LUMBAR NERVES. 415 



The Second intercosto-humeral nerve is much smaller than the 

 preceding ; it emerges from the external intercostal muscle of the 

 third intercostal space between the serrations of the serratus magnus 

 muscle, and divides into filaments which are distributed to the inte- 

 gument of the shoulder. One of these filaments may be traced in- 

 wards to the integument of the mamma. 



The cutaneous branches of the fourth and fifth intercostal nerve 

 send twigs to the integument of the mammary gland. The cuta- 

 neous branches of the remaining intercostal nerves reach the surface 

 between the serrations of the serratus magnus muscle above and 

 the external oblique below, and each nerve divides into an anterior 

 and a posterior branch ; the former being distributed to the integu- 

 ment of the antero-lateral, and the latter to that of the lateral part 

 of the trunk. 



The cutaneous branch of the last dorsal nerve is remarkably large ; 

 it pierces the internal and external oblique muscles, crosses the crest 

 of the ilium, and is distributed to the integument of the gluteal 

 region. 



LUMBAR NERVES. 



There are five pairs of lumbar nerves, of which the first makes 

 its appearance between the first and second lumbar vertebra, and 

 the last between the fifth lumbar and the base of the sacrum. The 

 anterior branches increase in size from above downwards, and form 

 the lumbar plexus. The posterior branches diminish in size from 

 above downwards ; they form loops of communication with each 

 other, and are distributed to the muscles of the lumbar region, and 

 to the integument over the sacrum in the same manner with the 

 posterior branches of the lower dorsal nerves. 



The lumbar plexus is formed by the communications and anasto- 

 moses which take place between the anterior branch of the last 

 dorsal and of the five lumbar nerves. It is narrow above and in- 

 creases in breadth inferiorly, is situated between the transverse 

 processes of the lumbar vertebra and the psoas magnus muscle, 

 and receives filaments of communication from the lumbar ganglia 

 of the sympathetic. 



The Branches of the lumbar plexus are the 



Musculo-cutaneous, 



External-c utaneous, 



Genito-crural, 



Crural, 



Obturator, 



Lumbo-sacral. 



The Musculo-cutaneous nerves, two in number, superior and infe- 

 rior, proceed from the first lumbar nerve. The superior musculo- 

 cutaneous nerve (ilio-scrotal) passes outwards between the posterior 

 fibres of the psoas magnus, and crosses obliquely the quadratus lum- 



