EXPI.ANATIOA Ol' ri.ATE XIII 



licstuiatiou of the jnw uiuscles of Tijroinio^ainu)^, representing the Dinosauria 

 Theropoda. and of Ciiuodnnthus, representing the Tlierapsida 



Fui. 1. — Tjinni noun urn i<. Superlieial muscles. 



As in many other reptiles, the capiti-mandibularis {('.ni.>i.\ was probably 

 differentiated into three layers, the more superficial layer of which {Cm.) is 

 analogous \Yith the masseter of higher types of mammals. The supratemporal 

 fenestra was probably filled l)y the middle and deep layers. The pterygoideus 

 anteri(»r may have tilled the si)ace beneath the preorbital fenestra. 



Figs. '1-'}. — Cinior/iiathihs. Jaw muscles. 



A distant approach to mammalian conditions is seen in the reduction vt the 

 jKisterioi' jaw elements and in the enlargement of the ascending ramus of the 

 dentary. W'ry probably the outer layer of the capiti-mandibularis was attached 

 to the lower border of the zygomatic arch in the position of its homologue, the 

 iiuimmalian masseter. The middle and deep layers fill the temporal fossa as 

 in niannnals. Cynognathus probably still retained the reptilian pterygoideus 

 anterior which does not api>ear to l)e homologous with either of the pterygoid 

 muscU's of mammals, but may possibly be i-epresented by the tensor tympani. 

 The capiti-mandibularis was in a better position to giA-e rise to these muscles. 

 A true depressor mandibuhe (D. ni. i was doubtless present and the general ar- 

 rangement of the muscles was reptilian in type. 



A. = articular ( inside) D. = dentary 



Ang. =:r angular P. art. =:prearticular 



Art. = articular (outside^ Snr. a.= surangular 



C'r. =: coi'onoid 



