arises in its normal place, and then, pushed upwards, so to speak, by the
huge opisthotic, runs into this superauditory crest, forming a ptero-prootic bone.

Q 2

116 MR. W. K. PARKER ON THE STRUCTURE AND

hind part of the septum is marked with hills and hollows that correspond with the
folds of the middle turbinal.

SUMMARY AND CONCLUSION.

In the present state of my research I can make but little use of comparisons, and
draw very few deductions. Most of the work already done is still in the form of
figures, with no written descriptions, and that is only about a fifth of the work laid
out for me in the Mammalian Class.

Nevertheless Iam much mistaken if the knowledge already obtained in this Order
of the Edentata, alone, is not of considerable value ; the living types composing it are
so far removed from each other by specialization that they, evidently—Family after
Family—represent large groups of forms that must have existed in the past.

As placental Mammalia, these types come, of necessity, into Professor Huxtry’s
highest group—the “ Eutheria ;” and yet in both the skull and the other parts of the
organization worked out by me, namely, the shoulder-girdle and sternwm, they come
nearer at times to the Prototheria than the Marsupials themselves—that middle
group, the Metatheria.

Therefore it occurs to me, and the author whose terms I have just used will, I be-
lieve, agree with me in this view, namely, that these Edentata are the direct children
of the Prototheria. That they passed through a Metatherian stage is a thing not to
be controverted, but I believe that it was not, in most cases at least, utilized—it was
an abbreviated prenatal stage ; they lost their Marsupial bones and never acquired
any Marsupial modification of their abdominal skin. A great satisfaction now arises
to me from the fact that my very narrow line of research brings me to the reiteration
of Professor FLoweEr’s views of the Edentata, znte se.

The Old World types are sharply divided from those of the New World ; but types
so ditferent in appearance and habits as the Sloth and the Ant-bear can be shown by
embryology, as well as by their general anatomical structure, to be, in reality, closely
related. Adaptive modification has done its utmost in these two cases; but it has
only masked, it has not destroyed, the essential fundamental conformity of these two
grotesque and aberrant types of Mammals.

I need not repeat here what I said in the Introduction as to my change of views
since the publication of my paper on the Pig’s skull (Phil. Trans., 1874, Plates
28-37), as to the general homology of the “ossicula audittis.” The researches of
Banrour, SALENSKY, and FrAsER have caused me to think over this question again,
and to doubt the conclusion that Professor Huxtuey first, and I afterwards, had come
to on this question ; if further research shows that the views of to-day are untenable,
I shall be ready to receive that fresh light.

When the development of the skull has been worked out in Family after Family
in the Orders that compose the whole Class, then will be the time for a general

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. U7

Summary, and we shall then be better able to appreciate the fragmentary nature of
the existing groups of Mammalia, and to imagine, in some degree, with the help of
Paleontology, what the lost kinds were like.

In working out this Order I have had constantly to refer to the structure and
development of the skull in the Sauropsida, and at the same time to be careful not to
call any modification of a low Mammalian type of skull Reptilian or even Sauropsidan.
I want a term of wider import than even Professor Huxtey’s title for the Mammalian
root-stock, namely, “ Hypotheria,” as that would only lie under the Prototheria, and
not under the Reptiles and Birds too. Proto-Amniota occurs to me, but unfortunately
the second existing group of Mammalia, the Marsupials or Metatheria, are themselves
proto-Amniota, having both that important foetal membrane and its correlated sac, the
allantois, in a primary, or at least an arrested, condition.

At present, therefore, I use a term which, I think, cannot be misunderstood,
namely, quasi-Reptilian, as its use does not suggest the idea of the possessor of such
a character being derived from a Reptilian stock.

Using this precaution, I freely, from time to time, refer the reader to my published
ficures of the parts of the growing skull in Serpents, Lizards, Crocodiles, and Birds,
because that, in some things, these highly specialized modern oviparous Amniota retain
certain structural characters that are manifestly archaic, and that can be easily
compared with their counterparts in the skull of the gill-bearing tribes.

Out of the great number of parts that are in conformity with what is seen in
the other Classes, especially in the Sauropsida, I have been anxious to eliminate
and put into prominence, characters that are peculiar to, and diagnostic, of the
Mammal. Some of these are as much so as the hair, and mammary glands, and are
therefore of great interest to the Morphologist. Yet the most striking and important
of these have to be plucked out of the very fire of controversy, so that the survey of a
wider and still wider field is urgently necessary ; that survey, fully made, will be the
work of years.

When speaking of these low forms—the Edentata—and asserting that they are
archaic, or arrested, or abnormal, I am, of course, thinking of such normal forms as
the Insectivora, and of the higher types that ascend above them—Lemurs, Carnivora,
Ungulata, &e. Happily, everyone is familiar with the structure of the skull, in the
adult, in these groups; and although these high forms have their own highest or
culminating type—yet that which is highest in a Mammalian skull, as such, can be
approximatively ascertained.

Suppression, or even abortive and abnormal development of, the teeth is always
attended with abnormal development of the extensive facial structures; these, it is
evident, modify the outward form of the head much more than any difference that can
arise in the form, or proportional size of the skull proper, so far as it is a mere box to
contain the central nervous system.

These remarks, it will be seen, have their bearing on the modifications to be seen in

118 MR. W. K. PARKER ON THE STRUCTURE AND

the skull of the Edentata. But for what is seen in Orycteropus, I should leave
the Marsupial type of skull out of question in the present comparison. All the New
World kinds, and the Pangolins of the Old World, may be considered in relation to
each group—to the Monotremata below them, and to the Insectivora above, or rather
outside, them.

As far as I can see at present, the parietals coalesce very early in the Monotremes,
and the large supraoccipital grows over to meet this quasi-reptilian roof, and form
the lambdoidal suture.

In the Edentata the parietals do not meet and coalesce early; but the supra-
occipital region is very large, turns over towards the parietals, and ossifies early, and
has no interparietal separating it from the parietals.

This takes place in all but Orycteropus, which has one of the largest inter-
parietals I have seen, and thus agrees with Marsupials, Insectivora, and the Mammalia,
generally, that have normal teeth.

The premaxillaries are very small in the Edentata, especially those that are abso-
lutely toothless ; Orycteropus has the best developed premaxillaries of any of the
meinbers of this Order, The maxillaries have the best development in Orycteropus,
and the feeblest in the Pangolins ; and they and the little Anteater (Cycloturus), have
only the rudiment of a jugal. That bone, although large, does not make a finished
zygomatic arch in the Sloths; it does in the Armadillos; it is quite normal in,
Orycteropus. The most Crocodilian development of the hard palate takes place
in the Ant-bear and the Tamandua; in Cycloturus the pterygoids go quite as far back
as in the large kind, and are attached to strong basipterygoid processes of the basi-
occipital bone. In the Sloths, especially Cholopus didactylus, C. Hoffmanni, and
Bradypus tridactylus, the pterygoids are very large and long, and in the last kind
form a great “antrum” on each side. The basioccipital bones have considerable
basipterygoid processes with no bones attached to them.

In Dasypus, the Manidee, and in Orycteropus, the pterygoid bones are quite normal,
but in the genus Tatusia, amongst the Dasypodidee, the short, thick pterygoids add
somewhat to the hard palate.

The lacrymal is absent in the Pangolins, huge in the Aard-Vark and Armadillos,
and smallish in the Anteaters and Sloths.

The squamosal is pneumatic in all these types, adding a considerable upper gallery
to the tympanic chamber; this agrees well with what is seen in Marsupials and
Insectivores.

The os tympanicum is feebly developed in all the Edentata, about equal to what
we see in Marsupials and Insectivora, but in none is there any such enlargement of
the drum cavity as is seen in some Marsupials, and a few Insectivora, formed by a
growth of the alisphenoid and a large “os bull ;” nor from a special wing of the
basisphenoid, as in the Hedgehog and Tenrec.

Where there are several teeth, as in Armadillos and the Aard-Vark, then the stapes

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. ig

is normal; in the Sloths with fewer teeth, and in the toothless Anteaters and Pangolins,
the stapes is a short columella ; in the lesser Anteater and in the Sloth a slight per-
foration may take place after ossification, but this element is imperforate in the
cartilaginous stage. I cannot find that the fore part of Mecker’s cartilage forms

‘

any part of the “ramus,” as Insectivora and other normal Mammals; it seems
simply to become absorbed, as in the Sauropsida. The angular and coronoid processes
of the lower jaw are well developed in all except the Pangolins; in them these parts
are more aborted than in the Echidna.

Also in the early embryo of the Pangolin the chrondrocranium, instead of equalling
that of a Frog or a Skate, as it does in most kinds both of this Order and of the
Mammalia, generally, is very feebly developed, almost as much so as in Serpents and
Lizards, and, as in the Serpent, the orbitosphenoidal plate, at least its upper part, is
a separate patch of cartilage.

In the osseous stage, the Armadillos of the genus Tatusia have their alisphenoid in
two pieces, like the two separate tracts of the cartilaginous orbitosphenoid of the
Pangolin, and in this genus, contrary to the rule of the Edentata, but according to
the rule of the normal Mammalia, the 3rd branch of the 5th nerve notches the hind
margin of the alisphenoid.

In the others it primarily notches the outer margin of that free-edged plate,
although it often becomes enclosed in bone, afterwards, thus, passing, in the adult,
through a well-formed foramen ovale. Only in the Sloth do [ find a bar of bone
enclosing the space through which the 2nd branch of the 5th nerve passes out, thus
forming the foramen rotundum.

And only in the Sloth do I find the foramen opticum, which begins as a perfect
passage, surrounded by cartilage behind, converted afterwards into a mere notch,
thus opening into the sphenoidal fissure. This is primary in Marsupials, and excep-
tionally so in Sorex vulgaris amongst the Insectivora ; in that type the nerve may or
may not have a bony bar formed behind it, afterwards. This variation may occur in
the same individual, the right and left sides differing. But in Marsupials, as in
the Sauropsida, there is, normally, no postneural cartilaginous bar, either in the
cartilaginous or the bony stage.

I shall refer to this imperfect list of modifications of the skull of the Edentata

in my next and following papers.

‘se

II. On the Structure and Development of the Skull in the Mammalia.-—
Part II. Znseetivora.

By Witu1amM KitcHen Parker, P28.
Received January 15,—Read January 29, 1885.
[PLaTes 16--39. |

Tue skull in this low group of placental Mammals (Hutheria) is of great interest,
and, knowing this, I have lost no opportunity, for many years past, of procuring
specimens of all sorts, and of all ages and stages. The native kinds, namely, the
Hedgehog, Mole, and Shrew, form perhaps, on the whole, as instructive a group as
could be found anywhere; they are related, and yet distantly, and the Mole comes in
well between the generalised Hedgehog and the very specialised Shrew.

Ihave beea able to follow the Hedgehog and the Mole through a large series of
stages, and the Shrew in four—so that these native kinds will now have the history
of their skull fairly written out. But the exotic kinds of Insectivora do not yield a
jot, in interest, to those familiar to us here; these I have been less fortunate in
procuring. Yet I think that I can now offer to the Society a sufficiently detailed
account to serve, by the help of the more exhaustive account of the skull in the
native kinds, to give a clear idea of the morphology of the skull in the more important
Families of this most instructive Order.

Any chance of my ever staying my hand from working at the Insectivora, and
getting to work at other Orders, has simply arisen from failure of further materials,
as to embryos and early young, so absorbing did the study of these types become.

The materials* for this present paper have largely poured in during the last three
or four years ; although I have been collecting, as opportunity has served, for a long
time, many of my specimens have been waiting for twenty years, and some were
prepared forty years ago.

Yet I feel now, more than ever, that any attempt at working out the morphology
of the Mammalian type of skull would have been premature if I had not devoted
much time to the lower types of skull seen in the oviparous Vertebrata.

* My hearty thanks are due to my friends for these, namely, to Messrs. CARPENTER, CUNNINGHAM,
Dozson, Giinruer, Wavrer Huarr, T. Rurert Jones, J. Murray, R. Mason, Norcarg, Penrosr, Souru-
WELL, G. West, and Professor MosELey.

MDCCCLXXXV. R

122 MR. W. K, PARKER ON THE STRUCTURE AND

For although, of necessity, none of these lie directly below the Mammal, yet they
are of great profit to the student of Mammalian descent, when the mask of their own
particular specialisation has been removed, and that which is essential to the Verte-
brate is seen in each “ platform,” lower and still lower, so as to help the mind to form
some useful, if inadequate, idea of the lost types that did underlie, and indeed give
rise to, the existing Mammalia.

The Common Hedgehog, besides being more easily obtained than most kinds, is,
I feel certain, one of the most generalised types in the Order: it has escaped further
from the Metatherian border than some (e.g., Lhynchocyon), that nevertheless show
much greater signs of advance towards the higher Eutheria. Thus the various
characters seen in Hrinaceus are none of them so low as some to be seen in the type
just mentioned, whilst none are so high as others. On the whole I look upon this
genus as most normal, for the Order itself, as well as a good instance of a low Eutherian
type, with which to compare any of the higher and more specialised kinds—a sort of
useful supra-marsupial norma,*

BIBLIOGRAPHICAL LIST.

ALLMAN, Professor George J., F.R.S. “On Potamogale.” Trans. Zool. Soe., vol. vi.,
1869 ; plates 1, 2.

Aston, G.R. ‘On an undescribed Shrew from Central America.” Proc. Zool. Soc.,
1877, pp. 445, 446.

Anperson, John, M.D. ‘On the Osteology and Dentition of Hylomys.” Trans.
Zool. Soc., VIIL, Art. XTII., pp. 453-467 ; plate 64; 1874.

Austen, N. J. “On the Habits of the Water-Shrew ” (Crossopus fodiens). Proe.
Zool. Soc., 1865, pp. 519-521.

Barsoza pu Bocaag, Dr. J. V. ‘Sur quelques Mammifeéres rares et peu connus
d'Afrique Occidentale qui se trouvent au Muséum de Lisbonne.” (Bayona
velox.) Proc. Zool. Soc., 1865, pp. 401-404.

Branpt, J. F. “On Solenodon.” ‘Memoirs of the Imperial Academy of Sciences of
St. Petersburg,’ 1832-3.

Cours Exuiorr. “ Precursory Notes on American Insectivorous Mammals ;” with
description of new species. U.S. Survey.

Dosson, G. E., F.R.S. “A Monograph of the Insectivora.” London : 1882-3.

Git, THEODORE. “ Synopsis of Insectivorous Mammals.” ‘ Bulletin of the Geological
and Geographical Survey of the Territories ;’ No. 2, Second Series. Washington ;
May 14, 1875.

* The Metatheria (Marsupials) are now in hand; an account of their skull will form Part IV. The

Prototheria (Monotremes) will not be delayed longer than is absolutely necessary; if possible, their
skull will be described in Part V.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 123

Gray, J. E. “A Revision of the Species of Golden Moles” (Chrysochloris). Proce.
Zool. Soc., 1865, pp. 678-680,
GuintHer, Dr. Aupert, F.R.S.
1. * Description of a New Species of Chrysochloris from South Africa.” Proc.
Zool. Soc., April 6, 1875, plate 43, p. 311.
2. “ Remarks on some Indian, and more especially Bornean Mammals.” Proc.
Zool. Soc., May 16, t876 (Tupaia), plate 36, pp. 424--427.
3. “ Notes on some Japanese Mammalia.” Proc. Zool. Soc., June 1, 1880
(Urotrichus and Talpa), plate 42, pp. 440, 441.
4, “Notes on the Species of Ahynchocyon and Petrodromus.” Proce. Zool. Soc.,
1881, pp. 163, 164, plate 14,
Hearp, Watter. ‘On the Development of the Mole (Zalpa Europaa).”
‘Quarterly Journal of Microscopical Science, July, 1883.
Mivart, Professor St. Groras, F.R.S.
1. “ Notes on the Osteology of the Insectivora.” Journ. of Anat. and Phys., I.,
1867, pp. 281-312; II., 1868, pp. 117-154.
2. “ On Hemicentetes, a new Genus of Insectivora, with some additional Remarks
on the Osteology of that Order.” Proc, Zool. Soc., 1871, pp. 58-79.
Parker, W. K. “ Shoulder-girdle and Sternum.” Ray Soc., 1868 ; plates
27, 28, pp. 210-213.
Perers, W.
1. “ Neue Saéugthiergattungen aus den Insectenfressern und Nagern.” Monatsber.
Akad. Wissensch. Berlin: 1846, 257-259.
2. “Ueber die Siugthiere-Gattung Solenodon.” Abhandl. Akad. Wissensch.
Berlin : 1863-64, pp. 1-22; plates 1-3.
3. “ Ueber die Classification der Insectivora” (besonders Friculus, Echinogale
und Potamogale). Monatsber. Akad. Wissensch. Berlin: 1865, 286.
SuNDEVALL, C. J.‘ Ofersight af sliigtet Erinaceus.”. K. Vet. Akad. Handigr.,
Stockholm, 1841, pp. 215-240. Isis, 1845, pp. 273-280.

Tuomas, OLpFiELD, F.Z.8. ‘Description of a New Genus and two New Species
of Insectivora from Madagascar.” Jour. of Linn. Soc. (Zoology), vol. xvi,
pp. 819-322. (Read March 2, 1882.)

124 MR. W. K. PARKER ON THE STRUCTURE AND

The following are the stages worked out in Hrinaceus europaeus :—

First Stage. Embryo of Erinaceus ewropeus, about two-thirds ripe ; 14 inch
long.*

Second Stage. The same species, about three-fourths ripe ; 21 inches long.

Third Stage. New-born young of the same species ; 24 inches long.

Fourth Stage. Young Hedgehog, two weeks old, or thereabouts; 3 inches
long.

Fifth Stage. Young Hedgehog, about a month old; head 14 inch long.

Sixth Stage. Young Hedgehog, two-thirds grown.

Seventh Stage. Young Hedgehog of first winter.

Eighth Stage. Adult Hedgehog, nearly, or recently—not old.

First Stage of Evinaceus europeus; embryo two-thirds ripe; 14 inch long.
(Plate 17, figs. 1, 2.)

In this solid little embryo, with the “panniculus” formed, the prickles beginning
to project (Plate 16, figs. 8, 9), the chondrocranium (Plate 17, figs. 1, 2), is no longer
pure cartilage.t

a. Dissected endocranium.

The floor and sides of this skull-barye are well formed, except that large cracks or
fissures show themselves below ; it is almost as fully formed of cartilage as that of a
young Skate of the same size, but shows some very remarkable modifications that are
diagnostic of the Mammal. For instance, the nasal capsule runs along the whole
extent of the rostrum, or intertrabecula. The sides of the barge-like structure have
given way, right and left between the ear and the eye, or between the auditory capsule
and the orbitosphenoid (0.s.); thus the alisphenoids are squeezed, as it were, outside
the rest of the structure, as if part of a wall should bulge out and break away from
the “ coping-stone.”

To those two characteristics I may add the extensive plate of perforated cartilage
“eribriform plate”) for the multitudinous nerves proceeding from the “ rhinen-
cepbala.’t

This irregularly pyriform chondrocranium is a very extensive and complex structure,
through the union, with the cranium, proper, of the fore and hind sense-capsules.

* Tn all the measurements I exclude the tail, unless it is specially mentioned ; the length is from the
snout to the root of the tail, the length of the head and body, separately measured, being added together.

+ In my next instanee—the Mole—I shall give an account of that earlier stage, before any bony
deposit has appeared. (See Plate 25, figs. 1, 2.

$ The only other type that shows a cribriform plate is the Myzinoid (see Phil. Trans., Vol. 174,
Plate 17, fig. 4, p. 401); in that case, however, only jive nerves pass out on each side, through a
perforated membrane.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 125

The front pair, or olfactory capsules, are half the length of the skull (fig. 17, alm,
ale.) ; the hind pair, or auditory (ch/.), take up much of the skull in its hinder part,
aborting, by their implantation, a large amount of the inferolateral walls in front of
the occipital arch. The roof is so largely open, when the investing bones have been
removed, that the sides and base can be studied as well from the upper, as from the
under, face.

On the wnder face of the skull (fig. 1) I have figured three bones of the vomerine
series, although they belong to the investing bones; this is because of their peculiar
relation to the olfactory capsules, and especially the parts called “ JAconson’s organs.”

Beginning at the snout (fig. 1, al.n.), we see that the external nostrils (¢.n.)
are at present inferolateral in position, being seen better on the lower (fig. 1) than
on the upper face (fig. 2). Their direction is oblique, and they are extensive open
spaces. he rounded and emarginate fore end of the snout is followed by the coils
that surround the nostrils, which widen out and are marked off by a groove; behind
these coils, the snout enlarges on the under surface into two large flaps, that meet
in the middle at an obtuse angle, which, however, is cut away, so to speak, and made
acute by the sinuosity of the selvedge of the flaps. Here the labyrinth has its walls
pinched in, before it expands to form the swollen olfactory or ethmoidal region. The
margining hind flaps of the snout are only partially free, yet they overlap (or rather
grow under) the two pairs of cartilaginous growths into which they are developed,
backwards. The outer pair of cartilaginous growths simply form the general wall of
the capsule, here called aliseptal (a/.sp.); the sides of the capsule which are con-
fluent with the septum nasi, above (fig. 2), are tucked under, below ; and inside their
edges another tract of cartilage is seen of, apparently, the same width as this arrested
floor. This submarginal tract is the inferior turbinal (7.tb.) and is really very exten-
sive, aS we shall see in the sections (Plate 18); it arises as a longitudinal outgrowth
from the inner face of the outer wall, and is half the length of the entire labyrinth

There are also two submesial cartilages, three-fourths the size of the inferior
turbinals ; these are retral developments of the snout, and I call them simply the
“recurrent cartilages” (re.c.); they are, however, very important, being the proper
capsules of JAcopsoN’s organs. These tracts only partially close in above, forming a
sort of trough in which the organs of Jaconson lie. They are elegant, somewhat
sigmoid, long, revolute leaves of cartilage, with their convex face looking outwards
and downwards.

Each leafy part is supported by a bone, the form of which they dominate, so that
each tract is also hollow on the face that looks towards the curved inner edge of the
cartilage ; it hes on the inside, back to back to its fellow: these are the front, paired
vomers (v’.), and answer to the paired vomers of the Snake and Lizard among
Reptiles.*

* In the two latter these paired vomers are very curiously modified, and have over them an extra pair
of bones (septo-maxillaries), the two bones on each side forming a capsule to the organ of Jacorson,

126 MR. W. K. PARKER ON THE STRUCTURE AND

Between these front paired vomers, the proper azygous vomer (v.), which only appears

in highly specialised types—as Teleostei, Chelonians, certain Birds, and Mammals—
passes its fore end between and above the paired bones, and then becomes carinate
to rest upon the hard palate; it widens behind to support the olfactory capsule, where
are developed the so-called “ middle turbinals.”

The aliethmoidal, or the olfactory region (a/.c.), is divided right and left into a
large antero-superior lobe and a small postero-inferior, The latter contains the
hinder part of the middle turbinal folds (m.tb.), and the former the whole of the
upper, and the fore part of the middle turbinals. A deep, sinuous valley is seen
between this bilobate swelling, right and left, and the great orbitosphenoidal wings
(0.s.), whilst, laterally, the cranium is narrowed behind the lateral ethmoidal region,
and then swells out still more in the orbitosphenoidal. All the sinuosities of the
lateral outline of the endocranium are gentle and very elegant ; there are several in
the auditory and occipital region, where the “stern” of the barge-like skull narrows in.

The nasal labyrinth, on its lower aspect, shows some of its complexity through its
fissures ; where the floor of the capsule is bound by the vomerine forks (nf, v.), there
it is seen to run forwards, right and left of the vomer, as a spike of cartilage.

This will be seen in its full size in the sections ; I have called it the “ precurrent
cartilage” (see fig. 8, pe.c.); it may reach the recurrent cartilage (rc.c.), as in Orycteropus ;
here, however, it does not quite reach it. In the hooked angular space between the
larger and lesser swellings of the ethmoid the foremost outgrowth of the middle
turbinals (m.tb.) can be seen.

Between the forks of the vomer the basicranial beam shows itself; here it is com-
posed of all the three prepituitary rods, trabeculie, and intertrabecula ; its anatomical
names here are perpendicular ethinoid (p.e.), between the forks of the vomer ; pre-
sphenoid (p.s.), for a short distance behind the forks; and basisphenoid (b.s.) still
further back, where it is perforate ; a primary, oval, pituitary opening being left at this

¢

part. Right and left of that space we see the “sphenoidal fissure,” which allows a
number of cranial nerves to escape—third, fourth, part of the fifth, and the sixth.

The great orbitosphenoid (0.s.) has its moderately broad base or proximal part
divided off from the presphenoid merely by an inferior groove ; it curls round behind
the ethmoidal masses (a/.e.), widening, expanding, and becoming convex. Nearly
half-way towards the outer margin is seen the optic foramen (II.), which lies nearer
the hind than the front edge of the band. The free upper edge of the orbitosphenoid
(0.s.) is not seen in this figure (see fig. 2), but it can be seen that the wide upper part
is continuous with the nasal capsule (a/.e.) in front, and with the supra-auditory
region of the side wall of the skull (s.a.c.), behind.

In this early vegetative state of the endocranium there is something very flower-like
in its various parts, both as to their shapes and their development. Right and left of
which is only partly supported by the feeble, and sometimes detached, recurrent cartilage. The fact is
that these curious and enigmatical organs dominate different skeletal parts in different types.

”

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 127

the widening skull-beam (d.s.), now becoming parachordal, and also osseous, there is a
large leafy growth, a broad petaloid, ear-shaped tract; this is the free, outlying
alisphenoid («/.s.). This ‘ wing” is broadly faleate, the handle being made by the
cutting away of its proximal part to widen the sphenoidal fissure ; the blade has its
antero-external, sharp edge equal to a quadrant ; its point is somewhat rounded; and
its back, looking towards the auditory capsule (chl.), is gently coneave. This hinder
wing does not quite reach to the margin of the continuous skull-wall (0.s., s.a.c.).
Half-way from the pituitary opening (py.) to the edge, and nearer the hind than the
fore margin of the wing, we see the foramen ovale for the third branch of the
trigeminal nerve (V*.), but there is no separate passage, as yet, for the second—the
foramen rotundum.

One-third of the hind margin of the alisphenoid is ossified ; the bony matter forms
a selvedge both to the foramen and the hind edge of the wing. Also behind the
pituitary hole there is a pyriform ossification as large as the two alisphenoidal centres
together; its broad fore end is perforated—part of the pituitary space; this bone is
the basisphenoid (.s.).

Behind this bone the basis cranii shows three wide convex tracts, margined by a
lesser concavo-convex tract, right and left. The Jeast convex of the three main parts
is cut away, so to speak, right and left, in a perfect semicircle, by the more convex
masses, each margin being bevelled down to a sharpish edge. This region is the
“‘spheno-occipital synchondrosis,” which gradually becomes less and less until the basi-
sphenoid bone (b.s.) meets the basioccipital (b.0.),

The large swollen part and the lesser sinuous margins, right and left, both belong to
the auditory capsule, the inferior surface of which is well displayed in this aspect. The
cochlea (ch/.) shows three coils, in front of which there is a fissure through which vessels
pass, and also the 7th nerve, which runs inside the eave or outer thickening of the ear-
capsule under the tegmen tympani (f.ty.). That archway is ended by the epihyal
(e.hy.) in its confluence with the opisthotic region of the ear-capsule, and under it the
7th nerve (VII.) runs, and behind it this nerve escapes ; its exit is through the stylo-
mastoid foramen, and before its exit it gives off its returning fork, the chorda
tympani, In front of the epihyal the fenestra ovalis {/%.0.) is seen, behind it the
fenestra rotunda (f7.), and inside that the enlarged fissure for the 9th and 10th
nerves (LX., X.)

Behind this cranio-auditory chink, the occipital arch is perforated a little nearer the
mid-line, for the hypoglossal nerve (XII.), and behind the epihyal that arch has a
definite paroceipital thickening of an oval shape.

Here the lateral ossification (¢.0.) has taken up much of the tract between the par-
occipital swelling and the condyle (oc.c.); it reaches the condyloid foramen (XIT.).
The enlarged cartilaginous tracts, right and left, that form the condyles give the hind
margin of the basis cranii an emarginate outline; into this emargination under the

128 MR. W. K. PARKER ON THE STRUCTURE AND

foramen magnum (f.m.) the notochord (nc.) still projects. It is embedded in the
middle of a roughly pentagonal bony plate, the basioccipital ().0.).

The structure of this fundamental and most instructive skull will be still better
understood by referring to the upper aspect (fig. 2).

Here the snout (a/.n.) is seen to be much shorter than below, and partly pinched off
from the next or intermediate nasal region, the aliseptal (a/.sp.), which, in turn, passes
a little suddenly into the enlarged olfactory region, proper, the aliethmoidal (a/.e.).

Here all is finished, the crested intertrabecula being confluent with the nasal roofs
throughout their whole extent ; a peculiarly Mammalian structure. The hind margin
of the double labyrinth, above, is elegantly bracket-shaped, the proper roof ending
thick-edged, in front of the huge lozenge-shaped, perforated, secondary roof, or cribri-
form plate (cr.p.). The partition wall, septum nasi (s.7.), in front, and perpendicular
ethmoid (p.e.), behind, is, at first, scarcely apparent, above ; then in the aliseptal region
it thickens out considerably, and the tract between the upper turbinals does this again,
but to a lesser degree. This top of the wall thickens out in front of the cribriform
plate, to fill in the space between the retiring roof; it then, in the rhinencephalic
fossa, narrows considerably, to swell out again as the presphenoid (p.s.). The perfora-
tions for the olfactory nerves are simply countless, two crescentic rows lie back to
back, close to the septum, and then about five more valleys, full of holes, run forwards
and inwards from the postero-external margin of the great fossa. On a higher level
than this valley full of holes are the roots of the orbitosphenoids (0.s.) which are not
so broad as the basal beatin from which they arise, the presphenoidal region (p.s.) ;
these frond-like growths of cartilage run up to, and beyond, the most bulging part of
the skull in front, and form a good floor and wall to the region of the fore-brain.

Confluent with the edge of the cribriform plate in front, they are free behind, and
have a thrice-notched margin there; their selvedge looks upwards, and, in front,
melts into the general ethmoidal roof; whilst, behind, it is continuous with the large
pterotic or supra-auditory crest (s.a.c.), which in turn passes insensibly into the
supraoccipital (s.o.). The roof of this skull, therefore, although open, or only covered
by the investing bones, rests upon a complete rim of cartilage, from the top of the
perpendicular ethmoid, in front, to the middle of the supraoccipital cartilage, behind.

But the mid-brain rests upon the bulgin

Oo”
Sas

, broken wall of the hinder sphenoid, and
the alisphenoidal plate, right and left (q/.s.), is seen, in this view, away from the eye
and partly hidden by the orbitosphenoid (0.s.). Down in the floor we see the optic
passages (IT.), the sphenoidal fissure for various nerves (V!*.), the foramen ovale (V*.),
and the fissure between the cochlea (ch/.) and the alisphenoid, through the inner part
of which the internal carotid artery enters.

Then in the auditory capsule itself the sieve for the 7th and 8th nerves (VIL,
VIII.); between the capsule and the skull the posterior lacerated foramen for the 9th
and 10th nerves (IX., X.); and through the contiguous exoccipital tract the proper
foramen for the hypoglossal (XIL.).

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 129

Likewise we see the three posterior sphenoidal osseous centres (al.s., b.s.), the three
lower centres of the occipital arch (¢.0., b.0.), and, also, the two upper centres that form
this subsequently single keystone piece or proper supraoccipital (s.o.)—as distinct
from the interparietal which may coalesce with it.

Over the auditory capsule the pterotic band (s.a.c.) is notched ; behind that notch,
looking downward, we partly see the recess under the arch of the anterior canal for
the ‘ flocculus cerebelli.”

Visceral arches of First Stage.

The mandibular arch of this stage (Plate 22, figs. 1, 2, m/., mk., b.mn.) is a remark-
able structure, being composed of both an outer and an inner “ramus.” Part of the
epibranchial element of the first arch will afterwards be described as the pterygoid
cartilage, the only remnant of the huge overgrowth of this part seen in Selachians.
The quadrate region is greatly masked in this case—that of the Mammal—for the
orbital process or “ pedicle” is suppressed, and the small pterygoid remnant is far off,
forwards, whilst the small reduced quadrate segment is thrown into the same line,
along the under face, as the large, well-developed lower segment, the ceratobranchial
element, or articulo-Meckelian rod. Moreover, comparing the upper segment (incus
or quadratum) with that of a Newt we see that its attachment to the skull is simply
by the “otic process,” close in front of the ampulla of the horizontal semicircular
canal. Also this segment turns inwards below, behind its articulation with the free
mandible, and has a narrow-necked, dilated process to articulate with the dilated
remnant of the extrastapedial (the flat face on the head of the stapes).

The articular region of the endocranial mandible is already a “ malleus,” and
already the “ processus gracilis” is there as a delicate ectosteal plate under the neck
of the malleus, where the long, rounded part, or MecKeEt’s cartilage, begins. The
special development of the Mammalian skull, with its much-tilted, auditory capsule,
and closely-fitting lower face, makes that hinge vertica/, which is horizontal in all the
Oviparous types. A short process on the inside of the cartilaginous malleus answers
to the “posterior angular process ” of the mandible of the Bird ; whilst the ‘ internal
angular process” of the Bird, especially that of the Fowl-tribe (Gallinacew), is largely
developed, but tethered to the centre of a radiating plate, and acted upon by one
special mandibular adductor muscle, now called the “tensor tympani.” The rim of this
radiating plate is becoming cartilaginous, and is part of the jointed, cartilaginous
lining of the ear-passage (meatus), but is ready to become bone, even now ; it does
quickly become the “annulus tympanicus.” Here, at present, the mandible, proper,
or MecKEL’s cartilage, becomes more and more solid, forwards, and somewhat flattened ;
it is well-nigh equal, at this stage, to that of a Selachian. It becomes alate or dilated
near the end, and then, in a peculiarly Mammalian manner, unites with its fellow, and
the two are finished off in front by a long basimandibular spike (figs. 1, 2, ).2n.).
But this huge main rod already lies in a groove on the inside of a rapidly ossifying

MDCCCLXXXV. s

130 MR. W. K. PARKER ON THE STRUCTURE AND

cartilage, which has, already, the form of the maxilla cuferior of a Mammal, for the
coronoid, condyloid, and angular processes (cp., cd.p., ag.p.) ave present, although not
yet ossified. The rest of this superficial tract will be described in the palatal aspect
of the skull as the glenoidal facet for the articulation of this superficial and secondary
mandible.

The pharyngohyal element of the 2nd arch is already specialised into a stapes by
growing as a ring to the stapedial artery, which traverses the auditory capsule exactly
where this little, free nucleus, formed in the topmost part of the hyoid facial fold, is
fitting itself into the secondary fenestra of the auditory capsule much as a Bird’s
femur sets itself into the widely-perforated “acetabulum.” The next or epihyal tract
(ehy.) is already confluent with the auditory capsule (Plate 22, fig, 3, e.hy., au.), close
below the ampulla of the horizontal canal; the facial nerve (VIL) runs under the
bridge formed by this junction.

The ceratohyal (c.hy.) is divided through its middle, but is continuous with the
epihyai above ; and this tape-like structure divides again near its base, developing a
short subcrescentic segment, the hypohyal (h.hy.).

The dilated, semicircular basal element (b.A.br.) rather belongs to the 3rd, or 1st
proper branchial arch than to the hyoid ; it carries not only the hypohyals, but also
the thyrohyals (¢.4y.), short out-bent, thick-ended rods, that articulate with the
thyroid cartilage, and are the distal remnants of the abortive 3rd visceral arch.

When once we are well assured of the points just given, all the rest of the
Mammalian facial metamorphosis becomes easy to follow, and the “new things” thus
produced become the most valuable diagnostics of the normal Mammalian face and
jaws.

Amongst the /ow Eutheria no better type than this can be found ; as a Mammal, the
Hedgehog is very normal, yet it is much less specialised than several of its congeners,
especially our other native Insectivora.

First Stage (continued).—Vertically-transverse sections.

This stage will now be illustrated by a complete series of vertically-transverse
sections through all the tissues of the head.

Ist Sectzon (Plate 18, fig. 1).—This is in front of the septum and catches the pro-
jecting parts of the alze nasi (w/.n.), and the openings of the external nostrils (e.n.).

2nd Section (Plate 18, fig. 2).—This is close behind the external nostrils in the
narrow beginning of the nasal passages (n.p.). The septum here (s.7.) is but little due
to the fore part of the crested intertrabecula, it is mainly formed by the confluence
of the alinasal folds (a/.n.), back to back. This projecting part of the snout is grooved,
above and below, through this union of the convex faces of the cartilages, which have
made a partition thick above and thin below. Close to the openings of the nose the
ale are most complete at the sides, and the lower parts are tucked in where they

—” =

CS a

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 151

support the lower part of the deep uncinate chink, the nasal passage (7.p.). Over the
out-turned hook of the section a mucous crypt, one of the many small distinct nasal
glands (m.g.), are formed between the cartilage and the Schneiderian membrane.

3rd Section (Plate 18, fig. 3).—This is from the hind part of the mobile, rooting
snout, and here the upper lips begin to show themselves as depending lobes, the
hollow of the palate now being more definite. Here the intertrabecula is as round as
in an embryo Bird or a Shark; but here there has taken place what is not seen in the
projecting part, the “rostrum,” in those very diverse Ovipara, namely, that the
alinasal folds (a/.n.) are confluent with the foremost part of this precranial rod, which
now takes the name of septum nasi (s.z.). Here each nasal tube is surrounded by
cartilage, the alinasals having developed each into an almost complete tube, the lower
part of which projects downwards far below the low wall of partition ; the two folds rise
again, back to back, although they do not touch. Each sweeping fold of cartilage is
indented infero-laterally, in correspondence with the form of the nasal passage, which
is now trilobate ; a mucous crypt (see also fig. 2, m.g.) is seen outside the upper lobe.

In several sections, between this and No. 2, the lower part of the ale nasi had
joined back to back, and the whole snout was thus confluent in all its parts and
formed a complete double tube, or non-segmented proboscis ; sections of other types
(Mole and Shrew) well show this.*

4th Section (Plate 18, fig. 4).—This is from behind the flexible snout, and now the
investing bones, most of which were removed from the endocranium (Plate 17, figs. 1, 2),
are seen in section as thin films of bone. The solid intertrabecula, with its crest, and
the confluent aliseptal folds of the nasal labyrinth (a/.sp.), now form a strong septum
nasi (s.7.). The alee are now free at their lower edge, but are enlarged there into a
pedate process, which thrusts the lining skin inwards as a rounded lobe, looking
downwards ; this is the first appearance of the inferior turbinal (7.tb.)—its fore end.
The lower parts of the cartilage, towards the middle, are now free from the base of
the septum (s.v.), their section is a hook, the lamina just bending outwards, then
inwards, below, turning round to support JAcOoBsoN’s organ (/j.0.); here seen at its
fore end.

These curious submesial retral outgrowths of the ale nasi are the “recurrent
cartilages ” (rc.c.). Between these are the front paired vomers (v’.), the bony part of
this locally modified skeletal structure ; they converge below, and are thin uncinate
splints (see Plate 17, fig. 1, 2’).

The enlarging nasal passage (7.p.) gives off from its main, vertical part, two outer,
and one inner, “horn,” the latter turning inwards, below ; here and there a mucous
erypt is seen.

The nasals (7.) and the premaxillaries ( px.) now come into view. Below, the fore
part of the lower face is cut across, in front of the dentary, but through the basi-
mandibular cartilage (b.mn.), here nearly circular in section, a tooth-pulp (¢.) is cut

* The dotted line in fig. 2, shows where the cartilage is complete in the next section

s 2

132 MR. W. K. PARKER ON THE STRUCTURE AND

across on each side of the cartilage, and in the lower skin the bristles show their
bulbs.

5th Section (Plate 3, fig. 5).—Here the septum (s.7.) is deepening, and its intertra-
beecular base is Jess bulbous. The nasal labyrinth has thicker walls, and besides the
expanding rudiment of the inferior turbinal (7.tb.), farther up, the pointed fore end of
the nasal turbinal (7.tb.) is cut across; a crypt is seen below it, and below the
inferior turbinal. The skeletal pacts that protect Jacopson’s organs (j.0., 7¢.c, v.’)
are larger here, and the cartilage forms a complete tube for a short distance ; above
are the nasals (n.); at the sides, the bony laminze belong to both the premaxillaries
(px.) and maxillaries.

Below, the basimandibular cartilage (b.mn.) is depressed; close in front of the
Meckelian rods, right and left, a tooth-pulp (¢.) is seen.

6th Section (Plate 3, fig. 6).—The septum (s.7.) is now much higher, and the bulb at
the base much less; the side wall is very thick, for here the nasal turbinal inside
(al.sp.) is beginning to clear itself of the wall; below it the inferior turbinal rudiment
is still seen. Here and there a mucous crypt is seen, and here JAcoBsoN’s organ
(j.0.) lies in a fold of the recurrent cartilage (re.c.), behind the closed part, and behind
the front-paired vomers. The nasals and maxillaries (7., mx.) now show more clearly,
and the latter are developing the diploé, and are giving off the palatine plate.

Below, the dentary (d.) appears, outside the distinct large oval section of each
Meckelian rod (ms.).

7th Section (Plate 3, fig. 7).—This section shows several new things. The deep
septum (s.7.) is cut through at the junction of the septum nasi, proper, and the
perpendicular ethmoid, the part that becomes solidly ossified in Mammals, in the true
olfactory region. Under it the median vomer (v.) is seen, and JACOBSON’S organs
are small at this their hind part. The nasal passages (”.p.) are now becoming very
complex or labyrinthic ; this is due to the greater development of the various turbinal
folds, now that the section is through the proper olfactory region. The nasal turbinals
(v.tb.) are, here, sharp and turned outwards at their free edge, whilst at the sides the
wall is giving off new buds, and the inferior turbinal (7.tb.) is dying out. A remark-
able free cartilage (7.tb.), oval in section, is seen in the principal cavity, covered with
a mass of tissue, like the rest of the mucous and submucous lining. ‘This is a
process which grows forwards from the lower part of the labyrinth, from the region of
the middle turbinal. It is large, here, but much larger in Orycteropus (see Plate 15,
fig. 1), in which I have called it the precurrent cartilage (pe.c.). The vomer (v.), the
nasals and maxillaries (7.,7..) are well seen here.

8th Section (Plate 18, fig. 8).—In this partial section the labyrinth is cut through
just in front of the great olfactory fossze ; the perpendicular ethmoid (p.e.) has a
submoniliform outline, due to three successive bulgings. The rudiments of the
turbinal outgrowths are seen here, namely, the upper and middle turbinals
(w.tb., m.tb.), and outside the latter, and just distinct from it, the thick trihedral

open

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 133

mass—the precurrent cartilage (pc.c.) at its hind part; in the next section (fig. 9)
it forms the front projecting part, inwards, of the middle turbinal (m.tb.).

The vomer (v.) is here cut through its middle, where it is roughly carinate ;
afterwards, this part will rest on the palatine plates of the maxillaries. These bones
(mx.) have here developed a large alveolar cavity, and a tooth-pulp is seen in the
alveolus ; the nasals have their place taken by the frontals (f). In the last, and in
this, the mucous crypts (m.g.) are abundant, especially below. The large oval section
of MEcKEL’s cartilage (mk.) is now overgrown with the diploé of the dentary (d.),
which also is developing an alveolus, with its tooth.

9th Section (Plate 18, fig. 9).—Here another partial section is given through the
forepart of the eye-ball (e.), and the middle of the rhinencephalon which is giving off
its fibres through a mainly membranous cribiform plate (er.p.). Here the septum (p.e.)
is much lower, and beneath it the vomer (v.) is beginning to divide into its hind forks.

The folds of cartilage are, here, confluent, so that the nasal passage is now in several
sections, and at the lower part a section of the space is growing towards the cavity
of the other side ready to form the proper “nasopalatine canal.” The maxillaries
and dentaries (m., d.) have here large alveoli with their tooth-pulps; the superficial
bone, above, is the widening frontal.

10th Section (Plate 18, fig. 10).—This is another partial section, made through the
middle of the eye-ball (e.), and the hind part of the nasal labyrinth, with the huge
olfactory lobes (rhinencephala) overlying a membranous cribriform plate. The nasal
wall now forms a protection to the “ fossa,” and beneath the floor (nf) the cartilage
runs nearly up to the low dividing wall (p.e.). Here the labyrinth is reduced to
two passages (i.p.), besides the common nasopalatine canal (7.p.c.) at the mid-
line, below. Here the forks of the vomer (v.) are cut across, and at this part the
maxillary meets the palatine ( pa.) on the palatal floor; outside, the former bone (mz.)
shows its large alveolar plates, as does the dentary (d.), below. At this part the
frontal is in reality in two pieces, as the next stage will show; the orbital plate being
separate from the upper part (/.).

L1th Section (Plate 18, fig. 11).—This section is through the back part of the eye-
ball (e.) and the front third of the hemispheres (C!’.). Here the true cranium comes
into the section, for the basal beam is now the presphenoid (p.s.), and the wall right
and left is the orbitosphenoid (0.s.).

The back of the olfactory labyrinth (n.w.) is cut through, and these limited tracts of
cartilage lie between the two regions of the anterior sphenoid (0.s., p.s.), and are con-
fluent with the basal mass. So, also, is the orbitosphenoid confluent, above, with the
top of the olfactory wall (see Plate 17, figs. 1, 2). The relation of the orbital plate of
the frontal (f}) to the orbitosphenoid (0.s.) is well seen here ; below, the bones of the
palate are thick tracts, dividing on their inner edge into an upper and a lower plate to
embrace, and protect, the nasopalatine canal (v.p.c.); these are, now, the ptery-

goids (pg.).

134 MR. W. K. PARKER ON THE STRUCTURE AND

Below, outside the tongue (tg.) and mouth cavity (m.) the compound lower jaw is
seen to be composed of three tracts of cartilage and two of bone; the latter answer
to the dentary and splenial, but these are not actually separate bones, at this
part. Then there is MEcKEL’s cartilage, or the primary mandibie, and two points of
“ramus.”
12th Section (Plate 18, fig. 12).—Here the razor has cut through the anterior

cartilage belong to the superficial cartilaginous

sphenoid (p.s.), continuously, missing the small optic foramen (see Plate 17, figs. 1, 2,
0.8., p.8., L.), most likely cutting in front of it. Thus the cranial cavity and membranous
cranium is more than half engirdled by this tract ; the upper deficiency is, at present,
only partially made good by the frontal bone. Here we encounter cartilage right and
left, below the flat presphenoid (0.s.), for the pterygoids are cut through here, and
they are largely preformed in cartilage (see in next stage, Plate 17, fig. 3, pg., pg.c.).
These bones only forma wall, on the right hand, and on the left, to the nasopalatine
canal (7.p.c.), and do not form a bridge, beneath it, as the palatines do. The mandible
is growing up, here, towards its coronoid process, above, and its angular process (ag.p.),
below ; the inner rod (mk.) lies in a groove of the ramus, near its lower part.

13th Section (Plate 18, fig. 13).—This section will be understood if reference is made
to the dissected skull (Plate 17, figs. 1, 2). The basis cranii is cut through at the hind
part of the presphenoid (p.s.), just where the basisphenoidal region begins. Here the
two trabecule are cemented together by the wedge-like end of the intertrabecula.
The large sphenoidal fissure is cut through, and several nerve-bundles (V.) are
seen in the interspace; because of the sinuous form of the margin of the orbito-
sphenoid (0.s.) that cartilage is cut through twice, immediately in front of the ali-
sphenoid, which lies in a lower plnne. The bulk of the pterygoid is still cartilaginous,

and so is the *

ramus” of the mandible (d.) at this part, where the coronoid and
angular processes (c7.p., cd.p.) are cut across; Mecket’s cartilage (mk.) forms a
large oval section at this part, and the dentary is spreading over it; the frontal (f2) is
seen outside and above the orbitosphenoid (o.s.).

14th Section (Plate 18, fig. 14).—This is a very instructive section and should be
compared with the dissection of the same and of the next stage (Plate 17, figs. 1, 2, 3).
The cranial cavity with the included brain (C") is here very large, and the basal part
of the skull is cut through where the floor is incomplete (b.s., py.), so that we have
here the exact form of the trabecule behind the intertrabecula; they are oval, with
the long axis horizontal. On each side, in a deep fossa, the great Gasserian ganglion
(V.) is seen, supported by the alisphenoid (q/.s.) which lies outside and below the
general plane of the skull floor and wall; it is ossified at its postero-external margin,
and its hollow upper face forms the floor of the trigeminal fossa. The orbitosphenoid
(0.8.) is narrowing towards its posterior band, and it is supported outside by the orbital
part of the frontal (#1), which runs far down into the hind part of the orbit, almost
touching the alisphenoid.

Two rods of cartilage, oval in section, but with their long axis vertical, are seen

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 135

under the basis cranii and protecting the narrow nasopalatine canal (i.p.c.); these
are the pterygoids (pg.c.) in their unossitied free part (“hamular process”). Outside,
and below, we see a part of the squamosal, its zyomatie region on the jugal (j.) ; and
inside it the glenoid facet (g/.c.) is cut along its whole transverse extent. A little
below it a section of cartilage appears, thick above and below and narrower in the
middle; this is the main part of the great superficial slab, a segment of which is
given off to form the glenoidal facet. The upper part is the condyle of the lower
jaw (cd.p.), the lower is part of the angle (wg.p.); the inside of the cartilage is
becoming bony ; in the concavity, on the lower part of the inner side, MEcKEL’s
cartilage (mk.) is still full-sized.

15th Section (Plate 18, fig. 15)—-Here the fore brain (C'.) is cut through near the
infundibulum, but the pituitary body (py.) is seen as a large separate quasi-glandular
mass resting upon the basis cranii near the beginning of the parachordals or investing
mass ().s.). These are flattish and ovoidal in section, the interspace between them
being the primary pituitary space at its hinder part. On the side, the orbitosphenoid
(o.s.) is still seen as a considerable band of cartilage; this is near the junction of the
frontal (f) and parietal bones. The Gasserian ganglion (V.) is cut across in its
hinder part, and the razor has caught the cochlea (above 7.c.) in its fore margin. This
is behind the hinge of the secondary mandible, and through the part of MrecKkenr’s
cartilage where the bony lamina that forms the ossifying centre of the malleus (m/.)
has appeared. Outside this the postglenoid part of the squamosal (sq.) is seen, and,
between the two, the foremost part of the tympanic cavity (c.ty.). The internal
carotid artery (i.c.) is seen entering the skull between the cochlea and the basi-
sphenoid (b.s.), and under it the Eustachian tube (ew.) is laid open as it is passing
towards the fauces or back part of the oval cavity (phw.); it opens into that cavity
between this and the last section (fig. 14).

Under this tube the cartilaginous lining of the first cleft is seen to extend (ew.c.) ;
this Eustachian cartilage is the innermost part of the partly segmented cartilaginous
tube which expands externally as the “ concha,” and which, in the part next outside
the Eustachian cartilage, becomes ossified, early, as the annulus tympanicus.

Four arterial branches are seen, here, cut obliquely across, one of them close beneath
and outside an oval section of cartilage, the ceratohyal (c.hy.). The one above it is
that part of the “common carotid” which gives off the “ stapedial artery,” to inosculate
with the artery of the lower jaw.

At the mid-line, below the palatouasal cavity, the pharynx is laid open, and right
and below it the hypohyal cartilages (h.hy.). Outside and in front of the cerato-
hyal the chorda tympant (VII“) is cut across, and outside and below these the main
facial nerve (VIT.).

16th Section (Plate 18, fig. 16).—This is through the widest part of the hemispheres
(C'”.), and also cuts across the large glandiform pituitary body (py.). Several large
uervous masses are cut through (VIL, VII.), close to the top of each cochlea (chl.). The

136 MR. W. K. PARKER ON THE STRUCTURE AND

basisphenoidal cartilage (b.s.) has a film of bone in it above and below; its outer edges
are beginning to coalesce with the cochlea, which are laid open. The orbitospbenoidal
band (0.s’.) is still large, and is separated by a large space from the inferolateral parts.
The processus gracilis has still a solid cartilage lying on it (ml.); outside this is
the postglenoid part of the squamosal. The meatus auditorius externus is partly
laid open, and the Eustachian cartilage (m.c.) is still seen under the cavum
tympani (c.ty.), which is here still partly the Eustachian tube. Beneath the
middle of these parts the epihyal (e.hy.) is cut across, and outside it the chorda
tympani (VII*.), with the main facial nerve (VII.) lower down, is exposed. The
larynx is below the pharynx (lz., phx.), and there is seen a film of bone outside,
the ramus (d.); a part of the cartilaginous framework of the larynx is seen in section.

17th Section (Plate 18, fig. 17).—This is another important slice, showing many
things. It is in front of the junction ‘of the orbitosphenoid with the crest on
the top of the auditory capsule ; the cochlea (ch/.) is near its widest part, it is just
in front of the proximate coil. We are now behind the great trigeminal nerve, with
its roots, ganglion, and branches, but the nerves proceeding from the ganglion geni-
culatum (VII., VIII.) are cut across, and the facial nerve (VII.) has entered its
“aqueductus.” The same nerve (VII.), and its inosculating anterior branch, the
chorda tympani, are seen outside the epihyal (ey. VII.).* Here the great meatus
externus (m.a.e.) is fairly laid open, and it is seen to be lined with cartilage
throughout ; it is indeed one more or less segmented tube, from the opening of
the Eustachian tube, within, to the conchal expansion, without. The pituitary
body (py.) is cut through in its hind part; the malleus, or dilated end of Mrcxet’s
cartilage (ml.), is partly seen, its head and the tip of the manubrium (mb.); the
rest of that process is indicated on the right side by a dotted line. The archway
over the facial nerve (VII.) is the fore part of the tegmen tympani, inside the head
of the malleus. The postglenoid part of the squamosal is seen, and on right and left
of the pharynx (phx.) the hypohyals (h.hy.).

18th Section (Plate 18, fig, 18).—This section is through the basis cranii where
the sphenoidal (b.s.) and occipital regions meet. The orbitosphenoidal cartilage has
here passed into the supra-auditory (s.«.c.), where this great crest is continuous with
the top of the auditory capsule. The left side of the figure is from a point in
front of the right, so that this section serves instead of two. ‘The left side is
through the base of the cochlea (ch/.), but in front of the cavity of the vestibule.
The cartilage lining the meatus externus (m.c.) is seen both in the outer opening and
under the dagger-shaped section of the cavum tympani (c.ty.); a small cavity at
present lying in the midst of a mass of indifferent tissue. The solid cartilage of the
‘“pterotic” region, close in front of the anterior semicircular canal (see the other
side «.s.c.), is not perforated until we come to the beginning of the aqueductus for
the facial nerve (VIL), which is cut across twice on the right side, both where it

* The lines are misdirected in this part of the figure.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 137

perforates the capsule, and where it begins its course under the tegmen, which is
imperfect here in its front part. At some distance below this auditory eave the
head of the malleus (ml.) is seen in section along the whole course of the
manubrium on the left side. Under the tympanic cavity and its cartilaginous floor
the epihyal (e.hy.) and its accompanying nerves, the chorda tympani and facial trunk
(VII, VII.) are seen cut across, and the hypohyal and thyroid cartilage (h.hy., lx.)
at the mid-line, below. On the left side the cartilage above the cochlea (ch/.) is
perforated by the facial and auditory nerves (VIII), and the right side has part of
the anterior canal (a.s.c.) visible.

There the tegmen is perfect, and the main part of the incus and its long crus is cut
through, the manubrium mallei (m/.) appearing beyond and below it. The hyoid and
its nerves are similar to what is seen on the other side, for the obliquity of this
section is very slight.

19th Section (Plate 18, fig. 19).—This partial section is one of the most important
in the series. The parietal (p.) is seen outside the pterotic or supra-auditory cartilage
(s.a.c.), but the squamosal which was seen in the last (fig. 18) is not figured. The
arch of the anterior, and the ampulla of the horizontal, semicircular canals (a.s.c., /.8.c.)
are cut through, besides several other spaces in the vestibule and proximal part of the
cochlea. The wall of the cochlea is cut through in front of the band of cartilage that
divides the fenestra ovalis from the fenestra rotunda, a band which in the Sauropsida
is uniformly ossified by the opisthotic centre; in Mammals that centre is much more
potent, and may, as in the next instance (Zalpa), ossify nearly all the proper capsule.
The auditory nerve and its ganglion (g. cochleare, VIII.) are seen in the meatus
internus, and externally the stapes (st.) by its base fills the fenestra ovalis. The
articular part or head of the stapes, which was nearly in view inside the long crus of
the incus on the right side of the last section (fig. 18) is now cut clean through, and
the stapedial artery (st.a.) is seen traversing the foot-hole of the stapes, on its way to
the inside of the maxilla inferior. This section is at the back part of the meatus
externus, and at the end of the tympanic cavity, so that here the epihyal (e.hy.) is
seen already confluent with the hind part of the tegmen ; the foramen stylo-mastoideum
is laid open and the facial nerve (VII.) is seen running downwards behind and outside
the epihyal, and the cavity of the tympanum (c.ty.) is seen inside, close to the artery.
The larynx (/z.) is seen below at the mid-line, and the basioccipital floor (b.0.) under
the hind-brain (C*).

20th Section (Plate 18, fig. 20)—Here the supra-auditory cartilage (s.a.c.) is close
to the supraoccipital, and the film of bone outside belongs to the squamosal (sq.).

The anterior and horizontal canals (a.s.c., h.s.c.) are cut across, and the hind part of
the vestibule at its junction with the cochlea.

The head of the epihyal is seen finishing the tegmen (t.ty.), behind, and the narrow
hind part of the cavum tympani (c.ty.) is shown, here, for the last time. The flat form
of the parachordals (b.0.), inclosing the notochord, is seen under the hind-brain (C’).

MDCCCLXXXV. T

138 MR. W. K. PARKER ON THE STRUCTURE AND

21st Section (Plate 18, fig. 21).—The anterior canal (a.s.c.) is here cut through where
it joins the posterior, and the horizontal canal (h.s.c.) is seen where it opens into the
cavity of the vestibule (lower part of vb.); the wall is imperfect on the inner side
(see also next stage, Plate 17, fig. 7). The lowest part of the posterior canal, and
its ampulla, is close behind this part. The posterior lacerated foramen (IX., X.) is
here cut across, and also the condyloid foramen (XII.) ; the basis cranii (.0.) is large,
here, and partly ossified. .

22nd Section (Plate 18, fig. 22).—The thick opisthotic region of the auditory capsule
is cut across, here, and the posterior canal at its beginning, above, is one with the
anterior canal (a.s.c.) ; below, it is close to the horizoutal canal (h.s.c.). On the inner
face the cartilage is thin, and there is a small vestibular cavity (vb.). The supra-
auditory cartilage (s.a.c.) is so cut across as to be some distance from the top of
the capsule; this is due to the shght obliquity of the sections. The vagus and
hypoglossal nerves (XI., X.) are still seen outside the bent basioccipital plate (b.0.).
This section is in front of the sides and condyles of the occipital arch, and is behind
the hole for the 12th nerve (XI1.).

Second Stage of Erinaceus europeus. Young, three-fourths ripe ; 24 inches long ;
head, * cinch.

This larger embryo serves well for showing the development of the ectocranium as
well as for the advancement made in the endocranium (Plate 17, figs. 3-8). Beginning
with the voof (fig. 4) we find a very orderly series of bony scutes along the mid-line ;
there are four pairs of these sub-median radiating centres that have all the appearance
of belonging to the same category, namely, a double row of subcutaneous scales
growing towards each other along the top of the head.

The foremost of these scutes, the nasals (n.), ave the smallest, they ave the tiling of
the cartilaginous nasal roof, and the septum nasi (s.7.) is seen between them. Like
shell-valves, with a pointed end, forwards, and a rounded broad end, behind, these
bones just cover the hinder half of the nasal labyrinth.

The next pair are four times as large, these are the frontals (7); they are narrow
in the middle and dilated at each end; they scarcely reach the nasals, in front, and
only touch the parietals (p.), behind, by their convex margin. There is a long
fontanelle running between them and the parietals up to the nasals, in front, and to
the supraoccipital (s.o.), behind; this is dilated in three places, especially in the
coronal region. The concave outer edge of the frontal does not run as far as to the
supraorbital ridge; this part and the orbital roof are covered with a distinct bone
(see also fig. 5, s.ob.). This single supraorbital scale bone is new to me in the
Mammalia, but familiar enough in the Oviparous forms—the Ganoid Fishes, below,
up to the Tinamous and some higher Carinate Birds, above. In all these, however,

it is broken up into two or more pieces.

DEVELOPMENT Of THE SKULL IN THE MAMMALIA. 139

The parietals (p.) are nearly twice as large as the frontals, and, behind them, the
interparietals (7.p.) are not much larger than the nasals (7.).

Besides the supraorbitals, the lateral and infero-lateral bones seen in this view are
the premaxillaries, maxillaries, lachrymals, jugals, and squamosals (pa., mx.; see also
fio. 3, 1., 7., sq.), these are better seen in the other views (figs. 3, 5, 6).

In the side view (fig. 5) the premaxillaries (pa.) are seen to be of normal size,
mounting upwards obliquely, and wedged in between the nasals and maxillaries above.
The outer or facial part of the maxillary is large, with its very large infraorbital
foramen (V*.) and its long concave preorbital and suborbital edge. Over the former
part the fore end of the supra-orbital (s.0b.) fits, and inside, below this, the smallish
perforated lachrymal scale (/., /.c), The jugal (7.) is a small thickish style, and is over-
lapped both by the jugal process of the maxillary and of the squamosal (m«., sq).
Where the uncinate supraorbital (s.ob.) and the swollen parietal (p.) meet in the post-
orbital region there the squamosal is seen, the fore part of its temporal plate, which
walls in the temporal fossa, it begins there, and the bone, dilating gently backwards, is
trifid behind, in its postglenoid end, where it just hides the ampullz of the anterior
and horizontal canals (q.s.c., h.s.c.) The parietals and interparietals (p., 7p.) meet over
the arched junction of the anterior and posterior canals (@.8.¢., p.s.¢.).

But the peculiarly normal Mammalian state of the superficial bones is best seen in
the lower view (Plate 17, fig. 3).

Here the increasingly perfect desmognathism of the skull and the great develop-
ment of tooth-pulps, asking for large sockets, are the factors that make the normal
Mammalian palatofacial structures so different from their counterparts in the Ovipara,
generally. Add to these the metamorphosis of the mandible, giving the last finish to
a face with limited motion, and we get the reasons for much that is novel in this type
of skull.

The premaxillaries (pz.) are largely hollowed out for the teeth, and their palatine
processes are, at present, short and small. The maxillaries (m.) send inwards a large
flange from their inner alveolar plate; beyond this, to the mid-line, another equally
large tract has been developed, the palatine plate ; it is joimed to the outer plate by a
broadish isthmus, and is never quite distinct from it. The palatine plate of the
palatine (pa.) is three-fifths the size of that of the maxillaries, and is perforated behind
its middle. The two bones wedge in between the maxillaries at the mid-line, and at
their hind part are deficient there. Outside they are thick, where they ascend to the
basis craniti.

The pterygoids (pg.) are merely small ectosteal tracts fastening upon and transforming
the thick, shori, rounded pterygoid cartilages (pg.c.), and spreading above them to
plaster the basisphenoid (b.s.) with a thin bony tract.

The lower edge of the jugals and squamosals (j., sq.) are seen in this aspect, the
latter is largely hidden by the wide three-lobed glenoid facet (gl.c.), which is placed
transversely to the axis of the skull.

140 MR. W. K. PARKER ON THE STRUCTURE AND

The end view (Plate 17, fig. 6) shows the roughly-oval interparietals, and the hind
part of the parietals and squamosals (/.p., p., sq.) as they fit on to the auditory and
occipital regions of the endocranium.

But a lower view of the upper palate, after the hard palate has been removed
(Plate 17, fig. 8), shows three more investing bones, namely, the front paired vomers
(v’.), and the vomer, proper (v.).

These paired bones are quite distinct from the palatine processes of the premaxil-
laries, and are delicate, narrow laminze, with an outside hook in front ; they are placed
vertically inside the recurrent cartilages (re.c.) and JACOBSON’s organs.

Wedging in between their hinder part we see the narrow, bifid fore end of the main
vomer (v.), which is roughly carinate in its fore half, and then flattens out, and is
alate in its hind half where it is applied, right and left, as an ethmoidal splint, serving
to bind the right and left floors of the nasal labyrinth together, as in Passerine
Birds ; this upper junction of the right and left halves of the face has been called
“ (Kgithognathism,” because of its peculiar development in Passerine Birds.

Eidocranium of Second Stage of Erinaceus europeus.

In the figure just referred to (Plate 17, fig. 8) we see the lower view of the alinasal
cartilages (a/.7.) and the outer nostrils (e.7.). Constricted suddenly, these parts give
off the neck of the curious, tongue-shaped recurrent cartilage (re.c.), which at its
fullest part grows quite round Jacopson’s organ (see Plate 18, fig. 5). Behind these
the floor of the nasal capsule, under the “ middle turbinals” (pc.c., the “ precurrent
cartilages”), is partly shown, and then the narrow, unossified mesethmoidal (p.e.), and
presphenoidal region (p.s.), and the very wide, ossified basisphenoidal (b.s.). This
bony plate is transversely oval and is perforated in front; this hole is the pituitary
space (py.).

In the /ower view (Plate 17, fig. 3), behind the hard palate, the endocranium is well
shown ; it is a broad osseo-cartilaginous structure. At the mid-line the presphenoid
and basisphenoid (p.s., b-s., also shown in fig. 8) come into view, but the latter is partly
hidden by the pterygoids ( pg., pg.c.), outside which the base of each alisphenoid (a/.s.)
swells into an egg-like process (e.pg., or “external pterygoid”), much more distinct,
now, than in the first stage (fig. 1).* Outside this swelling the cartilage is largely
ossified as the alisphenoid (a/.s.), which is perforated nearer its hinder, than its fore,
margin, by the 3rd branch of the 5th nerve (V*.); the rest of this nerve (V2)
escapes through the sphenoidal fissure.

The outer part of the orbitosphenoidal bony centre (0.s.) is just seen in front of the

* This part is similar to what is seen in the embryo (uterine) of Didelphys, and the counterpart of
which does develop even in some Insectivora (e.g., Rhyncocyon, Plate 36, fig. 5) into an “ anterior
tympanic recess,” or alisphenoidal bulla; this, however, in the Hedgehog becomes the external pterygoid

plate; a part which, in Kangaroos, co-exists with the tympanic wing of the alisphenoid.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA, 141

fissure; these parts will be better shown in the section (fig. 7). Where the wide
posterior sphenoid joins the auditory capsules (see also fig. 1) there we see a wide
transverse territory of cartilage, which, at its middie part, is the very extensive spheno-
occipital synchondrosis.

