248 DISSECTION OF THE ARM. 



where it gives offsets to the infraspinatus muscle anil the scapula, and 

 anastomoses with the dorsal branch of the subscapular, and the posterior 

 scapular artery of the suhclavian. 



Beneath the supraspinatus it furnishes a supraspinal branch for the 

 supply of the muscle, the bone, and the shoulder-joint. 



The companion vein of the suprascapular artery joins the external jugu- 

 lar vein. 



The suprascapular nerve (*) is a branch of the brachial plexus (p. 80). 

 When it reaches the costa of the scapula, it enters the supraspinal fossa 

 beneath the posterior special ligament. In the fossa it supplies two 

 branches to the supraspinatus ; and is continued beneath a fibrous band to 

 the infraspinatus muscle, in which it ends. 



The nerve gives some articular filaments to the shoulder-joint, and other 

 offsets to the scapula. 



The posterior scapular artery runs along the base of the scapula beneath 

 the rhomboid muscles, furnishing offsets to them and the surfaces of the 

 bone. It is more fully noticed with the dissection of the Back. 



The dorsal branch of the subscapular artery (6) (p. 33o) turns below 

 the inferior costa of the scapula, opposite the posterior of the two spaces 

 between the teres muscles. Entering the infraspinal fossa beneath the 

 teres minor, it supplies that muscle and the infraspinatus, and communi- 

 cates with the suprascapular artery. This vessel sends a branch along 

 the dorsum of the scapula between the teres muscles, towards the inferior 

 angle of the bone. 



SECTION III. 



THE FRONT OF THE ARM. 



Position. For the dissection of the superficial vessels and nerves on 

 the front of the arm, the limb should lie flat on the table, with the front 

 uppermost. 



Dissection. The skin is to be raised from the fore and hinder parts of 

 the arm and elbow-joint. To reflect it, make one incision along the centre 

 of the limb as far as two inches below the elbow ; arid at the termination, 

 a second cut half round the forearm. Strip now the skin from the limb, 

 as low as the transverse incision, so that the fat which contains the cuta- 

 neous vessels and nerves may be denuded. Between the skin and the 

 prominence of the olecranon a bursa may be seen. 



The cutaneous veins (fig. 76) may be sought first in the fat : they are 

 very numerous below the bend of the elbow, as they issue from beneath 

 the integument. One in the centre of the forearm is the median vein, 

 which bifurcates rather below the elbow. External to this is a small vein 

 (radial) ; and internal to it are the anterior and posterior ulnar veins, 

 coming from the front and back of the forearm. At the elbow these veins 

 are united into two ; one (basilic) is to be followed along the inner side, 

 and the other (cephalic) along the outer side of the arm. 



The cutaneous nerves may be next traced out. Where they perforate 

 the deep fascia they lie beneath the fat : and this layer must be scraped 

 througrh to find them. 



