244 



THE OSTEOLOGY OF THE REPTILES 



4. Tribe Cynodontia 



Especially characterized by a heter- 

 odont dentition, a secondary palate, 

 reduced posterior mandibular bones, 

 and two occipital condyles. Dentition 

 composed of from three to five incisors, 

 a canine, and seven to nine, rarely thir- 

 teen, molars, secodont or gompho- 

 gnath or cuspidate. Temporal opening 

 bounded by parietal and postorbital 

 above, usually by squamosal and post- 

 orbital only below; frontals small, ex- 

 cluded from orbital margin by the 

 union of the prefrontal and postorbital ; 

 postfrontals absent; parietals narrow; 

 a small parietal foramen, but no pre- 

 parietal bone ; tabular large ; quadrate 

 small; stapes long, stout or slender; the 

 pterygoids do not reach the quadrate; 

 probably a small ectopterygoid ; vomer 

 large, unpaired. Coronoid large. A 

 small acromion on scapula; scapula 

 with reflected anterior border; no clei- 

 thrum. Fifth carpale unossified; pha- 

 langeal formula 2, 3, 3, 3, 3, so far as 

 known. A thyroid foramen in pelvis. 

 Feet imperfectly known, the digits 

 short. Vertebrae amphicoelous ; no 

 dorsal intercentra. Twenty-eight pre- 

 sacrals, four sacrals. 



Family Nythosauridae. Septo- 

 maxillae on face; molars less cuspidate; 

 Jj] posterior mandibular bones less re- 



duced. 

 Middle Triassic. Nythosaurus Owen, Ictidopsis Broom, Gale- 

 saurus Owen, Platycraniellus v. Hoepen, South Africa. 



