THE CRANIAL NERVES OP SCYLLIUM. 109 



for a branch of the fifth rather than of the seventh ; careful examina- 

 tion shows, however, that the buccal, which is, as before, the most 

 superficial of all the ventral branches, can be traced up to the dorsal 

 root of the seventh from which it arises, as in the earlier stages. 



This origin of the buccal nerve from the root vn a has already been 

 noticed by Stannius, 1 who, however, as we have seen, did not refer the 

 root in question to the seventh. Stannius' figure of the nerves in 

 Chimcera? shows clearly the very superficial position of the buccal 

 nerve and its independence of both maxillary and mandibular nerves. 



Of the remaining branches of the seventh the anterior one (vn b) is 

 shown in fig. 11 at its origin, arising from a large ganglionic swelling 

 on the main or hyoidean branch of the seventh, and running forward 

 in close contact with the top of the spiracle (sp.), in front of which it 

 divides almost at once into two branches, the distribution of which is 

 shown in fig. 12; of these the anterior one (vii^a) runs downwards, 

 forwards, and inwards, giving off numerous branches to the roof of the 

 mouth. In fig. 12 the anterior branches of this nerve appear to cross 

 the posterior branches of the buccal, but it must be borne in mind 

 that at this point the two nerves are at very different levels, the 

 buccal being very superficial and the nerve (vn pa) lying very deep. 

 This latter is seen in transverse section in fig 7, which shows, on the 

 right side, its origin from the ganglion, and, on the left, its distribution 

 to the mucous membrane of the mouth. By comparing this figure with 

 fig. 6, the difference of levels between the two nerves will be at once 

 apparent. This anterior branch (vii pa) is the palatine nerve ; it has 

 already acquired by stage n its characteristic distribution, and under- 

 goes no further change of importance from this period up to the adult 

 stage. 



The second or posterior division (fig. 12, vn sp) of the nerve (vii b) 

 runs downwards and slightly backwards along the anterior border of 

 the spiracular cleft ; it gives off branches along the whole of its length, 

 the great majority of which run backwards to the mucous membrane 

 of the border of the cleft and to the spiracular branchia. This nerve, 

 which at this stage is of about equal size with the palatine, is the 

 spiracular or pree-spiracular nerve of zootomists. 



The only branch of the seventh still left for description is the main 

 trunk or hyoidean branch (fig. 11, Vii c), which forms the direct 



1 Loc. cit., p. 30. 

 8 Loc, cit., Taf. 1, fig, 



