MYOLOGY 177 



the dog, they unite only at the level of the middle third of 

 the radius, and interiorly they have two tendons ; in the 

 pig, the ox, and the horse they are completely united, and 

 there exists but a single tendon. 



The anterior extensor of the metacarpus, which is situated 

 behind the long supinator when the latter exists, occupies 

 the external aspect of the forearm ; its well-defined form 

 absolutely recalls the prominence on the superior part of the 

 external margin of the human forearm. 



It arises superiorly from the portion of the external border 

 of the humerus which is situated above the epicondyle and 

 behind the musculo-spiral groove. Its fleshy mass appears in 

 the angular space bounded by the brachialis anticus and the 

 triceps. The superior portion is covered by the external head 

 of the triceps ; yet, in the dog, the superior portion of its 

 humeral attachment is the only part so covered. This muscle 

 is directed forward and downwards ; it is also inclined a little 

 inwards in such manner as to proceed to occupy the anterior 

 aspect of the forearm. 



Its fleshy belly is narrowed below, and, towards the 

 inferior part of the forearm, is continued by a tendinous 

 portion which is situated on the anterior surface of the 

 carpus, after having traversed the median groove of the 

 inferior extremity of the radius. 



In the cat and the dog, in which the union of the two 

 radial extensors is incomplete, the two tendons are 

 inserted into the front of the base of the second and third 

 metacarpal bones ; consequently, as in man, into the meta- 

 carpals of the index and middle fingers. 



In the ox, the tendon, which is single, is inserted into the 

 internal and anterior half of the superior extremity of the 

 principal metacarpal. 



In the pig, this tendon is attached to the base of the large 

 internal metacarpal. 



In the horse, the corresponding tendon is attached to a 

 tubercle which is situated on the anterior surface of the base 

 of the principal metacarpal, a little internal to the median 

 plane of the latter. 



In order to properly understand and remember the re- 



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