682 PHYSIOLOGY OF SPECIAL NERVES 



2. SPINAL NERVES 



The anterior and posterior roots of the same side belonging to each segment 

 of the spinal cord unite peripherally to the spinal ganglion to form a mixed 

 nerve trunk. Each of these nerve trunks then divides into a dorsal and a 

 ventral branch. The dorsal branches are relatively small and supply only the 

 skin and muscles of the back; the ventral branches, which are much larger, 

 are allotted to the anterior and lateral parts of the neck, thorax, abdomen and 

 extremities. 



The dorsal branches all run separately to their destination; but with the 

 exception of the twelve thoracic nerves, the ventral branches anastomose freely 

 with one another, forming plexuses corresponding to the main divisions of 

 the body. 



A number of experimental and clinical researches have been made on the 

 distribution of the fibers arising from the different roots. We shall here pay 

 regard chiefly to the exposition given by Kocher on the relations obtaining 

 in man. 



A. SENSORY NERVES 



Each spinal nerve root, even if its fibers unite with others to form a plexus, 

 supplies a continuous region of the skin. These regions overlap, however, 

 so that a single region on the lateral aspect of the body is provided with a 

 twofold or even a threefold supply (Sherrington). 



Fig. 300 represents schematically, according to Kocher, areas of distribu- 

 tion of the different spinal roots. This is constructed on the basis of clinical 

 observations of patients with total lesions of the spinal cord. The boundary 

 lines in the figure mark the upper limits of sensibility for lesions at the 

 different levels. In reality the regions supplied by the different nerves, in 

 man as in animals, overlap considerably both above and below. The areas 

 blocked out in the figure represent therefore the central parts of the fields 

 actually supplied by the separate roots. 



B. MOTOR NERVES 



In the following table are summarized, after Kocher, the distributions 

 of the different motor roots: 



R OOT. MUSCLES. 



I C. Small neck muscles; sternohyoid; sternothyroid ; omohyoid. 



I C. Sterno-cleido-mastoid ; trapezius. 



III C. Platisma myoides. 



IV C. Scaleni; diaphragm. 



V C. Rhomboidei; supra- and inf raspinatus ; coracobrachialis ; biceps; 



brachialis anticus; deltoid; supinator longus and brevis. 

 VI C. Subscapularis ; pectoralis major and minor; pronator teres and 

 qnadratus; latissimus dorsi; teres major; triceps; serratus 

 magnus. 



VII C. Extensors and flexors of the wrist. 

 VIII C. Extensors and flexor longus of the fingers. 



