THE BONES. 



Fig. 42. 



outwards, is seen the posterior crest of the furrow of torsion, which separates the 

 latter from the posterior face of the bone. The internal face of the body of 

 the humerus, rounded from side to side, is not separated from the anterior 

 and posterior faces by any marked line of demarcation. It offers, near its 

 middle, a depressed scabrous process for the insertion of the adductor 

 muscles teres major and great dorsal of the arm. Towards its inferior 

 third it shows the nutritive foramen of the bone. 



Extremities. These are distinguished into superior and inferior. Both 

 are slightly curved, the first backwards, the second forwards, a disposition 

 which tends to give to the humerus the form of an S. 



The superior extremity is the most voluminous, and has three thick 

 eminences ; a posterior, external, and internal. The 

 first constitutes the head of the humerus; it is a 

 very slightly -detached articular eminence, rounded 

 like the segment of a sphere, and corresponding to 

 the glenoid cavity of the scapula, which is too small 

 to receive it entirely. The external eminence, named 

 the trochiter, large trochanter, and great tuberosity, com- 

 prises three portions, named the summit, convexity, and 

 crest of the great tuberosity. The internal eminence, 

 the trochin, little trochanter, or small tuberosity, also 

 presents three distinct portions, which, by their posi- 

 tion, correspond exactly with the three regions of 

 the large trochanter : these are so many muscular 

 facets. 



The great and small trochanters are separated 

 from one another in front by a channel called the 

 bicipital groove, because the superior tendon of the 

 biceps muscle glides over it; it consists of two 

 vertical grooves with a median ridge between 

 them. 



The inferior extremity of the humerus has an 

 articular surface corresponding to the radius and ulna. 

 This surface, elongated transversely, convex from 

 before backwards, and of greater extent within than 

 without, exhibits two trochlea separated by an antero- 

 posterior relief. 



The median or internal trochlea, the deepest, is 



2, External tuberosity; 3, lim . ited internally by a kind of voluminous condyle, 

 Articular head of the which corresponds to the inner lip of the humeral 

 trochlea of Man. The external trochlea is bordered 

 5, outwardly by a slightly salient lip, which corresponds 

 * *L W of , ^umerus of Man Above and 

 behind this articular surface is a wide deep fossa, the 

 olecranian (or condyloid), so named because it lodges the 

 rostrom of the olecranon in the extension movements of the fore-arm. It is 

 bordered by two eminences, the external of which is less elevated than the 

 internal. The first represents the epitrochlea, and the second the epi- 

 condyle, of the humerus of Man. In front, and above the inner trochlea, 

 there is another, but less spacious fossa, which receives the coronoid pro- 

 cess during extreme flexion of the fore-arm, and which, for this reason, it 

 would be convenient to designate as the coronoid fossa. Lastly, at the 

 extremities of the transverse axis of the inferior articular surface is 



POSTERIOR VIEW OP THE 

 RIGHT HUMERUS. 



bone; 4, External tu- 

 bercle and ridge ; 



booe y ; 



f ossa> 



