MORPHOLOGY OF THE LIMB-PLEXUSES. 



743 



II. Lower Limb. 



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bord 



the regions of the limbs no anterior cutaneous branches, derived from the limb nerves, 

 ply the trunk. The whole of the nerve is carried into the limb and is absorbed in its 

 ervation, and the dorsal and ventral trunks forming the limb-plexuses are to be looked upon 

 as homologous with the lateral and anterior trunks of an intercostal nerve. Two series of 

 anomalies in relation to the formation and distribution of the nerves to the limbs must, however, 

 be considered, because it has been suggested (Goodsir) that the nerves of the limbs are serially 

 homologous not with the whole, but only with the lateral branches of the anterior rami of 

 " e intercostal nerves. 



(1) Nerves in connexion with the primitive borders of the Limbs. At the preaxial 

 er of the upper limb, at its root, the fourth cervical nerve, which supplies the anterior and 

 lateral surfaces of the neck, is also distributed through the supraclavicular nerves to the skin of 

 both ventral and dorsal surfaces of the limb. The nerves and surfaces are here not merely 

 homologous, but in actual continuity. 



At the preaxial border of the lower limb, similarly, the first lumbar nerve, by means of the 

 ilio-hypogastric and ilio-inguinal branches, supplies on the one hand the buttock, in series with 

 the lateral branches of the lower thoracic nerves, and, on the other hand, the lower part of the 

 abdominal wall and the adjacent medial side of the thigh, in series with the anterior terminal 

 branches of the lower thoracic nerves. 



At the postaxial border of the upper limb the first and second thoracic nerves are concerned 

 in supplying trunk segments as well as parts of the limb. The first thoracic nerve, besides 

 supplying the limb through the medial cord of the plexus, also innervates at least the muscles of 

 the first intercostal space ; the second thoracic nerve is concerned in the innervation of the limb, 

 principally by means of its lateral branch only, which, as the intercosto-brachial nerve, supplies 

 the skin along the postaxial border of the limb and on its dorsal side. At the postaxial border of 

 the lower limb, in the same way, the third and fourth sacral nerves, partially implicated in the 

 innervation of the limb (through the tibial, posterior cutaneous nerve of the thigh, perforating 

 cutaneous nerve, and perineal branch of the fourth sacral nerve), are also engaged in supplying 

 the trunk (perineum) through the pudendal nerve. These peculiarities of arrangement of the 

 nerves at the borders of the limbs may be explained on the supposition that the segment corre- 

 sponding to the nerve named is only partially concerned in limb formation, and is, at the same 

 time, implicated to a greater or less extent in the formation of structures belonging to the trunk. 

 (2) The origin and distribution of the nerves at the postaxial border of the limbs present 



48 c 



