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THE DISTRIBUTION OF THE SPINAL NERVES. 
receives normally the whole contribution of the first thoracic nerve) the lesser internal cutaneous, 
the inner branch of the internal cutaneous, and the dorsal branch of the war nerve supply the 
dorsal aspect of the limb on its postaxial border. These nerves are in serial homology with the 
intercosto-humeral and lateral trunks of intercostal nerves. In the case of the umbo-sacral plexus 
similarly, in which the third sacral nerve does not divide into ventral and dorsal trunks, the 
small sciatic and tibial nerves containing the contribution from the third sacral nerves innervate, 
by means of the gluteal and external femoral branches of the former and the tibial communi- 
cating branch of the latter, the dorsal surface of the limb along the postaxial border, in series 
with the perforating cutaneous nerve and the perineal branch of the fourth sacral. 
These apparent anomalies appear to indicate that, instead of dividing into its proper dorsal 
and ventral trunks, the entire contribution of the spinal nerve concerned is in these instances 
carried undivided along the postaxial border of the limb in association with the ventral trunks, 
and that the dorsal subdivisions are thrown off successively as the plexus cords approach the 
periphery. Indeed, in the case of the small sciatie nerve, Eisler has shown that, when the 
peroneal and tibial nerves are separated at their origin, its gluteal and external femoral branches 
arise from and are connected with the former, and the perineal and internal femoral branches 
with the latter trunk. 
)F THE SPINAL NERVES TO THE MUSCLES AND SKIN 
OF THE LIMBS. 
THE DISTRIBUTION ( 
By dissection, experiment, and clinical observation, it is conclusively proved that 
as a rule each nerve of distribution in the limb, whether to muscle or skin, is made up of 
fibres derived from more than one spinal nerve ; and, further, that in cutaneous distribution 
a considerable overlapping occurs in the course of the several peripheral nerves. Moreover, 
the arrangement of the distribution of the nerves to skin and to muscles is not identical. 
In the case of the skin of the limbs, by the covering of the limb being drawn on to it from 
adjacent parts in the process of growth, cutaneous nerves are engaged, which are derived 
from sources not represented in the muscular innervation of the limbs. Again, among the 
muscles, some have undergone fusion, others have become rudimentary, and others again 
have altered their position in the limb. Bearing these qualifications in mind, it is 
possible to formulate a definite plan for the innervation of the skin and muscles of the 
upper and lower limb. The accompanying tables give an analysis of the distribution of 
the spinal nerves to the skin and muscles of the upper and lower limb respectively :— 
I. Upper Limb. 
A. Cutaneous Nerves. 
1. Dorsal (Posterior) Surface. 
| Spinal Origins. 
| : ; ; 
| Regions. ' » Nerves. Preaxial Postaxial 
| Nerves. Nerves. 
| eae = ———— ae ht — = = | 
Upper part (| Posterior primary division, ig Paige 
(preaxial) ~ cervical . : : .|045.6 
Geapalar, i | Cervical plexus, acromial 5s Ce BE Ze 
Lower part | | aaa _ primary divisions, : 
(postaxral) | LOTACIC . . 5 ; ; 1-7 
Intercostal nerves, lateral branches TT. 2. 3. 4 
fupeee part { Cervical plexus, acromial —. sr 3n4: 
F (preaxial)  \  Cireumflex  . , : : Cr 5.6. 
Deltoid- 
Lower part { Intercostal nerves, lateral 
(postuxial) — \ branches . : . ; T. 2.3. 
Fa F N my - Vp + 
Outer side | ce i ae = C2516 
(preavial) N yee pane , Upper external ae ae 
branch 5 : : ao) 7 Os 
Upper arm: i Enatl oral j bh a (5) Barid 
Tmner side |, Musculo-spiral, internal branch C. 8. 
caap ] 5 5; y x mm 
(postaxrial) | Lesser internal cutaneous Pd. 
; Intercosto-humeral ee 
