LEPUS CUNICULUS 337 



cut and the ends stimulated, it will be found : (i) that from the 

 distal end a message is conveyed to the muscles showing that it 

 contains motor or efferent fibres conducting impulses away from the 

 central nervous system, and (2) that from the proximal end a 

 message or sensation is carried to the brain, indicating that some of 

 its fibres are afferent or sensory. The whole nerve is therefore mixed, 

 containing both motor and sensory fibres. 



If the dorsal root be cut between the ganglion and the cord, and 

 stimulated, it will be found : (i) that from the proximal end a sen- 

 sory message is conveyed to the brain, and (2) that from the distal 

 end no results can be 

 obtained. The dorsal 

 root, therefore, is entirely 

 a sensory root and, like 

 all nerve fibres, its con- 

 stituents can convey a 

 message in one direction 



n v< FIG. 116. Illustrating the functions of the 



If the ventral root be spinal nerves. From Furneaux. 



severed before its poinf Divided at a ._ Irritated at t : pain . Irritated at 2 : 



of Union We Shall See : muscular contraction. 



(i) that stimulation of the 



proximal end produces no response, so that it contains no sensory 

 or afferent fibres, but (2) that stimulation of the distal end results 

 in movement. The ventral root is, therefore, a purely motor nerve. 

 The distribution of the spinal nerves calls for little notice, and 

 we need only deal with certain small points. The third spinal 

 nerve gives off a large branch termed the great auricular nerve, that 

 runs up the postero-lateral border of the pinna supplying the 

 neighbouring tissues. The fourth spinal nerve gives off a fairly 

 large branch that runs backwards below the roots of the others 

 receiving a tributary from the fifth nerve, and sometimes from the 

 sixth also. The combined trunk passes into the thorax as the 

 phrenic nerve to be distributed over the diaphragm. In certain 

 regions, noticeably the axillary and lumbar, there is a certain amount 

 of intercrossing of fibres from adjacent nerves constituting the 

 brachial and lumbar plexuses respectively. 



Sympathetic Nervous System. 



The sympathetic nervous system is constituted in funda- 

 mentally the same way as in the frog, but it is somewhat more 

 specialised, and the ganglionation of the two lateral trunks lying 

 beneath the vertebral column is not quite so regular. As we have 

 seen, each spinal nerve on emerging from the vertebral column 



z 



