750 



THE NEKVOUS SYSTEM. 

 Upper Limb. 



Lower Limb. 



The only exception to this rule is on the ventral (anterior) surface of the arm, where a sup- 

 pression of the muscle elements leads to an absence of the regular series of segmental nerves 

 (C. 8, T. 1) on its postaxial border. These nerves reappear in the forearm, and the occasional 



L/AfB 



DORSAL SURFACE 

 Shoulder Arm Forearm Hand 



Chest 



VENTRAL SURFACE 

 Arm. forearm JFand 



DIAGRAM of the segmental distribution of the muscular nerves of the upper and lower limbs. 



" axillary arches " may be regarded as the muscular elements usually suppressed, and, when 

 present, supplied by these nerves. 



Muscles with a Double Nerve-supply. The existence of more than one nerve to a muscle 

 indicates usually that the muscle is composite and is the representative of originally separate 

 elements, belonging to more than one segment or to both surfaces of the limb. In the case of 

 the pectoralis major, subscapularis and flexor digitorum profundus, adductor magnus, and soleus, 

 parts of the same (ventral or dorsal) stratum have fused, to form muscles innervated from the 

 corresponding ventral or dorsal nerves. The other muscles having a double nerve-supply 

 brachialis, biceps femoris, and (sometimes) pectineus are examples of fusion at the preaxial or 

 postaxial border of muscular elements derived from the dorsal and ventral surfaces of the limb, 

 which are correspondingly innervated by branches from both dorsal and ventral series : e.g. the 

 brachialis is innervated by the musculo-cutaneous and radial nerves ; the biceps femoris by the 

 peroneal (short head) and tibial nerves (long head) ; and the pectineus, by the femoral and 

 (sometimes) obturator nerves. 



B. Innervation of the Skin of the Limbs. While the scheme of cutaneous inner-ration of 

 the limbs is fundamentally segmental, yet the arrangement is confused and complicated by 

 various causes. The growth of the limb from the trunk has caused the skin to be drawn out 

 over it like a stretched sheet of india-rubber (Herringham), and at the same time the extent of 

 the dorsal area of the limb is increased at the expense of the ventral area. The central nerves of 

 the plexus remain buried deeply in the substance of the limb, only coming to the surface towards 

 the periphery. The proximal parts of both surfaces of the limb thus become innervated by 

 cutaneous nerves otherwise not necessarily concerned in the innervation of the limbs. Herring- 

 ham has shown that (A) Of two spots on the skin, that nearer the preaxial border tends to b( 

 supplied by the higher nerve. (B) Of two spots in the preaxial area, the lower tends to be supplied fa 



