HUMERUS. 



37 



with the sternum and scapula. The sternal two-thirds is convex 

 anteriorly, and the humeral third concave anteriorly. The upper 

 surface has a depression near the sternal extremity showing the 

 origin of the sterno-cleido-mastoid muscle. The inferior surface 

 has a roughness near the sternal extremity for the rhomboid or 

 costo-clavicular ligament, and near the humeral extremity a tubercle 

 and ridge for the coraco-clavicular ligament ; the space between 

 these two marks is for the subclavius muscle. The anterior edge 

 gives origin by its sternal two-thirds to the pectoralis major, and by 

 its humeral third to the deltoid. The posterior edge has a foramen 

 for the nutritious artery. 



The sternal extremity is thick and triangular, with a surface for 

 articulations with the sternum ; the posterior and inferior corner of 

 it is elongated, which contributes to the strength of the articulation. 

 The himneral extremity is flat and spongy with an articular face for 

 the acromion process of the scapula. 



In the male the bone is shorter, thicker, and more curved than in 

 the female. 



HUMERUS. 



The arm-bone is cylindrical, and reaches from 

 the shoulder to the elbow. The superior ex- 

 tremity presents a hemispherical head?' for articu- 

 lation with the glenoid cavity of the scapula, 

 separated by a deep groove, the anatomical 

 neck^ from the shaft of the bone. Below this 

 groove are two tuberosities, the greater,"* is 

 the external, and has three facets for the inser- 

 tion of stipra and infra-spinatus, and teres minor 

 muscles ; the lesser on the inner side^ is for the 

 insertion of the subscapularis. These tuberosi- 

 ties are separated from each other by a groove,*' 

 called bicipital^ in which plays the tendon of the 

 long head of the biceps muscle. The anterior or 

 external edge'' of this groove has the pectoralis 

 major muscle inserted into it, and the posterior^ 

 receives the latissimus and teres major muscles. 

 The surgical neck is between the insertion of 

 these muscles and the anatomical neck of the 

 humerus. About the middle of the shaft, and 

 upon its outer side, is a triangular roughness^ 

 for the insertion of the deltoid ; on the inner 

 side and a little below is a ridge for the coraco- 

 brachialis :*° below this ridge is the nutritious 



4 



Fig. 21. 



