120 THE SKELETOX 



serves for the origin of the external head; the part below for the internal head of 



the Irlreps. i- i i 



Tlu' lower extremity uf the humerus is flattened, and presents trom the uhiar 

 to the radial side the following parts:— a prominent process, the ulnar (internal) 

 condyle, from which the pronator radii teres arises, and to the lower part of which 

 the internal lateral ligament is attached. From this ligament the flexor carpi 

 radiali.-<, palmaris longus, flexor siiblimis digitorinn, and flexor carpi tdnaris muscles 

 arise. Posteriorly the condyle forms with the trochlea a groove traversed by the 

 ulnar nerve. External to the condyle there is the inferior articular surface, sub- 

 divided by a low ridge into the trochlea and the capitellum. The trochlea is, in 

 shajte, like the section of a pulley wheel; the ulnar extends much lower than the 

 radial edge; the articular surface is sliarply indicated anteriorly and posteriorly. 

 The trochlea fits into the greater sigmoid cavity of the ulna. Above the trochlea on 

 the anterior surface is the rounded coronoid fossa, which receives the coronoid 

 process of the ulna when the forearm is flexed. On the posterior aspect there is the 

 olecranon fossa, for the reception of the anterior edge of the olecranon in extension 

 of the forearm. These fossae in most humeri are separated by a thin translucent 

 disc of lione, sometimes merely by fibrous tissue, so that in macerated bones a 

 perforation, the supratrochlear foramen, exists. The radial head or capitellum 

 is received by the dei)ressi()n <m the summit of the radius; it is limited to the 

 anterior and lower surface of the humerus. Above, it terminates in a shallow fossa, 

 wliich receives the edge of the radius in flexion. The ridge between the trochlea 

 and the capitellum corresponds to the interval between the ulna and radius; the 

 shallow groove on the outer side of the ridge receives the inner margin of the head 

 of the radius. External to the capitellum is the external or radial condyle. It 

 is less prominent than the ulnar condyle, and gives attachment to the external 

 lateral ligament of the elbow, and to a tendon from which five extensor muscles 

 arise — viz. extensores carpi radialis brevior, digitorinn communis, minimi digiti, carpi 

 tdnaris, and the supinator hrevis. On the posterior aspect this condyle extends to 

 the edge of the trochlea, and gives origin to the anconeus. 



Muscles. — The humerus affords attachment for the following muscles : — 



Supra-spinatus. Flexor carpi radialis. 



Infra-spinatus. Palmaris longus. 



Teres major. Flexor sublimis digitorum. 



Teres minor. Flexor carpi ulnaris. 



Subscapularis. Supinator longus. 



Deltoid. Extensor carpi radialis longior. 



Pectoralis major. Extensor carpi radialis brevior. 



Coraco-V^rachialis. Extensor digitorum communis. 



Latissimus dorsi. Extensor minimi digiti. 



Biceps (occasionally). Extensor carpi ulnaris. 



Brachialis anticus. Supinator brevis. 



Triceps. Anconeus. 



Pronator radii teres. 



Ligaments.— To the upper extremity of the humerus the following ligaments 

 are attached: — 



Capsular. Gleno-humeral. 



Coraco-liumeral. Transverse humeral. 



To the lower extremity: — 



Internal hiteral ligament "I 



External lateral ligament I 



Anterior ligament j '^^ "^^ elbow-joint. 



Posterior ligament j 



Arteries.- The blood-suiiply of the humerus is derived from the suprascapular 

 and the anterior and i)()stenor circumflex arteries. Branches from these arteries 



