THE BONES OF THE UPPER EXTREMITY 85 



The Humerus (Arm Bone). This bone extends 

 from the shoulder to the elbow. It is divided into a 

 shaft, and an upper and lower extremity. 



The Upper Extremity. This includes the head, a 

 neck, greater and lesser tuberosities. The head is 

 directed upward and slightly backward, and makes 

 an angle of 140 degrees with the shaft. The head is 

 round and articulates with the glenoid cavity of the 

 scapula, being held in apposition by the ligaments of the 

 shoulder-joint. Below the head is a depression pass- 

 ing around the bone called the anatomical neck. The 

 great tuberosity is an eminence of bone situated on 

 the outer and anterior aspect of the bone below the 

 anatomical neck. It gives attachment to the supra- 

 and infraspinatus and teres minor muscles, which 

 turn or rotate the shoulder-joint and arm outward. 

 Lying internal to the great tuberosity is the bicipital 

 groove, which lodges the tendon of the long head of the 

 biceps muscle. Internal to the groove is another 

 smaller eminence called the lesser tuberosity ; it receives 

 the tendon of the subscapularis muscle, which rotates 

 or turns the shoulder- joint inward. 



The Shaft. This is cylindrical below the tuberosities 

 (and is known as the surgical neck) and triangular 

 below this portion. It is divided into external, internal, 

 arid posterior surfaces by anterior and lateral borders. 

 On the outer border, near the middle, is a rough 

 surface of bone called the deltoid eminence; it affords 

 attachment to the deltoid muscle. The middle of the 

 inner border receives the coracobrachialis muscle; 

 the lower three-fourths of the anterior aspect of the 

 shaft is covered by the origin of the brachialis anticus 

 muscle. The inner and outer borders become sharp 

 at the lower third, and are called the supracondylar 

 ridges. The posterior surface of the shaft is twisted 

 so that the upper part looks inward, its lower part 

 backward and outward. Its entire surface is almost 

 entirely covered by the origin of the inner and outer 



