CUTANEOUS DISTRIBUTION OF SPINAL NERVES. 



345 



their terminal filaments, so that there is probably no spot of the skin which 

 is supplied only by one spinal nerve (Sherrington). 



In the limbs, although the nerves have been mingled in the plexuses, there is a 

 similar principle to be recognized in their ultimate distribution, the fibres derived 

 from the several spinal nerves being supplied to definite continuous areas in 

 positions which are readily explained by reference to the mode of development of the 

 limb. Thus, the upper nerves are distributed along the preaxial side of the limb, 

 and the lower nerves along the postaxial side, while the intermediate nerves descend 

 along the centre of the limb, and supply only the more distal parts. The skin at the 

 root of the limb is not supplied by offsets of the limb-plexus, but by branches 

 of nerves which have been drawn out, as it were, with the skin of the adjoining 

 part of the trunk during the development of the limb. 



dorsal or ventral, m&ckcttt tine, 



Head 



Fig. 224. --SCHEME OF THE SENSORY SPINAL SKIN-FIELDS OF THE HIND LIMB OF MONKEY (Macacus 



rhesus). (Sherrington.) 



10, 11, 12, areas of lower dorsal nerves ; 1 7, areas of lumbar nerves ; 8 11, areas of sacral and 

 caudal nerves. Of the seven lumbar nerves in this monkey, the second and seventh correspond 

 respectively to the first lumbar and first sacral nerves of man. The overlapping of the skin-fields is not 

 indicated. The arrangement is the same on the dorsal and ventral aspects. 



Ths following rules have accordingly been formulated by Herringham from his 

 observations on the nerves of the upper limb, and have been confirmed by Paterson 

 for the lower limb : 



A. Of two spots on the skin, that -which is nearer the preaxial border tends to be 

 supplied by the higher nerve. 



B. Of two spots in the preaxial area, Ihe lower tends to be supplied by the loiver 



Fig. 225. SEGMENTAL CUTANEOUS AREAS FROM THE FIRST DORSAL TO THE FOURTH SACRAL, AS 



DETERMINED BY CLINICAL AND PATHOLOGICAL OBSERVATIONS IN MAN. (Head.) 



On the right side of the figures the areas are marked by different colours and modes of shading; on 

 the leftside the " maximum spots " (seat of most marked tenderness and pain) of the areas are shown. 

 The several dorsal, lumbar and sacral areas are indicated each by the initial letter followed by a number. 

 In C, C 7 is the seventh cervical spine, 3 to 12 are the corresponding dorsal spines, and L 1 to 4 are 

 lumbar spines. 



