BONES. 



notches in its lateral borders constrict its deepest part; a 

 longitudinal ridge, extending from the prominence of the ole- 

 cranon border above to the apex of the coronoid process below, 

 divides it into inner and outer parts, which respectively are 

 slightly concave and convex transversely. The small sigmoid 

 cavity, for the radius, is oblong and lies on the outer side of the 

 coronoid process, separated from the great sigmoid cavity by 

 a curved edge; it is plane vertically, concave antero-pos- 

 teriorly, and pointed in front where it joins the anterior 

 border of the coronoid process; the posterior border prolongs 

 the interosseous margin of the shaft. [195] 



The shaft is nearly straight, thick above but tapered below, 

 and divided into two surfaces by two borders. The outer (in- 

 terosseous) border is sharp in its upper three-fourths but faint 

 below. The posterior border curves outward above and in- 

 ward below, being continuous above with the borders of the 

 triangular posterior surface of the olecranon; it is sharp above 

 but faint below where it ends on the back of the styloid proc- 

 ess. The flexor surface, the front and inner side, presents a 

 ridge running from the tubercle to the styloid process. Just 

 below the small sigmoid cavity is a hollow triangular area, for 

 the bicipital tubercle of the radius, which is limited behind by 

 the interosseous crest, and in front by a line running obliquely 

 downward and backward from the outer edge of the coronoid 

 process. The lower fourth is limited above by a ridge which 

 runs downward and backward toward the front of the root of 

 the styloid process. The extensor surface is the back; supe- 

 riorly it extends on the outer side of the olecranon, behind the 

 sigmoid cavities; its upper third is marked off by an oblique 

 ridge running from the outer border; a faint longitudinal ridge 

 divides the part below this oblique ridge. [197] 



The inferior extremity has a rounded head from whose back 



and inner side a pointed process (styloid) projects downward ; 



a groove on the back and outer surface of this process extends 



upward on the shaft. The antero-external half of the circum- 



10 [145] 



