THE HUMERUS 149 



receives the pectoralis major. In the middle of the shaft it is rough and prominent 

 and gives insertion to fibres of the deltoid; below it is smooth and rounded, giving 

 origin to fibres of the brachialis, and finally it passes along lateral to the coronoid 

 fossa to become continuous with the ridge separating the capitulum and trochlea. 

 It separates the antero-medial from the antero-lateral surface. The lateral 

 margin extends from the lower and posterior part of the greater tuberosity to the 

 lateral epicondyle. Smooth and indistinct above, it gives attachment to the 

 teres minor and the lateral head of the triceps; it is interrupted in the middle by 

 the groove for the radial nerve (musculo-spiral groove), but the lower third 

 becomes prominent and curved laterally to form the lateral supracondylar 

 ridge, which affords origin in front to the hrachio-radialis and the extensor carpi 

 radialis longus; behind to the medial head of the triceps, and between these 

 muscles in front and behind to the lateral intermuscular septum. It separates 

 the antero-lateral from the posterior surface. The medial border commences 

 at the lesser tuberosity, forming its crest which receives the insertion of the 

 teres major, and continuing downward to the medial epicondyle. Near the 

 middle of the shaft it forms a ridge for the insertion of the coraco-brachialis and 

 presents a foramen for the nutrient artery, directed downward toward the 

 elbow-joint. Below it forms a distinct medial supracondylar ridge, curved 

 medially, which gives origin to the hrachialis in front, the medial head of the 

 triceps behind, and the medial intermuscular septum in the interval between 

 the muscles. This border separates the antero-medial from the posterior surface. 



Fig. 177. — A Diagram showing Pressure and Tension Curves in the Head 

 OF THE Humerus. (After Wagstaffe.) 



Surfaces. — The antero-lateral surface is smooth above, rough in the middle, 

 forming a large impression for the insertion of the deltoid, below which is the 

 termination of the groove for the radial nerve. The lower part of the surface 

 gives origin to the lateral part of the hrachialis. The antero-medial surface is 

 narrow above, where it forms the floor of the intertubercular (bicipital) groove, 

 and receives the insertion of the latissimus dorsi. Near the junction of the upper 

 and middle thirds of the bone the groove, gradually becoming shallower, widens 

 out and, with the exception of a rough impression near the middle of the shaft 

 for the coraco-brachialis, the remaining part of the antero-medial surface is flat 

 and smooth, and gives origin to the brachialis. 



Occasionally, a prominent spine of bone, the supracondylar process, projects downward 

 from the medial border about 5 cm. (2 in.) above the medial epicondyle, to which it is joined by 

 a band of fibrous tissue. Through' the ring thus formed, which corresponds to the supracon- 

 dylar f oraman in many of the lower animals, the median nerve and brachial arterj' are trans- 

 mitted, though in some cases it is occupied by the nerve alone. The process gives origin to the 

 pronator teres, and may afford insertion to a persistent lower part of the coraco-brachialis. 



The posterior surface is obliquely divided by a broad shallow groove, which 

 runs in a spiral direction from behind downward and forward and transmits the 

 radial (musculo-spiral) nerve and the profunda artery. The lateral part of the 

 surface above the groove gives attachment to the lateral head, and the part 

 below the groove, to the medial head of the triceps. 



The lower extremity of the humerus is flattened from before backward, and 

 terminates below in a sloping articular surface, subdivided by a low ridge into the 



