110 PROF. MARSHALL AND MR. SPENCER. 



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 (vin). 

 Immediately after the auditory nerve leaves it, the facial forms a 

 ganglionic swelling from which the communicating branch {N.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 (vii b) is 

 given off. The main stem of the seventh (vii 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, but 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 (vii c.) 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 (v b). The 

 posterior of the two branches (vii c, 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 dilatation 

 of which it ends. Of these two terminal branches of the seventh, 

 the anterior, sensory, and superficial one is the ramus mandibulars 

 externus of Stannius 1 and Gegenbaur, 2 while the posterior, muscular, 

 and deep branch is the ramus mandibularis intemus v. lyrofundus of 

 the same authors. Both these branches have already acquired, by 

 stage N, not only the characteristic distribution of the adult nerves, 

 but nearly all the minor branches as well. 



To recapitulate ; we find that by stage n the' seventh nerve has 

 acquired all the important branches of tha adult nerve, the main 

 trunks and many of the branches being fully developed at a much 

 earlier period — stage l. The seventh nerve at stage n has two roots, 

 a dorsal or primary, and a ventral or secondary. From the dorsal root 

 (vii a) arise two branches : (1) the ophthalmic (vii a) and (2) the 



1 Loc. cit., p. 65. 

 3 Loc, cit., p. 514i 



