OSTEOLOGY 45 



The Humerus. Location. The humerus constitutes the arm, 

 which, when at rest, lies parallel to the dorsal vertebrae. It articu- 

 lates superiorly with the glenoid cavity, a shallow ball-and-socket 

 joint, formed by the scapula and the coracoid; and inferiorly with - 

 the ulna and radius. 



Description. The proximal extremity of the humerus is provided 

 with a trochanter (Fig. n, G, No. 5) and a large oval head or caput 

 humeri, which articulates in the glenoid cavity. The head is an 

 elongate, semi-oval convexity, with the long axis transverse from the 

 radial to the ulnar side and with the ends continued into upper and 

 lower crests. The upper crest of the head of the humerus is on the 

 radial side and the lower crest on the under side. Under this latter 

 crest there is a pneumatic fossa (Fig. n,F,No. i), at the upper end of 

 which there is an opening into the bone, the pneumatic foramen, 

 which brings the air-sac into communication with the air space 

 of the bone. The shaft, or corpus humeris, is irregularly cylindrical 

 and slightly S-shaped. 



The proximal part of the shaft, which is expanded on the 

 palmar side, is concave across and convex lengthwise. The dis- 

 tal part is slightly flattened. The shaft of the humerus is almost 

 cylindrical. 



The distal extremity of the humerus is provided with two articu- 

 lar condyles, one of which articulates with the ulna and the other 

 with the radius. On the radial side of the palmar surface there is 

 a ridge; and on the ulnar side of the same surface there is a second 

 ridge diverging to the opposite tuberosity. The radial surface is 

 a narrow, subelongate convexity, extending from the middle, ap- 

 proximately, of the palmar surface, obliquely to the lower part of the 

 radial tuberosity. The two articular convexities, or trochlea, at the 

 distal end of the humerus are bent toward the palmar aspect, the 

 anconal aspect is the side on which the elbow is situated. The inner 

 convexity is the larger and articulates with the ulna. To the out- 

 side is the processus cubitalis humeri. The outer articulates with the 

 radius and is so arranged that the radius makes a greater flexion than 

 the ulna. At the lower end of the humerus there is a depression 

 which receives the anconeus of the ulna during flexion and extension 

 of the forearm. On the shoulder- and elbow-joint are found grooves 

 over which the tendons glide, at which places sheaths are provided. 

 This arrangement also aids in keeping the capsular ligament in 

 place. 



