9 o 



Anatomy of Skeleton 



ULNA (Fig. 70). This has a shaft, an upper end, and a lower end or head. The 

 upper end is its thickest part, and presents a deep notch, the great sigmoid cavity, 

 that receives the trochlea of the humerus : it is walled behind by the hook-like 



olecranon process, and in front and below by the 

 smaller coronoid process. On the outer side of the 

 coronoid process is the lesser sigmoid cavity, which 

 receives the head of the radius : a triangular area 

 below this has a sharp posterior margin for origin 

 of Supinator brevis. The coronoid process is pro- 

 longed downwards in front, having inner and outer 

 margins enclosing a rough tuberosity for insertion 

 of Brachialis anticus : the margins give origin to 

 muscles, the inner has a prominent tubercle at its 

 upper end for internal lateral ligament and Flexor 

 sublimis, and the outer reaches the front margin 

 of the lesser sigmoid cavity above, where the orbi- 

 cular ligament is fastened. 



The shaft has a prominent sharp outer or 

 interosseous border, a well-marked sinuous pos- 

 terior or subcutaneous border, and a badly-marked 

 rounded inner border. These separate three sur- 

 faces : the internal and anterior surfaces are con- 

 tinuous and afford origin to Flexor profundus 

 digitorum, but the poster o- external surface is 

 sharply denned by the interosseous and subcuta- 

 neous borders, and shows markings for some of the 

 deep extensor muscles. The lower fourth of the 

 front surface is marked off from the rest by an 

 oblique rough line, the pronator ridge, and gives 

 origin to Pronator quadratus. 



The lower end or head is slightly enlarged, 

 has a smooth articular surface on its rounded 

 periphery, externally and in front, for the radius, 

 a prominent styloid process for internal lateral 

 ligament of wrist, behind, below, and internally, 

 and a smooth articular surface external to this, 

 on the lower surface of the head, that is continuous 

 with the outer surface and articulates with the 

 triangular nbro-cartilage : a groove on the back, 

 between the head and the styloid process, is f6r 

 the tendon of Extensor carpi ulnaris : a notch on 

 the radial side of the base of the process is for 

 the attachment of the apex of the nbro-cartilage. 

 The shaft tapers from above, and is cylindrical in its lower part : it is concave 

 forwards, especially in the upper half or so. 



RADIUS. This bone increases in size from above down, is somewhat concave in 

 front, and decidedly concave internally, so that a broad area is provided in the middle 

 of the forearm, by it and the ulna and the interosseous membrane, for the origin of 

 muscles. It presents an upper end or head, a shaft, and a lower end. The head is 



FIG. 70. Right ulna. P.P. dig. origin 

 of Flex. prof. dig. ; E.M., E.L.P., 

 I. P. origins of Ext. ossis met., Ext. 

 Long, poll., and Ext. indicis ; P.Q. 

 origin of Pronator quadratus. To 

 tell right from left, hold the bone so 

 that the olecranon is above and be- 

 hind, and the small sigmoid cavity 

 (for the radius) on the outer side. 