Externally, it is notched, here, where the permanent “ foramen lacerum,” or jagged
passage, will be ; and nearer the mid-line it is perforated, right and left, by the internal
carotid artery (v.c.). Although the cochle (ch/.) show their form well, their cartilage is
confluent with that of the skull, proper, except behind, where the “ foramen lacerum
posterius ” will be, which is now a large oval hole formed by the 9th and 10th nerves
(IX., X.). The notched space in front of the capsule allows of the exit of the facial
nerve (VIL), the proximal part of which is not drawn in the figure; it is seen further
back under the tegmen tympani (¢.ty.), and then passing under the epihyal (e.hy.) to
escape through the stylomastoid foramen. On the side of each cochlea the stapes (st.)
is seen 7m situ, and behind the cochlea the foramerm ‘riundum (f7.). Behind this the
occipital arch shows a swelling, a rudimentary “ pai?xcipital.” Inside that eminence
the 12th nerve (XII.) passes through the condyloid foramen, which is almost sur-
rounded by the rudimentary exoccipital cetere. They,.‘\sioccipital (b.0.) is very

teptilian, being roughly pentagonal ; it is still marked by the notochord (nzc.).

The occipital condyles (o0c.c.) have a very Batrachian appearance, not being very
prominent, and very wide apart.

From the upper view (fig. 4) not much of the endocranium is seen, but the ali-
nasal region (a/.n.) is seen to have developed into a projecting snout, much longer
than in the early stage (fig. 2). Behind, the supraoccipital bone (s.o.) has become
single, and right and left of it the cartilage passes into the supra-auditory crest,
and the proper auditory capsule with its canals (p.s.c., h.s.c., 0.5.¢.).

In the side view (fig. 5) the projecting snout and nostril (a/.n., ev.) is seen,
and the valvular folds covering the nostril. In the orbit the lower frontal (s.0b.)
ossicle fails to cover the orbitosphenoidal cartilage (0.s.) with its orbital plate.
Below, the thick bulbous process of the alisphenoid (e.pg.) and the pterygoid nucleus
(pg.c.) are seen, and, behind, the outer face of the auditory capsule, with its canals
(a.8.¢., h.s.c., p.s.c.) 1s well shown, and also the tegmen tympani, and part of the
cochlea (ch/.). The epihyal (e.hy.) is confluent with the capsule behind the tegmen,
and the facial nerve (VII.) emerges behind it. Behind this stylomastoid foramen,
the paroccipital eminence, the condyle (oc.c.), the exoccipital (e.0.), and the supra-
occipital (s.0.) come into view.

So do those parts in the end view (fig. 6), where, however, they are displayed more
fully ; here especially we see how large the great foramen (jm.) is, as compared
with the hind skull, even with the investing bones (p., 7.p., sq.) still m place.

But the most instructive view of the endocranium is to be had by bisecting the
skull, vertically (fig. 7).

Now we see what a mere tube this skull is, even in the embryo, and also that the

142 MR. W. K. PARKER ON THE STRUCTURE AND

chondrocranium is nearly as perfect as in a Skate. Yet every true Mammalian
character is to be seen, well developed, and diagnostic.

The cranio-facial axis has two bones in its hinder third, not much larger than
the “synchondrosis” that separates them; these are the basioccipital and the basi-
sphenoid (b.0., b.s.) ; all the rest forward is pro-chordal, and composes the presphenoidal,
ethmoidal, and septal regions of the skull (p.s., p.e., s.7.).

The septum runs forwards, between the folds of the alinasal cartilage (ql.n.) in
front, a roundish part, perfect, or nearly so; then a narrow isthmus unites this part
with the proper septum nasi (s.n.), which passes, at present, without change into
the perpendicular ethmoid (p.e.), and this into the presphenoid (p.s.). This large
partition wall is a low triangle, the apex of which forms the rudiment of the crista
galli (cr.g.). The fore part, above, is continuous with the nasal roof (al.e., al.sp., al.n.) ;
the hind part divides the two great olfactory “possi, with their hollow, eribriform
floor (er.p.). The basal part of t{ great wall vs thick, this arises from the primary
solidity of the intertrabecula. §Vhere the alee nasi («/.n.) seem to end below, there
they give off the recurrent caftilages (re.c.), and these are strengthened by their
special splints, the anterior faired vomers (fig. 8, v’.); behind these, the intertrabecula
is supported by the large grooved vomer, proper (v.). From the crista galli (er.g.) to
the foramen magnum there is one continuous growth of solid cartilage, the fore part
of which becomes the crest of the orbitosphenoid (0.s.). Up to the sphenoidal fissure
(V'*.) the cartilage runs from the base to the top without any break save the
foramen opticum (II.), which passage is now enclosed in the wedge-shaped orbito-
sphenoidal bony centre (0.s.). This beginning of a large plate takes up all but the
lowest part of the stem of the great orbital wing, but only reaches one-third of the
way to the sinuous upper edge of the cartilage. Hence, a full fourth of the whole
side wall has given way outwards, and the top of the cartilaginous wall reduced to one
half its depth, forms an elegant archway over this breach; it is a very perfect arch,
but leans a little forwards. This doorway is only partly shut above by the ali-
sphenoid (al.s.), the part which has been thrust out; the lower half of this half-
opened valve is ossified, and the lower edge of the bony part has a large notch in it,
behind the middle ; this notch is finished by cartilage, and is the foramen ovale (V*.).
The basisphenoid ().s.) is growing into this tract of cartilage, and reaches further
backwards than the alisphenoid.

The cartilaginous side wall has then a second great archway larger than that caused
by the out-thrust of the alisphenoid ; here there is an actual suppression of the wall,
but the space, which looks a little backwards, is filled in by the large ovoidal cartila-
ginous auditory capsule. Over the capsule the cartilage is thinned out by pressure
of the lateral sinus (/.s.), which forms as perfect an arch as that over the alisphe-
noid. Under the arched swelling caused by the anterior and posterior semicircular
canals, which meet above, there is but a shallow concavity for the flocculus cerebelli.
Behind this hollow, there is an unciform opening, with its convex margin behind ; this

deficiency is caused by the “ recessus labyrinthi.”

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 145

The multiperforate meatus internus, further forwards, and the swollen proximal part
of the cochlea (ch/.), are well seen in this view, over the long spheno-occipital syno-
chondrosis. Between these tracts the bony and cartilaginous parts of the occipital
arch (s.0., ¢.0., b.o.), the passages for the postauditory nerves, and the occipital
condyle (oc.c.) are seen.

Visceral arches of the Second Stage.

The compound mandible has developed considerably since the last stage (Plate 22,
fig. 4), the dentary bone (d.) having grown round MrcKev’s cartilage (mk.) for some
distance, in its middle part, and the upper edge of the bone is now hollowing out to
form the tooth sockets. In front, the basimandibular (b.mn.) is less, and it is now
well defended by bone on its outside. Behind, the trilobate, semicartilaginous
“ramus” has assumed its permanent form, although the coronoid and angular processes
are equally cartilaginous with the condyloid or articular part. Under the latter,
MECKEL’s cartilage is being let into the bony plate ; behind this part it arches upwards,
and below the arched part the ectosteal malleai centre (m/. = articulare externum)
is enlarging. The malleal part of this primary mandible shows a small but distinct
posterior angular process (p.ag.), as the elbow of the manubrium (mb.), or internal
angular process.. The incus (7.) and the stapes (sf.) are still quite unossified, but they
are assuming their permanent form,

The annulus tympanicus (a.ty.) is a ecrescentic band of not very solid cartilage,
which is becoming bony along the middle; this bony tract will use up all the
cartilage, not leaving any to form a “ bulla.”

Third Stage of the Skull of Evinaceus europeus ; new-born young, 23 inches long.

In the “endocranium” at this stage we find a considerable advancement in growth ;
seen from below (Plate 19, fig. 1), and from above (fig. 2), it is roughly pyriform in out-
line, gradually enlarging up to the auditory region, and then suddenly lessening. The
short snout (fig. 1, a/.n.) has the nostrils (en.) lateral; this region has a definite
bracket-shaped selvedge where it comes in contact with the premaxillaries, and from
the submesial part of this hind edge the recurrent cartilages (7c.c.) are given off ;
these are large tongue-like tracts, convex infero-laterally and concave on the upper and
inner face, where, for a short distance, they form a perfect tube round each J ACOBSON’S
organ. They are supported on their inner face by the dagger-shaped front paired
vomers (v”.), whilst the vomer, proper (v.), runs in between them in front. That bone,
overlapping these parts in their hinder third, runs backward to the end of the
right and left subcranial recesses of the nasal labyrinth ; it is widely forked in its
hinder, and strongly carinate in its middle, third.

The aliseptal region (a/.sp.) narrows in at its middle, and then expands again to
become aliethmoidal (c/.e.).

144 MR. W. K. PARKER ON THE STRUCTURE AND

The inferior turbinals (7.th.) arise from its inner face, and can be seen in the space
right and left of the vomer. Where the vomer forks, there each fork supports the
inturned nasal wall, now the floor (7.f-), which is finished by the vomer. In the front
of this part the inturned walls give off the “ precurrent cartilages,” already de-
scribed. At present, the hinder region of the nasal labyrinth forms merely part of a
scroll, and has not yet closed in to finish the hinder recess. The very solid basal beam
is seen between the forks of the vomer, first as perpendicular ethmoid (p.e.), and then
as presphenoid (p.s.). The proximal part of the orbitosphenoid is hidden by the
recesses of the nasal labyrinth, the bony centre (o0.s.), can, however, be seen in its
upper part.

On a lower plane, the large alisphenoids (a/.s.), with their oblique sinuous outer
margin, are seen now to be largely ossified ; these bony plates are perforated by the
3rd branch of the 5th nerve (V*.), for they have a large foramen ovale a little behind
their middle. Between these wings and the basisphenoid (b.s.) there are still two
remarkable tracts of cartilage, one of these is the large synchondrosis between the
ale and the base, and the other is a button-shaped projection (e.pg.), between the
pterygoid (pg., pg.c.) and the foramen ovale (V*.), but a little in front of both.

This projection is the cartilaginous rudiment of the external pterygoid plate, which
in this broad-floored skull is in its normally Mammalian position, namely, a good
distance outside the correlated pterygoid, with its independent cartilaginous nucleus.*

In this type, and in many of its Insectivorous congeners, the basisphenoidal bony
centre ().s.) runs behind, largely, for some distance, into the alisphenoidal cartilage (al.s.) ;
this is a most important diagnostic of a true, normal, Insectivore. It is, however, a very
gentle modification of that which is diagnostic of the skull of the Marsupials, namely, a
“tympanic wing,” which grows backward from the alisphenoid. Here, the rudimentary
tympanic wing arises from that part of the alisphenoid which is ossified vicariously
from the basal centre ; thus the further growth of the tympanic wing 1s merely a shell-
like flange of the basisphenoid. Hence the bone which develops round the tympanic
aw-cell in the typical Insectivora, assisting the superadded annulus tympanicus, is
basisphenoidal. The alisphenoidal centre, in Marsupials, which forms the front part
of their drum-cavity, is supplemented by a large, crescentie “os bulls,” which
ultimately becomes ankylosed, in most cases, to the alisphenoid. Moreover, the
extensive pneumaticity of the basis cranii of the Insectivora, at this part, is very
Sauropsidan, and these types have also a considerable upper tympanic recess inside
the squamosal bone, as in Crocodiles, Birds, Marsupials, and Edentates. At present
the basisphenoid (Plate 19, fig. 1, b.s.) does not reach so far forwards as the ali-

* In the typical Ruminants, and still better, in the genus Oavia among the Rodents, this sphenoidal
outgrowth is seen to be manifestly the homologue of the “ basipterygoid process” of the Sauropsida,
growing as it does from the side of the basal beam. Its visceral correlate, the pterygoid cartilage, which,
indeed, dominates it, has undergone most remarkable structural modifications in the types in which it

re-appears, e.g., in Chelonia, Crocodilia, Passerine Birds, and, lastly, in the lower Mammalia.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 145

sphenoids, but it goes further backwards, yet there is a considerable tract of cartilage
separating it from the basioccipital.

A groove in its lower face leads to the still unclosed pituitary space (see fig. 2, py.) ;
whilst right and left it has a deeper groove filled by the terete pterygoid (pg.) with its
cartilaginous terminal nucleus (pg.c.). Behind the pterygoids, and in front of the
sinuous wedge-like growth of bone in the middle, there is a definite rudiment, as an
oblique ridge, of the future tympanic wing.

The broadest part of the skull is behind the posterior sphenoid ; here the huge
cochleze (chl.) display their coils, and outside them the broad tegmen tympani has
on its inside the groove for the facial nerve (VII), which escapes from the skull
behind the edge of the alisphenoid, This groove is protected behind by the confluence
of the epihyal (e.hy) with the auditory capsule ; the nerve escapes behind it, through
the stylomastoid foramen. In front of the epihyal, the fenestra ovalis (/s.0.) 1s
seen obliquely, and the fenestra rotunda (f:r.) mesiad of it. Behind the fenestra
rotunda, and further inwards, the large passage for the 9th and 10th nerves (IX., X.) is
seen, and behind that passage the lesser hole for the 12th nerve (XII.) The basi-
occipital (b.0.) is roughly hexagonal; the exoccipitals (¢.0.) are developing in the
hollow between the paroccipital convexities and the condyles (0c.c.).

The upper view of the endocranium of this stage (Plate 19, fig. 2) is shown with the
upper part cut away for the better display of the fundus cranii. The crenate hinder
margin of the nasal capsules is almost transverse, only a little concave, and is so
thoroughly pre-cranial as to display nearly all the large cribriform plate (cr.p.).
The top of the septum nasi (s.7.) and perpendicular ethmoid (p.e.) is seen at its
junction with the als or roof (al.sp., al.e); the middle part of the continuous partition
is thicker than the end. The upper part of the capsule is constricted twice, so as to
form a front, a middle, and a hind, enlargement. The lateral part is constricted, gently,
once. There is no definite cartilaginous crista galli (crg.), but merely a gentle rising
of the wall in front, directly behind the end of the roof:

The cribriform plate has floored the whole fossa, and this tract, as well as the
lateral walls, are confluent with the fore edge of the anterior sphenoid. The broad short
presphenoid (p.s.) is unossified, and it has in its middle a hollow, showing the double
nature of the bar. The orbitosphenoids (o0.s.), are ossified, proximally, close to the base,
in their hinder margin ; the fore part and the whole of the main wing still remain soft.
This pyriform centre is perforated by the optic nerve (II.), which escapes near the
hind margin, half-way up the ascending bony tract. The inturned upper edge has
been cut away, but the band is shown to run backward to, and to be confluent with,
the auditory capsule.

The hind margin of the orbitosphenoid (0.s.) is sinuously concave and hides the
more distinct alisphenoid (al.s.) at its fore edge. The basisphenoid (b.s.) occupies the
hind half of the small open pituitary space ( py.) ; it is separated by a large tract
of cartilage, as yet, from the basioccipital (b.0.). Both betore and behind, that centre is

MDCCCLXXXV. U

146 MR. W. K. PARKER ON THE STRUCTURE AND

seen, even above, to be creeping into the ale, the bony centres of which just touch the
foremost of these extensions of the basisphenoid. But more than a third of the hind
part of the ale is still cartilaginous ; the posterior external part dips below the
auditory capsule, just as the front margin does under the orbitosphenoid.

The sphenoidal fissure (V'*.) is an oblique reniform foramen, and to it a groove
for the 2nd branch of the 5th nerve runs from the large foramen ovale (V*.). A small
sphenotic flap of the auditory capsule overlies the alisphenoid, externally ; between
this part and the coiled cochlea the facial nerve (VII.) escapes, running first under a
bridge of cartilage from the foremost hole of the meatus internus (VII., VIII.). The
swellings outside the wall—which has been cut away horizontally—are due to the
horizontal and posterior semicircular canals (h.s.c., p.s.c.), the arch of the anterior canal
(a.s.c.) is cut away and its cavity exposed. The hollow for the flocculus is not well
shown in this view; behind it, the opening of the ‘“ recessus labyrinthi ” is seen.

Patches of bony cells are now to be seen, the beginnings of the extensive opisthotic
bone (op.). These are at the hinder margin of the cochlea in the lower view (fig. 1).
This bony deposit is to be seen, inside, in front of the large foramen for the 9th
and 10th nerves (IX., X.). This foramen and the condyloid (XII.) in front of it are
seen in the upper view with the exoccipital (¢.0.) creeping up to the latter; the large
six-sided basioccipital (b.0.) still lies in the centre of the large multiangular basal
cartilage, flanked, outside and behind, by the occipital condyles (oc.c.).

Visceral arches of Third Stage.

The outer and inner elements of the mandible (Plate 22, fig. 5) are still bound up
together, and are nearly equal in bulk. The new condyle on the “ramus” is at no great
distance in front of the primary morphological condyle

the short crus of the incus (2.).
This suspensorial segment is still unossified, and so is the stapes (st.) or uppermost
part of the next arch; but the malleal bony centre (ml.)is working into the cartilage.
The dentary (d.) has grown over MecKEL’s cartilage (im.) in one place, and is con-
verting that part into bone; in front of this ensheathed part the rod is very solid ;
its basal bar (b.1n.) is well formed, and turns upwards somewhat. The cartilaginous
ends of the three hind lobes of the ramus keep growing, part passu, with the rest ;
the annulus tympanicus (@.ty.) is now ossified.

The hyoid arch has been cut away where the epihyal (Plate 22, fig. 6., ei.) is con-
fluent with the auditory capsule (see fig. 3). The cartilaginous segments are solid and
strong, but are at present quite unossified.

Fourth Stage of the Skull of Evinaceus europeus ; young specimens, 2 weeks old ;
3 inches long.

This stage shows but little difference in the general form and condition of the endo-

cranium ; but the osseous centres are much more advanced (Plate 19, figs. 3-5). I have

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 147

figured the upper aspect as a perfect object, not having cut away the rim and roof of
the chondrocranium.

The general description just given of the third stage may serve on the whole for this,
but the bony tracts will be especially noticed The large front paired vomers (v’.)
protecting the recurrent cartilages (7c.c.) and JACcoBSON’s organs are still separate. The
proper vomer (v.) is becoming very strong, and its keel is now double, in front. On
each side of its forks, behind, there is a small bony tract ; these are the bones which
help to unite the two sides of the nasal labyrinth to each other and to the vomers ;
they are the hinder paired vomers (v’.) The folds of the middle turbinal (7.tb.) are
seen to be undergoing ossification ; the hinder pair of these centres is close to the
precurrent cartilaginous spikes, which run forwards on each side of, and above,
the middle keeled part of the vomer. The hinder part of the nasal labyrinth is
opened out somewhat, artificially, for display.

The large orbitosphenoidal bones (0.s.) are running upwards towards the marginal
band; below, they are beginning to ossify the basal tract, or presphenoidal region
(p.s.). The posterior sphenoid is now almost completely ossified, but the bones of the
alz and base (al.s., b.s.) are distinct. The external pterygoid process (e.pg.) is still
unossified. The three bones, measured across the foramina ovalia (V*.), are of equal
width ; but, further backwards, the basisphenoid is the widest of the three, having
taken in part of the cartilaginous ale. Here the hole, right and left, for the internal
carotid artery (7.c.) is fairly enclosed by the bony deposit of the basisphenoid. This
shows that we are not far from the Marsupials, and this agrees with what I have just
shown, namely, that the tympanic wings of the posterior sphenoid are basal, in the
Hedgehog, instead of being alar, as in the Marsupials, through the special posterior
dilatation of the basal bone in this type. The pituitary hole (py.) is now enclosed by
bone (b.s.) ; this hole is in the fore part of an inferior groove, right and left of which
the pterygoids (pg.), left in situ, have developed an upper dilated part, by which to
stick, like Limpets, to the basisphenoid; their cartilaginous nucleus (pg-c.) is not yet
all ossified.

The ossification of the auditory capsules is progressing rapidly. The opisthotic
centre (figs. 3 and 5, op.) reaches from the passage for the 9th and 10th nerves,
above the inner margin of the cochlea ; it encompasses the fenestra rotunda behind
(fig. 8, fr.), and runs up to the fenestra ovalis; above (fig. 5), it is growing round the
meatus internus. The prootic (pr.o.) is a much smaller centre ; below (fig. 3), it 1s
growing over the groove for the facial nerve at the inner edge of the tegmen tympani
(t.ty.), and above (fig. 5) it is running along under the anterior canal (a.s.c.) into the
recess for the “flocculus.” The basioccipital (b.0.) is increasing in size, but it is still
in the midst of a wide tract of cartilage; the exoccipitals (e.0.) are just enclosing
the condyloid foramina (XII.); the supraoccipital is widening over the foramen
magnum (f.7m.).

In the upper view (fig. 4), the fore part is seen to be quite unossified, but the

U 2

a

148 MR. W. K. PARKER ON THE STRUCTURE AND

orbitosphenoids reach their own cartilaginous base (p.s.). The well-ossified ali-
sphenoids (a/.s.) are seen articulating with the wide, extensive basal bone,* which
shows its pituitary hole in front, and has a low postclinoid ridge running across
behind the middle, it has, in front of it, a very shallow “sella.” The hinder part
of the floor is shown in the partial foure (5); but the huge supraoccipital tegmen,
with its wide, angular ossification (s.¢.) overlapped in front by two interparietals (7.p.),
are to be seen in the main figure (4). All the canals (a.s.c., h.s.c., p.s.c.) ean be seen
in this view where the large auditory capsules project outwards, like short ears, from the
sides of this curious cranial “vessel.” The exoccipitals (e.0.) can just be seen rising right
and left towards the postero-external margin of the supraoccipital osseous centre (s.0.).

Visceral arches of the Fourth Stage.

About one-third of MEcKEL’s cartilage (Plate 22, fig. 7, mk.) is now enclosed in a
canal formed by the dentary (d). In front of this buried part the cartilage rises and
swells into a thick mass, up to where it meets its fellow, from which junction the
basimandibular (b.mn.) grows forwards, and a little upwards.

The condyloid mass of cartilage is now much larger than that which still
remains unossified on the ends of the coronoid and angular processes. The parts
that form the ossicula (m/., 7, st.) have merely become enlarged without any

noticeable change ; the annulus (a.ty.) is also increasing in size.

Fifth Stage.—Skull of Evinaceus europeeus ; 1 month old ; head 14 inch long.

a. Investing bones.—The superficial parts of the skull have been worked out and
figured in this stage (Plate 20, figs. 1-3), as in the second (Plate 17, figs. 3-5),
and in the sub-adult (Plate 21, figs. 1-6).

In the upper view (Plate 20, fig. 2) we see what a strong roof the investing bones
now form to the very solid endocranium. The nasals (7.) are small, narrow bones,
and diverge in front; the frontals (f) are almost as large as the parietals (p.); they
are now in one piece on each side.

The large convex parietals have the frontals running in between them in the coronal
suture, and the double interparietal (/.p.) fits on to their concave hinder margin,
The sides of the hind skull are well buttressed by the squamosals (sq.), and the fore
part of the skull by the huge maxillaries (mzx.), and the middle-sized premaxillaries
(px.); the jugals (7.) are smallish ; the lachrymals are not well seen in this view.

Sut in the side view (Plate 20, fig. 8) the lachrymals (/.) are seen to be intraorbital ;
they are oval, have a large opening (/.c.) in front, and are very thin. The imbrication
of the subcutaneous scutes that invest the endocranium is well seen in this view,
The jugal was removed in the preparation figured, to display the interior of the orbit,
the inner wall of which is composed of the lachrymal, orbital plate of the frontal, and
maxillary, in front ; and behind, by the frontal, parietal, and squamosal ; it is a very

* For b.o. read b.s.

— we)

eet Men

DEVELOPMENT OF THE SKULL IN THE MAMMALIA, 149

open space. The postglenoid part of the squamosal (sq.) is short, the hind part of
the squama, in the end of the temporal fossa, is perforated. The facial nerve
(VIL) is figured, and also its chorda tympani branch (VII*.), passing to the large
inferior branch of the trigeminal (V*%.). The Ist and 2nd branches of that nerve
(V1, V2), are seen emerging from the sphenoidal fissure, the former re-entering the
skull through the main orbital foramen, and the latter running forward through the
ereat maxillary canal, and emerging through the supraorbital foramen.

The optic nerve (II.) is seen between the forks of the trigeminal (V!., V*.), emerging
from its own foramen opticum.

The investing bones, as seen from below (fig. 1), show the finishing of a very fine
piece of architecture ; the hinder superficial pieces, the tympanics, were removed to
display the proper cranial structures. This individual was just cutting its teeth ; the
huge sockets for which are shown with but partially developed dissepiments.

The premaxillaries have a large dentary part, and a small, short palatine process ;
over this, however, the anterior paired vomer (v’.), is seen, which afterwards makes
that process of the normal size.

The maxillaries (mx.) are enormous, being gravid with many large teeth, and, as the
palate is very wide between the tooth-rows, the concave palatine plates are of great
extent. There is, here, as in many of the Edentata, a sign of some distinctness of
the inner, from the submarginal, part of this bony roof. The inner part is wedged
in between the rami of the premaxillary (a.p,f) in front, and then an oblique ridge,
running backwards, and a little inwards, up to the posterior palatine foramen, marks
the inner part off from the outer. The outer part of the hard palate is a concave
tract, forming a lanceolate flange to the internal alveolar wall. The hinder part of
the alveolar tract is unfinished; the jugal process is short and sharp.

The palatine bones (pa.) are very elegant, and quite Metatherian in their
characters ; their palatal plates are sharp wedges, running forwards, together, between
the palatal plates of the maxillaries. An irregular subreniform fontanelle is seen
in each plate, near its middle, behind the thickening inside the posterior palatine
foramen (p.p,f.). Each bone has a thick subarcuate margin, as the finishing, behind,
of the palatal plate; these ridges are turned a little forwards as well as outwards.
Part of the subcranial tract of each bone is seen behind the hard palate, bounding
the nasopalatine canal; this is clamped by the pterygoid (pg.); outside this, the
palatine bone spreads into a hooked wing, which bends round the front of the
oblique, oval, small external pterygoid plate (e.pg.). The distinct upper vertical tract
of the palatine ends a little behind the anterior sphenoid (0.s.), then the wall is con-
tinued a short distance further back by the pterygoids (pg.), which are not distinct,
now, but have already coalesced with the sides of the wide basisphenoid bone (b.s.);
the lower part is terete, and ends in a short, free hamular process, which has, now,
used up all the cartilage.

The tympanics are not given in this figure; they have been removed, with the

ossicula auditis, to display the auditory region.

150 MR. W. K. PARKER ON THE STRUCTURE AND

The jugals (j.) are flat styles; the squamosals (sq.), riding over them, are seen to
swell out into a convex shell of bone clamping the parietal, and then to grow
inwards to be covered with the broadly-reniform glenoid facet (g/.c.). The post-
glenoid tract is here seen to bend in to the mastoid region of the ear-capsule, and to
end in three tooth-like processes.

Both the end view (Plate 19, fig. 6), and the cnner view (Plate 19, fig. 8), also show
the investing bones from their aspects.

Endocranium of the Fifth Stage of Erinaceus europzeus.

The vertical section (Plate 19, fig. 8) shows the whole of the craniofacial axis up
to the presphenoid (p.s.); behind, that the axis was cut along the middle, and only
half the skull was figured; this part is only two-fifths of the whole length. The
round snout has its own septum marked off from the proper septum nasi (s.7.) by a
considerable inferior notch, in which the Jacogpson’s, or recurrent cartilages (7¢.c.) are
seen to arise. These folded leaves are tubular in their most perfect part, and then
are open along the side.

Over the notch the intertrabecula (7.t7.) is very thick, but it diminishes very little
all along the base of the great ethmonasal wall (s.7., p.e.); itis ossified behind by the
orbitosphenoids (0.s.), in the presphenoidal region ; there is no separate median bone
there.

The front paired vomer, and the vomer, proper, (v’., v.), are shown in situ; the
nasals and frontals (7., f.) lie over the roof (al.sp., al.e.).

The short descending side of the low triangle formed by the great partition is
notched by the numerous olfactory filaments, and the cribriform plate (c7.p.) is seen to
the right of this crested tract, which has a small, special elevation, above—the crista
galli (c7.9.).

The anterior sphenoid is still continuous with the nasal labyrinth, in front, by the
fore edge of the great orbitosphenoidal cartilage (0.s.); the lower third of this tract
is ossified, and is perforated by the optic nerve (II.) near its hind margin, below.

The rest of that sinuous margin, passing into cartilage above, is now abruptly free,
the rest of the band, over the alisphenoid, and along the supra-auditory region (see
figs. 1-4) having been absorbed.

Thus the sphenoidal fissure (V" *.) is now very steep, and perfect; it 1s bounded
below by the cartilage still remaining between the fused orbitosphenoids (p.s.) and
the distinct basisphenoid (b.s.). The low-lying alisphenoid (a/.s.} is free, in front,
and bulges outwards; it is only notched in front by the 2nd bra» ch of the 5th nerve,
but is perforated by the 3rd branch (V*.), which forms a large foramen ovale near its
hind third; this is much the smaller wing, even now. The basisphenoid is both long
and wide; over its hinder half the cochlea is seen; the pituitary hole (see fig. 4) is

present, but the sedlar depression is slight.

a

DEVELOPMENT OF THE SKULL IN THE MAMMALTA. toh

The auditory capsule is largely ossified, especially on this, its inner, face ; the “ crest”
of cartilage is not quite gone, nor quite ossified. The recess for the flocculus (jl.7.)
under the arch of the anterior canal (a.s.c.) is about the size of the meatus internus
or vestibular eave leading to the foramina for the 7th and 8th nerves (VIL, VIIL.).
The other foramina ([X., X., XII.) in front of, and through, the occipital arch (s.0.,
¢.0., b.0.) are seen in this section.

Part of the outer view of the hind skull (Plate 19, fig. 9) shows the normal division
of the petromastoid into prootic, epiotic, and opisthotic centres (pr.o., ep., ep.), but
the wedge-like epiotic is not a very distinct tract; it is bound to the rest of the
main centre—the opisthotic—on its inner side.

There is still unossified cartilaye over the anterior canal, and outside its ampulla,
and that of the horizontal canal; the paroccipital process (p.oc.) is still cartilaginous,
and also the stem of the epihyal (e.hy.).

These parts are also seen in the end view (Plate 19, fig. 6), which displays the
occipital arch perfectly, and the auditory capsules partially ; the broad cartilaginous
tracts, here seen, give the whole structure depicted a diagrammatic distinctness.

In the lower view of this perfect skull (Plate 20, fig. 1) the broad snout in front, and
the broad basis cranii, behind, are displayed, fore and aft of the large investing bones
of the upper face and palate,

The hinder part of the anterior sphenoid (0.s., p.s.) is seen behind the hard palate,
in the roof of the nasopalatine canal, in the middle, and, right and left, in the wall of
the orbit. The top of the orbitosphenoid (o.s.) is still unossitied, and the presphenoid
has been formed by the fusion of the proximal parts of the ossified tracts, right and
left, of the two orbitosphenoids (see also Plate 19, fig. 8).

But the posterior sphenoid is freely displayed in this aspect, covered, however, in
one part, by the small pterygoids ( pg.) that have coalesced with it by their subcranial
flange.

The suture, right and left, between the alae and the base (q/,s., b.s.), is fast dis-
appearing, so that the whole tract which forms so large a part of the base and lower
wall of the cranium, proper, is now practically one bone. The well-formed temporal
squama (sq.) forms a slightly squamous suture with the outer edge of the alisphenoid
(al.s.), which, in turn, lies some distance outside the orbitosphenoid (0.s.). But in
this view the squamosals are seen only to form a thin clamp to the alisphenoids, which
stretch across the wide tract that intervenes between the hard palate and the auditory
capsules. In front of the squamous suture the alisphenoid is notched and uncinate at
its antero-external angle, and then has a somewhat notched, thick margin bordering

9

the sphenoidal fissure (V1, V*.). Behind this fissure the palatine bone is seen to hook

¢

itself round the front and outside of the small, oval, oblique “ external pterygoid
plate” (epg.). A moderate fossa is seen between this piece of carpentry and the
ankylosed pterygoid bone ( pg.), behind which a small foramen is seen. The foramen

ovale (V*.) forms a conspicuous opening, behind, and further outwards, than the

152 MR. W. K. PARKER ON THE STRUCTURE AND

external pterygoid plate. Behind the foramen the outer margin of the alisphenoid is
notched, gently, and then grows outwards again to form a wedge, which is strongly
jammed in between the squamosal and the petrous bone. Leading from the external
pterygoid plate to this wedge, inside the foramen ovale, is an elegant crest of bone,
concave, externally, and lying below the rough, dentated, hinder edge of the ali-
sphenoid. This is the boundary line of the junction of the basal and alar osseous
centres, and it is this tract which corresponds with the alisphenoidal part of the
bulla of a Marsupial, the root of its so-called “tympanie wing.” This and the
rest of the basisphenoid (b.s.) form a very peculiar structure, quite diagnostic of an
Insectivore, and, when suppressed, tells of a departure from the normal skull of this
Order. The fore part of the basal tract is pinched in so as to form a very narrow
passage ; the hind part widens into a semioval concave space. Right and left of this
space the basisphenoidal tympanic wings grow out; these are square tracts, notched
and uncinate behind, and hollow, externally, where they add to the general drum-
cavity. These hinder outgrowths of the basisphenoid are separated by a notch,
externally, and by a groove continued from the notch, internally, from the pre-
tympanic wing which has its homologue in the Marsupial. The cochlear part of the
opisthotic (ch/.) articulates on its inner side with the basisphenoid, and in its outer is
margined by the grooved tegminal tract which contains the horizontal semicircular
canal (fig. 3, h.s.c.). Here the fenestra ovalis (/s.0.), fenestra rotunda (/‘r.), and the
hinder opening of the groove for the facial nerve (VIL), bridged over by the epihyal
(e.hy.), ave all displayed.

The cartilaginous projection that contains the two front ampulle is separated by a
bony tract of the opisthotic from the next cartilaginous swelling—the paroccipital
(p.oc.); behind this the condyle (oc.c.) forms a third cartilaginous convexity. The
broad, short occipital ring has its transversely oblong basal piece (b.0.) separated, still
by a widish tract of cartilage, from the exoccipitals (¢.0.) ; these are bored by the
12th and notehed by the 9th and 10th nerves (XII., [X., X.).

The upper view (Plate 20, fig. 2) shows but little of the endocranium; but a dissected
skull, shown in its lowev aspect (Plate 19, fig. 7), as far as the first third of the basi-
sphenoid, displays several parts not yet described.

In this preparation several of the lesser splint bones were left, in situ, and figured ;
the premaxillaries (px.) are shown cut through their alveoli, horizontally, and we see
that their palatine process is, at present, very short. But the front paired vomers
(v’.) are close behind, and above, the sub-median part of those bones; they are long
splints, a little scooped on their outside, and are in close contact with the pointed fore
end of the vomer proper (v.), which runs in above them. Right and left of the paired
bones (v’.) we see the large cochleate recurrent cartilages (7c.c.), and, outside these, the
ossified inferior turbinals (7.tb.). The fore part of the upper and middle turbinals
(u.tb., m,tb.) is ossified ; but the greater part of the wall and floor of this large bulbous
labyrinth is still unossitied. The vomer (v.) is carinate behind its pointed fore end,

al i il ee

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 155

and the keel is grooved; the hinder two-fifths is in two forks, that run back and gently
bend in between the basal beam (p.e.) and the postero-inferior recesses of the basal
labyrinth. Here the winged divisions of the vomer serve to bind together the right
and left tracts of the nasal floor, under the fore half of the middle turbinal region.
‘This second upper binding together of the right and left face, making the skull doubly
desmognathous, is assisted by a pair of oblong splints, the posterior paired vomers
(v’.), which run from this great opening between the inferior and middle turbinals up
to the oval hinder recess, right and left, of the presphencid. When the middle
turbinal is well ossified in its lower as well as in its front part, then the three
vomerine bones and the ossified floor and turbinals all become an indistinguishable
tract of bone. This preparation is only figured up to the hind margin of the foramina
ovalia (V*.) ; the optic, ophthalmic, and maxillary nerves (IL, V'., V*.) are figured,
emerging from the optic foramina and sphenoidal fissures. The rest of the skull in
this aspect is seen in the entire palatal view (Plate 20, fig. 1).

Viceral arches of the Fifth Stage.

The lower jaw (Plate 22, fig. 8) is now almost complete, but there is a little cartilage
still left on the coronoid and angular processes. The latter (ay p.) is somewhat
incurved. The fore part of Mecket’s cartilage and the basimandibular rod (mk.,
bmn.) ave still present, but the freed part of the bar is now ossified as a large spatulate
processes gracilis (pr.g.), much larger than the manubrium (mp.).* The incus
and stapes (7., s¢.) are now ossified, and are seen in situ, so also is the annulus («.ty) ;
all these parts are shown from their inner fuce.

The hyoid arch (Plate 22, fig. 9) has acquired all its bony centres, but the thick,
erescentic hypohyals (h.hy.) are only ossified in their middle, and the upper cerato-
hyal (c.hy.) only half-way up. The epihyal (Plate 20, fig. 1, and Plate 22, fig. 9, e.hy.)
is ossified in the upper part directly from the bony substance of the opisthotie (op.) ;
it has no separate proper centre (“ tympanohyal”), nor splint (“stylohyal”).

Sixth Stage of Skull of Evinaceus europzeus ; young ; two-thirds grown.

These large young are profitable for study, because, although well ossified for the
most part, nearly all the sutures are very visible; a vertical section at this stage
(Plate 20, fig. 4) is very instructive.

In the fore part we see the rounded form of the snout, and the complete septum
that has grown forwards from the proper septum nasi between the alinasal folds (al.n.).
The whole partition wall, from the front of the snout to the fore-edge of the pre-
sphenoid (p.s.), is two-thirds the length of the whole craniofacial axis. The highest,
or hinder part, is ossified as the perpendicular ethmoid ( p.e.), and this reaches forwards
for nearly a third of the length of the wall behind the snout. The bone runs further
forwards above than below; laterally, behind, it is now confluent with the partially

* The letters of reference should have been m/

MDCCCLXXXV. pe

154 MR. W. K. PARKER ON THE STRUCTURE AND

ossified cribriform plate (cr.p.) ; behind, it gets to be a low thick wall between the
retral recesses of the nasal labyrinth. The septum (s.7.) is moderately thick from
above, where it gives off the aliseptal folds (a/.sp.) to the thick base ; that part shows
its thickness as a solid rod with a flat crest, from the low hind part to the equally
low foremost part of the septum nasi proper. There, the septum is notched, below,
and right and left of the notch the base of the alinasal folds gives off the recurrent
cartilages (7c.c.), large spatulate processes, tubular, proximally. The palatine process
of the premaxillary (p.px.) is seen in its thick part, the rest, separate, for some time,
as a front vomer, is given in outline in the figure, showing that it is inside the
cartilaginous process. The vomer (v.) is seen supporting the thick intertrabecular
base of the partition, and under this we see the thick inner edge of the palatine
plate of the maxillary (mz.) ; these bones are united’ by suture, and now we see why
the median vomer should have its keel double (see Plate 19, fig. 7, v.), for it articu-
lates with two plates beneath it, and these bones, doubly sutured together, divide
the right and left nasal passages from each other. This division ceases where this
suture ceases, and this is half-way between the external and posterior nasal openings ;
the latter open out behind the soft palate, which is strengthened right and left by
the descending plates of the palatine and pterygoid bones (pa., pg.). The cranial
cavity is roofed, and largely walled in, by the frontals, parietals, and interparietals
(f, p., U.p.), the ossified remains of the endocranium lying low down in the floor of
the skull. A round notch makes the orbitosphenoid bilobate ; above the front lobe
is a thin ragged tract lining the orbital plate of the frontal. Where these join
there the 1st branch of the 5th nerve (V!., ophthalmic) has entered (see also Plate 20,
figs. 3 and 5, V1!.), it is seen in this section riding over the outside of the cribriform
plate to gain the nasal cavity.. The longer, more regular hinder lobe of the orbito-
sphenoid (0.s.), passes inside the alisphenoid (c/.s.); these parts lie so low down that
neither the optic foramen, nor the foramen lacerum anterius, or sphenoidal fissure,
are seen in this directly lateral view. The parietal (p.) passes so well down the
skull wall that the squamosal—as in the Ostrich—is not seen, or scarcely at all; in
this inner view the elegant curve of the lateral sinus (/.s.) is seen near the lower edge
of the parietal.

The alisphenoid (qa/.s.) is here visible as a strong concave shell of bone, hidden,
however, in front, by the orbitosphenoid, and below by its own large basal beam (b.s.) ;
its thick ear-shaped hind part rides over the front of the cochlea, and the great
oval foramen (V*.) is seen opposite its front third; behind this part of the base the
sella turcica is seen as a shallow concavity, and the posterior clinoid wall as a mere
thickening of the base ; behind that thickening the postclinoid region dips downwards
—a normal state for this and the rest of the base (b.0.).

A solid tract of cartilage still exists between all the three basicranial bones, the
first of these (p.s.) is high, but it is not an independent presphenoid ; it is only
formed, as bone, by the juncture and ankylosis of the right and left orbitosphenoids.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 50

The ossified auditory capsule is seen over the second synchondrosis ; it 1s obliquely
fixed, large, and full of hills and hollows on this aspect. The supra-auditory tract of
cartilage has been largely absorbed, but its base was ossified, and that remains as a
rough crest to the capsule. Below this, in front, the anterior canal (a.s.c.) is seen with
its ampulla; an oblique rib of bone ascends from the cochlea to the crown of the
arched canals, the anterior and posterior. This arch and its hinder enlargement
behind the hollow for the flocculus (jl.7.) is not formed by the posterior canal and its
ampulla, but by the growth of a tubercle of bone inside that arch, bounding the
floceular recess behind, as the oblique ridge does in front.

The meatus auditorius internus (VII. VIII.) is a large archway, between which
the petromastoid bone swells into the fore part of the deep sulcus for the posterior
sinus, and for the exit of the 9th and 10th nerves; the hollow for the sinus opens
below into the foramen lacerum posterius. Behind that opening the lesser hole,
or condyloid foramen (XII.) is seen in the substance of the exoccipital (e.0.); the
condyle (cc.c.) is seen behind, the basioccipital (b.0.) in front, and the supraoccipital
(s.o.) above it.

The large rough wings of the basisphenoid are seen below the basal section and
behind the pterygoid bone (py.).

The inner view of the nasal labyrinth (Plate 20, fig. 5), obtained by removal of the
perpendicular ethmoid and septum nasi, shows the complex folds of the nasal, inferior,
upper, and middle turbinals (1.tb., 7.tb., w.tb., m.tb.), and here the ophthalmic nerve (V'.)
can be seen in its course along the interior of the labyrinth. Below the cribriform
plate (cr.p.), the right recess of the hindermost part of the nasal cavity is seen
running by the base where the ethmoidal and presphenoidal regions meet.

Seventh Stage of the Skull of Evinaceus europeeus ; young; three-fourths grown.

I have merely figured the outer auditory bones in this, a somewhat more advanced
a state retained only

stage than the last, as they are now in a very instructive state
for a few months longer, after which much absorption and modification of bone will
take place.

The outer view of the ear-drum and its chain (Plate 22, fig, 10), shows a condition
quite comparable to what is found in subadult and adult Marsupials. Moreover the
annulus (a.ty.), now rapidly strengthening its thickening inner edge, and has there a
row of small osseous points quite similar to those that are the only rudiments of the
tympanic ring in the Bird ; that feeble chain of bones is best seen in the Corvidee.

The processus gracilis of the malleus is several times larger than the manubrium
(p.gr., mb.) ; it isa strongly ribbed bar, which, appearing in front of its tympanic attach
ment, there shows a rudiment of the pretympanic hook so large in many Marsupials.
The body of the malleus is large, and the “ posterior angular process” (p.ag.), behind
the manubrium, is a semioval convexity. The short crus of the stout end well-made

x 2

156 MR. W, K. PARKER ON THE STRUCTURE AND

incus (s.¢,7.) is unusually short ; the long crus (/.c.2.) is also short, but is well inturned,
and has an oval facet for the head of the stapes.

That bone (s¢.) is rather high, has a long oval base, narrow, and somewhat snagery
sides, and has a tubercle on its neck, in which is a very rudimentary interhyal
(i.hy.), rooted in the base of the stapedial muscle’s tendon (st.m.).

Highth Stage of the Skull of Erinaceus europzeus ; nearly adult.

This skull is, conceivably, a very gentle modification of the type we are familiar
with in the Marsupials; it is just fairly within the Hutherian margin. The upper
and side views (Plate 21, figs. 2, 3) show that most of the sutures are still present, and
that where the sagittal is dying out, there a crest is forming between the top of
the large temporal muscles. Also a lambdoidal crest is seen behind the wide
interparietal (¢.p.), which, however, is confluent with the proper supraoccipital
(fig. 4, s.0.). The coronal suture is W-shaped, the bones being strongly dovetailed into
each other. The large, long nasals (n.), narrow behind, take up about a third of the
gently arcuate dorsal line of the skull; the frontals (f) flank them in front, but do
not reach the large ascending plate of the premaxillaries (pw.), the much larger
maxillaries (mx.) intervening. An oblique ridge separates a deep fossa above from
the large lachrymal passage (/.c.) below; this passage is on the edge of the orbit, but
most of the bone, now largely fused with the maxillary, is inside the orbit. The
orbital space opens freely into the temporal fossa, and the outlines of the bones that
form the whole of this concavity can be well seen for the most part, the fusion of the
lachrymal with the maxillary being exceptional. Down at the base of the orbit the
orbitosphenoid can be seen passing within the alisphenoid, and some distance outside
the former the alisphenoid and maxillary meet and form a narrow longitudinal bridge
over the thick edge of the palatine bone (pq.).

The infraorbital foramen (V*.) is large, and so is the canal that runs backwards into
the skull through the hinder part of the sphenoidal fissure, for the alisphenoid
(Plate 20, fig. 6, a/.s.) is deeply grooved for this large 2nd branch of the 5th nerve.

The jugal (j.) is moderately strong; it reaches the glenoid fossa, but is sharp
there ; it does not dilate, terminally, as in the Marsupials. Part of the basis cranii and
the auditory ring can be seen from the side view, but the lower view (Plate 21, fig. 1),
alone, displays these parts well. The premaxillaries and maxillaries (pa., mx.) at their
palatal junction leave a considerable space (a.pf), right and left, through which the
recurrent cartilages and J ACOBSON’s organs can be seen. The palatine processes of the
premaxillaries are long but lie above those of the maxillaries ; they have added to their
substance and length, the antero-lateral vomers or splints of J AcoBsoN’s organs. The
palatine plates of the maxillaries form a fine large concave roof; they are followed by
the imperfect plates of the palatine bones (pa.). The fenestra seen in each bone in the
5th stage (Plate 20, fig. 1, pa.) is now a deep notch open in front, for each palatine bone
is now formed in its lower part and fore half intoa flat fork with long ragged “tines ;”

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 157

the inner being the larger and uniting by a “harmony suture” with its fellow of the
opposite side. The ascending part of the palatines is strong and has coalesced with the
external pterygoid plates (e.pg.) on the outer side; they have not united with the
pterygoids (pg.). The hind margin of the hard palate, formed by the palatines, which
have not united with the maxillaries, is an elegant archway with a strong upper lintel
over it, formed by a thick rib on each of the palate bones; these ribs meet at the
mid-line at a very obtuse angle.

The elements of the basis cranii behind and below are fast coalescing with each
other ; the sutures of the hind skull, however (fig. 4), are most of them visible.

The paroccipital processes (p.oc.) are thickish and somewhat foliaceous ; they finish a
semioval occipital plane, with its large convex obliquely pyriform condyles (0c.c.). But
in front of the occipital arch the mastoid processes (fig. 4, op.) project like wings and are
there strongly sutured to the postglenoid process of the squamosal (sg.), which is
pneumatic, and has its own foramen. There is a large foramen lacerum posterius
for the 9th and 10th nerves, and a lesser foramen condyloideum for the 12th
(fig. 1, XI.).* The ossified auditory capsule has already been described (6th Stage,
Plate 20, fig. 4), but the posterior sphenoid, and the turbinal folds of the nasal
labyrinth, with the interior sphenoid can be well studied in this scarcely adult stage,
whilst the parts are still capable of being taken to pieces to a considerable degree.

The posterior sphenoid shown in its wpper aspect (Plate 20, fig. 6), is a large winged
bone, with a ragged outline and a multiperforate surface.

The large foramen ovale (V*.) is at the hinder and the middle third of each great
wing (al.s.); the 2nd and 1st branches of the 5th nerve pass with the lesser orbital
nerves out of the sphenoidal fissure.

The fore part of the bone does not fit itself to the hinder part of the anterior
sphenoid (Plate 21, fig. 7, 0.s., p.s.), except at the middle; the pointed fore end of each
large wing grows outside, free of the orbitosphenoid. The outer and hinder part of
each wing is rounded, and this upper surface is broken; it is strongly grooved where
the 2nd branch of the 5th escapes from the 3rd and runs forwards and inwards to
the great fissure. The narrow front part of the basisphenoid lies some height above
the wings, and the bone has several small perforations at this part. The hinder
broad part of this bar is very gently hollowed for the pituitary body, and the post-
clinoid wall (p.cl.) is extremely low.

The lower surface of the bone shows the greatest number of diagnostic marks of a
typical Insectivorous skull. The inferior wings, external pterygoid processes (e.py.), and
pterygoid bones (pg.), are well developed and have a good fossa between them. The
latter are distinct from the palatines, but have come away, in disarticulation, with the
basisphenoid, having already become anchylosed to it, above. Between these internal
plates the bone is sharply grooved, but, behind, between the tympanic wings, the basi-
sphenoid has a large cup-shaped recess which might have lodged some such body as

* For XI. read XII. in this figure.

158 MR. W. K. PARKER ON THE S'TRUCTURE AND

the pituitary. This recess is bounded, behind, by a snag from each tympanic wing.
These wings are deeply notched in front, on their outer side, and in front of the notch
the alisphenoid has a strong rib of bone running with its concave outline forwards to
join the external pterygoid process. This rib is itself notched in the young, but in old
specimens this notch is converted into a foramen. Here in this immature specimen
the hole is finished only on the deft side—vight in the figure.

The same parts are seen from the hinder aspect of the bone (Plate 20, fig. 8).

The anterior sphenoid (Plate 21, figs. 7, 8) is less than half the size of the posterior ;
it has coalesced with the compound ethmoidal bone, behind the extensive olfactory fossa
with the underlying eribriform plate (c7.p.). The sinuous wings (0.s.) are deeply
erooved, transversely, near their hind margin; these grooves lead to the optic fora-
mina (II.). These wings are formed by the ossification of only the proximal or
lower part of the original cartilage (see Plate 17); they lessen, forwards, like the
large wings, and grow down into a keel on each side before they unite to fori the
short presphenoidal bar.

This skull is doubly desmognathous, for the vomerine series of bones unite the two
halves of the nasal labyrinth into one common complex structure (Plate 21, figs. 7-9) ;
this is very common in the Mammalia; and is sometimes seen in Birds (e.g., Gymnorhina
—the Piping Crow of Australia), where the maxillary palatine floor has an ethmo-
vomerine floor completed above it.

The antero-lateral vomers have coalesced with the palatine plates of the premaxil-
laries, lengthening them considerably ; and the postero-lateral plates have coalesced
with the outside of the forks of the main vomer (Plate 21, figs. 7-9), the latter is a
long thickly carinate bone, bluntly pointed in front.

That which is most important to remark upon in the ossified nasal labyrinth itself is
that the various turbinals—nasal, inferior, middle, superior (7.tb., ¢.tb., m.tb., wtb.) --
are transformed into a light and porous kind of bone, but when the investing bones—

nasals, frontals, &e.—are peeled off them the wall is found to have been absorbed ; the
succeedaneum to this wall is the outer investing plate. Hence, these coils, when
stripped before they are anchylosed to the investing plates, have large vacuities
between them, displaying their folds. This is due to the fact that the secondary folds
or turbinals, ossify first, and only so much of the primary wall becomes ossified as gave
origin to these out-growths ; the intermediate spaces are absorbed, being pressed upon
and defended by the superficial bony plates.

The pre-olfactory region occupied by the inferior or maxillary turbinal (Plate 20,
figs. 9,10, front and side views) is very large, and this part is exceedingly complicated,
as indeed it is in most of the Eutheria; in the Rabbit and the Dog, as well as in the
Hedgehog.

The lower jaw (Plate 21, figs. 5, 6) is fairly intermediate between that of a Marsupial
and that of a high Mammal; the three proximal processes are all large and well formed,
and the lower, or angular, is somewhat inflected as well as thickened.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 159

The incus and stapes have altered very little since the last stage (Plate 22, figs. 10,
11, 7, st.); but the malleus (Plate 22, fig. 12) has lost all its large (metatherian) fore-
growth, only a fine, sharp, processus gracilis ( p.g7.) now remains.

The hyoid arch (Plate 22, fig. 14) is well ossified, now; the epihyal (e.hy.) is con-
tinuous with the ear-capsule, above, and is joined to the upper ceratohyal (c.hy.),
below, by a tract of non-segmented cartilage. The lower ceratohyal (¢.hy’.) is about
equal to the upper in size, and the hypohyal (h.hy.) is only half as long, but broader ;
all these as well as the basal piece and thyrohyals ().4.).7., thy.) are united by
joints, mostly with a perfect joint-cavity. The “annulus” (Plate 21, fig. 1, a.hy.) has
all its irregular bony nodules confluent with the main bar,

On the Skull of the Common Moie (Talpa europea).

My materials for working out this type have been very copious; my work links
itself on to that of Mr. Water Heaps (Quart. Journ. of Micr. Sc., July, 1883), to whom
_L am indebted for some of my best specimens.
These materials are divisible into arbitrary Stages, as follows :—
Stage 1.—Embryos of Mole, + of an inch long ;
round the curve formed by their head and body, the tail not being reckoned ;

(this and the next were measured

the rest were measured first from snout to occiput, and then from occiput to
root of tail, and these were added together to give the full length, of course,
excluding the tail).

Stage 2.—Embryos of Mole, 3 of an inch long.

Stage 3.

Stage 4.—Embryos of Mole, ? and $ of an inch long.

Embryos of Mole, 75 and 8 lines (twelfths of an inch) long.

Stage 5.—Embryos of Mole, | inch long.

Stage 6.—Embryos of Mole, 14 inch long.

Stage 7.—Embryos of Mole, 15 inch long.

Stage 8.—Ripe young of Mole, 13 inch long.

Stage 9.— Young Moles, three or four days old ; 14 and 14 inch long.
Stage 10.—Young Moles, 3 inches long.

Stage 11,-—Young Moles, two-thirds grown.

Stage 12.—Young Moles, three-fourths grown.

Stage 13.—Adult Moles.

First Stage-—Embryo of Mole, 4 veh long.

This stage (Plate 16, fig. 1) is, here, merely studied from its outer aspects ; it is
very profitable for comparison with the corresponding stage in other Mammalia and
in the Vertebrata, generally ; it is nearly half as long as a similar embryo of a large
Mammal would be.

About twenty-eight somatomes can be made out; the heart is still seen in a large

160 MR. W. K. PARKER ON THE STRUCTURE AND

pouch that projects from the ventral aspect of the embryo. The fore limbs are large
flat buds behind the middle of the larviform embryo, and the hind limbs are much
smaller and are curved inwards on each side of the rudimentary tail. The meso-
cephalic flexure is well marked, and the cerebral vesicles very large; the long,
lobulate hind-brain is covered with a very thin layer of tissue. The pineal elevation is
to be seen between the fore- and mid-brain, and the fronto-nasal process against the
former vesicle. Between these parts the notch which contains the rudimentary
olfactory organ is seen; this is bounded, above, by a band which runs into the large
maxillo-palatine lobe. This lobe is separated by a sharp notch, the oral opening, from
the rudimentary mandible, behind which is the hyoid fold, and the first branchial fold ;
these are separated by clefts.

Over the maxillo-palatine lobe the small eye-ball is seen, and over the hyoman-
dibular cleft the oval auditory sac,

Second Stage-—Embryo of Mole, + inch long.

[ have had sections* made of the embryos at this stage; these have been studied,
but not figured, as the tissues of the skeleton were in an indifferent state, and it is not
part of my plan, as a rule, to give histological figures.

The external form, however, in this stage is very important (Plate 16, figs, 2-4), as
the influence of heredity, which had begun to show itself in my first stage (fig. 1), in
the large size of the rudiments of the fore limbs, is here very evident indeed.

The limbs are now, evidently, pentadactyle ; but the fore limb is also very large,
and close to the head.

The folds of the outer skin are now perfecting themselves, we see the eye-ball
in its circular setting, the external meatus of the ear is formed, and the outer
nostril, with its rim complete.

Third Stage.—Embryo of Mole, 74 and 8 lines long.

In an embryo two-thirds of an inch long (Plate 16, fig. 5) the fingers and toes are
distinct, and the small pig-like creature has got a distinct circular eyelid ; the meatus
externus is very small, and encircled with a fold, and the nostrils are now well
fashioned.

The true hyaline cartilage is now differentiated, and in this stage I shall give a
description of the sections made from a specimen scarcely two-thirds of an inch
(7% lines) long. The dissected figures of the skull of the next stage (2 inch long,
Plate 25, figs. 2, 3) will serve, like a ground-plan, to explain both the sets of sections,
namely, those of the same stage, and those of this earlier embryo.

From about 200 exquisitely sectioned and perfectly stained slices of this small

* These and most of my sections were made for me by my son, Professor W. N. Parker; those of the
next stage were made by, and belong to, F. Penrose, Esq.

—s ee eee

te

a EE eee

so

i =

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 161

head—3} lines long—I have only figured twelve, but some of these are drawn as
separate half sections; they were somewhat oblique.

Section 1 (Plate 23, fig. 1).—This is close to the hind part of the alinasal region (al.n.),
at the beginning of the aliseptal. The nasopalatine canal is open below, and here,
behind the narial valves, the cavity is high and simple. The septum nasi and alinasal
folds (s.n., al.n.) are well developed; the thickness of the former, below, is due to
the size of the intertrabecula, and the cartilaginous walls are thickening above to
form the nasal turbinal, and below to form the inferior turbinal.

In the thick mass of tissue below the septum the recurrent cartilages (rc.c.) are
seen, they are placed subvertically, and are thick above and thin below ; outside them
JACOBSON’S organs (j.0.) are shown, and inside them the palatine processes of the
premaxillary (p.pa.).

The hind part of each premaxillary (px.) is cut through laterally, there are two
laminz of bone meeting, above, at an acute angle; below, in the mucous membrane,
a tooth-pulp (p.) is shown ; the nasals (i.) are forming, above.

Sections 2 and 3 (Plate 23, figs. 2 and 3).—These, which were one oblique section,
show, on the deepest side (fig. 3), the remarkable manner in which the rudimentary
nasal turbinal (7.tb.) encloses an oval space ; below that space the cartilage grows
inwards, and is pedate ; this is the inferior turbinal. Here, inside JACoBson’s organs
(j.o.), the recurrent cartilages (7¢.c.) are thick throughout, and the little vomerine
bones are not apparent. The maxillary (mz.) comes into the section here, and the
nasals (.) are seen, above. In this, as in the last, mucous crypts are seen here and
there between the lining of the nose and the cartilage ; the whiskers are cut through
in the outer skin, and a tooth-pulp is shown below.

Sections 4 and 5 (Plate 23, figs. 4 and 5).—These, which were one oblique section,
were made through the middle of the eye-bail (¢.) on one side, and on both through
the olfactory lobes (C™.). It also takes in the lower face, with the tongue (tg.). The
mass of soft tissue under the olfactory lobes will be differentiated into the cribriform
plate, the olfactory nerves passing through its meshes. This is behind the roof of
the nasal labyrinth, and thus the septum, here, the perpendicular ethmoid (p.e.), has
a free upper edge—the region of the crista galli.

In the side which is the foremost part (fig. 4), the nasal wall passes a little over,
above, and under, below, and sends inwards a large plate of cartilage, which is
bifurcated and very thick at its inner part Here we have the rudimeutary middle
turbinals (m.tb.). The same is seen on the other, or hinder, side, but above; the
section is near the orbitosphenoid, or fore part of the cartilaginous cranium, for it is
continuous with the nasal labyrinth (al.e.) ; the frontal bone (/”.) is seen outside it.
Also, below the bulbous base of the middle ethmoid, formed here of all the three
trabecule, the hinder forks of the vomer (v.) are to be seen; whilst below, on the
palatine ridge, the palatine plate of the palatines (pa.) is cut across. Below, outside
the base of the tongue (ty.), the dentary (d.) and MxEcKeEw’s cartilage (mk.) come into
view.

MDCCCLNXXY. y

162 MR. W. K. PARKER ON THE STRUCTURE AND

Section 6 (Plate 23, fig. 6).—This large partial section is through the back of the
eye-balls (e.), the front of the cerebral hemispheres (C'*.), and the hind part of the
nasal labyrinth. The perpendicular ethmoid (p.e.) is, as in the last, a wall standing
alone, rounded, but thinnish above, thick and bulbous below ; at present, the whole roof
of the labyrinth, or floor of the cranial cavity at that part, is void of cartilage; there
are two nasal passages (n.p.) on each side, and between them the rudimentary middle
turbinal is growing. The floor of cartilage is imperfect below ; the wall (a/.e) passes
into the orbitosphenoidal lamina,*above, and there is a fissure more than half-way
down. The raphe formed by the meeting together of the right and left palatal
lamin is strengthened, still, by the palatine plate of the palatine (pa.); a wide,
but not deep passage (7.p.c.) is seen above this second floor. The root of the tongue
(tg.), tooth-pulps, and the dentary bone (d.), with Mrcxer’s cartilage (mk.) inside it,
are all shown in the lower part of this section.

Section 7 (Plate 23, fig. 7).—Here the cerebral hemispheres (C'™.) are large, and the
wide orbitosphenoids (0.s.) form the floor of the cranial cavity; they are continuous
with the presphenoidal bar (p.s.), which is oval, with the long diameter transverse.
The wings themselves (0.s.) are thinner and then thicker, twice over. This section is
diagnostic of a Hutherian skull ; the alisphenoid (a/.s.) comes into the same section with
the orbitosphenoid (0.s.) lying outside it, and they have the Gasserian ganglion (V.)
between them. Here the pterygoid bones (py.) are cut across, and the little nodule
of cartilage, which becomes the pterygoid (pg.c.). We also see the undiminished
Meckelian rod (mk.) with the growing ramus of the lower jaw (d.) outside it. The
large nasopalatine canal is constricted in the middle, and has the ceratohyals (c.hy.)
in section below it.

Section 8 (Plate 23, fig. 8).—This section is through the fore part of the basi-
sphenoidal bar (.s.), close behind the presphenoid ; here it has been formed by the three
trabecular bars, the hind part of the intertrabecula wedging in between the paired
trabeculee,

The angle of the orbitosphenoid (0s’.), and part of its lower hind margin, has been
cut through ; this latter band is, however, far from the basal beam ; it lies over the huge
Gasserian ganglion (V.), the fore part of which is here seen in section ; this mass lies on
the out-thrust alisphenoid (a/.s.) which is hollow above, and has a thick upper edge.
On the inside of each alisphenoid the upper part of the corresponding pterygoid is
cut across, and below the alisphenoid is the lower jaw or dentary (d.) developing
outside Mecxev’s cartilage (mk.); it is an oblique long oval tract, hollow in the inside
where the rod of cartilage lies. The wide nasofaucial passage is constricted at its
middle ; below it, part of the larynx is seen, and on the outside the ceratohyal (c.hy.).

Section 9 (Plate 23, fig. 12).*—This section is directly in front of the pituitary body
and sella turcica; and here the alisphenoid is cut across, where it runs near the

* The re-arrangement of most of these figures as half-sections, so as to get them into a smaller space,
has produced some confusion ; the figures do not always follow in regular succession on the Plates; but

the numbers give the correct order, except in this instance.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 163

basisphenoid (b.0.),* the tympanic wings of which are seen as projections, below.
A small tract of each wing is seen above the internal carotid (7c) entering
the skull, and the orbitosphenoidal band (0.s’.) is also seen at one-third of the height
of the side-wall. The inner margin of the huge Gasserian ganglion (V.)—here
cut across its middle-—lies in the bend of the artery, it reaches more than halfway
outwards and upwards to the orbitosphenoidal band.

The angle of the outer mandible (mn.) is cut through, and below, and further
inwards, MECKEL’s cartilage (mk.).

Over MEcKEL’s cartilage the curved section of a considerable tube is seen, and also
under it and nearing outwards a much larger space; the upper cavity is the beginning
of the Eustachian tube, and the lower the tympanic cavity. Outside the latter
a patch of cartilage is shown; this is part of the meatus. Under the inner
edge of the tympanic cavity the epihyal cartilage (e.hy) is cut off close to its junction
with the ceratohyal ; and towards the mid-line the hypohyal (h.hy.) is severed near
the larynx (/x.), part of the cartilage of which is laid bare.

Sections 10 and 11 (Plate 23, figs. 9 and 10).—These two half sections show the
pituitary body (py.) above and in front of the ascending postclinoid cartilage, in the
upper surface of which we see the point of the notochord. The auditory capsules (ch/.)
are cut across; they lie a considerable distance from the basisphenoid (b.s.). The
orbitosphenoidal band (0.s.) is present here, it soon becomes the supra-auditory crest.
Over the auditory capsules the Gasserian ganglia (V.) are seen cut across in their hind
part, and below them the geniculate ganglia (VII).

In fig. 9, the tympanic cavity is cut across; outside and below it the meatus
cartilage is shown. The small upper piece is outside the head of the malleus (m/.),t
below which the body of the incus is seen, whilst its long crus is shown as
turning inwards towards the capsule; the fenestra ovalis is cut across at its front
margin in fig. 10, but the stapes is massed.

Section 12 (Plate 23, fig. 11).—In this partial section we see the basilar artery (b a.)
cut across obliquely over the hind part of the basioccipital (b.0.); here the large hind
part of the cochlea (chl.) touches the basisphenoid, ready to coalesce with it. The
orbitosphenoidal band (o.s’.) is now very deep, close in front of its supra-auditory
continuation.

The geniculate ganglion is still seen, and also under it the passage in the top
of the auditory capsule for the facial nerve (VII.), which enters its canal at this place.
The outer wall of the auditory capsule is deficient in two places here; the upper
deficiency is partly filled up by the base of the stapes (s¢.), it is the fenestra ovalis ;
between its base and apex the stapedial artery (st...) is seen as it passes to the inside
of the mandible. The other space, not stopped up by cartilage, is the fenestra rotunda ;
the outer part of the capsule with its tegminal projection (¢.ty.) is seen external

* The letters of reference should have been b.s., and only one line to 7.c.
} The line of reference to the figure is made too low down.
Y 2

164 MR. W. K. PARKER ON THE STRUCTURE AND

to the stapes, and the epihyal (ehy.) growing from it; the notochord (nc.) is
compressed in the middle of the basal cartilage.

Section 13 (Plate 23, fig. 18).—This partial section is near the last, and shows actual
fusion of the capsule with the basis cranii (b.0.), and the inferior position of the noto-
chord (nc.). The lateral band (0.s’.) is not yet continuous with the auditory capsule,
which is, here, cut through at the meatus internus. The tegmen tympani (¢.ty.), 1s
severed near part where the short crus of the incus is articulated, and the stapes (s¢.)
is cut through behind the middle, so that the stapedial artery has been removed.
The two fenestrae have a convex tract of the capsule between them.

