HOLLAND: THE OSTEOLOGY OF DIPLODOCUS MARSH 245 
Beginning at the point where the orbitosphenoids unite above we find a 
V-shaped fissure between the orbitosphenoids, which undoubtedly gave exit to the 
olfactory nerves. Just below this V-shaped opening the orbitosphenoids codssify 
for a short distance, and then by deep circular notches in their anterior margins 
(which notches are only separated by a short filament of bone on the median line) 
give exit to the second pair, or optic nerves. On the posterior margin of the orbito- 
sphenoids, about their middle, where they codéssify with the anterior surface of the 
alisphenoids, there are deep semicircular notches giving exit to the oculomotor and 
abducens nerves. Below the foramen just mentioned there are clustered three 
lesser foramina which evidently were intended to admit the anterior branches of 
the carotid artery and possibly also to give exit to veins. ‘These foramina on the 
right side of the skull appear as three separate openings. On the left side of the 
skull the openings have become fused so as to form a somewhat large trilobate 
aperture. 
Following the foramen which gives exit to the oculomotor nerves, at the point 
where the alisphenoids unite with the anterior surface of the exoccipitals and 
slightly below the level of the oculomotor foramen, there is a large foramen which 
is undoubtedly correctly determined as the trigeminal foramen. In outline, size, 
and location, it corresponds very closely to the trigeminal foramen in the skulls of 
recent reptilia. 
In the lower margin of the exoccipital bone, somewhat above the line where it 
coossifies with the basioccipital, are four openings. ‘The anterior opening which 
lies immediately behind the lower anterior wing of the exoccipital, which, as has 
been already said elsewhere, codssifies with the posterior wing of the alisphenoids, 
is a small foramen which very probably admitted on either side of the skull the 
posterior branches of the carotid artery. Immediately behind this is an opening 
which the writer interprets as the fenestra ovalis, leading away from which, along 
the lower margin of the paroccipital bone, is a groove which the writer interprets 
as the groove which held the stapes, which in the specimen in our possession is 
missing. Apparently no other location in the skull can be found save this for the 
exit of the auditory nerves, and a careful comparison of the skull with the skull 
of Sphenodon shows that this opening and the accompanying groove are closely 
analogous to the corresponding structures in the skull of the latter animal.’ Suc- 
ceeding this foramen is a foramen which the writer interprets as the exit for the 
glossopharyngeal nerves, and this foramen is in turn succeeded by a smaller fora- 
5Sphenodon has no external ,ear, agreeing in this respect with many other recent reptilia and ophidia. It is pos- 
sible that Diplodocus had no external ear. 
