1895.] SElfSOET CANAL SYSTEM OF FISHES. 289 



side of the head. A similar series of grooves are present in the 

 nasal region, these entering into connection Avith the terminal 

 pore of the supra-orbital branch of the main canal. There is no 

 anastomosis of the grooves of one side with the other. 



Innervation. 



In describing the cranial nerves of the Selachoid Ganoids (3) 

 attention was drawn to the great development of the facial nerve. 

 So far in the Physostomous Teleosts the trigeminal has been the 

 larger, and this is perhaps more evident in Esox Indus than in any 

 type previously described. 



The sensory canal system is innervated by the same four groups, 

 viz. the trigeminal, facial, glossopharangeal, and vagus. 



Tlie Trit^eminal Group. — The branches supplying the sensory 

 canal system are : — 



1. The ramus ophthalmicus superficialis. 



2. The ramus buccaUs. 



3. The ramus oticus. 



4. The ramus mandibularis. 



1. The ramus ophthalmicus superficialis is the most dorsal branch 

 of the trigeminal group (PI. XX. fig. 11). It passes forwards some 

 distance above the orbit and divides into two smaller branches, 

 which each terminate in a number of fine divisions some little 

 distance from the snout. The nerve lies beneath the supra- 

 orbital branch of the sensory canal, to which it gives off a series of 

 fine twigs. 



2. The ramus buccalis. — The main divisions of the trigeminal are 

 the ramus buccalis and the ramus maxUlo-mandibularis ; the former 

 is the anterior and more dorsal division and passes behind and 

 beneath the orbit, and then across the side of the face, where it 

 divides into two, each division further dividing into a number of 

 fine twigs which spread themselves over the terminal region of the 

 snout. From the main branch of the buccalis a fine branch passes 

 off to the sub-orbital branch of the main sensory canal, giving off a 

 series of fine twigs to the sensory organs (PI. XX. figs. 10, 11). 



3. The ramus oticus arises in close proximity to the ramus 

 ophthalmicus superficialis. It passes posteriorly and divides into 

 two, the dorsal branch innervating the main canal of the head 

 (fig. 10, r.ot.). 



4. The ramus maxillo-mandibularis is the largest division oE the 

 trigeminal group. It passes ventrally to the angle of the jaw, 

 where it divides into internal and external mandibular branches. 

 Some little distance above the internus the ramus maxiUaris passes 

 off (PI. XX. figs. 10, 11). The ramus mandibularis externus 

 innervates the mandibular canal ; it passes on the ventral portion 

 of the mandible and gives off two series of fine branches, one to 

 the canal and the other to the integument. The ramus internus 

 divides on the inner side of the mandible into numerous smaller 

 branches (PI. XX. fig. 12). 



Peoc. ZooL. Soc— 1895, No. XIX. 19 