Section 14 (Plate 23, fig. 14).—The top and bottom of the section are left out, and
the capsule is drawn with the investing basal cartilage (b.0.). Under this sinuous
thinnish plate of cartilage the notochord is seen, and above it the basilar artery.
The crest of cartilage is now the supra-auditory, and the recess outside it at its
junction with the capsule will be filled in by the squamosal bone. The tegmen
tympani is cut through behind the incus; but the fenestree (/s.0., fr.) are still in
view, the anterior and horizontal canals (a.s.¢., h.s.c.) are also seen.

Section 15 (Plate 23, fig. 15)—The supra-auditory cartilage (s.a.c.) is deficient
below, where it passes into the supraoccipital. From the great obliquity of the
capsule we still have the semicircular canals; the anterior (a.s.c.) and the horizontal
(h.s.c.) are here seen to be imbedded in solid cartilage; part of the vestibule is
seen below and within. The capsule is separated by a considerable space from the
basal cartilage (b.0.), which is thick and bracket-shaped; the notochord (n.c.) has
again reached the upper face of the investing mass of cartilage ; the vagus and glosso-
pharyngeal nerves (LX., X.) escape through the interspace, right and left, between the
capsules and the basis cranii; the foramen for the hypoglossal (XII., /: condyloideum)
has been laid open. These sections of the newly chondrified skull will be better
understood after I have described the next series.

Third Stage (continued).—Dissection of the visceral arches of an enbryo Mole;
3 inch long.

An inner view of these parts, in connexion with the auditory capsule, is shown as
drawn from an outspread preparation; the osteoblastic tracts had been removed from
MEcKEL’s cartilage (Plate 28, fig. 1). The part of the capsule containing the semi-
circular canals (a.s.c., A.s.¢., p.s.c.) is in its natural relation to the arches, and shows
their extreme obliquity. The capsule is cut away so as to show the base of the stapes
(st.) in the fenestra ovalis. That part of the hyoid arch which corresponds to the
epibranchial

the epihyal (ey.)—is seen to be outside the stapes, and to be con-
fluent with the capsule a little above the insertion of the head of the pharyngohyal
(stapes). The junction of the inturned end of the long crus of the incus (/.c.2.) is
from the eye in the figure, and is hidden by the base of the stapes, the perforated
stem of which is at a right angle to that part of the incus. Looking upon the short

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.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 165

crus of the incus (s.c.7.) as the morphological equivalent of the “ otic process” of the
quadrate of a Bird, Reptile, or Amphibian, and remembering that the “ orbital
process” is suppressed in this Mammalian suspensorium, we see by this figure that
the incus is well in front of the auditory capsule. Indeed, it is as definitely in front as
in the embryo of any of the Sauropsida, in some of which the otic process, ulti-
mately, runs backwards to be articulated with the fore edge of the occipital arch,
beyond the auditory capsule, altogether.

The body of the incus (7.), as well as its two crura, is already of the normal shape,
and so also is the malleal portion of the primary mandible, with its bulbous head, and
its large, forwardly-turned manubrium (ml., mb.). The large, terete, sigmoid Meckelian
rod (mk.), after uniting with its fellow of the opposite side, runs into a basimandibular
spike (b.mn.).

Here, normally for a Mammalian hyoid arch, but not for a branchial arch, as such,
there are three segments below the flat, rounded epihyal (e.y.), which is not united
with its own uppermost segment, but with the auditory capsule. Nor is it united
with the next segment, or upper ceratohyal (c.hy.), by cartilage, for that next lower
piece is fibrous above.

The two next segments are the straight lower ceratohyal (c.iy.), and the curved
hypohyal (h.hy.); this is the stoutest of all the segments. The common rudiment of
the basihyal, basibranchial, and first hypobranchiais (b.h.br., t.hy.), is a stout, well-
formed U-shaped piece, with the front edge of which the two hypohyals are articu-
lated. Over the tympanic cleft, the tympanic annulus (a.ty.) is seen, formed of a
crescent of tender bone round the membrana tympani (77.ty.).

Fourth Stage.-—Skull of embryo of Mole; 3 and $ of an inch long.
Dissection of the chondrocranium of an embryo Mole, 3 inch long.

The basal view of this skull (Plate 25, fig. 2) shows the distinctness of the olfactory
and auditory sense-capsules from the cranium proper, and the upper view (fig. 3)
displays the large amount of cartilaginous “tegmen,” in spite of the cruciform
fontanelle. The general outline of the skull is pyriform, the narrow nasal end being
the stalk ; this is dilated, in front, over the inferior external nostrils (e.7.), and again
where the alinasal region (a/.n.) ends, opening below at the beginning of the aliseptal
region (al.sp.), where the inferior turbinals (7.tb.) are given off. At its middle the
nasal labyrinth swells out, suddenly, so that it is itself pyriform, and ends in front
of the orbitosphenoid (0.s.) in a large and somewhat bilobate cushion ; the right and
left masses are separated by the perpendicular ethmoid (p.e.) which passes into the
septum nasi (s.v.). The long alinasal region is closed below, except at the sides,
in front ; and the hinder fourth of the main labyrinth is also perfectly floored with
cartilage. The open space between these two floored regions is largely filled up by
the huge recurrent lobes (rc.c.) which support JACcoBson’s organs; these tongue-like
tracts are three-fourths the length of the long open space, and are themselves supported

166 MR. W. K. PARKER ON THE STRUCTURE AND

on their inner face by the anterior paired vomers, which are very slightly separated
from the palatine processes of the premaxillaries (p.pw.); the whole of these bony
tracts has been figured here, in situ. In the dilated front end of the lower opening
the inferior turbinals (7.tb.) are seen, and the folds of the middle turbinal (m.tb.) in
the hinder rounded space. Where the floor turns inwards and upwards towards the
septum (p.e., s.7.), there it gives off a spike of cartilage which nearly reaches the
recurrent lobe; this spike is the precurrent cartilage. The line of junction of
the proper cranium with the nasal labyrinth (o0.s., a/.e.) is quite visible; the orbito-
sphenoidal region of the cranial wall and roof is very wide, and has a convex outer
face. The stem of each tract is narrow, and becomes, after ossification, the permanent,
small orbitosphenoid. Each band winds round behind the corresponding lobe of
nasal labyrinth, and is not flush with it, below ; the two bands are continuous with
the presphenoidal region of the prepituitary basal beam.

That beam is thickest where these bands join it ; it is mainly formed of the inter-
trabecula, for the paired trabecule are flattened against the median part, and then
cease between the hinder part of the right and left nasal floors, The chink between
the convex hinder edge of the orbitosphenoidal stem (0.s.) and the concave edge of
the alisphenoidal lobe (a/.s.) is ear-shaped and curves backwards, and is large and
round against the basal beam; this is the large sphenoidal fissure for the ophthalmic
and orbital nerves (V!.). The small optic foramen is oblique, and is hidden in this
view by the alisphenoid (see fig, 3, I1.).. The basal cartilage is very narrow between
the orbito- and alisphenoids, and then expands suddenly, to remain wide to the end
of the skull. Here, as in all typical Insectivores, the basis cranii in the early skull
is extremely wide, ready to become pneumatic in relation to the auditory function.
Even where the large cochlez (ch/.) push their coils right and left against the basi-
sphenoidal, at its junction with the basioccipital, region, it is still nearly four times
as broad as at the point where the presphenoid and basisphenoid meet.

The stem of each alisphenoid scarcely becomes pinched in, but its margins are both
concave, having the emerging orbital nerves in front of it and the swelling cochlea
behind. Just where the latter concavity is seen, there the sub-basal cartilage swells
out into a mammillate mass, which looks outwards and forwards, reaching three-
fourths of the distance ta the sphenoidal fissure. These solid masses, which look like
the basipterygoids of a Lizard or Bird, are the chondrocranial form of the ‘ tympanic
wings ;” when ossitied, they become pneumatic.

The alisphenoids (a.s.) are very remarkable; their broadest part is proximal, but
they dilate again at their outer, free edge, after becoming narrowed in by one-fourth at
their middle. Their front margin, which helps to form the sphenoidal fissure, is
concave, and their postero-external edge is cut away, so to speak, by the large
pupiform cochleze (ch/.), around which the posterior edge of the alisphenoid is carefully
bound, The hind margin is a large right-angled notch; the outer edge is sinuous,
rounded, and looks forwards and inwards ; all this outer part is swollen, but perforated,

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 167

equidistantly, in two places, by the 2nd and 3rd branches of the 5th nerve, thus
forming the foramen rotundum, and foramen ovale (V*., V*.). The thick semicircular
inner margin of this outer lobulated part stands off from the main plate, and the
whole of the outer part lies below, free of, and at a distance from, the orbitosphenoid,
which it overlaps considerably. This very diagnostic Mammalian alisphenoid is
followed, postero-externally, by a large fenestra, a space totally devoid of cartilage,
but which is being filled up by the squamosal bone; it is the upper part of the
tympanic space, and is traversed by the ossicula auditds. Round it, like a bow, the
orbitosphenoidal band (0.s’.) is bent, passing, behind and above, into the supra-auditory
cartilage (s.a.c.); below, this band forms the fore part of the tegmen tympani, and the
incus articulates, by its short crus, at the junction of this lateral band with the
auditory capsule. These capsules, in their basicranial setting, are very elegant
structures; they stretch from the tympanic lobes of the basisphenoid, antero-
internally, to the feebly-expressed paroccipital ridge, right and left, postero-
externally. The cochlez (c//.) show their three coils, and the fenestree rotande (fr.) ;
these are very large, and well seen from below.

The fenestra vestibuli is closed by the stapes (sf.), a small irregular ring of cartilage.
Up to the passage for the 9th and 10th nerves (1X., X.) the capsule is very distinct
from the chondrocranium, but in the mastoid region below the semicircular canals, and
where the posterior canal is imbedded, there is more or less fusion of these parts
The very large relative size of the occipital arch reminds one, at once, of that of the
Echidna; here the chondrocranium is as complete as in the Skate.

The notochord (ne.) is seen from below, up to the point where it rises into the post-
clinoid wall (see fig. 3, nc., p.cl.), in which the proper, primary axis of the animal ends,
and beyond which everything is of the nature of an outgrowth.*

An elegant narrow waist is formed to the basis cranii by the pressure of the large
cochleze ; behind this part the parachordal tract expands sinuously, and runs upwards
into the side walls. The whole hind part is very smoothly rounded, and the condyles
(oc.c.) are very flat, and have a sulcus across them ; the foramen magnum (/fm.) is
very large; the f. condyloideum (XII.) is small and far outwards, near the concave
edge of the arch.

The upper view (Plate 25, fig. 3) shows the roof of the nasal labyrinth, with its
long fore part, and its lateral lobular expansions right and left of the deep, multi-
perforate rhinencephalic recess (c7.p.). The crested intertrabecula, at its junction
with the hind part of the nasal roofs, above, shows a small crista galli (er.g.) ; the wall
below this part is thin above ; it is the top of the perpendicular ethmoid (p.e.), which
widens, gently, to pass mto the presphenoid (p.s.). The narrow, backwardly-curved

* There are two ways of looking at the prochordal tracts of the skull—the trabeculz and inter-
trabecula; some see in these parts a highly modified, first visceral arch; I confess that, at present, they
merely seem to be ongrowths of the proper axis to finish the new, highly expanded fore part of the skull;
made necessary, in the Vertebrata, by the great expansion, even in the lowest kinds, of the neural axis.

168 MR. W. K. PARKER ON THE STRUCTURE AND

stems of the orbitosphenoids (0.s.) show their optic perforations (IT.), close behind
the outer margins of the cribriform plate; thence the cartilage expands rapidly,
and curves over the sides of the roof as far inwards for some distance as the
lateral ethmoidal lobes (a/.e.); the line of union between these parts is still visible.
Narrowing from before backwards, and bowing outwards, the cartilage runs so as to
become, first, the supra-auditory (s.a.c.), and then the supraoccipital region (s.0.)

The neat, rounded selvedge of this cranial wall and roof (tegmen cranii) forms the
outline of a huge cruciform upper fontanelle, through which, the membrane being
removed, we see the floor of the cranial cavity. Much of what has been described in
the lower view is seen here from its upper face, but the low postclinoid wall (p.cl.)
and the large multiperforate meatus internus (VIL, VIII.) are only to be seen on this
face. Also the general smoothness of the gently concave inner surface of the
chondrocranium is to be noted, and, over the top, the manner in which the supra-
auditory part of the tegmen cranii flanks the fore edge of the occipital roof (s.0.), a
sulcus marking the distinct regions.

Fourth Stage (continued).— Visceral arches of the skull of an embryo Mole ; £ inch long.
J D Y 5 g

A. somewhat more advanced embryo than the last yielded me a very important
stage in the development of the visceral arches. The deep and the superficial jaw
are shown in relation, with the hinge-piece (incus) attached to the fore part of the
auditory capsule. In this inner view (Plate 28, fig. 2) the ampullz of the anterior
and horizontal canals (a.s.c., h.s.c.) are laid bare, and the short crus of the incus (?.)
is seen to be attached close in front of these parts of the membranous labyrinth ; that
process is very short and obliquely attached ; and in this shortness and obliquity
it shows an intermediate stage between the normal Mammalian incus, on one hand,
and the curiously arrested incus of a Monotreme, on the other. The long crus,
however, is well developed, and is articulated by its inturned discoidal end, with the
head of the stapes (s¢.), the base of which is turned towards the eye. The malleal
end of the deep mandible is well developed, and the fore-turned internal angular
process lies in the centre of a thick cushion of soft stroma—the future membrana
tympani (i.ty.). This is partly enclosed by a delicate lunule of bone, the annulus
tympanicus (a.ty.). The posterior angular process of the malleus is almost suppressed.
The main part of MEcKEL’s rod (mk.) is evenly terete and sinuous, but it is largest
near the head, and near the distal end; there it is continued into a median process, the
basimandibular (b.mn.), into which both the rods end. The only bony matter in this
primary mandible, as yet, is a short ring, or shaft, close behind the thick part, close to the
median rod. Morphologically speaking, this is a hypobranchial bony segment. Outside
all but the malleal portion there is, already, a well-formed superficial jaw, bony in front
and cartilaginous behind, and having a groove, on its inside, between its condyloid
and angular processes (ed.p., ag.p.) for the descending Meckelian rod, the bony
matter (d.) beginning to run up the unciform coronoid process (c.p.). Here, if there

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 169

were a coronoid bone, like that of a Reptile, this postero-superior part of the dentary
would be distinct. The inner alveolar plate corresponds to the splenial bone; an
angulare, a supra-angulare, or an articulare would have to be sought for on the malleal
part of the deep or primary mandible.

The stapes (st.) was dislocated out of the fenestra ovalis in making this preparation.
I did not figure the rest of the hyoid arch.

Fourth Stage (continued).—A series of vertically-transverse sections of the head of an
embryo Mole, # inch long from snout to root of tail.

During the time that the embryo of the Mcle grows from 15 mm. to 18 mm., the
tissues gain much increase of solidity ; this is, indeed, the best stage for studying the
structure and relations of the chondrocranium, and the superficial bony plates which
it draws to itself for increase of strength.

The long snout (see Plate 25, figs. 2, 5) admits of being sectioned into a large
number of slices; I have, however, only figured a moderate percentage of those that
were made in this case (Plate 23, figs. 16-19), which was an embryo of the same size
as that which was dissected to show the chondrocranium (Plate 25, figs. 2 and 3).

The Ist Section (Plate 23, fig. 16) is in front of the outer nostrils ; here the upper
part of’ the section is the narrower; the lower is the narrow part further back. Here
the septum nasi (s.7.) is perfect, and is dilated both above and below ; the alee (al.n.)
are thick above, turn inwards below, and the thick growth below turns upwards.
Part of the folded part below is so curled round as to appear in this section as a
distinct segment.

2nd Section (Plate 23, fig. 17).—This is close to the nostrils, and the nasal passages
are seen projecting outwards, right and left. The septum nasi (s.n.) is thinnest at
this part, and here the alie nasi (a/.n.) turn inwards abruptly, whilst the folds that
form the floor (7,f:) are reaching further upwards.

3rd Section (Plate 23, fig. 18).—Here the narial tubes are surrounded by cartilage,
for the floor has reached the roof (nf, al.n.), and now the septum (s.n.) is very thick
above, and of considerable thickness below the most dilated part.

4th Section (Plate 23, fig 19).—Here the roof and floor are confluent at the sides,
and in this section it is seen that the floor has turned inwards so as to project, laterally,
by its proper end, into the nasal passage, the fold uniting with the dilated septum
(s.n.)—or intertrabecula,

Here the mandibles are cut across in their fore part, and the basimandibular rod
(b.2n.) unites the two Meckelian rods (mk.).
5th Section (Plate 23, fig. 20).--This is behind the snout, in the front part of the
proper nasal labyrinth, which is now open below. Here the nasal septum is seen
to be merely the round intertrabecula—like that of an embryo Bird—with the nasal
roofs, however, united to it. The only remnant of the floor, so large and perfect in the

MDCCCLXXXV, Z

by its upper face.

170 MR. W. K. PARKER ON THE STRUCTURE AND

last section, is a retral tract of cartilage, convex on the inner face, where it touches the
septum, and concave externally; this is the “recurrent cartilage” (ie.c.) developed
for the support of JAcoBsON’s organ. Here the upper lips are seen, and have a hollow
palatine part between them ; below, the Meckelian rods (mk.), are distinct in the mass
of the lower jaw, over which the tip of the tongue is seen. The pulps of the whiskers
(vibrisse) are cut through in the outer thick skin.

6th Section (Plate 23, fig. 21).—Here the septum nasi is deeper, and the bulbous
part less; the aliseptal folds (a/.sp.) turn inwards below; the inturned part is the
rudiment of the inferior turbinal. The recurrent cartilage (7c.c.) was tubular between
this and the last section ; but it is now open again to the end; here it has JAcopson’s
organ (j.0.) in its concavity. The pulp of an incisor is seen, and MEcKEL’s cartilages
are getting some distance apart.

7th Section (Plate 23, fig. 22).—This is a remarkable section, and very instructive.
It is behind Jacopson’s organs and cartilages, and is seen to be girdled with bony
tracts—the nasals (v.) and maxillaries (mz.), with their palatine plates; the base of
the deep septum (s.7.) also is supported by the main vomer (v.). The septum becomes
thin above, as it passes into the broad and solid nasal roof (a/.sp.), which is convex
right and left and in the middle. The wall as it becomes floor turns inwards to form
the pedate rudiment of the inferior turbinal, which projects upwards so as to lessen
the nasal passage below. Below each shallow valley on the roof, a large lamina of
cartilage grows downwards and a little outwards, dividing the nasal passage into a
larger inner, and a lesser outer, space, both subvertical and somewhat pinched in at
the middle.

This is the “ nasal turbinal” (7.tb.), which for a short distance, fore and aft, and for
a short time during development, forms a complete secondary nasal septum on each
side of the septum proper (s.7.).

8th Section (Plate 23, fig, 23)—This is immediately in front of the olfactory fosse,
and through the fore part of the eye-balls (e.); this is the widest part of the complete
nasal labyrinth. The septum is now perpendicular ethmoid (p.e.), and the roof is in
the aliethmoidal region. The maxillary (i.) is cut through close in front of the
orbit, and again in the palatal region, right and left of which there is a tooth-pulp (¢.).
The vomer (v.) is cut through its middle, and over it the deep septum (p.e.) thickens
twice ; it also grows so as to lift the roof over it into a low rounded ridge. Inside,
near the septum, and at the upper part of the wall, there are small rudiments of the
upper turbinal folds (w.tb.), and half way down the wall grows inwards as a large mass
of cartilage, pedate in section ; this is the common rudiment of the middle turbinal
folds (m.tb.). The floor is cut throu
it ends far from the mid-line. Below, the dentary (d.) is cut through ; over it, outside,

oh behind the inferior (properly anterior) turbinal,
is a tooth-pulp, and further inwards MEcKEL’s cartilage (mk.); the tongue (tq.) is now
developing its frenui. The palatine plate of the palatine begins to be seen in section,

91h Section (Plate 23, fig, 24).—The olfactory lobes (C’.) are cut through the

tw)

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 171

middle in this section, and also the eye-balls (e). Here we have apparently an open
floor to the brain, which is the roof to the nasal labyrinth, for the cribriform plate is not
yet chondrified. The solid septum (p.e.) is still convex in two places, it stands quite by
itself in the section, for the lateral ethmoidal structures at this part, are far from
it, right and left; it is supported, below, by the vomer. There is still a small
upper turbinal rudiment, and the middle turbinal (.tb.) is in two folds; the floor
is strong, it is still at a great distance from the mid-line. Over the eye (e.) the
frontal (7) is seen, and the maxillary palatine plates, those of the palatines, and the
jugal bones ( pa., j.) ave seen in the roof and sides of the mouth. The tongue (¢g.) is cut
through its middle ; and the lower jaw is seen as a cruciform section of the dentary (.)
holding a tooth-pulp (¢.) above, and Mecken’s cartilage (mk.) below.

10th Section (Plate 23, fig. 25).—The cribriform plate (c7.p.) is here a large
membranous tract, right and left, hollow above and convex below.

The perpendicular ethmoid (p.c.) has lost one-third of its height, and is much
thinner above; the floor (nf) has now reached it, and each plate articulates with
its bulbous base. The wall and the last fold of the middle turbinal (m.tb.) are
thick plates, free above, and having their concave faces looking towards each other ;
the nasal canal is thus subdivided into two passages, the outer oval, and the inner
unciform, in section. Another cartilage has appeared above the low wall, and at a short
distance from it; this is the orbitosphenoid (0.s.); it is thicker below than above,
and convex outside; at a small distance outside it a much larger part of solid tissue is
cut through, this is the frontal (f-), which, however, only forms a wall—not a roof—
to the huge hemisphere (C™.).. The vomer (v.) is still seen in section, and the palatines
(pa.), with it, almost complete the fence round the bilobate nasopalatine passage.
Below, the dentary (d.) is thickening over MEecKeE’s cartilage (ih).

11th Section (Plate 24, fig. 1).—This section is through the hind part of the nasal
labyrinth, and the nasal passage (i.p.), right and left, is single, large, and heart-shaped.
This is the last section through the membranous cribriform plate (cr.p.), and the
perpendicular ethmoid (p.c.) is but little above half its original height ; the nasal wall,
being cut through obliquely to its plane, looks extremely thick. The ascending floor
is still articulated with the bulbous middle wall. Here the orbitosphenoid (0.s.) is
larger, and is sharp both above and below; it almost reaches the nasal wall. ‘The
frontals (f-), the palatine (p.), and the forks of the vomer (v.) ure seen in section ;
also Mreckev’s cartilage (mk.), and the dentary (d.) below.

12th Section (Plate 24, fig. 3)—This and the next section have been accidentally
transposed : the back wall of the nasal labyrinth is here seen and the fore part of
the Gasserian ganglion (V.).

This part shows a very deep orbitosphenoid (o.s.), resting by its thick base upon a
cartilaginous fold growing out from the back of the nasal labyrinth; although
the orbitosphenoid (0.s.) was cut through, the small optic foramen was caught
in this section. The presphenoid (p.s.) is almost trilobate, and is composed of the

Z 2

172 MR. W. K. PARKER ON THE STRUCTURE AND

three trabecular hars—the trabecule right and left, and the intertrabecula above.
the fore edge of the alisphenoid is not yet reached, but the fore part of the Gasserian
ganglion (V.) is shown. On the side of the wide, oblong nasopalatine canal (7.p.)
the pterygoid bone and cartilage (pg., pg.c.) are cut across, and below we have still
the dentary with Mrcxev’s cartilage (mk.), and also with the superficial cartilage that
forms the condyloid and angular regions ; the ceratohyals (c.hy) are also seen in this
section,

13th Section (Plate 24, tig. 2).—This partial section shows the orbitosphenoid (0.s.)
in two parts, the postero-superior band, and the hind margin of the stem ; the basal
part (p.s.) is fusiform. Below the stem of the orbitosphenoid, at a considerable
distance, the alisphenoid (q/.s.) is seen as a thickish plate, curved downwards, and
beaded at its outer edge, Its concavity makes a nest for the large Gasserian ganglion
(V.), which is protected above by the orbitosphenoid. ‘Two thick rods of cartilage
are cut through between the alisphenoids, one on each side of the broad nasopalatine
passage, they turn inwards and downwards, and are capped with a film of bone
above, these are the pterygoid cartilages, with the growing pterygoid bones (see
fig. 3), Below we see the mandible as one large folded tract of bone (d.) embracing
three cartilages; the middle of these is the Meckelian rod (mk.), the others are the
condyloid and angular parts of the superficial slab. Below the oral cavity (m.) the
ceratohyals (c.hy.) are seen.

14th Section (Plate 23, fig. 4).—Here the same parts are better seen, than in the
last, in a more symmetrical figure.

15th Section (Plate 24, fig. 5).—Here only the posterior band of the orbitosphenoid
(0.s’.) is seen, for the basal part (b.s.) now runs into the alisphenoid (q/.s.), which is
cut through proximally, at its postero-external angle. The Gasserian ganglion (V.)
still lies on it, at its proximal part, the cartilage dipping considerably to form a
nest for it. Here the basisphenoid (0.s.) is formed of the outspread and coalesced
trabecul, this part being somewhat in front of the pituitary space. The squamosal
(sq.) is seen outside the angle of the alisphenoid, and MercKet’s cartilage (mk.),
the latter, the end of the angular, and part of the articular cartilage (in.), are also cut
ACrOSs.

There are three cavities laid open, namely, the nasopalatine (7.p.c.), the mouth (m.),
and the larynx (/z.); the Eustachian tubes are also laid open in their inner half,
continuously with the nasopalatine passages. Besides the cartilage of the larynx, the
epihyal, and hypohyal (c.hy., h.hy.), are cut through.

16th Section (Plate 25, fig. 6).—This is from a little further backwards than the
last, and takes in part of the meatus auditorius externus, with its lining cartilage
(m.a.c.). This partial section is below the orbitosphenoidal band, and behind most
of the alisphenoid (a/.s.); outside the proximal part of that wing, which is cut through
below the Gasserian ganglion (V.), MECKEL’s cartilage (mk.) is seen high in position,

and large in size. The Eustachian tubes (ew.) are laid further open than in the last

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. L73

section, and besides the hyoid rods (e.hy., h.hy.), the thyvoid cartilage, as well
as the arytnoids (/z.) are cut across.

17th Section (Plate 24, fig. 7)—This section is through the basisphenoid (b.s.), close
behind the edge of the alisphenoid (a/.s.), which, however, is caught further outwards,
still bearing the Gasserian ganglion (V.). The hinder edge of the soft palate is cut
through, and the nasopalatine canal (n.p.c.) is nearly continuous here with the mouth
(m.). Besides the hyoid and cartilages (e.hy., hiy.), and the larynx (/2.), the upper
tracheal rings are seen in section. The tympanic cavity (¢.ty.) is laid open, and
also the inner part of the Eustachian tube (ew.); here the meatus cartilage (7.c.)
is thick. MucKket’s cartilage is now thick: it is the fore part of the head of the
malleus (7.) that is seen at this point; above it a small tract of the tegmen tympani
(t.ty.) is also brought into view ; outside these cartilages the squamosal is shown.

18th Section (Plate 24, fig. 8).—This section is behind the alisphenoid and through
the ganglion geniculatum (VII., VIII.) ; also, besides a small piece of the tegmen
tympani, the fore part of the cochlea (ch/.) is cut across. In this and the last section
the basisphenoid (b.0.)* is concave below, this is because the mammillary processes that
form the foundation of the “tympanic wings” are cut through (Plate 25, fig. 2, 0.s.).
In the hollow we see the large faucial passage (phw.), which opens into the larynx (/a.).
The laryngeal and tracheal cartilages are similar to those of the last section, and so
are the hyoid (e.hy., hiy.); beneath the epihyal, the chorda tympanic nerve (VII*.)
is seen in section. Inside the squamosal, and under the tegmen tympani, the whole
head of the malleus, with its manubrium, is shown; the latter pushing the membrana
tympani before it ; this is behind the Eustachian tube.

19th Section (Plate 24, fig. 9)—This section of the cranial basin is oblique and may
serve as two; the right side is from a point in front of the left ; and from the some-
what sinuous direction taken by the razor, some things on the left side belong to
points in front of the parts shown in the last (fig. 8).

The orbitosphenoidal band and part of the parietal (0.s’., p.) are cut across, above ;
whilst the squamosal (sg.) and the meatus (m.a.c.) are seen lower down. Here, again,
the head of the malleus (m/.) is seen in its whole extent, capped by the tegmen
tympani, and with its manubrium pushing inwards the membrana tympani.
Over the malleus, the ganglion geniculatum (VII., VIII.) is seen, and under the
tympanic cavity (¢.ty.) the ceratohyal (e.hy.). On that side the cochlea (chl.) is just
laid open, on the other it is cut across its middle. Between the two, the basisphe-
noid (b.0.)t has becomes thicker and narrower, and it is still concave below ;
it carries, here, the pituitary body (py.). The obliquity of the section is shown by
the form of the upper part of the fauces ( ph.) below the basis cranii.

The left side is very instructive, for it shows the other elements of the ear-
chain behind the malleus. This is the front view of the section, and thin as it is, the

* The letters of reference in this and the next figure should be b.s.
+ The letters of reference should have been J.s.

174 MR. W. K. PARKER ON THE STRUCTURE AND

incus (7.),* is seen to be nearer to the eye than the stapes, the fore margin
of which lay somewhat back. Here part of both the parietal and squamosal
(p., sg.) are shown and also the orbitosphenoidal band, now the supra-auditory,
where it rests upon the crest of the auditory capsule. Below that crest the
thick outer edge of the capsule is seen forming the tegmen tympani (¢.ty.) under which
the body of the incus (7) is shown, in front of the stapes. The canal for the facial
nerve (VII.), is cut through, outside the cochlea (ch/.), and under the cochlea part of
the vestibule is laid open just at the fore end of the fenestra ovalis. Under the
incus (¢.) a small cavity is seen, this is the hind part of the tympanic cavity which
is very small even further forwards; there is very much soft tissue filling in the
spaces here. Under the auditory capsule, on the outside, the epihyal is seen (see
also Plate 25, fig. 2, e.dy.), and to it is articulated the top of the ceratohyal (e.hy.).t

20th Section (Plate 24, fig. 10).—The description just given may serve for the
next section, but this being a little further back the hole in the stapes (s¢.) has been
reached. In this the facial nerve (VII.) was found in two places, besides the one
above, owing to the curve it takes in its course. The cochlea is most open on the left
side, and on the right it is cut through at its proximal part, and the vestibule is
opened through the fenestra ovalis.

21st Section (Plate 24, tig. 11).—This next oblique section shows the malleus (i.)
on the right side, behind its manubrium ; below it is the tympani cavity (c.ty.) and the
facial nerve and geniculate ganglion (VII, VIII.) ave seen above it. There is still a
considerable space between the auditory capsule (chl.), and the thick oblong section
of the basis cranii, now the basioccipital (b.0.). The hyod bar (e.hy.) is cut through
obliquely, and under it the facial part of the seventh nerve (VIL.) is shown. On the
left side the supra-auditory cartilage (s.a.c.) is continuous with the capsule, and go also
is the basioccipital plate (b.0.). Here the razor passed through the meatus internus
(VIIT.), and the fenestra ovalis ; in the latter the stapes (st.) is shown exactly through
its middle, with the stapedial artery (st.a.) threading it. The top of the epihyal only
is shown at the back of the tegmen (t.ty,), just where the short crus of the incus is
articulated, Under the stapes a small cavity is seen, part of the tympanic (c.ty.).

22nd Section (Plate 24, fig. 12).—This also is oblique, but is two or three sections
further back than that shown on the last figure. Here the right side shows the
stapes (s¢.) cut across with the stapedial artery (st.a.) threading it ; here, however, we
vet a section of the auditory capsule showing both the fenestra, the oval and the round
(fs.0., f.7.),and this also shows the meatus internus (VIIL). The tegmen tympani
(t.ty.)f is deeper here, and the inner edge of the capsule (ch/.) is seen to come down
upon the basal plate (b.0.) to unite with it. This plate is fusiform in section and
has the basilar artery (b.a.) upon it, and the notochord (n.c.) grooving its lower

* The line of reference in this figure is too short and does not reach the incus.
+ In this figure for i read ehy., and for e.hy. vead c.hy.

¢ The line of reference passes downwards instead of across.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 175

face ; the plate passes directly into the cartilage of the capsule on the left side.
There the vestibule (vb.) is laid open and the horizontal canal (h.s.c.) is exposed,

23rd Section (Plate 24, fig. 13).—'This is only a little more than half the floor of
the skull, The supra-anditory cartilage (s.q.c.) is now passing into the supraoccipital,
and is again free from the capsule. The horizontal canal (h.s.c.) is cut across its arch,
the posterior canal (p.s.c.) through its ampulla, and the anterior canal (@.s.c.), above.
The large space between the capsule and the basal plate allows the 9th and 10th
nerves (IX., X.) to pass, and the large size,and the thick edges of the basal plate
(b.0.) is due to the fact that the condyles are cut across, The notochord (n.c.) is
now directly beneath the basilar artery (b.a.); it is seen again in the attached wedge
of the was (axz.) ; the condyles of the atlas (at.) are also seen.

24th Section (Plate 24, fig. 13)—The basilar plate and condyles (0c.c.) are cut
across in this section in the fore part of the foramen magnum. The roof-cartilage
(s.a.c.) lies upon the auditory capsule. This latter shows inside it the hinder part.of
the horizontal canal, and the neck of the posterior canal (p.s.c.) close to the ampulla.
In this, as in the last, the cartilage is very solid above and behind the canals.

The Ist, 2nd,and 3rd vertebrie(ct.,ax.,and below it,a small nucleus),are partly shown.

Fifth Stage.—Dissection of the lower fuce and throat of an embryo Mole ; 1 ineh long.

There is very little difference between these parts in an embryo an inch long and
the same in one four-fifths of an inch (Plate 28, figs. 3 and 2). But in the larger
embryo I was able to get a side view of the stapes (st.). It is shown in the figure
dislocated from the incus (7.), and thus the triangular form and the round hole are
shown. The incus also has its discoid articular facet for the stapes turned towards the
eye. The facial nerve (VII.) is seen in its canal, and in front of it the epihyal (c.hy.)*
is seen to be confluent with the auditory capsule (au.), but only connected with the
ceratohyal (c.hy.) by ligamentous fibres. The extremely thick and soft membrana
tympani (i.ty.) 1s Just beginning to have an osseous deposit in its rim, and its fibres
radiate from the front of the manubrium mallei (mb.). The distal ossification on
MeEcKEL’s cartilage (mh’.) is elongating, and the dentary bone (d.) is creeping up the
coronoid and condyloid processes of the superticial cartilage (c.p., ed.p.). There is no

malleal ectostosis, at present.

Sixth Stage.—Dissection of lower face and throat in an embryo Mole; 1% inch long.
In an embryo a little more advanced than the last there are several things in the
facial arches worthy of notice. The superficial mandible (Plate 28, fig. 4) has not
only increased its bony matter, but the cartilage has become much more solid and in
larger quantity ; the middle process ending in the condyle (ed.p.), especially, is a thick
rounded mass; the glenoid cartilage (g/.c.) is seen capping the condyle. The hypo-
branchial element of the arch—the distal Meckelian ossitication—is now larger, and

* In the letters of reference the hinder c.hy. should have been e.hy.

176 MR. W. K. PARKER ON THE STRUCTURE AND

under the proximal part of this rod, where the malleal enlargement is, there is a small
ectosteal tract ; the future bony centre of the malleus. Also in the thick soft outer
disk of the tympanum there is a crescentic deposit of bone—the annulus. In this,
as in the rest, the short crus of the incus (7) is small and bent downwards; its
symplectic facet, the orbicular region of the long crus, is shown with the outline of
the base of the stapes (st.) round it ; this is the inner view of these parts. The epihyal
(e.hy.) is drawn as cut away from the auditory capsule; its lower end is connected
with the pointed top of the ceratohyal (c.hy.), the long upper piece of which is
beginning to ossify ; the lower piece (¢.hy’.) is no longer than the hypohyal (h.hy.),

oO

which is thick and curved. The basi-thyrohyal piece (b/.b7., thy.) is thick and
roughly U-shaped, with its angles squarish.

Seventh Stage.—A sinilar dissection to the last of an older embryo Mole ; 14 inch long.

This fifth inner view of the visceral arches (Plate 28, fig. 5.) shows another sign of
advanced growth ; the distal ossification of Mrckern’s cartilage is almost surrounded
by a splenial growth of the dentary (d.), forming the inner face of the mandible. The
dentary is also growing well round the thick tract that ends, above and behind, in the
condyloid process (cd.p.); this is capped by the glenoidal tract (gl.c.), a part derived
from the same superficial source. The soft disk round the membrana tympani (77.ty.) is
a more developed crescent of bone—the annulus (a.ty.). The head, both of the malleus
and. incus (ml.,7.), is smooth and rounded, and in each case has a very condyloid appear-
ance; the stapes (s¢.) is detached from the orbicular facet of the incus (¢.); it is a
stout cartilage, with a small circular hole, a distinct neck below its incudal head and
facet, and a thick rim to its base, or proximal plate. I see no interhyal (_ intra-
stapedial) nucleus of cartilage in the tendon of the stapedius muscle (st.m.).

Eighth Stage—Vertical longitudinal section of the head of a ripe embryo Mole ;
13 inch long from snout to root of tail.

In this preparation the interior of the right half of the skull was displayed with the
whole of the ethmoseptal part of the cranial axis.

The figure (Plate 25, fig. 1) will help to a proper understanding of the skull in its
earlier stages, both the sections and the dissections (Plates 23-25). The endocranium
is now undergoing ossification. The nasal region, from the back of the cribriform
plate to the front of the snout, is exactly of the same length as the cranium, measured
from the former point to the top of the foramen magnum. The great internasal septum
(s.2., p.e.) is twice as high behind, at the crista galli (ev.g.), than in front, between the
nostrils ; the dorsal line of this wall is sinuous; its lower edge is gently concave ;
behind the presphenoidal region (/.s.), the lower line of the skull is gently convex,

Between the nostrils, the floor and wall together form a sinuous tract ; behind this
part the calinasal artilage gives off the recurrent (or JACoBsoN’s) cartilage, right and
left (ve.c.). The great intertrabecular bar thickens the septum all along, giving its

—=*

———

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 177

sections a bulbous form, below. The cartilaginous crista galli (c7.g.) is a mere retral
point of the great septum ; below that point the outline is concave, and between the
large cartilaginous cribriform plates (c7.p.), it rises up at the meeting of the presphe-
noidal region with the perpendicular ethmoid.

From the middle of the presphenoidal tract (p.s.), to the foramen magnum, the skull
is drawn as cut along the mid-line; the front part is left entire. Right of the pre-
sphenoidal, the orbitosphenoid (0.s,) is seen helping to wall in the orbital region ; its
stem is ossified, and near the hind margin of the bony tract the small optic foramen
(II.) can be seen. Above the bone the stem broadens suddenly into an axe-blade of
cartilage, which reaches to the top of the skull in front, and also to the top of the
side wall, further back.

Then from the hind margin of the stem to the middle of the auditory capsule there
is an elegant archway of cartilage nearly equal to the orbitosphenoidal stem in
width. Over the junction of this arched band with the auditory capsule the cartilage
—supra-auditory (s.a.c.)—more than equals the great blade of the orbitosphenoid in
size. In reality it is twice as large, but the hinder two-fifths of this large crescentic
crest is ossified as the supraoccipital (s.o.). The roughly oval space below the orbito-
sphenoidal archway is filled up, in its antero-inferior third, by a small ruptured and
out-turned part of the side wall—the alisphenoid (q/.s.); the angle between this
auriform flap and the cochlea (ch/.) is filled by the huge Gasserian ganglion (V.).

The upper two-fifths of the space under the archway is void of cartilage, and is
finished by the investing bones—frontal, parietal, and squamosal. There is no pre-
sphenoidal bone; the orbitosphenoids will meet to finish that region ; the basi-
sphenoid (0.s.) is already present as a short tract in the middle of its own region. The
small lobulate alisphenoid is not ossified, it has two large foramina near its upper part,
the f. ovale (V*.) and the f. rotundum (V*.). The auditory capsule is relatively very large
and extremely oblique in position; it stretches from the hind margin of the ali-
sphenoid upwards and backwards to the lower edge of the supra-oecipital. The large
archway for the 7th and 8th nerves (VIT., VIII.) —the meatus internus—is very near
the great orbitosphenoidal archway, where it becomes supra-auditory. The pupitorm
cochlea (ch/.) lies in a clearly-margined space, right and left of which the basioccipital
and basisphenoidal regions meet. The anterior canal (a.s.c.) has its crown looking
backwards as much as upwards; it arches over a considerable fossa for the flocculus
cerebelli ; it is arched over by a very elegant crescentic channel for the lateral sinus,
which makes the cartilaginous crest very thin at that part. The gap (foramen
lacerum posterius) for the 9th and 10th nerves (IX., X.) is large, and the small
hypoglossal foramen (XII.) is seen close behind it in the occipital arch. Above that
hole the exoccipital bony centre (c.0.) is seen to occupy about a third of the side of
the arch, between the supra- and basioccipital centres (s.0., b.o.) ; the latter is a large
lozenge-shaped tract.

Various investing bones are seen in situ, namely, the nasal, frontal, parietal, mter-

MDCCCLKXXV. 2A

i78 MR. W. K. PARKER ON THE STRUCTURE AND

parietal, squamosal, part of premaxillary, maxillary, palatine, and vomer (Plate 25,
fig. 1, 1., fi, Puy VD SYny PPsH., MH., PO., V.).

Ninth Stage,—Dissections of the skull of young Moles, 3 or 4 days old ;
13 and 14 inch long.

Dissections of the skull of the larger of these young (14 inch long) serve to interpret
the adult skull as well as any of the stages.

The form of the skull is wedge-shaped (Plate 26), the widest part being very near
the end, and the whole skull structure narrowing forwards to the growing snout.
Seen from above (Plate 26, fig. 1), the normal investing bones are shown to increase
in size from before backwards, very remarkably. The oblong nasals (n.) are of con-
siderable width, but they are not so long as the uncovered snout in front of them ;
they are flanked by the premaxillaries and maxillaries (mz., pa.). The small convex
frontals (/.) added to these six bones of the face do not cover so large a surface as the
two parietals (p.); which, together, form half a large ellipse.

A considerable fontanelle (fo.) still exists along and across the skull in the frontal,
coronal, sagittal, and lambdoidal regions; the last of these is the largest space, but it
is partly filled up, behind, by a small semi-annulus of bone—the interparietal (i.p.).
Looked at from the side (Plate 26, fig. 3), other splint-bones come into view. In this
view the premaxillary (px.) is seen to have considerable facial tract, interdigitating with
the maxillary (m.) and reaching up to the nasal (v.). The maxillary is notched by the
frontal (f:) and has the small heart-shaped lachrymal (/.) set into its orbital edge, where,
also, the canal (/.c.) is seen just on the outer margin of the orbit. The canal for the
2nd branch of the trigeminal nerve (V*.) is not finished, and behind and below the
groove, first the jugal (7.) is seen as a small style, followed by the styloid jugal process
of the small, oblique, multilobate squamosal (sq.). That bone is very peculiar in this
small wedge-shaped skull, which is bent downwards, behind, at a considerable angle ;
nearly all the hinder half of the skull is unprotected by superficial bones, and the
squamosal, thereby, forms a small adherent scale on its antero-inferior surface.
Scarcely reaching the lower edge of the parietal in front, it recedes, downwards, from
that bone, leaving a large triangle of the endocranium bare; it is marked off into
two regions, one in front and above, narrow and forked, and the other behind and
below, wide and semi-ovate.

The broad upper tract in front of the proper squamous part has a sharp point, the
jugal process, which overlies the jugal bone (j.); under this fore part we see the
glenoid cavity (gl.c.). The lower and hinder lobe reaches by its rounded end nearly
to the stylomastoid foramen (VII.) and quite to the ampulla of the anterior and
horizontal canals of the ear (a.s.c., h.s.c.). The lower edge, rising forwards, forms the
eave of the tegmen tympani; under it is seen another superficial bone, the annulus
tympanicus (a.ty.), better seen from below (fig. 2). The frontal (f), half the size of

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 179

the parietal (p.), shows the foramen for the ophthalmic nerve (V'.) on its lower
margin ; its orbital plate leaves much of the endocranium (0.s.) naked; it shows no
signs of distinctness from the roof-plate of the bone, such as is seen in the Hedgehog.

The parietal is a fine shell of bone, and is the largest in the skull. The frontal and
parietal clamp each other mutually in the postorbital region, but the latter imbricates
itself on the frontal in the coronoid region ; from the top of that suture to the top of
the lambdoidal, the convex dorsal outline of the bone forms a large and accurate are.

The compound superficial mandible (d.) is almost perfect, but the coronoid,
condyloid, and angular processes (c.p., cd.p., ag.p.) are still cartilaginous ; they are
rounded and sub-equal.

In the lower view (Plate 26, fig. 2) the surface is only invested with superficial
bones in the narrow palatine region ; the occipital, and most of the sphenoidal, regions
are left bare.

Each premaxillary, carrying three teeth, is well developed, but the palatine
processes (p.px.) are largely hidden by those of the maxillaries (i. ; see fig. 5); the
antero-lateral vomers, also, are not seen, they have a very temporary and doubtful
existence independent of these processes of the premaxillaries. The vomer (v.), also,
is only partly seen, but is really very large and typical (fig. 5, v.), being wide, carinate,
pointed in front and forked behind, and has a semidistinct postero-lateral vomer
(v”.) attached to the outside of each fork.

The hard palate is well developed, three-fifths of it belongs to the maxillaries (mz.)
and the rest to the palatines (pa.), which have their palatal plate very large, perfect,
and typical ; yet the fore part of the median suture even of these bones is imperfect,
and the vomer (v.) is partly exposed; the maxillaries meet each other nowhere, at
present. The hinder and upper part of each palatine is a thick lobe of bone turned
outwards, behind, and bevelled on its inner face for the pterygoid bone (pg.). A club-
shaped cartilage adheres to the inferior surface of this small bone, the pointed end is in
front and the clubbed end is turned outwards, behind ; this is the pterygoid cartilage
(pg.c.), and is a genuine remnant of the endoskeletal upper jaw of a branchiate
type. The broad hind skull is seen from this aspect, flanked and supported by the
infero-lateral squamosals (sq.); the annuli (a.ty.) are seen as U-shaped bones—right
and left—with their crura looking outwards and backwards, and their arch almost
touching the pretympanic boss of the basisphenoid. These are all the investing
bones that I can discover at this stage.

The endocranium may now be described. I shall begin with the palatal (or basal)
part first (Plate 26, fig. 5). Looked at, as a whole, this is a very solid cartilaginous
structure, here and there undergoing ossification. The snout (a/.7.) with its inferior
external nostrils (e.n.) has a length about a fourth greater than its breadth ; it is
quite a continuous structure. The snout passes into the proper nasal labyrinth, not
only above and at the sides, but the floor, also, sends backwards a remarkable tongue-
like process—the recurrent or J Acopson’s cartilage (re.c.). This tract, right and left, is

2A 2

180 MR. W. K. PARKER ON THE STRUCTURE AND

very large in the Mole, and is half the length of the proper labyrinth, reaching
backwards almost as far as the inferior turbinals (¢.tb.), here largely hidden by the
inturned nasal wall (a/.sp.).

The tubular part of the recurrent cartilage is short ; the rest is convex below and
outside, and concave on the other face, where it is in relation to JACOBSON’s organ.
In front of the terminal point of these processes the labyrinth expands rapidly right
and left, and these moieties are then to be seen a pair of swollen cushion-shaped masses,
that first bend outwards and then converge towards each other, having only the basal
beam between them. Where that beam escapes from the vomer it is the perpendicular
ethmoid (p.e.) ; a little further back it is the presphenoid (p.s.), and has the stem of
each ala, or orbitosphenoid (0.s.) ossified ; thence, to the top of the skull, these rapidly
widening wings are cartilaginous. The posterior sphenoid is a very remarkable
structure ; it is ossified in its median or basal part only, at present; the anterior
sphenoid does not develop a median piece, but the basal beam receives its bony
growth from the ossifying ale.

The basal region of the posterior sphenoid is at present ossified for about three-
fifths of its length ; this centre (b.s.) is very broad, and is alate in front; it is not a
mere ossified basal beam, for whilst the anterior sphenoid forms its base from its ale,
the posterior sends its basal bony centre far into the proximal part of its wings—
right and left. Outside the hinder half of the basisphenoid, where it has narrowed
in so as to occupy but little more than the proper base (trabecular roots arising from
parachordals) there, right and left, we see a large rounded boss of cartilage just in
front of each cochlea (ch/.). This swelling part, or process (/g.), at the junction of the
ala with the base, is homologous with the cartilaginous “ lingula” seen in the embryos
of Crocodiles and Birds (Trans. Zool. Soc., vol. ii., part 9, plate 64; and Phil. Trans.,
1869, Plate 82). It becomes ossified very variously in these different types, but its
meaning is the same in all. Itis the root of an enlargement for the tympanic cavity—
the posterior sphenoid becoming pneumatic. Behind these bosses the basal part has
an elegant “ waist” and then broadens into large “hips,” on which the cochlee (chi.)
rest.

The alisphenoids (a/.s.) are still unossified ; they have a very broad. proximal part,
even beyond the cartilaginous bosses and the ale of the basisphenoidal centre; they
expand so as to grow round the pupiform cochlez, and then are so notched behind as
to leave a large oval space between their hind margin and the outer part of the
auditory capsule (chl.). In frout of this lateral fontanelle (or fenestra) each alisphenoid
(a/.s.) forms an ear-shaped free lobe, looking inwards and forwards; this lobe is bi-
perforate for the 2nd and 3rd branches of the 5th nerve (V*., V*.).

There is a cartilaginous tract between the new basisphenoidal and basioccipital
centres (b.s., b.o.) equal in size to each of these bones; the hinder centre (b.0.) is
peculiarly reptilian, being at present poly

gonal, and broader than it is long. The

chondrocranium is huge in this part of the head; from the waist-like synchondrosis

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 181

the basal region swells out into broad hips which end, behind, in the slightly convex
but very large condyles (0c.c.); these are wedge-shaped and have a sulcus across them
at their front third, they are almost pointed behind, when they reach nearly to the
end of the enormous foramen magnum (f.m.), the fore part of which is a semicircle,
whilst the hind part widens out irregularly. The fore margin of each condyle is gently
emarginate.

The hinder or opisthotic region of each large auditory capsule is completely con-
fluent with the corresponding side of the occipital arch ; the paroccipital region is a
mere gentle convexity. The exoccipitals (c.o.) can be seen outside the condyles as
narrow tracts of endosteal bone; the supraoccipital (s.o.) reaches the top of the
foramen magnum.

Outside the front part of the condyle (oc.c.), the condyloid foramen (XII.) is seen,
the 9th and 10th nerves (IX., X.) are seen in the distinct foramen lacerum
posterius, and the facial nerve (VIi.) is visible in this view, emerging from the f.
stylomastoideum, behind the epihyal (e.y.). The uppermost part of the hyoid arch—
the stapes (st.)—is shown, i situ, on the right side of the figure, and the incus and
malleus, with a part of Meckev’s cartilage (¢., m/., mk.) on the other side. The
“otic process” or short crus of the incus or quadrate—a secondary retral part of the
suspensorium of the mandible in the Ovipara, and which in them often reaches
beyond the auditory capsule to join the occipital arch—is here seen to be in front of
the semicircular canals. Both the mandibular elements of the ear-chain lie, now, in a
large vacuity of the chondrocranium, which is caused by the curious non-development
of the alisphenoid at that part. All round the pupiform cochlea (ch/.) the line of
separation of the capsules and chondrocranium, proper, is perfect ; and again, on the
outside, the opening into the lateral sinus (/.s.) marks off the epiotic region from the
supraoccipital cartilage ; but in front of the sinus-opening, laterally (fig. 3), and along
the paroccipital region (fig. 5), the confluence of the two structures has been complete.
The fenestra ovalis is filled by the stapes (st.), the fenestra rotunda (/7.) is seen
on both sides.

In the /ateral view (fig. 3), the supraoccipital, supra-auditory, and posterior
orbitosphenoidal tracts of cartilage (s.0., s.a.c., 0.s.), are seen to be confluent, and the
whole hind part of the skull, strongly bent downwards, is composed either of cartilage
or of cartilage-boue (endostosis). Over the foramen magnum the supraoccipital is
large, both high and wide, and the exoccipital (e.0.), is seen to be wider than the
lower view would indicate. There is no appearance of bone in the auditory capsule,
except over the front part of the anterior canal (a.s.c.), and the sinus-opening ; the
labyrinthic part of the capsule is still cartilaginous. ‘The oblique oblongo-crescentic
tract of bone seen, already, in the sphenotic and pterotic regions, is the first of the two
bony periotics formed in the auditory capsule in this type; notwithstanding its
growth along the crest of the capsule, and the fact that it does not help to enclose
the labyrinth, I consider it to be the “ prootic,” and the other, formed afterwards,
the “ opisthotic.”

182 MR. W. K. PARKER ON THE STRUCTURE AND

The tilting of the canal-region of the capsule is well shown in the side view ; the
fore part of the large anterior canal (a.s.c.) leans backwards, under the prootic bone
(pr.9.), at a right angle to the squamosal bone ; its hinder half, below the sinus-canal
is parallel with the outer edge of the occipital roof. The posterior canal (p.s.c.),
which joins the anterior, is parallel with the general direction of the occipital condyle,
and the horizontal canal (h.s.c.) rans downwards and backwards, from the end of the
squamosal to the exit of the facial nerve (VIL).

But for the ossifications of the hind skull, and the continuation of the nasal roof
cartilages to the end of the intertrabecular beam—a peculiarly valuable Mammalian
diagnostic—the upper view of the skull (fig. 4) might have seemed to belong to
a Skate. There is a large membranous fontanelle (/fo.), but it is well surrounded
by solid hyaline cartilage, and in several places the “ tegmen cranii,” or cartilaginous
roof is well developed.

The large and long nasal labyrinth is practically divisible into three regions,
namely, the snout, or alinasal (al.n.); the middle region with the nasal and inferior
turbinals, and, like the snout, supplied from the 5th nerve only (a/.sp.) ; and the true
olfactory region, containing the upper and middle turbinals—the aliethmoida] region
(al.e.). The fluted roof becomes concave near the end, and then terminates abruptly,
in an almost transverse line, at the middle of which there is a small projection—the
crista galli (cr.g.). The wide, lateral, olfactory regions, with their hill-and-valley
markings, reach backwards, right and left, beyond the end of the roof; the oblique
postero-internal margin is confluent with the front of the tegmen tympani, a part which
is continuous with the orbitosphenoid (0.s.). Its tegminal lobe has a sinuous inner
margin, it ends behind, in the narrowish posterior band that runs from the posterior
angle of the orbitosphenoid to the supra-auditory tract (0.s’., s.a.c.) ; this band is convex
on its outer, and concave on its inner, side. From the end of this band the cartilaginous
tegmen is almost complete, but the supra-auditory tracts (s.a.c.) do not meet, they are
separated at the middle by a large round notch, at the back of which there is already
a smallish crescentic interparietal scale (7.p.). These tracts, however, send forward a
thinner bilobate lamina, sharply marked off from the hinder main part by a crescentic
line, whose convexity is behind; this line, and the thinning-out of the tegmen, is
caused by the parietal bone. Behind the lateral band (0.s’.) the supra-auditory
cartilage is ossified, beyond the turning over of the roof, by the prootic (pr.o.).
Answering to the great size of the occipital arch, the supraoccipital (s.o.) is already
more than a third the width of the widest part of the hind skull, its sides are bilobate,
its extent, lengthwise, is from the fontanelle to the foramen magnum.

An upper view of the cranial floor (Plate 26, fig. 6), after the membranous
fontanelle has been removed and the orbitosphenoids (0.s.), lateral bands (0.s’.), and
the tegmen (s.a.c., p7r'.o’., s.o.) have been cut down to the top of the wall, shows some
things very instructively. The top of the great internasal septum (p.e.) projects
backwards, as a small triangular crista galli (c7.g.), and below that ends as an oblique,

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 183

rather thin, somewhat projecting wall-top, right and left of which we see the large
eribriform plate (cr.p.). Each plate is perfect, is circular in outline—as cartilage,
and is grooved obliquely, inwards and forwards ; it is also riddled full of holes for
branches of the olfactory nerve. The top of the presphenoid (p.s.) runs into the hind
part of the perpendicular ethmoid (p.e.) which is broad behind, and has the thick
crescentic top of each moiety of the nasal labyrinth pressing against it ; these curious
curved lobes, which are thick and bulbous against the median cartilage, and thin
externally, contain the hinder folds of the middle turbinal; they are separated from
the orbitosphenoids (0.s.) by a narrow chink. These latter tracts are ossified up to
the thick middle beam (p.s.) ; and the bony deposit is, now, complete for some extent,
proximally, and then it merely strengthens the fore edge of the tract up to the
anterior chink. At their inner third, and near the hind margin, these bony centres
show a small foramen opticum (II.). The hind margin of the orbitosphenoidal stem
is first convex, and then concave, and this sinuous line, the front boundary of the
sphenoidal fissure (V1.) is a good height above, and not behind, the fore edge of the
alisphenoid ; it crosses over the foramen rotundum (V*.)

The rest of the alisphenoid (a/.s.) is seen, away from the eye, behind and below the
orbitosphenoid (0.s.); the basisphenoid (b.s.) is, on this upper surface, of less lateral
extent than below ; it only passes for a small extent beyond its own boundary line.

The synchondrosis is large, and in it is seen the seat of the sella turcica (py.) and the
low transverse postpituitary wall (p.cl.). The middle fissure, right and left, between
the synchondrosis and the cochlez (ch/.) is wide; the “helix” projects upwards, but
is not so well seen as below; the meatus internus (VIL, VIII.) is wide and large.
The fore margin of the auditory capsules runs almost transversely across the lower
part of the base of the hind skull, and the outer two-thirds of this edge forms the
hinder boundary to the great infero-lateral fontanelle. The separateness of the
capsules from the chondrocranium, proper, is very perfect, especially on the anterior
and inner side; but above, it is more apparent than real, for there the great sinus
canal (/.s.) seems to part the crest from the tract containing the semicircular canals.
The whole arch of the anterior canal (a.s.c.) shows its convexity here, and under the
archway there is the large recess for the ‘“ flocculus” (f.r.). The lower part of the
occipital arch binds, sinuously, against the two huge capsules ; in this view we see
most of the exoccipitals (¢.0.) and all the basioccipital (b.0.), the fore edge of which
nearly reaches the post-clinoid wall (p.cl.). The cartilage is thick; it is perforated
by the 12th nerve behind the posterior fissure, and somewhat notched by the 9th and
10th nerves (IX., X.), in the margin, behind that fissure.

Ninth Stage (continued).—Visceral arches of a Young Mole ; 13 inch long.

I shall finish my description of the skull at this stage by an account of the inferior
arches of a somewhat smaller specimen than the one whose main skull has just been
treated of. The front fourth, and the hinder half, of the mandible are shown from the

184 MR. W. K. PARKER ON THE STRUCTURE AND

inner side (Plate 28, fig. 6). Here we see that the deep and the superficial mandibles
are both well developed; the basal cartilage (basimandibular, b.mn.) is still large at
the symphysis, and the subdistal part of Mrcxen’s rod (ims.), although undergoing
ossification (mk’.), and hidden partly by the splenial lamina of the dentary (d.), is stall
perfect up to its malleal end (ml.). That part (m/., mb.) is now undergoing endostis,
answering to the ectosteal plate applied to it; but the incus (7.) and the stapes (st.)
are still unossified. The annulus (a.ty.) is growing larger round the membrana
tympani (m.ty.), but the fold of skin that lies outside that membrane is still very
thick and spongy. The cartilage that pre-forms so much of the permanent mandible
is very solid, now; on the articular or condyloid process the glenoidal facet (g/.c.) is
figured, like a cap; it was derived from the same primary subcutaneous tract, and has
the same morphological meaning, as the slab which is ossified by the dentary bone.

Tenth Stage.—Young Moles ; 3 inches long from snout to root of tail.

When the young are more than one-third longer than in the last instance we get a
oreat advance towards the permanent condition.

In the side view of the skull (Plate 27, fig. 3) the jugal, squamosal, lower jaw, and
most of the hyoid arch are left out.

The long, non-segmented, decurved snout (al.v.) reaches half-way to the badly-
formed orbit. The valvular nostril (e.7.) is almost terminal, and is seen best in the
under face. The facial part of the premaxillary (pz.) is half as large as that of the
maxillary (mzx.); at present the canal for the maxillary nerve (V*.) is not finished
externally. On the process above it the small crescentic lachrymal (/.) rests, and the
canal (/.c.) is seen in front of the bone, on the face. The slender nasals (n.) and the
small frontals (f) are still distinct from each other, and from the facial plates of the
bones below them (px., mz.). The large parietal (p.) always keeps distinct from its
surroundings: the interparietal (7.p.) is now a broad, transverse plate between the
parietal and the supraoccipital (s.0.). The palatine (pa.) and the pterygoid (pg-),
with its terminal cartilage (pg.c.) still visible, can be seen below and behind them, the
annulus («.ty.). Behind the lachrymal (/.) the thin convex frontal shell (/) is turned
inwards suddenly in its orbital part. Near the hind corner of the orbital plate the
opening for the ophthalmic nerve (V1) is large and oval. Below that bony plate the
lateral ethmoidal mass (al.e.), and the cartilaginous top and bony lower part of the
orbitosphenoid (0.s.) can be seen, as also the emerging optic nerve (II.). The ali-
sphenoid, with its two large foramina (V*., V°*.), is seen outside and behind the orbito-
sphenoid ; below their foramina the broad basisphenoid (¢.b.s.) is exposed. Over
the drum of the ear (a.ty.) we see the large four-sided, infero-lateral fontanelle
( fo’.), which is hidden in the perfect skull by the squamosal. Behind that mem-
branous space a deep temporal bone is shown ; it is large, convex, and has a polygonal
outline; this is the prootie (pr.o’.), which has rambled away from the labyrinth, to

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. L85

ossify the chondrocranial wall. Behind and below that bone, the large labyrinth, in
this view, is unossified, and in the cartilage the semicircular canals can be traced
(a.s.c., hs.c., p.s.c.). The epihyal (ehy.) is seen descending, with the facial nerve
(VIL) emerging behind it; and from the posterior fissure, and from the condyloid
foramen the 9th, 10th, and 12th nerves are escaping (IX., X., XII.). Parallel
with the posterior canal (p.s.c.), and a little behind it, the junction of the opisthotic
with the occipital cartilage can be traced, and a little behind that the growing exocci-
pital bone (e.0.); under it is the condyle (0c.c.), The gentle, general curve is formed
by the parietal, interparietal, and supraoccipital bones (p., 7.p., s.0.); between the
latter and its side bone, the exoccipital (¢.0.), there is still much cartilage.

In the lower view of a skull at this stage, with most of the investing bones removed
(Plate 27, fig. 2), we see how much advance has been made. The long snout (a/.7.),
with its infero-lateral nostrils (e.7.), is followed by the labyrinth, proper, with the
peculiar supporting and conjugating investing bones that lie beneath it or between its
moieties. The premaxillaries (pz.) have very long laminar palatine processes (p.pz.),
(involving the antero-lateral vomers) ; these support JAcoBson’s organ and cartilages
(j.0., re.c.), and reach as far back as those tongue-shaped cartilaginous tracts. The
vomer (v.) is set between and above the palatine processes of the premaxillaries, and
its pointed fore end is hidden by them; its keel begins in their angle, and is very
short. The body of the bone first narrows and then suddenly widens between the
converging floor-plates of the nasal labyrinth (7.f.). In the chink right and left of the
recurrent cartilage (7c.c) the inferior turbinals (7.t).) can be seen ; then the gap widens,
and the upper and middle turbinal folds, now ossifying, are exposed (w.tb., m.tb.). But
where, as in Passerine Birds, the broad hinder part of the vomer connects the right
and left ethmoidal masses, there at each edge there is a small, additional postero-lateral
vomer (v”.), and outside it an osseous patch in the cartilaginous floor itself (n,/-).

The lateral cartilaginous tracts—floor and side-wall—first become constricted, and
then expand ; becoming, indeed, the upper broad unossified part of the orbitosphenoid
(o.s.). But the hind part of each half of the nasal labyrinth is seen to end, in a
bulbous form, right and left of the forks of the vomer, above which the end of the
perpendicular ethmoid (j.e.) passes into the short presphenoidal region (p.s.), still
unossified. The orbitosphenoidal bony centres (0.s.) can only be partially seen from
this aspect (see fig. 1), being hidden in front by the end of the nasal floor (v,/:), and
behind by the alisphenoids (a/.s.).

The posterior sphenoidal region is now well ossified ; it is exceedingly broad and
thick.

Referring to the early chondrocranium (Plate 25, figs. 2, 3, b.s., al.s.), we see that
the basisphenoidal region, just where the parachordals pass into the trabeculee under
the pituitary body, is greatly dilated, right and left. If two imaginary lines be
drawn obliquely backwards and a little outwards from the sides of the presphenoid to
the side of the narrow waist in the base, between the cochlex, then we shall get the

MDCCCLKXXV. 2 B

186 MR. W. K. PARKER ON THE STRUCTURE AND

true width of the basal beam. Such a width is kept for the basisphenoidal ossifica-
tion in the Marsupials, whilst all the part outside that definite bar is ossified by the
alisphenoid, which also takes in the whole region that is left bare in the Mole between
its alisphenoid and cochlea. Thus, in them, that thickening of the cartilage which is
the foundation of the tympanic ala is ossified by the alisphenoid, and the tympanic
wing has a large ‘‘os bullz” attached to it, behind and towards the mid-line. Here,
as in the Hedgehog, there is no os bulle, and the dilated pneumatic part of the

».

posterior sphenoid is ossified by the abnormally large median centre (b.s.).*
Behind the presphenoidal cartilage (Plate 27, fig. 2, p.s.) the ossified basal beam is
seen to be flanked, right and left, by an outgrowth, which grows into a lower plane,
and stretches outwards as faras to the under and inner edge of the alisphenoid (a/.s.).
These suboval masses look inwards in front, and are notched in that part ; their inner
margin is swollen and rounded, their outer and harder edge is sinuous. A large air
cell is forming on the outer part of the under surface, and the whole mass is spongy.

This very ornithic condition of the dilated and pneumatic basisphenoid is only a
modification of the parts quite similar to what I have just described in the Hedgehog,
where, however, the bones are more solid, and are devoid of this peculiar spongy
growth. Resting on this wide, pneumatic basisphenoid, we see the narrow oblongo-
crescentic alisphenoids with their large foramina—foramen ovale and foramen
rotundum (V*., V*.); the outer front corner of each bone lies under the corresponding
orbitosphenoidal cartilage (0.s’.). The rest of the cranium proper, is seen wedged, in
between, and expanding behind, the large auditory capsules. The synchondrosis is
lessening fast, and the rest of the parachordal region is occupied by the very Reptilian
basioccipital (b.0.). This relatively large plate is polygonal, has a notched fore edge,
a concave hind margin, and roughly-sinuous sides ; it is concave, right and left of the
mid-line. Behind it we see the huge, flattish condyles (oc.c.), which are reniform,
having a large notch on their inner edge; outside these we see the creeping ossi-
fication of the exoccipitals (¢.0.), and outside these a very low and narrow paroccipital
tract (p.oc.). The perforating foramen condyloideum (XII.), and the hinder foramen
lacerum (IX., X.) in front of, the occipital arch, are here seen.

