22 
PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
terior palatine foramina are present, the larger perforating the maxillary 
opposite the posterior lobe of the fourth premolar about half way between 
the base of that tooth and the median suture, while a second smaller fora- 
men perforates the maxillo-palatine suture. The basioccipital supports a 
median keel, which does not extend beyond the suture between this ele- 
ment and the basisphenoid. The pear-shaped bullae are hollow and are 
more or less completely fused with the basioccipital, producing a different 
arrangement of the cranial foramina in this region from that characterizing 
Hegetotkerium. Anteriorly, where most prolonged, the bullae are greatly 
flattened in the horizontal plane. The glenoid surfaces are almost flat, 
presenting downward and backward. They are separated from the post- 
glenoid process by a wide fossa, accommodating the non-articular portion 
of the madibular condyle when the mouth is widely open. 
Owing to the fusion of the basioccipital with the tympanic bulla, the 
carotid foramen is shifted posteriorly, fusing with the foramen lacerum 
posterius at the base of the paroccipital process. Traces of a septum 
dividing the two foramina are observable. Large condyloid foramina are 
present, in addition to which one or more small foramina pierce the basi- 
occipital on either side of the median keel in line with the carotid-lacerum 
posterius foramina. A single large foramen (probably vascular) is lodged 
in the groove between the tubular auditory meatus and the dilated mas- 
toid, while in Hegetotkerium three or four foramina are present in this 
region. Two foramina, lying side by side, perforate the suture between 
the meatus and the postglenoid process (postglenoid foramina). The 
foramen ovale and foramen lacerum medium are confluent, with vestiges 
of a dividing septum. Within the orbit, a deep groove leads forward to 
the infraorbital foramen. Posteriorly the course of this groove is back- 
ward and downward, terminating in the posterior palatine notches. Va- 
cuities within this groove communicate with the olfactory chamber. The 
foramen rotundum and spheno-orbital foramen are confluent. The pos- 
terior narial canal is connected with the spheno-maxillary fossa as in the 
hyraces. Several smaller foramina within the orbit are probably vascular. 
Complete fusion of the opposite halves of the mandible has taken place, 
leaving no trace of suture (PI. IV, fig. 15). The horizontal ramus 
increases suddenly in depth beneath the last molar and as suddenly 
decreases in depth posteriorly, producing a prominent convexity in this 
region, which is carried to a much greater extreme in Inter atherium. The 
