210 



THE SKELETON. 



Fig. 155. Left Humerus. 

 Surface. 



Posterior to its inner and back part, at either side of the 

 musculo-spiral groove. 



The Lower Extremity is flattened from be- 

 fore backwards, and curved slightly forwards; 

 it terminates below in a broad articular sur- 

 face, which is divided into two parts by a 

 slight ridge. On either side of the articular 

 surface are the external and internal condyles. 

 The articular surface extends a little lower 

 than the condyles, and is curved slightly for- 

 wards, so as to occupy the more anterior part 

 of the bone; its greatest breadth is in the 

 transverse diameter, and it is obliquely di- 

 rected, so that its inner extremity occupies a 

 lower level than the outer. The outer portion 

 of the articular surface presents a smooth 

 rounded eminence, which has received the 

 name of the lesser or radial head of the 

 Immerus; it articulates with the cup-shaped 

 depression on the head of the radius, and is 

 limited to the front and lower part of the 

 bone, not extending as far back as the other 

 portion of the articular surface. On the inner 

 side of this eminence is a shallow groove, in 

 which is received the inner margin of the 

 head of the radius. The inner or trochlear 

 portion of the articular surface presents a deep 

 depression between two well-marked borders. 

 This surface is convex from before backwards, 

 concave from side to side, and occupies the 

 anterior lower and posterior parts of the 

 bone. The external border, less prominent 

 than the internal, corresponds to the interval 

 between the radius and ulna. The internal 

 border is thicker, more prominent, and con- 

 sequently of greater length than the external. 

 The grooved portion of the articular surface 

 fits accurately within the greater sigmoid 

 cavity of the ulna ; it is broader and deeper 

 on the posterior than on the anterior aspect 

 of the bone, and is directed obliquely from 

 behind forwards, arid from without inwards. 

 Above the back part of the trochlear surface 

 is a deep triangular depression, the olecranon 

 fossa, in which is received the summit of the 

 olecranon process in extension of the forearm. 

 Above the front part of the trochlear surface 

 is seen a smaller depression, the coronoid 

 fossa, which receives the coronoid process of 

 the ulna during flexion of the forearm. These 

 fossas are separated from one another by a 

 thin transparent lamina of bone, which is 

 sometimes perforated; their margins afford 

 attachment to the anterior and posterior liga- 

 ments of the elbow-joint, and they are lined 

 in the recent state by the synovial membrane 

 of this articulation. Above the front part of 