The deeply notched antero-lateral margin of the great ear-capsule is bounded exter-
nally by the rambling bony growth of the prootic (pr.o’.). The inner edge of that
rounded notch, and the rest. of the opisthotic region behind it, and behind the cochlea
(chi.) is still unossified, and shows in this aspect the horizontal and posterior canals
(h.s.c., p.s.c.); shining through its semitransparent substance. The cochlea and the
contiguous part of the vestibule (ch/.) are well ossified; the fenestre are at right
angles to the general basal plane, and are not well seen in this view. From the outer

* Tn this remarkable pneumaticity of the basal and sub-basal parts of the skull, in relation to the
tympanic air-cavity, the fundamental structure is quite similar in the Crocodile, Bird, Marsupial, and

Tnsectivore: the after-modification gives the diagnostic, in each case.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 187

edge of this opisthotic centre the bony matter has run forwards, and a little outwards,
to the front of the cartilage, inside the antero-lateral notch.

An upper view of this dissected skull—peeled of most of its investing bones (Plate
27, fig. 1) shows the continuity of the elongated nasal labyrinth with the large orbito-
sphenoidal wing (0.s.). The long unjointed double nasal tube is but little enlarged,
although sinuous, up to the proper olfactory region (al.e.); there, in the swollen part,
the marks of the turbinal folds are seen outside, The fore brain and large olfactory
lobes overlie the hinder part of the labyrinth, and then the roof ends abruptly, a long
way in front of the end of the floor; there we see the large cribriform plate (c7.p.)
between the roof and floor, in two hollows, greatly perforated, and separated by the
perpendicular ethmoid (p.e.), which gives offa short cartilaginous crista galli (c7.g.),
above. The partial ossification of the turbinals, within, is shown in the lower view
(fig. 2) ; in this figure the cribriform plate and mesethmoid (cr.p., p.e.) have a small
centre, in the middle. Behind, the ethmoidal wall thickens, and right and left of
it the end of the capsules is swollen in front of the orbitosphenoidal bony centres.
These two bony tracts (0.s.) are subarcuate, narrow at their origin, and broader above;
where the cartilage enlarges suddenly, there they end near their hind margin ; half-way
outwards they are perforated by the small optic nerve (LI.). The short and narrowish
presphenoidal tract (.s.) is not ossified by them at present. Behind these parts the
basisphenoid (b.s.) is altogether abnormal, as compared with that of a Marsupial; it
reaches nearly as far outwards as the orbitosphenoids, and has the small ear-shaped,
biperforate alisphenoids (a/.s.) placed on its edges.

From side to side the basisphenoid is marked off into three nearly equal regions ;
the two outer of these have a rounded hind margin; behind the fossee marking them
off from the middle the cochlez (chl.) wedge in. Between the cochlez and the ali-
sphenoids there is a membranous space; and between the basisphenoid and the basi-
occipital (0.0.) there is a considerable tract of cartilage ; here, at its narrowest, part,
the basis cranii is very broad. Right and left the great misplaced prootic (p7.0’.) is as
well seen as in the lower view ; it has a vertical position, for the cartilage further back
turns inwards at its inner edge ; the opisthotic bony centre has crept outwards from
the well ossified cochlea (ch/.); its elegant coils are seen in this view, and behind them
the archway and recesses for the 7th and 8th nerves (meatus internus, Vil ay ole)
Backwards, and a little outwards from that passage, the huge anterior canal (.s.¢.) is
seen, and has its walls bony, but the recess for the flocculus (/l.7.) and the cartilage
round and behind the great canal, are still unossified, In this view the basioccipital
(b.0.) appears still broader and more reptilian than on the lower aspect ; its fore part
is still notched, where the bony cephalostyle was formed by the ossification of the
cranial notochord. Right and left of the notched hind margin of the bone we see a
large tract of cartilage separating the basal from the lateral bones-—the exoccipitals
(c.o.) ; the supraoccipital (s.o.), and the surrounding cartilage, has been cut away to
expose the cranial floor,

2B 2

188 MR. W. K. PARKER ON THE STRUCTURE AND

Tenth Stage (continued). —The visceral arches.

Notwithstanding the more specialised nature of the Mole, as compared with the
Hedgehog, some things in it are much more like what is seen in the Metatheria than
anything to be found in that larger and more normal Insectivore.

In these large “nestlings” the three lobes of the lower jaw (Plate 28, fig. 7, c.p.,
cd.p., ag-p-) ave still largely composed of cartilage. MucKEr's cartilage (mk.) is to a
great extent lost in the general dentary ossification (d.), but it is seen behind, wedged
in between the condyloid and angular processes of the jaw. The ossicula are now
largely ossified and the bony deposits forming the malleus (ml.) are exceedingly
instructive and very Metatherian. Besides the ordinary ectosteal tract, which has set
up endostosis in the head of the malleus, there is an almost distinet splint under the
neck of the malleus, which is the true counterpart of the os angulare of the Ovipara.
The manubrium (mb.) is mainly cartilaginous, but there is a fusiform epiphysis in the
middle of this process ; this is very noteworthy ; for in Lepidosteous and in Amica the
“articulare ” is ossified by two centres; and this is manifestly the additional centre
cropping up once more.”

The three most projecting parts of the incus (7.) are still unossified ; the short crus
(s.c.7.) is very small. The stapes (sf.) is merely indicated in outline ; so also is the
annulus; the epihyal (e.hy.) is confluent with the auditory capsule (aw.) where
the facial nerve (VII.) emerges. A short ligament connects that second segment of
the hyoid arch with the top of the subdivided ceratohyal (c.4y.); this is a gently curved
rod, occupied by a shaft of bone for half its extent. The next segment (c.hy’.) is only
two thirds the length of the upper, and is one-third thicker; it is just beginning to
ossify. So also is the still shorter and stouter hypobyal (h.hy.) which fits obliquely
on to the basi- and thyrohyals (b.h.br., thy.) ; these rods are ossifying, but the distal
half of the paired rods is soft. The annulus (Plate 25, fig. 18, .ty.) and the imperfect
cartilaginous tube of the meatus (7.c.) show the normal type of the outer ear, with
arrest of the concha ; it has four rudimentary rings.

Eleventh Stage.— Young Mole; two-thirds grown.

The side view of the skull at this stage (Plate 27, fig. 4) is very similar to that of
the last (fig. 3). I have, however, figured the squamosal, 7n situ, in this; the malar
or Jugal, is left out, here, for the better display of the fundus of the imperfect orbit.
The length of the figures is nearly the same, those of the larger specimen being some-
what larger, although they are magnified much less. f

The bones are much stronger and more polished, and the cartilage is rapidly
disappearing ; the snout (aln.) is relatively slenderer. The irabrication of the

* In the Green Turtle there are two articular centres: one the endosteal, developed late, and the

other the ectosteal, developed early, and just like the other-bony plates around it; these, however, are
merely the two elements of one ossification,

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 189

investing bones is now seen to be that of the one hehind on the one before it ; had
they taken up more of the ewtis vera they would have differed but little from the
bony scutes on a fish’s head. Below, there is now a more evident angle where the
premaxillary meets the maxillary ; in this latter bone the infraorbital foramen (V*.) is
still unfinished. It is covered over, in some degree, in the perfect skull, by the jugal
(figs. 5, 6, 7.). The frontals (f) have grown down well inside the orbit, but they
are singularly free from the usual orbital processes; the upper part there forms a
rounded eave over the retiring orbital plate. That plate has a very large oval
foramen for the ophthalmic nerve (V!.), and a lesser hole behind that in the extreme
part. The gap in the wall of the skull seen in the last (fig. 3, fo’.) is here shown as
filled up by the small oblique squamosal (sq.), the thin, sinuous upper edge of which
overlaps the antero-inferior part of the large parietal (see also fig. 3). There are
three sharp processes growing from the slanting lower edge of the squamosal. The
first is its own front corner, overlapping both parietal and frontal; the next is the
small, sharp jugal process; and the third is the postglenoid process. The hinder
swollen part over the auditory region is bilobate; the temporal fossa is extremely
small and ill-defined Over the roof, behind, the interparietal (7.p.) has grown so as
to be, relatively, the largest, or nearly so, to be seen in the whole class ; antero-
posteriorly, it is only one-third the extent of the parietal, but seen cross-wise, or at
the side, its extent is very large; it nearly reaches down to the exoccipital (¢.0.).
Below, the palatine (pa.) is seen a little, and the pterygoid (pg.) better; this has
still a nodule of cartilage on its hook (pg.c.). Under the very perfect system of
investing bones—which serve the purposes of “ashlar” in a building—the almost
completely ossified endocranium is partly seen. The orbitosphenoid (0.s.) does not
show its optic foramen well in this view (see fig. 8, 0.s., II.), but the sphenoidal
fissure, and the foramen rotundum and foramen ovale in the alisphenoid (al.s.,
V*., V°.) are displayed in this aspect. Under the alisphenoid, the broad, cellular
tympanic wing of the basisphenoid (¢.b.s.) is quite visible in this side view. A
remarkable amount of the very large skeleton of the auditory capsule is seen in this
figure. In the somewhat obtuse angle between the parietal and interparietals
(p., ip.) the polygono-ovoidal prootic wing (pr.o’.) is almost entirely displayed ; it is
very convex, and, if shorter, is much broader than the squamosal, for which it might
be taken in a cursory view of the adult skull. The opening from the lateral sinus is
behind the prootic wall-piece ; under that bone there is a large tongue-shaped epiotic
tract (ep.), it is not a distinct centre, but merely a lobe of the opisthotic (op.).* Under
it there is a foramen, above the large passage for the vagus and glassopharyngeal
nerves (X., [X.). The opisthotic region of the opisthotic bone, the proper “ mastoid ”
tract, is an irregular wedge of bone running from the post-temporal part of the
squamosal to the exoccipital (e.0.), with its almost suppressed paroccipital ridge ; that
bone is, like the mastoid region of the opisthotic, an oblique, irregularly-oblong tract.

* There is a deficiency in the lines of reference to these parts in this figure.

190 MR. W. K. PARKER ON THE STRUCTURE AND

Over it is seen the large, smooth supraoccipital, and below it the flattish condyle
(0¢.¢.).

At the fore part of the mastoid tract the epihyal and facial nerve (e.hy., VII.) are
shown in relation, and the 9th, 10th and 12th nerves are figured as they escape
from the skull. There is still a considerable tract of cartilage between the supra-
occipital, exoccipital, prootic, and opisthotic bones.

The upper view of this rapidly growing skull is shown in fig. 6; without the long
cartilaginous snout (a/.n.) this view would have been very imperfect. That finishes
this long, flattened, boring, wedge-shaped skull. Eight pairs of investing bones, and
one single pair—the interparietal—finish the upper and lateral parts of the skull ; they
are so developed and imbricated as to increase their general breadth up to the auditory
region, and then the skull ends in a somewhat irregular semicircle, not perfected
by any superficial bone, but by ossification of the walls and roof of the chondro-
cranium (s.0., p7.0’.).

A lower view (Plate 27, fig. 5), with the tympanics and ossicula removed, shows the
great progress in ossification and general development that have taken place, whilst
the young Mole has rapidly become twice as heavy as it was when only 3 inches long
—the last stage. The dentigerous semicircle formed by the premaxillaries (px.) with
their long palatine processes (p.px.), largely hidden by the maxillaries (mz.) is followed
by the long sinuous dentary line of the maxillaries; several of the molars are only
just cutting the gums with their sharp cusps. The palatine plate formed by the
palatine bones (pa.) is shorter and wider than that formed by the maxillaries, for the
suture between the two pairs of bones is very far forward ; the Mole has a very per-
fect and normal hard palate. The openings of JAcopson’s organs (j.0.) are seen in the
anterior palatine foramina, and the posterior foramina are large and wide apart, they
are in the line of the lateral suture between the palatines and maxillaries. The
palatine plates of the palatines have a beaded edge, and this thick or limbate margin,
which turns inwards and backwards to form the wall of the nasopalatine canal behind
the hard palate, is, altogether, bracket-shaped. The palatines go twice as far back on
their palatine plate, and are very solid and spongy where they embrace and support
the base of the skull. On to them, the pterygoids (pg.), are articulated, and they also
have a pedate expansion above, supporting the skull; their hamular process is not
quite ossified (pg.c.). The presphenoid (p.s.) is a long beam of bone, formed by fusion
of the orbitosphenoids, and separated by a considerable synchondrosial tract from the
basisphenoid (b.s.); this latter is a truly marvellous bony centre, and as far as my
experience goes is, in this creature, relatively wider than in any other type. In this
aspect, the basisphenoid runs across the whole basal region up to the floor of the
orbits, so that very little of the top of the skull can be seen right and left.

The fore edge is narrower than the hind margin; both are sinuous, and the outer
margin is rounded, and almost semicircular. ‘The anterior third, which is clamped
by the cranial plates of the pterygoids, has its floor perfect, but the bone is burrowed,

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 191

above the floor, there being a continuation there of the great pneumatic recess seen, right
and left, in the hinder two-thirds of the bone. Each recess occupies about halt the
large hinder tract ; the inner half is convex, and meets its fellow at the mid-line in a
deep fissure or sulcus.

All this wide, spongy, pneumatic structure is merely a peculiar Talpine modification
of the normal skull of an Insectivore, such as that of the Hedgehog, or the Tenrec.

The slender zygomatic arch (j.) is finished behind by the squamosal (sq.) with its
glenoid facet (gl. ¢.); this is close outside the tympanic recess of the basisphenoid. A
character is seen here which is only partly shown on the side view (fig. 4), namely,
that the squamosal after giving off its zygomatic process, and forming the sinuous plate
for the glenoid cartilage, grows round and under the skull, strongly clamping and
binding all the parts by a large squarish postglenoid plate, which grows obliquely
inwards and a little backwards, and is notched on its inner edge. The two plates,
right and left, hold the large auditory capsules as in a widely opened vice.

A considerable tract of cartilage separates the basioccipital (b.0.) from the car-cap-
sules; it runs backwards, and a little outwards ; it is almost straight, and passes nearly
into the cartilage of the condyle. Behind the postglenoid region of the squamosal, and
to some degree clamped by it, is the large prootic plate (p7.o.’). In the angle between
the squamosal and prootic plate (sy., pr.o’.) there is an oblong tract of bone, sub-
distinct ; this is the epiotic (ep.); it is bounded within by the hinder part of the
main opisthotic tract (op.), which has left a considerable tract unossified behind, up to
the small fusiform cartilaginous paroccipital ridge (p.oc.). In front of that cartilage,
up to the basisphenoid, there is a large irregular tract of the opisthotic visible below ;
this is beset with cranial landmarks. Close inside the front lobe of the under part of
the squamosal the ceratohyal (c.hy.) is seen, tied to the epihyal snag; behind this
the facial nerve (VII.) emerges through the stylomastoid foramen. Inside the nerve,
the hole for the internal carotid may be seen, and behind that, at a good distance,
the foramen Jaceruin posterius for the 9th and 10th nerves (IX., X.) is enclosed,
nearly, by the opisthotic; behind it, over the border, is the hole for the 12th nerve
(XIL.). There is also a crescentic hole under the notch of the squamosal. The use of
this I did not discover.

The foramen magnum (f.7.) has a neatly egg-shaped outline; in front of it the huge
basioccipital (b.0.) has a subpentagonal shape. The fore edge is very extensive and
gently sinuous, for this plate is notched and grooved in front, and this fore edge is
thick and spongy, answering to the hind part of the basisphenoid. Then, behind
each thickening, there is a round concavity, from which the bone becomes generally
gently convex up to the semielliptical notch at the fore part of the foramen magnum.
A large lozenge-shaped tract of cartilage, pierced on its outside by the hypoglossal
nerve (XII.), is seen between each postero-lateral edge of the basioccipital and the
condyles ; these (0c.c.) rise but little in front, and are grooved, crosswise, at their fore
third, and then on their hinder, narrower part, are more perfectly defined. Wedging

192 MR. W. K. PARKER ON THE STRUCTURE AND

in between the small cartilaginous paroccipital and the large condyle, the exoccipital
(e.0.) is seen, and behind the foramen magnum the crescentic lower edge of the
supraoccipital (s.0.).

In the end view (Plate 27, fig. 7) some of these things are better seen ; supplementing
ihe large, smooth parietals (p.), the great transverse interparietal (7.p., see also fig. 6)
stretches across the top of the occiput from one prootic plate (pr.o’.) to the other.
Under and behind that superficial plate the true supraoccipital is seen as a large and
almost semicircular ossification of the endocranium ; the lower transverse edge of the
plate is notched over the foramen magnum, and rises, and then falls, outside that arch-
way. A little cartilage exists at its outer edge, between it and the prootic plate
(pr.o’.), and this cartilage forms a short arched tract over each exoccipital, and then
fills in a square space over the notched hind part of the mastoid bone (op.). The
hindermost projecting part of each squamosal (sq.) can be seen, right and left, away
from the eye. Around the foramen magnum the crescented exoccipitals, capped, behind,
by the curious condyles—oval above, grooved, and then transversely lobate ; outside
the exoccipitals, the small fusiform unossitied paroccipital ridges (po.c.) are flanked
by the mastoid bone (op.).

A very instructive preparation was made of the diner face of the skull-floor
(Plate 27, fig. 8); the nasal labyrinth was largely cut away. The top of the upper
wall (a/.e.) ends in the short, cartilaginous crista galli (cr.g.); behind this, the top
of the ethmoidal partition wall (p.e.) and the contiguous part of the cribriform plate
(cr.p.) are ossified as a trowel-shaped centre, with the handle below. The rest of this
large, exquisite, double sieve, with its thickened rim, is still unossified. Behind, this
structure is embraced by the gently concave front margin of the orbitosphenoids (o.s.),
which now meet in the middle of the skull-floor and there lie upon the presphenoid,
which they have ossified (see fig. 5).

They are very narrow planks, bent backwards behind, forwards in front, and with a
sinuous hind edge, the middle part being the narrowest. The small, oblique optic
foramen (II.) begins at the inner third, and is behind the middle of the bony tract.

The posterior sphenoid is as remarkable from this view as from below (fig. 5). The
alisphenoids (a.s.), with their two foramina (V*., V*.), are about twice the size of the
orbitosphenoids, they project beyond their basal plate in front as much as they fall
short behind ; there they are free and pointed; in front, they are rounded and turn
under to the base of the skull; they are wide apart from the orbitosphenoid, and
the sphenoidal fissure (V4.) between the two plates is large. The huge basisphenoid
(b.s.) has a concave fore edge, and convex sides, and then ends bebind in four large sharp
cusps. The two submesial cusps reach much further backwards than the outer ;
between these pointed projections, externally, the whole bone is toothed and splintery,
and is attached to the rough toothed fore edge of the cochlear region of the ear-
capsule by fibrous tissue.

In front of the deep lateral notch, the bone, right and left, is gently concave, as

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 193

also is the middle part in front of the synchondrosis, but the sella turcica is badly
defined.

The prootic plates (p.vo'.) have been cut through ; between them and the proper
bony capsule there is a considerable tract of cartilage. The cochlea (cAl.) is much
masked by bony growths; the meatus internus (VIIL.) is large and very near the
inner edge ; there is a special foramen for the 7th (VII.).

The remarkable archway over the deep recess for the “ flocculus ” is ossified ; the
enlargement in front, on the outside, is due to the ampulla of the anterior canal (a.s.c.),
and its arch is over the archway; the common sinus for the anterior and _ posterior
canals runs, inside the thickening of this curious internal “ porch,” downwards and
forwards, on the inner side; the appearance of an ampulla below, and in front, where
it ends, is deceptive, that is due to a swelling of the vestibule (vb.).

The horizontal canal (/.s.c.) is not well seen from this aspect, its ampulla is only
visible under that of the anterior canal. The posterior canal (p.s.c.) is seen in the
postero-internal face of the porch where it meets the anterior canal, and where the
two pass into the common sinus on the inner side. The ampulia of the posterior canal
is formed after the arch has crossed and passed under that of the horizontal canal,
just where the latter is entering the vestibule; these parts lie at the bottom of the
bony labyrinth, just outside the passage for the 9th and 10th nerves (IX., X.). The
basal, and part of the lateral, regions of the occipital arch (b.0., ¢.0.), are seen, also; in
this figure, the hypoglossal nerve (XII.) is on the edge of the exoccipital ossification
on this inner side ; outside, or below (fig. 5), it is still surrounded by cartilage.

Inferior arches of the young Mole in the Eleventh Stage.

The malleus in this eleventh stage is thoroughly Marsupial in character.*

Seen from the inside (Plate 28, fig. 9) the head projects as a semioval mass, having,
behind, the saddle-shaped condyloid cartilage. Under the head there is a pneumatic
recess bordered by a sloping, sinuous edge of bone, from which the manubrium (77.)
is continued. That process is rather a round hook than an angular part, and the
whole hind margin is sinuous, without showing on this face any very definite posterior
process (ay.p.). The neck of the malleus is broad and irregular ; it is followed by a
rough, rounded, perforated lobe or crest. Then the bone dips and runs forwards as a
straight “ processus gracilis” (p.gr.). But this is only a part of the foregrowths of
the malleus, for beneath the upper lobe there is a lanceolate, almost distinct tract
(seen also in fig. 7, tenth stage), and in front of this, running away from the line of
MECKEL’s cartilage (see fig. 7, mk.), there is an elegant pretyiipanic sickle of bone,
enlarged and split at its end.

* My own figures of the Marsupial skull will show what I mean by this assertion; meantime the
reader is referred to Mr. Doray’s valuable paper on the Ossicula audités (Trans. Linn, Soc., ser. 2, Zool.,
vol. 1., plate 64, figs. 15-34).

MDCCCLXXXV. re

194 MR. W. K. PARKER ON THE STRUCTURE AND

On the outer face (fig. 10) that process is well marked off, as if it had formed
separately, and then became anchylosed to the straight process; here, also, the upper
lobe has a very distinct form and outline, behind, whilst the lower lanceolate tract is
less distinct.

On this face we miss the pneumatic recess, but get a view of the remnant of the
cartilage that separates the epiphysis in the manubrium (fig. 7, mb.) from the main
part of the bone. It is evident that, about the time of weaning the young Mole is

developing, in a rough, irregular, and abortive manner, the well-known “

angulare ”
and “supra-angulare” of the Oviparous tribes, in addition to the “articulare externum,”
and the two endosteal articular tracts that are found in Holostean Ganoid Fishes.
We shall soon see what becomes of all this eftort to restore the old compound
mandible.

The Ayoid arch (Plate 28, fig. 8), when detached from its two upper elements (the
epihyal and stapes), shows a considerable advance upon the last stage (fig. 7), all the
bony shafts are rapidly developing along the cartilaginous rods; the articulations,
also, are very distinct.

Tweljth Stage.—Young Mole; three-fourths grown.

Among my materials—gathered during the last forty years or more—I found the
malleus of a somewhat older Mole than the last ; it is of great importance, for it shows
(Plate 25, fig. 4, inner wew, fig. 5, outer view) the softening down, by absorption, of
much that was rugged and irregular in the last stage. The processus gracilis is still
very large, and is cochleate proximally; the crest and the pretympanic sickle are
gone. But the cartilage separating the manubrial centre (mb.) from the main bone,
on the outer side, is still evident. Of the same age also are the other ossicles here
figured, the incus (Plate 25, figs. 6, 7) and the stapes (Plate 28, fig. 11), and also the
annulus (Plate 25, fig. 11).

Both the orbicular facet for the stapes (/.¢.2.) and the short crus of the incus (s.¢.2.)
are feebly developed and look towards the Monotrematous condition ; the whole inner
face is open to the tympanic cavity.

The stapes (Plate 28, fig. 11) cannot be detached in this stage, as in the adults of
some other Insectivores, e.g., Myogale moschata and M. pyrenaica (see DoRAN, op. cit.,
p. 435).

This is a very remarkable modification (Plate 28, fig. 11, st.), and its transitoriness
in this type is also noteworthy; the Mole gets beyond Myogale in this respect. This
little bone is kept in its place by the ossification of the outer sheath of the stapedial
artery (st.a.); a sheath similar to that which protects the outer part of the internal
carotid in the Bird. There, the bony arterial sheath traverses the light diploé ofthe basis
cranii between the basitemporal plate and the proper spheno-occipital skull floor. Iam
under the impression that this sheath is formed just as the stapedial artery becomes

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 195

obliterated ; then the bony sheath, itself, soon afterwards, is absorbed ; these things
are enigmas to us at present.

The annulus tympanicus is shown in the young Mole, three inches long, from the
side (Plate 27, fig. 3, a.ty.); and the curious flat, imperfect ring is figured in several of
the earlier stages (Plates 26 and 28). In the adult it is wholly blended with the skull
floor, but during the first summer it remains distinct; that of the right side, in
this stage, is shown from its inner face (Plate 25, fig. 11); it looks like a well-made
annulus that has been crushed into a flat coiled band of bone. The outer opening
is roughly pyriform, quite pointed on the inner or lower side, and broad above, and
having its margins dentated. The part nearest the opening, outside, is very thin; then
the bone thickens up to the margin ; on the inner face the edge is seen to be strongly
ribbed by bony deposits. The anterior crus is very large, and grows along the
inside as a large rostral plate, looking backwards, and nearly meeting the sharp,
inturned, hinder crus. Thus the great inner opening, which is thrice the size of the
outer, is also transverse to it; it is a nearly finished oval, with the long diameter
at right angles with that of the outer opening. The great rostral process of the
front crus is grooved on the inside, outside its arched edge, for the still large

processes gracilis of the malleus (Plate 25, figs. 4, 5, p.yr.).

Thirteenth Stage.—Skull of the adult Mole.

I could have wished to have given figures fully illustrating the structure of the
skull in the adult Mole, but considerations of space have deterred me; I have,
however, figured the ossicula auditis (Plate 25, figs. 8-10), and the snout, in section
(Plate 25, fig. 14). This latter part has been affected by the generally intense ossifi-
cation of the skull, and not only the proper septum nasi (s.n.) has been well ossified
on from the perpendicular ethmoid, but that fore-growth of the septum (s.7.) which
divides the long alinasal region (a/.n.), in front of the premaxillaries, has acquired an
endosteal tract, almost to its front end; the teleology of this structure is evideut
enough, but it comes in as a part of the general osseous modification of this type,
which is everywhere intense.

The prootic plate, and the hinder or mastoid region of the auditory capsule, have
sutures separating them from the surrounding bones. The parietals, also, are always
free; they form a squamous suture with the frontals, which they overlap up to the
middle of the interorbital region, but the true squamous suture, between them and
the squamosals, is very slight ; they keep their own mutual saggital suture perfect.
With these exceptions the skull of a Mole has its bones as completely anchylosed
together as in any Bird; and the structure of the base of the skull is as light and
pneumatic as anything seen in any Passerine, or highest, kind of Bird. During the
first summer there is but little promise of the exquisite polish of the bones nor of the
excavated condition. they will soon attain to. Everything becomes smoothed down,

») 6) »

L9G MR. W. K. PARKER ON THE STRUCTURE AND

outside ; the hamular processes of the pterygoids are small but perfect, and behind and
outside them the whole of the wide hind skull is flattened, and bevelled, and polished
to a marvellous degree. On the inside, also, the surface is exquisitely smooth, and the
bone delicately cellular ; the cochlex have their bony walls polished and thinned down
so as to show the coils as if through a transparent medium, and the great porch for
the ‘flocculus cerebelli” is the most remarkable piece of miniature architecture I am
acquainted with. The bony tubes containing the semicircular canals strengthen the
porch at its margin, and the intervening bone roofing it is extremely thin. The
base of the skull now shows a shallow but distinct sella turcica, and behind it the
postpituitary wall is well defined, although rather low. The cribriform plate is very
large and abundantly perforated,

But the basal and basilateral regions of the skull, in its floor, although highly
polished, is marvellously broken up into hills and holes, because of the extreme delicacy
of the upper table of the bone; the supratympanic bony shell, the cochles, the
Jloccular porches, the pituitary cup, and postclinoid wall,—to say nothing of the fora-
mina and fissures for nerves, vessels, and the like,—make this little skull, in its inside,
a most admirable object for study and contemplation.

All this is true of the outside or lower surface, but the large flattened tympanic
annulus, completing the unlipped bony meatus externus, and thoroughly anchylosed to
the surrounding bones ; and the extensive air-galleries that are excavated inside the
huge basisphenoid, and the small squamosals, may be mentioned.

The ossicula auditts are figured and will now be described, as they show the last
specialisation of the inferior arches of the face.

The malleus (Plate 25, fig. 8, inner, and fig. 9, outer view) shows a very small processus
eracilis (p.gr.) and a small manubrium (mb.), whose axis forms one continuous curve
with the body of the bone. In front, under the head, but most on the inside, a consider-
able pneumatic recess is seen, and outside the obtuse angle (p.ag.) of the manubrium,
there is a loop-shaped ridge where the remnant of the last tract of cartilage was seen.
In this malleus almost the whole of the attempted mandibular structures has been
absorbed ; and the Metatherian type, at its lowest grade, has been exchanged for the
typical Eutherian form.

The incus has lost much of its typical Mammalian character * (see Plate 28) ; its
short crus (s.c.7.) has dwindled to a fine transverse style, the incurvation of the lower
part of the long crus (/.c.2.) is almost lost, and the orbicular facet is a mere oblong
condyloid tract.

Thus this little representative of the quadratum has lost, not only much of the “ otic
process” (= short crus), but also that special Mammalian character, the orbicular
plate on an inturned narrow neck, has greatly suffered degradation. Now this relapse is

* There include both the Marsupial and Placental Mammals, for in the former the incus has its

highest development; the long crus and the obricular plate being better developed than in the Eutheria,

generally.

}

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 197

in the Prototherian direction ; if carried further, and the bone were flattened out,
we should have an incus very similar to that of a Monotreme.

The long crus is hollowed out into a pneumatic boat, its long opening looks forwards
and outwards (fig. 9).

The stapes of the adult (Plate 25, fig. 10) is greatly altered from that of the larger
young (Plate 28, fig. 11), at the time when it is fastened in the fenestra ovalis by the
bony arterial tube.

Then it had narrow sides, and its incudal condyle had a rounder shape ; now, that
articular face is oblong, and the sides have become inflated, as also the base ; so that
the whole bone is a sort of lagena, with an oblong apex and a bulbous base ; whilst the
flattened sides are perforated, one by a large, and the other by a small, oval fenestra,
The sides of the base are neatly limbate, the rim being adapted to the edges of the
fenestra ovalis. That there is nothing in the structure of the skull of the adult Mole
that is not in harmony with the life and habits of the creature, I feel certain; but
questions of that sort are of less interest than the correspondences seen in this
terricolous Mammal with that we are familiar with in Reptiles (Crocodilia) and Birds.
Besides the general pneumaticity of the whole hind skull, we have the hollow counter-
parts of the quadratum, articulare, and columella of those high Sauropsida.

On the skull of the Common Shrew (Sorex vulgaris).

There are three native species of the Soricidee—Sorex vulgaris, S. pygmeus, and
Crossopus fodiens. I have worked out the skull in the first of these, comparing it in
its adult condition with that of the last, or largest, kind.

My materials yielded me four stages, as follows :—

Ist Stage.—Embryos, § ripe; 84 lines long from snout to root of tail (Plate 16,

figs. 10,°11).

2nd Stage.— Ripe embryos ; 94 lines long.

3rd Stage—Young from the nest, 10 or 12 days old; 14 inch long (Plate 16, fig. 12).

4th Stage. —Adult Shrews.

Besides these I obtained early embryos, with the somatomes well formed, a little
less developed than my earliest embryo of the Mole (Plate 16, tig. 1); these were merely
examined externally.

The First Stage here given was examined in sections, but as these corresponded
very literally with those of the younger Mole, already described, they were not
figured, In these almost ripe young the general form is such as one might imagine in
some early Tertiary types, in which the characters of the Orders of Mammalia now
existing had not been developed.

It is a simple pentadactyle form, very similar to my third stage of the Mole
(Plate 16, fig. 4), but having smaller fore limbs that are further back from the head.

198 MR. W. K. PARKER ON THE STRUCTURE AND

Along the annular folds of the outer skin the bud-like hair-pulps are seen cropping
up in corresponding rows, as though they had been planted by a farmer’s “ drill.”
The eyelids are developed, and closed over the eye-balls ; the concha auris is a kidney-
shaped fold of skin, the snout is, relatively, no longer than that of a full-grown
Mastiff, and shows little promise, as yet, of its future length.

Second Stage.—Ripe embryos of Sorex vulgaris, 9$ lines long
(about 4 of an inch, or 20 im.).

The chondrocranium (Plate 29, fig. 7), is undergoing ossification, but its general form
is not altered, and absorption of those parts of the cartilage which do not ossify has
scarcely set in; it serves well at this stage for comparison with the skulls of the Mole
and the Hedgehog at a similar stage of development (see Plates 17 and 25). In the
Mole the chondrocranium is less massive, relatively, than in the Hedgehog, and in the
Shrew less than in the Mole. The Hedgehog is the least modified and most. pri-
mitive type. The Shrew is the most modified, and that mainly through dwarfing, so
that some parts ave arrested, and others actually suppressed—as if for want of room
for them. They may easily have arisen from one common stock, and the Mole comes
in as a connecting link between the well-developed Hedgehog and the scant and
stinted form of the Shrew.*

Therefore we may look for signs of that peculiar form of degeneration which arises
from dwarfing. The cartilage may be expected to be scanty, and the number of
osseous centres lessened. :

In this ripe embryo of the Shrew the top of the nasal partition wall (Plate 29,
fig. 7, 8.1., p.e.) reaches half-way back to the front of the supraoccipital (s.0.); at its crown
it is much more than half the height of the skull; at its base, from the front of the
snout (al.n,) to the middle of the presphenoid ().s.), it is twice as long as from that
point to the foramen magnum.

The snout, itself, has only half the relative length it will have in ten or twelve
days——next stage (Plate 29, figs. 1-4). The septum in front is perforated and
circular ; then it narrows to half its width in front, and is narrowest in the front part
of the true septal region, behind the snout, proper. Thus between the large recurrent
or JACOBSON’S cartilages (¢c.c.)+ the thick intertrabecular base of the whole partition
wall (7.t7.) is formed into a low arch, and is especially thick where it descends again, as
it passes backwards towards the presphenoidal region. The thinner, main part of the

partition—septum nasi (s.7.), and perpendicular ethmoid (p.e.)—is very even, and forms
a low triangle, the hinder side of which is the shortest, and is the dividing line
between the two perforated (cribriform) plates (c7.p.) ; that line is a little arched, the
longer line in front, towards the snout (a/.sp.) is first convex, and then concave before
* The pygmy Shrew (Sorex pygmcus), is not only the smallest British Mammal; it is as nearly as may
be the smallest beast in the whole Class of the Mammalia.
+ For te.c. read rec.

DEVELOPMENT OF*THE SKULL IN THE MAMMALIA. 199

it passes into the gently arched snout (a/./.). The basal cartilage behind the cribriform
plate and uasal labyrinth is thick, but from being high and narrow, becomes depressed
and broad; thus the middle ethmoidal region passes into the short presphenoidal,
and that into the fore part of the basisphenoidal territory ().s.). That region is per-
forated and partly ossified (see Plate 30, fig. 18, b.s.). Here we meet, again, with the
open pituitary space which we found in the Hedgehog (Plate 17, figs. 1, 2, py.), but did
not find in the Mole (Plate 25, figs. 2, 3). Behind that passage the basal tract thins
out, becomes gently concave, thickens again, is again ossified, partly, as the
basioccipital (b.0.), and then ends, with a narrow cartilaginous selvedge, at the foramen
magnum. The primary fontanelle is very large, for the band of cartilage connecting
the great orbitosphenoidal wing (0.s’.) with the equally large supra-auditory tract
(s.a.¢.) 1s narrow.

The upper orbitosphenoidal expansion is confluent with the nasal wall in front; it is
sinuous, notched in a rugged manner, above, and its hind margin, both above and below
the narrow posterior band, is concave ; there is no optic foramen through its stem. The
optic nerve passes through the great sphenoidal fissure, in company with the orbital
nerves, as in Marsupials. The skull is unprotected by cartilage tor a very large space
both above and below the narrow band ; for that band, dipping a little, bounds a huge
space below of an irregularly oval shape, with its long diameter—which reaches from
the cribriform plate to the meatus auditorius internus (VIL, VIII.) —two-fifths the
length of the whole cranial cavity. Below, this space is partly occupied, in front by
the alisphenoid (u/.s.), and behind by the cochlea (ch/.). The alisphenoid (see also
Plate 30, fig. 18, a/.s.) is a small ear-shaped tract of cartilage, notched on its hinder
margin near its upper angle for the 38rd branch of the trigeminal nerve (V*.), and
lying quite outside the plane of the orbitosphenoid.

Thus the optic, 3rd, 4th, Ist and 2nd branches of the 5th, and the 6th
nerves all pass through the gaping sphenoidal fissure. Some distance behind the
proper alisphenoid the basis cranii becomes alate, and that small rounded wing is per-
forated and has its hinder margin adapted to the apex of the cochlea, on its inner side.
The posterior orbitosphenoidal band (0.s’.) runs upwards and forms a sinuous ribbed
edge to the supra-auditory plate (s.a.c.), the high upper margin of which has a convex
outline, and passes into the supraoccipital region (s.0.), already ossifying.

That spheno-pterotic tract (s.u.c.) is as broad as the inner face of the huge, genicu-
late auditory capsule (chl.), its hinder half, and the capsule, form the very perfect
semioval margin to the hinder part of the great lateral fontanelle. The archway
formed by the upper cartilaginous wall (s.a.c¢., s.0.) for the setting of the oblique upper
half of the auditory capsule, is much larger than is needed for that part; the whole
margin is occupied by the large, and accurately semicircular “ lateral sinus” (/.s.).

There are three arched and convex tracts to be seen in the postero-superior part of
the auditory capsule; the middle tract is nearest to, the hinder tract furthest from,
the eye. The foremost arched convexity contains the anterior canal (a.s.c.), and

a ee re

200 MR. W. K. PARKER ON THE STRUCTURE AND

the middle tract, which bulges inwards, the “sinus” or common tube of the anterior and
posterior canals. The latter is in the convexity that is just seen behind in the great
space for the lateral sinus; the hollow oval space between the first and second
arched convexity is for the “ flocculus cerebelli.” Where the antero-inferior and
postero-superior regions of the capsule meet, there, above, the inner and outer openings
of the short tunnel for the portio dura (VIL) are seen.

Below these holes the perforations for the portio mollis (VIIL) are seen in the
short arched meatus internus, and the space between the capsule and the basi-
occipital leads to the foramen lacerum posterius. There the outline of the capsule is
gently concave; in front of that part it swells again with the coils of the cochlea
(chi.), and behind it with the galleries of the vestibule (vb.). The halved occipital
arch is much narrower than the capsule in front of it ; we see the supraoccipital (s.o.)
and the exoccipital (¢.0.) already large centres; the condyloid foramen (XII.) and
the articular condyle (0c.c.) are both clearly seen in this view.

The investing bones are rapidly forming; the nasal (n.) above the septum, and the
vomer (v.) below: and the maxillary and palatine (mz. pa.) below the nasopalatine
passage (n.p.c.) are seen edge-wise.

The frontals (7-) are no larger than those of a Snake, but the parietals (p.) are
very large; and project from the outside, at the upper third of the front lateral
fontanelle, yet they fail to meet the small, low-lying squamosals (sg.), and there,
between them and behind the alisphenoid, there is a large pyriform tract entirely
unsupported, either by cartilage or bone.

In a dissection of the basis cranii at this stage, seen trom below (Plate 30, fig. 18),
we get further light upon the parts just described as seen in the inside of a halved
skull. The cartilage of the snout (a/.n.) is represented in this figure as detached
from the sides and roof of the septal region, but having the inferior tracts that grow
from it, namely, the recurrent cartilages (re.c.) attached. These remarkable capsules,
that contain Jacopsoy’s organs, arise as ale from the base of the septum in the lower
and hind part of the snout, then expand into horizontal lamirz, and then form a hook
round the opening of Jacossoy’s organ, enclose it entirely for a short distance. and
then only on the internal and lower side, thus forming a long cochleariform tract
which reaches half-way to the pituitary space (py.). On the inside of these cartilages
the palatine processes of the premaxillaries (v.pz.) run; they are thin vertical plates,
and show no separate anterolateral vomer attached to them. The Mole has the same
deficiency.

The vomer, proper, (.) is long and normal ; it is pointed in front. and slightly split
behind. Behind the sheathing vomer the intertrabecular bar widens, it is fitst
ethmoidal ( p.e.) and then becomes the presphenoid ( p.s.).

On each side I have figured the hind, closing part of the lateral ethmoidal regions
(nj.); the primary form of the so-called “sphenoidal sinus,” which has wedged in
here between the alisphenoid (a/.s.) and the base of the great orbitosphenoidal tracts

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 201

(0.s.). The narrow stalk of these great leafy growths of cartilage is out of sight ; it is
imperforate. A true Insectivorous diagnostic is seen in the sudden widening of the
basisphenoidal region (b.s.), which is jive times as long, and three times as wide as the
presphenoid, and has an open pituitary space (py.) in its middle, in which it agrees
with the Hedgehog and differs from the Mole. Around this hole the bony basi-
sphenoid (b.s.) is forming ; it is circular at present. The alisphenoids (a/.s.) are small
ear-shaped tracts of no greater extent than the cochlez (ch/.), and having an oblique
position, they look forewards as well as outwards, and are quite outside the
plane of the orbitosphenoids. A round notch is seen between them and the base, in
front ; they are gently sinuous in front and on the outside, whilst, behind, they have a
deep notch for the 3rd branch of the 5th nerve (V*.) near their outer angle. The base is
clear of all alate growths in its middle part, but, behind, it gives off a small perforated
erescentic wing which is applied to the fore end of the cochlea (chl.); this, however, is
soon lost, and the tympanic wing, so characteristic of the typical Insectivore, is
aborted. The spheno-occipital region of the basis cranii is elegantly cut away,
so to speak, to let in the rounded apex of the cochlea, right and left. The basi-
occipital centre (b.0.), nearly reaches the foramen magnum, and is growing fast
towards the lateral notches; it is polygonal and reptilian. A superficial tract of
cartilage and of bone, forming the pterygoid (pg.c., pg.) is shown attached to the base
of the skull. The visceral arches are well developed. I have figured the upper part
from the inner side (Plate 30, fig. 16) of the tympanic region. The malleal end of
MecKEL’s cartilage (mk.) shows a well formed head, a deep and wide tract beyond
the articular facet, a very large “‘ posterior angular process” and a short straight
“internal angular process,” or manubrium (m.m/.). The annulus (a.ty.) is already a
considerable crescent of bone. The incus (7.) is quite normal and well developed,
and so is the stapes (st.), the base of which looks towards the eye in this figure.

Ossitication has begun in the perichondrium of the neck of the malleus (m/.), below ;
it is a thin ectosteal tract.

Third Stage.— Young Shrews (Sorex vulgaris) from the nest ; 10 or 12 days old ;
and measuring 14 inch in length, from snout to root of tail.

The dissected skull at this instructive stage, in its upper view (Plate 29, fig. 1),
shows a cartilaginous snout (a/.n.), nearly as long as the long, and relatively large
nasals (7.). The nostrils (e.v.) are sublateral, and the snout itself is narrow at first,
and then widens so as to become ventricose where it passes under the investing bones.
Those bones are very thin at present, and show the elegant radiating lines of growth.
The premaxillaries (pa.)* run well up the face, wedging in between the much larger
maxillaries (mz.) and the nasals (7.) ; these two pairs of bones run backwards to about
the same extent at present, widening backwards. The small, almost Ophidian frontals

* Bor pa. read pe.

MDCCCLXXXV., 2D

202 MR. W. K. PARKER ON THE STRUCTURE AND

(/-) are much shorter than the nasals and about twice as broad on their upper face ;
that face is only one-third as large as that of the parietals, which are very large, have
a strongly marked wmbo, the primary centre, and have a small diamond-shaped
fontanelle between them and the frontals in which the coronal, sagittal, and frontal
sutures meet. These bones elbow outwards, strongly, over the temporal region, and lie
well over the squamosals (sq.), which are scarcely visible in this aspect. Behind, the
parietals are largely suppressed, a space (fontanelle) existing there almost equal to a
whole parietal ; this is beginning to be filled in, behind, by a bow-shaped band of bone,
the interparietal (¢.p.), which forms a transversely-long beading to the well ossified
and extensive supraoccipital bone (s.0.).

The side view (Plate 31, fig. 10) shows the form and relations of the parts just
described, and many other things besides. The snout (al.n., en.) is largely arched,
and reaches half-way to the middle of the badly-defined orbit. Under the long thin
nasals (7.) the premaxillaries and maxillaries (pw., mx.) are seen to form large thin-
walled troughs, for the huge tooth-pulps ; through which the sharp, red cusps shine,
ready to cut the gums.

In front of the orbit there is a process of the maxillary which is beginning to form
the nerve channel, but no separate malar bone; in an emargination of the maxil-
lary, above, a small lachrymal, with its canal (/., Je.), is seen.

The roof plate of the frontal (#) becomes convex at its edge, and then dips suddenly
to form the thin, vertical orbital plate, under which the small, but bulging, alisphenoid
(fig. 11, a/.s.) can be seen ; the orbitosphenoid is hidden by it, and by the frontal, in
this aspect. The lateral extent of the frontal is only haif that of the parietal, which
is a wall, in this case as uch as in our own skull. It lies over the frontal somewhat
at its antero-inferior angle, close behind the coronoid process ef the lower jaw (c.p.).
Large as is the parietal, it has two great deficiencies or emarginations, one above,
uready described, aud one along the hinder half of its lower margin. In this aspect
we see the squamosal (sq.) in its whole extent ; and much as this bone is modified by
the dwarfing of the skull, generally, it is normally Mammalian. It lies quite down at
the lower edge of the skull, rismg somewhat where it forms an abortive zygomatic
process, in front of the condyloid facet (cd.p.). The first two-thirds of the upper edge
is concave where it fits over the lower edge of the parietal, and the last third is
emarginate when it overlaps the prootic plate (pr.o’.). Behind, it interdigitates with
that plate in some degree. The postero-inferior margin is convex, for a short extent,
and then the lower edge looks quite straight, but is only partially seen, being curved
inwards (Plate 29, fig. 2, sq.). Under the squamosal, the tympanic (q.ty.) is just seen,
and under the face the characteristic mandible. This latter structure for its fore
two-thirds is a thin tooth-trough, behind which the large, elegant coronoid process
(c.p.} ascends, vertically ; its fore edge is two-thirds as long as the dentary part of the
ramus. The condyloid process (cd.p.), on the other hand, is very short ; looks down-
wards and backwards, covered with its cartilaginous coat. The angular process (ag.p.)

DEVELOPMENT OF THE SKULL IN THE MAMMALIA, 203

is, in the Shrews, very long and very slender, it runs backwards and a little inwards.
Some parts of the endoskeleton are best seen in this owter side view ; especially the
prootic plate (p7.o’.) and the proper mastoid region. The prootic plate, which takes the
work here of the “sphenotic and pterotic” of Fishes, and does but little of its own, is a
large shield-shaped ossification of the supra-auditory region of the cartilaginous endo-
cranium. Its arched top does not yet reach the emargination in the parietal, nor
the lateral sinus (s.c.), which now forms an elegant bow over the side skull, inside
the parietal for the most part, but exposed, behind. The roughly dentate lower
hinder edge of the prootic plate overlaps the ampulla of the anterior canal (a.s.c.) and
in some degree that of the horizontal canal (h.s.c.); then this bone meets with the very
extensive opisthotic (at h.s.c.). That bone can be seen behind the tympanic (a.ty.), and
also creeping over the junction of the anterior and posterior canals (q.s.¢., p.s.c.); much
of that part of the capsule (epiotic region) is still cartilaginous ; there is no appearance
of a distinct epiotic bony centre. Part of the interparietal (7.p.) is seen in front of the
supraoccipital (s.o.), and the occipital arch is seen edge-wise ; there is still cartilage
between the supra- and exoccipitals (e.0.) and the latter run up to the auditory capsule,
without forming any definite paroccipital process ; the condyle (oc.c.) is very large, and
looks obliquely downwards and outwards. The whole hind skull is gently convex and
very similar to that of the Mole, with which it agrees in having the large prootie plate.

The lower view (Plate 29, fig. 2) shows the large alveolar grooves, overfull of tooth-
pulps, with cusps cutting the gums; thus the marginal part of the premaxillaries ( pz.)
as well as of the maxillaries (mz.) is very wide and bulbous, The palatine processes
of the premaxillaries are very long and slender, and continuous with each anterior
paired vomer, right and left. The palatine plate of the maxillaries is large, and twice
the extent of that of the palatines (pa.); the suture between these four plates is
arched forwards, and the fore margin of each palatine is deeply notched ; there the
anterior palatine foramen is open in front.

The merely vertical and upper part of the palatines is short and swollen, and the
similar tracts formed by the pterygoids (pg.) are swollen also; the hamular processes
are small, but sharp; they have used up the primary cartilaginous nucleus. Of the
other investing bones to be seen in this aspect the squamosals (sqg.) are the most
striking ; they are much larger than they seem to be from the side view, being curled
round under the side of the skull in a remarkable manner. The postglenoid region is
very large; the preglenoid a short free spike; the glenoid facet (gl.c.) looks forwards
and a little inwards, and is, at present, a continuous selliform facet to the wide, thick
infero-anterior lobe of the bone. Inside the hinder portion of the squamosal, the
annulus tympanicus (q.ty.) is seen as a relatively large, very thin, imperfect ring of
bone, bending upon the emerging primary mandible—MEcKEL’s cartilage (imk.)—and
supporting a wide membrana tympani (m.ty.); the hinder crus has a widened part or
blade at its free end, and the fore end is dilated, but to a less degree. The vomer (v.)
is seen in its hind part, with its forks, supporting the perpendicular ethmoid (p.e.).

2D2

204 MR. W. K. PARKER ON THE STRUCTURE AND

Between the forks of the main vomer (v.), behind the middle ethmoid (p.e.) a small,
thick crescent of bone is seen lying crosswise with its convexity forwards ; this is the
independent presphenoid (p.s.), a bone not found in the Hedgehog and Mole.*

On this face the orbitosphenoids are not seen, or very slightly (see figs. 3, 4, 0.8.) ;
the basisphenoid (b.s.) is separated from the presphenoid by a broad tract of cartilage ;
the bony tract is four times as long as that synchondrosis, and, in front, three times as
wide. Behind, it is twice as wide, and so also is the spheno-occipital dividing
cartilage ; this is also somewhat more extended, axially, than the front tract. Here
we have the abortive development of the large diagnostic Insectivorous basisphenoid ;
it is very large, has stout shoulders, on which the alisphenoids (a/.s.) rest, but it is not
specialised for pneumatic purposes. The anterior fissura lacera ends in the rounded
notch between the forwardly-thrust alisphenoid, and the narrow anterior synchondrosis.
These parts will be understood better when we come to the disinvested endocranium
(figs. 8, 4); so also will the occipital arch and the auditory capsule.

The side view (Plate 31, fig. 10) is still more intelligible when the divided skull
is seen from the dnside (fig. 11); this also gives us one of the three views of the endo-
cranium, as distinct from its ectocranial investing scale-bones.

This view of the skull of a Shrew, about the twelfth night after birth, should be
compared with the counterpart figure of the skull of the ripe embryo (Plate 29, fig. 7) ;
thus the decadence of the deep chondrocranium and the development of the superficial
elements of the ectocranium will be understood. Measured along the basal line, the
septal and ethmoidal (continuous) regions of cartilage are five-sevenths the length of the
whole axial tract from the fore end of the snout to the foramen magnum; at birth
that fore part was two-thirds the whole length. It is the snout which has lengthened
most (relatively), as if to form a proboscis; but there is no segmentation of the car-
tilage enclosing the double tube. The basal line of the snout is strongly, that of
the septo-ethmoidal region feebly, arched ; nearly all the thick basal part is due to the
development of that azygous median prepituitary (= pro-chordal) rod, the inter-
trabecula ; for the trabeculee and cornua trabecule run but a short distance forwards and
only meet at the mid-line in the region immediately in front of the sella turcica.
Thus the middle element of the cranial fore-growths is as large as in the Selachian
Fishes and the embryo Bird. The foremost part of the septum (s.n.) is perforate—a
very common thing in Mammals, the ale nasi throwing themselves out from the middle
wall, in forming the valvular nostrils. Up to the anterior palatine foramina this wall
is very low; it then gently rises up to the top of the rhinencephalic fosse, with the
cribriform plate (c7.p.) as its floor; there is no crista galli projecting from the obtuse
angle from which the great partition descends, twice as rapidly as it ascended, until it
reaches the presphenoidal bony centre (p.s.).

The fan-shaped upper part of the great orbitosphenoid of the embryo (Plate 29,

* We shall see this again in Rhynchocyon ; and it is also present in some of the lesser Rodents (at any
rate in Arvicola, Mus, &ec.). Nevertheless, it is a Marsupial character.

Bey

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 205

fig. 7, 0.8.) is now much lessened (Plate 31, fig. L1, 0.s.); its posterior band has been
absorbed, leaving only a point to the hind corner of the wing; the hind edge is now
ossified as the narrow orbitosphenoidal centre.

The oblique, notched, anteriorly-placed alisphenoid (a/.s.) is only partly seen in this
view, because of its great out-thrust ; its base (b.s.) and the basioccipital (b.0.) are seen
to be rather thick plates of bone. The other elements of the occipital avch (s.0., ¢.0.)
are set in a crescent, whose convexity looks backwards; all the synchondroses are
large, as yet.

There are only two periotic bony centres—the prootie (pr.o’.) which forms the
curious wall-plate, and the opisthotic, which builds-in the labyrinth.

The mastoid region behind, enclosing the posterior canal (p.s.c.), and the arch of the
anterior canal (a.s.c.) are still invested with cartilage, but the common sinus, behind
the cerebellar fossa, has a bony inner wall. Everything in this skull, as in that
of the Mole, conforms to the dominant idea of a skull to be manipulated, so to speak,
into a smooth, elongated borer, so that it may resemble the head of a Weevil (Cureulzo).
Thus all the investing bones are thin, gently convex, and so imbricated as to thrust
out no projecting points, externally.

This section shows the nasal, frontal, parietal, and interparietal (7., /, p., 7.p.) above ;
and the premaxillary, maxillary, palatine, pterygoid, and tympanic (pw., ix., pa., pg.,
a.ty.), below. Infero-laterally, the trough-shaped squamosal (sqy.) is seen from the
inside as a narrow tract, arched above, but not reaching the rounded lower edge of the
parietal, and the concave edge of the latter fails to reach the arched top of the prootic
plate, thus there is a considerable lateral fontanelle or part formed of membrane only.
Near the lower edge of the parietal, the lateral sinus (s.c.) throws its elegant arch
over the inside of the skull, from the auditory capsule to the orbitosphenoid.

When the endocranium is seen divested of nearly all its investing bones, from
below (Plate 29, fig. 4), we have what seems to be a remarkably imperfect skull, even
considered as a basin, and not as a bow. What we see is a remarkable result of
dwarfing and elongation; there is a thrifty use of every kind of skeletal material, and
the substances used have been thinned out as far as could be done safely. Yet the
skull of a Child at the same stage, similarly prepared, would show the same elements
disposed in a similar manner, and there would be little difficulty in recogiising most
of the homologous parts.

The conchoidal narial region (e.n., al.n.), right and left, and the fluted double nasal
tube, are seen to form a very perfect cartilaginous structure up to the part where the
dentary region of the premaxillaries is attached. There the floor is cut away in a
rounded manner, and the nasal labyrinth is open below, almost to its end, where its
moieties do close in, independently of each other, right and left of the forks of the
vomer (al.e., v.). This open region begins by forming the long retral tracts that help
to encapsule JAcopson’s organs (figs. 4, 5, r¢.c., 7.0.) ; there is no Mammal in which I
have, as yet, been able more satisfactorily to work out these parts than in this young

206 MR. W. K. PARKER ON THE STRUCTURE AND

Shrew ; and this both in the dissections (Plate 29, figs. 4, 5), and the sections
(Plate 30).

Where the perfect narial floor ends, there on each side of the intertrabecular base of
the septum (Plate 29, figs. 4, 5, s.7.), a gradually increasing wing is given off, which, on
reaching the notch in the premaxillary—between the dentary margin and the palatine
process—at once expands, hooks itself round the front of the opening of JAcoBson’s
organ, and then completely surrounds that organ for a short distance. The rest of
the cartilage is like the bowl of a spoon, and protects the organ infero-externally.
Along the inside of each retral tract the palatine process of the premaxillary (p.pz.)
runs as a vertical lamina, connate, apparently, as in the Mole, with the anterior
paired vomers, Between the hinder third of these laminz the fore part of the long,
normal, main vomer (v.) is seen. The inferior turbinal is developed from the inside of
the lower edge of the nasal wall (al.sp.); the upper and middle turbinals (fig. 4,
al.e., m.tb.) from the inner face of the capsule in its dilated part. There, for some
distance, the floor is very deficient, the wall, simply bending inwards, with a sinuous
selvedge underneath ; at the end it finishes in a sort of pouch, right and left of the
forks of the vomer.

Where a kind of secondary desmognathism is made by the vomer (as in Passerine
Birds), there a small oblong tract of bone runs in between the main vomer and the
ossifications already forming in the nasal wall and floor; these little bones are the
posteriorpaired vomers (v”.). Behind the short exposed tract of the perpendicular
ethmoid (p.e.) the small crescentic presphenoid (p.s.) is seen, with its concavity looking
backwards ; a tract of cartilage, larger than this bony centre, separates it from the

next bony tract—the basisphenoid (b.s.).

The semiosseous orbitosphenoids are partly hidden in this view, but are fully shown
in the upper (fig. 3). The posterior sphenoid is well displayed in this aspect. The
basal bone (b.s.) is inordinately large for a Mammal, but small and aborted for an
Insectivore. It is, roughly, an equilateral triangle, with its hinder angle truncated,
and its anterior side transverse to the cranial axis; the imperfect lateral margins are
sinuous, so that there is a rounded lobe at each angle; this is the arrested ‘ tympanic
wing.” The alisphenoids (/.s.) are sutured to the fore edge of this lobe, right and
left, and run forwards and a little outwards; their rounded fore angle is not quite
ossified.

Each bone is a rough, notched, snagey wedge ; the notch is on the outer margin,
just a little in front of the projecting hinder angle or lobe. This is the imperfect
foramen ovale (V*.); it is a large vacuity, as seen from below. The scarcely ossified
fore end is rounded on its inside; it reaches to the middle of the incurved nasal
floor (al.c.) much beyond, and some distance below, the orbitosphenoid (0.s.); the
inner margin is notched both at this front part and at the hinder third. There is a
considerable membranous space between the alee and the narrow fore part of the base,
right and left.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 207

Then there comes, behind and outside the posterior sphenoid, a very large space, in
the dissected endocranium, which in the perfect skull (fig. 2) is only partly filled in
by the squamosal (sq.). This was the case very remarkably even in the skull of the
embryo (fig. 7), but the auditory capsule has not grown so much, since, as the rest of
the skull and snout (figs. 3, 4); it scants very much towards the great semicircular
space developed for its reception. The small perforated ala of cartilage seen in the
embryo growing right and left, from the basisphenoidal region (Plate 29, fig. 7; and
Plate 30, fig. 18), and coiling round the front of the cochlea
setting—is now absent; it has evidently been used up in the ossification of the
cochlea (chl.) ; it now exists as the toothed rim of its semicircular fore part. There
is still some cartilage between the prootic plate (p7.o’.) and the main part of the
capsule ; and also behind the bony top of the epihyal (e.hy.), as well as on the inner
face, above (Plate 31, fig. 11). The coils of the cochlea (ch/.), the fenestra ovalis and
fenestra rotunda (fs.0., f7.), and the great fissure widening for the exit of the 9th
and 10th nerves (IX., X.) are clearly seen in this lower view.

The wide basioccipital (b.0.) with its semicircular notch in front of the foramen
magnum ; the large reniform condyles (0c.c.) ; the exoccipitals (e.0.) separated by a
large tract of cartilage from the base, and that tract perforated by the 12th nerve
(XII.), are also shown. There is scarcely any paroccipital ridge to the exoccipital
bone, which, above, is separated by a definite tract of cartilage from the large, shield-
shaped supraoccipital (s.0.).

In the upper view (Plate 20, fig. 3) the nasal labyrinth is complete (al.n., al.sp.,
al.e.), and ends above, as below, in a rounded lobe right and left. The fluted top part
is very uniform up to the proper olfactory region ; that region is ossifying, rapidly, in
its middle. The grooved top, formed by the septum (s.7.) does not end in a car-
tilaginous crista galli ; from the median, notched part the margin of the nasal roof’ is
first concave, and this swells into the lateral, terminal convexity.

The great perforated floor, or lamina cribrosa (c7.p.), has, outside, a sublobate edge ;
the rest is evenly semicircular; more than half of the plate, with the top of the
perpendicular ethmoid, is ossified. In this curiously scanted skull there is a con-
siderable membranous space between the eribriform plate and the orbitosphenoid ;
these tracts (0.s.) are remarkable in several ways, and are almost the least normal of
any I have yet seen in the Eutheria. The top part is still fan-shaped, but the whole
of the large posterior band (see fig. 7, 0.8.) is gone. The sharp angle left is now
ossified separately (0.s’.), and the stem (0.s.) is also bony ; it does not reach more
than two-thirds of the way to the upper margin of the wing. The lower end is
pedate, and is beginning to form a suture with the base (p.s.); it is then reduced to
a mere rod, which curves forwards and backwards twice, becoming flat, but still narrow,
above.

There is no optic foramen, as in Marsupials ; but in front of the main bar, below its
middle, there is, in a notch, a separate spicule of bone (0.s”.), a third bony centre to

helping to complete the

208 MR. W. K. PARKER ON THE STRUCTURE AND

this abortively developed orbitosphenoid. The sphenoidal fissure is a long space
under the orbitosphenoidal bar, and over the alisphenoid; through it, not only the
orbital, but the optic, nerves also pass. The hinder half of the alisphenoid (al.s.)
only can be seen in this view; the bone is twisted over the notch for the 3rd
branch of the trigeminal (V*.). The notches and shoulder of the basisphenoid (b.s.)
are well seen; there is scarcely any sellar concavity on its upper face. Much
cartilage is still seen m the synchondrosis between the two basal bones and between
the elements of the occipital arch; and also, above, where the auditory and supra-
occipital regions unite. The cartilage in the auditory recesses (see Plate 31, fig. 11,
.8.C., p.s.c.) are scarcely visible in this aspect, but the capsule appears to be almost
wholly ossitied; the base of the floccular recess, the holes for the portio moliis
(VIIL.), and the bridge under which the portio dura (VII.) runs, are well seen.
In front of the very shallow imeatus internus the capsule sends forwards a bony snag,
which helps the toothed rim of the cochlear region to give some bony support to
the largely membranous region in front of it.

Third Stage (continued).—Dissections of the visceral arches of the young Shrew.

I have not figured the fore half of Meckxrt’s cartilage, which still persists, not
larger, but not evidently lessened, inside the lower jaw (see Plate 29, fig. 2). Towards
the malleus (Plate 29, fig. 6, ms.) it is seen as a solid terete rod, having a bony style
supporting it further forwards than the manubrium (mb.) extends. But that primary
style of bone has grafted itself upon, and set up extensive ossification in, the head of
the malleus (i/.). This rambling bony tract has forced its way down to the neck of
the manubrium, but has left a large core of cartilage in the middle of the head.
The partly bony head of the malleus is quite normal, and has the tensor tympani
(¢.t.m.) attached to its inner face ; but the manubrium and the posterior angle of the
part from which it springs are very remarkable. The slender manubrium looks like
the tube of a retort, the bulb of which is imitated by the angle; the main part of
the head projects well, backwards, below the articular facet ; the bony matter then
forms a ring round a contracted tract, or waist ; from this part the bulbous tract hangs,
so to speak. Thus the bulbous head, the enlarged body, and the subglobular
“anole” form three enlargements, all in one line, and that at a right angle to
Meckew’s cartilage, and to the manubrium. The incus (¢.) is rather small, and its
articulation with the malleus is becoming indistinct ; the short crus (s.c.7.) 1s very
short ; the long crus (/.c.7.) is rather longer than ordinary ; the head is unossified, and
so also is the inturned orbicular facet.

The stapes (st.) is large, relatively, and has a perfectly stapedial shape ; it is nearly
all bony, the top and base being still soft; I could not find any separated interhyal
in the tendon of the stapedius muscle (s#.7.).

The short crus of the incus fits into a little cup close above the part where the

—_

-

——a

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 209

epihyal (e.hy.) has fused with the auditory capsule; here the bone (aw.) extends; but
the main part of the unusually well-developed epihyal is still cartilaginous, and is
continued without any segmentation into the unossified part of the ceratohyal
(Plate 29, fig. 6; and Plate 31, fig. 12, c.hy.). Half the upper ceratohyal is ossified—
its middle part; then comes a joint, and then the short, lower ceratohyal (c.hy’.),
which, in turn, articulates with the short, ossifying hypohyal (h.hy.).

The latter, in turn, articulates with the almost straight, transverse, nearly ossified
basihyal (b.4.b7.), which has, articulating with it, the ossified, short thyrohyal rods

(t.hy.).

Third Stage (concluded) —Vertically transverse sections of the Nestling Shrew.

A description of these sections will throw further light upon the structure of the
skull at this stage.

Section 1 (Plate 30, fig. 1)—This is through the outer nostrils (e.7.), and shows
how the roof (a/.n.) turns inwards to form the narial valve, and how the floor, also, of
the opening, is cartilaginous ; many of the vibrisse are seen in section in the thick
skin of the snout, in this, and in the following sections.

Section 2.—Here (Plate 30, fig. 2) the narial valve is seen in the hind part of each
nostril; it curves downwards at its free end; the ale nasi (al.n.) are confluent, back
to back.

Section 3.--In this (Plate 30, fig. 3) there is a definite tract of the septum nasi
(s.n.) with an enlarged—intertrabecular

base. The narial valve is gone, and the
cartilage that formed it is now confluent with the floor, so that there are two perfect
narial tubes (7.p.) at this part.

Section 4.—At this part (Plate 30, fig. 4) the floor and walls are separating, again ;
the floor, right and left, touches the lower part of the septum, which is carinate below
its bulbous part.

Section 5.—The tubes now (Plate 30, fig. 5) are not surrounded, below, by cartilage,
and the floor is in two short, oblique tracts; the almost vertical wall turns inwards
below, and the septum, still carinate, is much thicker; these narrow floor-tracts are
those that give off JAcoBson’s (=recurrent) cartilages (Plate 29, fig. 5).

Section 6.—We are now (Plate 30, fig. 6) behind the snout, and through the
premaxillary (px.), with its thin walls, and its relatively huge incisor teeth (see also
fig. 7, t.) just developing in these large, swelling pulps. The double tube is con-
tracted here, the top is still flat, and the septum (s.7.) is very thin above and thick
below ; the enlargement at the bottom of each inturned wall (al.sp.) is the rudi-
ment of the inferior turbinal (7.tb.), at its very beginning, in front. The rods of
the recurrent cartilages (7c.c.) are seen lying obliquely below the bulbous intertra-
becula (s.7.); below, the fore part of the lower lips are seen in front of the dentary
bones (i7.).

