ARSINOITHERIU^r. 
]5 
partly filled in life by the tympanic, which is wanting in all the skulls hitherto 
examined. The upper posterior edge of the pterygoid within this opening forms 
the inner border of a deep groove lying between it and the squamosal and probably 
representing the foramen lacerum medium (the foramen lacernm anterius of some 
German authors). 
• As already remarked, the boundaries of the alisphenoid and orhitosplienoid are 
by no means clear. The alisphenoid appears to send down a long narrow plate to 
the outer face of the vertical palatine plates, with which its lower end is intimately 
fused, forming a prominence which is seen in PI. I. at the end of the reference-line 
running from the letters Further up, this alisphenoid plate is perforated by the 
short wide alisphenoid canal (text-fig. 4, al.c.), the anterior opening of which lies within 
the anterior edge of the ])late, which is continued upwards and forwards as a prominent 
downwardly directed crest of bone, forming the outer side of a deep groove, at the 
bottom of which there are several foramina in addition to the alisphenoid canal. The 
most important of these is a large somewhat vertically elongated opening, the foramen 
lacerum anterius { foramen sphenoidale of some authors). Above and slightly internal 
to the foramen lacerum anterius, and separated from it by a narrow bar of bone, is the 
smaller and more rounded optic foramen (Pis. I., II. ; also text-fig. 4, ii.) opening 
into a groove, of which the upper edge is constituted by a continuation of the 
crest formed by the border of the alisphenoid plate, the lower edge being much 
less prominent and probably approximately marking the lower border of the 
orbitosphenoid, in which the foramen itself is no doubt situated. Above and 
in front of the optic foramen there is a very small aperture, probably for a 
blood-vessel. 
Several more or less nearly complete casts of the cranial cavity have been made, 
that upon which the accompanying figures (text-fig. 5) are based being taken 
from the skull figured on Pis. I. and II. (M. 84G3). It is the only one in 
which the prominence marked and. is shown, in consequence of the partial 
preservation of the inner portion of the periotic. In all the others the loss of 
the auditory bones leaves a large vacuity on either side of the basicranial axis, 
as above mentioned. 
A detailed account of the brain-cavity will not be attempted, and some of the 
more important characters only are here referred to. The olfactory lobes {ol.) 
are large, but not so large in proportion to the rest of the brain as in the 
Amblypoda. The cerebral hemispheres (A.) are far more developed than in that sub- 
order, the frontal region being especially prominent and rounded. The surface of the 
cast is almost smooth, and in the absence of a distinct rhinal fissure it is difficult to 
say what portion of the cerebrum belonged to the neopallium. The only trace of 
a sulcus seems to be that marked s., running upwards and backwards on the side 
of the brain from behind and beneath the olfactory lobes. 
