THE LIMBS. 



295 



the case with the typical lateral cutaneous nerves, divides into 

 a dorsal division for the extensor muscles (musculo-spiral, posterior 

 circumflex, supra-scapular, etc.) and ventral for the flexor muscles 

 (median, ulnar, musculocutaneous) (Fig. 238). 



Clinical and experimental research has shown that each of the 

 seven or eight segments contributes to the cutaneous supply of 

 the limb. The classical investigations of Sherrington in the 

 segmental distribution of the sensory nerves in the limbs of apes, 

 showed that they are arranged in a definite and orderly manner 

 (Fig. 240). The sensory distribution of the spinal nerves in the 



vent, line — 



perineum, 

 anus 



Fig. 240. — Diagram to show the typical Manner in which the Posterior Nerve Roots 

 are distributed in the Lower Limb (based on Sherrington's researches into the 

 sensory distribution of the limb nerves of apes). 



human arm is shown diagrammatically in Fig. 239. The distribu- 

 tion of the motor nerves of each segment is the following : 



5th Cervical. — To extensor muscles which raise the shoulder, 

 extend the arm, fore-arm and proximal phalanges. 



6th Cervical. — To adductors and extensors of the arm, flexors 

 of the thumb. 



7th Cervical. — Rotators outwards of the shoulder and flexors of 

 the middle phalanges. 



8th Cervical. — Flexors of the fingers and extensors of the 

 carpus. 



1st Dorsal. — Flexors of fingers, the interossei, adductors of 

 thumb. 



It will be thus seen that in the motor segments, not muscles 

 but actions are represented ; hence the formation of the plexuses 