Section 7.—This (Plate 30, figs. 7, 7A) 1s through the fore part of JAcoBson’s

MDCCCLXXXV. 2

210 MR. W. K. PARKER ON THE STRUCTURE AND

organs (j.0.) and the perfect part of the cartilage. The roof (al.sp.) is now arched,
with a very small median groove; this roof is very thick for some distance, and
then thins out below, where it is bulbous. The upper three-fifths of the septum
(s.n.) is of the same thickness as the main part of the roof, and then suddenly
swells into a large bulb, witha flattened basal outline. Here the cartilaginous capsules
of JAcOBSON’s organs (7c.c.,) are at their perfect part. They are solid above,
and nearly vertical where they fit obliquely to the septal base; then they curve
outwards to form an oval cavity (for JAcoBsoN’s organ, j.0.), and are keeled and turned
inwards below. In the middle of the pyriform space between them the thin palatine
plate of the premaxillary is seen to rest obliquely on the top of the inner face of the
tubular part. The nasal passage opens into the palatal space below; the nasals
(n.) are cut through above, and the fore part of the maxillaries (m.) with a
tooth and its pulp (f.) on each side. Three mucous follicles (m.s.) are seen in the
interspace between the mucous membrane and the aliseptal cartilage. This part is
close behind the anterior palatine foramina, and here the palate is rugous and sub-
carinate in the middle.

Section 8.—This (Plate 30, fig. 8) is through the open part of the recurrent
cartilages (re.c.) and the hind part of the palatine processes of the premaxillaries.
The thick aliseptal wall has now formed a definite rudiment of the nasal turbinal
(v.tb.), but the rudiment of the inferior turbinal (7.tb.)* is still very imperfect. The
nasals were present, but not figured, and part of the maxillaries (m.x), with a pulp,
are cut across and the fore part of the vomer (v.). Also, below, the dentaries and
their teeth-pulps (d.) are seen.

Section 9.—Here (Plate 30, fig. 9) the vomer (v.) comes fully into view behind
the palatine processes of the premaxillaries (see Plate 29, figs. 1, 2, 4, 5). The
nasals (n.), and the maxillaries (m.,), with their palatine plates ascending to articulate
with the vomer, are all clearly seen. Also the dentaries (d.) below, with their teeth.
Here the nasal and inferior turbinals (1.tb., 7.tb.) have good rudiments. The front
of the tongue (tg.) and the lower jaw (d.) have been cut through, below.

Section 10.—Here (Plate 30, fig. 10) the nasal labyrinth is widening towards
the true olfactory region; the septum is deeper and less bulbous below. The
inferior turbinal rudiment is no longer seen, but the nasal (2.¢b.) is still in view.
The nasals, maxillaries, and dentaries (mz., d.) are still seen in section.

This section is behind the angle of the mouth; the tongue (tg.) is now at its
middle.

Section 11.—Here (Plate 30, fig. 11) the eye-balls (e.) are cut through their front
part, and the nasal labyrinth, largely osseous, is cut across where the nasal, upper, and
middle turbinals (7.tb., «.tb., a.tb.), can all be seen; the floor is ossified at this
part. The nasals, vomer, maxillaries, and palatines (n., ma., pa.) are here cut
through, and the dentaries (d.) below. In the last (fig. 10) the nasal passages

* The line in the figure is carried too low.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 211

were separate, here they communicate, below, under the vomer; here the middle of
the palatine skin is keeled again; it was flat in the last two sections

Section 12.—In this section (Plate 30, fig. 12) the fore part of the olfactory lobes
(C™.) are cut across as they lie in the large fossee upon the ossifying cribriform plate
(cr.p.). Part of the roof-cartilage is seen right and left, and from the walls and floor
copious turbinal growths (w.tb., m.tb.) ave seen. Here, the frontals (/-) are perfect and
roof the whole over, whilst below, the palatines and vomer (pa., v.) are seen in
section, protecting the small, square naso-palatine passage (i.p.c.).

Here the perpendicular ethmoid (p.e.) is spear-shaped above, and clubbed below ; it
is very thin for the most part. The jugal process of the maxillary (j.) is seen, the
mandibles and teeth (d.), with tongue, below.

Section 13,—This (Plate 30, fig. 12) is from a little further back behind the general
roof, and where the frontals (f:) do not meet in the middle; one description may serve
for both of these sections.

Section 14.—This (Plate 30, fig. 13) is through the hemispheres (C!.), the great
fontanelle, at the back part of the frontals (/:), and the large orbito-sphenoidal wings
(o.s.); the basal part, here, is behind the middle ethmoid, and is the front of the
presphenoid. The cribriform plate still comes into section in its hindmost part ; this
is where the skull-walls (0.s.) are united to the olfactory capsules. This is behind the
vomer, and the low bulbous section of the basis cranii (p.s.) lies over a triangular
section of the nasopalatine passage. The bony alisphenoid («/.s.),* is seen outside the
nasal wall.

The palatines and pterygoids overlap at this part, and here the frontal (/) gets well
under the skull in the imperfect orbit.

The articular and angular processes of the lower jaw (cd.p.) and MeckEv’s cartilage
(mk.) are cut across, close in front of the ear-drum.

Here the nasal cavities are small, oblique, and reniform in section, in this, their retral
subcranial part. The wall, although well coiled round the cavity, does not completely
wall it in; the median cartilage (p.s.) is some distance from the walls.

Section 15.—In this partial section (Plate 30, fig. 14), the basioccipital (.0.) 1s cut
across in its front part; on the side, at some distance, the cochlear and part of the
vestibular region of the auditory capsule are cut through; the wall, very thin, is
ossified. The prootic plate (pr.o’.) is seen in section, with the hind part of the
squamosal (sq.) outside and below it. The ossifying opisthotic region, outside and
below the vestibule, shows the facial nerve (VII.) in its whole course—infra-cranial,
auditory, and extra-cranial—escaping close behind the sigmoid hyoid arch (e.hy., e.hy);
the stapes (st.) is partly seen, and also the folds of the concha auris (me., 7.@.e.).

Section 15.—In this still more limited section (Plate 30, fig. 17) the ossifying auditory
capsule is cut through across the fenestra ovalis (/%.0.) and the bar between it and the
fenestra rotunda. The well-formed stapes (sf.) is seen im situ; its head and neck and

* The line in the figure is too short.
2E 2

212 MR. W. K. PARKER ON THE STRUCTURE AND

its base are still cartilaginous, and the long crus of the incus (l.c.2.) has its distal part
attached. The opisthotic and epihyal (ehy.), at their junction, are cut through, and
the continuation of that bar, unossified, into the ceratohyal (c.hy.). The facial nerve
(VIL.) is seen escaping from the foramen stylomastoideum.

Section 16.—In this section (Plate 30, fig. 15) more than half is figured; it shows the
basis cranii (b.0.) cut through in the fore part of the foramen magnum ; the fore
part of the condyles (oc.c.) are in section; and the atlas and axis (at., av.) also come
into view. The occipital roof (s.0.) is ossified above, and below, runs (s.a.c.) into the
top of the auditory capsule over the anterior canal (q.s.c.). Below, the posterior canal
(p.s.c.) 1s cut across ; the thin, inner wall of the vestibule is ossified ; the thick outer
part is still cartilaginous,

Fourth Stage.—The skull of the adult Shrew (Sorex vulgaris).

The interpretation of the skull in its perfect state will now be easy, in spite of its
great unlikeness to that of an ordinary good-sized Mammal, or even of that of a
typical Insectivore.

Seen from above (Plate 31, fig. 1) the peculiar tenuity of this small skull is shown ;
the long bi-tubular snout (a/.n.) is half the length of the dorsal line of the ossified
cranium. Laterally, however, the projecting premaxillaries (pw.) protect the cartilage
in its hinder third. The preorbital region and half the orbital, together, from one
continuous bony growth ; faint signs only of the sutures between the nasals, frontals,
premaxillaries, maxillaries, and lachrymals (7., /, px., mx., 1.) being visible. The tooth-
sockets make the sides sinuous, and they only diverge, increasing the breadth very
gently, up to the jugal processes of the maxillaries.

The foramen infraorbitale (V*.) is very large, and well seen in this aspect ; the space
between the frontal and the jugal process of the maxillary is a sharp notch. From
that notch to the general swelling of the hind skull the cranium enlarges but little ;
the upper part of the coronal suture runs straight across the middle of the skull-waist ;
it is well-toothed and somewhat squamous, the frontals (/:) being imbricated by the
parietals (p.). The frontals are but little larger than in a Snake; but in that Reptile
the frontals remain distinct, whilst the parietals coalesce—just contrary to what takes
place in this little Mammal. The parietals (p.) cover about four times as much space
as the frontals, they are far from each other, and from all the surrounding bones,
except the squamosal, in front. The saggittal and Jambdoidal sutures are well-
toothed, like the coronal; the general surface of the bone is smooth—polished, as it
were—and gently convex. The fore part, helping to form the orbits, is narrow ; the
rest becomes almost twice as wide. Flanking the frontals the squamosals can just be
seen, giving additional width to the temporal region. The middle half of the lamb-
doidal suture has, set in it, a transverse plate of bone which projects forwards into the
notched parietals in front, and lies straight along the fore margin of the supra-
oceipital (s.o.), behind ; this bone, which is slightly crested, is the interparietal (7.p.).

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 213

The interparietal is small for an Insectivore, but the true supraoccipital (s.0.) is
unusually large, and suggests at once a Monotrematous relationship. The thrice-
convex hind margin is wide, but the fore edge runs across the skull to the post-
temporal region, and is nearly as wide as the two parietals, together, at their widest
part. Moreover, the tract covered by the supraoccipital tegmen is almost as extensive
as that which is covered by the frontals.

In the side view (Plate 19, fig. 3) the peculiarities of the Soricine skull are well
shown ; a Mammalian skull, truly, but reduced to its utmost tenuity. There is a
general parallelism in the downward and forward curve of the various parts; the
snout also is thus followed by the premaxillaries (px.), with their notched and ferru-
ginous teeth—like the mandibles of a Beetle—and the elements of the skull, further
back, dip in front, in like manner.

Back, as far as to the coronal and squamous sutures, which are largely persistent,
there is no sign, in this view, of composition; the badly formed orbit has the frontal
coming well down on its inside, but it merely dips inwards a little, it forms no brow ;
nor is there any definite post- or preorbital wall or outwork.

For such a snout the maxillary nerve (V’.) has to be very large, for the lips are
thick, and the vibrisse well developed; the canal, therefore, is very large, and it is
perfected by the maxillary, which has a stump of bone in the jugal region ; the canal-
wall for the infraorbital nerve is itself perforated. The lachrymal (/.) is melted into
the fore edge of the maxillary, and the sphenoidal wings, front and hinder (o.s., al.s.),
are all confluent with the overlying membrane-bones ; so also are the palatine bony
tracts with the bones above them. In the inner and lower face of the undefined orbit,
the sphenoidal fissure (II., V'*.) is seen as a large channel, opening obliquely ; this is
due to the fact that the alisphenoid (a/.s.) embraces the orbitosphenoid (o.s.), growing
freely outside it.

The curious, low-lying, oblong squamosal (sq.) opens in front as two short blunt
blades, which seem to bite the outspread alisphenoid; this is due to the fact that,
whilst the jugal process is aborted and has no jugal bone to lie upon, the condyle
(glenoid cavity) has become subdivided into two tracts of articular cartilage, one
above and one below. Thus the two-faced condyloid head of the lower jaw
(figs. 8, 4, cd.p.) is really held between the two blades of the squamosal. In the
erescentic hollow behind these blades the normal pneumatic foramen is seen ; the bone
there is narrower, then broadens somewhat, and then, dipping gently, ends as a rounded
or ear-shaped lobe in the re-entering angle formed by the prootic plate (pv’.0’.), and the
mastoid region of the ear capsule (op.). Under its concave edge—greatly turned
inwards (see fig. 2, sg.)—the tympanic (a.ty.) can just be seen. The structure of the
skull in the temporal region is very elegant; the larger hind skull is finished by the
large parietals (p.), which imbricate the frontals in the postorbital region, and throw
themselves backwards and downwards, over the hinder auditory region, clamping all
the parts with their toothed edge. They come down with a straight edge to the

214 MR. W. K. PARKER ON THE STRUCTURE AND

slightly overlapping squamosals, with which they partly coalesce, and then ride over
the prootic plates, with a concave edge; then, as if for purposes of architectural
ornament, the “lateral sinus” (s.c.) throws its low arch over the whole of these
temporal sutures; three foramina are seen close to it, one in front, one in the middle,
and another over it, near its hind part.

Wedged in between the parietal and squamosal, the curved prootic plate (pr-.o’.) is
seen; its fore-part is like a pruning knife; its hind part passes insensibly into the
epiotic and opisthotic regions, where the three canals (a.s.c., h.s.c., p.s.c.), by their
burrowing, mark the outer face of the bone, which is very thin over them. The
occipital condyles (0¢.c.), are large, bold, and pyriform in outline; between them and
the opisthotic region (op.) the ex-occipitals (¢.0.) are wedged, scarcely forming any
definite paroccipital process. Over the whole, like half a dome, the great supraoccipital
(s.0.) is seen.

The lower jaw (seen from the cnside) is very small, but strong; it is hinged half
way between the front of the nasal bones and the occiput. The coronoid process
(figs. 3, 3a, c.p.) is high, vertical, and scooped on its inner face; the articular process
(cd.p.) is sub-triangular, thick, and has a two-faced condyle (gl.c.); the angular process
(ag.p.) is long, terete, and incurved at its end; the dentary canal (neuro-vascular passage)
begins under the muscular fossa of the coronoid process. The teeth, here, as above,
are curiously mimetic of the mandibles of Coleopterous Insects—the food, especially
of the Shrew, who, himself, is less than some of the members of the Beetle Family.

In the lower view (Plate 19, fig. 2) the snout (al.n.) is partly supported by the pro-
truding incisors; and the bony palate, between the fine dental armature, is a high
triangle, whose short base is behind; this boundary is directly transverse, but some-
what bracket-shaped, and is strongly limbate. The longitudinal extent of the pre-
maxillaries (pw.) is one-seventh that of the whole hard palate ; they are very partially
distinct from each other, and from the maxillaries (mwx.); the anterior palatine
foramina (a.p,f.) are small. So also are the posterior foramina (p.p,f), and they are
some distance in front of the persistent palato-maxillary suture. The fused maxillary
plate is subcarinate in its middle third, under the junction of these bones with the
vomer ; the fore half of the middle palatine suture persists, and that part of the hard
palate has four small foramina; its fore margin wedges in between the maxillaries,
and yet its extent is less than half of the plate formed by the latter bones.

The jugal processes of the maxillaries projecting beyond the last tooth-socket make
the narrow-waisted part, next following, very remarkable. In the distance, the orbital
plates of the frontal and the rounded supraorbital edge are seen beyond the open
region of the palate. The thick, spongy walls of the nasopalatine passage (n.p.p) are
equal in width to that passage; and the roof, where the forks of the vomer (v.) end, is
perforated with holes and slits.

The pterygoids and palatines (pg., pa.) are thoroughly fused together, and are
equally confluent with the posterior sphenoid (al.s., b.s.). The hamular processes

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 215

of the pterygoids are small, terete, short, parallel, and unusually near together.
Behind them there is a small foramen, right and left, and still further back, another
pair of holes, wider apart, near the junction of the basisphenoid with the basioccipital
(b.s., b.o.). The basis cranii, from the perpendicular ethmoid (over the thick hind rim of
the hard palate) to the foramen magnum, is a peculiar structure ; in front it is narrow,
but behind the pterygoid hooks it widens out rapidly into two triangular wings,
where the ali- and basisphenoid are anchylosed together. The basal plate then narrows
gently and sinuously up to the middle of the basioccipital region, and then gently
widens to the end, until it becomes just half the width of the widest sphenoidal part.
The median part is made into a broadish and rather shallow groove by a thick, ribbed
part, the rudiment of the hinder part of the tympanic wing of the typical kinds ; these
thickenings run up to the occipital condyles ; but they do not enlarge the tympanic
cavity. The inner (and also lower) facet of the glenoidal cavity (gl.c.) turns inwards
and lies under the foramen ovale—now perfected by a bony hinder bar ;—so that this
hole is not seen, either laterally (fig. 3) or from below (fig. 2); the longitudinal
direction taken by this nerve passage is indicated in both figures by a bristle (V*.).
The inner edge of the squamosal, where it curls under the skull, is sinuous ; it diverges
from the outer edge of the basis cranii, so as to leave a large space, the hind margin of
which is finished by the opisthotic region of the auditory capsule (op.). This pyriform
space, with its wide end behind, is as large as the dilated posterior sphenoidal region
of the basal and basilateral parts of the skull; it is largely finished by membrane—a
permanent basilateral fontanelle. This space in the macerated skull occupies nearly
all the side of the hinder or postorbital part; it is heart-shaped, being filled in
somewhat in front by the postglenoid wing of the squamosal (see fig. 3). In the
undisturbed state of the parts where the huge auditory capsule is kept in its place by
ligamentous tracts, the hinder and outer part of each great fontanelle is filled in by
that complex, intercalated labyrinth.

But on the lower face, between the squamosal and the basis cranii, this fontanelle is
only partially latticed across by the small annulus and the ossccula, which, with the
drum-membrane, only half hide this great gap. In this under aspect the cochlea (ch/.),
that part of the vestibule which passes into the tegmen tympani and overarches the
facial nerve and ossicula, and the part containing the horizontal and semicircular
canals (h.s.c., p.s.c.), are all well seen. The large, pyriform condyles (o0c.c.) and
the oval foramen magnum (/fm.) surrounded by the elements of the occipital arch
(s.0., €.0., b.0.), are shown in this view.

When the auditory capsules have been loosened out by maceration, and are examined
separately (figs. 4 and 5; oblique views of the inner and outer side), then we find
that the capsule has used up and carried with it, in its ossification, a large amount of
the primary endocranium, not properly belonging to the capsule. Not only is there a
pterotic and a sphenotic tract of this kind, but, as I have already shown, the small
alee that originally grew from the basis cranii behind the pituitary region, have been

216 MR. W. K. PARKER ON THE STRUCTURE AND

ossified by the corresponding opisthotic centres, and made to serve as a rim to
the cochlea.*

Seen obliquely from the outside (fig. 5) there is, above and in front, the shell-like
prootic plate (pr.o’.), and below it a similar, but lesser wing-like growth of bone. The
cochlea, (ch/.) is also crested, the crest running forwards into a sharp point. A notch still
persists where the two bony centres meet in front; below that notch the canal for the
facial nerve (VII.) is seen at both ends, and below and outside its foramen of exit
(stylomastoid) a thick, hooked club of bone runs across between and outside the
two fenestree—fenestra ovalis, and fenestra rotunda (/%.0., f7.); the clubbed part is
the stump of the epihyal (e.y.) confluent with the capsule.

The anterior canal (a.s.c.) shines through the thin bone, and the posterior and
horizontal canals (p.s.c., h.s.c.) project from the surface of the opisthotic region.

On the inside (fig. 4) the anterior canal stands out as an elegant arch over the deep
and large floceular recess, which is bounded behind by a sharp crest of bone inside
which is the common sinus of the anterior and posterior canals. Three convexities
are seen below the recess; these are, from before backward—the ampulla of the
horizontal canal (/.s.c); that of the anterior (a.s.c.) and the third rising is formed by
the vestibule (v).). Below these mammillary risings the great porchway for the
auditory nerve (VIII.) and the bridge over the facial (VIT.) are shown; and there is a
small tube behind, on the edge of the capsule: in front of these foramina the coils of
the cochlea are partly hidden by the limbation of its margin, running into the
anterior sharp process,

The small, strong annulus (figs. 6, 7, a.ty.) quite enclose an oval space, although the
crura do not coalesce; the hinder crus has a broad, bilobate end, which overlaps the
somewhat pointed end of the front crus, and from the outside (fig. 6) partly hides the
manubrium mallei (mb.). The fore part of the annulus projects, being also dilated
considerably ; below, and at both ends, the outer face is convex ; the upper crus is
ridged and grooved below the ridge. On the inside (fig. 7) there is but little con-
cavity ; this is for about a third of the inner rim, in front of the sharp groove on which
the processus gracilis of the malleus (.gr.) lies.

That process is styloid, slightly decurved, and diverges from the manubrium, which
runs straight along the long axis of the elliptical space formed by the annulus for the
membrana tympani; it traverses three-fifths of that axial line; and is very slender
and straight, with a gently bulbous free end. The neck of the malleus (m.) is flat,
and rises suddenly into the rounded head, which is confluent with the head of the
incus (7.). Half-way down below the condyloid region the bone projects as an obtuse

* There is nothing new in the morphology of the skull; in the Frog each of the three great lateral
bony centres that harden the chondrocranium takes up both a sensory and a cranial tract; thus we have
a “sphenethmoid,” a “ prootico-alisphenoid,” and an “ opisthotico-exoccipital.” In osseous Fishes the
semicircular canals run far into proper chondrocranial regions, and are ossified by tracts that have a

double morphological significance—e.g., the ‘ sphenotic ” and the “ pterotic.”’

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 217

angle, the hinder edge is then notched twice, and then comes the solid bulbous “ pos-
terior angular process” (p.ag.) of this highly modified “ articulare.” The main part of
the malleus has ribbed edges, is limbate, and the neck is flat and thin; on the inside
the root of the manubrium is thick and rough.

The incus (7.) shows signs of degradation, being fused with the malleus and
reminding the observer of the arrested and, in the adult, fixed state of that segment
of Echidna. The short crus (s.c.7.) is a mere snag; the long crus is very long, feeble
and bent forwards ; the neck of the orbicular condyle is well bent, very thin, and
carries a well-made circular facet for the stapes. That bone (fig. 8, sf.) is a miniature
model of a stirrup, thoroughly normal, and unusually perfect in form. The hyoid
arch, proper (Plate 31, fig. 9), has become much stronger, and yet more slender, than
in the young stage (fig. 12). The cartilaginous continuation of the epibyal, from its
bony stump (fig. 5, ehy.) to the top of the upper ceratohyal (fig. 9, c.hy.), Is a
complete band of cartilage; the next tract is slender and curved, and is unossified
in its lower third; the lower ceratohyal (c.hy’.), the hypo- basi- and thyrohyals are
largely ossified ; the latter (t.4y.) are much longer now, and are bent outwards in the
middle.

The interior of the skull was not figured; nor any of the figures made from an
old specimen. The cribriform plate is very large, oblique, and richly perforated ;
the median ethmoid, between its halves, is thin, but strong; all the parts, inside the
front of the cranial cavity, are well ankylosed together. The orbitosphenoids have
very narrow edges to the hind margin of the cribriform plate ; the basisphenoid has a
very slight sellar depression. In old skulls the parietals coalesce with the frontals
and with the fore half of the upper part of the squamosals; so that the sutures left
are the hinder main part of the sagittal, that between the parietal and interparietal,
and the hind part of the squamous suture.

Yet these remains of sutures, the independence of the extensive auditory cap-
sules, and the general thinness and elasticity of the larger bony tracts defending
the brain, all help to make this small skull more or less flexible under accidental
pressure.

I have not added certain figures made from the skull of the adult Water Shrew
(Crossopus fodiens); it merely differs from that of the Common Shrew (Sorex vul-
garis) by its larger size, greater robustness, and a somewhat more intense ossification
generally. The orbitosphenoids are wider, and the “ foramen ovale ” is quite visible on
the lower aspect of the skull; in the common kind (Plate 31, fig. 2) the bristle (V*.)
is seen to pass over the incurved lower glenoid process ; there is a notch between it
and the hind corner of the alisphenoid (a/.s.), and then a bridge of bone between this
notch and the fore-end of the great infero-lateral fontanelle. In Crossopus fodiens
the emerging nerve is bounded in front by a tract of bone, where the notch is in the
lesser third ; here it appears to pass through the neck of the lower glenoid process ; as
a matter of fact, the foramen is made by the confluence of the alisphenoid with that
part of the squamosal.

MDCCCLXXXV. oF

218 MR. W. K. PARKER ON THE STRUCTURE AND
On the skull of the Centetidee.

My materials for working out the structure and development of the skull in this
peculiarly Mascarene Family of the Insectivora are as follows :-—

A. Stage 1.—An embryo of the largest kind—Centetes ecaudatus—7 lines long,
(head 3, body 4), (Plate 16, fig. 13); this is intermediate between my Ist and
2nd Stages of the Mole (Plate 1, figs. 1, 2, 3).

Stage 2.—A three-fourths ripe embryo of Centetes ecaudatus, 144 inch long.

Stage 3.—Young individuals of Centetes ecaudatus, 34 inches long.

B. Almost adult specimens of Hemicentetes madagascuriensis and H. nigrescens.

C. An adult Hriculus nigrescens.

D. An adult (or nearly) Microgale longicaudata.

Stage 1 (Plate 16, fig. 13).

In the smallest embryo the snout is just beginning to project from the front of the
face; the brain vesicles (C"., C*., C%.) are very large ; the eye-ball is very small, and
surrounded by a circular lid ; the concha auris has commenced its folds ; the limbs are
mere flaps; and the tail is, relatively, longer than in the more advanced specimens ;

the head is very large, relatively.

Stage 2.—Embryo of Tenrec, Centetes ecaudatus, 144 inch long (Plate 16, fig. 14).

The head is still (and always will be) very large in proportion to the body; the
tail is a mere stump, the limbs are well-formed. The eyes, and their lids, are very
small, and so are the outer ears; the snout is now a considerable structure, running
in front of the lips.

The skull (Plate 32) has acquired a large amount of solidity from ossification, both
external and internal; the whole structure is very evenly conical, with the snout
as its obtuse apex.

The investing bones.

Seen from above (Plate 32, fig. 1) the endocranium only comes into view at the two
ends ; behind, it is largely ossified. The scale-like superficial bones of the roof, the
nasals, frontals, and parietals (n., f., p.), show their radiating lines of growth; as
to size, the nasals are broader, the frontals much longer, and the parietals much
shorter than in the Mole and Shrew; they are more normal in this type. A large
fontanelle (/o.) still exists above, it spreads into sharp wings, right and left, in the
coronal region, and in the lambdoidal to a less degree, where it runs back as a large
semicircular notch in the huge, roughly crescentic interparietal (7.p.). Here this super-
ficial cranial element that is absent from all the Edentata except Orycteropus, but
constant in the Insectivora, as in the Marsupials beneath them, attains its highest

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 219

relative development. The premaxillarics and maxillaries (px., mx.) are not well seen
in this view.

In the side view (fig. 3) the premaxillaries (pa.) are of the average size, and show
a diamond-shaped oblique facial plate, which wedges in between the nasal and
maxillary on each side. The maxillaries (ma.) are nearly half the length of the whole
bony skull; the postero-superior angle runs somewhat into the orbit, and inside this
process, and the one below it, the small lachrymal and its canal (1., dc.) are seen. That
space is triangular, but under the sharp style that bounds it below, there is a deep
chink along which the maxillary nerve (V*.) passes; it is unprotected on its outer
side ; behind this chink the general alveolar roof runs for a considerable distance.

The frontals (f.) have a thick supraorbital edge, and a large concave orbital plate.
The growing parietals (p.) run forwards obliquely under the postorbital edge of the
frontals, just meeting the upper and front angle of the alisphenoid (al.s). Thence,
each parietal runs backwards to the antero-external edge of the azygous interparietal
(i.p.); the obtuse re-entering angle formed by their junction exposes the huge
auditory capsule.

There are no jugals; each squamosal (sqg.) applies its small squamous plate over
about a third of the lower edge of the parietal, rather in front of its middle. The
jugal process does not reach so far forwards as the squamous; it only serves to
carry the glenoid facet (gl.c.); the postglenoid process is very small, and the post-
temporal plate small; its sharp hinder angle reaches half-way over the horizontal
canal (h.s.c.) Under the squamosal the annulus (q.ty.) is just seen, and the pterygoid
(pg-) with its cartilage (pg.c.) behind the alveolar angle of the maxillary (vu..).

The lower jaw (d.) is well formed, and most of the cartilage on its three processes is
ossified. The coronoid (c.p) is twice as prominent as the angular (ag.p.), and the
condyloid (cd.p.) is rounded, and definitely marked off by a neck. The splenial region
is seen in this inner view to be deficient inside MeckeEt’s cartilage (mk.), (a part soon
to be described), this is ossified, and fills a large groove all along the ramus.

The lower view (fig. 2) shows the superficial bones that form the hard palate ; the pre-
maxillaries (see also tig. 4, pa.) form the narrow fore part of a long ellipse, truncated
behind. The dentary region is shorter and thicker than the palatine process. The
two palatine processes together form a long lanceolate, leafy structure, with their flat,
high suture, simulating a mid-rib. I could find no separate front paired vomers ; as in
the Mole and Shrew, these are probably connate with the premaxillary.

The short jugal process of the maxillary projects beyond the last large tooth-pulp ;
of these I find five large pulps in each maxillary, and three small ones in the pre-
maxillary.

Inside the crenate alveolar wall the palatine plate of the maxillary is divided by a
groove into two subequal narrow tracts. Each of these ends in front in a sharp spike,
the outer binding on the inside of the alveolar plate of the premaxillary; and the inner
on its palatine process ; thus the anterior palatine foramina are very long slits.

2F %

220 MR. W. K. PARKER ON THE STRUCTURE AND

Between the sides of the palatine plates of the palatine bones and those of the
maxillaries there is an oblique, fusiform fenestra. The former bones (pa.) are like two
blades, they are closed, at their suture, which is nearly half as long as the maxillary
suture, and have their handles behind the hard palate. On each side, at their broadest
part, they nearly touch the alveolar plate of the last tooth ; they then bend iny yards and
become a mere oblique short tract of the wall of the nasopalatine passage. This
wall is finished by the pterygoids (pg.), which are bent inwards and downwards also,
behind, where they are capped with a nucleus of cartilage (pg.c.); their basicranial
flange is moderate and continuous. There is no mesopterygoid centre. The tympanic
(a.ty.) is a narrow U-shaped bony staple, with its fore limb sinuous, and lobate at its
end,

The vomer (figs. 4 and 6, v.) is an extraordinary structure ; the main median bone
is relatively smallest in the Marsupials, and largest in the Tenrec, if we except the
abnormally long-faced Cetacea.*

The low septum (fig. 6, s.r.) and the large thick vomer (v.) at once suggest the com-
parison with those of the Cetacea. This bone overlaps two-thirds of the recurrent

cartilages (re.c.), becomes roughly carinate, pinches in a little, and then gives off an ala,
right and lett of the sharp split in its hinder end. The whole bone is rough and
cellular, and in the hind part is undergoing absorption along certain lines, the meaning

of which we shall see in the next stage.

Second Stage of Centetes ecaudatus (continued).—Endocranium and visceral arches.

The exposed part of the nasal labyrinth—the snout (a/.n.)—is barrel-shaped ; the
nostrils are latero-terminal; the rest of the large labyrinth is not figured, but I have
shown the septum (fig. 6, s.n., p.e.) and the recurrent cartilages (figs. 4-6, re.c.); these
are tongue-shaped, scooped tracts, and are quite normal. The highest part of the
perpendicular ethmoid (fig. 6, p.e.), between the large oblique olfactory fossze is in
reality low, but the septum nasi, proper (s.7.), is a crest to the huge, thick intertra-
becula, scarcely higher than that bar. Where the septum divides the snout, there it
becomes deficient, and, indeed, the partition in front of that oval fenestra is mainly
formed by the fusion, back to back, of the ale nasi (adn.); the snout is bent
downwards considerably.

The basis cranii behind the perpendicular ethmoid (figs. 4, 5,t p.e.) is beginning to
ossify as the presphenoid, but the independence of this centre is doubtful in this case,
as the orbitosphenoids (0.s.) have met over the middle bar (fig. 5) and are closely
embracing it. These wings are about two-thirds the size of the alisphenoids (ad.s.),
already they are quite ossitied and have lost the large superlateral tract of cartilage,

* This species—Centefes ecaudatus—is the one land Mammal that rivals the Whale in the relative
length of the head—it is one-third of that of the body.

+ Figs. 4 and 5 are from the dissected endocranium after it had been pressed out so as to display the

parts,

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 221

which did not ossify, but was absorbed. Each of these bony plates is widest above
and narrowest in the middle, and the large optic foramen (II.) is well in the middle of
the proximal part. When fully seen from above (fig. 5, 0.s.) the hind margin has two
emarginations, one large, in the middle, and one small, near the base ; the projection
between these notches has, on the right side, a small additional nucleus of bone (o0.s*.).

The posterior sphenoid is at this early stage a single bone, for the base and the ale
(b.s., als.) have already largely become confluent ; the lower surface (fig. 4) is much
larger than the upper (fig. 5), this is mainly due to the great tympanic development
in the base; but the ale are partly overlaid both by the orbitosphenoids and the
cochlez (0.s., chl.); the alisphenoids are most remarkably out-thrust in these and
other normal Insectivores. Half the cartilage between the basisphenoid and the
presphenoidal tract of bone (fig. 4, b.s., p.s.) belongs to the former and half to the
latter; also, behind, there is much cartilage between the basioccipital (b.0.) and the
basisphenoid.

There the basal beam has doubled its width; but that is only two-fifths of the
whole width of the basisphenoid, which has two crescentic wings, shell-like out-
growths, placed back to back, with their hollow face outside. In front, these tympanic
wings only reach half way along the basisphenoid ; behind, they overlap the basi-
occipital, so that they are retral in relation to their origin. The whole inferior sur-
face of the posterior sphenoid is broken up into ridges, grooves, and holes. On each
side, in front, there is a rough ridge parallel with the basal cartilage and bone; these
are for the fixation of the basicranial flanges of the palatines and pterygoids. Outside
these, separated from them by a fossa, there is, right and left, a triangular wing, the
external pterygoid process (e.pg.) ; the hollow is the pterygoid fossa; these wings
spread further out than the tympanic wings, behind, and they resemble them in form.

Outside the front of the curved tympanic wing there is a rough foramen (f. ovale, V*.)
which on the inside (fig. 5) is a mere notch. Outside and in front of this is the hinder
opening of the alisphenoidal canal (fig. 4, a/.s.c.), and on the same oblique line, looking
outwards and forwards, is a semioval fossa, its truncated end being at the edge of the
great wing (al.s.). On the inside this is not seen, and the bony wing has a generally
concave face in front of and outside the foramen ovale (V*.). The posterior clinoid
wall (fig. 5, p.cl.) is low and broad; there is, however, a very definite sellar
depression,

The auditory capsules --here artificially squeezed outwards to display their parts—
are large and pyriform ; they are quite normal in having two subequal osseous centres
—the prootic and opisthotic (pr.o. op.). The latter, on the lower face (fig. 4),
embrace the base of the cochlea (ch/.), and the two are fast approaching each other
over the first coil. The prootic (pr.o.) is creeping backwards, and (fig. 5) along the
front edge of the capsule.

The opisthotic is seen from below (fig. 4, op.) creeping round as an unciform shell,
behind and under the cochlea and vestibule; it has already formed the familiar ‘nter-

222 MR. W. K. PARKER ON THE STRUCTURE AND

fenestral bar between the fenestra ovalis and the fenestra rotuada (fs.0., Jr.) ; above
(fig. 5, op.) it has formed a roughly erescentic shell round the inside of the meatus
internus (VIL, VIII.). On the inside, the great anterior canal (a.s.c.) arches over the
large but shallow fossa for the ‘floceulus” (/l.7.); the convexity behind this fossa is
formed by the sins, common to the anterior and posterior canals. Below (fig. 4), the
horizontal and posterior canals are seen. These views have, however, to be corrected
by the other figures (figs. 1-3) when the parts had not been subjected to pressure.
Above (fig. 1), the top of the huge auditory convexity is seen, and then the posterior
canal (p.s.c.) can just be seen where it has passed away from the anterior,

On the side (fig. 3) all the three canals (a.s.¢., /.8.c., p.s.c.) are seen, showing through
the hyaline cartilage, in their natural position, and leaning backwards: a normal state
of things for a Mammal.

Below (fig. 2), in the undisturbed condition of all the cranial elements, the
horizontal and posterior canals (h.s.c., p.s.c.) come well into view and meet at a right
angle. But the ampulla of the horizontal canal is, here, hidden by the epihyal (e.hy.),
which is confluent with the capsule, and by the facial nerve (VII.) passing through
the stylomastoid foramen.

The occipital arch must be described from the figures of the complete skull (figs. 1-3)
as well as from those of the outspread endocranium. The keystone (figs. 1, 2, s.0.) is
very large, and its evenly emarginate fore edge is adapted to the hinder round edge
of the still larger interparietal (.p.). The cartilage is wide between it and the
exoccipitals (e.0.), and they are separated by a tract, half their own width from the
polygonal basioccipital (b.0.) whose hind margin is notched to form the fore boundary
of the large foramen magnum (f-m.). The occipital condyles (o0c.c.) are long-oval in
size and shape, and are moderately convex.

The foramen condyloideum (XII.) just behind the chink for the 9th and 10th nerves
([X., X.) is through the thick cartilage in the lower edge of the ex-occipital.

The deep mandible (mk.) in its proper mandibular part, inside the superficial
“ramus” is now invested, roughly, with bone, possibly derived from the dentary (d.).
Under the condyloid process of the ramus (cd.p.) the proximal part of MrcKe.’s
cartilage has acquired a styliform ectosteal plate, and this is spreading over, and
growing into, the head of the malleus (m/.) nearly up to the articular condyloid facet
for the incus. That facet is deep and selliform ; below it, the hinder margin of the
malleus is semicircularly notched, and has an unciform angle.

From this angle, and from the lower edge of the bony centre, the main enlargement
grows obliquely forwards ; it then dips to form a subglobular posterior angular process
(p.ag.) from which the manubrium (fig. 7, mb.), arcuate and dilated at its free end, passes
forwards. The incus (7.) is perfectly normal ; its straight, conical “short crus” (s.c.2.)
is large, and its “long crus” (/.c.7.) is thick, well inturned, and hasa short-oval orbicular
plate for the stapedial head ; the body of the incus is rapidly ossifying from the hinder
concave margin. The stapes (st.) is very short, has an almost circular fenestra, and

DEVELOPMENT OF THE SKULL IN THE MAMMALTA. 223

a very perfectly limbate margin, with a flat outer face all round, for insertion into the
fenestra ovalis. I did not find any interhyal segment. ‘The short round epihyal
(tig. 2, e.hy.) is followed by membrane up to the equally small hypohyal (fig. 8, A.hy.).

The basal piece (b.h.br.) is a longish transverse bar, narrow in the middle where it is
beginning to ossify, and then where it reaches the hypohyals it is thicker ; thence, at
a very obtuse angle, the thyrohyals (¢.hy.) grow outwards and backwards, without any
sign of segmentation from the basal piece.

Third Stage.— Young of Centetes ecaudatus ; 34 teches long.
I. The investing bones of the skull.

At this stage, before the development of the crests and ridges seen on the hind
skull in the adult,* the general form is like that of a Mole, or still more of a Shrew,
as there are no jugal bones. Very little of the great fontanelle is now visible at the
junction of the parietals and frontals, and the whole investiture of bony plates is
strong and smooth; ossification takes place very rapidly in this type, but not so
rapidly as in the Marsupials, whose premature birth is provided for by precocious
ossification of the skull. 3ehind the moderately long, and rather slender snout
(al.n.), the skull is at first narrow, and then widens gently to its orbital ‘‘ waist ;” the
temporal region is the widest, notwithstanding the great size of the maxillaries with
their large teeth and tooth-sockets (Plate 33, fig. 1). In the wpper view, we see that
the nasals (fig. 2, 7.), flanked by the premaxillaries and maxillaries (px., max.), are
long, and already give promise of the intense ossification of the Tenrec’s skull.

The notch between the nasals in front is followed by a suture dividing their fore
third, and behind, there is a slight division ; for the rest they are thoroughly confluent.
The frontals (f.) are longer than the nasals, but their mutual suture—the frontal—is
only two-thirds the length of the bones, as the nasals run their double wedge far in
between them. The frontals, in turn, to a less degree, divide the parietals (p.), and
their strong suture—the sagittal—is only two-thirds the length of the frontal suture.
There is a remarkable amount of mutual inter-wedging above, in the preorbital region,
for the frontals divided by the nasals run forwards between the maxillaries and the nasals,
whilst the lesser premaxillaries do the same between the nasals and maxillaries, in
front, so that the latter only reach the middle part of the nasals for a short distance.

The supraorbital region of the frontal passes very gently down into the orbital, and
each bone gently widens out to the postorbital corner. From the V-shaped coronal
suture the parietals widen at first very little, and then suddenly in the temporal
region; they are bounded behind by the huge interparietal (v.p.), and divided from
it by the lambdoidal suture.

The suture is, here, an inverted \/, and is similar to the coronal; its crura are
coneave in front, those of the coronal are arched forwards. The dentation of these

* See Dorson’s “ Insectivora,” Part ii., Plate 8, figs. 1, La.

224 MR. W. K. PARKER ON THE STRUCTURE AND

non-persistent sutures is very strong, as in the Salamander’s skull. The hinder outline
of the parietals and interparietals, together, is a very neat semi-circle, just flanked,
and made to look irregular by the partial view, in this aspect, of the squamosal,
auditory, and supraoccipital bones.

In the side view (fig. 3) the parts just spoken of as flanking the great roof-bones,
come fully into sight, as also the bones of the upper face, so imperfectly seen from
above.

Behind the deflected snout (al.n.), the strong, oblique, unciform premaxillary facial
plate (px.), is seen with its sharp and rather large teeth ; over it the nasal (n.) is seen
somewhat ; the maxillary (mz.) is nearly half the length of the whole bony skull, and
is a notable prophecy of what this bone, with its heavy burden of teeth, will become
in the great herbivorous Eutheria; from its rounded edge, closely fitted to the
premaxillary, it runs backwards as far as the coronal suture, ending there as a flat, free
jugal process. A low triangle, its posterior edge is shorter than its anterior, and
that is the most irregular. That irregular edge bounds the front of the badly enclosed
orbit ; near its upper part, the squamous, perforated lachrymal (/., /c.) fits into a deep
recess, and below this the great infraorbital foramen (V*.) runs on, forwards, as a large
groove ; it is very feebly finished, outside, by an arched bar which articulates with the
lachrymal. Behind that suture the maxillary is seen as a large rounded lobe of bone,
the outer alveolar wall of the two last molars, and the jugal process, ali in one tract.
Even now the frontals and parietals have separate convexities, that of the former is
the higher of the two. The orbital plate is notched where the Ist branch of the 5th
nerve (V1) re-enters the skull, and there the frontal, parietal, orbitosphenoid and ali-
sphenoid, all approach each other. In the temporal region the parietal swells over the
squamosal, whose seale-like temporal flange overlaps the lower edge of the former;
it is sharp at its fore corner, where it lies on the projecting alisphenoid, and it turns
upwards in its post-temporal region, to bind, tightly, between the parietal outside, and
above, and the auditory capsule within, and below. The oblique retreating front
margin of the squamosal is notched, and meets its outer oblique edge at an obtuse
angle, beyond the glenoid cavity (gl.c.); it scarcely projects at all as a jugal process.
The lower postglenoid facet binds upon the canal-region of the auditory labyrinth
by its oblique, toothed, and notched posterior margin. This side view shows the
interparietal (7.p.), the pterygoid hook (pg.) and the annulus (aty.). At present,
therefore, the temporal fossa is badly enclosed, and the sagittal and lambdoidal crests
have no existence.

In this same side view the mandible is seen as an almost crescentic bone ; the axis
of the ramus and of the high coronoid process (c p.), being coincident. The three
processes are almost equal, for the smallest of the three, the angular (ag-.p.) is larger
than it seems to be as seen from the side; seen endwise (fig. 34) it has a thick
limbate inturned edge, and is manifestly Marsupial.. The condyloid process (cd.p.)
is oval, transverse, and has the narrow end inwards. The dentary canal can be seen

—

un

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 22

from behind, protected by a wing of bone in the true coronoid region, and the
remarkable thickness, roundness, and solidity of the ramus is also shown.

The lower view (Plate 21, fig. 1) shows a large pyriform tract, two-thirds of the
whole inferior area, covered with superficial bones. The premaxillaries (px.) have a
considerable dentary edge, and long, slender, compressed palatine processes. Each
large maxillary (mx.) shows on this face three tracts, first, the series of alveoli,
expanding from before, backwards; then the outer part of the palatine plate wrought
into subtransverse ridges, and hollow with perforations ; and, close to the mid-line, a
narrow tract, on a higher level. The two halves of the palatine plate end, in front, as
spikes, the inner binding on the palatine process, and the outer on the dentary
region, of the premaxillary. The inner tracts run short behind, the palatines (pa.)
wedging in, in an irregular manner; the outer reach as far backward as the alveolar
walls, binding strongly on the outer face of the open part of the palatines. The rough
splintery fore part of the palatine plate of the palatines is split for some distance,
and then towards the transverse ribbed edge, behind, shows the posterior palatine
foramen (p.p.f.). Where the nasopalatine passages open, there both at the middle part
and the sides each palatine bone is thick and solid; and then, suddenly thinning out,
they bind on the small subparallel blunt-hooked pterygoids (py.); the pterygoid
fossee are very indefinite.

Over the opening of the nasopalatine canal the vomer (v.) is just seen in its
hinder part ; and on the right side of the figure the annulus (.ty.) is shown, with its
thick twisted anterior, and its sharp posterior, crus. The orbital plate of the frontal
(f) is seen in the distance, and the squamosal (sq.) shows its obliquely oval glenoid
facet (gl.c.), its stunted jugal process, and its short, strong, three-limbed postglenoid
tract, with the postglenoid pneumatic foramen, close to the glenoid cartilage.

On the hinder face of the skull (fig. 4) we get an imperfect view of the parietals,
interparietals, squamosals, and tympanies (p., @.p., sq., @.ty.).

On the inside of the skull, with the septum (s.n., p.e.), perfect, and shown from its
left face, we get an instructive view of the investing elements of the skull. In front
we see the nasals (n.) above, and the palatine process of the premaxillary (p.pz.)
severed from its body below; and behind it, at the lower edge, the palatine plate of
the maxillary and palatine (p.me., pa.), and the free retral hook of the pterygoid
(pg.), growing from its ascending plate.

Above, the frontals (f.), at their edge, and in their orbital region, and the parietals
and interparietals (p., i.p.); the imbrication of the parietal over the frontal is very
great; that of the squamosal (sqg.) below, over the parietal, is very moderate ; over
this latter squamous suture the elegant furrow for the lateral sinus (s.c.) is well seen.

But the most remarkable of all the investing bones still remain to be described, and
are best seen in this view; these are the large vomers (Plate 33, fig. 5, v., ’., v”.). In
the earlier stage (Plate 32) I failed to find a distinct anterolateral vomer ; this bone
appears to be connate with the palatine process of the premaxillary, as in some other

MDCCCLXX XV. 2G

226 MR. W. K. PARKER ON THE STRUCTURE AND

kinds. It is represented here (Plate 33, fig. 5) by the rising on the upper edge of the
palatine process of the premaxillary (p.p.) close in front of the foremost vomer (v’.).

Here the posterolateral vomers that bind the hind part of the main vomer (v.) to
the lateral ethmoidal masses (Plate 33, figs. 5 and 8, v’.) are well developed but not
large.

The main vomer of the unripe embryo (Plate 32, fig. 6, v.) was shown to be
extremely large, thick, and spongy ; now (Plate 32, figs. 5, 8) it is in three pieces,
and these are not arranged on one plane, as in the Marsupials (which, as I shall show
in my next paper, have many separate vomers) but the large upper bone (v.) lies in
the trough of the two lower pieces. These occupy about the first and second third
of its length (see also fig. 8, showing the hind part of the second lower piece (v’.), and
the hind third of the main bone v.).

The subdivision of a primarily single centre is much more frequent in the higher
Vertebrata than I had imagined, a process curiously in contrast with that more
familiar phenomenon—ankylosis of primarily distinct bones. 2

This special peculiarity of the Tenrec, and of the Centetide, generally, as I shall
soon show, is, after all, merely a modification of the Marsupial type of structure, and
it is not the only instance in its skull of a new Insectivorous character formed by a
very gentle modification of an old Marsupial one.*

I have already referred to the only other splint-bone to be noticed, namely, the
annulus tympanicus (figs. 1, 8, 4, «.ty.); this, as seen from the inside, separated from
the skull (figs. 6 and 7, a.ty.), is an imperfect ring of bone, convex on its outer side,
ribbed at the edge and then scooped on the inner side; it is irregularly crenate on
its inner, growing edge; its elongated front limb binds strongly on the outer side of
the huge processus gracilis of the malleus (p.g7.).

Third Stage (continued).—On the endocranium of the Young Tenrec.

By a comparison of what is shown in the various figures just referred to we shall be
able to understand the structure of the inner skull; the younger stage (Plate 32) will
help us in the interpretation of its parts and regions.

The snout (fig. 3, ad.n.), as seen from the side, leans over at the fore end; the
nostril (e.7.) is large, oblique, and well surrounded by a valvular fold ; it is also made
more complex by an internarial lobe, above. The fenestra in the fore part of the
septum, seen in the last stage (Plate 32, fig. 6, s.n.), is now filled in with cartilage,

* The process itself, by which a thick spongy bone splits into concentric lamin, is quite like that
which is seen in the bark of the Plane tree (Platanus). Considered architecturally, in the building of
the skull, it is oddly unlike anything wrought by art or Man’s device; and as a mode of the imbrication
of bony scutes, everywhere, from the Ganoids to the highest Mammals, so familiar to us, this is
(apparently) unique. The greater part of the huge rounded septo-ethmoidal base, or intertrabecula,
lies over one large semitubular balk, which is, itself, sheathed by two similar but smaller semitubular

pieces.

iy
/

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 22

and the great partition is complete from front to back (Plate 33, fig. 5, a/.n., s.2., pe);
that tract, now partly bony (p.c.), is almost three-fourths the length of the whole
basicranial axis, for a time, in this young suckling. The huge rounded intertrabecular
base of the septum is, in the figure, largely hidden by the vomers, whose swelling
form, however, tell of the bulk of the mass of cartilage covered by them. The septum
nasi (s.n.) is low, and the perpendicular ethmoid (p.c.) rises to no great height
between the large cribriform plates (c7.p.). There is no cartilaginous crista calli;
from the free margin of the partition, a little forwards and then backwards, two-thirds
of the way to the presphenoid (p.s.), the perpendicular ethmoid is bony, already.
Bone is now seen in the base between the two orbitosphenoids; this is the pre-
sphenoidal region (p.s.), doubtfully or only partially independent as a bony centre.
The orbitosphenoids (0.s.), and alisphenoids («/.s.) are scarcely seen at all in this
internal sectional view, they lie down so low, infero-laterally. But their upper margin
is shown, and in the other lateral view (outside, fig. 3) their structure and relations
can be seen.

The optic nerve (fig. 3, II.) emerges above and inside the wide sphenoidal fissure
(V2); its passage through the middle of the proximal part of the orbitosphenoid
was shown in the last stage (Plate 32, fig. 5, 0.s., II). The orbitosphenoid is also
seen —-in the distance-—in the lower view (Plate 33, fig. 1, 0.8.) bound upon by the
orbital plate of the frontal (/).

The posterior sphenoid forms a very large part of the endocranium, and attains
here its fullest development as a special (Insectivorous) type. The overlapping of
the orbitosphenoid by the alisphenoid is seen well in the side view (fig. 3, 0.5. al.s.),
and in that aspect the foramen ovale (V*.) and the additional hole or hind opening of
the alisphenoidal canal (a/.s.c.) in front of it also ; the front overlapping lamina mounts
up, and is seen under the junction of the frontal parietal and squamosal ; the external
pterygoid process is aborted. Below (fig. 1), the posterior sphenoid is seen to extend
from the place where the maxillaries overlap the palatines in front, to the foramen
lacerum posterius (IX., X.), behind ; thus this great region ends, behind, opposite the
middle of the basioccipital (b.0.). This extreme front and hind extension is peculiar
to the typical Insectivora, and is due to the forward growth of the alisphenoid at a
good distance outside the orbitosphenoid, so making the sphenoidal fissure a side
passage to the skull; whilst, behind, the tympanic wings of the basisphenoid grow
beyond their root, and thus extend that bone, backwards.

There is still some cartilage at the mid-line in the fore part of the presphenoidal
region (fig. 5, p.s.), but where the two orbitosphenoids have met further back the
bony base is complete, and that tract has already coalesced with the fore part of the
independent basisphenoid (b.s.) (see also Plate 52, figs. 4, 9, p.s., b.s.), the basi-
sphenoidal region is full twice the extent of the presphenoidal. The remarkable
hollow under the fore part of the basisphenoid of the Hedgehog (Plates 17, 20, and 21)
is also seen here, and the pituitary floor (sella turcica) is perforated ; this hole,

Piel

228 MR. W. K. PARKER ON THE STRUCTURE AND

however, appears to be secondary and not primary as in the Hedgehog. I did not
see it in the embryo (Plate 82, figs. 4, 5, b.s.), so that this character is not primary,
as in the Hedgehog.

The tympanic wings (¢.b.s.) are more clearly marked off from the main basal bone
than in the Hedgehog, and thus a clue is got to their real nature; they are mere
periosteal outgrowths, and, had they arisen independently, their homology with the
“ossa bulle” of the Marsupial would have been seen at once; they are the
morphological equivalents of those bones. These tracts are roughly in the shape of
the shell of a bivalve Mollusk, but they grow inwards; in front, the right and left
processes meet. Behind this junction only a small triangular space of the basi-
sphenovidal bone is seen, it is somewhat apiculated ; at the middle, the synchondrosis
is still present. These shells (or wings) grow outwards and backwards some distance
beyond their root.

The alisphenoids are confluent with their common key-stone piece (al.s., b.s.), they
are very large, reaching from the fore-third of the tympanic wings (fig. 1) to the
bottom of the coronal suture (fig. 3). Thus they lie over the large tympanic cavity in
its front-third; they also, like their basal piece, have developed a large tympanic
wing (t.al.s.) in front of the tympanic cavity ; this wing has converted the hinder

gs. 4, 5; and Plate 33, figs. 1, 3) into a foramen—the

angular notch (Plate 32, fig

JSoramen ovale (V*.).

The hole through the alisphenoid, further forwards, is the hinder opening cf the
alisphenoidal canal («/.s.c.); the 2nd branch of the trigeminal escapes through the
sphenoidal fissure. The subdistinct tympanic alee of the basisphenoid, the very large
alisphenoids, and their tympanic wings, are all characters that are Marsupial, or
nearly so.

But the internal carotids do not enter the skull through the basisphenoid ; there is
no foramen rotundum; there is a hollow recess under the basisphenoid, and the
alisphenoids have broken away from the general skull wall, far outside the orbito-
sphenoids. In Marsupials, however, this does not take place, but the planes of these
alze are coincident, and the alisphenoid, as well as the orbitosphenoid, ossifies
upwards into the great supero-lateral band of cartilage.

All these things are intelligible; these low Eutheria are developing typical
characters, which are curiously mixed up with certain archaic characters inherited
from the forms on a lower level (Metatheria), from which these Insectivores once
sprung,

The auditory capsules are relatively less now than they were in the unripe embryo
(Plates 32, 33), only the supra-auditory crest—running into the supraoccipital, where
it is joined by the exoccipital—is still cartilaginous.

The cochlez (fig. 1, chl.) are well formed, and their position is almost transverse ;
the tegmen tympani is burrowed by the facial nerve (VII.), which emerges
behind and within the stunted epihyal (e.hy.); behind the stylomastoid foramen)

DEVELOPMENT OF THE SKULL IN THE MAMMALIA, 229

the opisthotic region grows into a distinct mastoid process. The fenestra ovalis (/80.)
is seen inside the canal for the facial nerve, and the large fenestra rotunda (/f.7.) is
reniform, being notched somewhat in front. A considerable tract of the bony capsule
is seen behind the squamosal (figs. 3, 4); the canals (c.s.c¢., h.s.c., p.s.c.) mark this
part, but the anterior canal is best seen on the inside (fig. 5), in front of the recess
for the “ flocculus (/l.7.).” Behind this moderate hollow the thickened bone contains
the common sinus of the anterior and posterior canals. The large meatus internus
(VIL, VIIL.) is oblique, going backwards and downwards ; the passage for the facial
nerve, in front, is well marked. The occipital arch has its elements still separated by
considerable tracts of cartilage; the basioccipital (b.0.) is a sinuous, transversely
polygonal plate, sharply notched in front, where the notochord ran, and having a
concave margin behind, at the foramen magnum. ‘The supraoccipital (s.0.) is a large
shield of bone, thickened and convex along its middle, and arching over the foramen
magnum by its lower edge. The exoccipitals (e.0.) form a very small paroccipital
ridge behind the mastoid process ; the foramen condyloideum (XII.), close behind and
within the posterior lacerated foramen (IX., X.), is large. The whole arch is sinall
relatively to the rest of the skull, and this is Eutherian in this respect.

MECKEL’s cartilage (figs. 3, 6, mk.) is being lost in the mandible in front ; where it
has become free behind, tracing it backwards and upwards, it is still quite thick and
is endosteally ossified, continuously with its proximal part, the malleus (m/.). The
primary ossification (Plate 32, fig. 7, ml.) is ectosteal, and now, on the inside, this is
roughly and imperfectly subdivided into three bony laths, binding the front of the
head of the malleus, which is now well ossified throughout, the endosteal tract seen
in the early state (Plate 32, fig. 7, m/.) having used up all the cartilage except the
selliform condyle.

Here we have the counterpart, first, of the endosteal or inner articulare of the
Sauropsida ; and then the outer articulare, the supra-angulare, and the angulare of
the endocranial mandible, in a state of imperfect differentiation.

Below the condyle the malleus projects towards the incus (7.), the head is then bent
on itself, growing obliquely forwards ; it gives off two processes, manifestly equal to
the internal and posterior angular processes of the Bird; the latter is represented
here by a rounded knob (ay.p.), and the former by the long straight, slender
manubrium (mb.). On the outside the malleus is strongly tied by the anterior crus
of the annulus (figs. 7 and 8, a.ty.); behind that bar the malleus grows into a crescentic
foliaceous plate and is concentrically grooved to a less degree in front of the condyle,
and much more in front of the foliaceous outgrowth. All these things admit of no
Teleological interpretation, but show that the hinder third of the Sauropsidan type of
mandible is here aborting itself, so to speak, into an Eutherian malleus.

The incus (fig. 6, 7.) is well formed ; the short crus (s.c.7.) straight and conical, and
the long crus (/.c.7.) is short, capped with an orbicular facet where it turns inwards
to articulate with the stapes.

230 MR. W. K. PARKER ON THE STRUCTURE AND

The stapes (st.) is thoroughly typical, having an unusually large foot-hole. I see
no interhyal in the hinder of the stapedius muscle (st. m., see also Plate 32, fig. 7).

The very Marsupial os hyoides (fig. 9) has small, unossified hypohyals (h.hy.) on a
transverse basihyal (b.h.br.); this is ossified now, and so are the thyrohyals (t.hy.)
which are now segmented from it; they were not in the last stage (Plate 32, fig. 8).

Going back again to the olfactory region, we find that the nasal, inferior, upper,
and middle turbinals (fig. 10, 2.tb., 7.tb., w.tb., m.tb.) are large and well developed, but
at present they are cartilaginous.

For a description and figures of the adult skull the reader is referred to Dr. Dopson’s
invaluable work (Part I., p. 72; and Part IL., plate 8). The whole structure is as much
modified from what I have shown in the young (Third Stage) as that is from the skull
of the unripe embryo (Second Stage). Its great length, and the large size of its
transverse and longitudinal crests, make it one of the most remarkable skulls in the
whole Order.

On the skull of Hemicentes (sub-adult).

For figures and a description of the adult skull of this type the reader is referred to
Prof. Mtvart’s Paper (Proc. Zool. Soc., Jan. 17, 1871, p. 58), and for a further
account of this type to Dr. Dopson’s Monograph (Part L, p. 69).

Fortunately, my specimens—one of H. madagascariensis (Plate 34, figs. 1-5), and
another of H. nigrescens (Plate 34, figs. 6-9)—were not quite full-grown, and therefore
yielded me better results for my special work than older skulls would have done.

On the investing bones of the skull of Hemicentetes.

This extremely elongated skull gains its great length, as in most other Mammals
with a long head, not by elongation of the premaxillaries, as in longirostral Birds, but
by the great length of the maxillaries and nasals.

The upper view (Plate 34, fig. 2) shows that the nasals (”.) are more than half the
length of the bony skull; they are much separated in front, and their suture only
reaches to the middle; in their hinder half they are completely anchylosed. The
fore part of each is a mere style of bone ; the united hind part is a convex lanceolate
tract, overlapped at its edges by the thin internal edge of the divaricated frontals (/.).
The facial plate of the premaxillaries (pz.) is about a fifth of that of the maxillaries
(mx.), but the upper margin is extended backwards between each nasal and maxillary,
so as to keep those bones apart for the front half of their related edges. Each
maxillary shows two regions laterally, the lower or alveolar is seen in the distance in
this view, but the upper is in full view, it runs well up to the badly defined orbit ; the
whole of this upper facial tract is a long, gently convex lath of thin, but strong, bone ;
it reaches a little further backwards than the nasals, and, below and behind, shows
between itself and the alveolar part, the infraorbital opening (V*.).

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 231

The frontals and parietals (/:, p.) have a nearly equal waval length, but the former
are far inferior to the parietals in width.

The frontal and coronal sutures are perfect, at present, and are semi-squaimous ; the
two frontals mutually overlapping each other, in this place and that, and the parietals
overlapping the frontals laterally.

here the frontals are wedged in between the nasals and maxillaries there they are
very thin, sharply angular in form, and splintered at their edges.

Behind, they run in between the parietals, with strong dentations ; their orbital edge
is rounded and smooth, and has a gently arcuate outline. The parietals (p.) run
as far forwards, below, as they retreat, above; inside the gently concave temporal
fossee, they swell together, into a dome-like structure, which is divided by the sagittal
suture. This is larger than the general convexity of the frontals ; but it is enlarged
still more by the subconcave part which extends into the temporal fossa. The
squamous suture with the squamosal (sq.) is not well seen from above; the wedge-
like fore part of the interparietal (7.p.) is more clearly defined than its narrow,
extended outer wings ; it is rather a large bone, and is convex above, where it fits to
the fore margin of the supraoccipital (s.o.). It there forms the lambdoidal crest ; but
the sagittal crest has not any existence, at present, and there is a shallow concavity
running across the skull where the parietals and interparietals meet, which connects
together the two temporal fossze.

The side view (Plate 34, fig. 3) brings out things that are not well seen from above ;
it shows a dorsal line gently sinuous, with even fewer interruptions than the lateral
outline which is broken by the hind part of the maxillaries ; compared with normal
skulls it looks as though it had been artificially elongated whilst in a plastic state ;
the great distance of the teeth from each other increases this appearance. The
dentary edge of the premaxillary ( pz.) is only one-tifth the extent of that of the
maxillary (m.); the whole line is gently sinuous, convex in front and behind,
and concave in the middle. The nasals (n.) are scarcely seen from this aspect, but
the maxillary is well displayed, with its upper facial plate, its infraorbital hollow
passage and narrow bridge (V*.), and the hills and hollows caused by the series of
teeth. The maxillary ends, behind, in thin lobes, the upper of these is broad, and
overlaps the small angular lachrymal (/.) with its canal (/.c.) in front, in the notch
between the upper and lower outer lobes; the lower lobe is sharp and upturned, it is
the end of the alveolar region. The third lobe is a flattish tridentate tract, further
inwards, and binds upon the palatine (pa.). The orbital plate of the frontal (/-) runs
down to the middle tooth of this inner lobe of the maxillary ; its hollowest space is
the shortish tract between the lachrymal and the overlapping parietal. ‘The hmder and
most convex part of the frontal where it passes under the parietal is not marked by
any lines or grooves, but in front of that tract it is sinuous, rising and falling over the
turbinal coils within, which shine through it, as through a thin plate of horn. The
hinder margin of the orbital plate is notched, deeply, by the outstanding alisphenoid

232 MR. W. K. PARKER ON THE STRUCTURE AND

(a1 s.), and behind this part the narrow fore corner of the parietal lies over it. The
parietal, in this aspect, is seen as a fine shell of bone, with its hinder three-fourths
overlapped by the squamosal. That scale is perforated at its hinder part, near the
almost straight squamous suture.

The squamosal (sq.) is ribbed (or limbate), outside, the fore part of the thick edge
being the rudiment of the jugal process, which however scarcely projects beyond the
glenoid cavity (g/.c.). The thick, ribbed edge dips and forms the post-glenoid tract
behind its middle; it then rises, and runs into the low lambdoidal crest, which is
formed above by the interparietal (7.p.). The palatine (pa.) is hidden by the maxillary
in this aspect, but the pterygoid (pg.) is seen with its short, blunt hook ; the tympanic
(a.ty.) also just comes into view.

The dentary region of the lower jaw (d.) is not much more than half the length of
the ramus ; it is as remarkable for its slenderness, as the hinder, shorter part is for its
breadth. The coronoid process (c.p.) is small, and uncimate ; it is separated from the
large, well-formed condyloid process (cd.p.) by a round notch. The angular process
(ag.p.) is separated from the condyloid by a round notch twice as large as the upper :
it is twice as large as the coronoid, and also uncinate ; hooking towards the coronoid
hook. Below, the angular process is notched and another third sharp hook is seen ;
there (see also fig. 5) the bone is very thick, and both the thickening and the hook
are curved inwards, as in Marsupials. The outer face of the broad divided part of the
ramus is made concave by the outward leaning of the coronoid process (fig. 5).

The /ower view (fig. 1) shows the peculiar lathiness of the palatal region, the bones
having much the character of those investing the face of the embryo of a longirostral
Bird.

The premaxillaries (pa.) show four parallel tracts; the two outer are the alveolar,
and the two inner are the palatine regions, and these are separated by a deep cleft,
ending in a round notch in front, where JAcoBson’s organs (j.0.) open in the anterior
palatine foramina. Right and left of the median suture each maxillary palatine plate
is sphit half-way backwards to the palatine bone (pa.); the inner spikes bind on the
inner spikes of the premaxillaries, and the outer splintery, interalveolar tracts bind
against the alveolar tracts of the premaxillaries. Then each palatine plate of the
maxillary is hollow at the mid-line, and against the alveoli, and convex along its
middle, up to the palatine bone, which impinges upon the hinder third of the
maxillary. This latter bone then divides into a short jugal and a long inner process.
The hollow behind the last tooth is the infraorbital canal (V*.), and the small, bony
bridge over it is seen in the distance. The palatines (pa.) are very long, nearly as
long as the submesial part of the maxillary palatine plate; they run in under those
tracts, first with an inner, and then with an outer spike ; only their front two-fifths is
complete up to the mid-line, for they soon form a thick short process, which meets its
fellow at an obtuse angle over the open nasopalatine passage, Each palatine is there
convex, and a little broader than the open space in the middle ; the bone widens to

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 233

bend on the end of the maxillary, and is then cut away, so to speak, to receive the fore
part of the ascending plate of the pterygoid (pg.). The latter spreads out under the
basisphenoid (b.s.), and is ankylosed with it, some distance behind and above the
hamular process or hook. In this view the orbital region of the frontal (/)) is seen in
the distance, a large space existing between it and the bulging alisphenoid. On the
right side of the figure the annulus (a.ty.) is shown; it is well formed, convex
outside, has a retreating, broad, notched, anterior crus, and a strong, crescentic hinder
crus; both these crura are strapped on to a strong ridge of the squamosal, inside and
behind the oval glenoid cartilage (gi.c.). Round that facet the latter bone is thickened
everywhere, though the inner and front part of that thickening is the stunted jugal
process. The post-glenoid tract bends back against the bony auditory capsule and the
inner edge is excavated, and united by a serrated suture with the tympanic wing of
the alisphenoid (a/.s.), thus helping to form the tympanic cavity, as well as to enlarge
the tegmen tympani.

