20 



transmits the origins of tlie two rig'lit oblique muscles of 

 the eye. The ethmoid cartilage appears on the surface of 

 the skull on each side of the mesethmoid immediately 

 above the vomer. It is bounded by the parasphenoid, the 

 prefrontals, mesethmoid and vomer. 



Yomer (Vo., figs. 1, 2, 3). — A median unpaired bone 

 consisting of an anterior head and a posterior ^haft taper- 

 ing to a point. The latter is firmly fixed into a long 

 tapering cavity in the base of the parasphenoid to such an 

 extent that the extremity of the parasphenoid is brought 

 very near the anterior end of the vomer. The cavity in 

 the parasphenoid lodging the vomer is quite distinct from 

 that immediately above it for the ethmoid cartilage and 

 the left prefrontal. The head of the vomer is markedly 

 asymmetrical, and has a laminate process on each side, the 

 right of which is appreciabl}^ larger than the left. In 

 front the vertical face is inclined towards the eyeless side, 

 thus further deflecting the motion of the intermaxillary 

 cartilage, and hence the jaw apparatus, to that side. The 

 vomer is bounded by the parasphenoid, prefrontals, 

 ethmoid cartilage and mesethmoid. 



Parasphenoid {Pa.S., figs. 1, 2, 3). — A very long un- 

 paired bone with a prominent keel. It is ver}^ asymmetri- 

 cal, taking at the region of the alisphenoids a sharp turn 

 towards the eyeless side. Behind it fits into a depression 

 on the base of the basioccipital, and forms a portion of the 

 floor of the cranial cavity in front of the latter bone, its 

 dorsal surface being here deeply grooved. Its relations 

 in front to the ethmoid cartilage, left prefrontal and 

 vomer have been described above. The parasphenoid is 

 bounded by the basioccipital, prootics, alisphenoids, left 

 prefrontal, ethmoid cartilage and vomer. 



Nasal {R.Na., figs. 1, 2, 3). — Only the right nasal is 

 present — the left having completely aborted with the 



