44 THE ANATOMY OP THE HORSE. 



fibres seem to be inserted into the ligament. In front of the joint the 

 tendon of the biceps is separated from the ligament by a pad of fat. 



Movements. — The joint belongs to the class of enarthrodial or ball- 

 and-socket joints, and the amount of its mobility should be proved by 

 manipulation before the removal of the muscles. If the scapula be kept 

 fixed it will be found that the humerus can be carried backwards so as 

 to diminish the angle formed by the meeting of the bones. This is a 

 movement of flexion. Or the humerus can be carried forward in the 

 same plane as in the preceding movement, but increasing the angle. 

 This is extension. Or again, the humerus may be moved in a lateral 

 direction either outwards or inwards. When, in the living animal, it 

 is carried inwards the limb is thrown towards the middle plane of the 

 body, and is said to be adducted; The opposite movement, by which 

 the limb is carried outwards from the middle plane, is termed abduction. 

 Two other movements are permitted in the joint, viz., rotation and 

 circumduction. In rotation the humerus, without change of place as a 

 whole, turns round its own axis. In circumduction the shaft of the 

 humerus moves so as to describe the surface of a cone. 



(These different terms having been here defined at length, their 

 application in the case of the other joints of the body will be readily 

 understood.) 



The shoulder-joint of the horse is thus possessed of considerable free- 

 dom of movement ; but still, the range of its mobility, owing to the 

 absence of a clavicle, and to the different disposition of the pectoral 

 muscles, is much more restricted than in the human arm. 



Directions. — The muscles which surround the joint must now be 

 removed, care being taken not to cut the capsular ligament. 



The Capsular Ligament loosely surrounds the articular ends of the 

 bones, and may be conceived as having the form of a double-mouthed 

 sack, one mouth being attached around the rim of the glenoid cavity, 

 and the other at the periphery of the head of the humerus. The wall' 

 of this sack is comparatively thin, but in front it is strengthened by 

 accessory fibres that pass in a divergent manner from the coracoid 

 process to the outer and inner tuberosities. These correspond to the 

 coraco-humeral ligament of man. 



Directions. — If, in the removal of the muscles, the ligament has been 

 preserved perfectly intact it will be noticed that though a considerable 

 force be exerted to pull the articular surfaces from each other, they still 

 remain in contact. If, however, an incision be made in the ligament 

 the air will be heard to rush into the joint, while the bones separate 

 to the extent of half an inch or more. In the shoulder then, as in 

 other joints, atmospheric pressure is to be included among the agents 

 keeping the articular surfaces in contact. The capsular ligament is to 

 be slit up so as to expose the smooth and glistening aspect of the 



