DISSECTION OF THE ANTERIOR LIMB. 25 



condyle of the humerus, where this bounds the musculo-spiral groove ; 

 and by a second tendon, in common with the extensor pedis, from a 

 depression which is placed external to the coronoid fossa. Its inferior 

 tendon lies in the largest and most internal of the verticle grooves at 

 the lower end of the radius ; and, after gliding over the front of the 

 carpus in a synovial sheath, it is inserted into a rough projecting surface 

 on the antero-internal aspect of the upper extremity of the large meta- 

 carpal bone. 



Action. — It extends the maims on the fore-arm. 



The Extensor METACARri Obliquus (Plates 8 and 9). This is the 

 representative of the extensor muscles of the thumb in man. It arises 

 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, where 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), 

 represents 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 outer side of the upper end of the radius. It consists of two 

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

 which lie close together, but are distinct from each other. These ten- 

 dons pass in common through a vertical groove at the lower end of the 

 radius, and over the front of the carpus, where they are provided with 

 a synovial sheath. In the dissection of the metacarpus and digit the 

 tendons will be pursued to their insertion, the outer and smaller 1 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 outer side of the upper end of the radius, from the line of junction 

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



1 This is sometimes termed the muscle 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 Thiernexxr. 



