398 CHARLES CLIFFORD MACKLIN 



The portion of the wing above the foramen rotundum is known 

 as the lamina ascendens, and ends laterally in a somewhat sharp 

 angle, which projects freely outward and forward. The upper- 

 most angle, rather more blunt, is to be seen almost immediately 

 under the lateral edge of the optic foramen. The dorsal surface 

 of the lamina ascendens is convex, and terminates dorsally in a 

 ridge, bordering the foramen rotundum laterally. 



The lowest portion of the wing is marked by a blunt angle, 

 lying below and a little medial to the foramen rotundum, and 

 representing the processus pterygoideus. The innermost ex- 

 tremity of the wing presents a more sharply marked angle, 

 which projects freely inward, where it comes into close contact 

 with the parasphenoid bone, or internal pterygoid plate, the 

 upper extremity of which lies immediately ventro-medial to it. 

 Medially and caudally this angle is separated from the alar 

 process by a well-marked groove, — ^the deepest part of the cir- 

 cular groove which surrounds the union of the alar process and 

 the lateral portion. 



The outer margin of the lateral portion projects farther for- 

 ward than the medial (fig. 14) so that its ventral face looks 

 inward as well as forward. There is no trace of a lamina ptery- 

 goidea, perforated by the internal maxillary artery, such asVoit 

 describes in the skull of the rabbit. 



Histologically, modification of the cartilage cells in the upper 

 lateral portion of the wing indicates beginning endochondral 

 ossification; Mall found the first trace of the alisphenoid bone 

 in an embryo of 58 days. Medial to the foramen rotundum the 

 cartilage is thinner and of younger character than that else- 

 where in the lateral portion, indicating that this was the part 

 which was, perhaps, latest to form. 



Gaupp has pointed out that the brain-case of the mammals 

 has, in the orbitotemporal region, been enlarged by the inclu- 

 sion of a space which, in the lizards, lies below the primitive 

 side-wall of this region, and to which he has given the name 

 'cavum epiptericum.' This space is the ventral continuation 

 of the cavitj^ which has been described by Voit in lepus as the 

 cavum supracochleare. Voit has found in an early rabbit embryo 



