SENSE ORGANS. 



521 



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, 

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



olf 



FIG. 249. Side view of chief cranial nerves of Elasmobranchs. 

 Slightly modified from Cossar Ewart. 



olf., Over olfactory nerve ; ch., over cerebral hemispheres ; cb., over 

 cerebellum; 111.0., over medulla oblongata ; ;., mouth; inx., 

 maxillary branch of 5 ; inn.^, mandibular branch of 5 ; tnn.j, 

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

 0.J.5, superficial ophthalmic of 5 ; o.p., ophthalmicus profundus ; 

 o.s.j, superficial ophthalmic of 7 ; ^V., nostril ; 3, oculomotor ; 

 e.g., ciliary ganglion; 5, trigeminal ; /.., inner buccal ; o.b., 

 outer buccal ; -jb., buccal of 7 ; /., palatal of 7 ; sp., spiracle ; 

 c~/i., chorda tympani ; -j.hu/, hyomandibular of 7 ; 8, auditory ; 

 7:."., ear ; 9, glossopharyngeal ; 10, roots of vagus ; /. 10, lateral 

 nerve of vagus ; z'.io, intestinal nerve of vagus ; i'-5', gill-clefts. 



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 gang- 

 lionated cord along each side of the vertebral column. 



Sense organs. - 



(a) The eyes (see p. 476). The iris has a fringed upper margin. 



(b) The ears (see p. 475). The vestibule is connected with the sur- 



face by a delicate canal the aqueductus vestibuli a remnant 

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

 auditory capsule is covered only by the skin, forming a kind of 