In the end view (fig. 5) the investing bones (7.p., p., sq.) are but little seen; a side
view of the septum of the olfactory organs (fig. 8) shows the large and remarkable
vomerine series of bones. These are quite similar to those of Centetes (Plate 33) ;
there is a large upper semitubular vomer, proper (v.), and two lesser semitubular
bones sheathing it (v’.). Behind, the main bone has attached to it a pair of postero-
lateral centres (v”.); the antero-lateral vomers are not distinct from the palatine
processes of the premaxillaries (p..).

The endocranium of Hemicentetes.

The snout (al.n., e.n.) is straight and bulges at the end and below; the nostrils are
surrounded, except below, by a valvular fold of cartilage, they look downwards and
forwards, and the antero-inferior face of the snout is oblique. The fore part of the
septum nasi (fig. 7, s.z.) is obliquely oval, answering to the form and direction of the
snout ; the rest is a very low crest to a very solid and well-marked intertrabecula
(.tr.). Where the septum becomes ethimoidal there it rises into a low triangle, and is
ossified as the perpendicular ethmoid (p.e.) ; it has a kidney-shaped swelling with the
“hilus” looking forward, just in front of its free inter-olfactory crest. The whole septum
is rather saddle-backed ; it has a considerable cartilaginous tract behind, between the
large bony plate and the presphenoid (p.s.). The latter tract is hidden from view in
the lower aspect (fig. 1) by the main vomer (v.); the orbitosphenoids (o.s.) can be seen
in the side view (fig. 3), they are perforated by the optic nerve (II.) as can be seen by
looking forwards through the foramen magnum. In that figure the alisphenoids (a/.s.)
can be seen both above, where they form the curious thin dentate outer wall to the
intersphenoidal passage, and also below, where the hinder openings of the alisphe-
noidal canal (al.s c.) is seen a little in front of the foramen ovale (V.). That canal
opens in front into the general cavity of the wide “sphenoidal fissure” (or passage).

MDCCCLXXXV. 2H

psy MR. W. K. PARKER ON THE STRUCTURE AND

In the lower view (fig. 1), the foramen ovale (V*.) is seen just inside the stunted
jugal process of the squamosal and the glenoid facet (g/.c.), but the canal (a/.s.c.) is
hidden by a lamina of bone, and the extremely outward position of the thin shell-like
alisphenoidal wall is seen, and the crescentic notch that emarginates its oblique front
edge. The huge alisphenoid—nearly as large as in a Marsupial—forms, behind the
foramen ovale (V*.), an oblique strongly dentated suture with the inner edge of the
squamosal, and then becomes hollow over the tympanic cavity, outside the tympanic
wing of the basisphenoid. The hinder edge of that supratympanic lamina is deeply
notched, and terminates close in front of the cochlea (ch/.).

The shell-like tympanic wings of the basisphenoid (¢.b.s.) reach as far forward as the
foramen ovale (V®.) in front, and nearly to the fenestra rotunda (f.r.) behind ; they are
manifestly “ bulle ” that have lost their distinctness from the basisphenoid, whilst the
hollow cavity of the greatly extended alisphenoid is, as surely, the counterpart of the
tympanic wing of that bone seen in Marsupials. The hollow, in front, under the
basisphenoid, is present, but it is not so much marked as in Centetes ; the rest of the
basisphenoid is of an hour-glass shape and is somewhat carinate; its hind edge is
bracket-shaped and is separated from the basioccipital (b.0.) by a clear synchondrosis.

The auditory capsules are ossified ; there is, however, some cartilage near the
horizontal canal (fig. 1, h.s.c.); this is the small epihyal (e/y.) in front of the
foramen stylo-mastoideum (VIL). The cochlea (fig. 1, cl.) is well formed, and the
fenestree (/s.0., fr.) are seen outside and behind it, also the chink and channel for the
facial nerve (VII.) emerging from the cranial cavity. The horizontal and posterior
canals (h.s.c., p.s.c.) are seen on the outside, showing through their thin bony walls.
Behind the posterior canal there is a bony ridge, and then a suture between that ridge
and the short paroccipital process (p.oc.). The basi- and exoccipitals (fig. 1, b.0., 8.0.)
are confluent ; the supraoccipital (figs. 1, 4, s.0.) is a very large distinct shield of bone,
cut away in a semicircle, over the huge foramen magnum ; the condyles (0c.c.) are
large, pyriform, and wide apart.

The “ossicula,” separately figured on a large scale and seen from within (fig. 9),
attached to the thick-rimmed middle-sized aunulus (a.ty.), are worthy of note.

The cartilage is gone in front and has left a large tongue-shaped processus gracilis
(p.gr.), twice as large as the manubrium (7.), and parallel with it. The body of the
malleus is at a right angle with these handles, and is of great extent. Over and in
front of its condyloid facet there is a large solid helmet of bone ; behind that facet the
hind margin projects backwards as a rounded elbow; and below the root of the
manubrium there is a subglobular “ posterior angular process” (ag.p.)—a familiar
Sauropsidian remnant.

The incus (7.) and the stapes (st.) are large, well-formed, and quite typical.

A small hypohyal (fig. 6, h.hy.), equal to the epihyal (fig. 1, ey.) above, is attached
to a transverse basal bar (b.h.br.), and from this proceed the two short diverging thyro-

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 235

hyals (t.hy., cornua majora—I1st hypobranchials), separated from the base by cartilage,
but not segmented off.

Skull of adult Ericulus nigrescens. (Male.)

The hinder half of the palutal view of the skull of this type has been figured
(Plate 35, fig. 11); this is a very instructive skull, and typical of the Mascarene
modification of the Insectivorous type ; nearly typical, as respects the Order itself, in
its modern development.*

The palatines (fig. 11, pa.) end in a straight line at the end of the hard palate ;
they are behind the maxillaries, and have the well-formed pterygoids ( pg.) attached,
subvertically, to them.

In the roof, the vomer (v.) is seen sheathing the perpendicular ethmoid, and the
forepart of the presphenoid (p.s.); the orbitosphenoids (v.s.) are not seen in this
view, except a little in front of the great fissure (V!*.). Like the presphenoid, the
forepart of the huge basisphenoid (b.s.) is of moderate width, and flat; it is rendered
somewhat concave by its union with the pterygoids.

The sub-pituitary hollow is perforated, above, as in Centetes; behind it the basi-
sphenoid broadens out, and behind, both it and the basioccipital (b.0.) for some
distance are subcarinate ; this ridge is due to the bulging of the earliest bone deposited
round the notochord. The tympanic wings (¢.b.s.) are not symmetrical, that on the
left side being much the larger of the two; a notch separates these shells in front,
from the equal and well-developed tympanic wings of the alisphenoid (f.a/.s.). These,
with a similar process of the squamosals (sq.), form the antero-external outline of the
obliquely oval tympanic spaces. These spaces are roofed, in front, by the same bones,
and, behind, by the oblique, well-formed cochlez (ch/.). From those helices, to the fore
edge of the great sphenoidal side gallery, out of which the Ist and 2nd branches of the
half the cranial floor; it is an

trigeminal nerve (V!*.) emerge, is a large space
unmistakable Marsupial character. But the foramina are typical for an Insectivore ;
this foramen ovale (V°.) is finished behind by the tympanic shell of the alisphenoid,
and for a distance, in front, equal to its own width. Another oval hole of the same size
is seen, but it has not its long axis outwards and backwards as in the foramen ovale,
but inwards and backwards; this is the hinder opening of the alisphenoidal canal
(al.s.c.) ; the anterior opening being made into the common sphenoidal fissure or side
passage. The squamosal (sg.) has a stunted zygomatic or jugal process, and a large
oblique saddle-shaped glenoidal facet (gl.c.). Where the bone widens towards the
tegmen tympani (f.ty.), and bounds the tympanic cavity, there is a short postglenoid
tract and a small post-glenoid foramen.

The external part of the ossified auditory capsule outside the tegmen has grown
beyond its contamed horizontal canal (compare with Microgale, figs. 1, 3, h.s.c.) into an

* The original skull from which this figure was made is in the Biological Laboratory, South
Kensington Museuin,

2H 2

256 MR. W. K. PARKER ON THE STRUCTURE AND

ear-shaped mastoid process, not unlike, in size and form, the gienoid region of the
squamosal close in front of it. The openings here are numerous; inside the post-
glenoid foramen and outer tympanic wall the canal for the facial nerve (VIT.) is seen,
and further backwards and outwards, behind a stunted and ossified (epihyal) (e.hy.),
the same nerve ( VII.) escapes through the large stylomastoid foramen. Nearly oppo-
fenestra ovalis and fenestra rotunda

site, but much further inwards the two fenestrze
(/s.0., f) are seen, and the large foramen lacerum posterius, or the common chink
for the exit of the 9th and 10th nerves (IX.. X.) in front of, and further out than the
foramen condyloideum for the 12th nerve (XII.) in the exoccipital (c.0.).

The supraoceipital (s.o.) can be just seen behind the foramen magnum (fm.); the
lateral and basal tracts (e.0., b.o.) are ankylosed. The condyles (0c.c.) are roughly
pyriform, with the narrow part in front ; each exoccipital grows out into a large, thick,
down-turned paroccipital process (p.oc.). This is unusually large and well developed
for one of the Jower Eutheria. The whole occipital arch is distinct from the auditory

capsules in front of it.

The skull of the adult Microgale longicaudata.

The skull, and indeed the whole skeleton of this small, very long-tailed Tenrec,
resembles, very closely, that of the Common Shrew (Sorex vulgaris, see Plate 31) *
both in size and form, But there are very important differences between the two, and
on the whole this dwarf kind is but little altered, except in form, from the Cen-
tetidee of a more normal size. The snout (al,n.) is somewhat shorter than in the

Shrew ; it is similarly deflected.
Investing bones of the skull of Microgale longicaudata.

In the upper view (Plate 35, fig. 2) the sutures are largely filled up, yet their place
is seen in various markings. There is, however, one long, almost perfect, median suture
from the snout to the lambdoidal suture, and the coronal is only filled in below.
The premaxillaries (pw.) are of considerable length, and are well wedged in between
the nasals (n.) and maxillaries (mx.) above. The upper tract of the maxillaries is
about equal to the nasal with which it is fused; they project over the lachrymal
(fig. 3,1.) ; the alveolar part of the maxillary is seen in the distance. The boundaries of
the frontals (f) can be seen above, wedging in between the nasals and maxillaries in
front, and between the two parietals behind; through their thin walls the ethmoid
and its turbinal folds can be seen in the front half; the hinder half, apiculate before
and behind, is smooth and gently convex. Swelling to a width one third greater than
that of the frontals, the parietals (p.) nearly hide the lateral parts (sq., ep.). Each
forms its own round convexity (see also fig. 5, p.), the sagittal suture lying in a
furrow. The bracket-shaped lambdoidal sutural line has a remarkable setting of

* See also Dopsoy, op. cit., Part ii., Plate 8, figs. 3-3f.

oni ai

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 237

bones in a half-ring; these are undoubtedly the progeny ef two primary interparietal
scales that united at the middle and then broke up again in fresh places. There are
three main pieces, subcrescentic in form; the convexity of the middle piece being in
front, and of the other two behind ; these are embedded along this wavy line of suture,
besides several small pieces, like the fragments of the larger tracts. This curious breccia
is very instructive; the median piece is the proper interparietal (7.p.), and the main
lateral pieces (s.t.) are the counterparts of the familiar supernumerary temporal bones,
or “‘supratemporals” of the Lacertilia. Bones so situated and so related are common
enough in the Ganoid Fishes, and in those Teleosteans (Siluroids) that come nearest
to them in their cranial scutes.

The side view of this skull is curiously minetic of that of the Shrew (Plate 31), but
the teeth are sharply diagnostic. Almost everything is revealed through the thin horn-
like bony walls in this most exquisite little skull; the roots of the sharp teeth show
through the outer alveolar wall; there is no special jugal process beyond the last of
the series. The maxillary overlaps the frontal above, and then has a round notch
in which the lachrymal and its canal (/., /.c.) can be seen, although this fine film of
bone has lost its sutural enclosures. Then there is a sharp spur, under and inside
which the bone is hollowed out, and becomes a canal for some distance, opening in
front on a very large infraorbital foramen (V*.). Above the sloping postero-superior
edge of the maxillary, which is parallel with that of the ethmoidal region, a large
tract of the badly-defined orbit, half its upper, and most of its lower inner face, is
marked by the rich turbinal folds—middle and upper—of the lateral ethmoids. In
the middle of their hinder boundary, sloping downwards and backwards, there is a
large vascular foramen ; and the curled lower edge of the orbital plate of the frontal
is notched in the middle, below and in front of the larger notch, for the ophthalmic
nerve (V!.). Here, at the postero-interior part of the open orbit, a lobular tract is seen,
at the bottom of which the orbitosphenoid, pierced by the optic nerve (o.s., II.), can
be seen imperfectly,

Behind that oblique bony edge, which runs backwards and downwards, and is formed
by the frontal, in front, the parietal above, and the squamosal behind, the lateral sinus
(s.c.), throws its exquisite arch, clearly shining through the diaphanous walls of the
parietal in its temporal region. Half-way between the end of the arch and the supra-
temporal bone there is a rough vascular foramen, close to the ragged hind edge of the
parietal.

The squamosal (sq.) is about equal to that of the Shrew, but its temporal squama is
higher, and is lobulate ; it is confluent with the parietal in front.

The thick outer edge forks in front; and in the fork the glenoid facet (y/.e.) les ;
the upper fork does not grow forwards as a definite zygomatic process.

The ribbed outer edge then goes backwards and a little upwards, and then spreads
into an oblique four-sided enlargement, before it ends, as a sharp spike below the

238 MR. W. K. PARKER ON THE STRUCTURE AND

hinder crus of the sinus canal (s.c.); the rest of the squamosal will be seen from below
(fig. 1).

Here there is a real additional temporal scale-bone, or supratemporal (s.t.), but in
those other dwarfed types—the Mole and the Shrew—the apparent second temporal
bone was shown to be only a peculiar rambling of the prootic bone into the pterotic
region—a part, in fact, of the chondrocranium, ossified by a periotic bony centre.

Here, the likeness of this, the smallest of the Tenrecs to the dwarfed Shrew, is
seen to be largely superficial ; they are very wide apart, zoologically.*

The slender hamular process of the pterygoid ( pg.) can be seen passing backwards
from the thick palatine wall, and the annulus (a.ty.) also comes imperfectly into view
in this aspect. The mandible (d.) is long, gently arched downwards, sinuous above,
through the swelling caused by the teeth roots, and gently convex below. The
coronoid process (¢ p.) is a blunt, high triangle; the condyloid (cd.p.) is neat and
rounded ; the angular process (figs. 3, 4, ag.p.) is slender (almost Soricine) and
somewhat incurved, below.

The lower view (Plate 35, fig. 1) shows a well-formed hard palate; the maxillary
(mx.) fits by a sharply-pointed end against the premaxillary (pz.), and the palatines
against the maxillaries by a transverse, deeply toothed suture, in front of which each
maxillary has a small fenestra. In front of that suture there are two, and behind it
one, strong subtransverse ridge. The maxillaries bind against the open part of the
palatines by a vertical plate, and the latter, after forming a strongly ribbed end to the
hard palate, finish as a thick spongy wall to the nasopalatine passage; this is enlarged
behind, as it narrows m, by the pterygoids with their delicate hooks; all the parts, here,
are ankylosed together, so that the upper flange of the pterygoids is not distinguish-
able from the sphenoid bones, or the palatines from the pterygoids. The hinder part
of the main (upper) vomer (v.) is seen in the roof of the nasopalatine passage; the
other vomers could not be exposed either in this skull or that of Eiculus (fig. 11)
without injury to the preparation. I take it for granted that in these parts these
two kinds agree with Centetes and Hemicentetes. The squamosal (sq.), like the
alisphenoid (a/.s.), is dominated by the middle part of the organ of hearing. The
outer part of the roof of the drum-cavity is formed by a shell-like ingrowth of the
squamosal, behind and within the reniform glenoid facet (gl.c.).

The annulus (figs. 1 and 7, a.ty.) is strong, and well made for so small a beast, and
has a considerable external convexity. Its rim is well-finished, its anterior crus binds
upon and holds the processus gracilis (p.gi.), and its posterior crus is thickened where
it is tied to the posterior angular process (ay.p.) of the transformed articulare.

>

The end view gives the relations of the parietal to the interparietal and super-

* There is no Soricine type as large as the Great Tenree (Centetes ecandatus), with which that large
Insectivore might be compared; but the largest that can be found must be worked out, and the two
compared together, if we would know how much in our little Shrew, and in this litle Microgale, is due

to their dwarfing.

—

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 239

temporals (p., 7.p., s.t.), but it scarcely shows the squamosal (sq.) ; the form of the skull
thus seen is reniform, with the hilus below, and is gently convex, with many
sinuosities.

Endocranium of Microgale longicaudata.

I have no inner views of this skull, but through the huge foramen magnum
(fig. 5, fim.) the large eribriform plate is seen to have two deep antero-superior
recesses ; and the orbitosphenoids to be pierced by the optic nerves in the middle of
their basal regions ; the shallow sella turcica, and the deep recessus flocculi, in the
auditory capsule, can also be seen thus, without injury to the prepared skull.

At this point and that the endocranium can be seen from without (Plate 35,
figs. 1-5). The nonsegmented deflected snout, with its sublateral nostrils (a/.n., e.n.),
is exposed ; but the form of the true olfactory region can be traced and seen through
the semitransparent frontals. The orbitosphenoid (figs. 1, 3, 0.s.) is seen but little in
any of these figures ; the optic nerve (fig. 3, I1.) is shown as emerging in front of the
great sphenoidal side-passaye, out of which escape the 3rd and 4th, the Ist and 2nd
branches of the 5th, and the 6th, nerves. The alisphenoidal canal (a/.s.c.) is short and
its anterior opening, although less perfect than in the Dog, is plainly shown by a
deep notch in the front of the alisphenoidal wall (a/.s.); the foramen ovale (V*.) is
well seen both in figs. 1 and 3, laterally ; the suture between the alisphenoid and
squamosal above (fig. 3, a/.s., sq.) is indistinct. In the basal view (fig. 1) the whole
posterior sphenoid is displayed, a structure equally elegant and instructive. The sub-
pituitary hollow is obsolete, the basisphenoid running backwards as a rounded balk
from the presphenoidal, up to the basioccipital, region (fig. 1, p.s., b.s., b.0.).

Behind, in the latter region, the exposed part of the bone is a mere chink, owing to
the proximity of the tympanic wings of the basisphenoid, which almost touch, back to
back, like the aliseptal cartilages of the nasal labyrinth. These shell-like periosteal
outgrowths (exogenous ‘ossa bulla”) are broad, notched, and out-turned in front ;
behind, they are pointed, and the last third of the strong aponeurosis is not ossified ;
so that these wings (or shells) do not finish the floor of the large tympanic cavity, but
a large membranous space is left, bounded by the annulus in front, the bony ala inside
the occipital arch, behind, and the mastoid process (op.) externally. On the other
side, where the annulus has been removed, and the cochlea (ch/.) exposed, the imper-
fection of the bony floor of the skull is seen. In front of the large auditory region
the skull has a very fenestrate appearance, the two openings of the alisphenoidal
canal (a/.s.c.) and the large foramen ovale (V*.) cause this. The alisphenoids do not
end after letting out the 8rd branch of the trigeminal nerve ; a thick bar of bone runs
across behind the foramen ovale, this is continuous, now, with the basisphenoid within,
and supplemented, externally, by a similar wing or bar of the squamosal (sq.). This
bony boundary of the drum-cavity is continued backwards by the outer (tegminal) edge
of the squamosal, so as to form, roughly, a quadrant, which ends close in front of the

240 MR. W. K. PARKER ON THE STRUTCURE AND

stylo-mastoid foramen (VIT.). That tegminal edge of the squamosal runs inwards as
a vaulted roof to the cavum tympani, nearly half-way across. Inside, the cochlea fills
up the space behind, but, in front, the retral growth of the alisphenoid (q/.s.) fills in
three-fifths of the remaining space and sends backwards a spur to the cochlea, which
divides the rest into a large outer, and a small inner, fenestra, covered only by the
dura mater. This structure is Soricine, but it is also Marsupial; it is much more
Marsupial in character than that which is seen in the Shrew.

The suture between the squamosal and alisphenoid is nearly lost, but the former
sends downwards a thin lamina of bone which shows where they have joined ; close
inside the glenoid cartilage the squamosal is bent inwards, and appears as a convexity
in the fore part of the tegmen. The (Marsupial) alisphenoidal wing (a/.s.) is extremely
thin, and coils over backwards as a sharp selvedge. The basisphenoidal wings (¢.b.s.)
are much deeper and more hollow than they appear at first sight, in the basal view
(fig. 1).

Behind (fig. 1), the relatively spacious tympanie chamber is partly closed in, and
filled up, by the remarkable auditory capsule, which is thoroughly ossified, and retains
its distinctness all round its border ; it is, however, not so loosely set in the skull as
in the native Shrew, or as in our native Bat (Pipistrelle).

The tilting of the auditory capsules is shown in the side view (fig. 3), and the
horizontal and posterior canals (h.8.c., p.s.c.), are seen in that and also in the posterior
view (fig. 5), and in the lower view (fig. 1). There is no prootic wall-plate in front
of the smoothly convex part, through the walls of which these canals are seen.

The facial nerve (VII.) is seen emerging close behind a small, separate epihyal bone
(e.hy.); inside these parts the fenestrze of the capsule lie out of sight. Inside and in
front of the posterior canal, and of that part of the labyrinth into which it opens,
there is a convex oval enlargement of the postero-inferior face of the cochlea (chi.),
hiding its fenestra, which opens in front of, and above, the oval swelling, and exter-
nally forms the front margin of the foramen lacerum posterius ([X., X.). The basal
and lateral upper elements of the occipital arch (b.0., e.0.) are fused together; the basi-
occipital is short axially, and the lateral parts each form a small paroccipital process
( p.oc.) close outside the large pyriform condyles (0c.c.). The supraoccipital (s.0.) 1s a
large shield of bone, well in the back of the skull, and not lying over, as a hind
teymen, as in the Mole and Shrew. It is quite distinct from the auditory capsules,
and is fused with the lateral elements of the arch (e.0.); lying over a very large
foramen magnum, round, but with a recess in front, it is a relatively great shield of
bone, with a large circular convexity in the middle, separated by two oblique fossve
from a subcrescentic convexity, right and left.

The supratemporal pieces (s.f.) impinge upon the bone over each fossa; it arches
very accurately over each auditory capsule above and outside, where it has ankylosed
with the exoccipitals (e.0.). The whole of the upper margin of the supraoccipital is

DEVELOPMENT OF THE SKULL IN THE MAMMALIA, 241

somewhat everted (fig. 2); the exoccipitals are pierced by the hypoglossal nerve
(fig. 1, XII.) ; as usual, these foramina are very wide apart.

The ossicula auditis,—hyoid arch, and meatus-cartilage of Microgale longicaudata.

The malleus (fig. 7, ml.) is remarkable in this, and in other small Insectivora; here
the transverse extension of its main part is carried to the extreme, and here also the
posterior angular process (ag.p.) is wrought into a very ornamental form, like a carved
fruit-ornament ; it is, as it were, suspended from the part which gives off the strong
manubriam (mb.). The processes gracilis (p.gr.) is about equal to the manubrium ;
they are very far apart, and diverge, evidently; each is a twisted and thick-edged
blade of bone, the back of which is in the inner side. The head is less definitely
hooded than in the larger Centetidee, but the large posterior margin is more elbowed ;
the condyloid face is deep and oblique, but not large. The incus and stapes (figs. 8, 9,
z., st.) are quite typical, relatively large, and very elegant in form; the short crus of
tbe incus (s.c.7.) is larger than in the Shrew; the stapes, most neatly finished, shows
no interhyal on its neck.

The hyoid arch has a separate epihyal above (figs. 1, 3, e.y.), and has also an upper
and lower ceratohyal (fig. 6, c.hy., c.hy’.), the former is attached by ligament to the
epihyal, above. The short hypohyals (h.hy.) are articulated to a process of the basal
bar (b.h. br.), whose thyrohyals (¢.hy.) are not distinct, but short, and diverge greatly.

Thus this small kind approaches our native Insectivora in the structure of its hyoid
arch, which is much more perfect than in the kinds just described.

When the meatus externus is dissected, and the lining cartilage opened out (fig. 10),
it is seen that there are three imperfect annuli, separated by deep notches, inside the
continuous concha, the proximal edge of which has also two round notches.

The skull of the embryo of Rhynchocyon cernei; 4 inches long from snout
to root of tail.

This is the largest of the Elephant Shrews of the African mainland, and is from the
eastern part, near Zanzibar.

The Macroscelidee, of which this is an outlying member and the largest of the
family, are extremely unlike the insular forms from Madagascar, just described ; this
particular kind is the more interesting as being a native of that part of the African
continent which lies nearest to that large and most remarkable island, which is not
African. The Macroscelide, however, have a wide African distribution, contimental
and insular, and this large kind—Phynchocyon—is somewhat aberrant.

So much does this type differ from the forms already described, namely, our native
types and these from Madagascar, and also from those yet to be noticed, that, con-
sidered from the standpoint of their cranial morphology, I am surprised at the colloca-

MDCCCLXXXV. 21

242 MR. W. K. PARKER ON THE STRUCTURE AND

tion of such diverse forms into a single Order of the Eutheria. But in this, as in many
other types of Vertebrata, the highly compound cranial region retains a large number
of archaic characters that are suppressed or lost in the body, and especially in the soft
organs.”

The investing bones of the skull of the embryo of Rhynchocyon.

In this apparently nearly ripe embryo the bones as seen from above (Plate 36,
fig. 1) form a nearly perfect roof to the rather long cranium. Of these the fore-
most, or nasals (7.), are only moderately long and broad ; they are two-thirds the length
of the frontals (f:),and of the same length as the sagittal suture. Rounded in front, they
widen up to the triradiate suture, where they, the premaxillaries, and maxillaries
(px., mx.), meet ; they are then somewhat pinched, and widen a little, once more, to
unite with the frontals.

In strong contrast with what we see in the Mole and the Shrew, the frontals (/)
are nearly as wide as, and nearly one-fourth longer than, the parietals (p.), and
although, together, they have a well-formed mid-orbital waist, they are very wide even
there. Towards the still open, four-cornered fontanelle (f0.), the main upper part of
these bones is gently convex ; this convexity narrows, forwards, and there is a definite
fossa marking it off from the supraorbital margin, which is very neat and finished, and
quite unlike what we have just seen in the more typical Insectivora. Slightly over-
lapping the frontals, and wedging into their lower and hinder edge, the parietals ( p.)
give a great breadth to the intertemporal region; their convexity, above, is greater,
altogether, than that of the frontals. The conspicuous temporal fossa runs round
them, on the side and behind, up to the large triangular wedge of bone that shortens
the sagittal suture and separates the two bones from the supraoccipital ; this triangle
of bone is the interparietal (7.p.).

Laterally, the premaxillaries, maxillaries, lachrymals, jugals, and squamosals ( pa.,
m., 1., 7.. sg.) can be seen flanking the great, gently convex, pyriform roof; all these
are better seen, however, in the side view (fig. 3).

Here we find that the premaxillary ( px.) is one-fourth the length, and one-half the
greatest height, of the maxillary (mz.); its facial plate, thus seen, is notched in front,
where it embraces the snout, and behind, when it is dinted by the maxillary ; above,
instead of wedging in between the nasal and maxillary, it is actually rounded off.
The maxillary is swollen in front where it runs against the premaxillary; above,
where it runs up to the frontal, still more; and below, under the lachrymal and
jugal bones (2, 7.). That Jast swelling is the outer alveolar wall of the last tooth,

2
.

and above it there is a large and deep fossa for the maxillary nerve (V*.), but this
* Whilst very grateful for what the Zoologists send me, I feel no ways bound to their groupings of
the types. Their zeal for Taxonomy is not always according to knowledge, and by their hard and fast

lines they often put asunder what Nature has joined, and leave together types that are not closely

related, but merely mimetic, or isomorphie.

ee

os

I aan

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 243

nerve has no maxillary bridge over it at present. The lachrymal (/.) has a large,
pentagonal facial plate ; its thick orbital margin is somewhat notched, and inside that
notch is the canal; the thickness of the orbital margin, which helps the frontal
and jugal to give finish to the orbital ring for nearly three-fourths of a circle, is so
large as to hide the interorbital plate of the bone and its canal.

Lying between the aberrant Tupaia and the typical Hrinaceus, this type tends to
finish its orbital ring, especially in the perfection of the supraorbital rim of the
frontal; there is, however, no free postorbital process, the ribbed edge merely runs
back and binds upon the parietal. The frontal is perfect in the upper half of the huge
orbital cup, but unfinished, behind; yet giving promise of the Lemurine orbit—a
promise fulfilled in Zupaia, soon to be described.

Behind that very extensive hollow, thin orbital plate, the parietal (p.) just comes in
and divides it from the squamosal ; the rest of the parietal is seen to be convex above,
and gently pressed inwards over its lower edge, which has two large shallow emargi-
nations ; the one, in front, over the squamosal, and the other, behind, over the huge
auditory capsule. The triangular interparietal (7.p.) is sinuously united to the parietal
above, and hooks round its rounded hinder margin, lower down. From the middle of
the lower edge of the parietal to the lachrymal the outworks of the skull are completed
by two bones, the squamosal (sq.) and the jugal. The latter bone (j.) is strong for an
Insectivore; it protects the maxillary nerve (V*.), wedges into the lachrymal and
maxillary, is grooved and broad in front, outside, and ends as a blunt style below the
jugal process of the squamosal, some distance in front of the glenoid facet (g/.c.). The
squamosal (sq.) just rests its spike upon the jugal, and then broadens out into the
glenoid tract, which is covered with a subconvex oval cartilage looking inwards and
somewhat forwards (see fig. 2, gi.c.), and into the oval, hollowed, temporal plate,
which overlaps more than half of the lower edge of the parietal. The jugal spike
runs into the thick outer part, whose upper edge is sharp and sinuous, first convex
and then concave, where it runs up and meets the squamous or temporal edge. The
lower margin has two concavities, the glenoid, and tympanic, and two processes, the
post-glenoid and the post-temporal, the latter is the larger of the two; under these
we just see the tympanic annulus (a.ty.).

The mandible (d.) is scarcely developed into distinct processes, behind ; the coronoid
(c.p.) being very low; the rounded condyloid process (cd.p.) is separated by a
rounded notch from the small, sharp, angular process (ag.p.); the ramus, with its
swollen alveolar space, and teeth just cutting the gums, is gently convex, below, and
with a slightly arcuate outline runs forwards to its narrow, pointed fore end.

In the palatal view (fig. 2) there seems nothing, at first, to remind one of the Mar-
supial ; in this, Rhynchocyon agrees with the two types next to be described, namely,
Galeopithecus and Tupaiu, The general form of the palate is roughly oval, but emar-
ginate at its narrow, fore end, and having a broken or dentate hind margin. ‘The
premaxillaries ( pa.) are of short extent, being largely overlapped by the maxillaries

21 2

244 MR. W. K. PARKER ON THE STRUCTURE AND

(mx.). The alveolar walls of the only wpper incisor tooth are imperfect behind ; this
tooth is often wanting in the adult. The openings for Jacopson’s organs (j.0.) are far
forwards, and the palatine processes of the premaxillaries are largely hidden by those
of the maxillaries.*

The maxillaries (mx.) show three parallel regions in this view: the alveolar, with
the large tooth-sockets and teeth just appearing; the submarginal, with oblique
ribbings and hollows; and the sub-mesial, separated from the ribbed part by a crack,
or sharp, roughish fissure, which looks very much like a suture. The outer part binds
on the premaxillary, and the inner tract on its palatine process, hiding most of it.
The submesial tract rises somewhat where it meets its fellow, so as to form a definite
fossa; these two tracts fail behind, being aborted by the counterpart tracts of the
palatines.

These bones (pa.) form a very elegant winged part of the hard palate, for the
posterior palatine foramina notch them, close behind the fissure, in the maxillary plate,
and inside the foramen they each have a round lobe running forwards, and outside
it another, which fits obliquely to, and extends beyond, the end of the maxillary.

In front, these palatine plates of the palatines are hollow where they meet, and then
this shallow fossa runs obliquely outwards on each bone, leaving the middle part
convex. The hind margin, as a whole, is transverse, but it is deeply crenate, there
being two notches on each side the projecting ends of the bone at the median suture.
The orbital, or ascending, part of the palatines is steep, hollow inside, and gently
convex outside; the hind half of each plate embraces the side of the presphenoid,
and, slightly diverging, is joined by the small subvertical pterygoid (pg.), which
diverges still more, and has a nucleus of cartilage (as in the Hedgehog and Mole) on

its hamular process. I find no trace of the mesopterygoid—a test-bone for Marsupial
relationship. Nor does the jugal (malar—j.) come near the glenoid facet; here,
again, this type is normally Eutherian. The squamosal (sq.) has a short, triangular
jugal process, overlying that great bone, and behind it the concave glenoid cartilage
has a pyriform outline and an oblique position—inwards and a little forwards, also.

The lateral and post-glenoid part of the squamosal is rather feeble, and is bound
upon by the tympanic (a.ty.); its processes are best seen in the side view (fig. 3) ;
the hollow face of the wide orbital roof (f.) is seen in this view, in the distance,

The annulus («.ty.) is like a large capital G with the top looking backwards ; it
gives a wide space for the membrana tympani, has a large trowel of bone on
its front crus, and has the hind crus inturned and blunt. The cartilage of the
Eustachian tube (ex.) is large, as in Marsupials, and as in Marsupials, behind and
outside it, but inside the proper thick annulus, there is a thin crescentic “ os bullae ”

* The abortive development of the single upper incisor, and the perfect condition of the hard palate,
carry us far away—upwards—from the Marsupial territory. These things foreshadow what will be seen

in Bats, some Lemurs (Lepilemur), and, ultimately, in the Ruminants.
} J J wv?

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 245

(0.b.), exactly as in young Marsupials; the annulus thickens in front, just where it
lies under the front crus of the os bullee.

There are here five vomerine bones, as in the embryo Hedgehog, and Armadillo; the
main bone or vomer proper (fig. 5, v.) is strong and carinate, and bluntly pointed at
both ends ; it is short for so long a skull, and its keel is very thick. The two antero-
lateral vomers (v’.) are the largest I have seen, as yet, reminding one of their large
cupped counterparts in the Ophidia and Lacertilia ; they are ovato-oblong, and sculp-
tured in their infero-external face, and are like two chaff scales of the Oat. The fore
part of the main vomer (v.) is hidden by these two bones ; the recurrent or J ACOBSON’S
cartilages (7'c.c.) are seen outside them.

The narrow hind part of the main vomer (v.) is partly hidden by the two large
postero-lateral vomers (v”.), which, as far as I know, are in this case relatively larger
than in any other Eutherian ; they are perfectly Metatherian in size and relations,
nearly meeting in the middle, having there a ribbed edge, and sending outwards a
large rounded lobe from their middle part; they are each nearly as long as the
main vomer, and are twice as long as the antero-lateral pair (v’.). The hind part of
each postero-lateral vomer (v.) just overlaps the base of the orbitosphenoid (0.s.) and
reaches the presphenoid (p.s.). The above are the whole of the investing bones I
have been able to find in this type.

Endocranium of Rhynchocyon cernei.
y y

The deep parts of this skull are as remarkable as the superficial ; the diagnostic
characters of several Orders meeting in one endocranium. That tract of the nasal
labyrinth which is in front of the proper olfactory region is very long (Plate 36,
fies. 4-7), and is segmented in all but its foremost and hindmost part ; there are
thirty double rings, and this is as true a “ proboscis” as that of the Elephant. So
long is this proboscis that the completely closed part is half as long as the whole
labyrinth, which, altogether, is twice as long as the basis cranii, proper.

The nostrils (e.n.) are nearer the lower than the upper face of the snout, and are
very near its end ; the valvular coil of the nostril is very complete, and terminates m
a free outer process. There the double tube is very narrow, but widens gently to
twice its first width, it is then constricted twice, and swells again before the definite
enlargement for the middle turbinals begin. There is then a deep constriction, and
then the whole structure swells out to almost tenfold the width of the neck of the
double snout-tube. Those swollen bags of cartilage do not meet each other below
(fig. 5); above (fig. 4), they are deeply excavated, behind a short, perfect roof-region
to form the two large circular multiperforate olfactory fossze, each floored by the cup-
shaped cribriform plate (cr7.p.). Above, the septum (p.e.) terminates in a bulbous,
free “ crista galli” (cr.g.), but the sloping hind margin of the wall continuous with the
cribriform plate, and notched where the multitudinous branches of the olfactory nerve
pass through from the cranial into the nasal cavity (see fig. 7, p.e.), becomes much

246 MR. W. K. PARKER ON THE STRUCTURE AND

thimer than it is above. Above (fig. 4) the inflated olfactory chambers turn round
behind, and clasp the fore part of the orbitosphenoid (0.s.); there they are sharp or
angular, but below (fig. 5), they end as rounded pouches, clasped by the base of the
orbitosphenoids, and separated by the base of the perpendicular ethmoid (/.c.), where
it is floored by the two large postero-lateral vomers (v”.). These huge olfactory pouches
reach nearly as far outwards as the equally large auditory capsules (chl.), although these
latter are separated by the mass of the hind brain. Where the palatine processes of the
premaxillaries are given off, and in the space between them and the alveolar margin of
those bones (figs. 2 and 5), there the floor of the snout is emarginate and soon
ceases ; its hind selvedge being elegantly bracket-shaped. In that emargination lies
the openings of JACOBSON’s organs (j.9.), seen in the anterior palatine foramina. For
the rest there is a large ovato-oblong open space divided at the middle by the
great septum and its splints. In front, the recurrent cartilages (7¢.c.), are seen out:
side the antero-lateral vomers (v’.); for some distance, then, the inferior turbinals (7.b.)
are also seen; but the nasal turbinals are out of sight, and the upper and middle are
well within the great pouches. All these parts are cartilaginous at present; their
detailed structure is quite like what I have already described in the Hedgehog and the
Mole—by dissections and sections.

But the axial part of the nasal labyrinth (Plate 24, fig. 7) deserves special notice ;
it is mainly formed by the huge intertrabecula (7.t7.), which is as large relatively as in
the embryo Bird, or in an average Selachian Fish. When we come to the long-faced
Cetacea we shall see this element playing an important part—as in the embryo Bird—
in the formation of the face, serving as a model on which the huge facial splints are laid ;
in them, however, the olfactory organs and their outer openings are drawn backwards,
and this bar runs forwards independently of them; here, as is normal for a Mammal,
the nasal roof is continued along its whole extent, and the alinasal part, runs round
its front end.

In the rounded front of the snout the internarial septum is fenestrate (d.nf.), a
common thing in low Eutheria; and at that part the septum itself is largely formed of
the alinasal cartilages, that, placed back to back, have coalesced with each other as well
as with the median intertrabecular bar. Now, here, for the whole length of the aliseptal
region, this is the case, so that up to the true olfactory territory the intertrabecula
itself, is only slightly crested, the top of the low septum is, in reality, merely the con-
fluent ale, or roof cartilages. Hence, in this low wall, the first three-fifths is septum
nasi, part of it roofed by the alinasal and part by the aliseptal tracts ; these tracts are, of
course, continuous, but they are true morphological regions. Of the hinder two-fifths,
the first half is twice as high as the septum in front of it; it is now the perpendicular
ethmoid (/.c.), then it lowers again, at first suddenly, and becomes a mere rounded bar,
which passes insensibly into the presphenoid (p.s.), most of which is already ossified,
The roof has several regions, well marked out ; beginning at the front of the snout, we
see the alee nasi turned round and formed into the coiled nostril-valves, then comes a

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 247

narrow neck; these parts are all in a continuous tract of cartilage. But from the
middle of that narrow neck up to the part under the triradiate suture formed by the
nasals, premaxillaries, and maxillaries (compare figs. 1 and 4), each nasal tube is
segmented into narrow rings, all of which, except those at the end (fig. 5) are
perfect below. Yet at the mid-line each ring loses its distinctness, being confluent,
above and below, with the septum.

This is a true proboscis, quite like that of an Elephant, and like that of the
Myxinoid Fishes, except that it is double instead of being single, as in those
permanent larve, with their primordial ‘ cribriform plate.” A little in front of the
part which swells with the middle turbinals, these rings cease; there are thirty of
them on each side.

The ossification of the proper cranium is very abruptly marked off from the
unossified olfactory labyrinth. The anterior sphenoid is but little less than the
posterior ; it is in three “ centres,” but little united as yet, for the presphenoid (».s.)
is here, as in Sorex and the Marsupials, as distinct an element as the basisphenoid
(b.s.); it is of the same length and not much narrower, but is somewhat hour-glass
shaped. The orbitosphenoids have a large and pedate downgrowth proximally (fig. 5,
0.8.), which fits close to the corresponding postero-lateral vomer (v’.) by the fore part
of its pedate process,

The orbitosphencids lie well over the hind part of the olfactory fossee*and their
cribriform floor (ci.p.), and form a concave margin to that part, for they project far
beyond their basal piece, fore and aft; most behind. Towards each other, right and
left of the median ethmoidal wall-top, they are rounded and notched, and behind their
junction with the presphenoid they have a large notch

a quadrant. Their outer margin,
directed backwards outwards and upwards, is crenate, and the hind margin is also
sinuous ; its inner part ending as a spur just inside the foremost angle of the alisphe-
noid (al.s.). Hence these alee do not, with their own basal piece, finish the “ sphenoidal
fissure ;” it is completed by the posterior sphenoid, base and wing, with the help
of the pre-basisphenoidal synchondrosis. The widened hind part of the presphenoid
runs into the large oblique sphenoidal fissure, making it reniform, instead of oval.

The optic, as well as the orbital, nerves pass through this large, dilated fissure ;
there is no optic foramen ; thus there are three Marsupial characters in this anterior
sphenoid: (1) the orbito-sphenoid is only slightly overlapped by the alisphenoid—
there is no gap, only a small squamous suture ; (2) there is no optic foramen; and
(3) the presphenoid is an autogenous bony element. The posterior sphenoid has about
the same extent, axially; but laterally, it is one third larger, or nearly. The basi-
sphenoid (b.s.) is as long as the presphenoid (p.s.), and is about one-fourth wider, on its
upper face (fig. 4). It has a small open pituitary space (as an Erinaceus and Sorex),
but the seat of the sella is shallow ; there are no tympanic alee. The alisphenoids (/.s.)
are larger than they would seem to be, viewed merely from the upper surface (fig. 4) ;
they are best seen from below (fig. 5). The 3rd branch of the 5th nerve (V*.) passes

248 MR. W. K. PARKER ON THE STRUCTURE AND

through a large round notch in the middle of the hind edge of the bone, and the bone
grows under the nerve for some distance in its passage to the lower jaw. The alee are
set on to the base obliquely, and the suture is on a level with the flatter upper face of
the basisphenoid (fig. 4).

If there is no tympanic ala to the basisphenoid, that part being a separate “ os bullee ”
(fig. 2, 0.0.), there is nevertheless a large tympanic ala (¢.al.s.) growing from the hinder
and under part of the alisphenoid ; in form this hollow growth is like an ordinary
tympanic annulus, being crescentic, and having a wide convex face and a ragged
opening looking outwards. All this is truly Marsupial, and if these alee coalesce with
the ossa bullze in the adult the conformity is perfect.

The auditory capsules are extremely large, and the petrous region is well ossified ;
but the mastoid region is almost wholly cartilaginous. The fore margin is convex
and bulbous, where the capsule, by its cochlear region (ch/.) fits into the large inter-
space between the alisphenoid and exoccipital (e.0.); but higher up the fore margin
is notched and sharp in front of the ampulla of the anterior canal (a.s.c.), the upper
margin is free, but the hinder has coalesced with the occipital arch, yet not so as to
obliterate the boundary line.*

In the upper view (fig. 4) the coiled cochlear region (ch/.), the meatus internus
(VIL, VIII), and the base of the recess for the flocculus are seen, but the main
part of that hollow is hidden by the subvertical part of the capsule, unossified, and
showing the form of the arch of the great anterior canal (a.s.c.). In the side view
(fig. 3) the large convex mastoid region shows the elegant sweep of the horizontal and
posterior canals (/.s.c., p.s.c.), the latter giving a smooth, rounded form to the mastoid

ce

margin of the capsule, with no “ mastoid process.” Beneath (fig. 5), the prootie and
opisthotic bones are wholly amalgamated, the fore edge of the capsule and the cochlea
being one common tract of bone—probably never quite separate centres, but developed,
as in many Mammals, in a generalised way, as also is frequently the case in the
Anurous Amphibia. The 7th nerve (VII.) can be seen running in its canal, reappear-
ing inside the tegmen tympani, and burrowing again, to escape through the stylo-
mastoid foramen, close behind the epihyal (ey.). In this view also (fig. 5) the
fenestrae (/s.0., fr.) of the auditory labyrinth are well seen, divided, as in Marsupials,
by a wide opisthotic bony tract. Then comes the wide interspace, or foramen lacerum
posterius (IX., X.), and the actually perforated exoccipital (e.0.) (XII.) for with the
exception of the olfactory sieve, the hypoglossal nerve is the only one which passes
through a proper endocranial foramen ; the 7th and &th perforate a sense-capsule, and
not a part of the true cranium.

The occipital arch follows the auditory capsule, finishing the skull in a smooth and

* This embryo was probably ripe, or nearly so, yet the development of bone in the skull is very
remarkable, and quite like the early ossification of the Marsupial skull; the sharp free edges of the
infero-lateral bones have been formed by arrest of the ossifying process, combined with absorption of a
large tract of chondrocranium.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 249

rounded manner ; the paroccipital ridges of the exoccipitals are scarcely marked, and
the supraoccipital (s.o.) is gently convex. The basioccipital (b.0.) is large, and
through the bulging of the bony sheath of the notochord (cephalostyle), subcarinate
in front, below. The condyles (oc.c.) are large and obliquely reniform, and there
is, besides these, much cartilage still left between the bony centres of the arch ;
the foramen magnum (f1m.) is very large, and pyriform in shape.

The ossicula audittis are already well developed, Mecket’s cartilage being absorbed
or used up in the lower jaw. The malleus (fig. 6, m/.) is almost completely ossified ;
the processus gracilis is still one-third larger than the manubrium (mb.), which is
short and straight, and nearly parallel with the processus gracilis. The head of the
malleus is bulbous and large, the posterior angular process (ag.p.) forms a small
cartilaginous elbow to the manubrium, The hind margin of the bone is oblique and
sinuous ; altogether this malleus is very much unlike what is seen in the Mascarene
types. The incus (7.) is quite typical, and has, for an Insectivore, a very large
processus brevis (s.¢.7.). The stapes (s¢.) is nearly typical ; it is higher, however (or
longer), and has a smaller fenestra than that of the typical Insectivora ; it is fairly an
intermediate form between the typical and the Marsupial stapes. Its neck and base
are not yet ossified completely ; I see no interhyal on the tendon of the stapedius
muscle.

The slender epihyal (fig. 3, e.iy.) cartilage is continuous both with the auditory capsule
above, and with the upper ceratohyal (c.hy.) below ; that tract is now a slender bony
rod, separated by a cartilaginous piece half its length from the lower ceratohyal (c.hy’.),
which is straighter, shorter, and stouter. The bypohyal segment is solid, conical,
short, and articulates by its base with the basal bar ; it is, at present, unossified.

The thick basal hyoid is U-shaped, and has a bony centre on both the base, proper
(b.h.br.), and in the thyrohyals (¢.hy.).

The emargination of the fore edge of the basihyal, and the general breadth of the
whole of the hinder tract, makes this part, also, intermediate between the hyoid of a
typical Insectivore and that of a Marsupial.

On the skull of the Colugo (Galeopithecus).

My materials for this type are as follows :—

Stage 1 (a).—A naked, but apparently ripe, embryo of Galeopithecus volans (locality),
53 inches long from snout to root of tail, with the umbilicus thick and soft.
Stage 2 (B).— A young specimen of Galeopithecus philippensis, 8 inches long to root

of tail (well covered with hair).
Stage 3 (c).—A second young form of the same kind, one-fifth larger.
Stage 4 (p).—Two adult specimens of G. philippensis, which were taken with the two
young individuals, in the Philippines, by Professor Mosexry, F.R.S., during the
MDCCCLXXXV. 2K

\

250 MR. W. K. PARKER ON THE STRUCTURE AND

“ Challenger” expedition, and put into my hands by Joun Murray, Esq.; and
one dry skull of the same species ; locality unknown.*

Stage 1, AA—The embryo of Galeopithecus volans ; 54 inches long.

The figures given of this embryo (Plate 16, figs. 15, 154) at once show its utter
unlikeness to the normal Insectivora ; it belongs, undoubtedly, to their level or plat-
form, but its relation to them is doubtful in the extreme. To the group below—the
Marsupials—it is related, and to a group above—the Chiroptera—it is also related,
as I shall show anon.

T shall not enter into either the zoological characters, or the visceral anatomy of
this type, but speak of what I have found in the developing skull. Biologists can
then deal with the evidence as to the Insectivorous or Chiropterous nature of this very
archaic beast, at their leisure.

Stage 1 (A).—Skull of Galeopithecus volans ; embryo, 54 inches long.
a.—Investing bones.

The general appearance of the dissected skull, with the investing bones complete
upon it (Plate 37, figs. 1, 2; and Plate 38, fig. 1) is very similar to that of a young
Phalanger, or Cuscus, of the same size, but about three months old,t but the form is
in reality intermediate between that of the skull of those Metatherian types, and that
of the young Pteropus, or Frugivorous Bat. By keeping these comparisons in mind
we shall be able to see the meaning of many things in this type, which, however, has
some unique characters ; these are strange and unique, because the kindred of the two
Colugos are all extinct. This skull is very flat or depressed, and its great breadth
across the middle gives it an almost oval outline; the short snout scarcely breaking
such a supposed circumscribing line, and the occipital region being merely sinuous,
instead of regularly arcuate. The roof (Plate 37, fig. 2, wpper view) is mainly com-
posed of three pairs of bones that form a very regular series; these are the nasals,
frontals, and parietals (7., f, p.), and behind these is the single interparietal (i.p.),
once, no doubt, composed of a pair of centres. The nasals (n.), flanked by the
maxillaries and premaxillaries (ma., px.), are as long as the parietals, and nearly as
long as the frontals. They are pointed in front and very broad behind, stretching out-
wards so as to be sutured to most of the fore margin of the frontals. Here, at once,
we see the effect of the general depression of this peculiar skull, almost unique in the
class, in its flatness and breadth. The frontals are well formed, and from the lachry-
mal to the parietal grow outwards as a neat supra-postorbital ledge ; a large supra-

* The large size of the embryo which had, apparently, been taken from the uterus—as there was no
shrinking whatever of the umbilicus—and the remarkable differences, soon to be described, between it
and the other kinds, satisfy me that this belongs to the large species, Galeopithecus volans.

+ At birth the Australian Marsupials range from the size of a new-born Mouse to that of a new-born

Rat; this larger size is what is attained by Macropus major.

DEVELOPMENT OF THE SKULL IN THE MAMMAILIA. 251

orbital foramen is seen near the front of this bony selvedge. The postorbital processes
seem to clasp the parietals behind; these, the largest of the series, carry on and
increase the general, gentle convexity of the skull-roof; the frontals wedge into them
before, and the interparietal (7.p.) behind, so that the sagittal suture is scarcely more
than two-thirds of the length of the frontal. The fore edge of the interparietal (7.p.)
makes the lambdoidal suture bracket-shaped; that transverse, oblongo-oval bone,
raises a new convexity over the hind brain; at present, the parietals are scarcely
imprinted at all by the top of the temporal muscle.

This skull, which reminds one of anything rather than that of an Insectivore—for the

Colugo might be called a small primordial Herbivore, with a parachute—has pneumatic

squamosals as in the Marsupials ; the squamous suture is seen in this upper view, and
also the swelling of the bone caused by large air-cells outside the temporal fossa, The
short zygomatic process is also seen in this view, and the thick top edge and hollow
inner face of the jugal or malar (j.) which reaches far back, as we shall see in the other
figures. Another thing is seen here in this marvellous little Herbivore, namely, the great
backward extension of the maxillaries (mz.), with their large dentary region (see also
figs. Land 3). We see also, obliquely over the growing hind sockets, the hinder opening
of the infraorbital foramen or channel for the 2nd branch of the 5th nerve (V*.).
Outside that passage, in the antero-external part of the orbit, there is another large
passage, this is the lachrymal canal in the lachrymal bone (Lc., 1), a large perforated
shell of bone growing out upon the face, as well as forming a large part of the orbital
cup in front.

All these things want supplementing by the lateral, lower, and end views of the
skull (figs. 1 and 3; and Plate 38, fig. 1).

The side view (Plate 38, fig. 1) shows that the face is deflected considerably

an
and that there is a definite hollow between the nasal and frontal

embryonic character
regions above.

The orbital and temporal regions run into each other, but the enclosure of the post-
orbital region is begun.

In the adult (Plate 39, fig. 3) the cranial cavity and the upper nasal region, from
the end of the snout to the crista galli are equal; now (Plate 38, fig. 1), the brain-
cavity measures nearly twice the upper nasal length ; this is an early and also a Mavr-
supial state of things, and would have been still more remarkable in an earlier embryo.

The nasals have a very convex dorsal outline, and dip where they slightly overlap
the frontals laterally ; they are in sutural relation with the deep facial plate of the pre-
maxillaries and maxillaries (px., mx.) ; the upper edge of the former is extensive, being
three-fourths as large as that of the maxillaries. Two-thirds of the exposed outer face
of the maxillaries is suborbital ; a hollow, beginning in the premaxillary, runs along the
maxillary up to the lachrymal (/.); near its end there are two small infraorbital fora-
mina (V*.); the first hole is small on both sides ; they, however, are very variable, as in

one adult Philippine Colugo, I find two openings on each side, and in another four on
bl ara 2)
4K 4

bo

52 MR. W. K. PARKER ON THE STRUCTURE AND

both sides. At present, the thickening of the orbital edge is formed by the lachrymal,
and the maxillary is hollow up to it; below, the whole alveolar region is swollen but
sinuous, it reaches to within a very short distance of the preglenoid convexity. The
lachrymal is very large; its infraorbital plate was best seen in the last figure (Plate 37,
fig. 2,1.); there it is seen to carry on the orbital ring, forming at least a quadrant ; its
swollen outer facial part corresponds to the excavated infraorbital tract (see the upper
view). Riding over and outside the last two alveolar swellings of the maxillary, the
large jugal (j.) begins narrowish and convex, and then forks, and becomes somewhat
concave. The foremost upper fork tends to unite with the postorbital process of
the frontal, and then to make a perfect orbital ring such as we shall see in the
next type (the Lemurine Tupaia). This large jugal, like that of a Marsupial,
a diagnostic Metatherian character.

grows over the fore part of the glenoid cartilage
Most of the side of the skull is taken up by the enormous squamosal (sg.) which,
measurement for measurement, is as large as the parietal.*

The squamous suture is very extensive ; when seen from above (Plate 37, fig. 2) it is
seen to be formed by overlapping the parietal, although it just touches the interparietal.
The junction of the jugal with the zygomatic process of the squamosal is extensive, and
its lower part is plastered by the glenoid cartilage ; the glenoid cavity is deep and
looks forwards and downwards, and is supported behind by a large postglenoid ridge.
Behind that, the bone is cut away in a circular manner, with toothings over the ear-
drum; then from its postero-inferior angle it rises obliquely, being furthest backwards
above, and has its thin rounded hind edge notched just below the middle, where it
overlaps the mastoid region.

The suture with the alisphenoid (a/ s.) in front is short and almost vertical; from it
the temporal fossa runs backwards and upwards. The pterygoid hook (pg.) is just
seen below the jugal and inside the small external pterygoid process of the alisphenoid
(e.pg.). The annulus (a.ty.) is very instructively imperfect for comparison with the
next stage (fig. 4), where it already forms a vertical opening or slit with bony lips.
Here (fig 1) it lies under the tegmen tympani as a shallow saucer-like bone, pro-
jecting in front, hiding its hinder and front crura inside the squamosal, and
developing a rudiment from the hind crus which will become the hinder and lower
part of the vertical bony meatus.

The mandible (figs. 1 and 2, d.) is decurved like the upper face, quite unlike the
ascending “ mentum” of Cuscus ; so also the extended and out-turned angular region
(ag.p.) is unique ; it does, however, show an inflated inner face, as in Marsupials. The
condyloid process (ed.p.) is not very sharply defined ; the condyle itself is oval, with
the long axis transverse; the coronoid process (c¢.p.) 1s small, oblique, and sub-
uncinate ; the whole ramus is sigmoid in its general outline.

* Here the skull of a young Cuscus maculatus, of the same size as this large embryo of Galeopithecus

volans, comes in in a most timely way; that type is to me the most generalized Marsupial I have seen,

and the squamosal in it is only less than that of the embryo Colugo.

Sa ee a

eT a ee

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 253

The under view (Plate 37, fig. 1) is remarkable for its size, both in length and breadth ;
its length is considerably greater than that part of the basis cranii which lies behind
it, and its breadth is equal to that part—the main part—which is formed by the
maxillaries and palatines. The general form of the palatine region is oval, but
irregular in front, and emarginate behind. Laterally the large alveolar tracts with
their pushing teeth (some of them are cut) are very large ; there are no teeth in the fore
part of the premaxillaries, but two in each, on the side; these, however, are small.
The fore margin of the premaxillaries is narrow, where they meet in a very obtuse
angle; the lateral part of each bone projects forwards, and is subuncinate. The
slender palatine processes of the premaxillaries (p.px.) are hidden, behind, by the
maxillary palatine plates ; when these are removed (Plate 39, fig. 1) then they can be
seen as long, slender, arcuate, compressed bars, having no distinct antero-lateral
vomers attached to them; but these bones may have become confluent with them.
Through the narrowness of the premaxillaries in front, and the deficiency of the
maxillary plates towards the mid-line, the anterior palatine foramina are very large ;
they are oval, and show a considerable tract of the recurrent cartilages (7¢c.c.), behind
the opening of JAcoBson’s organs (/j.0.). Behind the emargination the maxillaries
scarcely meet for some distance, but the last two-thirds of their suture is perfect ;
right and left of this part the bone is concave, but this hollowing of the roof is much
less than that which is found in young Marsupials; the sides also are hollow, thus
there is a general crescentic convexity along the middle of each palatine plate. The
hard palate is not extended backwards more than one-sixth further by the palatines
(pa.), but they are strong bones, and the whole hard palate shows nothing of that
economy of bony deposit seen in Marsupials and typical Insectivores. The skull set
up, and with the palate towards the eye, shows, here, a very elegant double archway
to the two nasal passages. The thick, ribbed margin of the bones projects where they
meet, so that the end of the hard palate is bracket-shaped ; in front of each thickening
the oblique posterior palatine foramen (p.p.f.) 1s seen. These narrow curved
palatines lie like scales under the maxillary plates, and their curved thin fore edge
retreats, laterally, and then turns a little inwards, where it is pressed against the
alveolar wall of the two last teeth. The thick side wall of the open part still gently
curves inwards ; it is separated outside from the palatine portion by a large sharp
notch. The shell-like orbital or ascending part of the palatines meets the hinder part

of the main vomer (v.), almost reaching as far backwards as its four terminal prongs.

The small pterygoids ( pg.) also ascend, and below, where they are spliced obliquely to
the palatine wall of the great nasopalatine canal, they end, behind, in the hamular
process, which is small, flat, and turned outwards; it is supported, outside, by
the equally small external pterygoid process (e.pg.). The pterygoid is very small, as
in the Marsupials, and this comes from the fact that what is generally, in the higher
mainmals, the upper or basicranial flange, is here, as in the Marsupials, a long, tongue-
shaped mesopterygoid (ms.pg.). This flat bone is sharp in front, where it wedges in

254 MR. W. K. PARKER ON THE STRUCTURE AND

between the palatine and pterygoid, and blunt behind, where it partly hides the basi-
sphenoid (b.s.); its front part hides the side of the presphenoid (p.s.); it is gently
arcuate, the convex side being towards the mid-line. To see the rest of the splints
of the fore part of the skull the palatine plates have to be cut away (Plate 39, fig. 1).
The main vomer (v.) is five-ninths the length of the whole bony skull, measured along
its base. Its blunt point fits in between the hinder third of the palato-premaxillary
bars; there it becomes subcarinate, widening gently; its broadest hinder part is
distinctly keeled, and that keeled part is exposed in the open nasopalatine passage
(Plate 37, fig. 1). The subcarinate part is strongly clamped by the bones of the hard
palate, and thus the nasal passages are divided. The postero-inferior part of the nasal
labyrinth is underfloored by lateral bones, behind the great inferior openings which
have the maxillary plates as their floor; but for these plates the greater part of this
region would be “schizognathous.” Behind, however, the ‘desmognathism” is
double—upper and lower ; this is caused by the meeting together of the notched orbital
plate of the palatines and the “ postero-lateral vomers” (v”.)—two triangular wedges
of thin bone that by their most acute angle fit in between the vomer and recurrent
cartilage in front, have their obtuse angle external, and their less acute angle wedged
in between the vomer and palatines. These bones are larger than usual for even an
Insectivore, but are not distinctly Metatherian—as in Rhynchocyon, where they nearly
meet behind the median vomer. Thus the creature sways, so to speak, everywhere,
between a normal Eutherian and one of the Metatheria. The strong jugals (j.)
bind against the maxillaries in front and widen out; they then thicken, are hollow
outside, and end obtusely just over the glenoid facet (g/.c.).° The great pneumatic
squamosals (sq.) show some of their most marked characters in this aspect, for both
the hinge (gl.c.) and the pneumatic cavities are to be seen from below. The zygomatic
process is short, the glenoid facet is concave, oval, and almost transverse,—it looks
obliquely downwards, and forwards, and retreats a little at its inner end. The post-
glenoid ridge is large and thick, and the bone extends inwards beyond it, clamping
the alisphenoid (al.s.), and nearly reaching the cochlea (ch/.). The outer edge is
tucked, as it were, under the skull and round the top of the tympanic cavity.

Behind, the squamosal embraces the mastoid part of the ear-labyrinth, and that
edge is, close in front of the arrested and coalesced, epihyal (e.hy.). The roof of the
tympanic cavity—tegmen tympani— is largely formed by the squamosal, and that
roof opens into the air-galleries above, that give the sinuous appearance, and apparent
thickness to the bone (fig. 2, sq.).

The tympanic ring (a.ty.) is in a remarkable state of development for an embryonic
Insectivore ; its development is equal to that of a Rodent or a Herbivore (Ungulate).
But although large, the bone is shallow—a mere saucer, and the air cavity in it is very
limited as to depth; but this is compensated by the extensive galleries that are developed
in the squamous and mastoid regions (see in the adult, Plate 39), This tympanic
dish (Plate 37, fig. 1, a.ty.) has a spout in front, an accurate round notch—the

—

other,

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 255

opening—on its outer edge, and a small unfinished part bebind that notch; its
general form is round and gently concave above and convex below, but it runs into
crenations at the postero-external margin, and also (Plate 38, fig. 1, a.ty.) is developing
a process which is the rudiment of the compressed bony meatus externus (see Plate 38,
fig. 4, a.ty.).

The end view (Plate 25, fig. 3) shows the imbrication of the roof-plates as they fit
upon the occipito-auditory region; the parietals, interparietal, and squamosals
(p., i.p., sq-) are thus seen, and the latter show their sinuous enlargements, due to the
excavations within them.

Endocranium of embryo of Galeopithecus volans ; 1st Stage (A).

Many things belonging to the inner cranial structures can be seen in the dissected,
but perfect, skull (Plate 37, figs. 1-3; and Plate 38, fig. 1); but only when the invest-
ing bones have been removed are the deep parts thoroughly visible.

Such further dissections are figured in lower and upper views (Plate 39, figs. 1, 2),
with some of the investing bones, left for the most part in outline
landmarks.

, te be useful as

The short, broad snout (al.v.) has its nostrils (e.n.) near the end, and rather under-
neath ; the snout narrows in front, broadens behind the nostrils, and then is some-
what pinched in.

From the middle of the floor, which crosses over the premaxillaries (px.), the
recurrent cartilages (rc.c.) are given off, these grow round the opening of JACOBSON s
organs and then run along on their inner and under side as their proper, but imperfect,
capsule. These curious retral growths of the snout are twice as long in this species as
is normal, a fact the meaning of which I cannot explain, but which will be understood
when our knowledge of these parts is more advanced.

The inferior turbinals (7.tb.) are very feeble, but the foremost coil of the middle
turbinal series (m.tb.) is very large indeed—beoth in width and in length ; it extends
forwards twice as far as usual: three other coils of this series are seen behind it.

Above (fig. 2), in this species, the olfactory labyrinth (al.e.) is seen to be short, and
not very wide; this is partly due to age, and is partly a specific distinction. The
whole fuce being shorter and broader in this embryo than can be accounted for by
difference of age ; the thick top of the septum (p.c.) does not end in a definite crista
galli. The top of the great septum (p.e.) is very oblique, it is narrow, and has a
smaller perforated plate (e7.p.), right and left of it, than is usual in Insectivores. This
eribriform plate is quite unlike that of the Hedgehog or the Mole, and is quite like
that of a young Frugivorous Bat (Cynonycteris collaris), now before me. Its upper
recesses are shallow, its size is small and sub-oblong—widest above—and its perfora-
tions are comparatively few ; the Frugivorous Bat on one hand, and Cuseus on the

gives us the two cribriform plates most like it. A tract of median cartilage is

256 MR. W. K. PARKER ON THE STRUCTURE AND

seen above, behind the cribriform plate, which is the end of the perpendicular ethmoid,
and the beginning of the presphenoid, All the fore part of the basis cranii on the
under surface (fig. 1) up to this point is hidden in the lower view by the vomers. In
the upper view (fig. 2) the orbitosphenoids have lost their large cartilaginous upper
part, and now form two oblique, four-sided wings (0.s.) that have met, and largely
coalesced below, to form a long presphenoidal region, as in the Hedgehog and the
Mole; the Shrew, as I have shown, agrees with the Marsupials in having an
independent presphenoid; that is a rare thing among the Eutheria, but is seen in
small Rodents. The optic foramen (II.) is very large—a good Lemurine character—
and the bar enclosing it, behind, is strong; here we are far away from the Mar-
supials. There is still much cartilage between the presphenoid and basisphenoid (b.s.) ;
the fore margin of the latter is bilobate, and its sides show some remnants of the
expanded parts that in typical Insectivores form the tympanic wings ; there are two
irregular knobs on each side. The alisphenoids (ql.s.) are still distinct from the basi-
sphenoid, they are one-third larger than the orbitosphenoids, and overlap them by
their inner and anterior angle much more than in Rhynchocyon and the Marsupials ;
this corresponds with what we see in Bats, but is quite unlike the peculiar over-
lapping growth of the alisphenoid in typical Insectivores. Each wing is ear-shaped,
narrowing in behind, and so deeply notched for the Ist and 2nd branches of the 5th
and the orbital nerves in front (V'. ?), and by the 3rd branch (V*.) bebind, that there
is only an isthmus of bone one-third the extent of the wing between the two great
round notches ; this is equally true of these parts ina young Pteropus. When the
soft. tissues are removed between the posterior sphenoid and the auditory capsules
(fig. 2), then a very irregular middle lacerated foramen is seen, this is bounded postero-
laterally by the squamosal (sg.). That bone covers nearly all the auditory capsule,
externally (Plate 38, fig. 1, sq., op.), and below (Plate 39, fig. 1. op.), only a small
mastoid tract is seen clamped by the squamosal, perforated by the facial nerve (VIL),
and having in front of that foramen (stylomastoid), a very small rough bony elevation,
the arrested and confluent epihyal (e.hy.). There the bony capsule is pinched, for the
exoccipital (e.0.) nearly meets the squamosal in front of the epihyal knob. Then the
auditory labyrinth expands, running inwards and forwards, and showing, from behind
forwards, the heart-shaped fenestra rotunda, the oval fenestra ovalis, and the notch
in front of the latter, through which the facial nerve (VII.) passes to get under the
tegmen tympani (¢.ty.) ; the whole fore and under part is the smallish, obtuse cochlea
(chl.).

