104 JOHN BEARD. 
nerves by various zoologists, with what justification we shall 
see later on. 
DorsaL Root or tHE FourtH anp Firra Sreements, 
Seventa Nerve or Faciatis. 
As already described by Balfour' and Marshall,? the seventh 
nerve arises from the neural crest in the region of the hind 
brain and just in front of the auditory capsule. 
These authors further agree in assigning a common root of 
origin for the seventh and auditory nerves. Marshall has, how- 
ever, in one of his early works, drawn attention to a line of 
division between the ganglia of the auditory and facial nerves in 
the chick. Now, although the rudiments of the facial and audi- 
tory nerves lie very closely together, I consider that at first 
the two are really distinct. The facial grows downwards and 
outwards from the neural crest, and just under the epiblast. 
When it reaches the level of the notochord part of it fuses 
with the sensory thickening above the hyoid arch, and just 
above the future hyoid cleft. The rest passes on (fig. 20) to 
the lateral muscle plates of the hyoid arch. At the point of 
fusion with the sensory thickening the ganglion is formed. Of 
this, one stage is figured in fig. 20. In this condition the 
nerve is to be regarded as passing through an ancestral stage. 
Its condition is then figured in the diagram of a typical 
dorsal root (fig. 50), which passes from the brain to the 
primitive branchial sense organ and its associated ganglion 
above a gill-cleft, and from which ganglion a nerve passes 
along the posterior side of the cleft to the muscles of the 
gill. 
In later stages the ganglion is still partly fused with the 
skin, but it soon separates, leaving behind it the rudiments of 
several branches. 
These branches are the supra-branchial, the pre-branchial, 
1 Balfour, ‘Comp. Embryol.,’ vol. ii, p. 377. 
2 Milnes Marshall, “Head Cavities and Associated Nerves in Elasmo- 
branchii,” ‘ Quart. Journ. Micr. Sci.,’ 1880; also, ‘Nervous System of 
Chick,” ‘ Quart. Journ. Mier. Sci.,’ 1878. 
