THE NERVOUS SYSTEM 139 
and glossopharyngeus nerves, or are connected with their ganglia, 
may possibly be retrogressive in nature; but we cannot enter 
further into their study here, as to do so would lead us too far 
into Comparative Anatomy, and be beyond the purpose of this 
work. 
The variations which are continually taking place in the 
brachial and lumbo-sacral nerve plexuses, in connection with the 
shifting of the limbs and their girdles during development, have 
been already considered in detail (ante, pp. 95 and 96). 
THE SYMPATHETIC SYSTEM 
Here also extraordinary variations are to be found in the 
form, number, and size of the gangha of the main trunks, in the 
peripheral plexuses, and in the connections between the two chief 
trunks; but, except in the caudal portion of this system, we are 
not justified in assuming that we have to do with retrogressive 
phenomena. 
