120 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 192. — The two sternoclavicular joints, together with die costosternal articulations of the two upper 



ribs, seen from in front. The right sternoclavicular joint has been opened by a 



sagittal section (f). 

 Fig. 193. — The left shoulder and acromioclavicular joints seen from above and from the inner surface (£). 

 Fig. 194. — The left shoulder-joint seen from behind, the long head of the triceps being cut and 



the terminal portions of the supraspinatus, infraspinatus, and teres minor muscles cut 



and turned outward (f). 



Fig. 195. — The left shoulder-joint seen from behind and above. The acromion process has been 

 removed, and the neighboring muscles treated as in the preceding figure (f). 



Fig. 196. — The socket of the left shoulder-joint after removal of the articular capsule and the tendon of 

 the biceps muscle (f). 



Fig. 197. — A frontal longitudinal section of the shoulder-joint, parallel to the tendon of the long head of 

 the biceps (|). 



THE ACROMIOCLAVICULAR ARTICULATION. 



The acromioclavicular articulation (Figs. 193, 194, and 196) is the joint between the acromial 

 articular surface of the clavicle and the acromial articular surface of the scapula, and it conse- 

 quently forms the connection between the two components of the shoulder girdle. The articu- 

 lation may contain an articular disc, but it is small and varies greatly in the degree of its develop- 

 ment; it is frequently incomplete and often entirely absent. The upper portion of the articular 

 capsule is the strongest, and is still further reinforced by the acromioclavicular ligament (Figs. 

 194 and 196), which connects the bones forming the articulation. 



A strong ligamentous connection between the acromial end of the clavicle and the scapula 

 is effected by the coracoclavicular ligament (Figs. 193 and 196), which passes from the upper 

 surface of the base of the coracoid process to the coracoid tuberosity of the clavicle. The liga- 

 ment is composed of two parts, an anterior flat quadrangular portion, known as the trapezoid 

 ligament, and a posterior triangular one, broad above and narrow below, the conoid ligament. 

 Between the two the subclavius muscle is inserted. 



The acromioclavicular articulation has but a slight range of motion. The coracoclavicular ligament acts as a 

 check ligament, just as the costoclavicular ligament does in the sternoclavicular articulation. The relative position of 

 the two bones, can scarcely be changed voluntarily, but passive movements, producing a change in the angle between 

 the two bones, etc., occur. The small, indistinctly bounded, and usually flat articular surfaces allow of a displacement 

 of the two bones, but the direction of the movement is not determined by the shape of the articular facets. 



THE LIGAMENTS OF THE SCAPULA. 



There are three ligaments attached to the scapula (Figs. 193, 195, and 196) which do not 

 belong to any of the neighboring joints. These are the coracoacromial ligament, the superior 

 transverse ligament, and the inferior transverse ligament. 



The coracoacromial ligament (Figs. 193, 194, and 196) is a flat, tense, strong ligament which 

 connects the anterior margin of the acromion with the posterior surface of the anterior extremity 

 of the coracoid pjocess. It is situated immediately above the shoulder-joint. 



The superior transverse ligament (Figs. 193 and 195) is a short, tense ligament which bridges 



