696 ULNA. 



Its development is from three points, one for the body and 

 one for each extremity. Ossification begins in the radius 

 during the sixth week, shortly after that of the humerus. 

 At birth both extremities are cartilaginous. In the lower 

 end an ossific point is seen about the close of the second 

 year, and in the upper end from the fifth to the seventh, 

 the bone being completed about the twentieth year. It 

 is articulated to the humerus, ulna, scaphoid and lunar 

 bones. 



THE ULNA, (Fig. 218.) 



The ulna is situated at the inner side of the radius, the 

 palm of the hand being uppermost. It is triangular in 

 shape, and consists also in a body and two extremities. The 

 body presents three ridges and three surfaces. The external 

 or radial ridge is most prominent, runs the greater part of 

 the length of the bone and gives attachment to the inter- 

 osseous ligament ; the anterior ridge is round, and has the 

 flexor profundus and pronator quadratus attached to it; 

 the posterior ridge is distinct above and gives attachment 

 to the anconeus. Between these ridges are so many sur- 

 faces all covered by muscles. The anterior surface has a 

 foramen a little above its centre, looking obliquely upward, 

 and conducts the nutritious vessel. The superior extremity 

 is much larger than the lower and forms the greater por- 

 tion of the elbow-joint. It presents two processes ; the one 

 anterior and smaller, called coronoid; the other posterior 

 and much larger, termed olecranon. The coronoid process 

 is triangular and sharp, and is received into the anterior 

 cavity of the lower end of the humerus. Its anterior sur- 

 face gives insertion to the brachialis anticus muscle. Its 

 outer surface is hollowed into the lesser sigmoid cavity, 

 which articulates with the side of the head of the radius. 



The olecranon process has its posterior surface covered 

 by a bursa, and is rough for the insertion of the tendon of 

 the triceps, and its extremity presents a point which is 

 received into the posterior or greater cavity of the humerus. 

 Between these two processes is a large concave surface, 



