Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 91 



of the process forms the ventral part of the hmd edge of the orbit 

 and the larger part of the lateral edge of the orbital opening of 

 the eye-muscle canal. Between the petrosal and the hind edge 

 of the process, in the angle between that hind edge and the lateral 

 edge of the body of the bone, lies the internal carotid foramen 

 (icfr, Figs. 7, 18). A small process of bone sometimes separates 

 the anterior edge of this foramen from the hind edge of the 

 lateral wing of the bone, the foramen thus being partly en- 

 closed in the parasphenoid. 



The anterior end of the parasphenoid is thin and is overlapped 

 ventrally for a considerable distance by the hind end of the 

 vomer, a depressed region on its external surface receiving the 

 latter bone. On the dorsal surface of this part of the para- 

 sphenoid, there is a long median ridge which fits into a correspond- 

 ing groove on the ventral surface of the chondrocranium. Pos- 

 teriorly, toward the middle of the orbit, the ridge gradually 

 disappears. This ridge may represent the beginning of the 

 formation of the vomer bone of mammals from the parasphenoid 

 of fishes (No. 7, p. 458). 



On the ventral surface of the parasphenoid, between its 

 lateral wings, there is a strong median ridge which separates the 

 surface of insertion of the adductor arcus palatini of one side of 

 the head from that of the corresponding muscle of the other side. 



The Eye-Muscle Canal is large, extending from the basi- 

 sphenoid, backward, almost to the extreme hind end of the skull. 

 Its anterior end is wide, its posterior end narrow, the canal taper- 

 ing gradually from one end to the other. Its orbital opening, on 

 each side, is formed by the anterior edge of the lateral wing of 

 the parasphenoid, by a part of the anterior edge of the petrosal 

 and a part of the basisphenoidal process of that bone, by the in- 

 ferior surface of the horizontal .wing of the basisphenoid, and by 

 the shank of the latter bone. The shank of the basisphenoid 

 separates the anterior end of the canal into its two parts or 

 openings. 



The roof of the eye-muscle canal is formed by the wings of the 

 basisphenoid, by the membrane that closes the pituitary opening 

 of the cranial cavity, by both the anterior and posterior portions 

 of the mesial, horizontal processes of the petrosals, and by a 



