490 PROF. MILNES MARSHALL AND W. B,. SPENCER. 
difference of levels between the two nerves will be at once appa- 
rent. This anterior branch (vit pa) is the palatine nerve ; it has 
already acquired by stage n its characteristic distribution, and 
undergoes no further change of importance from this period up 
to the adult stage. 
The second or posterior division (fig. 12, v1 sp) of the nerve 
(virZ) runs downwards and slightly backwards along the ante- 
rior border of the spiracular cleft; it gives off branches along 
the whole of its length, the great majority of which run back- 
wards to the mucous membrane of the border of the cleft and to 
the spiracular branchia. This nerve, which at this stage is of 
about equal size with the palatine, is the spiracular or pre- 
spiracular nerve of zootomists. 
The only branch of the seventh still left for description is the 
main trunk or hyoidean branch (fig. 11, vite), which forms the 
direct continuation of the main stem of the nerve. This, as is 
seen from fig. 11, arises from the ventral or secondary root of 
the seventh, and is at its origin closely connected with the 
auditory nerve (v1). Immediately after the auditory nerve 
leaves it, the facial forms a ganglionic swelling from which the 
communicating branch (J. c’.) to the fifth nerve is given off ; 
beyond this point it is continued for a short distance as a stout 
nerve with comparatively few ganglion cells; this very speedily 
dilates into the large ganglionic swelling on the top of the 
spiracular cleft, from which the anterior branch (vir 4) is given 
off. The main stem of the seventh (vit c) continues its course 
downwards, running along the anterior border of the hyoid arch 
and very close to the posterior border of the spiracular cleft ; 
during this part of its course it contains few or no ganglion cells, | 
it gives off a number of branches, of which the first is the largest, 
from its posterior border which supply the muscles derived from 
the wall of the third head cavity (3). A short distance below 
the lower edge of the spiracular cleft the nerve divides into two 
branches, of which the anterior (vit cl.) runs forward along the 
lower border of the mandibular arch, sending numerous branches 
to the integument of this part and extending forward so as to 
come into very close relation with the posterior branches of the 
maxillary division of the fifth (v4). The posterior of the two 
branches (vic, 2) into which the seventh divides continues 
the direction of the main stem, and runs down in the hyoid 
arch just in front of the third head cavity, in the terminal dilata- 
tion of which it ends. Of these two terminal branches of the 
seventh, the anterior, sensory, and superficial one is the ramus 
mandibularis externus of Stannius! and Gegenbaur,? while the 
1 Loe. cit., p. 65. 
* Loe. cit., p. 514. 
