THE DISTRIBUTION OF THE SPINAL NERVES. ; 629 
- A. Innervation of the Muscles of the Limbs.—The following laws appear to be applicable 
to the upper and lower limbs alike :— 
1. No limb-muscle receives its nerve-supply from posterior primary divisions. 
2. The dorsal and ventral strata of muscles are always supplied by the corresponding dorsal and 
ventral branches of the nerves concerned. The ventral muscular stratum 7s more extensive than the 
dorsal; the ventral nerves are the more numerous, and the additional nerves are postaxially placed. 
The spinal nerves supplying muscles of the upper limb are C. 5, 6, 7, 8 (dorsal), and C. 5, 6, 7, 8, 
T. 1 (ventral) ; the nerves for the muscles of the lower limb are L. 2, 3, 4, 5, 8S. 1, 2 (lorsal), and 
L. 2, 3, 4, 5, S. 1, 2, 3 (ventral). 
3. The dorsal and ventral trunks of the nerves are distributed in the limb in a continuous, 
segmental manner ; so that, “of two muscles, that nearer the head end of the body tends to be 
supplied by the higher nerve, and that nearer the tail end by the lower nerve ” (Herringham). 
4. The nerves placed most centrally in the plexus extend furthest into the limb, and the more 
preaxial nerves terminate sooner in the limb than the more postaxial nerves. 
Upper Limb. 
Dorsal Surface. Ventral Surface. 
Muscles of shoulder . C. 3, 4, 5, 6, 7, 8. Muscles of chest MONS (GaSe ae ll 
a ares ACL Wieetet .. arm Be MG stay GM Tic 
Wi forearmy | C216. 7: a. fOrearnny .  OaGiia onl le 
+ lnminel 5 X05 GZ, th (A Wp 
Lower Limb. 
Muscles of thigh and Muscles of thigh . L. 2, 3, 4, 5,8. 1, 2, 3. 
buttocks J |. Osa Do al oe _ leg Ue e Slee os 
Muscles of leg and foot L. 4, 5, 8.1. fs foot SAS Shellie & 
The only exception to this rule is on the ventral (anterior) surface of the upper arm, where a 
suppression 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 
UPPER L/MB 
DORSAL SURFACE VENTRAL SURFACE 
Shoulder Arm foreazsm Hand Chest Arm Forearm Hand 
LOWER LIMB 
DORSAL SURFACE VENTRAL SURFACE 
Thigk && Buttock Leg Foot Thigh Leg Foot 
Fic, 451. 
ScHEME 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, supphed 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 one or both surfaces of the limb. In the case of the pectoralis major, 
subscapularis and flexor profundus digitorum, adductor magnus, and soleus, parts of the same 
(ventral or dorsal) stratum have fused, to form muscles innervated from their corresponding 
ventral or dorsal nerves. The other muscles having a double nerve-supply—brachialis anticus, 
biceps flexor cruris, 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: ¢.g. the brachialis 
anticus is innervated by the musculo-cutaneous and musculo-spiral nerves; the biceps flexor 
cruris, by the peroneal (short head) and tibial (long head) nerves; and the pectineus, by the 
anterior crural and (sometimes) obturator nerves. 
B. Innervation of the Skin of the Limbs.—W hile the scheme of cutaneous innervation 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 
40 4 
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