68 



TOPOGRAPHICAL ANATOMY OF 



The necessity for many and powerful ligaments in connection with 

 the joint is obviated by the presence of the numerous strong muscles 

 that closely surround the articulation and hold the bones in their 

 place. As has been previously noted, the thick insertions of the 

 subscapular and infraspinous muscles act functionally as collateral 

 ligaments; while the supraspinous, biceps, and triceps have bony 

 attachments within a short distance from the joint. A further factor 

 in retaining the bones in apposition is atmospheric pressure ; for, 



Origin of m. 

 M. supraspinatus. biceps brachii. 



M.. biceps brachii. 



Scapula. 



M. coracobrachial. 

 Joint capsule. 

 M. subscapularis. 



M. capsularis. 



Fig. 47.— Medial Aspect of the Shoulder Joint. 



1. =The line of attachment of synovial bursa of m. biceps brachii. 

 2.= The line of attachment of synovial bursa of m. coracobrachialis. 



though the bony surfaces are separated with difficulty so long as' 

 the joint capsule is intact, if an opening is made into the capsule 

 the bones may be separated to the extent of 2 or 3 cm. 



The only ligament connected with the joint is a capsule (capsula 

 articularis) attached 1 or 2 cm. from the margins of the glenoid 

 cavity of the scapula and the head of the humerus. The capsule 

 is strengthened by elastic fibrous bands, notably so by one that 

 springs from the base of the coracoid process of the scapula, 

 and splits into two limbs that are attached to the greater and 

 lesser tubercles of the humerus. On opening the capsule it will be 

 observed that its synovial lining is not, in the horse, in any way 

 connected with the synovial (mucous) sheath of the biceps tendon. 



Although movement at the shoulder joint is possible in all 

 directions, flexion and extension alone are of any marked degree of 



