DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
67 
situ ; over them, the orbitosphenoid and alisphenoid (V 1 . to V 3 .) 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 
1st branch of the 5th nerve (V 1 .) passes. This also enters the skull again by one of 
the more marked orbital foramina (V 1 .), in the anterior angle of the orbital plate of the 
frontal (/). Behind the palatine {pa.), the foramen rotundum (Y~.) is seen close to 
the sphenoidal fissure, and where the alisphenoid, squamosal, and pterygoid meet, the 
foramen ovale (V 3 .) 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; tins is clearly shown in the hinder end, view of this preparation (Plate 13, 
fig. 7, o.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, o.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 ( al.s.) are seen in this end view, bulging out beyond the orbital 
plates; the end view of the basisphenoid ( b.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 {i.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 (sq.) show their large pneumatic opening. 
The under view (fig. 6) shows the lower face of the nasals (n.), and the frontals (/.’) 
with them 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 them “ lambdoidal ” suture 
with the huge supraoccipital ( 5 . 0 .) 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 them 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 {pg.), behind. The proximal region of 
each alisphenoid (Yh-Y 3 .), is hidden in this view by the pterygoid, but the base (b.s.) 
K 2 
