1410 



CLINICAL AND TOPOGRAPHICAL ANATOMY 



General surface form. Landmarks. — The following surface-marks, of the 

 greatest importance in determining the nature of shoulder injuries, can he made 

 out here: — The clavicle in its whole extent, the acromion process, the great 

 tuberosity, and upper part of the shaft of the humerus. Much less distinctly, 

 the position of the coracoid process in the infraclavicular fossa and the head of 

 the humerus through the axilla can be made out. The anterior margin of the 

 clavicle, convex medialty and concave laterally, can be made out in its whole 

 extent, the bone, if traced laterally, being found not to be horizontal, but rising 

 somewhat to its junction with the acromion. The stemo- and acromio-clavicu- 

 lar joints have been referred to at p. 1363. 



The frequency of fracture of the clavicle is explained chiefly by its exposure to shocks of varied 

 kinds from the upper extremity, inseparable from the out-rigger-like action of the bone and its 

 early ossification. On the other hand, the main safeguards are the elasticity and curves of the 

 bone, the way in which it is embedded in muscles which will damp vibrations, and the buffer- 

 bond fibro-cartilages at either extremity. The looseness and toughness of the overlying skin 

 explain the rarity of compound fracture here. The junction of the two curves is the weakest 

 spot and the usual site of fracture. The weight of the limb acting through the coraco-clavicular 

 ligaments and overcoming the trapezius is the chief factor in the downward displacement; the 

 pectoralis minor and serratus anterior acting on the scapula draw the acromial fragment for- 

 ward. The tip of the acromion, when the arm hangs by the side with the hand supinated, is in 

 the same Une as the lateral condyle and the styloid process of the radius. On the medial side, 

 the head and medial condyle of the humerus and the styloid process of the ulna are in the same 

 line. Thus the great tuberosity looks laterally, the head medially, and the lesser tuberosity some- 

 what forward. Between the two tuberosities runs the intertubercular (bicipital) groove, which, 



Fig. 1128. 



-Transverse Section through the Right Shoulder-joint, showing the 

 Structures in contact with it. (Braune.) 



Clavicle 



Acromion 

 Supra-spinatus 



Infra -spina tus- 



Teres minor 



Teres major 

 Latissimus dorsi' — 



Deltoid 



Pectoralis major 



Tendon of subscapularis blended 

 with the scapular ligament 



Coraco-brachialis and short head of biceps 



Axillary vessels and nerves 



with the arm in the above position, looks directly forward. In thin subjects its lower part 

 can be defined. Its position can be marked with sufficient accuracy by a line running down- 

 ward from the acromion in the long axis of the humerus. Besides the tendon and its synovial 

 sheath, the insertion of the latissimus dorsi, the humeral branch of the thoraco-acromial artery, 

 and the ant(;rior circumflex artery run in the groove. When the fingers are placed on the acro- 

 mion and tlie thuiiil) in the axilla, the lower edge of the glenoid cavity can be felt; and if the 

 humerus be rotntcd (the elbow-joint being flexed), the head of the humerus can be felt also. 



The characteristic roundness of the shoulder is due to the great tuberosity 

 lying under the deltoid (fig. 1130). In dislocation the loss of this roundness is 

 due to the absence of the head and tuberosity and consequent projection of the 

 acromion. 



This normal projection of the deltoid renders it impossible to place a flat straight body in 

 contact with both the acromion and tlie lateral epicondyle at the same time (Hamilton's dis- 

 location test). Below the junction of the lateral and middle tliirds of the clavicle, between 

 the contiguous origins of the pectoralis major and deltoid, is the infraclavicular fossa, in which 

 li(! tlio cephalic vein, the (hiltoid brancli of the thoraco-acromial artery, and a lymphatic node 

 which may l)e involved in obstinate, tubcrculo.sis of the cervical groups. On pressing deeply 

 here, the coracoid process can be made out if the muscles arc relaxed, and the axillary artery 

 compressed against the second rib. 



On raising the arm and abflucting it, tlie different parts of the deltoid can often be made out 

 — viz., fil)res from the lower border of the s|)ine of the scapula, the lateral edge of the acromion, 

 and the lateral third or more of the front of the clavicle; the characteristic knitting of the surface 



