244 DISSECTION OF THE UPPER LIMB. 



bone are the circumflex vessels and nerve, and the upper part of the 

 biceps muscle. In front of the humerus is the coracoid process with its 

 muscles. 



Dissection. By following back the posterior circumflex vessels and 

 nerve through a space between the humerus and the long head of the tri- 

 ceps, (r, their connection with the axillary trunks will be arrived at. In 

 clearing the fat from the space a branch of the nerve to the teres minor 

 muscle is to be sought close to the border of the scapula, where it is sur- 

 rounded by dense fibrous tissue. 



Arching outwards in front of the neck of the humerus, is the small 

 anterior circumflex artery: this is to be cleaned. 



The circumflex arteries arise near the termination of the axillary trunk 

 (p. 335) ; they are two in number, and are named anterior and posterior 

 from their position to the neck of the humerus. 



The anterior branch is a small artery, which courses beneath the 

 coraco-brachialis and biceps muscles, and ascends in the bicipital groove 

 to the articulation and the head of the humerus : it anastomoses with 

 small offsets of the posterior circumflex. 



The posterior circumflex artery (fig. 74, ), larger in size, winds back- 

 wards through a space between the humerus and the long head of the 

 triceps, and is distributed chiefly to the deltoid muscle, in which it anasto- 

 moses with the acromial thoracic and upper profunda arteries. 



Branches are given from it to the head of the humerus and the shoulder 

 joint, and to anastomose with the anterior circumflex artery. It supplies 

 branches likewise to the teres minor, the long head of the triceps, and the 

 integuments. 



The circumflex nerve (fig. 74, *) leaves the arm-pit with the posterior 

 circumflex artery (p. 335), and bends round the neck of the humerus, 

 beneath the deltoid muscle in which it ends. Many and large branches 

 enter the deltoid, and terminate in it; one or two filaments pierce the 

 fibres and become cutaneous. 



Branches. In the axilla it gives an articular filament to the under part 

 of the shoulder-joint. Behind the humerus it furnishes an offset to the 

 teres minor ( 3 ), which has a reddish gangliform swelling on it. And at 

 the edge of the deltoid it gives origin to the cutaneous nerve ( 2 ) before 

 noticed. 



The INFRASPINATUS MUSCLE (fig. 74, B) occupies the infraspinal part 

 of the scapula, and extends to the head of the humerus. The muscle 

 arises from the infraspinal fossa, except at three spots, viz., the neck, and 

 the lower angle and inferior border where the teres muscles are attached ; 

 it arises also from the lower side of the spinous process, and from the special 

 fascia covering the surface. Its fibres converge to a tendon, which is in- 

 serted into the middle impression on the great tuberosity of the humerus, 

 and joins the tendons of the supraspinatus and teres minor. 



A part of the muscle is subcutaneous, and the fibres arising from the 

 spine of the scapula overlay the tendon : the upper portion is concealed 

 by the deltoid ; and the lower end, by the latissimus dorsi. The lower 

 border is parallel to the teres minor, with n liich it is sometimes united. 

 The muscle lies on the scapula and the humero-scapular articulation, but 

 between it and the joint is a small bursa. 



Action. With the humerus hanging it acts as a rotator outwards; and 

 when the bone is raised it will move the same backwards in concert with 

 the hinder part of the deltoid. 



