THE BONES OF THE ANTERIOR LIMB 



201 



v5 i- 



tmi 



The Humerus 

 The humerus (Fig. 93) is typical 

 of the long bones of the proximal 

 and middle segments of the fore and 

 hind limbs in consisting of a central 

 portion, the body or shaft of the bone, 

 and of proximal and distal extremities 

 for muscle attachment and articu- 

 lation. The proximal extremity bears 

 on its medial side a smooth, convex 

 projection, the head of the humerus 

 (caput humeri), for articulation with 

 the scapula. The articulation is nom- 

 inally a ball-and-socket joint, or enar- 

 throsis, but the articulating surfaces 

 are somewhat restricted, and the 

 muscular arrangements of the limb 

 are such that the range of lateral 

 motion (abduction and adduction) 

 is small. Immediately in front of 

 the head of the bone there is a small 

 elevation, the medial tuberosity or 

 lesser tubercle (tuberculum minus). 

 It is separated by a longitudinal 

 furrow of the anterior surface, the 

 intertubercular groove (sulcus inter- 

 tubercularis), from a much larger 

 lateral elevation, the lateral tuberosity or greater tubercle (tuber- 

 culum majus). Extending distad from the latter is a triangular 

 area, the deltoid tuberosity (tuberositas deltoidea), the tip of 

 which reaches almost to the middle of the bone and forms a 

 pronounced angle on its anterior surface. These tuberosities are 

 for muscle attachment, mainly for the insertion of muscles moving 

 the shoulder-joint. 



The distal extremity of the humerus bears a grooved articular 

 surface, the trochlea humeri, for articulation with the radius 

 and ulna. On its lateral side is a smaller surface, the capitulum 



e.m.- 



Fig. 93. Anterior surface of the 

 left humerus: c, capitulum; c.h., 

 head of humerus; e.l. and e.m., 

 lateral and medial epicondyles; f.r., 

 radial fossa; s.h., deltoid tuberosity; 

 s.i., intertubercular groove; t.h., 

 trochlea humeri; t.mi. and t.mj., 

 lesser and greater tubercles. 



