OBSERVATIONS ON THE CRANIAL NERVES OF SCYLLIUM, 485 
roots, a larger one immediately in front of the auditory, and a 
smaller one passing to it from the fifth. 
Jackson and Clarke’ describe the combined fifth and seventh 
nerves in Lehinorhinus as arising by three roots; an anterior 
inferior root (v a), itself with two well-marked rootlets, a second 
root (v 3) arising by a well-marked superior rootlet from the 
lobus trigeminus and by a smaller inferior one, and a third root 
(v y and vit) closely connected with the second one. 
Balfour? describes the fifth nerve in Scyddiwm stellare as arising 
by three roots :—(1) an anterior more or less ventral root; (2) 
a root rather behind this arising by two strands, a dorsal and a 
ventral, and closely connected behind with the root of the 
seventh; and (3) a quite distinct dorsal and posterior root 
situated slightly behind the dorsal strand of the second root. 
The seventh nerve is described as arising by a single root close 
to, and behind, the second root of the fifth. 
On comparing these descriptions of adult Elasmobranchs with 
our own observations on embryos and adults we are led to the 
following conclusions : 
The fifth nerve in the adult arises by two roots : 
a. An anterior one arising from the ventral surface of the 
medulla by two non-ganglionic rootlets, whose distinctness varies 
much in different adult Elasmobranchs. These rootlets are the 
tertiary or anterior roots of our embryos (figs. 10, 11, and 14, 
vy). This root corresponds to the first root of Stannius, the 
anterior root (a) of Gegenbaur, the anterior inferior root (v a) 
of Jackson and Clarke, and the anterior root (1) of Balfour. 
6. A posterior larger ganglionic root, the ventral or secondary 
root of our embryos (figs. 10, 11, and 14, v3). This is at first 
quite distinct from the root of the seventh, but during the later 
stages of development gradually approaches this latter, and in 
the adult cannot be clearly distinguished from it. 
This root is the anterior part of the second root of Stannius ; 
the ventral division ((3) of the posterior root (4) of the fifth of 
Gegenbaur; apparently the inferior rootlet of the second root 
(v 6), and possibly part of the third root (vy and vit) as well, of 
Jackson and Clarke; and the second root (2) of the fifth of 
Balfour. 
The seventh nerve in the adult arises by two roots: 
a. A dorsal root arising far up the side of the medulla, at the 
junction of the thickened sides and thin roof of the fourth ven- 
tricle. This root is the primary or dorsal root of the seventh 
nerve of our embryos (figs. 2, 3, 6, 9, 12, 14, and 15, vir a), 
* “The Brain and Cranial Nerves of Zehinorhinus spinosus.” ‘Journal 
of Anat. and Phys.,’ vol. x, p. 81 , 
2 Op. cit., pp. 194 and 195, 
