MUSCLES OF THE ARM AND FORE-LEG 447 



a ridge at the postcro-external part of the superior third. Insertion — to 

 the supero-external and posterior part of the olecranon. Action — to extend 

 the arm. 



Teres externus is situated upon the postero-external part of the 

 shoulder. Origin — from a little tubercle just below the supero-posterior 

 angle, and from the lower border of the scapula. Insertion — to a ridge 

 descending from the outer tubercle of the humerus, and to the ligament 

 which extends from the outer tubercle to the outer condyle of the same 

 bone. Action — to flex the scapula on the humerus, or the humerus on the 

 scapula. 



ScAPULO HUMERALis EXTERNUS Hcs upon thc postero-external part of the 

 shoulder. Origin — from the inferior two-thirds of the posterior border of 

 the scapula, just above the glenoid cavity, and from its dorsal surface. 

 Insertion — to the middle of the ridge extending from the outer tubercle of 

 the humerus. Action — to flex the humerus, and draw it outwards. 



THE ANTERO-EXTERNAL HUMERAL REGION 



HuMERALis EXTERNUS lies on the infero-external side of the upper arm. 

 Origin — from the infero-posterior, inner, and outer surface of the body of 

 the humerus, and winds round that bone. Insertion — to the suj)ero-anterior 

 and internal part of the radius. Action — to flex the arm. 



THE POSTERO-INTERNAL HUMERAL REGION 



Anconeus is situated upon the hollow space between the condyles. 

 Origin — from the supero-posterior part of the lower third of the humerus. 

 Insertion — to the antero-external boi'der of the ulna and capsular ligament 

 of the joint. Action — to extend the elbow, and to protect the capsular 

 ligament during the movement between the two bones. 



MUSCLES OF THE ARM AND FORE-LEG 



Extensor metacarpi magnus is situated on the anterior part of the arm 

 Origin — from a ridge situated at the antero-external part of the humerus, 

 and also from a depression just above the extei'nal condyle of the humerus. 

 Insertion — to the antero-superior part of the os metacarpi magnum. 

 Action — to extend the leg. 



Extensor pedis is situated upon the antero-external part of the arm. 

 Origin — from the fore-part of the external condyle of the humerus, and 

 from a ridge just superiorly placed to it ; from the outer part of the head, 

 and from the anterior and supero-external part of the body of the radius ; 

 and from the capsular ligament of the elbow joint. Insertion — to the 

 coronal process of the os pedis, adhering firmly to the capsular ligament of 

 the fetlock joint. Action — to extend the knee, metacarpals, and pasterns, 

 and to elevate the toe. 



