88 OSTEOLOGY, OR ANATOMY OF OSSEOUS SYSTEM 



and shaft. Its external surface presents the lesser sigmoid 

 cavity, and just below it a small area giving attachment to 

 a part of the supinator brevis. The inner surface is slightly 

 concave, and bounded in front by a prominent margin, termi- 

 nating above in a rounded eminence. To the eminence one 

 head of the flexor sublimis digitorum is attached, to the ridge 

 the deep head of the pronator radii teres, and on the surface 

 itself one portion of the flexor profundus digitorum finds 

 origin. Often a fasciculus of the flexor longus pollicis arises 

 from the lower part of this surface. 



FIG. 18 



Anterior Bordei 



---Anterior S-urfa<-f 



External^ 

 Surface 



Interosseous 

 Border 



Internal 

 Surface 



-Posterior Surf 'ace -- 



Posterior Bordei 



Showing a transverse section of the radius and ulna and indicating their borders 



and surfaces. 



The great sigmoid carity, articulating with the trochlea, 

 looks upward and forward, and is bounded above by the ojec- 

 ranon and below by the coronoid ^rorv.v.sr.v; it is concave from 

 above down, and is traversed by a longitudinal ridge, which 

 is a half-circle. 



A slight constriction is seen across the middle -of the cavity. 

 The part external to the ridge is broad and convex above the 

 constriction, concave in its other subdivisions. 



Continuous with this cavity is the small sigmoid cavity on 

 the outer side of the base of the coronoid; it is concave from 



