78 



THE BONES. 



Fig. 43. 



surface ; 6, Two diarthrodial facets elongated transversely, cut on the 

 posterior outline of the large articular surface, with which they are con- 

 founded by their superior border ; they correspond 

 to similar facets on the ulna ; 7, Below these, a 

 roughened surface which extends to the radio- 

 ulnar arch, and is in contact with an analogous 

 surface of the same bone through the medium of 

 an interosseous ligament ; in the Horse this liga- 

 ment rarely ossifies. 



The inferior extremity, flattened from before 

 to behind, presents: 1, Below, an articular sur- 

 face elongated transversely and somewhat irregu- 

 lar, responding to the four bones in the upper 

 row of the carpus; 2, On the sides, two tube- 

 rosities for ligamentous insertion, the internal 

 salient and well circumscribed, the other external 

 and excavated by a vertical fissure, in which passes 

 a tendon ; 3, In front, three grooves for the 

 gliding of tendons ; tire external is the largest, and 

 vertical like the median; the internal, the nar- 

 rowest, is oblique downwards and inwards; 4, 

 Posteriorly, a strong transverse ridge which sur- 

 mounts the articular surface and serves for the 

 insertion of ligaments. 



Structure and development. The radius is a 

 very compact bone, and is developed from three 

 centres of ossification : one for the body and two 

 for the extremities. 



2. UJ.na. 



This is an elongated, asymmetrical bone, in 

 the form of an inverted triangular pyramid, applied 

 against the posterior face of the radius, to which 

 it is united in adult solipeds. It offers for des- 

 cription a middle portion and two extremities. 



Middle portion. This has three faces wider 



ie ol , e - above than below, and three borders which become 

 cranon: 4,Radio-ulnararch; ..-,,.,.'. . j ^-i i mi 



Supero-external tuberosity joined at the inferior extremity of the bone. The 

 6, Radio-ulnar articular sur- external face is smooth and nearly plane. The 

 faces for the humerus; 7, internal is also smooth and slightly hollowed. 

 Bicipital tuberosity; 8, The anterior ig f orme d to correspond to the radius, 

 bnait or body or the radius ; -, , . ... , , ., ; 



9, Grooves for tendons. and presents peculiarities analogous to those of 

 the posterior face of that bone. Thus there is 



found in proceeding from above to below: 1, Two small diarthrodial 

 fleets j 1 2, A rough surface ; 3, A transverse groove for the formation of 

 the radio-ulnar arch; 4, A triangular surface, studded with rugosities, 

 which occupies the remainder of the bone to its lower extremity. The lateral 

 borders, external and internal, are sharp, and, like the anterior face, are in 

 contact with the radius. The posterior border is concave, rounded, and thicker 

 than the other two. 



Extremities. The superior extremity comprises all that portion which 

 exceeds the articular surface of the radius. It constitutes an enormous 

 1 It is represented in Man by the smaller sigmoid notch, 



EXTERNAL FACE OP THE 

 RADIUS AND ULNA. 



1, Ulna; 2, Point of the ole- 



