Explanation of Plate VII 

 Jaw muscles of streptostylic reptiles: Iguana and Vara nits 



Figs. 1 and 2. — Iguana. (Muscles mainly after Mivart.) 



The superficial muscles are shown in Fig. 1, and the deep muscles in Fig. 2. 



The capiti-mandibularis is divided into three layers, which have the same 

 arrangement as in Sphenodon. The pterygoideus anterior (Pt. ant.) differs 

 from that of Alligator in being confined to the posterior part of the skull. 



Figs. :J-o.— Vara nuts. ( Muscles mainly after Watkinson.) 



The superficial muscles are shown in Fig. 3, the middle layers in Fig. 4, 

 and the deep layers in Fig. 5. 



In correlation with the extreme mobility of the jaws the pterygoid muscles 

 are differentiated into four distinct elements, pterygoideus anterior (Pt.ant.), 

 pterygoideus posterior {Pt.post.), pterygo-sphenoidalis (Pt.s.), and pterygo- 

 parietalis (Pt.pa.). These arc probably all derived from the primitive ad- 

 ductor mass and along with the three divisions of the capiti-mandibularis are 

 innervated by V,. 



