144 



BONES OF THE ABM. 



condyle (13) projects but little, whilst the inner condyle (14) 



Fig. 149. Fig. 150. forms a considerable promi- 



nence which projects inwards; 

 the condyles afford an exten- 

 sive surface for the attach- 

 ment of the muscles of the 

 fore-arm ; behind the 'inner 

 condyle is a deep fossa (19), 

 for receiving the olecranon pro- 

 cess of the ulna, and above 

 the condyles, on the front of 

 the bone, is a pit (18) for 

 receiving the coronoid pro- 

 cess of the same. Fig. 149 

 gives a front view, fig. 150 

 a back view of the humerus ; 

 fig. 151, the round head and 

 tubercles (3, 4); fig. 152, 

 the lower surface of the con- 

 dyles, (15) is the surface on 

 which the head of the radius 

 plays, (16) receives the sig- 

 moid cavity of the ulna, and 

 (17) is a groove for the pas- 

 sage of the ulnar nerve. 



[ 273. The fore-arm con- 

 sists (fig. 153) of two bones, 

 the RADIUS and the ULNA, 

 which are the homologues 

 of the tibia and the fibula. 

 These bones lie nearly pa- 

 rallel to each other, the ra- 

 dius (1) on the outer, and the 

 ulna (11) on the inner side of the arm; they are united by 

 ligaments, and by a fibrous membrane stretched across the 

 interspace between them ; they have, however, a considera- 

 ble range of motion upon each other and upon the humerus. 

 The flexion and extension of the forearm is performed by the 

 ulna (1), which forms, with the humerus, a true hinge joint. 

 At its upper part we observe the olecanon process (fig. 

 153), which locks into a cavity (fig. 150, 19) on the posterior 



Fig. 151. 



Fig. 152. 



