118 Bulletin American Mtiseum of Natural History. [Vol. XXVII, 



Primitive, reptilian characters of the Cynodoniia. 



The Cynodont skull (Figs. \B, '2B) is distinguished from the generalized 

 mammalian skull by characters which appear for the most part to be of 

 a primitive rather than divergent nature. Separate pre- and post-frontals 

 and (except in Bauria) a post-orbito-malar bar are retained, the opposite 

 occipital condyles are continuous across the mid-line, the basioccipital is 

 extremely short, the palatine plate of the maxillary is short, the secondary 

 palate is limited to the anterior part of the skull; the pterygoids are large 

 anteriorly but are smaller than those in Sphenodon and the Therocephalia; 

 ending anteriorly in large flanges/ running inward toward the middle 

 line and overlapping the basisphenoid; alisphenoids diverging posteriorly; 

 the reduced quadrate and articular apparently had not yet begun to func- 

 tion as accessory auditory ossicles (see below). The skeleton of Cynodonts 

 differs from that of mammals in many important particulars. A well de- 

 veloped proatlas is present. The cervical vertebrae of Cynognathus (Seeley, 

 1895.4, p. 98) bear large separate intercentra, structures which are not found 

 in the cervical vertebrae of mammals, but which may be represented by the 

 chevrons in the tail and possibly by minute intercentra in the lumbar region 

 of certain Insectivores, especially in the embryo (see however p. 265 below). 

 The dorso-lumbar vertebra^ of Cynognathus (Seeley, Joe. cit., p. 105) bear 

 peculiar broad, flattened ril)s which curve backward, and distally overlap 

 each other. 



The femur of Cynognathus (Seeley, ioc. cit., p. 120) is very primitive and 

 seems to indicate that the limb was held well out from the body. The 

 greater and lesser trochanters together form a great broad curved crest 

 upon which rests the small sessile head; the femur thus contrasts sharply 

 in form with all known mammalian types. 



In Diademodon the lesser trochanteric ridge is not so big and offers a 

 better, but still distant, comparison with the Monotreme type (Broom, 

 1905.4, p. 100). The pelvis in Cynognathus is typically reptilian in its 

 broadly triangular ilium (Seeley, 1895.4, p. 113). That of Diademodon is 

 noticed below (p. 119). 



Characters in wiiirJi the Cynodontia foreshadoic tJie Mammalia. 



Skeleton.— The atlas of Cynocjnathvs (Seeley, 1895.4, pp. 100-102) 

 resembles that of Ornithorhynchus in the median ventral extension of the 

 anterior facet. The cervical vertebrae also bore ribs. 



1 These flanges were called "transverse palatines" by Seeley but Broom (1909.2) has 

 recently proved that they are entirely comparable with the mammalian pterygoids. 



