88 ANNALS NEW YORK ACADEMY OF SCIENCES 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Depressor mandihulce (D. m.). — ^This is a double-headed muscle, as in 

 most urodeles. The anterior portion arises on the posterior face of the 

 squamosal, the posterior from the dorsal fascia. They are inserted on 

 the outer, dorsal face of the posterior end of the mandible. 



AMBLYSTOMA 

 Plate V, Figs. 6, 7 



The remaining urodeles are very similar in musculature, at least in the 

 three forms studied in this paper. About the only difference is the separa- 

 tion of the lower, inner part of the temporal mass to form a separate 

 pterygoideus posterior. 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY V^) 



Capiti-mandibularis superficialis (C. m. s.). 



= Masseter. 

 Capiti-mandibularis profundus (C. m. p.). 



= Posterior slip of the temporal. 

 Pterygoideus posterior (Pt. p.). 



= Pterygoideus. 

 Pterygoideus anterior (Pt. a.). 



= Anterior head of the temporal. 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (IXXERVATED BY VII) 



Depressor mandibularis (D. m.). ' 



Reptilia 



chelydra 

 Plate VI. Figs. 1, 2 



The primitive chelonian Proganochelys is the earliest Icnown representa- 

 tive of the Chelonia. Unfortunately it is known only by the cast of the 

 interior of the shell. Although the skull is unknown it was probably of 

 the heavily roofed type, something like that of the existing Chelone. 

 Watson (1914, pp. 1011-1020) describes the Permian genus Eunotosaurus 

 as a probable ancestor of the Chelonia. It is quite probable that the 

 ancestral chelonians were like the cotylosaurs with the temporal region 



