408 THE ANATOMY OF THE HORSE 



efforts of impulsion are communicated to the trunk b})- the posterior members, 

 without interfei'ing with the transmission of locomotive force, permit but a 

 slight gliding movement of their arthrodial surfaces. Indeed, this articula- 

 tion seems exclusively designed to prevent the fractures to which these bones 

 would be incessantly exposed, were they attached in a more intimate manner, 

 as, for example, by bony union. 



ISCHIO-PUBIC SYMPHYSIS 



The two ossa innomixata are firmly united together in the median 

 line below, by the corresponding edges of the ischium and pubes. In 

 the foal this is a distinct joint, possessing an inter-articular cartilage, 

 and some transverse ligamentous fibres above and below ; but in the adult 

 horse the two bones are firmly united by ossification, and the ossa inno- 

 minata together form a complete arch, without the slightest movement 

 between them. 



THE SHOULDER JOINT 



The scapulo-humeral articulation, commonly known as the shoulder 

 joint, belongs to the division Diarthrosis ; subdivision, Enarthrosis. It is 

 formed by the scapula uniting with the humerus, at an obtuse angle. 



The articular surfaces which compose this joint are the head of the 

 humerus, and the glenoid cavity of the scapula. On examining these bones, 

 described and illusti^ated at pages 376-7, it will be seen that the head of the 

 humerus is semi-globular, while the cavity in the scapula is very superficial, 

 and incapable of maintaining the former in its place without some collateral 

 aid. It is somewhat remarkable that the ligaments of this joint are ex- 

 tremely weak, being confined to the lax fibres surrounding the synovial 

 capsule, which is so loose that after removing all the other soft parts, and 

 making a small opening into the joint, the two bones may be readily separated 

 for some distance ; these fibres are superiorly fixed around the margin of the 

 glenoid cavity, and infeiiorly round the head of the humerus. Chauveau 

 states that a ligament descends from the coracoid process of the scapula, 

 which diverges and becomes inserted into the tubercles at the anterior part 

 of the head of the humerus. He also states that it is loose, and therefore 

 facilitates jnuch motion, but it is not easy to separate it from the capsular 

 ligament. This is longer posteriorly than anteriorly, and presents postero- 

 laterally two stays, similar to two pieces of tape. The external one, arising 

 from the outer lip of the glenoid cavity, is attached to the outer and back 

 part of the head of the humerus. The internal one arises from the inner 

 edge of the glenoid cavity, and is attached to the inner and back part of the 

 head of the humerus. 



But this deficiency in ligaments is made up by a much more powerful 

 material in resisting dislocations. The whole joint is surrounded by elastic 

 muscular fibre or by tendinous bands, having the same kind of support — thus 

 it has in close apposition the following muscles, viz. — 



