1 48 ELEMENTAL Y ANA TOM Y. [LESS. 



The hinder surface of the shaft presents an oblique groove 

 (called musculo-spiral), passing from above downwards. 



The upper end of the humerus shows a large, rounded head, 

 covered, when fresh, with cartilage and articulated to the 



flenoid surface of the scapula by a synovial joint, while a 

 brous bag (or capsular ligament) invests the whole articu- 

 lation. 



The head is placed, not on the middle of the summit, but 

 on its inner and hinder aspect, so that its axis does not coin- 

 cide with that of the shaft. 



A little below and on the outer side of the head are two 

 blunt prominences. One of these, termed the greater (or 

 radial) tuberosity, is on the outer side of the summit of the 

 bicipital groove. The other is called the lesser (or ulnar) 

 tuberosity, and is placed on the inner side of the bicipital 

 groove. 



The lower end of the humerus expands considerably, 

 having a lateral prominence, termed a condyle, on each side, 

 but the internal condyle projects further inwards than does 

 the external condyle outwards. 



Between these projections is placed the lower articular 

 surface of the humerus for the bones of the fore-arm. 



This articular surface is irregularly concave and convex. 

 At its outer part is a rounded prominence, called the capitellum, 

 which joins the outer bone of the fore-arm or radius. Internal 

 to this is a pulley-like surface (the trochlea), which joins the 

 inner bone of the fore-arm or ulna. There is a deep cavity 

 in front of the humerus immediately above the trochlea. 

 This is called the coronoid fossa, because it receives the 

 coronoid process of the ulna. 



There is another fossa, also above the trochlea, but on the 

 hinder surface of the humerus. This is called the olecranal 

 fossa, from the part of the ulna which it receives when the 

 arm is straightened. Sometimes a perforation connects 

 together these two fossae 



The ends and processes of the humerus ossify separately 

 as epiphyses, and coalesce at about the twentieth year. 



5. The RADIUS is also a long cylindrical bone, expanded 

 more or less at each end and flattened in front, i.e. when the 

 arm is dependent and the palm turned forwards. 



Towards its upper end the bone, just above a roughened 

 prominence the " tuberosity" is narrowed into what is 

 called the neck, from which rises the head, concave above 

 and articulating by a synovial joint with the capitellum 



