THE RABBIT. 99 



cord, as it were, sends a general order for muscular con- 

 traction to be accelerated or inhibited in a particular region ; 

 and the sympathetic translates this into the necessary de- 

 tailed orders. But it has no power of reflex action. 



The metamerism of the sympathetic chain is imperfect in 

 the neck- region, where only three pairs of ganglia are found 

 an anterior (or superior) cervical close to the head and 

 a middle and posterior (or inferior) cervical near the sub- 

 clavian artery. In the head the disposition of the 

 sympathetic is still more obscure, but there are some four 

 pairs of ganglia that appear to belong to it. 



From several of the hinder thoracic ganglia of the 

 sympathetic fibres come off and unite into a great splanch- 

 nic nerve on either side. These pass back through the 

 diaphragm and across the aorta into the mesentery, between 

 the co3liac and superior mesenteric arteries. Here they pass 

 into another set of ganglia, from which accelerator and 

 inhibitor fibres are finally distributed to the unstriped 

 muscles and secretory fibres to the gland-cells of the abdo- 

 minal part of the alimentary canal. These ganglia have so 

 many fibres radiating out from them as to have a stellate 

 appearance and somewhat indefinite shape. The largest 

 ganglion is called the codiac ganglion, and the second the 

 superior mesenteric, after the arteries near them. A small 

 renal ganglion really a portion of the coeliac may or may 

 not be recognizable as a distinct ganglion. The whole of 

 these ganglia and nerves are collectively spoken of as 

 the solar plexus. There is also a more distant inferior 

 mesenteric ganglion near the artery of the same name. 



5. Spinal Nerves. Most of the spinal nerves are dis- 

 tributed to the skin and muscles of the region they belong 

 to ; but a few deserve more special mention. The third 

 cervical nerve sends off a large branch (great auricular 

 nerve) to the external ear. The fourth cervical has a branch 

 which, after receiving tributaries from the fifth and sixth 

 cervical, runs back along the precaval vein and by the side 

 of the heart to the diaphragm the phrenic nerve. If this 

 nerve is injured at any point in its course, the diaphragm 

 no longer acts, breathing ceases, and death quickly ensues. 



