572 



SHOULDER JOINT (NORMAL ANATOMY). 



is formed by the bone, whilst the edges are 

 constituted by the adjacent muscles ; in- 

 feriorly, the interstice becoming smaller de- 

 generates into a groove, which continues to 

 separate the muscles from each other, until 

 at length the clavicular fibres of the great 

 pectoral unite with the deltoid, and are in- 

 serted conjointly with it into the humerus. 

 In this muscular interstice the cephalic vein 

 is lodged, which, ascending to the triangular 

 space below the clavicle, there dips into the 

 axilla, and joins the axillary vein. The 

 descending branch of the thoracica aero* 

 mialis (arteria thoracica humcraria) descends 

 in the same groove, twisting in a spiral 

 manner around the cephalic vein. More 

 deeply still the ligamentum Income, enclos- 

 ing between its layers the subclavius muscle, 

 may be seen. The axillary vein and artery, 

 brachial plexus of nerves, and interior to these 

 and crossing before them, the lesser pectoral 

 muscle, may also be made apparent in this 

 space ; but to bring these latter parts into view, 

 the anatomist must first freely separate the 

 muscles from each other. 



It has been proposed by Hodgson, in order 

 to place a ligature around the axillary artery 

 in the first stage, to cut between the pectoral 

 and deltoid muscles, and then to separate the 

 clavicular attachment of the great pectoral to 

 an extent sufficient for insulating and tying 

 the artery. 



As in other radiated muscles, the tendinous 

 structure of the deltoid is chiefly placed in 

 its interior ; as many as three or four laminre 

 attached to the bone above, penetrate into 

 the substance of the muscle, and multiply 

 the points of origin of its fleshy fibres. The 

 fasciculi, of which the deltoid muscle is com- 

 posed, like those of the glutaeus maximus, 

 which is its analogue in the lower extremity, 

 are remarkably coarse and large. 



When the deltoid is cut across and reflected, 

 the following parts are found in relation with 

 its deep surface ; anteriorly is seen the cora- 

 coid process and the insertions of the pectora- 

 lis minor, of the coraco-brachialis, and of the 

 short head of the biceps into its inner edge, 

 and of the ligamentum bicorne (coraco-clavk 

 cular ligament) into its summit ; external to 

 the coracoid process is a triangular space, 

 the sides constituted by the opposed edges 

 of the coracoid and acromion processes, 

 the apex placed superiorly at the clavicle, the 

 base inferiorly formed by the convex promi- 

 nence of the head of the humerus ; this space, 

 filled by the coraco-acromial or triangular 

 ligament, should be familiar to the surgeon, as 

 the point of the knife must be here introduced 

 when disarticulation at the shoulder-joint is 

 being performed after the method of MM. 

 Champesme and Lisfranc. Immediately be- 

 neath the coraco-acromial triangle the capsular 

 ligament is situated, and a large bursa (sub- 

 deltoid) which intervenes between it and the 

 deep surface of the deltoid muscle ; still lower 

 down, the insertions of the capsular muscles 

 into the tuberosities of the humerus, also the 



neck of the humerus, and the bicipital groove, 

 present themselves. The bicipital groove 

 looks directly forwards and lodges the long 

 tendon of the biceps ; into its anterior edge the 

 tendon of the pectoralis major is inserted, 

 whilst those of the latissimus dorsi and teres 

 major take attachment to the very bottom of 

 the groove, passing a little below the level of 

 the former. The anastomosis of the circum- 

 flex arteries, and the circumflex nerve in a 

 great part of its course, constitute also re- 

 markable relations to the deltoid, separating 

 it from the neck of the humerus ; and under 

 the posterior division of the muscle are placed 

 the infra-spinatus, teretes and latissimus dorsi 

 muscles, with the triangular and quadrilateral 

 spaces which they circumscribe. ( Vide SCA- 

 PULAR REGION.) 



The anterior and the posterior fibres of the 

 deltoid may act independently of each other, 

 and draw the arm forwards and upwards, or 

 backwards and upwards, respectively. The 

 central portion of the muscle is the principal 

 abductor of the upper extremity ; although 

 its insertion is at a considerable distance from 

 the fulcrum, and the power arm of the lever 

 on which it acts is therefore of considerable 

 length, yet the efficient power of the muscle, 

 relatively to its size, is feeble, owing to the 

 fibres whilst in action being invariably parallel 

 to the lever which they are raising. In this 

 action the deltoid is assisted by the supra- 

 spinatus muscle. 



SCAPULO-HUMERAI, ARTICULATION. The 



scapulo-humeral articulation is formed by the 

 contact of the head of the humerus with the 

 glenoid cavity of the scapula. This, the prin- 

 cipal articulation of the upper extremity, is 

 placed at the superior and external portion of 

 the trunk, behind the line of the axis of the 

 hip-joint ; an arrangement which is produc- 

 tive of this advantage, that the most impor- 

 tant motions of the upper extremity (those in 

 the direction forwards) a have a more exten- 

 sive range than if the articulation had been 

 located nearer to the anterior aspect of the 

 thorax. 



The arrangement of the articular surfaces 

 and of the ligamentous structures belonging 

 to the shoulder joint, accords with the general 

 plan on which the bones and articulations of 

 the upper extremity are constructed ; " the 

 disposition and structure of the bones of the 

 upper extremity afford a marked contrast to 

 those of the lower ; the latter are organs of 

 support, and therefore are solid, firm, strong, 

 and withal elastic. The former are destined 

 to perform extended motions, as well as 

 minute and nicely adjusted ones, and there- 

 fore, while they possess all the requisite 

 strength, they are light, present little expanse 

 of surface, and are articulated by numerous 

 very moveable articulations." (Todd and Sow- 

 man's Physiological Anatomy, vol. i. p. 147.) 



The varied uses fulfilled by the upper ex- 

 tremity, added to its remarkable mobility, 

 especially predispose the shoulder joint to 

 accidents; but as we proceed we shall take 



