386 ANATOMICAL TECHNOLOGY. 



and trace the nerve to its origin, as sliown in Fig. 105 and 106. 

 Then it may be followed peripherad, but great care should be 

 taken not to injure the N. cutaneus internus or break the anas- 

 tomosing iilament from the iV. musculo-cutaneus (§ 1022). In the 

 concavity of the elbow the M. pronator teres should be divided and 

 the nerve followed in the antebrachium as described for the radial 

 artery (§ 944). 



§ 1026. N. musculo-spiralis (Fig. 104, 105, 106; Quain, A, I, 

 692 ; Gray, A, 679). — The musculo-spiral nerve is formed largely 

 from the 8th cervical nerve, although it receives branches from the 

 1st cervical and the 1st thoracic ; it is the largest offset from the 

 brachial plexus. It winds obliquely around the humerus, com- 

 mencing at about its middle, being' accompanied by the superior 

 profunda artery (§ 945, B). After reaching the cephalic side of 

 the brachium, the nerve divides into two parts, which are known as 

 the radial and the posterior interosseus nerves. 



N. radialis. — This is the smaller of the two branches into which 

 the musculo-spiralis divides. It becomes subcutaneous as it emerges 

 from between the MM. ecfotriceps, hracMalis and clavo-deltoideus 

 (Fig. 74), near the distal end of the brachium. It then follows the 

 course of the radius, remaining subcutaneous through the whole 

 length of the antehrachium. This nerve is closely associated with 

 the musculo-cutaneous. The single large superficial vein of the 

 arm also follows its course. It is partly cutaneous in its distri- 

 bution. 



§ 1027. N. interosseus posterior. — This is the larger of the two 

 branches into which the musculo-spiralis divides. It passes along 

 the dorsal side of the antebrachium to the wrist. This nerve is 

 almost wholly muscular in its distribution. 



Dissection. — The skin should be toi-n from the dorsal and ce- 

 phalic sides of the brachium, then the muscles carefully cut along 

 the course of the nerve. The N. radialis will have been exposed 

 in the study of the miisculo-cutaneus. The N. interosseus may be 

 followed by cutting and tearing the muscles very cautiously with 

 a tracer. 



§ 1028. N. ulnaris (Fig. 104, 105, 106; Quain, A, I, 588 ; Gray, 

 A, 677). — The ulnar nerve arises from the 8th cervical and the 1st 

 thoracic. It passes along the brachium parallel with the iracMal 

 artery as far as the elbow, and then turns to the dorsal side of the 

 elbow. It passes along the dorso-caudal border of the antebra- 