Above (fig. 2), the capsule is well displayed ; it has a rough keel in front of the
proximal cochlear eminence, behind which, running inwards and a little backwards,
are several holes. The porched meatus internus, on the inner side, contains several of
these, the outermost being for the facial nerve (VII.) and the other for the auditory
or portio mollis (VIII.). The former passes under a thick bridge of bone, and then

runs round and escapes through the notch in front of the fenestra ovalis (fig. 1, fs.0.,.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 257

VIL). Then comes the arched part containing the anterior canal (a.s.c.) bent over
the hollow for the flocculus cerebelli ; the arch runs backwards and inwards to meet
the occipital arch, strongly clamped by the thick hollow squamosal (sqg.). From the
bridge over the facial nerve there is on the left side a short, and on the right side a
long, spur of bone, running upwards towards the arch of the anterior canal. The
whole auditory capsule is well ossified, just a little cartilage remaining in the mastoid
eminence (op.) and along the epiotic margin, but the occipital arch has still large
synchondroses (Plate 37, figs. 1-3; Plate 38, fig. 1; and Plate 39, figs. 1, 2).
The supraoccipital (Plate 37, fig. 3, s.o.) is a large shield of bone, round above,
notched below, and with sinuous sides ; it was, evidently, double at first, is convex
above, and aloug the middle, and is a little scooped for muscular attachment infero-
laterally. Then comes a large triradiate tract of unossified cartilage, below which
there is, outside, the mastoid bone (op.), and inside, the exoccipital (¢.0.); the former
ends in a small cap of cartilage. The curved exoccipitals are everted against the
mastoid bone, but they keep well inside it, and form no definite paroccipital pro-
minence. The condyles are long (deep) and roughly creseentic—broad above, narrow
below

and help to enclose a large foramen magnum (/:m.).

The basioccipital (Plate 39, figs. 1, 2, b.0.) is twice as long as the basisphenoid, it is
narrow in front, broad behind, subconcave above, and subcarinate below ; it is
separated from the lateral ossifications by a large tract of cartilage, aud is perforated
by the large hypoglossals (XII.), and notched by the vagus and glossopharyngeal
(x, EX):

So far advanced is the embryo before birth—equal to that of a young Marsupial
eight months old—and the Marsupials ossify their skull earliest of all kinds—that the
processus gracilis of the malleus (Plate 37, fig. 4) is already only half the size of the
manubrium (mb.). The posterior angular process (p.cg.) is a distinct knob, but
small; the head of the bone is bulbous. The incus (7.) is very bulbous, and is very
similar to that of a very different Order of Herbivores, namely, the Ruminantia
(Doran, plate 61, figs. 12-21). The short crus (s.¢.7.) is very short and small, and the
long crus (/.c.7.) although normal in form, is small as compared with the bulbous
body. The height and basal breadth of the stapes (sf.) are about equal, the fenestra
is small, as in those Marsupials that have this hole ; the interhyal is arrested.

The ceratohyal (Plate 38, fig. 3, chy.) is in one slender subfalcate segment, with
the lower part ossitied; the hypohyal (h.Ay.) is less than half of the length of the
ceratohyal, but it is thicker; it is not ossified. Nor is the U-shaped basal cartilage
(bh.br.) which has flat and uncinate thyrohyals (t./y.), not yet segmented from the basal
tract, which is small and narrow. This os hyoides is quite unlike the perfect arch of the
British Insectivora and the East African Rhynchocyon ; it is better developed than
that of the larger Centetidee, and is about equal to that of a Marsupial at the same
stage of development. The small, simple concha (Plate 37, fig. 5), shows an imperfect
segmentation of the annuli inside the dilated leafy growth of cartilage.

MDCCCLXXXV. 24

258 MR. W. K. PARKER ON THE STRUCTURE AND

Stuge 2 (B).—Young of Galeopithecus philippensis; 8 cnches long from snout to
root of tail,

The investing bones of the skull.

The side view of the skull (Plate 38, fig. 4) reminds one of that of an Ewe, or of a
Llama, just as the incus, as we have seen, is like that of the Ruminants ; the side
view of the head in the embryo of the other species (Plate 16, fig. 154) suggests the
same resemblance. Anyhow, whatever it is Véke, the skull is as unlike that of a
normal Insectivore as it can well be. The centre of the orbit is at the middle of the
length of the whole skull, including the snout; the facial part is much shorter in the
embryo of the other kind (compare Plate 38, figs. 1 and 4). More than a third of
this large orbit—Lemurine as to size—is unenclosed behind ; it is more circular than
in the young specimen. Through advanced growth, the hollow over the fore part of
the orbits, and the deflection of the snout, are less marked. Now, the highest convex
part, above, is parietal (p.), and the supraorbital ridge is higher than the upper face
of the frontals cay and the convex dorsal line of the nasals (n.) is a little less
rounded, The embryonic curve of the whole skull is now much less evident ; but
the straightening process is not finished yet. The premaxillary ( px.) rans further
into the maxillary (w.) in the facial suture, and the latter is much more outspread
in the preorbital region, quite flush with the lachrymal (/.) The latter bone encloses a
fourth of the orbit, and a third of its actual rim, Its canal is well inside the edge, as
in the Hyrax, and not outside as in Bats, Lemurs, and most Marsupials. These latter,
asa rule, have two canals—one in Phalangista. The facial part of the lachrymal is a
large lunule and the orbital a thin polygonal plate. The small double infraorbital
foramen (V*.) 1s below the convex preorbital margin of the maxillary. The developed
orbital rim hides the inner opening when looked at in this aspect. The orbital edge
and postorbital process of the jugal (j.) are better grown now, and the latter is not
so far back; it is nearly over the middle of the well-developed cheek-bone. A tri-
radiate concavity traverses the Jarge orbital plate of the strong-browed frontal (75
that shallow fossa ends below and behind in a rounded notch, which is made into
a foramen (f. orbitale) for the re-admission of the ophthalmic nerve (V4) inside the
skull-wall. The frontal bone interdigitates with the parietal (p.) under and behind
the postorbital process, and then that gently swelling roof-bone runs back to the trans-
verse interparietal (7.p.). Behind the f. opticum (see fig. 1, II.), the large alisphenoid
wedges apart the frontal, parietal, and squamosal ; the latter (sq.) is squarish, and large
enough to hide most of the side of the bind skull; it corresponds with that of an
Eastern Marsupial ; in Didelphys it is much smaller; it is in remarkable contrast
with that of Hrinaceus and Rhynchocyon (Plate 20, fig. 3; and Plate 86, fig. 3); in
Pteropus and Lepilenur the pavietals throw the squamosal down to the side, and, in
their much fuller growth, overshadow it.

eS ee os

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 299

Here the zygomatic process, the glenoid cavity, the postglenoid ridge, the supra-
tympanic notch, the temporal fossa, the tempora squama, and the post-tympanic
angle are all in a high state of development. Below and inside the elegant sigmoid
jugo-squamosal suture we see the internal pterygoid hook, and the small external ptery-
goid plate (pg., e.pg.). Built well into the deep rounded tympanic notch of the squa-
mosal, we see the strong compressed bony meatus externus (m.t.c.), standing out from the
general tympanic dish (a.ty.) ; it is open above, as the squamosal is below ; together
they make a vertical narrow bony-lipped passage to the shallow drum-cavity and its
extensive upper galleries—that is, after the membrana tympani has been removed

from the inside of this narrow porch. The lower jaw (figs. 4 and 5) has, already,

nearly assumed the adult form, with its deflected mentum, its oblong dentary region,
its small unciform coronoid process, its non-pedunculate condyle, notched behind, and
its wide out-turned angular region, with an incurved inner edge.

The lower view (Plate 37, fig. 6) shows some contrasts with that of the embryo of
the other species (fig. 1) that cannot all be put down to a further stage of development.
Here we must make allowance for two causes of difference—age, and diversity of
species. *

Here (Plate 37, fig. 6) the alveolar tracts are more nearly parallel than in the
other kind (fig. 1), and this is not merely due to advance in growth, but is partly
also specific. The fore part of the premaxillaries (pz.) is slenderer, and the maxillary
palatine plates have grown further forwards.

With this fuller development of the palatine plates, the hollowness of the palate in
its middle—a remnant of the old Marsupial feebleness of this part—is almost gone,
although the mid-line is hollow, and a shallow fossa runs right and left, cross-wise,
near the hind margin of the maxillary plates. The palatine plates of the palatines
(pa.) are like those of the other kind, but they are more extensive, and in this stage we
have a complete sutural analysis of the peculiarly elegant archways of the nasopala-
tine passages of the adult Colugo. The squamous suture of the maxillaries and
palatines is arched, but runs transversely in this case, and the narrow fissure between
the flat part and the ribbed edge is widened out into a very remarkable uncinate con-
cavity, ending sharply, outside, in the posterior palatine foramen (p.p-). Here,
again, we see the sharp angular space between the palatine part and the mere side
wall, which turns inwards to join the feeble pterygoids (pg.), which have a basicranial
tract, ending in a toothed edge, between the orbital plates of the palatines and the
long tongue-shaped mesopterygoids (i.s.pg.). These latter reach nearly to the basi-
occipital (b.0.).

* The difference is as remarkable as the similarity (Plate 37, figs. 1 and 6); and if these two wazs can
show such curious and notable modifications, although so close akin, there can be no difficulty in
imagining a large number of similar but greater differences in structure in whole hosts of related forms,
which may at one time have existed, and which were, probably, potent in species, genera, and even sub-

families.

OR 16 0%

260 MR. W. K. PARKER ON THE STRUCTURE AND

The splint bones that support the basis cranii, lying on a higher level, are the
vomer and the ‘ parasphenoid ;” the former (fig. 6, v.) is here seen to be the common
keystone of this very perfect double archway of the nasopalatine passages (7.p.c.).
The keel of the vomer wedges itself in between the ribbed edges and the two palatines,
and these complete the divisions of the common nasopalatine channel ; its broad sides
then unite by harmony with the orbital plates of the palatines, so that it is conjoined
with those bones both in the middle and also right and left. These lateral flanges of
the vomer end as free spikes under the presphenoid (p.s.), and the middle, shorter

ce

part is also split. But the other bone just mentioned—the “ parasphenoid ”—is not
seen in the embryo of G. volans (fig. 1), nor, indeed, in any other Mammal examined
by me, as yet.*

This small style of bone lies under the foremost two-thirds of the basisphenoid (b.s.),
but is very distinct from it; it resembles, at first sight, the ridge often seen under
the basioceipital, which is due to the ossification of the sheath of the notochord ; but
this tract is wholly pro-chordal, It is the exact counterpart of the parasphenoid of
the Lacertilia, which disappears as mysteriously in some kinds as in G. volans ; in
the case of two closely related Cyclodonts—Cyclodus nigroluteus and Trachydosaurus
rugosus: in the latter it has been taken away, and in the former it has been left.
Here the Marsupial condition of the well-developed jugal (7.) is seen again (fig. 6, 7.),
and a still more extensive development of the equally Marsupial squamosal (sqg.) with
its thick, crescentic, hollow postglenoid process, its large pretemporal part clamping
the alisphenoid (al.s.) and its extensive swollen post-temporal plate. The tympanic
(u.ty.) is, here, most instructive as to the interpretation of the thoroughly ankylosed
adult skull (Plate 39, figs. 3-8). This bone, now well-formed, is a remarkable shallow
dish with a most irregular outline, and a crescentic convexity in its deepest part,
the convex outline of which runs close to the fissure for the exit of the glossopharyngeal
and vagus nerves (IX., X.). ;

Where, as a rough wedge, it runs forwards and reaches the mesopterygoid, there it
has a considerable oblique foramen, the Eustachian opening (ew.); this is surrounded
by cartilage in the embryo (fig. 1). Externally it is jammed in between the post-
glenoid and post-temporal elevation of the squamosal (sq., see also Plate 38, fig. 4,
a.ty.). ‘Thus, since birth, it has finished the bowl of the dish and formed the deep
two-lipped spout—the bony meatus externus.

In the end view (Plate 37, fig. 7) the parietals (p.) are seen with their lower
edge forming the top of the temporal fossa, which half is scooped out of the squamosal
(sqg.). The swelling of the post-temporal part of the latter bone (see also Plate 38,

* T shall have to describe a pair of bones found in membrane, and added to the basisphenoid, when

IT come to other and higher kinds of Eutheria; these have long been known in Man as the “ linguls

’ ”

sphenoidales.”” I strongly suspect that they are the ‘‘basitemporals ”—symmetrical remnants of the
parasphenoid—so well seen in Birds and the Crocodilia (Phil. Trans., 1869, Plate 82, fig. 2, 0.t.; and

‘Trans. Zool. Soc., vol. 11, plate 66, fig. 3, b.f).

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 261

fig. 4, sq.), close to the large air cavities within, is also well seen. The interparietal
(.p.) has begun to develop the occipital crest so large in the adult (Plate 39, fig. 4).

Stages 2 and 3 (B and c).—Showing endocranium and certain of the investing
bones of Galeopithecus philippensis.

These two stages differ but little from each other, and for the advance of the endo-
cranium may be taken together. In the longitudinally vertical section (Plate 38,
fig. 7) the cranial cavity, and the nasal labyrinth are equal in length; the former
overlaps the latter in front. The obliquity of the top of the perpendicular ethmoid
(p.e.) is such as to make a very obtuse angle with the top of the general septum
(p.e., s.n.), whilst it is almost in a line with the basis cranit behind, just rising a
little at the crista galli (ce7.g.). The recess for the olfactory lobe, lying on the
oblique cribriform plate, is not large—very little in advance of the same in the
Marsupials. Only about a fifth of the general partition (p.e.) is ossified at present ;
this is a long way from the presphenoid (p.s.) and does not reach the bottom ; the
intertrabecula itself is hardly touched, only its crest.

This is a very long septum (p.e., s.v.) for so short a snout; in most of the Insecti-
vora it is that part which prolongs the septum, forwards ; here, it is the elongated
facial region itself, with but little alinasal addition. The deflection of the whole face
is still evident, and the end of the septum is almost in a line with the general palatal
tract. Behind that part the opening of JAcoBson’s organ (j.0.) and the fore part of
its cartilaginous capsule of the near side is shown; behind, where it is cut across, the
vomer (v.) is seen.

That long trough of bone is half the length of the cranio-facial base, reaching from
the front third of JAcopson’s (recurrent) cartilage (rc.c.) to behind the middle of the
presphenoid (p.s.). As it supports the intertrabecular base of the nasal partition, so
it is itself supported by the bones of the hard palate (p.mz., pa.) at their junction
along the mid-line; thus the nasal cavities as they pass towards this hinder opening
are kept distinct.

Over the septum nasi (s.v.) the nasal (7.) is seen, and the frontal (f) over the
ethmoid, and over the cavity of the skull in front. At this stage the roof-bones are
thick; the parietal receives the hinder angle of the frontal into a notch, laterally,
and is partly overlapped by, and partly overlaps, the frontal. The well-ossified
anterior sphenoid (0.s., p.s.) is seen in this view, the wing rising into a rounded angle,
and having the large optic foramen (II.) near its hind edge below ; the presphenoidal
tract is rather thick, and is longer than the bony plate

basisphenoid (b.s.)—behind
it. The alisphenoid (q/.s.) leans against the orbitosphenoid, and rises to the same
height ; it overlaps it in front, and is then only partially visible in this view.

The short basisphenoid (b.s.) dips a little, but gets no postclinoid ridge again, behind;
there is a small tract of cartilage between all these basal bones (p.s., b.s., b.0.). Under

262 MR. W. K. PARKER ON THE STRUCTURE AND

the basisphenoid the parasphenoid (pa.s.) is seen. Between the alisphenoid and the
auditory capsule there is a large semi-oval space filled in by the squamosal (sq.),
which is hollow inside, the concavity being a continuation of that formed by the
parietal, Above the hind corner of the squamosal and over the upper and front
part of the auditory capsule the parietal forms a thick and rough rudiment of the
“tentorium cerebelli.” Under that rafter-like bar the squamosal (sq.) shows a roughly
triangular inner face, which hes outside the arch of the anterior canal (a.s.c.), and
supports the lower half of the fore edge of the supraoccipital (s.o.) ; the re-appearance
of the squamosal inside is due to its great height, especially behind. The auditory
capsule is subvertical in position, and in this view shows the great arch over the
recessus flocculi, the multiperforate meatus internus (VIII), with the bridge over
the facial nerve (VII.) a thickening where the posterior canal (p.s.c.) begins, and a
somewhat notched edge where the 9th and 10th nerves (IX., X.) emerge. The basi-
occipital (b.0.) is thick in front and thin behind; it is one-third longer than the basi-
sphenoid (b.s.). By an obtuse angle it wedges in between the capsule and the lateral
oceipital (e.0.), which is a broad and high bone, having a large oblique hole for the
hypoglossal nerve (XII.) not well seen in this aspect, and a small posterior condyloid
foramen (p.c.f.). The supraoccipital (s.o.) and interparietal (¢.p.) now form one large
shield-shaped bone, finishing the postero-superior face of the skull, and articulating
with the parietals and exoccipitals, but kept apart from the petromastoid by the
large post-temporal part of the squamosal,

In the side view of the smaller young of G. philippensis (Plate 38, fig. 4) the snout
with its valvular opening (a/.7., ev.) is seen in front, and the top of both the orbito-
sphenoid and alisphenoid (o.s., a/.s.) laterally, in the fundus and back of the orbit.
Here it is seen that the alisphenoid reaches much higher than the inner view (fig. 7)
would seem to show. The occipital condyle (oc.c.) is seen in both these views, and
some part of the mastoid (op.), the exoccipital (e.0.), and the supraoccipital (s.0.).

In the basal aspect (Plate 37, fig. 6) several important parts are displayed, not
covered by the superficial bones. In front, the alinasal region shows with great dis-
tinctness the origin of the recurrent cartilages (rc.c.); the external nostrils (e.n.)
are more terminal, as in Marsupials, than in the other kind. The presphenoid, basi-
sphenoid, and basioccipital (p.s., b.s., b.o.) are displayed, with the parasphenoid (pa.s.)
under the middle piece; the basisphenoids and basioccipitals are much wider in this
space than in the other. The alee are not much displayed, and the alisphenoid is
largely overlapped by the squamosal. The small mastoid process (op.), with the stylo-
mastoid foramen and epihyal in front of it, and the exoccipital void of any distinct
paroccipital process, are also well seen. The subcircular foramen magnum ( fm.) is
bordered by the large projecting semioval condyles (o0c.c.), and, behind, the supra-
occipital (s.0.) can be seen finishing the great doorway.

Part of another lower view in the larger young (fig. 8.) shows the foramen
ovale (V*.), the channel for the facial nerve (VII.), the fenestrae—fenestra ovalis

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 263

and fenestra rotunda ( /s.0., f7".)—in the auditory capsule, the outlet for the facial, glosso-
pharyngeal, vagus, and hypoglossal nerves (VII., [X., X., XII.) ; a bristle shows the
opening from the ear-drum into the labyrinth of air-cells in the squamosal (sq.).

The end view of the skull, younger specimen (Plate 37, fig. 7), shows the well-built
occipital arch, with its elements distinct ; the large foramen magnum, the outstanding
condyles (0c.c.), and the mastoid process (op.) all well set in under and within the
great investing plates.

There is a remarkable difference between the hyoid arch in the lesser and larger of
these young Philippine specimens (Plate 38, figs. 6 and 8).

In the former (fig. 6) this part is not so well developed in some respects as in the
embryo of the larger species, for the hypohyal h.hy. is not segmented off from the
ceratohyal (c.hy.), whilst the latter region is not ossified, but the hypohyal region
has an oval centre, The basal and thyrohyal regions have now each a small bony
tract.

In the larger young (fig. 8,) these parts are much more advanced, and the hypohyal is
segmented off from the ceratohyal ; each of these is rapidly ossifying, and so are the
basal piece and thyrohyals ; but these are continuous in the cartilaginous interspaces.

Stage 4, p.—On the skull of the adult Galeopithecus philippensis.

This is one of the most remarkable skulls to be found in the whole of the Eutherian
division of the Mammalia; it is, thus, like the skull of a Serpent
yet specialized, in its own way, to the uttermost. Just now, I am only responsible for

a low type, and

the skull; the structure of all the rest of its organization must be accounted for and
argued about by others; but I must mention the size of its brain-cavity (Plate 39,
fig. 3), as showing how small a brain this creature has. The proportion that the
foramen magnum bears to the greatest intercranial breadth will serve my purpose,
as I cannot go further into that matter. In the adult Guleopithecus philippensis
and in the sub-adult Cuscus maculatus, that opening is two-fifths the greatest breadth
of the skull inside ; in Lepileniuir mustelinus it is only one-third, and in Loris gracilis,
and Pleropus medius, only one-fourth.

In the cranial characters that have been already described in the young specimens
and embryo, I have shown that there are several things that are manifestly Meta-
therian, but these are not the same things as those that show a Marsupial affinity in
the Hedgehog and its allies ; they belong to another set of parts.

I have already spoken of the help the young of Cuscus maculatus—one of the
lowest and most generalized of the Eastern Marsupials—has been to me in the study
of the growing skull of the Colugo, I now find that with the adult skull of that
species, and the adult skull of a great Frugivorous Bat (Pteropus medius) I have
the two extremes, with the skull of Galeopithecus half-way between them. Not but that

this bizarre type has its own unique characters; this might have been expected, for it

264 MR. W. K. PARKER ON THE STRUCTURE AND

is left alone

at most with but one companion—the other species—and its proper’
Family must have suffered very largely from causes of extinction. This is one of the
lightest and most highly polished of all skulls—quite Bird like in this respect, and in
the thorough fusion of all its cranial elements.

The impression that rises first is that it is a foliaceous skull (Plate 39, fig. 4), as
unlike other more familiar skulls, as the Leaf Insect is unlike normal Orthoptera.
The temporal and nasal regions are about equal, the orbital one-third shorter; this
opens into the temporal, behind. The general convexity of the upper surface is made
gently sinuous by the special convexities of the various bony elements of which it is
composed ; these have just been described, and will enable anyone to understand the
finished and fused adult skull, in which, instead of sutures there are fine, and often
clear, depressed lines. There is a supraorbital fossa on each side, as in aquatic Birds, as
though it had a pair of nasal glands; these end sharply behind, and lead to a supra-
orbital foramen, which is further forward than in Pteropus and its allies. Over the
small hemispheres, as in Marsupials, the frontal region is flat, in front, and then rises
gently ; the whole brain cavity has its form revealed in this way by a definite con-
vexity, the outworks being well marked off. The orbit has the posterior fifth
incomplete, for the finely turned supraorbital ridge ends in a large uncinate leaf of
bone, the postorbital process and the jugal has a clean edge, growing up towards the
postorbital process of the frontal; the lachrymal projects inward in the preorbital
region, and forms about a fifth of the actual ridge of the orbit ; its canal is small. In
front of the lachrymal and jugal there is the small, but double, infraorbital foramen.
The ridges on this skull serve the purposes both of beauty and of use ; the hind edge
of the postorbital process curves forwards and then, at its sides, over the swelling
brain-cavity, becomes the supratemporal ridge, which converges towards its fellow,
getting within a half of the front distance, as they meet on the top of the inter-
parietal. There the temporal fossa rounds itself, and is enclosed by the transverse
occipital edge (Plate 39, fig. 4). This large oval enclosure, half as long again as the
orbital territory, has then below it a low oblique wall which is very strong behind, and
runs down over the meatus externus ; and, with two rounded elevations, one small and
the other large, the sharp boundary line passes into the hinder edge of the ascending
uncinate postorbital process of the jugal bone, This outer boundary—orbital and
temporal—is greatly bowed outwards in this depressed skull, in sharp contrast with
the same parts in the neat narrow skull of Pteropus, Along the middle of the
extensive temporal fossa, for the wide origin of the huge temporal muscle, the
convexity of the wall of the skull cavity is clearly seen. The side view of the
temporal region in this skull shows nothing new to the student of the higher
Mammalia, but the form and condition of the parts is both Marsupial and also unique.
Only the narrow outer end of the large transverse glenoid cavity is seen in this
aspect of the skull, but the large postglenoid process, the notch for the deep
tympanic trough, and the part of the squamosal overlying the mastoid process are best

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 269

seen in the side view. Then the post-temporal and mastoid regions are concave, turn
obliquely, and are swollen and sinuous, with the great air-cells within, which are well-
marked on the outside, every cell marking its own convexity. The supraoccipital
ridges, vertical and transverse, can be seen in this view, and the large projecting
occipital condyle.

The end view (Plate 39, fig. 4) shows the gently hollow sagittal region (7.p.) ; the
outspread, foliaceous postorbitals (p.o.); the widely extended glenoidal part of the
squamosals (sq.); the post-temporal region of the same bones, overlapping the mas-
toids (op.); the projections further forwards of the postglenoid ridges, and the free
fore legs of the tympanic (a.ty.). The large foramen magnum is seen to be somewhat
elliptical, with the long axis transverse; over it the supraoccipital forms a low arch,
and on that bone, above, there is a keel, derived first from the interparietal ; and from
the top of the keel or crest a transverse ridge, right and left, enclosing the supra-
occipital region.

The very large condyloid foramina (XII.) are well seen inside the foramen magnum,
in front of the large subpedunculate condyles ; then the occipital arch is constricted,
and the paroccipital ridges are obsolete, but the mastoid grows inwards over that
region, and forms a thin-edged floor to the passage for the 9th and 10th nerves. The
general form of the great hard palate in the adult is oblongo-elliptical, and it is
half the length of the whole basal tract. The anterior palatine foramina are large
and oval, the posterior palatine foramina are moderate, far back, and far apart, lying
in the fossa of the palatine plate of the palatines, close to the junction of these bones
with the maxillaries.

The general surface of the hard palate is gently hollow, margined by the edentulous
part of the narrow premaxillaries, in front, by the large sockets and teeth laterally,
and by the exquisitely wrought, thickened and ribbed edge of the narrow palatines,
behind. These plates grow backwards to receive the crest of the vomer, and then
arching forwards, run round the posterior nares, curving in again to form a waist in
the open part, and then ending in a sharp ridge, turned outwards, which ends in the
small unciform external pterygoid process. Inside these alisphenoidal hooks there is
a more delicate pair of hooks, the hamular processes of the pterygoids. The hinder
edge of each pterygoid is notched above the hook, and then runs backwards and
outwards in a sharp ridge, reaching the foramen ovale. The keel of the vomer ends
between the pterygoids; then the skull is made carinate by the slender acicular
parasphenord, is then gently convex along the middle, and becomes subcarinate in
front of the foramen magnum.

The transverse well-margined glenoid cavities, underlapped behind by the thick
incurved postglenoid process, might belong to some stout Carnivore.

The neat foramen ovale lies between the glenoid facet and the cranial part of the
pterygoid ; behind and inside it is the ragged opening of the Eustachian tube, floored
by the sharp, rough fore lip of the tympanic bone. The keeled bottom of the deep,

MDCCCLXXXV. 2M

266 MR. W. kK. PARKER ON THE STRUCTURE AND

folded meatus externus wedges in between the postelenoid process and the mastoid ;
the latter is an oval, ear-shaped tract, subconcave below, with a limbate margin, and
a narrower hole in its inner, proximal part; that hole is the stylomastoid foramen,
and a small convexity in front of and outside it is due to the fusion, with the mastoid,
of a small epihyal.

Behind and within the ear-shaped base of the mastoid process the smallish opening
for the 9th and 10th nerves is seen. The opening for the 12th nerve, behind, and for
the internal carotid arteries, further forwards, are very large indeed. Only half of the
large strongly curved occipital condyles can be seen in the lower aspect of the skull.

A section of the skull of the adult (Plate 39, fig. 3) shows three convexities along
the dorsal line: the first long, over the nasal labyrinth; the next somewhat shorter,
over the front parietal region ; and the third short, over the ear-capsules and hind brain.
The great septum (p.e.) is ossified over all the proper ethmoidal territory and most of
the proper septal ; this latter is elongated in front by the partition of the snout (s.z.,
al.n.), which hooks, downwards, in front. From it the recurrent or JAcopsoyn’s cartilage
(rc.c.) proceeds, scarcely lessened in relative size since birth (Plate 39, fig. 1, re.c.).
‘The ridge of the perpendicular ethmoid (p.e.), behind and above, forms a very obtuse
angle with its top in front, and a very acute angle with the axis of the skull, behind
and below, thus the cribriform plate lies well down in front of the proper cranial cavity.
The septum bulges downwards in the true olfactory region, and rises again where
the perpendicular ethmoid passes into the presphenoid (p.e., p.s.); inside that part
the optic foramen (11.) and sphenoidal fissure (V'?.) can just be seen. The nasals and
frontals form the wall-plate of the great partition; below, the vomer (v.) has become
fused with the palatine plates (p.m., pa.) dividing the nasal channels, below. Under-
neath, the right channel can just be seen, and further back the palato-pterygoid side
wall (pa., py), and the lip of the tympanic («.ty.) under the Eustachian opening. The
basis cranii (0.s., 6.0.) is thin and sinuous, thickest behind, where it dips and forms the
free fore margin of the foramen magnum. But little sella: depression exists inside
the foramen ovale (V*.). Above, the frontal and parietal (/., p.) form a thinner roof
than in the young (Plate 38, fig. 7); there is a rudiment of the tentorium cerebelli
growing from the inner face of the parietal, and from the fore edge of the auditory
capsule. The arch of the anterior canal (a.s.c.) is well marked, the prootic bone is
crested, roughly, above it ; below, is the deep floccular recess (fi.7.), and below that
the multiperforate meatus internus (VIII), and the bridge over the facial nerve (VIL).
The large openings for the 9th and 10th (IX., X.) and the 12th nerves (XII.) are also
seen in this aspect. Above, the vertical and transverse ridges of the supraoccipital
(s.o.) are seen projecting beyond the line of section, which was on the left of the
middle.

In front of the auditory capsule the septa between the large air-cells shine through
the inner table of the squamosal (sq.).

In the front view (Plate 39, fig. 5) the huge foremost coil of the middle turbinal

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 267

(m.tb.) is seen thrusting itself forward over the feeble inferior, and under the small
nasal, turbinals (7.tb., 7.tb.); here the cartilaginous part of the partition has been
removed, and the front of the bony part (s.7.) is towards the eye; it is hollow below
where it has not ossified, and rests upon the grooved vomer (v.) in front of the palatine
processes of the premaxillaries (pz.). A vertical slice of the skull in the region of
the meatus (Plate 39, fig. 6, a.ty., m.a.e.), and through the glenoid cavity (gl.c.), shows
the large air-cells of the squamosal (sq.) and their somewhat radiating arrangement.

In a part of the hind skull cut across horizontally (fig. 8) the air-cells of the
squamosal and mastoid (sq.,op.) are shown ; where these two bony parts have coalesced
behind, there the cells are very regular and their septa for some extent radially
arranged. In this figure the parasphenoid (pc.s.), pterygoid (pg.), external pterygoid
process (¢.pg.), and glenoid cavity (g/.c.) are shown. The tympanic lip, under the
Eustachian tube (ev.), is not injured, but the dish itself is largely cut away and the small
tympanic cavity (c.ty.) exposed, inside and above which is the small melon-like cochlea
(chl.) and the fenestree (fs.0., fr.), and also the opening for the 9th, 10th, and 12th
nerves (IX., X., XII.) ; the latter are very large, but are only seen obliquely in front
of the occipital condyle (0c.c.).

The lower jaw of this beast might belong to some generalized Herbivorous
Ungulate ; it is indeed almost a miniature of that of the Hippopotamus. ‘To say
nothing of its unique pectinated front teeth, the general shape is very remarkable,
with its depressed mentum, oblong ramus, short uncinate coronoid process, transverse,
sessile condyloid, and deep out-turned angular, process, the edge of which is thickened
inwards ; its whole shape is half a circle.

The malleus (Plate 39, fig. 7, m/.) has lost all its processus gracilis (p.gr.), except
one or two sharp prickles ; the manubrium (mb.) is strong, curved, dilated at its end,
and sinuous outside. The incus (7.), like that of the Ruminants, has a heavy, solid
body, with short processes (s.c.7., /.¢.7.,); the stapes (st.) is somewhat inflated and
hollow behind, and at its base oval ; there is a minute interhyal bone in the tendon of
the stapedius muscle (7.hy., st.in.).

The hyoid bone (Plate 38, figs. 9 and 10) shows a hypohyal as large as the cerato-
hyal (h.hy., e.hy.). The basal bar (b./.b7.) is concave in front, and has a right and left
tubercle hehind ; the thyrohyals (¢.hy.) are large, uncinate, and separate, as bony tracts,
from the base ; all these bones are flat and splintery.

On the skull of the adult Tupaia Javanica.

This is another very isolated form of the Insectivora; I can only mention here
certain peculiarities of the structure to be seen in the adult skull, hoping at some
future time to be able to describe its development.

The Tupaia is another instance to be added to Rhynchocyon and Galeopithecus, in
which a clear prophecy of higher signs of development is combined with characters

2m 2

268 MR. W. K. PARKER ON THE STRUCTURE AND

most unmistakably Marsupial ; the sudden ascent, so to speak, above the general level
in these types has been partial, and combined with a failure to free themselves
from low and archaic characters derived from an ancestry belonging to an inferior
erade.

As to the relative size of the brain this is evidently one of the highest of the
Insectivora; it may be said in this to approximate at once to the Lemurs and
the lower Carnivora. To the Lemurs it is comparable also in possessing a large and
well developed orbital ring, rare in low forms, keeping its own special character
in having a huge oval fenestra in the jugal arch, where the squamosal overlaps the
jugal bone.

The hard palate is less complete than in Galeopithecus, but more perfect than
is normal for an Insectivore. The external pterygoid approaches that of the adult
Petrodromus, where there is a large oblique lamina of bone outside the proper ptery-
goid. But in the embryo of the closely allied Rhynchocyon, at this part there is
manifestly a shell-like tympanic wing to the alisphenoid, as in Marsupials. Here in
Tupaia there is a hole through the root of the external pterygoid process ; this is
evidently the counterpart of the alisphenoidal canal of certain Insectivora, Carni-
vora, &¢.; in size, that process equals what we have in Marsupials. The supra-
orbital foramen is very large, and is further forwards than in Galeopithecus ; in Pteropus
it is still farther back.

But the annulus tympanicus and os bullae are not only well developed, they are
also the almost perfect counterparts of what we find in the lesser Australian Marsupials,
especially Petaurus sciureus; the greater degree of anchylosis, which has completely
fused these two elements of the ear-drum, is the only difference I can find in the two
types. The lower jaw is a good intermedium between that of a Marsupial and that
of a normal Eutherian.

SUMMARY AND CONCLUSION.

Although this paper is confessedly only a fraction of what is necessary to be done
in this polymorphic Order, it at least shows how difficult a group it is to handle.

For the Insectivora are set in the midst of the other Mammalia—low and high ;

they might be called the Biological stepping-stones from the Metatheria to the
Eutheria.

One thing can be done, even now, with the present fragmentary knowledge of the
structure and development of the Insectiyorous types—we can assure ourselves that
these types are immediately above the Marsupials; that they have the Bats
(Chiroptera) obliquely above them; that their nearest relations must be sought for
amongst extinct Eocene forms; and that lowly as they are—arrested and often
dwarfed to the uttermost, so that Nature could not safely go further in that direction,

eee

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 269

they are, one and all, rich in prophetic characters that have come to perfection in
larger and nobler types.

I think it will not be denied that, in the ascent of the types, the Chiroptera are
above the Insectivora, and as it were a sort of special “new leader” from that
stock, and that the Insectivora are more or less transformed modifications of what is
characteristic of the Marsupials.

I suspect that the existing Insectivores just yield the Zoologist one of his groups
of types classed together because he knows not what else to do with them ; not forming
a proper, clear, special branch, or “leader” of the Mammalian life-tree. They form one
group, under one designation, just as the poor of this Metropolis form a group; their
brand is simply lowliness ; they differ, ‘nter se, almost as much as the whole remainder
above them differ. The higher forms, however, because of their elevation can afford to
be subdivided again and again, into Order after Order,

If we could descend and see the transforming and newly-transformed Placentalia of
the Eocene epoch, then the Morphologist and the Zoologist would find common ground ;
the Taxonomy of the latter, however, would be as useless as the titles and distinctions
of modern society to some undeveloped race of savage men.

The evidently extreme specialization of the existing Monotremes or Prototheria, and
their manifest close relationship to the Edentates
almost extinct in the Old World, and not potent in genera and species in the New—

a strange, lowly group of Eutherians,

makes it necessary for me, in the present stage of my research, to leave them until I
have mastered both them and the great Marsupiai sub-class. Of the latter, however,
I can speak already ; and as no interpretation of the meaning of the parts seen in a
Eutherian skull can be made until they are read in the light of the structure of the
quasi-reptilian skull of a Marsupial, I shall in this summary compare the two types
together, using the lower and older as a measure of the higher and newer type of
skull.

Anatomists are familiar with the characters of the skull in adult Marsupials ; to
these may be added others that have turned up to me in the study of the
development of that type. When these are seen in the light of the types outside
and below the Mammalia, then that which is typical in a high Mammal, as such, can
be formulated, and the specialization of this great branch of the Vertebrate stock be
understood.

I will therefore, here, give a list of the more important and striking cranial
characters of the Marsupials, promising to bring forward, as early as possible, the
figures and descriptions of the skull in various stages and in many kinds.

But before making this comparison of the characters of the skull in the Marsupials
with what is seen in the Insectivora, I will state that in the latter—a mere “ Order”—
the diversity is four-fold that to be found in the Marsupials, which are worthy to be
put, not as a mere Order, but as a “ Sub-Class.”

270 MR. W. K. PARKER ON THE STRUCTURE AND

For in these, whether they be Eastern or Western types, the uniformity on the
as remarkable as the diversity seen in the Insectivora.

whole is very remarkable

The problem put to the Morphologist, however, is to explain why the characters
that distinguish a Marsupial from a high or Eutherian Mammal are, for the most
part, characters which the former possess in common with the Sauropsida: the residuum
of proper, unique Metatherian characters, neither to be found in the higher Mammals
on one hand, or in the Sauropsida on the other, is but small.

Another crucial difficulty is this, namely, the Sauropsida, which of all others help
us most in the interpretation of the Marsupial skull, are not those to be found in low
Reptilian, but in the highest Avian, types.

Of all Birds the Passerinze are the noblest and most marvellously specialized for
their own peculiar mode of life, having many accomplishments and high intelligence.

Yet it is from this Order of Birds that I have had most help in this matter, finding
in their skull special structures which closely correspond with what is most remarkable
in that of the Marsupials.

There are several characters in the superficial or investing elements of the skull of
Marsupials that are unlike what we find in the highest forms of placental Mammalia,
but which linger in the lower :—

(a.) The frontals ave very small in proportion to the parietals, and the squamosals
are relatively, especially in the young, inordinately large, as large as the frontals.

(b.) The lachrymals are not only large and have generally a facial plate, but they
have, as a rule, two canals.

(c.) The palatine plates of the maxillaries and palatine bones form an extremely
hollow or dome-like structure, and by the time the creature is full-grown much of
their substance has been absorbed, so as to leave larger or smaller fenestree ; thus there
is an attempt to return to the schizognathous condition of those parts seen in many
Sauropsida,

(d.) The palatines are often formed of several pieces, very irregular patches of bone,
and their irregular centres are largely absorbed or united with the main parts in the
adult.

(e.) The pterygoids are very small, and their basicranial part limited, on account of
the constant separate development of a large mesopterygoid.

(f.) The main vomer is often relatively small; there is, nearly always, a pair of
antero-lateral vomers, protecting the cartilaginous capsule of JACoOBsoN’s organs, and
large postero-lateral, and other, or postero-medial vomers ; these are very irregular and
unsymmetrical in the young Cuscus, especially, in which I find ten vomerine bones.

(y.) The floor of the tympanic cavity ossifies before the cartilage is ripe, but in two
subequal centres—the annulus and “os bulle ”— inside the latter a larger folded
cartilage protects the Eustachian tube, and outside the former the meatus externus is
protected by a more or less segmented tube of cartilage, which ends outside in the
continuous concha auris.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 271

(1.) The jugal (or malar) bone is large, and reaches back so as to he over the
cartilage of the glenoid cavity, thus helping to form the joint.

(i.) The angular part of the lower jaw is greatly incurved, forming a remarkable
hollow inside.

In the endocraniui there are some very curious structures, that differ from what
we find in the high forms of Mammalia, but which mostly agree with what is seen in
the Sauropsida :—

(a.) The nostrils are sub-terminal and give off large tongue-shaped cartilages to
protect JACOBSON’S organs.

(b.) The whole nasal labyrinth is small, especially in the young, not more than
half as large as in an average Placental Mammal, and the cribriform plate is less
depressed in front, and very limited in size, and is square in form.

(c.) The orbitosphenoids do not form the presphenoid by meeting together below,
but the presphenoid is as independent as the basisphenoid.

(d.) There is no special optic foramen in the orbitosphenoid, but the optic nerve
passes through the common sphenoidal fissure with the orbital nerves, and the Ist
branch of the 5th; the 2nd branch, like the 3rd, has its own foramen rotundum, as im
Man, and many other Eutheria.

(c.) The next character is one of the most important: it is this, namely, that the
orbitosphenoids are flush with the alisphenoids. The latter, which are extremely
large, ossify a tract of the general cartilaginous side-wall of the embryonic skull—
and not a free flap of cartilage, merely

the highly developed “ chondrocranium,”
continuous with the basal bar, as in the Eutheria. For in these latter the more
bulky brain pushes out the lower part of the side-wall of the skull, leaving for some
time a band of cartilage, which runs free from the alisphenoid, passing on from the
orbitosphenoid up to the supraoccipital. In front, the orbitosphenoid is confluent
with the ethmoid, so that but for the breach in the wall, made by the alisphenoid,
there would be, even in Placental Mammals, a chondrocranium very similar to that
of the skull. This breach does not take place anywhere among the Vertebrate types
until we get above the Marsupials. The other character just mentioned, namely, the
absence of a special optic foramen, is of similar import; there never is such a foramen
until we are among the Placental Mammalia.

(f) The alisphenoid helps to form the drum-cavity by developing behind its small
external pterygoid process a shell-like growth, similar to the “anterior tympanic
recess” of Carinate Birds. Thus, as the squamosal is a labyrinth of air-cavities,
opening into the upper part of the drum-cavity, these and the tympanic recess in the
alisphenoid greatly enlarge the space for air, Indeed, not only those parts, but the
mastoid region of the auditory capsule, and the sides and top of the occipital arch, all
became pneumatic—as in Crocodiles and Birds.

(g.) The internal carotid arteries pierce the basisphenoid submesially—that part of
the basis cranii is not perforated in the Eutheria,—-and the clinoid processes and the
concavity for the pituitary body are but little developed.

272 MR. W. K. PARKER ON THE STRUCTURE AND

(1.) The limited, suberect, and flattish cribriform plates, and the small frontals are
the necessary correlates of a small brain-cavity and brain. The occipital plane corre-
sponds with those parts, being suberect: it forms but little more than a right angle
with the general basicranial axis.

(7.) In the Marsupials, as well as in the Monotremes, we see the “ ossicula audits ”
i making, so to speak. In all the three subdivisions of this class—Monotremes or

Prototheria, Marsupials or Metatheria, and Placentals or Eutheria—the lower jaw is
broken up, the larger front part becoming the persistent mandible, and the shorter
hind part the malleus, whilst the starved and modified quadrate becomes the cneus.

For a long while in the growing Marsupial the malleus is manifestly a compound
bone; it is an “‘articulare” with an internal and a posterior angular process, as in
the Fowl. On it the “angulare” can be seen, and sometimes, as in the half-grown
Koala (Phascolarctos), a “supra-angular” too.

The working mandible attached to a new pier on the jugal and squamosal is com-
posed of a sort of morphological mixture of a large inferior labial cartilage, a dentary
bone, with coronoid and splenial regions, and the greater part of MrcKeEn’s cartilage
—the true primary ramus.

(j.) The topmost segment of the next arch (pharyngohyal) is often a “columella,”
and not a stapes. In the early young and embryo of the Marsupials it is V-shaped,
its greater front fork enlarging above and forming the inverted base of the columella
or stapes, and the lesser hind fork becoming, after a time, detached and then ossified,
and forming the interhyal.

In Fishes, the uppermost element of a branchial arch (and the hyoid is a branchial
arch) often forks; in the Sturgeon these become two separate pieces, as in this
particular case of the embryo Margupial. There is not much to remark upon in the
rest of the hyoid arch, the functional suspensory part.

For comparison with the Insectivora the existing Marsupials do not yield me all
the archaic characters I want.

For the existing low Eutheria are, of course, the descendants of Metatheria that
were much more generalized and archaic than any now existing ; these latter, during
the whole Tertiary period, must have undergone, on their own low platform, many
adaptive changes that would make them look very strange beside the Marsupials of
the Secondary epoch, if these latter could be restored for comparison.

The best type of Insectivore for general comparison is the Hedgehog (Hrinaceus
curopeus), as it shows the least suppression of parts, and the best development of
that which is diagnostic, so to speak, cf the Order.

In it the greater investing bones of the skull are similar to those of the Marsupial,
but the nasals and squamosals are smaller, and the frontals are larger. In the hard
palate there is a considerable relapse, as in Marsupials, certain tracts of bone being
absorbed, but it has no mesopterygoids, and only five vomers; yet the antero-lateral
pairs are well developed.

DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 273

Moreover the tympanic region has only one “annulus,” the outer bone, There is no
separate “os bull.” Instead of the latter there is a crescentic shell of bone which
grows from the basisphenoid, greatly increasing the size of the tympanic cavity. In
the endoskeleton, in front of the tympanic cavity, there is a remarkable ridge of bone
growing outwards from the alisphenoid. That ridge is the remnant of the alisphenoidal
tympanic wing of the Marsupial, and a shell of bone growing from the basisphenoid is
the same morphological element as the separate “os bulls,” but it has lost its in-
dependence. The higher Mammalian type is fully reached in the thorough freedom
of the alisphenoid from the general cranial wall. This character, indeed, is intensified
into the special diagnostic of an Insectivore, for it lies almost wholly outside the
orbitosphenoid. Here the sphenoidal fissure—which in this case lets out the Ist and
2nd branches of the 5th, but not the optic, nerve, that nerve having its own foramen in
the orbitosphenoid,—is not a mere gap, but a side passage, a sort of sphenoidal
corridor, right and left.

In these things the Hedgehog is higher than the Marsupials, but in some others it
is lower, or more archaic. These latter characters, which suggest an uprise from a
more generalized type than the existing Metatheria, are—irst, the development of a
considerable rod of solid hyaline cartilage in the pterygoid region, a remnant of the
pterygo-quadrate of the Ichthyopsida ; and secondly, the presence of a persistent
pituitary hole, which is connected with a curiously specialized structure, only seen in
typical Insectivores, namely, a hollowing out of the basis cranii beneath the pituitary
region.

A third archaic character, not seen in the existing Marsupials, is the huge relative
size, long persistence, and separate distal ossification of MEcKEt’s cartilage, so that in
the embryo Hedgehog, and even in the Nestling, the primary lower jaw is as large as
in Fishes, generally, scarcely excepting the Selachians. ;

The ossicula auditts are typically Eutherian ; we have lost the imperforate stapes or
columella, the interhyal is very small or absent, and the malleus and incus are
much like what we find in the higher Mammals generally. The pneumaticity of the
skull is much reduced ; and the olfactory region is almost double the relative size of that
of a Marsupial. In the head of another family of the Insectivores, namely, the Mole
(Talpa europea), there is much that is in accord with what is found in its distant
relation, the Hedgehog, but in it there are evident signs of degradation, or of relapse
into what is Marsupial in character.

The nasal labyrinth is relatively immense, and the skull walls below, laterally, and
behind, are as exquisitely pneumatic as in the Flying Marsupial (Petaurus), the Bird,
or the Crocodile. The swollen basis cranii, all air galleries within, is so excavated that
the hinder sphenoid, both base and wings, largely helps the flat single tympanic to
form the drum-cavity.

The pituitary hole does not exist, but there is a considerable pterygoid cartilage ;
the ossicula, in the adult, are normal, but a curious special character is seen during

ossification, In the young the bone grows along the sheath of the stapedial artery,
MDCCCLXXXY. 2N

274 MR. W. K. PARKER ON THE STRUCTURE AND

which for a time hoids the stapes in its place ; it is, however, absorbed afterwards, but
remains in the related genus Myogale. In nearly half-grown young Moles the malleus
is quite like that of the Marsupials, and it is an evident articulare, with copious wild
growths of bone, sub-distinct and answering to the “angulare” and “supra-angulare”
of a Reptile or Bird. This malleus in its articular part has two endosteal and one
ectosteal bony centres. Mrcken’s cartilage, long continuous with the malleus, is
nearly as massive as in the Hedgehog, and has a more distinct separate ossification in
its subdistal part—a long independent, but temporary hypobranchial bone.

The Mole shows a most remarkable development of the endocranium, which, twenty
years ago, suggested to me that its skull retained unmistakable Monotrematous
characters. In the large young of the Echidna and Ornithorhynchus the solidity of
the chondrocranium is immense—like that of a Chimeroid Selachian—and the investing
bones are thin and splintery. Ihave not made out the mode of ossification of the
inner skull in those types, but im spirit, if not in the letter the Mole agrees with them,
that is in the great development and independence of the inner skull. The “opisthotic”
bones ossify the normal petromastoid region, whilst the “prootic” bony centre
begins in its right place on the front edge of the cartilaginous capsule and then runs
away from it into the wall of the skull; thus there is a large bony tract in the
temporal region, between the small squamosal and the large interparietal, which is not
one of the ordinary outer cranial bones, but an endocranial bony tract, overshadowing
and yet imitating the true temporal bone or squamosal. This bone is represented by
three separate centres in Osseous Fishes, namely, the prootic, pterotic, and sphenotic,
whilst their true auditory region is ossified by the epiotic and opisthotic ; the epiotic
is only subdistinct in the Mole.

If I am asked why I dive so far down for my illustrations instead of being satisfied
with what Reptiles and Birds would show me, my answer is that those are often of
no use for comparison, for they are as thoroughly specialized for their own mode of life
as the Mammalia, generally, and are as completely, and often more completely, trans-
formed from the original archaic type or types.

Thus the Mole, like most of the Edentata lately described by me, suggests as the
root-stock of the Eutheria, generally, not Marsupials (Metatheria) as we know them,
but Prototherian forms, in which, in ages long past, the existing Monotremes and
Marsupials had a common origin.

The Shrew (Sorex vulgaris) represents another family of the Insectivores, the
Soricide. It combines the characters of the Mole and Hedgehog with peculiarities
of its own that are manifestly due to dwarfing ; many things are suppressed, as if
there was not room in so small a skull for their development. The pituitary hole
re-appears, and the pterygoid cartilage—but the tympanic wing of the alisphenoid
and of the basisphenoid are gone; the malleus does not show itself so unmistakably
Marsupial, and Mrckev’s cartilage is slenderer. The sheathing alisphenoids are well
seen ; the squamosal is small, low down, and devoid of a jugal process ; the jugal bone

is suppressed,

a
ial

DEVELOPMENT OF THE SKULL IN THE MAMMALIA, 2

So much for the British representatives of three families of the Insectivora—the
Erinaceidee, Talpidee, and Soricide. .

The Mascarene Insectivora are all so evidently related as to suggest at once a
common origin ; these are the Centetidee, the largest of which is the Tenrec (Centetes
ecaudatus) ; the other genera treated of in this paper are Hriculus, Henmicentetes, and
Microgale.

These are almost typical Insectivora, but they agree with the Shrews in having the
jugal bone suppressed ; they are also more Marsupial than our native kinds.

In these types the normal characters of the skull of an Insectivore are combined
with a remarkably Marsupial tympanic wing to the alisphenoid, but the os bullee is not
free, it is merely an outgrowth of bone from the basisphenoid. The pituitary hole is
present, and in the larger species the curious basicranial excavation ; also the optic
foramina ; whilst the sphenoidal side passages are remarkably developed.

As in the genus Phalangista among the Marsupials, and Talpa and Sorex among
the British Insectivora, the antero-lateral vomers are evidently suppressed, or have a
very temporary independent existence. The postero-lateral vomers are rather small,
as in the Hedgehog.

In the embryo the main vomer is relatively as large as in the embryo Whale, and is
curiously cellular or spongy.

In Nestlings this one primary azygous centre has broken up into three; one, the
largest, above, and two lesser, below, sheathing it, as it sheathes the base of the nasal
septum. Now this multiplication of the vomers, proper, is thoroughly Marsupial ; it is
unique, as far as I know, in the mode of its subdivision into secondary bony centres.

In the African (Continental) Family of the Elephant, or Jumping, Shrews (Mascrosce-
lidze), as illustrated by the largest forms—Petrodromus and Rhynchocyon—we have a
curious mixture of Marsupial (Metatherian) and Eutherian characters, so that they
‘are very abberant as Insectivores.

The Marsupial characters are most remarkable, these are: 1, the absence of an
optic foramen; 2, the alisphenoid, scarcely overlapping the orbitosphenoid ; 3, tym-
panic wings to the alisphenoid, well marked hollow shells in the embryo; 4, large
antero-lateral vomers and postero-lateral vomers as large as in average Marsupials,
and, as in many of them, meeting and uniting at the mid-line; 5, a large, distinct
“os bulle,” which makes a tympanic cavity as large as, and much like that of,
Petaurus or Phascolarctos.

On the high Eutherian side we have, in the embroyo, frontals as large as the parietals,
and, strangest of all anticipations of Mammalian specialization, a long proboscis, com-
posed of thirty double rings of cartilage, a structure quite similar to the proboscis of
an Elephant. The mesopterygoids are suppressed, but the pituitary hole is present.

Galeopithecus and Tupaia are manifestly annectent. I shall treat of them, again,
when I come to the Bats and Lemurs.

2N 2

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

List OF THE ABBREVIATIONS.

The Roman numerals indicate nerves or their foramina.

ag. Angulare.

ag.p. Angular process.

ale. Aliethmoid.

al.n. Alinasal.

als, Alisphenoid.

al.s.c. Alisphenoidal canal.

al.sp. Aliseptal.

apf. Anterior palatine foramen.

a.s.c. Anterior semicircular canal.

at. Atlas.

aty. Annulus tympanicus,
On. ~ Axis,

au. Auditory capsule.
b.a. Basilar artery.

b.h.br. Basihyobranchial.
baun. Basimandibular.

bo. Basioccipital,

b.pg. Basipterygoid process.
bs. Basisphenoid.

C. Brain.

cau. Concha auris.

cd.p. Condyloid process.
chi. — Cochlea.

chy. Ceratohyal.

c.p. and cr.p. Coronoid process.
erg. Crista galli.

erp. Cribriform plate.
ctr. Cornu trabeculie.
c.ly. Cavum tympani.

d. Dentary.

dic. | Dentary canal.

e. Hye.

chy. Epihyal.

en. External nostrils.
eo. Exoccipital.

cp. Epiotic.
epg. External pterygoid.

CU. Eustachian tube.

7: Frontal.

fa. Foramen magnum.

jur. — Floccular recess.

fo. Fontanelle.

fir. Fenestra rotunda.

fs.o. Fenestra ovalis.

gl.c. Glandular crypts.

yf and gl.c. Glenoid cavity or cartilage.
hy. Uypohyal.

h.s.c. Horizontal semicircular canal.
i. Incus.

i.ag. Internal angular process.

Gs Internal carotid.

iby. Interhyal.

ifl. Inferolateral fontanelle.

if. Internasal fenestra.

inf. Infundibuluin.

ip. Interparietal.

i.tb. Inferior turbinal.
it. Intertrabecula.

1v. Investing mass,
VE Jugal.

j.o. J ACOBSON’S organ.
z Lachrymal.

Le. Lachrymal canal.

led. Long crus of incus.

ls. and s.c. Lateral sinus.

le. Larynx.

m. Mouth.

m.a.e. External meatus

mb. and manl. Manubrium mallei.
m.c. Meatus cartilage.

m.g. Mucous gland.

mk. MEcKEL’s cartilage.
ml. Malleus.
mn. Mandible.

MR. W. KE. PARKER ON THE SKULL IN THE MAMMALIA.

ms.pg. Mesopterygoid, p.t. Post-temporal.

mt.c. Mastoid cells. ptr. Posterior tympanic recess.
m.ty. Membrana tympani. pty. Pretympanic process of malleus.
ma. Maxillary. _ pe. Premaxillary.

n Nasal. py. Pituitary region.

nC. Notochord. rec. Recurrent cartilage.

nf. Nasal floor. rub. Recessus vestibuli.

up. Nasal passage. s.a.c. and s.t.c, Supra-auditory cartilage.
u.p.c. Nasal palatine passage or canal. — s.ag. Supra-angulare.

nth. Nasal turbinal. sc. and Ls. Sinus canal.

nv. Narial valve. sci. Short crus of incus.

ob, Os butllee. su. Septum nasi.

oc.c. Occipital condyle. | S.0. Supraoccipital.

op. Opisthotie. sob. Supraorbital.

0.8, Orbitosphenoid. | sp. Splenial.

p. Parietal. | sq. Squamosal.

pa. Palatine. _ sg.c. Squamosal cells.

p.ag. Posterior angular process. «st, Stapes.

p.cl. Posterior clinoid. LSet Supratemporal.

p.e. Perpendicular ethmoid. | sta. Stapedial artery.

pg. Pterygoid. _ sth. Stylohyal.

pg.c. Pterygoid cartilage. _ stm. Stapedius muscle.

pg. Postglenoid process. _ tals. Tympanic wing of alisphenoid.
pgr. Processus gracilis. i.b.s. 'l'ympanic wing of basisphenoid.
phe. Pharynx. | tg. Tongue.

p.m. Palatine plate of maxillary. | the. Thyroid cartilage.

pn. Posterior nares. | thy. Thyrohyal.

pu. Pneumatic foramen. ir. Trabecula.

p.ob. Postorbital. tt. Tentorium.

p.oc. Paroccipital. t.tm. Tensor tympani.

p-p.f- Posterior palatine foramen. tty. Teomen tympani.

p.px. Palatine process of premaxillary. | wtb. Upper turbinal.

pr.o. Prootie. utr. Upper tympanic recess.

ps. Presphenoid. _v.,v., Vv’, Vomerine bones.

p.s.c. Posterior semicircular canal. vb. Vestibule.

Figures.

10
11

MR. W. K.

PLATE 1.

PARKER ON THE SKULL IN THE MAMMALIA.

Number of
times
magnified.

Embryo of Unau (Cholopus didact og ; about half ripe
(1st stage); side view

The same ; front view

Early ante yo of iui ens

front view

? sp.) (Ist stage) ;
The same; side view bes So ee ee
Advanced embryo of Panvelin (Manis brevicaudata),
from Ceylon (2nd stage); front view

The same; side view

Embryo (one-third ripe) of ernie (I. atusic th Ae id
(1st stage); side view

The same; front view

Head of nearly ripe embryo of Aart: vane (0% spits ‘opus
capensis) ; upper view

The same; side view

The same; front view

nat. size.
ditto

1
lg

iT

Py)

1+

nat. size.
ditto

4 nat. size.

ditto
nat. size.

885 Plate |

I

Phat. Trams

Weet, Nevonan & Co imap

PLATE 1.

Number of
times
macnifiod.

Eanbevo of Unau (Cholopus vulseta'us); about half ripe
{ist stag~e}; side view .

nat. size.
ditto

front view

Retly pies 2 Purgolin (Manis ! sp.) (1st stage) ;

ir (>. 2 2 ld,
The see cu: & tee 13
AG ent Fy 1, vepieendate),

Hearn ' nat, size.”
w te ditto

jvat stare): side yiew a ad 2
Tus came; frontview .. : 2

Head of nearly ripe on Aer’ Vark (Or ycteropus

ipensis) : power yw 4 nat. size.
ditto

nat. size.

‘bi’ Qyrae ! side yew

front view. sas @ se Ge a el

int Saye

tm

Phil. Trans. 1885 Plate |

West Nevonan & Co von}

} Parker & Coward delethth, ~

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA,

PLATE 2.

Figures.

Number of
times
magnified.

Tatusia hybrida (1st stage) ; embryo 13 inch long (snout
to root of tail); section of skull; inner view .

The same*; fore part of lower jaws; upper view

The same ; lower jaw; inner view

The same ; auditory region; outer view ee ee

The same; part of ethmoidal region, with turbinals
exposed, and rudiment of cribriform plate shown

lower view :
The same; skull; upper view
The same; skull; side view

Tatusia hybrida; 2 inches long (2nd stage); skull;

—
“I Co ST
Dl Wi Wl wl

a
~“N (J)
whe

lor er)

* This figure is not numbered on the Plate; it is below fig. 4.

: Prrvile or Phil. Trans. 1885. Plate 2. ©

va

-boamnie

iv
Parkes & Coated). Weet Newman stump

WHT del

lat eT ee et. Se

y ae a) bur ay : Pep ii Hy
it ih
ip a lie

MK.W. K. PARKER ON THE SKULL IN THE MAMMALIA.

7 -
PLATE 2
7
gas (75; ee ae !
: | Figures.
: |
ioe 5 fet See et Oe os es es er 1
|
i | 1 | Patusia hybrida (st stage); embryo 13 inch long (snout
V4 | | to root of tail); section of skall; inner view. . . .
: | 2 | The same*; for: pact of lower jaws; upper view .
’ . *
| 3 | The same; lower jaw: innerview. . . ..
4 The same; auditory region; outer view ae?
5 The same; part of ethinoidal region, with turbinals |
| exposed, amd rudiment of crilifua plate shown . 5
6 | Tatusia hybrida; 2 inches iorg (2nd stage); skull; |
| lowerview . . : |
7 | The same; skull; upper view
8 | the same; slealie veils eet ele Pes ees Le |

a 0 RS

* This tigure is not numbered on the Plate; it is below fig. 4.

Parker. Phal. Trans. 1885. Plate 2.

byrne

Parker & Cowerd |ith West Nevansan &Coimp
WK P dei

MR. W. K. PARKER ON

THE SKULL IN THE MAMMALIA.

PLATE 3.
| Number of |
Figures. times
magnified.
|
1 Tatusia hybrida (1st stage); embryo; 13 inch long; Ist |
of a series of vertically-transverse, thin, transparent |
sections . - = | 24
2 The same; 2nd section . a 24
3 The same; 3rd section . | 24
4 The same; 4th section . é | 24
5 The same; 5th section . : 24
6 The same; 6th section . 24
" The same; 7th section . 24
8 The same; 8th section . ee ee ae 24
9 The same; part of 9th section . . . . . . =... 14
9A (read 10); The same; 10th section 14
a The same; 11th section 103
ae, The same; 12th section . . » »« +. + « + 103
a The same; part of 17th section (Plate 4, fig. 5) 125

i
=
ug
~
9 is
D ” :
| 2
j 2
E ~— : :
74 Semcon o — ee 7
E 4 es eatin ta shoe Fis ae? ots ;
~ E F 5 be ® yo af. Bp oF * . c
4 i #BS . = }
7 F ; f ;
a
~

teanosy xy wr ee ee

Figures.
t

1

|
| |
| |

‘

6

9.4 (read 10);
| ji

|
L At pl

The same ;

‘a ra alll,

,

Riek, W. K. PARKER ON THE SKULL

PLATE 3.

Tatusia Aybrida (1st stage); embryo:
of a series of vertically-transverse,

sections .

| The same; 2nd section .
| The sanie; 3rd section .

The saroe; 4th seetion
The same:

The same;

5th section

6th section .

7th section .

The same; 8th section. .
The same; part of 9th section
10th section

{1th section

12th section

The same ;
The same ;
The same;

The same; part of 17th section (Plate 4, len 5) eae 125

IN THE MAMMALIA.

12 inch long; 1st |
thin, transparent |

24

|
| 24

Phal.Trans. 1885. Plate 3.

x 2H

2

1x 24

Ca

Bes @

oq) oP
12 09 @d @s

@@x 4”

a, eta aap

20 so 0d Gow

>
oP &
Pen te a? we

®

a=

© ad

= Wana ae

/ >)
ao ©

s

RIUN — Ba =

a

& Coward del et hth

Parker

np

t Newmand& Co ix

Tatusia hybrida

MR W, K, PARKER ON THE SKULL IN THE MAMMALIA,

PLATE 4.

Figures.

Number of
times
magnified.
(Continuation of same series); 13th section . 103
The same; 14th section 104
The same; 15th section 103
The same; 16th section 104
The same; 17th section 103
The same; 18th section 104
The same; 19th section 12
The same; 20th section 12
The same; 21st section i
The same; 22nd section 1
The same; 23rd section 12
The same; 24th section 12
The same; 25th section i,

Phil. Trans.1885 Plate 4

& » 1042 -

a emp ssineaa Mab Ion saan
TOE oie

pe a |

oy Sal ed

oie

A2ees ee

TE.

a

egg EEE Sy

ge

eee

West, Newman de Co imp

Tatusia hybrida,

Figures.

im 09

5
6
7
vy

vy

MR W. K, PARKER ON THE

oy iii
; int , ; Car
es : ae S ty a) ae
SKULL IN THE MAMMALIA,

7 5 : _ 7 7 :
| |

PLATE 4.

(Continuation of same series); i3th sevtion .

The same;

14th section
15th section

: 16th section
: 17th section

he same :
‘he same ;
Y

he sarae ;

8th seclion
14th section
20th section.

; 21st section
e: 22nd section

| The same ;
The same ;
The same ;

28rd section
24th section
25th section

. . * * *

Phil. Trans. 1885 Plate 4

x 10%2 + x 1072

Parker & Coward deletlith West,Newman & Co imp
WK? dir on
Tatusia hybrida

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 5.

