Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/45

Rh The humerus is the bony constituent of the upper arm. Its proximal end articulates with the scapula; it articulates distally with the radius and ulna of the fore arm. Between these two extremities is the shaft, or body, of the bone. The head is a prominent oval enlargement at the proximal end, which fits into the glenoid cavity, furnishing the articulation with the scapula. The lesser tuberosity is a low knob located immediately in front of the head on the medial surface of the bone. The greater tuberosity is a dorsoventrally elongated projection on the cranial surface of the humerus, immediately in front of the head, extending also on to the lateral surface of the bone. The intertubercular groove separates the two tuberosities. The deltoid tuberosity is a very prominent rough-edged ridge running, on the ventral surface, from the greater tuberosity about half way to the distal end of the humerus.

The articular surface at the distal end of the bone is saddle-shaped to receive the corresponding surfaces of the radius and ulna. This end of the bone is flattened. It bears two depressions immediately above the articular surface — the radial fossa on the ventral side to receive the radius during flexion of the arm, and the olecranon fossa on the dorsal side to accomodate the olecranon process during extension. The medial epicondyle is a prominent cylindroid process medial to the saddle-shaped articular surface. The lateral epicondyle is a broad process located laterally near the distal end of the bone.

The radius and ulna support the fore arm, the former lying anterior to the latter. The two are firmly bound together by the interosseus ligament. The body of the radius bows forward and outward. Dorsally it expands abruptly, forming the head, which bears an oval surface for articulation with the humerus. The posterior side of the head is flattened, and rests against a similar surface