98 



Bones of the Upper Extremity. 



Olecranon 



Incisura _ 

 radialis 



- Incisura semilunaris 



Processus 

 coronoideus 



Tuberositas ulnae 



Foramen nutricium 



Crista interossea 



Margo volaris 



Fades volaris 



|- Capitulum ulnae 



Processus styloideus 

 Circumferentia articularis 



123. Right ulna, ulna, 



from in front. 



The ulna (see also Figs. 124, 

 127129, 146) is a long, cylindrical 

 bone which is thicker at its upper than 

 at its lower extremity. It lies on the 

 side of the forearm corresponding to the 

 little finger, is united above by a joint 

 with the upper arm, below, only in- 

 directly, with the carpus; it is united 

 by joints with the radius both above 

 and below. 



It is divisible into a shaft or 

 corpus, and two extremities. 



The shaft, corpus ulnae, is 

 bent slightly so as to be convex toward 

 the side of the little finger and is 

 triangularly prismatic. Of its three 

 surfaces, the fades medialis (0. T. 

 internal surface) on the side cor- 

 responding to the little finger is narrow; 

 it goes over at the rounded margo 

 volaris (0. T. anterior border) in front 

 and the margo dorsalis (0. T. posterior 

 border) behind, into the broader fades 

 volaris (0. T. anterior surface) and 

 fades dorsalis (0. T. posterior surface). 

 These meet radialward in the sharply 

 projecting crista interossea (0. T. ex- 

 ternal or interosseous border). A fora- 

 men nutricium often lies near the crista 

 interossea at the middle of the length 

 of the volar surface and leads into a 

 canalis nutridus directed proximalward. 



