ADAMS, PHYLOGENY OF THE JAW MUSCLES 129 



squamosal. It would probably have its origin on the inner side of the 

 squamosal and quadratojugal, with a few fibers running to the quadrate 

 and extending ventrally ; it would be inserted on the borders of the supra- 

 meckelian fossa of the mandible. It is on the outside of the mandible in 

 the Anura ; but from the shape of the skull and the mandible there is no 

 chance for it to be inserted there in Eryops. The muscle is split in the 

 Anura and so the masseter of Eryops might have had two parts, the 

 smaller one posterior, in the region of the small quadrate. 



Capiti-mandibularis medius (C. m. m.). — This temporal slip of the 

 adductor mass would be under the superficial portion and over the ptery- 

 goid muscle. It would have its origin on the inner side of the parietal, 

 with perhaps a slight attachment on the postfrontal. It would be inserted 

 in the suprameckelian fossa. The muscle could extend quite far in the 

 parietal region, taking hold under the skull roof. Possibly the deep part 

 of this mass may have had a separate slip, corresponding to the capiti- 

 mandibularis profundus or "pterygoideus externus" of reptiles. 



Pterygoideus anterior (Pt. a.). — The pterygoid muscle of Eryops was 

 probably not homologous with the so-called "pterygoid" of the frog, but 

 was more probably homologous with the anterior pterygoid muscle of 

 primitive reptiles. The pterygoid bone is quite different from that of 

 Anura, in that it has a descending flange, much like that of the Croco- 

 dilia, that fits snugly along the inside of the mandible and serves as a 

 guide for it. As this flange in the reptiles is functionally connected with 

 the anterior pterygoid, it seems probable that Eryops had an anterior 

 pte^goid muscle that extended along the pterygoid bone as far as the 

 orbit. A pterygoid muscle is needed here for mechanical reasons, as 

 from the teeth one would judge that the jaw was used differently from 

 that of Anura, and there is need of a muscle here to oppose the pull of 

 the temporal muscles, which would tend to pull the symphysis apart. 

 Thus a pterygoid in this region would steady the jaw and pull the jaw 

 forward against the other muscles. It would have to be inserted in the 

 suprameckelian fossa, possibly extending to the back part. 



Capiti-mandibularis profundus (C. m. p.). — There is a strong possi- 

 bility that there was a deep slip of the adductor mass, deep under the 

 muscles, that would correspond to pterygoideus posterior of the reptiles. 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Depressor mandibular. — The articular of Eryops does not have the 

 posterior process and the muscle must have been inserted on the under 

 side of the articular. In some American Museum specimens the mandible 



