146 ANNALS NEW YORK ACADEMY OF SCIENCES 



Homologies of the Jaw Muscles in the Eeptilia • 

 (Table III) 



The jaw muscles of the Eeptilia and Aves show the same division into 

 masses as do those of the Pisces and Amphibia. There is the same group- 

 ing of the masses into muscles innervated by V3 and by VII and they 

 have the same relative position as in the lower forms. The muscles show 

 more specialization, as there is a higher specialization of the skull in 

 Reptilia and Aves and consequently a more complex musculature. In 

 the reptiles the capiti-mandibularis mass is more homogeneous than in 

 the Amphibia, and while the pterygoid muscles have separated off, the 

 capiti-maiidibularis superficialis remains attached. In the birds there is 

 a complete separation of the muscles. 



The great specialization in the higlier or streptostylic reptilian skulls 

 is correlated with the great complexity of the musculature. The Reptilia 

 are divided arbitrarily into two groups according to the fixity or mova- 

 bility of the quadrate ; but this is a relative division, for all stages are 

 found between the streptostylic and the monimostylic conditions. The 

 jaw muscles of the Eeptilia may be grouped according to the innervation, 

 as follows : 



MUSCLES OF THE CAPITI-MAT^DIBULARIS OR TEMPORAL GROUP 

 (INNERVATED BY V^) 



Capiti-mandibularis. 



(«.) Superficial slip (not separate). Masseter. 



{!)) Medius slip (not separate). Temporal. 



(c) Profundus slip (not separate). Deep layer. 



{d) Cranio-pterygoid. 

 Pterygoideus anterior. 

 Pterygoideus posterior. 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 {INNERVATED BY VII) 



Depressor mandibulas. 



MUSCLES OF THE CAPITI-MANDIBULARIS GROUP 

 (INNERVATED BY V^) 



CapUi-mandihularis. — This muscle is not divided into separate muscles, 

 but the conditions suggest the divisions to appear later in the mammal- 

 like reptiles, (a) The outer or superficial slip may apparently be traced 

 from the fish to the mammal. It always arises from the squamosal region 



