90 ANNALS NEW YORK ACADEMY OF SCIENCES 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY J\) 



Capiti-mandibularis (Cm.). — This represents the large capiti-man- 

 dilmlaris of the other reptiles and the adductor mandibularis of fishes, 

 or at least a part of it. It is peculiar in the turtles in that they have 

 developed a great occipital spine that supports this muscle. It arises on 

 the following bones : prootic, quadrate, parietal, squamosal, occipital spine, 

 opisthotic. It is inserted on the posterior part of the mandible. 



Pterygoideus anterior (Pt. a.). — This is the large pterygoid muscle of 

 reptiles with a monimostylic skull. It covers the floor of the pterygoid 

 and palatine region and has a firm hold on the edge of the palatal vacui- 

 ties. It arises on the pterygoids and palatines, extending almost under 

 the eyes, from the parietal, pterygoid, prootic and quadrate. It is in- 

 serted on the inner face of the prearticular. It does not wrap around 

 the mandible on the outside as it does in most reptiles. 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Depressor mandihulce (D. m.). — The backward growth of the squa- 

 mosal has captured this muscle so that it now is attached to it, instead 

 of to the parietal, as in most reptiles. In Chelydra the whole origin 

 is on the large and prominent squamosal, which may be explained by the 

 assumption that the growth of the squamosal pushed back on the depressor 

 mandibuh^ (parieto-mandibularis), and that, gradually, the attachment 

 on the squamosal became more important, and finally the origin on the 

 parietal was lost, as a result of the shifting of the bones of the skull. 

 The depressor mandibulse is attached along the upper, posterior face of 

 the squamosal and is inserted on the under surface of the articular. 



There is much in the condition of the skull in turtles to suggest the 

 cotylosaurs, and I assume that the muscular system must have been 

 similar. 



SPHENODON 

 Plate VT. Fiss. ,3, 4 



The supratemporal fenestra of Splienodon gives exit to the temporal 

 portion of the capiti-mandibularis on top of the skull, while the lateral 

 temporal fenestra permits the masseter portion to expand freely in masti- 

 cation. Owing to the fixed or monimostylic condition of the quadrate, 

 there is very little movement either of the fore part of the skull upon 

 tlie back part or of the pterygoid region. In correlation with this 

 immobility the specialized pterygoid muscles are absent. 



