the Skull of Diademodon. 325 



This seems to me good evidence that the tympanic is not 

 derived from a bone whose main if not its only function is 

 the protection of the under surface of the ear. 



I am therefore unable to accept the identification of the 

 problematical bone in Cynodonts called by Broom tympanic 

 with the bone of the same name in Mammals. If a mamma- 

 lian homologue must be found for it^ the entotympanic, 

 which stretches from the tympanic to the basisphenoid in 

 Tapaia, seems the most suitable ; but as this bone does not 

 seem to be of wide distribution in the Mammalia, it is 

 probably a neomorph. 



The resemblances of the Cynodonts, and, indeed, of 

 Therapsids generally, to Mammals have been commented on 

 by all authors from the time of Owen^s original description 

 till to-day, and almost all recent descriptions of their 

 remains have been written from the mammalian standpoint. 

 The preceding description is one of the few exceptions, and 

 it was not until I had spent many days in fruitlessly trying 

 to identify the various foramina by comparison Avith marsu- 

 pial and insectivore skulls that I commenced a comparison 

 with other reptiles. 



The resemblances of Therapsids to Mammals are : — 



1. The presence of a single zygomatic arch formed by the 



squamosal and jugal. (Owen, Seeley, Broom.) 



2. The division of the teeth into incisors, caniues, and 



cheek-teeth. (Owen, Seeley, Broom.) 



3. The mode of insertion of the teeth. (Owen, Seeley.) 



4. The presence of a secondary palate in Cynodonts. 



(Seeley, Broom.) 



5. The presence of a median vomer (developed from the 



parasphenoid ?). (Broom.) 



6. The great reduction of the quadrate and the bones of 



the lower jaw except the dentary. (Seeley, Broom.) 



7. The presence of a long distinct external auditory 



meatus. (Gregory.) 



8. The double occipital condyle of Cynodonts. (Seeley.) 



9. The general resemblances in the vertebral column. 



(Seeley.) 



10. The very mammalian form of the scapula and pectoral 



girdle. (Seeley, Broom.) 



11. Tlie build of the humerus. (Owen, Seeley, Broom.) 



12. The presence of an olecranon process. (Seeley). 



13. The structure of the carpus. (Seeley, Bardeleben, 



Broom.) 

 Ann. & Mag. N. Hist. Ser. 8. Vol. viii. 22 



