52 THE UPPER EXTREMITY 



other boundaries are the same as those seen from the 

 front. 



The term triangular space is the name given to another 

 intermuscular interval which becomes apparent when the 

 muscles in this region are cleaned and separated. It is 

 placed nearer the inferior angle of the scapula, and the long 

 head of the triceps intervenes between it and the quadrilateral 

 space. It is bounded above by the subscapularis ; below by 

 the teres major; and laterally by the long head of the 

 triceps. The circumflex artery of the scapula should be followed 

 into this space, and cleaned up to the point where it dis- 

 appears around the axillary border of the scapula under cover 

 of the teres minor. 



Dissection. Having now traced the posterior circumflex artery of the 

 humerus and the axillary nerve as far as possible, through the quadrilateral 

 space, the position of the limb should be reversed. Turn it so that its 

 dorsal surface is uppermost, and, everting slightly the posterior border 

 of the deltoid, define the boundaries of the space as they are seen from 

 behind. At the same time clean the circumflex vessels and the axillary 

 nerve as they issue from the space to reach the deep surface of the deltoid 

 muscle. Care must be taken not to injure the branch which the axillary 

 nerve gives to the teres minor. 



The deltoid muscle may now be divided close to its origin and thrown 

 downwards ; in doing this preserve the acromial branch of the thoraco- 

 acromial artery which runs in the line of incision beneath the deltoid. 

 A large bursa which lies between the deltoid and upper aspect of the 

 capsule of the shoulder-joint must also be kept intact. 



Parts under cover of the Deltoid. The deltoid covers the upper 

 part of the humerus, and is wrapped round 'the shoulder-joint so as to 

 envelop it behind, laterally, and in front. The full rounded appearance 

 of the shoulder will now be seen to be due to the muscle passing over the 

 expanded proximal end of the humerus. When the head of the bone is 

 displaced the muscle passes more or less vertically downwards from its 

 origin, and the dislocation is recognised by the squareness or flatness of 

 the shoulder. Behind, the deltoid covers the muscles which arise from the 

 dorsal aspect of the scapula as they pass laterally to reach the great 

 tubercle of the humerus ; in front, it covers the upper part of the biceps 

 muscle, and overlaps the coracoid process and the muscles attached to it. 

 In relation also to the deep surface of the deltoid are the circumflex vessels 

 of the humerus and axillary nerve. 



Bursa Subacromialis (Subacromial Bursa). This is a large 

 bursal sac which intervenes between the acromion and deltoid 

 above, and the upper aspect of the capsule of the shoulder- 

 joint below. It facilitates the play of the proximal end of 

 the humerus, with its capsule, on the under aspect of the 

 acromion and deltoid. Pinch a portion of it up with the 



