PRIMORDIAL CRANIUM OF THE CAT 381 



Jayne ('98) has described, in the skull of the adult cat, a ptery- 

 goid process presenting a well defined internal pterygoid plate or 

 process and a variable external plate or process. Union of the 

 originally separate pterygoid bones wdth the alisphenoid takes 

 place very early, and sutures or lines indicating their boundaries 

 cannot be found in the adult. The pterygoid elements are rep- 

 resented therefore, as processes of the aUsphenoids. Reighard 

 ('02) describes an external pterygoid muscle, taking origin from 

 the external pterygoid fossa whose surface includes the lateral 

 aspect of the external pterygoid plate of Jayne, and an internal 

 pterygoid muscle springing from the internal pterygoid fossa ; the 

 latter is bounded in part by the medial surface of the external 

 plate. The internal pterygoid plate terminates in a hamular 

 process, related, in the usual manner, to the tendon of the ten- 

 sor palati. The origin of these two bony processes was found in 

 the present study in cat embryos of 7 cm., and 23.1 nam., the 

 external process being an extension of the endochondral ossifica- 

 tion of the pterygoid process of the ala temporahs, the internal 

 process consisting of an ossification, at first in membrane and 

 subsequently in cartilage, in connection with the separate ptery- 

 goid cartilage. The latter accords with an early stage of the 

 human internal pterygoid plate as described by Fawcett ('10), 

 both in its early ossification (it is the first part of the sphenoid to 

 ossify in the cat) and in the ossific process, proceeding primarily 

 in membrane and later in cartilage. The external plate is feebly 

 developed in the cat, but its ossification in relation to that of the 

 ala temporalis is nevertheless, in principle, the same as in man. 

 It will be remembered that the Vidian nerve runs along the mes- 

 enchymal junction of the pterygoid cartilage and pterygoid proc- 

 ess of the ala temporalis; now, although no suture or fine can 

 be found in the adult skull indicative of the original limit of the 

 pterygoid bone toward the alisphenoid, as Jayne has stated, yet 

 the course of the bony walled Vidian canal of the adult can be 

 taken as marking this boundary. 



Carotid foramen. The epipteric cavity in the cat embryos is 

 limited, toward the primary cranial ca\dty, by a membrane whose 

 relations to the base of the skull are of considerable interest as 



