THE SENSORY CANAL SYSTEM OF FISHES. 515 
(iii) The largely developed rostrum. 
The principal nerve groups innervating the sensory canal 
system are the trigeminal, the facial, and the vagus. The 
fact of the trigeminal actually innervating a part of the sen- 
sory canal system is of special interest, seeing that Ewart (25) 
found that in Lemargus and Raia the innervation proceeded 
from the facial and vagus only.} 
The cranial nerves of Polyodon have been briefly de- 
scribed by van Wijhe in his memoir on the cranial nerves of 
Ganoids? (82). For purposes of comparison I have reproduced 
his figure, and it will at once be seen that there are a number 
of important differences between his description and figure and 
those here given (Pl. 40, figs. 9 and 10). 
Van Wijhe (82, p. 240) states that the specimen he worked 
at was a young one and only small. It is probably owing to 
the fineness of the nerves in such a specimen, of which he 
frequently makes mention, that our accounts differ so widely 
from one another. 
The Trigeminal group may be divided into five branches, 
viZ.— 
1. The Ramus opthalmicus superficialis. 
2. The Ramus opthalmicus profundus. 
3. The Ramus maxillaris. 
4. The Ramus mandibularis. 
5. The Ramus oticus. 
1. The ramus opthalmicus superficialis is the most anterior 
branch of the group, and passes forwards dorsal to the orbit 
and on the inner side of the olfactory capsule. 
2. The ramus opthalmicus profundus is given off from the 
main branch of the trigeminal, and lies ventral to the ramus 
opthalmicus superficialis and much deeper. In front of the 
1 Ewart treats of the ramus oticus as distinct from the trigeminal nerve. 
2 « Als ich Spatularia untersucht, kannte ich die Wichtigkeit des Ver- 
laufes der Schleimcanale noch nicht, sodass ich nur sagen kann, dass der 
mandibulare Zweig vor dem Spritzloche das Cranium verlasst, langs dem ~ 
Vorderrande des Hyomandibulare und dann zwischen Unterkiefer und Hyoid 
verlauft. Hr liegt unbedeckt in der weissen Haut und fallt sogleich in die 
Augen; seine Wande sind verknéchert”’ (p. 247, § 4). 
voL. 36, PART 4,—NEW. SER. MM 
