188 SKELETON. 



separated by a deep fossa, named bicipital, from its lodging the 

 tendon of the long head of the biceps muscle. This fossa is 

 continued, faintly, for some inches down the os humeri; its 

 lower part being bounded, externally, by a rough ridge, indi- 

 cating the insertion of the pectoralis major, and internally by 

 another ridge, not quite so strong or rough, indicating the in- 

 sertion of the teres major and latissimus dorsi. 



The body of the os humeri is the part extended between its 

 extremities. The superior half presents a more cylindrical ap- 

 pearance than the inferior, which is rather triangular. On the 

 middle of the bone, externally, two inches below the insertion 

 of the pectoralis major, exists a triangular elevation into which 

 the deltoid muscle is inserted. At the internal margin of the 

 bone, and on a line with the latter, is the insertion of the coraco- 

 brachialis muscle; and between the two is the orifice of the canal 

 for the nutritious artery. The front of the os humeri, in its 

 lower half, is flattened on each side down to its inferior end; on 

 these surfaces is placed the brachialis internus muscle. On a 

 line with the posterior end of the greater tuberosity, and a lit- 

 tle below it, an elevation is formed for the origin of the second 

 head of the triceps extensor cubiti. The posterior face of the 

 bone is flattened from this point down to its lower extremity, 

 and accommodates the last named muscle. 



The articular surface for the elbow joint is very irregularly 

 cylindrical. The part that joins the radius, presents itself as a 

 small hemispherical head, placed on the front of the bone, and 

 with its axis looking forwards. Just above it, in front, is a 

 small depression for the head of the radius in its flexions. The 

 surface which is in contact with the ulna, is more cylindrical, 

 but still irregularly so ; for its middle is depressed, w r hile the 

 sides are elevated: the internal side is much broader and more 

 elevated than the external. The lesser sigmoid cavity is just 

 above the front of the ulnar articular surface, and receives the 

 coronoid process. The greater sigmoid cavity is in a corre- 

 sponding place behind, and receives the olecranon process: the 

 bone where it separates these cavities is very thin; sometimes 

 it is even deficient. 



