88 Field Museum of Natural History— Geology, Vol. VI 



noid and squamosal, mesially with the basioccipital, and posteriorly 

 with the paroccipital process and the post-tympanic process. The 

 tympanohyal lies mainly in the lateral wall of the bulla. 



The adjacent foramina. — Eustachian canal not visible; Van 

 Kampen reports the same condition in T. cristatum. Possibly con- 

 fluent with the ovale and lacerum medium. 



Foramen ovale and foramen lacerum medium :^ confluent, forming 

 a large oval opening in the alisphenoid. 



Foramen lacerum posterius: situated at the postero-internal 

 comer of the bulla on the suture between the bulla and the exoccipital. 



Carotid foramen: small, orifice situated in the posterior wall of 

 the bulla antero-external to the orifice of the foramen lacerum 

 posterius. 



Condylar foramen: large, immediately postero-internal to the 

 foramen lacerum posterius. 



Stylomastoid foramen : opens externally in the cleft between the 

 crista meati and the post- tympanic process; orifice somewhat closer 

 to the vagina processus hyoidei than to the porus. 



Post-glenoid foramen: situated a short distance behind the 

 glenoid articulation; orifice divided into two parts by a small bridge 

 of bone lying transversely across it. 



A variable number of small vascular foramina extend posteriorly 

 from the post-glenoid foramen to the squamoso-tympanic junction. 



The arrangement of these foramina conforms, in the main, to 

 the usual notoungulate pattern. Two exceptions may, however, be 

 noted. The post-glenoid foramen is placed considerably farther 

 forward than is usual in the order, a condition which is perhaps due 

 to the fusion of the post-glenoid process with the squamosal. The 

 position of the carotid foramen differs somewhat from that seen in 

 other families of the suborder. In the Hegetotheriidae this foramen 

 is situated between the basioccipital and the mesial side of the 

 bulla, while in the Interatheriidae it lies behind the bulla and 

 immediately mesial to the foramen lacerum posterius (Sinclair, 1909). 

 A comparison with Typotheriopsis indicates that Pseudotypotherium 

 agrees more closely with the Interatheriidae than with the Hegeto- 

 theriidae in this respect. In Typotheriopsis the foramen lacerum 

 posterius and the carotid foramen are in the same position as in the 



1 1 previously stated (1932, p. 23) that these foramina were apparently sepa- 

 rated by a septum in a skull of Cochilius volvens, F. M. No. P13424. Examination 

 of an excellently preserved skull of the same species collected by the Scarritt Pata- 

 gonian Expedition (A.M. No. 29651) shows that this is not the case. 



