PISCES 179 



and is connected with the medulla behind the auditory nerve, 

 and after passing through the hinder part of the auditory 

 capsule the nerve is distributed to the first branchial cleft 

 and the pharynx. It is a mixed nerve. 



X. Vagus. The vagus ganglion is connected to the wall 

 of the medulla by several roots. Its nerve passes through 

 the auditory capsule behind the glossopharyngeal. It divides 

 into two branches : (1) giving off branches which bifurcate to 

 supply the last four branchial clefts and then passes downwards 

 to supply the heart and stomach; (2) the lateral branch, 

 which is the nerve of the lateral line and is directed posteriorly 

 along the dorsal wall of the body to reach the lateral epidermis 

 of the tail. 



The spinal cord gives off numerous spinal nerves which 

 are segmentally arranged in pairs. The nerves result from the 

 union of dorsal and ventral roots after these roots have passed 

 out from the neural canal. The dorsal roots are ganglionated 

 and sensory, and the ventral roots are simple and motor. The 

 large pectoral fin is innervated by a fusion of the anterior 

 spinal nerves, forming the brachial plexus. 



The sympathetic system originates from the spinal ganglia 

 and consists of a ganglionated cord lying just below and lateral 

 to the vertebral column, the ganglia being connected with the 

 spinal nerves by rami communicant es. 



Sense organs are developed with relation to the brain and 

 act as distant receptors. 



The nasal organs consist of two sacs which are open below 

 and are in the skate and many other Elasmobranchs connected 

 by a groove each with the mouth. Each organ arises as an 

 ectodermal involution, and the nerve in connexion with the 

 involution as a ganglion. The epithelium is greatly increased 

 in area, and the cavity interrupted by folds. The sensory 

 cells are brought into contact with the water which enters the 

 chamber and convey impressions of what answers in water 

 to the olfactory function of air-breathers, a chemical stimu- 

 lation of dissolved substances. The function is related to 

 taste, as is that of the sensory canals of the skin. 



The eye presents the typical craniate structure. It arises 

 in the paired optic cups which are outgrowths of the 



