THE PINEAL ORGAN OF MAMMALS 



301 



parietal foramen, which becomes still further reduced in the Cynodont 

 reptile Glochinodontoides gracilis (Haughton) (Fig. 206). In this the two 

 parietals are fused and the antero-posterior ridge between the temporal 

 fossae, mentioned on p. 268, is already prominent. In the skull of the 

 small Ictidosaurian ■ reptile (Fig. 228) found in beds of a 

 later period (Rhoetic or Lower Jurassic) the development of this longi- 

 tudinal ridge is still more pronounced, the parietal bones being fused 

 throughout their whole length and the parietal canal having disappeared 



Tab 



Fig. 206. — View from above the skull of a primitive Cynodont Reptile, 

 Glochinodontoides gracilis, Haughton. Natural size. (After Broom.) 



The two parietal bones have fused to form a median longitudinal crest. The 

 pineal foramen is still present and is oval in form. The parietal bones share 

 in the formation of the temporal fossa. 



Al. S. : ala of sphenoid. 



E. Oc. : ex-occipital. 



F. : frontal. 



LP. : inter-parietal. 

 J. : jugular. 

 L. : lacrimal. 

 Mx. : maxilla. 

 N. : nasal. 



Par. : parietal. 



Po. O. : post-orbital & post-frontal. 



Pr. F. : pre-frontal. 



Pr. Mx. : pre-maxilla. 



5. Oc. : supra-occipital. 



Sq. : squamosal. 



Tab. : tabular. 



completely. In this animal, besides the keel-like interparietal crest, there 

 are two occipital condyles and the articulation of the lower jaw with the 

 base of the skull is still more mammalian in type than it is in the preceding 

 forms, for although the joint between the articular and quadrate is still 

 present, the dentary almost reaches the squamosal. For these and other 

 reasons the Suborder Ictidosauria is regarded as forming one of the connect- 

 ing links between the cynodonts (dog-toothed reptiles) and the Mammalia. 

 A more human type of the parietal region of the skull-roof is met with 

 in the Gorgonopsian reptile Scylacops capensis (Broom). This, although 



1 iktISes, weasel-like. 



