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 
