OSTEOLOGY 37 



is the arm, while that between the elbow and wrist is the 

 forearm. 



The humerus is the long bone in the arm. Its upper 

 extremity presents for examination a rounded head, which 

 articulates with the glenoid cavity of the scapula, and two 

 eminences, the greater and the lesser tuberosity.- The cir- 

 cumference of the articular surface of the head is known as 

 the anatomic neck. Since the constricted portion of the 

 bone below the tuberosities is frequently fractured, it is 

 called the surgical neck. The lower expanded extremity 

 of the humerus is flattened from before backward to form 

 the condyles. The internal condyle articulates with the 

 ulna, while the external articulates with the radius. 



The ulna is the inner bone of the forearm; it is longer 

 than the radius, and helps to form the elbow-joint, but 

 does not enter into the formation of the wrist- joint. The 

 upper end presents a curved process, called the olecranon, 

 and the cavity thus formed articulates with the humerus, 

 and is called the sigmoid cavity. 



The radius is the outer bone of the forearm, and is 

 shorter than the ulna. The upper rounded head helps 

 to form the elbow-joint; the lower end articulates with the 

 carpus to form the wrist-joint, and is subject to many 

 injuries, the most common of which is that known as 

 "Colics' fracture." Many suits for malpractice have 

 been instituted as the result of this injury, the physician 

 often being held responsible for bad results that followed 

 carelessness on the part of the patient. 



When the radius and ulna are parallel, the foramen is 

 said to be supinated; when the bones are crossed, the 

 forearm is pronated. 



THE HAND 



The bony framework of the hand is made up of the 

 carpus, which consists of eight bones, the metacarpus, 



