THORACIC LIMBS 



575 



FIG. 443. 





, 



At Birth. 



Its anterior and posterior margins are directed obliquely downward 

 and backward. The surface is continued below upon the posterior 

 surface of the styloid process. 



The external border of the head is occupied by a small circular 

 or shield-shaped convex facet for articulation with the inner side of 

 the lower extremity of the radius. It faces forward, downward, and 

 inward. 



The anterior surface of the head has the same general shape as the 

 posterior. It is rough and convex from side to side and concave from 

 above downward ; it is marked by vascular fora- 

 mina. The antero-external end is encroached 

 upon by the radial facet and separated from 

 the styloid process by a deep pit, in which is 

 inserted the ulnar end of a strong ligament. 



o O 



Its posterior part is continuous below with the 

 surface of the styloid process. 



The posterior border of the head is rounded, 

 and varies in breadth and degree of promi- 

 nence. 



The styloid 1 process is the lower end of the 

 bone produced backward and inward. It pre- 

 sents small, unimportant lateral surfaces and a 

 rounded terminal surface. This is oval, the 

 long diameter being directed nearly antero- 

 posteriorly. The whole surface is smooth and 



convex. It articulates with two bones of the 



w 



wrist as follows : by the anterior third of its At fo,-ty- 

 inner side with the cuneiform, and by the 

 posterior two-thirds of its inner side with the 

 pisiform. Its outer part furnishes attachment 

 for ligaments. 



Nomenclature. The word ulna is the name of a Latin measure 

 of length equal to half a metre. It is derived from the Greek 

 olene, meaning the arm. Celsus called the ulna the cubitus, the cubit, 

 also a measure of length. 



Both ulna and cubitus have been used for the elbow-joint. The 

 German equivalent is das Elboyenbein, the French is le cubitus. 



1 From stilus, a pen, and (Gr.) eides, like. 



four Days. 



At One Hanilrnl 

 ami Twenty Days. 



PLAN OF THE DEVELOP- 

 MENT OF TIIK ULNA FROM 

 THREE CENTRES. 



(Natural size.) 



