76 TOPOGRAPHIC AND APPLIED ANATOMY. 



FIG. 30. .A posterior view of the shoulder with the quadrangular and triangular spaces. 



spinalus muscle, partly covered by the deltoid, passes from the infraspinous fossa to the greater 

 tuberosity of the humerus. The teres minor, in relation with the lower border of the preceding 

 muscle, runs from the axillary margin of the scapula to the greater tuberosity of the humerus; 

 its lower border is approximately parallel to the upper border of the teres major muscle. Since 

 both of these muscles are crossed by the long tendon of the triceps (which lies behind the teres 

 major, but in front of the teres minor), as shown in Fig. 30, it will be seen that two spaces are 

 formed, a quadrangular space and a triangular space. 



1. The quadrangular space is bounded by the neck of the humerus, by the teres minor, 

 by the teres major, and by the long head of the triceps (see Fig. 30). Within this space, the 

 axillary artery may be exposed from behind; the posterior circumflex artery and the circumflex 

 nerve may also be seen as they pass into the substance of the deltoid from the inner surface of the 

 muscle (see page 75). 



2. The triangular space is bounded by the long head of the triceps and by the teres major 

 and minor muscles. In this space may be seen one of the two terminal divisions of the sub- 

 scapular artery, the dorsalis scapulae (see page 74). This vessel turns around the axillary border 

 of the scapula to its posterior surface, where it is covered by the infraspinatus muscle, and runs 

 upward to anastomose with the suprascapular artery below the root of the acromion (see page 74). 

 This anastomosis forms an important collateral path after occlusion of the axillary artery. If -the 

 axillary artery is followed downward along the inner side of the humerus, it will be seen to emerge 

 as the brachial artery below the united tendons of the latissimus dorsi and teres major muscles. 

 In the triangular slit between the humerus, the long tendon of the triceps, and the external head 

 of the triceps, the brachial artery gives off the superior profunda, which runs posteriorly and 

 accompanies the musculospiral nerve. 



Shoulder- joint (Fig. 31). This joint has the widest range of motion of any joint in the body. 

 The articulation is formed by the head of the humerus and the glenoid cavity of the scapula. The 

 humeral head is covered by cartilage and the articular surface of the glenoid cavity is enlarged 

 (deepened) by the glenoid ligament. As a consequence of the incongruity between the two 

 articular surfaces, the head of the humerus projects far beyond the edge of the glenoid cavity. 



The lax capsular ligament passes down from the circumference of the glenoid cavity and is 

 attached, anteriorly, to the anatomic neck of the humerus (i. e., the groove bounding the articular 

 cartilage); posteriorly, to the bone somewhat below the anatomic neck. It bridges over the 

 bicipital groove (sulcus intertubercularis) which lodges the long tendon of the biceps. This 

 structure is enclosed in a tubular reflection of the synovial membrane, the vagina mucosa inter- 

 tubercularis, which is the deepest portion of the joint when the body is held erect and which is 

 often markedly distended by exudate when the shoulder-joint is inflamed. The greater and 

 lesser tuberosities are outside of the joint. The synovial membrane is also reflected beneath the in- 

 sertion of the subscapularis muscle, forming the bursa mucosa subscapularis. This is the weakest 

 portion of the capsular ligament ; it is the place where the head of the bone leaves the capsule 

 in the common subcoracoid dislocation. A second weak place is to be found in the deepest part 

 of the joint between the margins of the subscapularis and the teres minor muscles (see Fig. 30).. 



