96 EDWARD PHELPS ALUS, JUN. 



Infra-orbital Canal. 



The general course and position of all the lateral canals of 

 the adult Mustelus has been well given by Garman (21). 

 That author makes use of a special nomenclature which I 

 shall adopt only when wishing to designate the various 

 sections of the several canals, elsewhere making use of the 

 nomenclature now ordinarily employed by other authors. The 

 term infra-orbital canal will be used to designate that part 

 of the so-called main infra-orbital canal of my earlier works 

 that is innervated by the buccalis and oticus facialis. In 

 Mustelus the section so innervated extends from the anterior 

 end of the canal back to the supratemporal cross-commissure. 

 The point at which this commissure arises from the main line 

 in different fishes is, as will be later explained, apparently 

 not a fixed one. 



The infra-orbital canal of Mustelus, in my 12*2 cm. embryo, 

 and also in the adult, begins near the lateral edge of the 

 anterior end of the ventral surface of the snout, and there 

 communicates directly with the supra-orbital canal. From this 

 point the canal first runs mesially a very short distance, and 

 then turns backward in a short curve. It then continues 

 backward and somewhat mesially, and reaches the middle 

 line of the head somewhat in front of the transverse level of 

 the nasal aperture, curving gradually mesially shortly before 

 reaching this point. There it anastomoses completely with 

 its fellow of the opposite side, the two canals united 

 turning sharply backward in the median line. At about 

 the transverse level of the middle of the nasal aperture the 

 two anastomosed canals separate, each canal turning sharply 

 laterally, and then curving slightly forward until it reaches 

 the very edge of the nasal aperture. There it turns back- 

 ward and slightly laterally at a sharp angle, and, curving 

 gradually more and more laterally, passes posterior to the 

 nasal aperture toward the lateral edge of the snout. Before 

 reaching that edge, and not far from it, it makes a double 



