MUSTELUS L^.YTS. 153 



ophthalmicus profundus issues from the brain case, after 

 having re-entered it near the anterior end of the orbit. It 

 is evidently the homologue of the branch s. of.^ of Ewart's 

 (18) descriptions of other selachians. 



Slightly anterior to the large lateral branch to organs 1 to 

 16, a lateral branch is given off to supply organs 59 to 64 

 supra-orbital, which]organs_lie in or near the distal one of the 

 two bends of the supra-orbital canal immediately in front of 

 the eye. 



Anterior to this point the main nerve, running forward, 

 comes to lie in the angle between the side wall of the 

 brain case and the dorsal surface of the bulging side wall 

 of the nasal capsule. The ramus ophthalmicus pi'ofundus, 

 having issued a second time from the cranium, here lies 

 slightly ventro-lateral to the main ophthalmicus superficialis, 

 the large general sensory branch of the latter nerve lying 

 slightly dorso-mesial to it. As the main nerve continues for- 

 ward, in this position, it soon reaches a point where the 

 cartilaginous side wall of the brain case is entirely replaced 

 by membrane, this perforation of the cartilaginous skull being 

 the much enlarged prefrontal opening of Gegenbaur's descrip- 

 tions of the adult. The nerve here lies lateral to the now 

 membranous side wall of the brain case, on the dorsal surface 

 of the cartilaginous nasal capsule, slightly lateral to its highest 

 point. In this position it runs forward, and soon gives off, 

 from its dorsal aspect, two large ampullary sensory branches 

 which run at first forward, and somewhat dorsally and 

 mesially. The more superficial of these two branches here 

 soon breaks up and supplies the organs of that sub-group of 

 the superficial ophthalmic group of ampul'ae that has its sur- 

 face pores on the dorsal surface of the head mesial to the 

 orbit. The ampullae themselves, of this group, lie, in 

 12*2cm. embryos, along the lateral surface of the membranous 

 anterior end of the brain case, and immediately dorsal to the 

 nasal capsule. The tubules of the lateral ampulla of this sub- 

 group lie internal to, and separated by membrane from, the 

 tubules of that sub-group of the ophthalmic ampullae that has 



