THE CRANIAL NERVES OF SCYLLIUM. 107 



account of its very close relation with the maxillary division of the 

 fifth nerve. 



At stage l the only changes of importance are, (1) that the several 

 branches have increased in size, and, excepting the branch vn d, which 

 has a very straight course and ends abruptly in the skin, have 

 divided into secondary branches near their terminations ; and (2), that 

 a small anterior branch has arisen from the hyoidean nerve (vn c), 

 some distance from the brain, which runs forward over the top of the 

 spiracular or hyomandibular cleft, and then down in the anterior wall 

 of the spiracle, i.e. in the posterior portion of the mandibular arch ; 

 this branch will be referred to as vn b. 



The several branches of the seventh nerve at stage n are well shown 

 in the diagrammatic figures 11 and 12. The ophthalmic branch (vn a) 

 is seen in fig. 12 arising from the base of the primary or dorsal root 

 (vn a) as a stout nerve, which expands very shortly after its origin 

 into a large somewhat fusiform ganglion, beyond which the nerve runs 

 forward as a stout trunk to the extreme anterior part of the head. 

 Throughout its course it lies just beneath the external epiblast, and 

 immediately dorsal to the ophthalmic branch of the fifth (v a), with 

 which it is in very close relation ; like this latter nerve it gives off 

 branches along its whole course to the integument of the neighbouring 

 parts, the branches being few in number at the proximal end, and 

 much more numerous distally. A short distance before its termination 

 this nerve, like the ophthalmic branch of the fifth, is crossed at a 

 considerable angle by the nerve iT (fig. 12). 



The connecting branch (N.c'.) between the seventh and fifth nerves 

 is well seen in figs. 11 and 12 j it is now shorter and wider than at 

 stage l (fig. 10), and contains very numerous ganglion cells along its 

 whole length. 



The superficial portion of this nerve (vn d) is not shown in fig. 11, 

 but is represented along its whole length in fig. 12; it is a stout nerve 

 with a remarkably straight course; it gives off no branches at all 

 along the greater part of its length, but near its distal termination 

 divides rather s^^ddenly into a number of branches, which end in the 

 integument of the maxillary process, the most anterior of them 

 extending forwards almost as far as the hinder border of the olfactory 

 pit. The relations of this nerve to the maxillary branch of the fifth 

 are very curious ; the two nerves are very close together, the branch 

 of the seventh lying, as at the earlier stage, immediately superficial 



