410 



THE ANATOMY OF THE HORSE 



THE ELBOW JOINT 



Or the HUMEno-RADio-ULNAR ARTICULATION. — This joiiit is formed between 

 the lower extremity of the humerus above, and the junction of the radius 

 and ulna below. It is a complete hinge, and has no power of pronation or 

 supination as in man, consequently there is no necessity for the peculiar 

 additional joint between the radius and ulna, observ- 

 able in man and partially in the dog and cat ; but the 

 two bones are firmly ossified together in the adult, 

 as already described at page 379. 



These hones are connected together by three liga- 

 ments, two lateral (an internal and an external), a 

 capsular ligament, and a synovial capsule. 



The internal lateral ligament arises from a fossa 

 on the side of the internal condyle of the humerus ; 

 it takes a vertical course, expanding as it descends : 

 and is inserted partly on the roughened inner border 

 of the articular cavity of the radius. Its middle fibres, 

 which are the longest, take the same course as the 

 former, assuming while passing over the radius the 

 shape of a cord, which is inserted into the inner and 

 fore part of the radius about three inches below the 

 former insertion. 



The external lateral ligament is shorter but sti^onger 

 than the internal. It ai^ises from the superior fossa 

 and ridge surrounding it, on the outer surface of the 

 external condyle of the humerus, and is inserted into 

 the tuberosity on the upper and external part of the 

 radius. Its superficial fibres take a vertical course, 

 whilst its internal fibres take an oblique direction, 

 from top to bottom and from back to front. 



TAe capsular ligament is attached by its superior 

 boi'der to the surfaces surrounding the condyles of the 

 humerus ; by its inferior border, to the circumference 

 of the superior part of the radius ; and by its posterior 

 border to the circumference of the articular surface of the ulna. 



The synovial membrane is shoi't anteriorly, very extended, and spread out 

 posteriorly ; where it forms three sacs, which tend to facilitate flexion of 

 the joint. 



TuE MOVEMENTS of the elbow joint are confined to flexion and extension, 

 it being a pure hinge, but these actions do not take place exactly in the 

 same plane. For instance, if the knee is bent and the foot brought up to 

 the elbow, the frog will not correspond with that projection, but will be 

 almost entirely outside it, while the knees will also be wider apart when 

 both are flexed and raised towards the bosom, than when the horse is stand- 

 ing. This arrangement is brought about by the oblique direction of the 

 pulley-like articular surfaces on the humerus, ulna, and radius, and appears 

 to be designed to prevent the foot from hitting the opposite leg as it passes 

 it in trotting. When the obliquity is insuflicient, either cutting of the 



Fig. 46.— Posterior \'iew 

 OF LEFT Elbow Joint. 



A. Inferiorthird of the liu- 



menis. 



B. B. External and internal 



condyles. 



C. Oleeranou process of 



ulna. 

 r>. Tiadius. 



1. External lateral liga- 



ment. 



2. Internal lateral liga- 



ment. 



3. 3. Fibro - cartilaginous 



substance uniti iig the 

 ulna to the radium. 



