THE ANATOMY OF THE HORSE. 43 



synovial apparatus developed in connection with the perforans tendon 

 where it plays over the navicular bone. It lines the deep face of the 

 tendon, and is reflected on to the navicular bone and interosseous liga- 

 ment. It also extends above the navicular bone, where it is in contact 

 with the synovial membrane of the coffin -joint and that of the metacarpo- 

 phalangeal sheath. 



THE SHOULDER-JOINT. 



This joint is formed between the glenoid fossa of the scapula and the 

 head of the humerus. It is enclosed by a single capsular ligament 

 lined internally by the synovial membrane. The absence of lateral or 

 other retaining ligaments in connection with the joint, is compensated 

 for by the numerous tendons which pass from one bone to the other in 

 close relation to the capsular ligament. These muscles are as follows : — 

 the siipraspinatus, infraspinatus, teres minor, biceps, and small scapulo- 

 humeralis. The last passes over the joint behind, where some of its 

 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 caiTied 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 diff"erent 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 

 freedom 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 



