70 OSTEOLOGY. 



THE FOREARM. 



The bones of the forearm are the radius and the ulna, which 

 in the young animal are distinct, but in the adult become firmly 

 united by ossification, and are sometimes described as one bone, 

 the OS antibrachii. We describe them separately. 



RADIUS. 

 (Pl. I. L.) 



The radius is a long bone, and occupies a vertical position 

 between the humerus and the carpus. The shaft is flattened 

 and curved, with gradually expanding extremities ; its anterior 

 surface is smooth, and covered in the fresh state by the extensor 

 muscles of the knee and foot ; and its posterior surface, concave 

 from above downwards, and covered by the flexor muscles, 

 presents towards its external border a rough triangular surface, 

 which commences in a slender point near the middle of the bone, 

 and terminates two or three inches below the proximal end, cor- 

 responding with the anterior surface of the ulna, to which it is 

 attached by interosseous ligaments in the young animal, and by 

 ossification in the adult. The shallow transverse groove above 

 this surface assists in the formation of the radio-ulnar arch, and 

 the nutrient foramen of the bone is close to the groove. On the 

 inferior third of the internal border of the shaft is a ridge to 

 which the radialis accessorius muscle is attached; the external and 

 internal lateral surfaces are rounded, and have no distinct separa- 

 tion from the anterior and posterior surfaces. 



The 'proximal extremity, larger than the distal, is widest from 

 side to side, and presents an articular surface, divided into two 

 depressions, the glenoid cavities, which receive the condyles of 

 the humerus ; the inner is the largest, and articulates with the 

 internal condyle, the outer having a slight eminence on its centre 

 which corresponds with the depression in the trochlea. A rough 

 ridge round the articular surface gives attachment to the capsular 

 ligament ; the anterior part has a prominent lip, the coronoid 

 process, in its centre, and near its internal border a rough 

 eminence, the hicipital tuberosity, for the insertion of the tendon 

 of the flexor brachii, and part of the humeralis externus muscles. 

 On each side of the articular surface is a roughened portion for 



