PTERYGOID, EPIPTERYGOID, AND ALISPHENOID 245 



primitive connection with the pterygoids, a connection which has been 

 lost in the Dinosaurs and Crocodiles. In Diadectes the alisphenoids, or 

 epipterygoids, have essentially the same relations as in Sphenodon. Wat- 

 son 11 goes even further than Broom ; he finds that in Cynodonts there is 

 no suture separating the temporal portion of the alisphenoid from the 

 pterygoid. He shows that the basal portions of the pterygoids in all their 

 relations with surrounding bones and nerve openings correspond pre- 

 cisely with the basal portion of the alisphenoids, and that the temporal 

 portion of the pterygoids correspond with the temporal portion of the 

 alisphenoids. 



Watson also holds that the true mammalian pterygoids have not been 

 derived from the reptilian pterygoids at all, but from the ectopterygoids, 

 or transverse bones, as originally suggested by Seeley. Watson's thor- 

 ough analysis of the topographic relations of the elements in question 

 virtually amounts to a demonstration of the suggested homologies, pro- 

 vided one accepts on other grounds the view that the Cynodonts are 

 closely related to the stem of the Mammalia. The view that the basal 

 portion of the reptilian pterygoid gave rise to the basal portion of the 

 alisphenoid also explains in a very satisfactory manner the fate of the 

 reptilian pterygoid. The backward extension of the palatines, carrying 

 with them the ectopterygoids and separating them from their primitive 

 connection with the mamillaries, also offers a highly reasonable explana- 

 tion of the peculiar position of the mammalian pterygoids and does away 

 with the necessity for regarding the so-called pterygoid wings of the alis- 

 phenoids as neomorphs in mammals. But what of Gaupp's view that the 

 mammalian alisphenoids have been derived from basipterygoid processes, 

 such as are seen in lizards? 



In the Cynodonts, as described by Broom and Watson in the place of 

 the basipterygoid processes, we observe flanges of the alisphenoid which 

 firmly embrace the basisphenoid on either side. These flanges are ex- 

 ternal to the openings identified by Broom as the carotid foramina ; they 

 are external and inferior to the roots of the trigeminus nerve. In these 

 relations they parallel the basipterygoid processes of the lizard and are 

 homologous with the alas temporalis or cartilage Anlage of the alisphe- 

 noids of mammals. 



Hence I think that Gaupp's comparisons of embryo lizards and embryo 

 mammals do not prove that the mammalian alisphenoids are homologous 

 with the lizard basipterygoid processes, but that the resemblances oh- 



11 The skull of Diademodon. . . . Ann. and Mag. Nat. Hist. (8), vol. vlll. 1911. 

 p. 305. 



