6oo 



PHYLUM CHORDATA : CLASS PISCES — FISHES 



2. A ganglionated root, arising in front of all the 



others, from which arises the lateral branch 

 innervating all the posterior sensory tubes. 



3. From the fourth branchial branch arises the gang- 



lionated intestinal which innervates the heart and 

 the stomach. 



The spinal cord lies in the cartilaginous neural archway 

 above the vertebral column, is divided by deep dorsal and 

 ventral fissures, and gives off numerous spinal nerves, 



/??/?./ 



Fig. 337. — Side view of chief cranial nerves of Elasmobranchs. 

 — Slightly modified from Cossar Ewart. 



olf., Over olfactory nerve ; c.h., over cerebral hemispheres ; cb., over 

 cerebellum ; m.o., over medulla oblongata ; m., mouth ; mx., 

 maxillary branch of 5 ; wn.5, mandibular branch of 5 ; mn.y, 

 mandibular branch of seventh nerve ; a. 1-5, groups of anipuUao ; 

 0.S.5, superficial ophthalmic of 5 ; o.p., ophthalmicus pro- 

 fundus ; o.s.y, superficial ophthalmic of 7; N., nostril; 

 3, oculomotor ; e.g., ciliary ganglion ; 5, trigeminal ; i.b., inner 

 buccal ; o.h-., outer buccal ; 76., buccal of 7 ; p., palatal of 7 ; 

 sp., spiracle ; ch., chorda tympani ; y.fim., hyomandibular of 

 7 ; 8, auditory ; £., ear ; 9, glossopharyngeal ; 10, roots of 

 vagus ; /.lo, lateral nerve of vagus ; i.io, intestinal nerve of 

 vagus ; i'-5', gill-clefts. 



formed as usual from the union of dorsal (sensory) and 

 ventral (motor) roots. The first sixteen or eighteen nerves 

 form the brachial plexus, which supplies the pectoral fin. 



The sympathetic system consists of a longitudinal 

 ganglionated cord along each side of the vertebral column. 



Sense org-ans. — 



(a) The eyes (see Fig. 312). The iris has a fringed upper margin. 



{b) The ears (see Fig. 311). The vestibule is connected with the sur- 

 face by a delicate canal — the aqueductus vestibuli — a remnant 

 of the original invagination. A small part of the wall of the 



