ANATOMY IN A NUTSHELL. 61 



external part of the Brachialis anticus. The internal surface gives attachment 

 to the Coraco-brachialis opposite the Deltoid, and below this to the internal 

 part of the Brachialis anticus. 



The posterior surface has the two lower heads of the Triceps and the mus- 

 culo-spiral groove separating them. The lower part of the hone articulates 

 with the radius and ulna: the part which articulates with the radius is called 

 the radial head or capitellum and is on a higher level than the part which artic- 

 ulates with the ulna which is called the trochlear surface. These two articula- 

 ing surfaces are separated by a ridge. Above the radial head on the external 

 surface is the radial depression for the head of the radius to fit into when the 

 forearm is flexed; above the trochlear surface on the internal surface is the 

 coronoid depression for the coronoid process of the ulna; above the trochlear 

 surface on the posterior surface is the olecranon depression for the olecranon 

 process of the ulna. 



The internal condyle is more prominent than the external one. and is on 

 a lower level. It gives attachment to the Pronator radii teres, the common 

 tendon for some of the flexors of the forearm, and the internal lateral ligament. 

 The external condyle is less prominent than the internal one and gives attach- 

 ment to the common tendon for the attachment of some of the extensors of the 

 forearm as well as the Supinator longus and external lateral ligament. 



Ossification. — The ossification is from seven centers, occasionally eight. 

 One for the shaft appears about the eighth week of intrauterine life. The one 

 for the head the first year, one for the great tuberosity the third year; occasion- 

 al]}' one for the lesser tuberosity. These three coalesce at the 17th year and join 

 the shaft about the 20th year. At the distal extremity there are four centers 

 of ossification; one for the capitellum appears at the 3rd year; one for the in- 

 ternal condyle at the 5th year; one for the trochlear at the 10th year; one for 

 the external condyle at the 14th year. 



The nucleus of the internal condyle joins the shaft in the 18th year, while 

 i lie other three nuclei coalesce and join the shaft the 17th year. 



Articulation. — It articulates with the scapula, radius, and ulna. Its artic- 

 ulation with the scapula makes the shoulder-joint, a description of which is 

 given in Lesson IX; and its articulation with the radius and ulna makes the 

 elbow-joint. 



Elbow-joint.— (Plates XXXVIII-XXXIX.)— This is a movable joint (dia- 

 throsis) and belongs to the sub-class ginglymus (hinge-joint.) The part be- 

 tween the trochlear surface of the humerus and ihe greal sigmoid cavity of the 

 ulna is a ginglymus joint, but the part between the capitellum of the humerus 

 and the head of ihe radius is an arthrodial join! (gliding.) The pari between 

 the lesser cavity of the ulna ami the head of ihe radius is a trochoides. The 

 anterior ligament is continuous with the internal and external lateral ligaments 

 covering the joint in froni and being itself covered by the Brachialis amicus; 

 above, it is attached to the humerus above the coronoid and radial fossae and 

 in front of the internal condyle; below, it is attached to the anterior surface of 

 the coronoid process of the ulna and the orbicular ligamenl and the neck of the 

 radius. 



