78 THE SUPERIOR EXTREMITY 



and spine of the scapula, and turn it towards its insertion into 

 the humerus, taking care not to injure the circumflex humeral 

 arteries and the axillary nerve. Note the tendinous intersections 

 which run through the substance of the muscle, then clean the 

 vessels and nerves which are exposed. The axillary nerve 

 enters the back part of the shoulder region through the posterior 

 part of the quadrangular space, accompanied by the posterior 

 humeral circumflex vessels, and at once divides into an anterior 

 and a posterior division. Before it divides, whilst it is in the 

 quadrangular space, immediately below the shoulder-joint, it 

 gives off an articular twig to the joint, which should be secured. 

 The anterior division accompanies the posterior humeral cir- 

 cumflex artery round the surgical neck of the humerus. It 

 supplies the deltoid and sends branches through it to the skin on 

 its superficial surface. Clean both the nerve and the vessel ; 

 then turn to the posterior branch and secure the twig to the teres 

 minor muscle, upon which there is a gangliform enlargement. 

 The posterior branch terminates as the lateral cutaneous nerve of 

 the arm, which turns round the posterior border of the deltoid 

 to gain its superficial surface. It has already been dissected 

 (see p. 69). Clean the teres major and minor muscles which 

 spring from the posterior surface of the axillary border of the 

 scapula, and pass to the humerus, and note the strong septum 

 of deep fascia which separates them. Clean the long head of 

 the triceps which arises from the upper part of the axillary 

 border of the scapula. Then examine the subacromial bursa, 

 which lies directly below the acromion, on the insertion of the 

 supraspinatus. If the wall of the bursa is quite entire a blow- 

 pipe may be thrust into it. It can then be distended, and if 

 unilocular it may be inflated to about the average size of a hen's 

 egg. It varies much in size, however, in different subjects. 

 Open the bursa and examine its extent with the finger or a 

 blunt probe. Its interior is sometimes divided by fibrous parti- 

 tions into two or more loculi. Now turn the limb on to its 

 posterior aspect and clean the proximal parts of the coraco- 

 brachialis and the short head of the biceps brachii which spring, 

 by a common tendon, from the tip of the coracoid process of the 

 scapula. Pull the short head of the biceps and the coraco- 

 brachialis medially and expose the tendon of the long head of the 

 biceps lying in the intertubercular sulcus of the humerus, but do 

 not displace it at present. Now pull the short head of the biceps 

 and the coraco-brachialis laterally and .clean the insertion of the 

 subscapularis it is inserted into the lesser tubercle of the 

 humerus on the medial side of the intertubercular sulcus. Clean 

 also the anterior humeral circumflex artery, trace it to its division 

 into an ascending branch, which runs to the shoulder -joint 

 along the intertubercular sulcus, and a transverse branch, which 

 anastomoses with the posterior humeral circumflex artery, and 

 then re-examine the structures which lie directly under cover of 

 the deltoid and note their relative positions. 



PARTS UNDER COVER OF THE DELTOID. The deltoid 

 covers the proximal part of the humerus, and envelops the 

 region of the shoulder-joint behind, laterally, and in front. 

 It also covers the coracoid process of the scapula. It is 



