246 COMPARATIVE AETHEOLOGY 



ELBOW JOINT 



Ox. — No important differences exist. The upper part of the interosseous 

 radio-ulnar hgament is commonly ossified in the adult. 



Pig. — There are no important differences. The radius and ulna are so firmly 

 united by the interosseous ligament as to prevent any appreciable movement be- 

 tween them. 



Dog. — The joint capsule is reinforced in front by an oblique ligament which 

 arises on the front of the lateral condyle of the humerus above the joint surface, 

 and joins the terminal part of the biceps and brachialis below. There is a strong 

 reinforcement of the postero-medial part of the capsule, which extends obliquely 

 from the medial side of the olecranon fossa to the ulna, just above the processus an- 

 coneus. The lateral ligament is much stronger than the medial one. It is attached 

 above to the lateral epicontlyle of the humerus, and below chiefly to the eminence 

 distal to the neck of the radius; but part of it inclines backward and is attached to 

 the ulna. The middle part of the ligament is wide and forms a sort of cap over the 

 proximal tuberositj' of the radius. From this part a band, the annular ligament 

 of the radius (Lig. annulare radii), extends across the front of the proximal end of 

 the radius and ends on the ulna; although incorporated in the joint capsule it is 

 easily defined. The medial ligament is more slender. It arises from the medial 

 epicondyle of the himaerus and passes deeply into the proximal part of the inter- 

 osseous space, ending chiefly on the posterior surface of the radius a little medial to 

 the attachment of the lateral ligament; there is also a small attachment to the 

 interosseous border of the ulna. This ligament is very oblique. An elastic band 

 (Ligamentum olecrani) extends from the lateral surface of the medial epicondyle 

 to the anterior border of the ulna. 



There are two radio-ulnar joints. The proximal radio-ulnar joint (Articulatio 

 radioulnaris proximalis)is included in the capsule of the elbow, but is provided with 

 an annular hgament, as described above. The distal radio-ulnar joint (Articulatio 

 radioulnaris distalis) is formed by a concave facet on the radius and a convex one on 

 the ulna, and is surrounded by a tight capsule. The interosseous membrane unites 

 the shafts of the two bones; its proximal part is specially strong and is attached to 

 prominences on both bones. The movements consist of limited rotation of the 

 radius (ca. 20°), carrying the paw with it. The ordinary position is termed prona- 

 tion; outward rotation is supination. ^ 



THE CARPAL JOINTS 



These have the same general arrangement as in the horse. Numerous minor 

 differences naturally exist, but must be excluded from this brief account, which 

 contains only important special features. 



The lateral and medial movements are freer, especially in the dog, but flexion is 

 not so complete : the anatomical explanation of these facts lies in the nature of the 

 articular surfaces and certain ligamentous differences. The collateral ligaments are 

 much weaker, the long lateral one being especially small in the ox. Two obhque, 

 somewhat elastic bands cross the front of the radio-carpal and intercarpal joints. 

 The proximal one is attached to the distal end of the radius and passes downward 

 and outward to the ulnar carpal bone; the other one connects the radial and fourth 

 carpal bones in a similar fashion. 



In the ox the short collateral ligaments are well defined; a ligament connects 

 the accessory carpal with the distal end of the ulna, and strong volar bands connect 



' These movements are best seen in man, in whom the back of the hand may be turned for- 

 ward (pronation) or backward (supination). In the dog the rotation is much restricted and is 

 freest when the elbow is flexed. 



