THE SYMPATHETIC NERVOUS SYSTEM 77 



i. The roots of the nerves : dorsal and ventral, 

 ii. The obliquity of the middle and posterior roots. 



iii. The cauda equina, formed by the roots of the 

 hinder nerves together with the filum tenuinale. 



iv. The ganglia on the dorsal roots as they pass 

 through the intervertebral foramina : these are 

 covered on their ventral surfaces by whitish cal- 

 careous patches (the periganglionic glands) which 

 form conspicuous objects on either side of the 

 vertebral column. Remove these patches carefully 

 to see the ganglia. 



II. The Sympathetic Nervous System. This consists of a 

 longitudinal nei-vous band on each side of the body, connected 

 by branches with the several spinal nerves. The two main 

 sympathetic 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-foUowing : 



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, haemorrhoidal, 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 paii's of cranial 

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

 backwards. (See Figs. 12, 14 and 16.) 



