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 
