128 ANNALS NEW YORK ACADEMY OF SCIENCES 



Eryops 

 Plate XII, Fig. 1 



The massive, frog-like skull of Eryops, a Permian stegoceph, is restored 

 with the armran type of musculature, though some modifications have 

 been made because of the changes that have taken place in the anuran 

 skull. The skulls of the stegocephalians and of the Anura are strikingly 

 similar in general pattern; that of Eryops with the dermal roofing bones 

 covering the whole skull; that of the Anura with these bones modified, 

 partly eliminated, and all more or less sunken beneath the skin. The 

 large palatine vacuity is similar in both. Gregory has suggested that the 

 ancestor of the Anura was an animal much like Eryops, but that through 

 the changes of the geologic ages the anuran skull became simplified, 

 specialized, and the dermal temporal covering became fenestrated, partly 

 as a result of the action of the muscles. The pterygoid region has changed 

 slightly and has lost the flange that in Eryops projects down in a very 

 reptilian-like manner. The mandibles are quite similar, although Eryops 

 did not have the backward extension of the articular for the insertion of 

 the depressor mandibular as in the frog, and the frog has lost the promi- 

 nent suprameckelian fossa in the mandible that is so prominent in Eryops. 

 In the Anura the muscles are all very far back on the skull, and we may 

 assume from the Eryops skull that its muscles had a similar position, 

 except that to make the jaw stable it should have had an anterior ptery- 

 goid muscle on the floor of the downwardly projecting pterygoid process. 

 The loss of the anterior pterygoid muscle in the Anura is a peculiar spe- 

 cialization which, very probably, had not been attained by Eryops. 



The restoration of Eryops gives the following muscles: 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY V z ) 



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

 Capiti-mandibularis medius (C. m. m.). 

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

 Pterygoideus anterior. 



MUSCLES OF THE DEPRESSOR OR DIGASTRIC GROUP 

 (INNERVATED BY VII) 



Depressor mandibular. 



MUSCLES OF THE ADDUCTOR OR TEMPORAL GROUP 

 (INNERVATED BY V 3 ) 



Capiti-mandibularis superficialis (C. m. s.). — The masseter element 

 would occupy the posterior part of the skull in the space under the 



