1026 



THE NERVOUS SYSTEM 



nerve and the superficial branch of the obturator nerve. The upper middle area is supplied 

 by the second, and third sacral nerves through the posterior femoral cutaneous (small sciatic) 

 nerve, and the lower middle area by the first sacral nerve through the sural (external saphenous) 

 nerve. The lateral area is supphed by the fifth lumbar nerve through the lateral sural cutaneous 

 (fibular communicating) branch of the common peroneal (external popliteal) nerve (fig. 776, 780, 

 781). 



The skin of the dorsum of the foot is supphed principally by the fifth lumbar and by the 

 first sacral nerves; the majority of the nerve-fibres travel by the superficial peroneal (musculo- 

 cutaneous) nerve, but the adjacent sides of the first and second toes are supplied by the femoral 

 (anterior crural) nerve and the side of the dorsum of the little toe is supplied through the 

 sural (external saphenous). 



The skin of the region of the heel is supphed by the first sacral nerve, the medial surface 

 and medial part of the under surface by the medial calcaneal branches of the tibial (calcaneo- 

 plantar) nerve and the posterior, external, and lower aspects by the sural (external saphenous) 

 nerve (fig. 776). 



The sole of the foot in front of the heel receives cutaneous fibres from the fifth lumbar 

 and the first sacral nerves; the medial area, which includes the medial three and a half digits, 

 being supplied by the medial plantar nerve which conveys fibres of the fifth lumbar and the first 

 sacral nerves; and the lateral area by the fifth lumbar nerve through the lateral plantar nerve. 



The medial side of the foot is supplied by the first sacral and fourth lumbar nerves through 

 the saphenous nerve and the lateral side by the fifth lumbar nerve through the sural (external 

 saphenous) nerve. 



The skin of the scrotum and penis is supphed by the first lumbar nerve through the ilio- 

 inguinal nerves, and by the second and third sacral nerves through the perineal and dorsal penile 

 branches of the pudendal (pudic) nerve. 



The cutaneous areas of the lower extremity which have been demarcated by Head and 

 Thorburn are shown in fig. 780. These do not conform wholly with each other nor with the 

 areas given in more detail in fig. 776, due probably to individual differences in subject and 

 observer and to the difficulties coincident with the overlapping of the areas. Fig. 781 is more 

 general in character and is considered more approximately correct. 



The homology of the parts of the plexuses of the upper and lower extremities is not well 

 carried out in the distribution of the nerves. The radial and great sciatic nerves are similar 

 to the extent that the one arises from the posterior cord of the brachial plexus and the other 

 from the sacral plexus, and that the one is distributed to the dorsal aspect of the arm and the 

 other to the dorsal surface of the lower extremity, but the great sciatic supplies the sole of the 

 foot, and the plantar muscles, whereas the radial does not supply the palm of the hand and the 

 palmar muscles: 



THE SYMPATHETIC SYSTEM 



The so-called sympathetic system is that portion of the peripheral nervous 

 system which is especially concerned in the distribution of impulses to the 



Fig. 782. — Diagram showing two stages of the Migration of the Primitive Ganglia 

 FROM the Ganglion Crest; A. the Division of the Primitive Ganglia into Spinal 

 and Sympathetic Portions, and B. the Formation of the Nerves. 



Neural 



Sympa 



glandular tissues, to the muscle of the heart and blood-vessels, and to the non- 

 striated muscular tissue of the body wherever found. Since these tissues are most 



I 



