DISSECTION OF THE ANTERIOR LIMB. 25 



The Extensor Mbtacarpi Obliquus {Plates 8 and 9). This is the re- 

 presentative of the extensor muscles of the thumb in man. It a7'ises from 

 the outer side of the radius ; and its tendon, after passing obliquely 

 downwards and inwards over that of the great extensor, is inserted into 

 the head of the inner small metacarpal bone. It lies in an oblique 

 groove at the lower end of the radius, Avhere the play of its tendon 

 is facilitated by a small synovial bursa. 



Action. — Like the preceding muscle. 



The Extensor Pedis, or anterior extensor of the digit (Plate 7), 

 repi'esents the extensor communis digitorum of man. At its origin it 

 lies immediately to the outer side of the extensor metacarpi magnus, but 

 at the lower part of the fore-arm the extensor metacarpi obliquus emerges 

 from between the two muscles. It arises, by a tendon common to it 

 and the extensor metacarpi magnus, from a depression external to the 

 coronoid fossa ; also from the external lateral ligament of the elbow, and 

 the external tuberosity at the upper end of the radius. It consists of 

 two parallel portions of unequal size, and these are succeeded by two 

 tendons wdiich lie close together, but are distinct from each other. 

 These tendons pass in common through a vertical groove at the lower 

 end of the radius, and over the front of the carpus, where they are pro- 

 vided with a synovial sheath. In the dissection of the metacarpus and 

 digit, the tendons will be pursued to their insertion, the outer and 

 smaller * joining the tendon of the extensor suffraginis, while the inner 

 and main tendon becomes inserted into the pyramidal process of the os 

 pedis. 



Action. — This muscle extends in succession the interphalangeal joints, 

 the fetlock, and the carpus. 



The Extensor Suffraginis, or lateral extensor of the digit (Plates 7 

 and 8), is a smaller muscle than the extensor pedis, to the outer side of 

 which it lies. It is the homologue of the extensor of the little finger in 

 man. It arises from the external lateral ligament of the elbow, from the 

 external tuberosity at the upper end of the radius, from the line of 

 junction of the radius and ulna, and from the outer border of the radius. 

 Its tendon passes first through a vertical groove on the external tuber- 

 osity at the lower end of the radius, then through a synovial sheath at 

 the outer side of the carpus, and it Avill subsequently be followed to its 

 insertion into the first phalanx. 



Action. — It is an extensor of the fetlock and of the cax'jjus. 



Directions. — The nerves and bloodvessels on the front of the fore-arm 

 must next be sought, and in order to fully expose them, some of the 

 foregoing muscles must be cut. The biceps is to be cut about its 



' This is sometimes termed the mv.scle of Phillips. Occasionally there occurs, to the inner side 

 of the preceding, another and smaller fasciculus, with a slender tendon which joins the main tendon 

 before reaching the carpus. This is the muscle of Thieniessc. 



