92 ALUS. [Vol. XVIII. 



corresponding median, horizontal portion of the basioccipital. 

 Its sides are formed by the thin, ventral, laminar portions of the 

 bodies of the petrosals, and by corresponding ventral portions of 

 the basioccipital. These latter portions of these three b^nes are 

 concave internally and convex externally, and the portions of 

 opposite sides of the head approach each other, but do not meet, 

 in the mid-ventral line. A relatively wide, median, longitudinal 

 opening is thus left between the ventral ends of the bones, the 

 opening extending the full length of the bottom of the canal. 

 This median opening, which is not closed anteriorly, is the hypo- 

 physial fenestra of Sagemehl's descriptions of other teleosts. It 

 is covered and closed ventrally by the parasphenoid, a median 

 portion of the dorsal surface of that bone forming the floor of the 

 eye-muscle canal. 



Arising from the hind edge of the shank of the basisphenoid 

 there is a median membrane which extends backward to the hind 

 end of the eye-muscle canal and has its insertion there. Its 

 ventral edge is free, excepting, perhaps, at its anterior end. Its 

 dorsal edge is inserted on the ventral surface of a stronger, hori- 

 zontal membrane, which also extends the full length of the eye- 

 muscle canal. The lateral edges of this horizontal membrane 

 are free in the anterior quarter, approximately, of its length. In 

 the posterior three fourth of its length they are inserted on the 

 lateral walls of the canal; that is on the internal surfaces of the 

 petrosals and the basioccipital. The horizontal membrane separ- 

 ates the eye-muscle canal into two parts, a dorsal and a ventral 

 one, the dorsal part being much the larger of the two. The 

 median, vertical membrane partly separates the ventral part of 

 the canal into two lateral halves. The horizontal membrane gives 

 insertion at its anterior end to the rectus superior muscle, and, on 

 a part of its ventral surface, to the rectus internus. It lies ven- 

 tral to the rectus externus, that muscle arising entirely from the 

 side- walls of the eye-muscle canal and not from the dorsal sur- 

 face of the membrane. The vertical membrane lies between the 

 two recti interni, but does not give origin to any important part 

 of their fibers. The horizontal membrane thus seems to be de- 

 veloped in some connection with the tendinous insertions of cer- 

 tain of the recti muscles, the vertical membrane being, perhaps, a 

 posterior continuation of the interorbital membrane. 



