150 



THE SKELETON 



trochlea and the capitulum. The trochlea is the pulley-like surface which extends 

 over the end of the bone for articulation with the semilunar notch (great sigmoid 

 cavity) of the ulna. It is constricted in the centre and expanded laterally to form 

 two prominent edges, the medial of which is thicker, descends lower, and forms a 

 marked projection; the lateral edge is narrow and corresponds to the interval 

 between the ulna and radius. Above the trochlea are two fossae : on the anterior 

 surface is the coronoid fossa, an oval pit which receives the coronoid process of 



Fig. 178. 



-Ossification of the Humerus; the Figure also shows the Relations of the 

 Epiphysial and Capsular Lines 



Unites with the shaft at the twentieth 

 year. The upper epiphysis is 

 formed by the union of the nucleus- 

 for the head, greater tuberosity, 

 and that for the lesser tuberosity. 

 These form a common epiphysis 

 before uniting with the shaft 



Capsular line- 



Shaft begins to ossify in the eighth 

 week of intra-uterine life 



Capsular line 



Nucleus for the medial epicondyle | 

 appears at fifth, fuses at the - 

 eighteenth year 



Nucleus for trochlea appears at the 

 tenth year 



ii« 



'Al 



Nucleus for lateral epicondyle ap- 

 pears at fourteenth year 



Nucleus for capitulum appears in the 

 third year 



The centres for the radial epicondyle, 

 trochlea, and capitulum unite to- 

 gether and form an epiphysis which 

 fuses with the shaft at the seven- 

 teenth year 



the ulna when the forearm is flexed ; on the posterior aspect is the olecranon fossa, 

 a deep hollow for the reception of the anterior extremity of the olecranon in exten- 

 sion of the forearm. These fossse are usually separated by a thin, translucent 

 plate of bone, sometimes moroly by fibrous tissue, so that in macerated specimens 

 a perforation, the supratrochlear foramen, exists. The capitulum, or radial head, 

 is much smaller than the trochlea, somewhat globular in shape, and limited to 

 the anterior and inferior surfaces of the extremity. It articulates with the con- 



