252 JouRNAi> OF Comparative Neurolocjy. 



these rudiments corresponding to each cranial nerve grows 

 ventrad, unites with the central organ by means of root 

 fibres, probably growing out centripetally, and comes to lie 

 on the outer side of the mesoderm, between this and the epi- 

 dermis; while the rudiments of the spinal ganglia (of the 

 trunk) proceed ventrally on the inner side of the mesoderm, 

 thus between this and the central organ. These cranial 

 ganglia rudiments, designated by Beard ^'■neuralganglia^'' 

 fuse at the level of the chorda with a thickened place in the 

 epidermis dorsad of the neighboring gill cleft, which thick- 

 ening represents externally the rudiment of a " branchial sense 

 organ," internally that of a ganglion belonging to the latter, 

 the '•'•lateral ganglion.'''' Here the elements of the neural and 

 lateral ganglia blend indistinguishably with each other; there 

 thus arises the definitive and apparently single ganglion of the 

 cranial nerve in question. This separates from the epidermis 

 — that is, from the rudiment of the branchial sense organ — 

 but remains connected with the latter by a nerve strand, the 

 suprabranchial nerve (dorsal branch of Van Wihje). From 

 the ganglion are developed distally three nerves, namely, the 

 JV. prcebrajtchialis , JV. postbranchialis , and \. pharyngezis. 

 As to the N. suprabranchialis, it is, according to Beard, clear 

 that it arises from the epidermis; for the N. praebranchialis he 

 accepts the same mode of formation. With regard to the two 

 other nerves, he remains undecided whether the epidermis 

 takes part in their formation. (^) Beard regards it as cer- 

 tain in the case of the postbranchial twigs of the vagus(-) 

 and in the case of the trigeminus (mandibularis).(') 



For the trigeminus the same law of formation is said to 

 obtain, inasmuch as the mouth represents a pair of gill clefts. 

 But where gill clefts, with the musculature belonging, have 

 entirely disappeared, yet sense organs persist, there, accord 

 ing to this author, the structure is simplified; the N. post- and 



1 Quart. Jour. Mic. Sc, Vol. XXVI, 18S6, p. 102. 



2 Ibidem, p. no. 



3 Ibidem, p. 113. 



