62 ANATOMY OF THE WOOD RAT 



heads, then extends deep to the biceps and is inserted onto 

 the brachial ridge of the medial border of the ulna. 



These three flexor muscles are served by the musculo- 

 cutaneous nerve. 



Of extensors there are the following five : 



Mm. epitrochlearis triceps medialis 



triceps longus anconeus 



triceps lateralis 



M. epitrochlearis (figs. 7, 29) is the most superficial 

 muscle of the inner brachium, and has origin by stout 

 aponeurosis from the medio-distal portion of the latissimus 

 dorsi. Insertion is upon the superficial fascia over the 

 inner arm proximad and distad of the elbow. 



In Teonoma it is slightly heavier. 



The triceps brachii had better be treated as three dis- 

 tinct muscles, as follows: 



M. triceps longus (figs. 6, 7, 13, 29) has origin by 

 muscle fibers and aponeurosis upon its medial belly for 

 some 10 mm. near the distal end of the axillary border of 

 the scapula. Insertion is by a stout tendon onto the 

 proximal end of the olecranon. 



In Teonoma origin is slightly broader. 



M. triceps lateralis (figs. 6, 13, 28) has origin by 

 aponeurosis from the greater tuberosity of the humerus. 

 Insertion is by aponeurosis for a distance of some 10 mm. 

 along the proximal portion of the caudal border of the 

 ulna. 



M. triceps medialis (figs. 6, 13, 28, 29) arises along the 

 posterior border of the shaft of the humerus beginning 

 just distad of its medial process, and insertion is by muscle 

 and tendon fibers onto the dorsal surface of the olecranon. 



M. anconeus (figs. 13, 29) is a very short muscle located 

 superficially upon the medial side of the elbow. It has 

 origin from the medio-caudal part of the medial epicondyle 



