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ZOOLOGICAL SOCIETY OF LONDON. 



PAPERS. 



10. Comparison between the Lower Jaws or' the Cynodont 

 Eeptiles Gomphognathus and Cynognathus. By Dr. 

 Branislav Petrol ie vies *. 



[Received March 6, 1918 : Read May 7, 1918.] 

 (Text-figures 1-8.) 



Being occupied at the end of last year (1917), when in London, 

 with the problem of the double articulation of the lower jaw, 

 which is to be expected in the direct reptilian ancestors of the 

 Mammals, I was led to examine the lower jaws in the specimens 

 of the Theriodont Reptiles that are preserved in the Natural 

 History Museum. One of the skulls in question, that described 

 by Seeley in 1895 as one of the two specimens of Gomphognathus 

 from Lady Frere, (S. Africa), struck me on account of the strange 

 appearance of its lower jaw. On comparing carefully this latter 

 with the lower jaw in Cynognathus crateronotus, described by 

 Seeley in 1895, I have arrived at the conclusion that the difference 

 between them is a very considerable one, and that in the lower 

 jaw of Gomphognathus we have the greatest known development 

 of the dentary bone in any theriodont reptile, a development 

 representing the initial state of the double articulation, if not the 

 actual double articulation itself. 



The main points of difference in the lower jaws of Gompho- 

 gnathus and Cynognathus are the following : — 



1 . In Gomphognathus the articular bones are placed inside and 

 laterally at some distance from the dentary bone, whilst in 



* Communicated by Dr. C. W. Andrews, F.R.S., F.Z.S. 



Proc. Zool. Soc.— 1918, No. XY. 15 



