THE CRANIAL NERVES OF SCTLLIUM. 121 



division of mandibular branch ; vn c, hyoidean branch of seventh ; 

 vn c 1, ramus mandibulars externus, or branch of hyoidean to 

 mandibular arch ; vn c 2, ramus mandibularis interims, or terminal 

 branch of hyoidean to walls of third head cavity ; vn d, buccal branch 

 of seventh ; vn a, primary, or dorsal root of seventh ; vn /3, secondary 

 root of seventh ; vm, eighth, or auditory nerve ; ix, ninth, or glosso- 

 pharyngeal nerve ; ix a, ramus dorsalis of ninth nerve j ix b, hyoidean 

 branch of ninth ; ix c, branch of ninth to first branchial arch ; x, 

 tenth, or pneumogastric nerve ; x b, anterior branch of tenth nerve 

 in first branchial arch. 



Figs. 1 & 2. Transverse sections through the hind-brain of a Scyllium 

 embryo, intermediate between stages i and k. x 90. 



Fig. 1, showing dorsal (primary) and ventral (secondary) roots 

 of fifth nerve ; also the second or mandibular head cavity. 



Fig. 2, showing origin of dorsal (primary) roots of seventh 

 nerve from neural crest ; also the third or hyoidean head 

 cavity. 

 Figs. 3 & 4, Transverse sections through the hind-brain of an embryo 

 of stage k. x 90. 



Fig. 4, showing the fifth nerve, arising by its ventral or secon- 

 dary root alone. 



Fig. 3, showing the dorsal and ventral roots of the seventh 

 nerve. 

 Figs. 5 to 7. Transverse sections ^through the hind-brain of an 

 embryo of stage n. x 20. 



Fig. 5, showing the ventral roots of the fifth nerves, the 

 ophthalmic branches of the seventh nerves, and the ter- 

 minations of the maxillary branch of the fifth and the 

 buccal branch of the seventh nerve ; also the first head 

 cavity. 



Fig. 6, showing the dorsal and ventral roots of the seventh 

 nerve, the buccal branch of the seventh aud maxillary 

 branch of the fifth, and the connection between these two 

 nerves ; also the second head cavity. 



Fig. 7 shows on the left side the ventral root of the seventh 

 nerve, the termination of the sixth nerve in the rectus 

 externus, the mandibular branch of the fifth nerve, the 



