320 INTERKAL ANATOMY OF HOKSE. 



branches to the muscles of the abdomen and muscles of the 

 flank, to the testes and "stifle-joint,''; and the last two form a 

 plexus. The sacral send their superior branches to the muscles 

 at the side of the sacrum, and their inferior branches to the 

 pelvic cavity, and to the anus and penis. The coccygeal 

 supply the tail. 



The sympathetic nervous system consists of a number of gan- 

 glia which are detached from the central nervous system but 

 connected with it by nerve-fibres. This nervous system con- 

 sists of a chain of ganglia on each side of the spinal cord. 

 This system controls the vascular system, and thus affects 

 animal heat : it is also connected with involuntary muscular 

 action. 



