THE LIMBS OF THE HOKSE 25 



Vv. brachialis et axillaris. — Generally speaking, the veins of 

 the region receive tributaries corresponding to the like-named arteries. 

 Some differences, however, may be noted. The brachial vein is fre- 

 quently double near the elbow, in which case the artery is flanked 

 by a vein on each side. In the same region the brachial receives 

 a strong communicating branch from the cephalic vein. 



The external thoracic vein may join the brachial instead of the 

 axillary, and frequently it receives the thoracodorsal vein. 



The external thoracic vein is not really a satellite of the artery 

 of the same name. Beginning superficially in the lateral wall of the 

 abdomen (Hank), it pierces the cutaneous muscle, to reach the lateral 

 border of the deep pectoral muscle, along which it travels into the 

 axilla. 



The main veins of the arm lie behind the corresponding arteries 

 until the region of the shoulder is reached. Here the axillary vein 

 crosses the medial face of the artery, so that, by the time the 

 vessels have arrived at the first rib, the vein is the more ventral 

 of the two. 



Dissection. — Proceed now to the examination of the lateral aspect 

 of the shoulder and arm. Though not strictly necessary, it makes for 

 convenience if the remains of the trapezius muscle be removed. In 

 cleaning the surface of the scapular muscles, look for the terminal twigs 

 of the circumflex scapular artery a little proximal to the shoulder joint 

 and in line with the spine of the scapula. 



A branch (n. cutaneus brachii lateralis) of the axillary nerve appear- 

 ing from underneath the deltoid muscle, and running across the lateral 

 head of the triceps and down the front of the brachialis muscle into the 

 forearm, should also be secured. 



M. supraspinatus. — The supraspinous x muscle fills the whole 

 of the supraspinous fossa of the scapula from which it takes most 

 of its origin. Some of its fibres, however, spring from the scapular 

 cartilage, and some arise from the common septum between the supra- 

 spinous and subscapular muscles. At the coracoid process the muscle 

 splits into two parts, which form an arch over the biceps tendon, 

 and are inserted into the anterior portion of the greater and lesser 

 tubercles of the humerus. On a superficial examination both inser- 

 tions appear to be wholly fleshy. Deeper investigation, however, 

 reveals a core of tendinous tissue. It should also be noted that 

 both parts of the insertion are closely connected with the joint- 

 capsule. Not infrequently a synovial bursa lies between the supra- 

 spinous muscle and the coracoid process of the scapula. 



M. deltoideus. — The deltoid 2 muscle occupies the angle formed 



1 Supra [L.], above. Spina, see footnote, p. 27. 



2 Deltoides [L.], triangular; AeXra [Gr.], the letter A, or delta; eiSos (eidos) 

 [Gr.], shape. 



