36 DR. A. MILNES MARSHALL. 



and that the two epiblastic formations — nerve and sensory 

 epithelium — completely fuse together. This complete fusion at 

 an early period, before any definite histological differentiation 

 has set up in the nerve, is a point of considerable interest in 

 connection with the much debated question of the continuity of 

 nerve fibres with epithelium cells in the adult. If complete 

 fusion of nerve and epithelium occurs at a very early period, how 

 are we to determine whether a given cell in the adult is nervous 

 or epithelial in nature or origin P^ 



I have devoted considerable attention to the early stages of 

 the seventh and eighth nerves, and am perfectly confident that 

 they do arise, as described above, as one outgrowth ; and as the 

 seventh nerve is a segmental nerve I regard the auditory as a 

 branch of it. Even if the auditory had proved to have a sepa- 

 rate origin it could hardly be a segmental nerve, since there is 

 no room for one, as far as visceral arches and clefts are con- 

 cerned, between the facial and glosso-pharyngeal. 



I have not noticed an anterior branch to the seventh, like that 

 described by Balfour in Elasmobranchs/ but have suggested 

 above that such a branch, when present, is not to be considered 

 as a ramus dorsalis, but as part of the commissure connecting 

 the seventh with the nerves in front of it. 



The glosso-pharyngeal nerve. — I have already shown^ that the 

 glosso-pharyngeal and vagus nerves are developed from a single 

 outgrowth on either side from the neural ridge in the posterior 

 part of the hind brain, and behind the auditory involution. The 

 roots of the two nerves remain in connection with one another, 

 but at an early period the outgrowth divides distally into an 

 anterior branch — the glosso-pharyngeal, and a posterior one — the 

 vagus. 



In fig. 22, IX, the condition of the glosso-pharyngeal is shown 

 at the ninety-sixth hour. It is a slender nerve running down- 

 wards behind the auditory capsule to the upper part of the angle 

 of the second visceral cleft, where it expands into a ganglionic 

 swelling. From the ganglion two branches are given off — a 

 posterior larger one, which runs downwards along the anterior 

 border of the first branchial arch, and an anterior smaller one, 

 not shown in this figure, which arches over the top of the cleft, 

 and runs down along the posterior border of the hyoid arch. 



In fig. 2-5 the same parts are shown at the one hundredth hour 

 on a slightly larger scale. The visceral arches and clefts are 

 rather more clearly shown here than in the preceding figure. 



' Vide also Balfour, 'Journal of Anat.,' loc. cit., p. 411. 

 ' Loc. cit., p. 405, seq. 

 " Loc. cit., p. 508. 



