THORACIC LIMBS 557 



below. It is limited, on the outer side, by a rounded border ; above, 

 it meets the anterior surface of the extremity at a right angle ; on 

 the median line, it passes into the articular surface for the ulna. It 

 is strongly convex from above downward and slightly convex from 

 side to side, and is received into the shallow oval articular surface 

 on the head of the radius. 



The articular surface for the ulna is known as the trochlea. 1 It 

 differs from the capitellum in being convex from above downward and 

 concave from side to side. It is limited on the inside, in front and 

 below, by a sharp crest, and behind by a groove which separates it from 

 the posterior surface of the inner condyle. It is limited on the outside, 

 at the back, by the sharp crest which forms the inner margin of the 

 posterior surface of the outer condyle ; below and in front the outer 

 side is continuous with the capitellum. The articular surface is covered 

 with a layer of cartilage, and is received into the greater sigmoid 

 cavity of the ulna. 



Above the capitellum the anterior surface of the lower extremity 

 is marked by an oval depression for the edge of the head of the radius 

 in extreme flexion of the forearm, and above the trochlea is a similar 

 depression for the coronoid process of the ulna. On the posterior 

 surface of the extremity, above the trochlea, is a very large, deep 

 pit, bounded laterally by the edges of the posterior surfaces of the 

 condyles, and becoming gradually shallow as it ascends the shaft. 

 The lower part of the pit receives the superior lip of the sigmoid 

 cavity in extreme extension of the forearm. There is often a second 

 oval depression above this lower part, which receives the end of 

 the olecranon process. The capsular ligament of the elbow-joint 

 is attached to the lower extremity at the borders of the articular 

 eminence. 



Nomenclature. The humerus of the Romans was the whole 

 shoulder, including both flesh and bones. The three bones which 

 support it were known as ossa humeri, each as an os humeri. The 

 term os humeri was gradually restricted to the one bone of the upper 

 arm, and then the bone itself was called humerus. As synonyms we 

 find os humeri and os brachii. The German word is das Oberarmbein, 

 the French, rhumerus. 



Determination. If the humerus be held with the anterior surface 



1 From trochilia (Gr.), a pulley. 



