THE SYMPATHETIC NERVOUS SYSTEM. 87 



on either side of the vertebral column. Remove 

 these patches carefulhj to see the ganglia, 



II. The Sympathetic Nervous System. This consists of a 

 longitudinal nervous band on each side of the body, connected 

 by branches with the several spinal nerves. The two main sympa- 

 thetic trunks lie, in front, close to the dorsal surface and alongside 

 the vertebral column : further back they are in close relation 

 with the dorsal aorta, alongside which they run. 



Each sympathetic trunk receives a branch from each of the 

 spinal nerves of its side, and at the junction of each of these 

 branches with the main trunk there is a ganglionic enlargement. 



The coccygeal or tenth spinal nerve, unlike the others, is 

 connected with the sympathetic by more than one branch: 

 the actual number of these branches is not constant, but is 

 said to vary from two up to as many as twelve. 



From the sympathetic ganglia nerves are given off to the 

 bloodvessels and viscera, the chief ones being the following : 



i. The cardiac plexus is formed by nerves arising 

 from the first sympathetic ganglion : the plexus 

 is a meshwork of nerves on the auricles, and 

 around the great vessels at their openings into 

 the heart. 



ii. The solar plexus lies on the dorsal surface of the 

 stomach : the nerves are derived mainly from the 

 third, fourth, and fifth ganglia. 



Hepatic, renal, genital, hsemorrhoidal, and vesical plexuses 

 also exist in connection with the liver, kidney, reproductive 

 organs, large intestine, and bladder respectively. 



III. The Cranial Nerves. There are ten pairs of cranial 

 nerves in the frog, which are numbered in order from before 

 backwards. (See Fgures 13 and 15). 



To dissect the cranial nerves expose the brain by removing the 

 roof of the skull as already described, and then follow the special 

 instructions given in the case of the more important nerves. 



1. The olfactory nerve, the special nerve of smell, arises 

 from the anterior end and outer side of the olfactory lobe, 

 and is distributed to the membrane lining the nasal 

 cavity. 