Number of
Figures. times
magnified.
1 Tatusia hybrida; embryo; 3 inches long (8rd_ stage) ;
endocranium; upper view... .... . 32
2 The same; endview. . .. . 33
3 The same ; auditory region; outer view . . . . « . 13%
4 Tatusia hybrida; embryo; 2 inches long (2nd stage) ; .
auditory region; outer view . . ; 13%
5 Tatusia peba; embryo ; 3 inches long (4th ae skull ;
lower View = wea Ree eee es 348 33
6 The same ; vertical section of skull; inner view . . . 33
‘é The same; skull; endview . ..... - 33
8 The same; ossiculaauditis . . . . . . 114

Phil. Trans. 1885. Plate

=
West,Newman & Co 1mmp

W.K.P del.
Parker & Coward hth.

1-4,Tatusia hybrida,; 5-8,T peba.

or

MR. W. K, PARKER ON THE SKULL IN THE MAMMALIA,

Tatusia hybrida; embryo: 2 taches long (3rd stage);

endocranium ; wpper vies il ea
The same; end view. . ul
The same ; auditory region; wuwter View . . . . . |
Tatusia hybrida; embrys; “ saches long (tnd stage);
auditory region ; outer vio

Tutusia peba; embryo ; 3 inctes long (4th stage); skull;
lower view... .

The same ; vertical seetion or akull; inner view . . .

The same; skull; endview . . .....

The same ; ossicula auditts

Namber of

times
magnified,

Phil. Trans. 1885. Plate 5

pag

mean - -

Pov ‘s.0
West, Newman &Co am

WK.P del
Parker & Coward hth

1-4,Tatusia hybrida ; 5-8,T. peba

_——-- ~~

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA

PLATE 6.
|
_ Number of
Figures. | times
| magnified.
|
ik | Tatusia hybrida ; ripe embryo ; 4 inches long (5th stage) ;
skull ; lower view. 24
| The same; upperview. . . . . . . .. ss + 24
3 The same ; side view 24
34 | The same; lower jaw ; inner view 24
4 |The same; end view. 21
5 | The same ; os hyoides ; under view 24
6 The same ; ossicula audittis ; outer view . 64
7 The same ; auditory capsule ; inner view . | 6
8 The same; outer view... ... .... ~~. | 6
9 Tatusia peba ; new born (#); 4% inches long (6th stage) ; |
endocranium; lower view . . . . . . . ss =| 24
10 The same ; os hyoides ; under view. 3
Li The same ; auditory region ; outer view | 6
|

Phil. Trans 1885. Plate 6.

re)
” erect

W.K.P del |
Parker Chard dith | West, Hewman%&Cormp

t 1-8,Tatusia hybrida; 9-11,T. peba.

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 6
= ) Namber ot
Figures. | i times
| | | magnified.
ae aa, Oe re Oe nae.
| 1 | Tatusia hybrida ; ripe embrve 5 4 incives long (Sth stage); |
| skull; lower view. 24
| 2 - The same ; upper view . 24
3 The same; side view . . . . . ae eee 24
| 34 | The same; lower jaw ; inner view . eye te 24
4 The same; endview ... . wee en als 24 |
| 5 | The same; os hyoides; under view ee ie 22
| § The same ; ossicula andittis ; outer vie = oe ee 63
7 The same ; auditory capsule : inner view yeas a 6
| 8 | The same; outer view 4 ~ vt iyeual. 6
| 9 | Tatusia peba; new born (7): 44 inohes loug (6th stage) ;
| endoecranium; lower view . . . cae SA 24
10 | The same; os hyoides; under view. . . . . .. . 3
\1 | The same ; auditory region ; outer view 6

Phil. Trans 1885. Plate 6.

nem

nuty ay

W.K.P del West, Tiles 7
Parker ® Coward lth Vest Tlewrnan & ine
1-8,Tatusia hybrida; 9-11,1 peba

Figures.

a oF

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 7.

Number of
times
magnified.

Dasypus villosus; ripe embryo; 43 inches long (5th
stage, continued) ; skull; under view

The same ; upper view .

The same; side view .

The same ; lower jaw ; inner view .

The same; skull; end view .

The same ; os hyoides ; inner view .

The same ; ossicula auditis; outer view...

. tamed 4c
Pam ee. p.0t

vir

if

re i

& Covrara ki Ga

Wee Pornan &Co imp

Dasypus villosus.

2 7
MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA,
: : a : : :

LN

.

PLATE 7.

Figures.

ee eee

cee
Dasypus villosus; sipe embry» <_ inches long
stage, continued); skull; under view
The same; upper view. . . . .
The same; side view A
The same ; lower jaw ; inner view |
The same; skull; end view . :
The same ; os hyoides ; mner meu |

The same ; ossicula auditis; outer mew .
a ?

Phil. Frans 1885 . Plate

rr

-stm™

rreonl

West, Newman & Co nmp

Parker & Coward lith
W.K P. del ac nat.

Dasypus villosus

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 8.
Number of
Figures. times
magnified.
1 Unau (Cholopus didactylus) (2) ; embryo ; 31 inches long
(1st stage) ; skull ; lower view . <i 4
2 The same ; upper view . 4
3 The same ; side view 4
4 The same; end view eee 4
5 Ai (Bradypus, Ayeiopnemne ate 7 sp) ee
5 inches long (2nd stage) ; skull ; lower view . ; 3
6 The same ; side view : 3
( The same ; right malar bone . ; : 3
8 The same ; nasal region of skull; side view of oui 3
9 The same ; showing turbinals. 3

Phil. Trans.1885. Plate 8.

WKB; slats

1-4 Cholopus, 59 Bradypus.

wT,

; i) iv

MR. W. K. PARKER ON THE seUUL IN a MAMA AI TA.)
it 7 -

PLATE 8.

Figures.

—— nn A re ee eee neers

1 Unau (Cholopus didactylus) = > emiryo; 3 + inches long
| (1st stage) ; skull; lower view > ames tek OUST 4
i 2 The same; upper view. . . . ; ae Ny
: | 3 | The same; side view . . . . © ; | 4
| 4 The same; end view . . Lb) 4 nh! Rene
5 Ai (Bradypus, Aa erat cere 7 SP. 4; embryo ;
7 5 inches long (2nd stage) ; skull; loser view .. 3
6 The sames, sideeiew) isa. eeetic A) te th eae © a)
; | 7 The same ; right malar bone. . . “roe 3
| 8 | The same ; nasal region of skull; side vow of been ; 2
9 | The same ; es turbinals. ; | 3
Sa & |
|
:

Parker & Coward
WK_P. delad nat

1-4 Cholopus,

C
c

J ae

~o Bradypus

‘iy

Phil. Trans. 1885. Plate 8

ce

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 9.

Number of
times
magnified.

Figures.

1 Cholopus Hoffmanni ; young ; 8 inches long (3rd stage); |
Bicalleselower view secs) gaan ee nen nie eens uae

g The same; upper view

3} The same; side view ... .. ... «6 5. 6

4 Whesames end wiew., « ; . « 2. #8. # « =e

5 The same; lower jaws; underview . ..... .

6 The same; ossicula audittis ; inner view ; :

7 The same ; ossicula audittis and auditory capsule ; outer
WHEW cas eee ee ce ce

8 Bradypus (Arctopithecus) (2nd stage); lower jaw and
ossicula audittis; Imner view . . . . . . ee

9 Cholopus didactylus (%) (1st stage); the same parts ;

Ue VANE 4 4 5 9 4 56 G o 6 & 6 ee

ot

fee
Ot CU Ole oe or)

Or

Phal. Trans. 1885. Plate9.

0 MI Pct oh wie
el) Piycter ®. Covarh itch,
CUE a eee ie L= "489 Cholopus: @ Bradypus.

. Poe
MR. W. K. PARKER ON THE SKULL IN THE MAMMATIA. : Pd

PLATE 35.

Number of
times
magnified,

i Cholopus Hoffmanni ; young ; 8 inches long as sissy ast: Oa
skull; lower view . Om) Pan ea ‘1 14

ys The same; upper view . | 14
3 The same; side view si 14
4 The same; end view. — | te
5 | The same ; lower jaws; under view i¢
6 | The same; ossicula audiitis ; inner view eo 6
7 | The same; ossicula auditts and auditory eepeue ; outer |

| view... eval 6
8 | Bradypus (Avibopithena\: (2nd phage) ; ras jaw and

| ossicula auditis; Inner view . . . . 1... es 4
9 Cholopus didactylus (2) (ist stwge); the same parts ;

- iter viewe © fj oe Gees O el awed 02 re 6 |

‘

Phil. Trans. 1885. PlateY.

5 Le ie basen Lith West Newman%Co imp
l-7&2 Cholopus: 8 Bradypus.

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 10.

| Number of
Figures. times
| magnified.
1 | Cycloturus didactylus; young; head, 14 inch long;
skull; lower view . 3h
2 The same; upperview. . . .... . ae 34
3 The same; side view . . . «© 2 4 » « « « 3g
3A The same; lower jaw; innerview. . . ..... 35
4 The same ; end view of skull. . & 33
5 The same species; larger specimen; 44 inches long ;
head, 14 inch ; ossicula auditiis ; outer view . 10
6 The same ; os hyoides; inner view. . . . . 10
7 The same ; vertical section of skull; inner view 31
8 | The same; part of skull, showing turbinals 3h
9 |The same species; lesser specimen; temporal region
oblique; lower view. . . ..- =.=. -+46-. 62
10 The same; larger specimen; vomer and related parts ;
nieve Valve fees os 5 ol 6 US Ul UC 6

Phil. Trans 1885 Plate 10.

West, Newnan & Cop

aT lee Wi

id il

White T " on i r

WOM PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 10.

Cycloturus didactylus; young; lead, 34 inch long;

The same; larger specimen; vomer 24) isda parts ;
lower view . tol T1 ta alee Dee ln Ps Pee oo ee 6

skull; lower view . 3h
2 The ganing tupperwview.. 2) 4 be ede ee fay meee ls 34
3 | The same; side view ... . 5t
34 | The same; lower jaw; inner view 3}
4 | The same ; end view of skull . We Ld 35
& The same species; larger specimen; 4} anes long ; |
| head, 14 inch; ossicula audittis ; outer view / 10
6 | The same; os hyoides; immerview. . . . . . ..{| 10 )
7 | The same: vertical section of skull: inner view 3h i}
a The same; part of skall, showing turfnals . 35 '
7) 9 The same species; lesser specisnen; temporal region |
t oblique ; lower view . | 62
|

Phil. Trans 1885 Plate 10.

Sos hiner emsatanrenostent

NID XX & ty Vib

West Newman &Co ip

W.K.P. del.adnat
Parker & Coward lith

Cyecloturus

MR. W. K, PARKER ON THE SKULL IN THE MAMMALIA.

———ooreee

PLATE 11.
Number of
Figures. times
magnified,
1 Pangolin (Manis ?sp.); embryo; 23 inches long
(1st stage); skull; lower view® . 4
| ye The same ; upper view . 4
3 The same; side view 4
4 The same ; end view 4
5 The same ; os hyoides ; upper view 4
6 The same ; lower jaw and auditory region ; inner view 6
7 Manis brevicaudata; embryo; 43 inches long (2nd
stage); skull; sideview ... . « - «== « %| C
8 The same; under view. ....... . . . 4.4 2,

* All the parts behind b.o. and oc.c. should have been drawn in shade; they belong to the roof.

Phil.Trans.1885 Plate 1. |

thot

eh le

tire , ght fw al.

) WP del ad mat

J +) Parker Cowardhte,

Mearils.

47 ih : °1 te ip
lo » . 7 5 ee it cee -

WR W. K PARKER ON THE SKULL iN THE

PLATE 1:

irau
x umber of

| | r times. a ‘|
i Pi magnified, |
- SMa octet one Be ee ee
| 7
? 1 | Pangolin (Manis —— ? sp.); embryo; 24 imches long
v | (ist stage); skull: lower view’ 2 2.) sil : 4
- 2 i The same; upper View 4.0. 2). 4). F 4
y 3 The same; side view ore .4 4
- ! 4 | The same; end view : -? : ed 4.
’ 5 | The same; os hyoides : iss oer ao rn oe | 4
| 6 | The same; lower jaw anc aoditory region ; Inner view . | 6 |
| 7 | Manis brevicaudate; emiege. 4% inches long (2nd (aie
| stage); skull; sideview . 2. (0. 6 1 4. so] 2
8 | The same; under view . ee ey rer) ee ee | ay

* Ad) the parts bebind 6.0. and os.c. should have been drawn in shade; they belong to the roof.

Phil.Trans.1885 Plate 11.

bowen + -_

H ty
mk ear r] ee :
wieml AX “hl anty

r bovere

ml

\

y

re

iy Ya ee g

/ bmn ; gh fmm

‘ WKP del ad wat cd.p ;

' Parker Coward hth. West,Newman & Co.1m}
Manis

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 12.
| | | Number of
Figures. | times
magnified.
] 1. 7 7
| 1 — Manis brevicaudata (as in figs. 7 and 8 of last Plate) ;
| ‘skulls upperyiew* . = 2.5) « =» om « fe 3
2 | The same; endview. ... . 3
3 | The same ; os hyoides ; inner view . 3
4 | The same ; lower jaw and ossicula auditts; inner view . AL ;
5 The same ; both lower jaws; fore part of under view. 44 |
6 Manis Temminckii ; young; 2nd day after birth; head, | | |
2+ inches long (3rd stage) ; skull; lower view g | .
vi The same ; upper view . 2 |
8 | The same; side view ....... .. .. . | 2;
9 |The same; end view. 2
10 | Lower jaw; inner view. . . . . . . . 2
iY | The same part; with ossicula auditis ; inner view. . . 22 |
12 | The same; stapes and part of incus 8 |
13 _ The same ; os hyoides ; inner view . 22 ‘
= a 7 eee .
* In any want of correspondence between the number of times a figure is said to be magnified, on

the Plate, and in the descriptive page, the latter gives the true number.

Phil. Trans.1885. Plate 12.

WAP del aduat
-~ Parker & Coward Lae

7 Manis.

_

iy
:

;
a -
MR. W. K. PARKER on. me SK Ub IN HU : ita,

7 ee

' : mi

_ PLATE 12 li
7. : _
- Dc Aik ips eae ie
te Me
: | Figures. | 3 fh
ae eke Doe ees. |
7 ee a
| 1 | Manis brevicaudata (as in figs. ?
: a | | Bletil: lpper view?) 1 ba Ws ele la) eee .
; | 2 | Thesamey Onc, Few) 2 bas als! oe plone! 3D
| 3 he same; os hhyoides: immerview. . 2... 2...
" 4 | The same ; lower jaw aa/ casicula anditis; inner view .
7 5 | The same : butt lower jo : fore pert of under view. .
a. | 6 | Manis Temmriski ; young ¢ Bnd « tay sifter birth; head,» 7a
| | 24 inches jong ard stage sku, lower view . .. | 2
: | 7 The same ; upper view . ; : 2
| 8 | The same ; side view : 2
m | 9 | The same;‘end view 9. «3: «es 42) us 2
i a) | Lower jaw; inner view. . . a et eee rae
il | The same part; with ossicula andittis : ; inner view. . 22
bb. | The same; stapes and part of incus . . . . a
| 13 / The same ; os hyoides ; inner view . 22
H | P}
a 7 a. oer ie eee Ay ono) Site (ae
~~ * In any want of correspoudeuce between the number of times a figure is aud to be ninguited, of

_ the Plate, and in the descriptive page, the latter gives the tre number.

Phil.Trans.1885. Plate 12.

bmn

West Newnan &C® imp

WK.P del. adnat
Parker & Coward lith

Manis

MR. W. k. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 13.

bo

oo - CO

Number of |
times |
| magnified.
Manis Temminckii (3rd stage); left part of basis eranii ;
la Wervicw aa bree ce: Sc. Se ee ea 3
| Manis ?sp.; adult (4th stage); skull; part of lower
RELVES ae lee Bite cate ii Sy ieee, pee, ee 14
| The same; cribriform plate; hinder view. . 2. . 2.) 14
The same ; front view of nasal region . ae ee 1d
Bradypus tridactylus, Linn. ; half-grown (4th stage) ;
part of skull; side view . . ........, 14
The same; lower view. . .......2.2.~. 14 |
The same; hinder view ........2... 13 |
The same ; os tympanicum ; outer view 2 |
The same ; inner view Aw fees 450 oh. ee 2 |
Bradypus (Aretopithecus) (2nd stage) ; skull; hind view 2 |
The same ; section of basisphenoidal region . =v 2
Manis brevicaudata (2nd stage) ; vertical section of skull ;
inner view ee:
|

Phil. Trans (885. Plate \3.

1-4,&12,Manis. 5-l1,Bradypus.

. : ran = wer
MR OW. K. PARKER ON THE

| Manis Temminehiy (3rd stage:

lower view
Manis
view
| The same;
| The same :
Bradypiis tradecinius
part of akult;

eribrifora nave

i

front view af

SiGe view

The same: lower vie
| The same; binder
The same :

The same; inner view

view

os tyn

?sp.; adult «ith

es Sorts Me
ck %),

Mpanicums > ui

-

ey 2

SKULL IN THE MEA iM

+

wart of basis cranii ;
skull; part of lower

hes? <F 2 oes

{4th stage);

tet 4 on

Bradypus (Avetopithceus) (and stave . skuli; hind view
The same ; section of basisphenoidal VEBION 262) |, '
Manis brevicaudota (2nd stage); vertical section of aie

inner view

!

—
Oh PIR A

Nw we

bs

Phil. Trans (885. Plate 15.

WEP. deladmat

Parker % Cowara hth

1-4&12,Manis. 5-ll,Bradypus.

MR. W. K. PARKER ON THE § SKU ILL IN TH a M

PLATE 14.

Aard-Vark (Orycteropus ye sy a ripe ey al

skull; lower view* . . ;

2 The same ; upper view .

a The same; side view . . . . . . 2... do.
4 Thesame? hind view. = 4 29. 1. 2. 22 2 4 =! do.
5 The same; vomerine region; lower view .

* These figures should have been marked x 12 and x 23, ig those of the next Plate.

Phii. Trans A885. Plate \4.

Paes Caen

TN ce sagan
Ld Ly ae hh

a man & Co mp

WK. Pid)el ad ant
Parker & Coward 2

MR. W K. PARKER ON TRE SKULL IN ‘TEE MAMMALIA.

PLATE 14.

| umber of
Figures. times
| magnified,
1 _ Aard-Vark (Orycteropus capeiia’s) : nearly ripe embryo;
skull; lower view* is nearly
2 The same ; upper view . do.

| The same; side view
| The same; hind view ;
The same; vomerine region; lower view

onse Hgures should have been marked x 14 and » 24, like those of

ve next Plate.

sth -“f

+e

Vin” XY
ehy-

c.0-

ov

p.0¢

oc.e

Vi
© W.K.P.del admat.
Parker & Coward ith.

eteropus

agp

capensis.

h.hy*

Phil. Trans A885. Plate \4:.

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 15.
Number of
Figures. times
magnified.
1 Orycteropus capensis (continued); endocranium ; lower
VICW =. o: a Geode ae es wer see eee | leeneanly
2 The same; upper view. . . . . . . ..... do.
3 The same; septum nasi and vomer; side view . . . . do.
4 The same; ossicula auditis; immer view... . . . 4
5 Cholopus didactylus (%) (1st stage), vertical section of
SVeplllantcyenglyen 95 6 5 6 5 wea eee eo a 4
5A The same; separate; anterior paired vomer. . . |. 20
6 The same; vomerine region of skull; lower view . . . 4

:
k >
Phil. Trans. 1885. Plate ld ;

1% ore | that
via ayy AW et Mee Vath

veteropus

MR. W. K. PARKER ON

Hl
| a ae

Orycteropus capensis (comtinius) ,

| The same ;

2; septum nasi and yo

| The same; ossicula audtite .

Cholopus didactylus (?) (=
skull; inner view .

uppex view .

| The same; separate; anterior paired vomer
| The same; vomerine region at skull; lower eee

i, YS THE MAMMALIA.

Number of
tires
magnified.

endocranium ; lower
: i
14 nearly

| do.

wide view. o.. | do.

ww. 4
vertical on of |

sl 4

20

“i ‘

———

gm

= gel

a ee

Parker.

WK P del.wdnat,
Parker & Cownrd lita

=—chl

i 57,6, Cholopus.

Phil. Trans .\885. Plate

15.

ed ee ae Nae i

Wieiros
wv ,

MR, W. K, PARKER ON THE SKULL IN

PLATE 16.

Tulpa europad (lst stage); embryo, + inch long; side
VIGVW <i ah i de fT ey asco te

Tulpa curopaa (2nd stage); embryo, } inch long ; side
VIEW

The same; front view

The same; lower view of head

Talpa evropad (8th stage); § inch long
Tulpa europa (oth stage); embryo byt; inch long; front

view of upper part

The same; side view of upper part .

Mrinaeeus europaeus (Ist stage); embryo, 1) inch long ;
side view

The same; front view

Sorex vulgaris (ist stage); embryo, # inch long nearly ;
side view.

The same: front view the ac hee

10 or 12 days old

Centetes ecaudatus (Ast stage); embryo, 44 inch lone .

Centetes ecaudatus (2nd stage) ; embryo, bya inch lone

nestline

Sorex vulgaris (Srd stage) ; ¢,

Galeopithecus volans (Ist stage) ; embryo nearly ripe
‘The same ; side view of head.

Rhynchocyon cernei; embryo, ripe, or nearly ripe

THE MAMMALIA,

Number of
times
magnified
or reduced,

NIN ON
ol tl

wi— wl a

Ly

Q Wd
3 hat. size.

2 do,
$ clo.

Pha. Trans. \886. late 16,

b+ a4

Weer, Newman t Co vp
Insectivora,

Ficures

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 16,

Number of
times
magnified
ov reduced,

7

Talpa europea (1st stage): embryo, 4

inch long; side
WIGW ts 740 [2 es & LT aeons <> Te

Talpa europea (2nd stage}; embryo, 4 inch long; side
View, Oye Os: BOR Pte ee ee

The same; front view

The same; lower view of head

Talpa ewropea (8th stave? :

Talpa europac (5th steps? ;

tincodone'y:) Sieh is eee &

em>rye L5'y inch long; front
view of upper part

The same; side view ef upper jar:

Lrinaceus europeus (ist stage); emouryo, 1) ineh long ;
side view. ;

The same ; front view

»«

Sorex vulgaris (ist steve), erabrye, 7 inch long nearly

side view. :
The same; front view q rr rr a
Sorex vulgaris (8rd stage); nestling, 10 or 12 days old .
Centetes ecaudatus (1st stage); embryo, 3's inch long .
Centetes ecaudatus (2nd stage); embryo, 144 inch long .
Galeoprthecus volans (1st stage) ; embryo nearly ripe
The same; side view of head. . . . . . .
Rhynchocyon cernei; embryo, ripe, or nearly ripe

)

r= OT

Wir Sle

nat. size.
do.

dt? iN oo|to

do.

Pil. Trans. 1886. Plate 16.

5 x3}

West, Newman & Co 1mp

WK.&MP,P. del.ad nat
Parker & Coward hith Inseetivora

oN Oo >

MR. W. K, PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 1%,

Figures.

Erinaceus europaeus (1st stage); embryo, 14 inch long ;
endocranium ; lower view .

The same; upper view . 7

Erinaceus europaeus (2nd sue) e ripe young, 1 ane
long; dissected skull ; lower view

The same ; upper view .

The same ; side view

The same; end view

The same ; section :

The same; part ot’ basal view, a ee raat reriowed

Number of
times
magnified,

Phil Teams \S85. Plote V7.

WKP del ad mat. ‘ West, Newman &C® imp
_ Parker & Coward lith- Erinaceus.

MR, W. K, PARKER ON THE §

PLATE 17.

ee rf

Number of pi,
times) |

magnified, | —

peer teeters | tennant oe aetna seroma cere enn erm rreme | ee ee fe el

1 | Arinaceus europuus (ist stage); embryo, 14 inch long;

| endocranium ; lower view .
The same; upper view. . .
Brinaceus evroprus es stage); ripe young, 2 ae

long ; dissected skull; lowar view .

The same; upper wiew ,
The same; side view
The same; end view

| The same; section
The same; part of basal view, w a ee nals peor

Parker. Phil. Trans \885. Plate V7.

WHE de) ad mat ‘ West Ne nan &.

Parlar Be Cowasd 0 Frinaceus
s

MR. W. K. PARKER ON THE

PLATE 18.

SKULL IN THE MAMMALIA.

Number of
Figures. times
magnified.
1 _ Erinaceus europeus (1st stage); embryo, 1} inch long ;

Ist of a series of vertically-transverse sections al

2 | The same; 2nd section . itil
1 The same; 3rd section . 11
4 |The same; 4th section . Al
5 |The same; 5th section . 11
6 ' The same; 6th section . 11
‘4 The same; 7th section . 12
8 | The same; 8th section . 12
9 |The same; 9th section . 12
10 | The same; 10th section 8
ill |The same; 11th section 8
12 | The same; 12th section 8
ites |The same; 13th section 8
14 The same; 14th section 8
15 | The same; 15th section 8
16 The same; 16th section 8
iy The same; 17th section 8
18 The same; 18th section 8
19 The same; 19th section 8
2 The same; 20th section 8
21 The same; 21st section 8
22 The same; 22nd section 8

¢

Phil.Trans.1885.Plate 18.

4
hs Ht Nisan
iki te
7 fb .

Lays | Mtawina nes nmtonarn lye

*
Mince Water

ernst

Nerds ieee

ae Mere ee in

*

” Parker & Coward del. et hth. P
Be ARR die: ; : EFrinaceus.

West jncwrrnnni & CF snup

i iti A
NTH CHB MAMSATEA, ae
1s Dh 7

‘
-

‘.

4
wa w. Kk PARKER ON THE SKUL
‘

- :

i PLATE 18.
_ en ee ene
! - Number of a
' ; je . | a Hi
: iL 1 ls Se eas
7 ieee : Ee |
a | 1 Brinaceus curopeus (ist stage}: embryo, 14 inch long: | ;
“a0 | Ast of a series of vertically-transverse sections . i
Prd 2 |The same; 2nd section . | tl
7 | Hi | The same; 3rd section . | cal
7 | 4 | The same; 4th section . ta
i, | 5 | The same; 5th section - il
i. 6 The same; 6th section . . he
a 7 . The same; 7th section . | 12
8 | The same; 8th section . | 12
io 5 The same; 9th section . H 12
- 10 The same; 10th section | 8 ;
| li | The same; 11th section rey 0
Se 12 The same; 12th section a 4 °e,: 2 | a |
. | i ‘The same; 13th section . |. Pe aes 8 .
14 The same; 14th section 8
| 1% ' The same; 15th section 8
1% | The same; 16th section 8
| | ty | The same: 17th section 8
. ti | The same; 18th section 8
| The same; 19th section §
: The same; 20th section 8
£1 The same; 21st section 8
| The same; 22nd section 8

Phil. Trans.1885.Plate 18

IO pete

borne

t Newman & C§ LUE

; Parker & Coward del et hth =
} W.K.P. dir Erinaceus

Migures,

MR, W. K, PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 19.

Erinaceus europaeus (3rd stage); new-born young, 24
inches long ; endocranium ; lower view .

The same ; upper view .

KNrinaceus europaeus (4th sta) eccy, 2 Ree ane
3 inches long; endocranium; lower view .

The same ; upper view . eo :

The same; part of endocranium ; upper view aie

Erinaceus europaeus (Sth stage); 1 month old; head,
1} inch long; dissected skull; end view

The same; part of endocranium, with some aie
retained ; lower view

The same ; section of skull

The same ; part of skull; outer view of patito y region .

Number of
times
magnified,

cap)
=
a
3
rt
A
~
ws
ir 3
oe
~~
e
N
3
A 3
S
~
=
~

Erinaceus.

3+. ad nat

Parker 5.ccward ath

|

De
ey ; ne

MR. W. K, PARKER on THE SKULL IN THE MAMDMAL

PLATE 19.

Krinaceus enropeus (irc stage); new-born young, 24
inches long; eudocraniumn: lower view. . . . . .

The same; upper view ee ae ene?

Erinaceus evropens (4th stage); suckling, 2 weeks old ;
2 inches long; endocranian ; lower view .

The same; upper view. . «© . . .

The same; part of endocraniam: upper view

13 inch long; dissected skull; end view

The same; part: of endocranium, with some splints
retained ; lower view .

The same; section of sku . . .. aoe

|
| Epinageus europeus (Sth stage); 1 month old; head,
|
|
| The same; part of skull; outer view of acre region .

W.K.Pdel.adnat
Parker & Coward lith.

viva’

oe

Firinaceus.

a

Phil. Trans. 1885. Plate 19

hh

occ

West

a

Tewman &Co amp

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 20.
Number of
Figures. times
magnified.
1 Erinaceus europeus (5th stage, continued) ; skull; lower
|) NIC Wes eee oe ee oy eee ee ee Clee 3
2 | The same ; upper view . 3
3 The same; side view ..... . 3
4 Erinaceus europeus (6th stage); young, 3 grown ; section
(ee eevee ele ; 22
5 The same (part) ; with septum removed . Md 22
6 Erinaceus europeus (Sth stage); sub-adult; posterior
sphenoid ; upper view 23
if The same; lower view. . . . 24
8 The same; end view, behind. . . . oa 24
9 The same ; inferior (maxillary) turbinals; front view . 24
10 The same; internal view . . ..... +... 24

Prail. Trans. 1885. Plate ZO

Wy 2h nuit West Newman &Co imp

Pacicany. CoWare lith
Erinaceus,

r 2, ¢ y
MR. VW. K. PARKER ON THR SKULN IN. a AM v1 ay

} ‘

PLATE 20.

Figures,

ee J a ee Se a ee eet

1 Erinweus europeus (ath stage, continued); skull; lower
VIEW sits ae bees 3 ah Seles 2 eee oe oe Se

The same; upper view . ie Wnt ees

The same; side view . . . . 2 Si = hoes

Lirine ceus europeus (6th sta ae)s 3 young, g grown ; section
of s eau 4? oe ; :

| The sime (part) ; with septa: remo: al

Evinaceus europeus (8th stage); sa arbult ; phere
sphonoid; upper view . . . . ;

| The seme; end view, behind. .
The seme; inferior (maxillary) tarbine!s ; fants view .

|
t
The s.me; lower view. . . . . ee ar
The sume; internal View . . . ... . on es

Phil. Trans. 1885. Plate 20.

W.K P. del adset,

Parker& Coward. lith

Erinaceus.

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA,

PLATE 21
ee a ne eee a
| Number of
Figures. | times
magnified.
- - |
1 Erinaceus europeus (8th stage, continued); sub-adult ;
skull ; lower view. 12
2 The same ; upper view . 12
3 The same ; side view | 12
4 The same; endview .......... . .4 13
5 The same ; lower jaw ; outer view . 12
6 The same ; inner view 12
rg The same ; nasal labyrinth ; upper view 24
8 The same ; lower view . 24
9 The same ; side view 24

| ee

=. 7

a
(Phil. Trans. ABB5. Plate 21.

we "
Bal a

Erinaceus., -

MR. W. K. PARKER ON

Erinaceus europaeus (0!

skull ;

The same;

| The

The

| The
' The

|

| The

The

same

Same 5

Same

lower view

3

a

>

>

same ;
The same ;

Same ;

same ;

upper wie

side view

end view

aN

lower jaw:

inver Views

sicie

Ne
lo wer Tew

vie Ww

THE

SKULL IN THE MAMMALIA.

rs

|

| Number of

| ma magnified.

continued) ;

sub-adult :

|
|
|
7
|

|

|
times |
a

—
“)

Bl wl WP cleo Coes cle

bo

bo to

ad

Parker.

Parker % Coward delet lth

ta bi

Frinaceus

Phil. Trans. 18809. Plate 2

West Newman &U

i

amp

MR. W. K. PARKER ON THE SKULL IN THR MAMMALIA.

Number of
Figures. times
magnified.
| Erinaceus europeus (a series of stages of visceral arches);
deep and superficial mandible and ear-drum ; inner
view (Ist stage); embryo; 1} inchlong . . . . «| 8
2 The same ; fore part of deep mandible ; upper view . . | 16
3 | The same ; hyoid arch ; oblique view . . . . . . . | 8
4 2nd stage; embryo; 24 inches long; deep and super-
ficial mandible ; and ear-drum ; inner view . . . . 6
5 3rd stage ; ripe young ; 24 inches long ; the same parts ;
inner VIEW & “Sa geo feel ee Mer GR EG 54
6 The same; hyoid arch; upper view. . . . - . - . 54
7 4th stage ; young, 2 weeks old; the same parts; inner
VIOW Ahk, Sle ee Ceres Mee sea win ean ee 4
8 5th stage ; head, 14 inch long; same parts ; inner view . 3
9 The same; hyoid arch; upper view. . . . 3
10 7th stage; 3 grown; ear-drum ; outer view . 8
11 | The same; inner view... .. | 8
12 Sth stage ; adult ; malleus; outer view . 8
13 | The same ; annulus tympanicus ; outer view. 8
14 | The same ; hyoid arch; upper view... 22
|

(ORT Fane 1885. Plate 22.

it Ss Pema

Bi | WAKA ood
Parker & Coward iith

Nd) aes un Lees

f

Wi

Figures.

VE MW K PARKER ON THE

| Lrinaceus europeus (a series ot

SKULL IN THH M

stages of visceral arches);
bie and ear- -drum ;
tA inch lone. 2 2k OG

HM +t

deep and superficial win inner
view (Ist stage) ; embryo

The

The same ;

same ; fore part of deep mandible; upper view

hyoid arch Miews i) 0) 22. Qe

b
znd stage; embryo; 2) inches long ; deep and super

ficial mandible ; and ear-civeum: immerview . . . .

3rd stage; ripe young ; 24 imches long; the same parts ;
inner view .

The

4th stage ;

same ; hyoid aa upper view

young, 2 seats old: the sa

yiew . .
5th stage ; head, i inch long ; same paris ; inner view .

The same ; hyoid arch ; upper view. ae ieee

7th stage; # grown; ear-drum; outer view. . . . .
The s
Sth stage ; adult ;

The

The same ;

Same SANHEr VIEW 5 vb Le ella a) ah lel lee
malleus; outer view . . ..
same ; annulus tympanicus: outer view. . . . .

hyoid arch; upper view .. . . . . .

:

s: inner j

sLMALTA.

Number of

| times
| mnagnified.

in
tole cole

oO GO

wo ow wo wo

. Cobo

|

Phil. Trans. 1885. Plate 2 2.

bmn

bmn

bow

WAK.P del. West
Parker & Cowa~d iith

Newman & C° amp

Mma CeI1S

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 23.

Number of
Figures. | times
| magnified.
] Talpa europea (3rd stage) ; embryo; 7% lines long ; Ist
of a series of vertically-transverse sections . . . . 13
2 The same; 2nd section. . . . . . . . + «© « 13
3 The same*s ord Section 29s 24. 2 Semen 13
4 The same; 4th section. . . ... .. +... 13
5 | The same? Sthesections 9) = . ...9 5 Soe 2 = 13
6 | The same “Bt SECO Mew jae) on) nk >) ye) eee ez
7 The sames 7th Section @ bels- =;) 24 2) ee ee 13
8 The same: Sth section. ie 2 4 a) eS Ses 13
9 | "The sames 10bh section. gee. 4 ee 2 2) oo sascemne 13}
10 | The same Peli ROCHON, Weed: a; 1 ee ae 13
i | The same: 12th section =~ + « =» 2 . 8 «© » aes Ih
12 | The same; 9th secon «92 . - « 2 « + = = ys 13
13 | Thesame; 13th section . . . . . . . eee. 18}
14 | Thesame; 14thsection . .... . > As aes 13
15 The same ; 15th section rr ee ee 1
16 — Talpa europea (4th stage); embryo; } inch long; Ist of
a series of vertically-transverse sections . . . . .- 13
| 1 Mhersame > 2nd Seculons. tsa annennAcnnennc: sen ennnE-amnnE 13
18 'Dhé Games Sra Sections _celeeay aes fa. seer eee 1133
| 19 ) The same » 4th section « 41.4 302 3 22° =) See 13
| 20 The games 5th section i 12 2 4] 2 > ae 13
| 21 | "The same: 6th. section. «ee eee es ee es 13
pay | The same; 7thsection. . . .. +: ++... « . 18}
23 The same; 8thsection. . . . . . . . ee es . 13
24 The same: 9th section. . © « 1 © «1 s @ | @ 13
| 25 The came? 10th section” =. “-PGhee eases eae oon 13
|

wt Pk il. Trans. 8!

West, Newman & C2 imp.

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 23.

Number of
times
| magnified.
Tulpa europea (8rd. stage) ; embryo; 74 lines long; Ist |
| of a series of verticaliy-transverse sections . . . «| 13
| The same; 2nd section. . . . . . «s+ ss s i3
| The same; 8rd section. . . . ae ee 13

The same; 4th section . ree? oe By, 5 | 13
| The same ; Ath sectigue.- Gyn Gs). eh da ee enn 13
The same ; 6th section .
The same ; 7th section .
The same; 8th secticn .
he same ; 10th section
The same ;_ 11th section
The same; 12th section
|

eal
4

The same; 9th section .

The same; 13th section ais yi lg
The same; 14th section ; b ae! 13
The same ; 15th section mak | 13
Talpa europea (4th stage), embryo, 9 rect tong; Ist of |
a series of vertically-tramsyverse seciiumS . - 1 ee 13
' The same; 2nd section. . . . . nee: 13
The same; 3rd section. . . . . EB ees 1123
The same :-4th sectioniy. 9) 412. Goel i ep ieee 13
The same ;-Sth section «. ; .)), . 4 21h) J 2 . & 13
The-same + 6th section «.).¢ 72). 729. The ay 13
The same; 7thsection. . . . «6 2 + +e w 1 | 13
Thesame: 8th section . . 0 2 a 4 Ae ae me Gs | 13
The same; 9th section. ©. 2. 2. . 6 2 1 1 we 13
Theisame > L0th-section «”..1 1) 4% We Lee | i

Phil.Trans.1885.Plate 23.

West Newman & C2 imp

Parker & Coward del et th.
W.K.P. dir. Talpa

.

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 24,
Number of
| Figures. times
| magnified,
| 1 The same (continued); 11th section 2. 2. 2. 2. 1. 134
| 24 The same; 12th section. SG 3 = eee 134
| a The same; 13th section . . . . :. Oe oe 134
4 The same; 14thsection . . ......2.2.~. 13% |
5 The same; 15thsection ........42.2.~. 135
6 The same; 16th section . . ......2.2.~. 135
rg The same; 17th section ...... +... +. ./{ «418%
8 The same; 18thsection . . . ..... 2... 134
9 The same; 19th section . .....2.2.2..~. 133 |
10 The same; 20th section . 2. 2. 2. 2 2 133
iB Mhersanre y2ilstesection..- aac. ew wea ee ee ee 134
il, The same ; 22nd section. a ee ee 134 |
13 The same; 23rd section . . . . .....~.~. 133 |
14 The same; 24th section . . ...: ..... Nass

Phil. Trans 1285. Plote 2+

Write uiucw. West, Newman &C? imp
Parker & Coward lith. °

Talpa Europea.

~

TO GO eB C3 tl

OD

MR. W. K. PAREER ON THE SKULG IN THE MAMMALIA.

Ne Same 3

The

PLATE 24.

same 5
Oo SaMeE 5
same ;

same
Same

2

,

oy

?

same ;

Same ;

Same

> Same ;
Same ;
Same 5

?

>

>

The same ;

e same (continued) ;

12th section

20th section
21st secticn
22nd section
25rd section
24th section

Number of
times
magnified.

Phil. Trans 1885. Plate 2.4.

WKP direx P : ; -
Parker & Coward lith West, Newnan &C° imp

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 25.

Number of
Figures. times
magnified.
ih Talpa europea (Sth stage); ripe young, 12 inch long;
vertical section of head 63
2 Talpa europea (4th stage); embryo, ¢ ch long; endo-
cranium, lower view . 10
3 The same ; upper view . ee : ee 10
4 Talpa europea (9th special, eth Senet stage) ; young
mole, 3? grown; malleus; inner view . . . . . 10
i The same ; outer view 10
6 The same ; incus ; inner view 10
7 The same; incus; outer view . . a. hs ee 10
8 Talpa europea (loth special, 13th poner stage) ; adult ;
malleus and incus; inner view 10
9 The same; outer view 10
10 The same ; stapes; side view . 10
11 Talpa europea (12th stage); young mole, ? grown;
annulus tympanicus; inner view. . . . . . . 63
1h Talpa europea (8rd stage); embryo, } inch long ; hori-
zontal section of snout ; ko ie OOmeis 65
13 Talpa europea (10th stage); young mole, 3 inches long ;
annulus and meatus externus . ft cel a: ee let 62
14 Talpa europea (13th stage); adult; vertical section of

snout.

Wi Adel ad mat
Pathe c \Corard ith

lalpa

europea.

Phat. Trans. 885, Plate

pam
eb

Wt Wo K PAN KEE on THE SKULL 1

PLATE 25.

Yipnres:

_ | ‘

Leipa europea (Sth stage}: ripe young, 12 inch long ;

- | vertical section of hearl hod Be Sem ae Bee nea
2 | Talpa europea (4th sce). embryo. ¢ inch long; endo-
| eranium, lower view. . . . . 1.0. se wee 0?
2 | The same; upper view ia. (oe 10.
_ 4 Talpe european (Us speciel, 12th general stage) ; young
oe | mole, 3? grown: saeiiwiss Mmerview . 2. . 1... 10
¥ 5 | The same; outer vic @ J ie ie ae ee ae 10
=A 8 | The same; Incusi immer views... . 1k eee 10
a 7 | The same; inewa; cares stow .. ; 10
oy 8 | Talpe europea At: syeoket, 13th oaceelie og) ae ,
ae | malleus and incws. Gres view . ; Dey te | 10
iy 9 The same; outer views. ak pose ey ee | AIS 10
o 19 The sume; stapes ; side view. Pe soe « 10.
i} | Talpa europen (isis stage); young mole, 2 grown;
; ; | annulus tympanivus; inner View. 2. 2. 1... 6. 63
_ 1g 17 Talpa european (2ra stage); embryo, 3 inch long; hori- .
| gontal section of snout. . . . .. . coke “6h?
1S ) Lulpa europea (L0th stage); young mole, 3 ele: long ;
| annulus and meatus externus. . . . . .... 65
: ‘ — Falpe exropea (18th stage); adult; vertical section of
' SONG eee eee ee ee Ce Ry 33
4 :
7

Fes Phil. Trans. 1885. Plate 25.

i
4 x ic
CL eat vinevist
{
H
|

_p.e
apis
-vz
i aoe
x ve
RY- care : -6.6
; os’ al.s
st_
~-Vwi
S.c.€ chtl
“piel 9 10
bo
20 tae mb
tet -
a ;
' pag
10 «70
~-S7L
13
7
WK Pdel adnat ae .
7 Parker & Coward lith West Newman &Co imp

Talpa europea

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

aon fF WwW Ll

PLATE 26.
———---—
Figures.
it Talpa europea (9th stage); young, 1¢ inch long; dis-

sected skull ; upper view
The same; lower view .
The same; side view
The same; endocranium; upper view .
The same; lower view .
The same; inner view (part) .

Number of
times
magnified.

Phil. rans (S85 Plate 26.

W.K P.del.adnat. ; 7
Pariser & Coward lith se
Talpa europea.

Weal Nevonan & Co wnp.

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 26
|
| ; Number of
Figures. | times
| magnified.
| : |
1 Talpa europes (St stage); young, 14 inch long; dis- |
| sected skull: upper view 62 |
| 2. | The same; lower view . 63
| . .
3 | The same; side view ha
| 7 p |
4 The same; endocranium ; upper view 63
| 5 | The same; lower view. . . | 6e |
6 | The same; inuer view (mart). . 62
| ’ it | 3
a ee Rey Beene a _

Phil. Trans ISS85 Plate 26.

W.K P.del.adnat

Parlser& Coward lith

Wert, Newman & Co,amp.

Talpa europea

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 27.

|
Number of |
Figures. times
| magnified.
|
| lL Lalpa europea (10th stage); young mole, 3 inches long ;
endocranium ; upper view 33
2 The same; lower view eee Se. 3?
3 The same; dissected skull with some bones removed ;
side view «ae 33
4 Talpa europea (11th stage); young mole, 3 grown;
skull, with jugal bone removed ; side view 34
5 Same skull (perfect) ; lower view 34
6 The same ; upper view . 34
7 The same ; end view a 34
8 The same ; inside of hind skull . 33
|
|

Phil Trans (885. Plate 27.

ed One

“Aare

ica
Pian

in’ al wer
Marion ev aed Bun Mout Beonrion, &Codmep.

= talipa europree

MR. W. Kk. PARKER ON THE SEULL IN THE MAMMALIA,

PLATE 27,

a in
{
| » | Number of
| Wigures times
ai | magnified.
1 Lalpa europad (10th stage) ; young mole, 3 inches ai | |
endoeraniiun ; pe view | 33 |
| ‘
Z) | ne same; lower view... cope te ee ee | 33 )
3 | The same; disse ar "skll with some bones removed ; ,
side view. Le > fe ehh 2 cee | 32
4 | Zalpa europea (tith stage); young mole, $ grown: |
| skull, with juga] bone removed ; side view “| 32
5 Same skull (perfect); lower view . . . . . at
| 6 The same ; upper view . | 3h
v4 The same; end view. 31
8 The same ; inside of hind duit 4 33
|

i

|
|
'
t
i
‘
1
1
1

Phil Trans 1885. Plate 27.

Pro.

W KP. del admat
Parker & Coward bth

lalpa BPUrOoOpcCced

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 28.

Figures.

Number of
times
magnified.

oo

Talpa europea ; first of a series of stages of the visceral
arches, the main figures all drawn from the inside (3rd
stage of the whole series) ; embryo mole, 3 inch long .

The same (2nd special, 4th general stage) ; embryo, $ inch
long i, “Soar ee re a ae

The same (3rd special, 5th general stage); embryo mole,
1 inch long a oe a a

The same (4th special, th erica stage); embryo mole,
14 inch long : ee

The same (5th special, 7th general stage); embryo mole,
13 inch long é a ee

The same (6th special, 9th general stage) ; suckling mole,
2 or 3 days old. ae frag

The same (7th special, 10th general stage); young mole,
3 inches long

The same (8th special, Lith general stage); young mole,
9

3 grown ; hyoid arch; upper view
The same; malleus ; inner view.

la al

The same ; malleus; outer view .

The same species (9th special, 12th neue stage) ; stapes
in situ

10

10

10

10

LO

10

10

10

10

10

10

10 « ta

West, Nevanan &Co imp. ¥

Talpa europcea,

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 28.
| Navober of
Figures. | times
7 | magnified,
|_ eS eee ee
] | Talpa evropea ; first of a series of stages of the visceral
arches, the main tigures all drawn trom the inside (3rd
stage of the whole series) ; embryc mole, 3 inch long . | 10
2 The same (2nd special, 4th general stave) ; embryo, # inch |
| long ie eee : | 10
3 The same (3rd spee atid 5th general ste an enbiye mole, |
1 inch long . a ts pees | 10
4 | The same (ath special, Sth general stage); embryo mole, |
| inchlong . . eae er ee 10
5 The same (5th special, 7th general stuge); embryo mole, |
| Idinechlong . . . RTA 1 3) ou. (abbas ee et 10
6 The same (6th special, 9th general stage); suckling mole,
2 or 3 daysold, [g <b Bi 4. ate poe ee 10
7 The same (7th special, 10th iy. stige); young mole,
3 inches long oe) se eee 10
R | The same (8th special, 118k gene fei stage); young mole,
| 3 grown; hyoid arch; upper view . . . . .. . 10
Hy) The same; malleus; inner view. . . . .... .| 10
19 , The same; malleus; outer view. . . | 10
il The same species (9th special, 12th hegecal stage) ; stapes |
imsitit 6h es eee rs er rere Pon BA | 10
|

Plal. Trans \8S85. Plate 28.

bAwby

‘
'

WEP del adnat

5 C West Newman & Co very
Parker & Coward lith fest | nan

Talpa europea,

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 29.
Number of
Figures. times
magnified.
l Sorex vulgaris (8rd stage); dissected skull of young
| shrew, 13 inch long ; upper view . 8
2 | The same; lower view . 8
3 The same ; endocranium ; upper view . 8
4 The same; lower view . 8
5 The same as tows pate fae eae es 29,
6 | The same; ossicula audittis; outer view. . . . . . 20

0 | Sorex vulgaris (2nd stage), 94 lines long (19mm.) ; section
|, Of skulle 2525 $.. Gewese, 07. 12

Phil .Trae« (885. Plate29.

su

van’

s b.o°
wpe o4 West Newman &C° imp

WKP del adnat.
Parker «Coward lith

Sorex vulgaris.

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 24,

Number of

Vigures. times
magnified.

oe ae a ans i Lee Ss ee |

i | Sorex vulgaris (8ra stage); <hesected skull of young

| shrew, 13 inch lony: upper view 8

2 The same; lower view 8

3 The same; endocraniumw upper si 8

4 The same; lower view | 8 a)

5 | The same as fig. 4; part . . °. or ata 220° iY

fi | The same; ossicula audittis; outer view . . . 2... 20

7 Sorex vulgaris (2nd stage), 94 lines ‘org {19mm.) ; section

Gr SkGH aire at as Meg pe ete eee |e 12

Phil.Trams 1885. Plate29.

eS ae ee ee ae ae
Pe pe (Py, bs cht vil vill’ /Ix,x
: sq bo
WKP del ad nat mpc 3% West Newman &C® imp

Parker «Coward lith

Sorex vulgaris.

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 30.

Number of
Figures. times
magnified.
1 Sorex vulgaris (3rd stage) ; young 13 inch long ; first of
a series of vertically-transverse sections of head. . . 12

2 The same; 2nd section. . ....... 2.44. 12;

3 The same; 3rd section .

4 The same ; 4th section .

i The same; 5th section .

6 The same ; 6th section .

7 The same; 7thsection. ...... .... .'4 1,
7A Rhea Baie: (parti Gtent ai)... te <a og pean eee 46
8 The same; 8thsection. ........... 12
9 The sames Sthysectiona. ake. pyr Meek ote enn en 12
10 The same; 10th section . ...... 2.2.2.4. 12
L1 The same? Wit section 4. fig. Se es Be 5 Paoeeeee 12
2 The samez) LOthssections 4) 38 ee afar > pe a eee 12
3) Thesame* Sth section. G7) u- ae = — eee | 12
L4 The sames ditch section! 21 wk eae. ee 12
15 Thesame: 5th section 92 2 9. =) acu neene 12
16 Sorex vulgaris (2nd stage) . . . . . » . ws. 20
17 Ditto (3rd stage) ; ossicula audittis; imner view . . . 20
18 The same ; endocranium (part); lower view (2nd stage) . 133

Fhat. Trans 1885, Piate &O.

8.x 12

12

Wr arrex etdel. _
Parker & Coward lith. ‘We st, Newman & C° imp.

; Sorex Vulgaris.

Mk, W. E. PARKER ON TH SRULL IN THE MAMMALIA.

PLATE 30.

1 _ Sorex vulgaris (3rd stage); young 1} inch long ; first of
__aseries of vertically-transverse sections of head . . .
2 | The same; 2nd section .
5 | The same ; 8rd secticn ,
4 | The same; 4th section
3 | The same; 5th section .
5 | The same; 6th section .
7 | The same ; 7th section .
7A | The same (part of ig. 7)
Q | The same; 8th section .
) | The same; 9th section .
10 The same; 10th section
ih | The same; 11th section
{2 | The same ; 12th section
3 | The same’: 13th.section “2... ¢!\9S))2 .! G4
4 | Theisame: 14thsection =) 2°.) 2 abt 2 onG
15 | Thesame; 15thsection . . 2 . + 1s se a
16 Sore vulgaris (2nd stage)
17 Ditto (8rd stage) ; ossicula auditds ; inner view :
18 | Phe same ; endocranium (part); lower view (2nd stage) .

Number of
times
toagnified.

12

46

Parker Phat.Trans 1885. Plate 30.

W.K FP direx etdel, 1
Parker & Coward lith We st, Newman & C®° imp

a
:
u =
. es
Sar 5
4 7
7 - .
AS = a
.
’
~
- :
: =
7 en |
, 4
a0
/—
:
;

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 31.

Number of
Figures. times

magnified.
1 | Sorex vulgaris (4th stage) ; skull of adult ; upper view 5
2 The same; lower view D
3 The same; side view ee Bs)
3A The same ; end view of lower jaw 5
4 The same ; petromastoid bone ; inner view 12
5 The same ; outer view oe See 1192
6 The same; malleus, incus, and tympanic ; outer view . 18
7 The same ; inner view 18
8 The same; stapes; side view ae 18
9 Sorex vulgaris (4th stage) ; adult ; ite ral inner view 7
10 The same (8rd stage) ; skull; side view fe
il The same; section; side view 7
12 The same ; hyoid arch 12

Phil. Trans. 1885.Plate 31.

West, Newim an &C° tree

Hl
‘

WK P. del. ad net, 7 ty

Parker & Coward lith. Co

Sorex vulgaris.

MR. W.

PLATE 31.

. PARKER ON THE SKULL IN THE MAMMALIA

Number of
Figures. times
magnified.
1 | Sorex vulgaris (4th stage); skull of adult ; upper view . 5
2g | The same; lower view 5
3 | The same; side view -1 o
3A The same ; end view of lower jaw . 5
4 _ The same ; petromastoid bone ; inner view 12
5 | The same ; outer view TP | 12
6 _ The same; malleus, incus, ann tympanic ; outer view. . | 18
7 The same ; inner view . ie! 18
8 | The same; stapes; side view : es 18
9 | Soren vulgaris (4th stage); adult ; hy in sh inner view 7
10 The same (8rd stage); skull; side view ‘6
11 The same; section; side view ii
12 | The same ; hyoid arch | 12

——

inal

Parker.

W.K P del. ad nat,
Parker & Coward lith

Phil. Trans. 1885.Plate 31.

agp

iD

gl.c\
cd.p aq Pp

bh br

hohy

West Newman &C° imp

Serex vulgaris

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 32.

Figures.

ft

Number of
times
magnified.

Centetes ecaudatus (2nd stage) ; embryo ; 144 inch long ;
skull ; upper view

The same; lower view .

The same ; side view ee

The same ; endocranium ; lower view .

The same ; upper view . a ode > et oll

The same; ethmo-septal region ; side view

The same; ossicula audittis ; inner view

The same; hyoid arch ; inner view .

a cig”
ub. sic
-¥e

4 i

VL, Wil

--op

—--@.0

oy

i
Wout, Ne-rerarepy ch Jaa?
—

Centetes.

PLATE 32.

0
_ i | Centetes ecaudatus (2nd stage); embryo ; 144 inch long ;
| skull ; upper view a 5L
; ,
: | 9 | The same; lower view . / | 5h
3 | ‘The same: sidé View Js tL ee a pel ibe. 2 Shoes at 5+
y, 4 | The same ; endocranium ; lower view . | 5d
» MM 35 4 ‘ TOUT ; :
| 5 | ie same ; upper ay ; ane [ot | 54
6 | The same ; ethmo-septal reyisn ; side view . 8
. i . . . .
y 7 | The same; ossicula audits: immer View . . . . . . 20
| 8 | The same; hyoid arch; inner view. . . . . . . . 133
| |
’
.
+
,
|

Phil. Trans. 1885. Plate 32.

| x 53

-bs

-e.hy
-t.b.s
Vil
Cd ; i . *0L.S.C
“he. $6
p-s.e

bmw

-t.hy

W.RK.P del.ad nat West Nevonau®Co imp
Parker & Coward lith

Centetes

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 33.

Centetes ecaudatus (3rd stage) ; nestling Tenrec ; 34 inches

Figures.
1
long; skull ; lower view

2 The same ; upper view .
2 The same ; side view :
BA The same ; lower jaw; end view
4 The same; skull; end view
5 The same ; skull in section —
6 The same ; ossicula and tympanic; inner view .
is The same ; bones (part); outer view
8 The sare ; part of vomerine region ; lower view
9 The same ; hyoid arch ; upper view

10

The same; nasal labyrinth ; side view .

Number of
times

magnified.

Venteles.

1

2
3
3A
4

© CON! Ge or

s
i

|

:

K. PARKER ON THE SKULL IN THE

PLATE 33.

MAMMALIA.

.

Centetes ecaudatys (2rd stage); nestling Tenrec ; 34 inches
long; skull ; lower view

The same ; upper view .

The same; side view .

The same ; lower jaw; end view

The same; skull; end view

‘The same; skull in section

The same; ossivula and tympani: immer view

| The same; bones (part); outer view

The same; part of vomerine region ; wwer view

The same ; hyoid arch; upper view .

The same ; nasal labyrinth; suie view.

.

t

Number of
times
magnified.

Phil. Trans.1885. Plate 33.

ee pe ILD.
> i

|

-Pombe

Mw del ad nat.
axker & Coward lth

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 34.

Number of
Figures. times
magnified.
1 Hemicentetes Madagascarensis; sub-adult ; skull ; lower
view . . 35
2 The same; upper view . 34
2 The same ; side view 34
4 The same; end view 34
5 The same; lower Jaw; endview .... . . 34
6 — FHemicentetes nigrescens ; sub-adult ; hyoid arch ; inner
view . . .. . 35
i The same; ethmo-septal region 3h
8 The same; with vomers 77 situ 34
9 The same ; ossicula and tympanic ; inner view 15

WXKP del.
Parker % Coward ith -

vot as eel,

sa

Hemicentetes.

ve be

Gx

para meme Mal

ca v

Weet Neveman& Co amp

Han me

MR. W. B, PARKER ON THE SKULL IN THE MAMMALIA,

PLATE 34

Figures. |

a

i | Henucentetes Moduagescarensis; sub-adult ; skull; lower
view . . i ae oe

ys | The same; upper view .
5 The same; side view
A | The same; end view
5 The same; lower jaw; endview . . . . .

| 6 Hemicenietes nigrescens; sub-adult; hyoid arch; inner

IEW goa ase eee ago

, The same; ethme-septal region . . . .
8 | The same; with vomers jn situ. .
9 The same; ossicula and tympanic; inner view. . . .

Number of
times
magnified,

os & Gt G
Grim ual cols Colt Col

ww co
Colm Colmt Cole

nad

I A a TT ta,

Parker.

W KP del

x, 7. rae

Hemicentetes

Web

ag po

Gx

3s

Wert

ty

bRovwl

(Newman &C° imp

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 35.

KF OO AN DO >

a

Number of
times
magnified.
1 Microgale longicaudata; adult ; skull ; lower view 54
2 The same ; upper view . Om
3 The same; side view .... . 54
The same; end view of lower jaw . 5s
The same; skull; end view . ... . a
jel

| The same ; hyoid arch; inner view. . .

| The same; malleus and tympanic; inner view
The same; incus and stapes; inner view .
The same ; incus; outer view

|The same; meatus-ceartilage . . . . .

Ericulus nigrescens ; adult ; lower view of skull (part) .

pep bs

b b
Co = me Re RK eC
Calms ea|to Gs[to Oo|to Ls|to oo

:

aie Se gee
Ta asian

av iey SLES

Ves we le or.

tute paiiew
lie ee eT deal

Figs. 1-10. Mierogale., Fig. ll. Ericulus

bat

A : : : 7
. F -_

a a

: um [7 pis - i 7 net, ty
‘MR. W. K. PARKER ON THE SKULL IN THE MA if
af ante

PLATE 35.

|
| Pigures, |
|
nen ee nn SD veel
i i
; Microgale longicaudata ; adult ; skull : lower view
. 2 i The same; upper view. . . . . + + + 5 + Ab
: FD) | Thesame; sideview . .. . ee oT at
7 . .
: 4 The same; end view of lower jaw. . . . . 1 s - |
- 5 _ The same; skull; end view . oT ee a.
_ 7 Th : -s Ee tence .
7 ; 6 The same; hyoid arch; inner view. - . - . . : 54
: 7 ‘The same; malleus and tympanic; immer view... . 213
7 8 The same; incus and stapes: inner view. 6 0. 2. 6 | 212
7 i) | The same; incus; outer view . . . . . se. es 214
7 . ii} ‘The same; meatus-eartilage . . . 2 1. 1s ee 212.
: | 11 Eviculus nigrescens ; adult; lower view of skull (part) . 3e
a ee eee ee Sere ee Pe alae.
7
:

Phil. Trans. \885 Plate 35.

ri

nee

ee piesiaae

3
#

titb=-Yi= —

: Ny aoe
es SNA

West. Newman %&C° img

iy
/ :
j W.K.P del

Parker & Cowerd lith

Figs. 1-10 Miecrogale. Fig. ll. Ericulus

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 36.

Figures.

NO oO — WH DO

Rhynchocyon cernei; embryo; 4 inches long; skull;

upper view .
The same ; lower view .
The same ; side view
The same; endocranium ; upper view .
The same ; lower view . ,
The same ; ossicula audittis ; inner view .
The same; ethmo-septal region .

Number of

— times

magnified.

a

i
de bo © ww WwW OW

pete C8 oie

7

)
: 7 7 ae eet - re nth
rr W. kK, PARKE i coe kaa IN oun MALIA

PLATE 36,

|
|
| ; "
| i — Rhynchocyon cernei: embryo; 4 inches long; skull;
| ‘tpper view S04 aig 8°). is ye bo Be
. | 2 | The same t lowerview Ww. nie ek om yale) lal ee be ee 30
7 | 3 |The same; side view . . . - 1 es ee ees 3
4 The same; endocranium ; rea ViEwWhs vhhe ob ealbe fos] Bm
5 The same; lower view. . . . e OSS & Paes g 3
_ G | The same; ossicula audittis ; inner view .
7 a The same; ethmo-septal region .

Phil. Trans. 1885 . Plate 36.

al.
“p
al.s --2 y : y --py
chl --pr-o
Sic. VIL VAL
== 07)
heSic. = IX, X

‘e.hy \

a ‘wel
~ chy

--¢.hy'
“-t.hy

W.K.P del.ad.nat. ¥ Te
West, Ne ran & w
Parker & Coward lith : oe meee tale
Rhyneh oeyon

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA

PLATE 37.
Number of
Figures. | times
magnified.
I _ Galeopithecus volans (1st stage); embryo; 54 inches long ;
skull; lower view . 22
2 The same ; upper view . a
3 | The same ; end view. 48 Z ars
4 | The same; ossicula audittis; outer view . 2 2... 6
5 | Thesame; conchaauris .......... ./ =
6 — Galeopithecus philippensis (2nd stage); young; 8 inches
| long; skull; lower view. . . . ...... ./4 14
fd The same; endview. . . . . . . . 14
8 The same species (3rd stage); larger young; part of |
skull; lowerview.,..-. 2 .) 2 . } s aoe ee! 21

an ®& C° imp.

eleull's lower wicwies G Gc \ lena ten eanea ef cs 24

——— oY oe
vi ee
TAS |
MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA
PLATE 37.
Number of
| Figures. times
magnified.
Le
| Galeopithecus volens (1st stage); embryo; 54 inches long ;
skull; lower view. . . . . >. s+ «1 1 es 22°
2 | Thesame; upper View. . . . 2... 2... 23
3 The same; end view. yer: eM 23
4 The same; ossicula auditis: onter view . .. 6
5 | Thesame; conchaauris . . . . . ro 3
6 Guleopitheeus phibppensis (2nd stage); young; § inches |
long; skull; lower view. . . eyes aa ee 12
? °o
7 The same; end wew. a TSE ae ; 14
8 The same species (3rd stage); larger young; part of |

Phil.Trans.\885 . Plate 57

Parker

wl

(np

== 0.5

--©.Pg
pg-- 4-cils
gl.c-- ~---ms. pg oP ase

West,Newman & C° imp

W.KP delad.mat
Parker & Coward lth.

Galeopithecus

MR. W. K. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 38.
Number of
Figures. times
magnified.
1 | Galeopithecus volans (1st stage); embryo; 54 inches long;
skull; side view 22
2 The same ; lower jaw ; inner view 23
3 The same ; hyoid arch ; upper view. or tat 4
4 Galeopithecus philippensis (2nd stage); young; 8 inches
long; skull; side view . 14
5 The same ; lower jaw; end view. . 2... eel 3
6 The same; hyoid arch ; upper view . 3
14 Same species (3rd stage); section of skull . . 2... 14
8 The same; hyoid arch ; upper view. 3
9 Same species (4th stage); adult ; hyoid arch ; side view . 3
10 The same; upper view. . ......... ~~. 3

Phil. Trans. 1885. Plate 3

nity

WK P.del.ad mat. West, Newman & C° imp.
Parker %& Coward lith.

Galeopitheeus.

Vigures.

MR. W. kK. PARKER ON THE SKULL IN THE MAMMALIA.

PLATE 38
: Toa
| Nuiber of
times
| magnified
| |
— Galeopithecus volans (1st stage); embryo; 52 inches long; |
| skull: side view 2
i The same ; lower jaw ; inner view 22
| The same; hyoid arch; apperview. . . . ah 4
| Galeopithecus philippensis (2nd stage); young; & inches
long; skull; side view . 1z
The same; lower juw; end view, 3
| The same; hyoid arch; upper view . 3
Same species (8rd stage): section of nldal) gos mle Lie
The same ; hyoid arch ; upper view. Pee | 3 |
Same species (4th stage); adult ; hyoid arch; side view. 3

The same; upper'view.. w 6. 4) 4h) bos oe

Phil. .Trans. 1885. Plate 38.

b-heor

pemiwe

pope

9x3

10% 3

~-b.hbr

W.K P.del.ad mat
Parker % Coward lith
Galeopithecus

MR. W, K. PARKER ON THE SKULL IN THE MAMMALIA

PLATE 39.

Number of

Figures. times
magnified,
1 Galeopithecus volans (1st stage); endocranium; lower view 22
2 The same; upper'view. . . : &. 23
3 _ Galeopithecus philippensis (4th sare Adults section of
skull 13

4 The same ; end view. 13
5 The same ; front view a ; 2
6 The same ; vertical section of tenon region 3
7 The same; ossicula audittis ; outer view ; 8
8 The same ; lower view of skull, with part sawn away. 3

a

Phil. Trans. 1885. Plate

-

ag

7
oa

=

~
a

ro

og -p'

,
"tb

aa ee

del ad nat. Wast. Newsman &C® san
ker & Coward lith. , =
a . wt Galeopithecus.

—

- .
Pensa dol oy a
; aie 7

7)

z ey an af, "| Lu:
MR. W, K. PARKDR 01 N THE ‘SKULL IN Lo

a hy Ia uf
'. AD he i
PLATE 39. ne 1 va

{2 : ; ae
1 | Guleopithecus volans (ist stage}; endveranium; lower view
The same; upperview. . . . : 1) eepreen

3 fraleopithecus philipgzeasts (ath stacey aduls cadipe of
es area aren Leake ted . he
4 | The same; end view. f te!
5 | The same; front view . . MALE es
6 The same ; vertical section of temporal wegim «6... 30
5 7 The same; ossicula audiths; outer View . . 5. 2... 8
8 | The same; lower view of skull, with part sawn away. . 3
} {

, es ae eS ec ese ae a ee ee en eer ee

| Parker. Phil. Trans. 1885. Plate 39.

i?
t-
W.K.P. del ad nat At, tN met

Parker & Coward lith =
Galeopithecus

ise

i

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it on
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1
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