Structure of the Therocephalian Skull. 71 



peiliaps actually fuses with tliat bone, but in the very primi- 

 tive Fteroplax it is undoubtedly distinct. 



Tahulare. — Tiie Stcgoceplialian tabulare is a dermal bone 

 associated with the opisthotic exactly as the postparietal is 

 with the epiotic. It always retains this articulation in 

 ('otylosaurs wherever it is recognizable, as, for example, in 

 Seynioitria. In Captorltinus the bone called by Case the 

 quadrato-jugal, if it really be a se[)arate bone, is undoubtedly 

 a tabulare iiaving its normal relation to the end of the 

 opisthoiic; its unusual appearance here is due to the fact that, 

 instead of forming a horizontally expanded plate, it forms a 

 vertical one on the back of the .skull, and it extends far down 

 because the end of the opisthotic to which it is attached is 

 bent downward, instead of pointing upwards as it does in 

 Setjvtouria and all JStegocephalia. 



The bone which 1 hold to be a tabulare in Therapsids 

 occurs in Deinocephalia, Therocephalia, and Cynodontia, 

 where it always extends down outside the post-temporal fossa 

 to articulate with the end of the opisthotic; it lies entirely on 

 the back of the skull, and obviously belongs to the same 

 transverse row as the interparietal, which 1 have shown 

 above to be probably homologous with, the Stegocephalian 

 postparietal. 



In Aiiomodontia it is usually either absent or, perhaps, but 

 improbably, iiidistiiigui.--hably fused with the squamosal, but 

 it is very probable that the bone on the posterior surface of 

 the type skull of Lystrosaurus declivis which Owen and 

 Lydekker have supjioscd to be part of the parietal is really a 

 very reduced tabulare. 



Wlien describing the skull of Diodemodon I held the 

 tabulare, which I now know to be a separate bone, to be a 

 part of the parietal, liroom has recognized the separate 

 nature of the bone in Cynodonts and Moscops^ a Deiiio- 

 cephalian, but has called it an opisthotic, a determination 

 which is obviously inadmissible now that we know the 

 perlectly normal opisthotic described above and the position 

 of the fenestra ovale in Cynodouts and of the internal ear iu 

 DicT/nodon. 



The resemblance of this bone to the pars mastoidea of the 

 petrosal of marsupials, which is the basis of Dr. Broom's 

 detern)ination, is, however, so close as to suggest that that 

 part ot the bone is really separate, and that it may be found 

 to develop as a membrane-bone, and subsequently come into 

 contact with the cartilage bones of the periotic capsule. 



