37o 



MANUAL OF ELEMENTARY ZOOLOGY 



against its lining, through which it can be seen if the 

 vein be opened. It represents several nerves fused, and 

 gives off across the floor of the sinus a branch to every 

 branchial arch behind the first, each such branch bearing 

 a prebranchial branch to the preceding arch. Shortly 

 after leaving the skull the vagus gives off a lateral line 

 nerve, which runs along the side of the body, rather deep 

 among the muscles, and supplies an organ in the skin 

 known as the lateral line, which will be mentioned later. 

 After giving off the last of its branches to the branchial 

 arches, the vagus passes downwards to supply the heart 

 and other viscera (Plate XVIII.). 



These nerves and their principal branches may be 

 summarised as follows : 



The comparison of the cranial nerves with dorsal and 

 ventral roots of spinal nerves which was made with regard 

 to the frog (p. 75) holds good for the dogfish and all other 

 vertebrates. A feature of their distribution which was not 

 obvious in^the latter animal is that certain of them (the 

 fifth, seventh, ninth, and tenth) give branches to the 

 visceral arches. Each such branch gives off an afferent 

 pretrematic branch to the arch in front of that which it 

 chiefly serves (in the case of the fifth nerve this branch 

 passes to the upper jaw). The post-(re?natic branch is 



