THE ULXA, OR ELBOW BONE 



187 



flexion of the forearm. Its upper surface is smooth, concave, and forms the lower 

 part of the greater sigmoid cavity. The under surface is concave. At the junction 

 of this surface with the shaft is a rough eminence, the tubercle of the ulna (tuberos- 

 itas ulnae), for the attachment of the oblique ligament of the middle radioulnar 

 articulation and the Brachialis anticus muscle. Its outer surface presents a 

 narrow, oblong, articular depression, the lesser sigmoid cavity. The inner surface, 

 by its prominent, free margin, serves for the attachment of part of the internal 

 lateral ligament. At the front part of this surface is a small, rounded eminence 

 for the attachment of one head of the Flexor sublimis digitorum; behind the emi- 

 nence, a depression for part of the origin of the Flexor profundus digitorum; and, 

 descending from the eminence, a ridge which gives attachment to one head of the 

 Pronator teres. Generally, the Flexor longus pollicis has an origin from the 

 lower part of the coronoid process by a rounded bundle of muscle fibres. 



The greater sigmoid cavity (incisura semilunaris) is a semilunar depression 

 of large size, formed by the olecranon and coronoid processes, and serving for 

 articulation with the trochlear surface of the 



humerus. About the middle of either lateral ****** process 



border of this cavity is a notch which con- 

 tracts it somewhat, and serves to indicate 

 the junction of the two processes of which 

 it is formed. The cavity is concave from 

 above downward, and divided into two 

 lateral parts by a smooth, elevated ridge 

 which runs from the summit of the olecranon 

 to the tip of the coronoid process. Of these 

 two portions, the internal is the larger, and 

 is slightly concave transversely; the external 

 portion is convex above, slightly concave be- 

 low. The articular surface, in the recent 

 state, is covered with a thin layer of hyaline 

 cartilage. 



Flic lesser ii|pnoid cavity (incisura radi- 



>long, articular depres- 



jter side of the coronoid 



the lateral articular sur- 



le. radius. It is concave 

 rd, and its extremities, 

 '; . ;erve for the attach- 



ligament. In the recent state it is covered with a thin layer 



FIG. 146.- 



-Upper extremity of left ulna. 

 Outer aspect. 



tdnae), at its upper part, is prismatic in form, and curved 



ran! and from without inward, so as to be convex behind and 



trt is quite straight; its lo\ver part rounded, smooth, and 



tit tapers gradually from above downward, and presents 



<^ borders and three surfaces. 



anterior or palraa.i border (maryo volaris) commences above at the prominent 



loid process, and terminates below in front of the styloid 



irked above, smooth and rounded in the middle of its extent, 



( Flexor profundus digitorum; its lower fourth, marked 



border by the commencement of an oblique ridge on the 



for the origin of the Pronator quadratus. It separates 



internal surface. 



^dorsal border (margo dorsalis) commences above at the apex 

 taneous surface at the back part of the olecranon, and 



