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THE NERVOUS SYSTEM 



brachial plexus; a middle which is supplied by the seventh cervical nerve as above, and a medial 

 area supplied by the eighth cervical and first thoracic nerve through the medial antibrachial 

 cutaneous (internal cutaneous) nerve. On the dorsal side of the forearm there are three areas: 

 — (1) a lateral supplied by fibres of the fifth and sixth cervical nerves through the musculo- 

 cutaneous nerve; (2) a middle, which receives fibres of the seventh, and probably some from the 

 sixth and eighth cervical nerves through the lower branch of the dorsal antibrachial cutaneous 

 of the radial (inferior external cutaneous branch of the musculo-spiral nerve), and (3) a medial 

 which receives the eighth cervical and first thoracic nerves through the medial antibrachial 

 cutaneous (figs. 776, 779). 



The palm of the hand is supplied by the sixth, seventh, and eighth cervical nerves through 

 the superficial radial (radial) nerve, and through the median and ulnar nerves. The super- 

 ficial radial supplies the radial side of the thumb by its palmar cutaneous branch. The re- 

 mainder of the palm and the palmar aspects of the fingers are supplied by the median and 

 ulnar nerves through their palmar cutaneous and digital branches, the median supplying 

 three and a half digits and the ulnar the remaining one and a half (figs. 776 and 779). 



The dorsal aspect of the hand is supphed by the sixth, seventh, and eighth cervical nerves, 

 which reach it through the superficial radial( radial) and through the median and ulnar nerves. 

 The superficial radial supplies the lateral part of the dorsum and the lateral three and a half 

 digits, except the lower portions of the second, third, and half of the fourth digits, which 

 receive twigs from the median nerve; the ulnar nerve supplies the ulnar half of the dorsum of 



Fig. 780. — Diagram of the Cutaneous Areas of the Lower Extremity. (After Head.) 



K-' > 



the hand, including the medial one and a half digits. The areas supplied by definite spinal 

 nerves, according to the observations of Head and Thorburn, are shown in figures 778 and 779 

 respectively. 



The Cutaneous Areas of the Lower Extremity 



The segmental arrangement of the cutaneous areas of the lower extremity is not so well 

 retained as in the upper, due largely to a greater amount of developmental shifting of the parts. 

 Both of the lines separating the areas of the lumbar (cephalic) and the sacral (caudal) parts 

 of the lumbo-sacral plexus lie on the dorsal aspect of the limb. The nerves from the lumbar 

 part of the plexus are distributed to the entire anterior and the medial and lateral surfaces of 

 the limb and to the muscles of the anterior and medial portions of the thigh and the anterior 

 portion of the leg, whereas the cutaneous nerves from tlie sacral part of the plexus are con- 

 fined to a narrow strip along the dorsal aspect of the limb (fig. 781). However, the muscular 

 distribution of the .sacral part is as much expanded as its cutaneous area is contracted; it supplies 

 the muscles in the donsul jjortions of the hip, thigh and knee, the whole of the dorsal part of 

 the leg and ankle and the i)lantar muscles of the foot. 



There are six cutaneous areas in the region of the buttock, three upper and three lower. 

 Of the ui)per areas the lateral is supi)lied by the anterior primary divisions of the last thoracic 

 and first lumbar nerves through the iliac branches of the last thoracic and the ilio-hypogastric 

 nerves; the middle upper area receives the lateral divisions of the posterior primary branches 

 of the upper three lumbar nerves, and the medial upper area is supplied by twigs from the lateral 

 branches of the posterior primary divisions of the upper two or three sacral nerves (figs. 776, 

 780). 



