,S26 THE NERVOUS SYSTEM 



The skin of the region of the heel is supphed by the first and second sacral 

 nerves, on the inner surface and inner part of the under surface by means of the 

 calcaneo-plantar branch of the }tosterior tibial nerve, and on its posterior, external, 

 and lower aspects by the ext^-rnal saphenous nerve (fig. 469b). 



The sole of the foot in front of the heel receives cutaneous filaments from the 

 last two lumbar and the first two sacral nerves, the inner area, Avhich includes the 

 inner three and a half digits, being sujiplied by the internal plantar nerve which 

 conveys filaments of the fourth and fifth lumbar and the first sacral nerve, and the 

 outer area by the first and second sacral nerves through the external plantar nerve. 



The inner side of the foot is supplied l\v the third and fourth lumbar nerves 

 through the long saphenous nerve, and the outer side b}' the first and second sacral 

 nerves through the external saphenous nerve (fig. 469b). 



The skin of the scrotum and penis is supplied by the first lumbar nerve through 

 the ilio-inguinal nerves, and the second and third sacral nerves through the per- 

 ineal and dorsal penile branches of the pudic nerves (fig. 469b). 



SYJIPATHETIC NERVES 



The sympathetic nerves were formerly supposed to be a separate system, 

 linked, it is true, to the cerebro-spinal system by numerous communications, yet 

 possessing, in their ganglia, a certain governing power independent of the cerebro- 

 spinal axis. It is now very generally admitted that the sympathetic nerves are 

 merely the visceral branches of the spinal nerves, but they differ from the somatic 

 nerves in the following respects: (a) in the individual fibres being of smaller calibre 

 than the somatic nerve-fibres; (h) in the great preponderance of non-medullated 

 fibres; (c) in the fibres being interrupted in the nerve-cells, which are contained in 

 a chain of ganglia which is called the gangliated cord of the sympathetic, and often 

 also interrupted in secondary and tertiary ganglia, of which the semilunar ganglia 

 and the nerve-cells in the plexuses of Auerbach and Meissner are examples; and 

 (d) in the tendency that these nerves show to form extensive and closely-meshed 

 plexuses. 



The somatic nerves are the nerves Avhich supply the bodj^-wall as distinguished 

 from the viscera. They have been described above as the cranial and spinal nerves. 



Certain visceral nerves — for example, the visceral branches of the third and fourth sacral 

 nerves — do not join the gangliated cord. While the sj'mpathetic nerves, taken as a wliole, can 

 no lunger be regarded as a separate sj'stem, certain ganglia connected with the syuii>athetic are 

 capable of automatic action ; for example, the ganglia in the heart and in the intestinal walls. 



The sympathetic system, as usually described, consists of (a) a pair of gangliated 

 cords Avhich are placed on the front and sides of the vertebral column; and (6) 

 three great prevertebral plexuses containing many ganglia; and (e) numerous 

 terminal ganglion cells situated close to or within the various organs and vessels. 

 One of the plexuses, the cardiac plexus, is contained in the thoracic cavity. The 

 other two, which are termed the solar and hypogastric plexuses, are placed in the 

 abdominal cavity. The gangliated cords will be first described. 



. GANGLIATED CORDS OF THE SYMPATHETIC 



The gangliated cords of the sympathetic consist of a series of ganglia united 

 together by intervening cords. These ganglia are of a reddish-grey colour, soft in] 

 consistence, but enclosed in tolerably firm investments of connective tissue. The 

 nerve-cords uniting them are pearly grey in colour. Morphologically speaking, 

 there should l)e thirty-one pairs of ganglia, that is to say, a j)air corresponding to 



