Anntils of the South African Museum. 



by Dr. Broom. He sectioned a small Gorgonopsian skull and found 

 that the bone which forms the median bar behind the palate and 

 which has consistently been called the basisphenoid is, in reality, 

 the vomer: and that the basisphenoid proper is a small ossification 

 king hot ween the basioccipital and vomer and not appearing on the 

 ventral surface of the skull. 



It is difficult to understand how. if it is the homologiie of the 

 parasphenoid of the Amphibia, the vomer should appear in the 

 Therapsids as a median bone on the palatal sin-face. The evolu- 

 tionarv tendency in the Amphibia and lower Reptiles is to crowd 

 the parasphenoid away from the palate by an enlargement of the 

 ptervgoids in the mid-line and to make of it a thin vertical wall of 

 bone: and once it had attained this form, as in the Dinocephalia, it 

 is unlikelv that a reversal would take place in order to force it once 

 uirain between the ptervgoids on to tin 1 palate. 



In a paper prepared for the \Villiston Memorial Volume and not 

 vet published. I have considered the same subject briefly. A small 

 skull named there Whaitsiella was considered to have a median 

 vomer and to be ancestral to the aberrant form Whaitsia which 

 delinitelv has no vomer. Further examination of Whaitsiella leads 

 to doubt as to the presence of a median bone on the palate. The 

 little skull is much crushed and cracked, and the supposed sutures 

 mav be cracks. The supposed hone lies ventral to the pterygoids 

 and certainlv has no connection with what has hitherto been known 

 as the basisphenoid; and it may very possibly be a Hake of the 

 pterygoids. Certainly Whriifxiii has no median bone on the palate: 

 and whether it be a Gorgonopsid or a Therocephalian it yields 

 ipiite definite evidence on that point. 



Ci/nosuchnf; wliaiisi almost certainly has no median vomer in the 

 posterior part of the palate, although there is no actual median 

 suture seen separating the pterygoids which have lost the anterior 

 prolongation: while Ictidopsis likewise lacks the bone. The accumu- 

 lation of evidence furnished by the specimens studied here seems 

 to lead to the view that the median "vomer'" of the Cynodonts is 

 the homologiie of the paired prevomers and is due to the backward 

 shift on the palatal surface of these bones which in the earlier 

 Therapsids make up the interchoanal bar. Their function as sup- 

 ports for .lacobson's cartilage are usurped in the Cynodonts by the 

 palatal processes of the prenurxillae : but they still play, in Ci/nidi-o- 

 gnathus, a part in the formation of the internasal septum. 



If this view be correct then, in the line of evolution of the Cyno- 

 donts. we should see a progressive backward growth of the prevo- 



