170 THE MUSCLES. 



angle of the olecranon and is inserted into an oblique ridge 

 which forms the dorsal limit of the furrow. The tendon is 

 separated from the floor of the furrow by a synovial bursa. 



(2) The intermediate portion (anconeus internus) (Fig. 77, 

 k; Fig. 79, /z; Fig. So,;/). 



Origin (Fig. 82, g} by fleshy fibres from a triangular area 

 proximad of the middle of the dorsomedial surface of the 

 humerus. The length of the area equals about one-fourth the 

 length of the bone. Its apex points proximad and is almost 

 continuous with the apex of the area of origin of the long por- 

 tion. 



Insertion (Fig. 87, z ) by short tendon-fibres into the medial 

 border of the ventral and proximal surfaces of the olecranon. 

 It is connected with the tendon of the long portion. 



(3) Short portion (Fig. 79,7; Fig. 77, /). 



Origin (Fig. 82, h) from the outer surface of the bony bar 

 which encloses the supracondyloid foramen of the humerus, as 

 far as the medial epicondyle. 



Insertion (Fig. 87, e) by fleshy fibres into the medial border 

 of the olecranon distad of the tuberosity for the insertion of the 

 caput longum. 



Relations of the caput mediale. Lateral surface with the 

 caput laterale (Fig. 75, /z), the humerus, and the anconeus (Fig. 

 80, /). Dorsal surface with the caput longum (Fig. 77, z), 

 the epitrochlearis (Fig. 65, r\ and the teres major (Fig. 

 79, </). Ventral surface with the biceps (Fig. 77, g). 



Action of the Triceps. The entire triceps group forms a 

 powerful extensor of the forearm. The short portion of the 

 medial head tends also to rotate the arm outward, so as to 

 supinate the hand. 



M. anconeus (Fig. 80, /). A triangular muscle on the 

 outside of the elbow-joint from the humerus to the ulna. 



Origin (Fig. 83, z'). An irregularly triangular area at the 

 distal end of the dorsal surface of the humerus. The area of 

 origin is limited laterally by the sharp lateral supracondyloid 

 ridge. It sometimes extends onto the lateral epicondyle. 



Insertion (Fig. 86, d). The lateral surface of the ulna from 

 the distal margin of the semilunar notch to the proximal end 



