THE CRANIAL NEEVES OP SCYLLIUM. HI 



buccal (vn d), both of which appear to be purely seusory nerves. 

 The connecting branch (N.c'.) to the fifth nerve, though it appears 

 in longitudinal section (fig. 11) to be a distinct branch, in transverse 

 sections (fig. 6) seems to be only the deeper portion of the buccal 

 nerve. From the ventral root arises the main or hyoidean branch 

 (vn c), from which the branch vn b runs forward over the top of the 

 spiracle, dividing, almost immediately, into the palatine (pa) and 

 spiracular (sp) nerves, whilst the hyoidean itself divides distally into 

 the sensory ramus mandibularis externus (v c, 1), and the motor ramus 

 mandibularis internus (v c, 2). 



The Sixth (Abducens) Nerve. — Concerning the development of the 

 sixth nerve our observations simply confirm the account already given 

 by one of us. 1 



The whole length of the nerve is shown in longitudinal and vertical 

 section in fig. 13 (vi), where it is seen arising from the base of the 

 brain by a number of small non-ganglionic roots which unite to form 

 a slender nerve ; this nerve runs forwards a short distance, then turns 

 downwards, pierces the investing mass (i.v.), and ends in the posterior 

 extremity of the rectus externus muscle (r.e.). 



Fig. 7 shows the sixth nerve in transverse section at the same stage 

 (n) : on the left side of the figure the termination of the nerve in the' 

 rectus externus is seen ; while on the right side, which is taken from a 

 more posterior section, one of the roots of origin is shown. This figure 

 shows that the roots of the sixth are considerably nearer the mid- 

 ventral line than are the secondary roots of the seventh nerves, and 

 also that the sixth and seventh nerves are quite independent of one 

 another. At stage n the sixth nerve appears to be altogether behind 

 the seventh, but in stage o it is situated rather further forwards, so 

 that the same section may pass through the roots of both nerves. 



"We have not yet detected the sixth nerve in embryos younger than 

 stage l : concerning the morphological value of this nerve we adhere 

 to the opinion already expressed that it is to be viewed as bearing the 

 same relation to the seventh that the anterior root of a spinal nerve 

 does to its posterior root. 



The Eighth (Auditory) Nerve. — This nerve also we can dispose of 

 briefly : at stage K it appears as a large ganglionic posterior branch of 



1 Marshall, loc, cit., pp, 89—93 



