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, 
my Fig. 75, #; Fig. 80, 7). 
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, 2) 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, 4) 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, ¢) 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, #), the humerus, and the anconeus (Fig. 
80, 7). Dorsal surface with the caput longum (Fig. 77, 2), 
the epitrochlearis (Fig. 65, 7), 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, 2).—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, @).—The lateral surface of the ulna from 
the distal margin of the semilunar notch to the proximal end 
