384 ANATOMICAL TECHNOLOGY. 



§ 1021. N. cutaneus internus (Fig. 104, 105, 106 ; Quain, A, I, 

 585 ; G-ray, A, 675). — The internal cutaneous nerve arises wholly 

 from the 1st thoracic. It becomes subcutaneous at about the distal 

 third of the brachium, emerging from between the epitrochlearis 

 and biceps muscles about opposite the point where the JV. radialis 

 emerges from between the biceps, clavo-deltoideus and ectotriceps 

 (Fig. 74) ; hence it is liable to be destroyed in removing the skin or 

 in the exposure (§ 1017) unless care is taken. It gradually curves 

 from the dorso-caudal to the ventral aspect of the arm, and is dis- 

 tributed mostly to the skin of the brachium and antebrachium on 

 the caudal and venti-al aspects. 



Dissection. — It is best to isolate the 1st thoracic near its origin 

 to find the origin of the internal cutaneous nerve ; it may then be 

 traced peripherad, or it may be found on the ventral side of the 

 arm, where it becomes subcutaneous, and traced in both dii-ections. 

 The presence of the nerve of Wrisberg has not been satisfactorily 

 determined in the cat. 



§ 1022. N. musculo-cutaneus s. cutaneus externus (Fig. 104, 

 105, 106; Quain, A, I, 587; Gray, A, 674). — The musculo-cutaneous 

 nerve arises from the ventral surface of the 6tli and 7th cervical 

 nerves. It is also closely connected with the N. medius (Fig. 106). 

 It i^asses almost directly toward the shoulder joint, and when near 

 the trocMn gives several filaments to the coracoideus and biceps 

 muscles. It passes entad of the long head of the M. coracoideus, 

 and continues distad along the brachium, resting on the caudal 

 aspect of the biceps. Opposite the Fm. epitrocJileare, a small 

 branch is given ofi" which anastomoses with the iV. medius through 

 the foramen. In the concavity of the elbow it passes entad of the 

 M. biceps to its cephalic aspect. On the antebrachium it is subcu- 

 taneous and extends along the cephalic border of the arm parallel 

 with the N. radialis (Fig. 105). It is distributed to both skin and 

 muscles, as the name indicates. 



Dissection. — Commence near the shoulder joint and trace it first 

 centrad to determine its origin and communications, then peripherad 

 along its whole course. It vrill be necessary to employ a tripod or 

 other magnifier in tracing the anastomosis with the median at the 

 elbow. On the antebrachium the nerve is very near the surface, 

 hence the skin and fascia should be removed only by degrees and 

 while keeping the nerve in sight. 



§ 1023. NN. subscapulares (Fig. 104, 105, 106; Quain, A, I, 



