322 ROBERT J. TERRY 



Pterygoid cartilage (figs. 1, 3, 24). In the model of the cranium 

 of the 23.1 mm. embryo the pterygoid cartilages appear as a pair 

 of irregular but symmetrically formed bodies lying one on either 

 side of the naso-pharyngeal duct and adjacent to the alae tem- 

 porales. Each cartilage presents a short cyhndrical, transversely 

 placed pedicle and, continuous with it and in a dorso-ventral 

 plane, an elongate, bent plate. The pedicle consists of dense 

 mesenchyma continuous with the perichondrium of the margin 

 of the pterygoid process of the lannna ascendens; in the center 

 bone has begun to form. The N. pterygoideus (Vidiani) turns 

 dorsad upon the posterior aspect of the joint between the pedicle 

 and pterygoid process to enter the spheno-orbital fissure. The 

 plate-shaped part of the pterygoid cartilage presents a flat free 

 surface directed forward, a medial concave margin tm-ned toward 

 the naso-pharyngeal duct and a lateral convex margin giving 

 attachment to the M. pterygoideus. In structure the lamina 

 consists of mesenchymal syncytium, within which bone has 

 formed in two regions. One center lies in the dorsal half of the 

 plate ajid is continuous with the ossific center of the pedicle; 

 the second is found in the ventral half and seems to be separated 

 from the first by a stratum of unossified tissue, broad at the mar- 

 gin and surfaces of the plate, but becoming narrower toward 

 the center. I find it impossible to state whether the two bony 

 centers so clearly separated one from the other at the margins 

 of the lamina are entirely distinct throughout. A mesenchymal 

 condensation surrounds the pterygoid cartilage, extending for- 

 ward, becoming somewhat less compact, and finally joining the 

 mass of mesenchyma in which the palate bone is forming. This 

 mesenchymal mantle extends dorsally toward the cranial base 

 without, however, quite reaching it. 



The region named cavum epiptericum by Gaupp ('05) and 

 interpreted in its relation to the cranial cavity of mammals by 

 this investigator ('02) as an acquisition of a space which, in rep- 

 tiles, is extracranial, presents some interesting peculiarities in 

 the embryos of cat. First, the epipteric cave with its contained 

 structures is, in the absence of those bones which in the adult 

 form the lateral wall of the skull in this region, wholly outside 



