118 PHYSIOLOGY FOR NURSES 



One branch, of more importance, is the phrenic, or 

 chief inspiratory nerve since it carries motor impulses 

 to the most important of the inspiratory muscles, the 

 diaphragm. 



The brachial plexus is largely devoted to the upper ex- 

 tremity. One of its branches supplies the serratus mag- 

 nus f an accessory respiratory muscle, but most of them 

 are mixed nerves some of the fibers of which convey cu- 

 taneous sensations from all parts of the upper extrem- 

 ities, while motor branches supply all the muscles which 

 move this great lever, even those muscles which spread 

 out over the back and chest. 



The thoracic nerves run mainly between the ribs in- 

 tercostal nerves supplying motor impulses to the mus- 

 cles of the same name, which makes them respiratory 

 nerves, while their sensory fibers convey cutaneous sen- 

 sations from the skin of the thorax and a large part of 

 the abdomen. The lower thoracic nerves supply ths 

 broad muscles of the abdomen and are thus expiratory 

 agents. 



The lumbar plexus gives rise to those nerves which 

 supply sensation to the skin from where the last inter- 

 costal leaves off to where the sacral plexus takes up the 

 work, and motor impulses in the same area. The first 

 of the lumbar nerves supplies the skin over the upper, 

 outer part of the hip and others carry the distribution 

 over the front and inner side of the thigh and, by one 

 long branch, along the inner side of the leg as far as the 

 big toe. The skin over the external genitals is supplied 

 in part by this plexus. The muscles supplied are those 

 forming the lower part of abdominal wall, some in the 

 back of the abdomen and pelvis and those on the front 

 and inner side of the thigh. Briefly the muscles which 



