882 MR. WAIiTEE E. OOLLINGE ON THE SENSOBT [DeC. 17, 



4. Innervation. 



In view of recent researches upon the innervation of the sensory 

 canal-system in fishes, the results obtained in Ghimmra are ex- 

 ceedingly interesting and quite unlike what I expected. 



Until quite recently it M^as generally assumed that the inner- 

 vation of the sensory canal-system in fishes proceeded from the 

 trigeminal group of nerves. Ewart (6 & 7), who was the first to 

 carefully investigate this matter in the Elasmobranchii, has shown 

 that the whole system is innervated by the facial complex, ramus 

 oticus and vagus, " the fifth taking no part in innervating the 

 canals." In the Ganoidei, AlHs (1) and others have shown that 

 this innervation still obtains, supplemented in Poh/odon (3) by the 

 trigeminal. In the Teleostei (5) the facial is almost entirely 

 replaced by the trigeminal group ; and, judging from comparative 

 smallness of the branches of the facial in Protopterus (13) and 

 Lepidosiren, we may safely assume that the fifth also innervates 

 the canals in the Dipnoi. 



From the nature of the skeleton, the fact that the sensory canals 

 persisted as open grooves, and the presence of ampullary canals, in 

 all three features showing a close affinity with the Elasmobranchs, 

 I expected to find an innervation solely from the facial ; but the 

 condition which actually exists is just the reverse, for we find an 

 enormous development of the branches of the trigeminal nerve, 

 particularly of the ramus ophthalmicus superficialis and profundus 

 and ramus buccalis. 



Before describing the distribution of the nerves I would point 

 out that Stannius (17), as early as 1849, stated that in Callorhyn- 

 chus certain parts of the canals were innervated by the ramus 

 buccalis and ramus maxillaris superior of the fifth nerve. 



The Trigeminal Group consists of the following main branches : — 



1. The ramus ophthalmicus superficialis. 



2. The ramus ophthahnicus profundus. 



3. The ramus buccalis. 



4. The ramus maxillaris. 



5. The ramus mandibularis. 



1. The ramus ophthalmicus superficialis is the most dorsal and 

 anterior branch. Previous to entering the orbit it joins with the 

 facial by a commissure (PI. LII. fig. 7, V. com.), and some little 

 distance in front of this joins with the branch which on entering 

 the orbit divides into the ramus buccalis and ramus maxillaris. 

 The superficiaHs passes across the orbit and through a foramen at 

 the opposite side. In its course across the orbit it gives ofE six 

 dorsal branches. 



2. The ramus ophthalmicus profundus passes beneath the two 

 commissures referred to above and below the superficialis. Ante- 

 rior to the orbit both superficialis and profundus anastomose and 

 then break up into a multitude of fine branches, which innervate 

 the supra-orbital branch of the main sensory canal of the head. 

 (PI. LII. fig. 7.) 



