36 THE SURGICAL ANATOMY OF THE HORSE 



posterior radial artery, and accompanying this are two additional posterior 

 radial veins. All these structures are placed between the flexor metacarpi 

 internus and the back of the radius. On the inner surface of the radius 

 is shown a large vein. This is the Internal Subcutaneous Vein of the 

 Forearm or Median Vein, which at a slightly higher level splits up into 

 the median basilic and median cephalic veins, the former piercing the 

 posterior superficial pectoral muscle to join the posterior radial and 

 ulnar in the formation of the brachial vein, and the latter being continued 

 upwards along the groove between the mastoido-humeralis and the 

 pectoral muscle. On the anterior aspect of the radius we have the small 

 anterior radial artery with its accompanying vein, and in front of these 

 vessels is presented the section of a large muscle. This is the extensor 

 metacarpi magnus. 



Lying on the front of the radius, but towards its outer side, is the mus- 

 culo-spiral nerve, which it will be observed is close to the line of apposi- 

 tion of the extensor metacarpi magnus with another muscle. This latter 

 is the extensor pedis. Behind the extensor pedis we find a transversely 

 elongated strip of muscle which towards its right extremity is in close 

 proximity to the ulna. This muscle is the extensor suffraginis, and it is 

 wedged in between the extensor pedis in front and another muscle, the 

 flexor metacarpi externus, behind. The extensor pedis, extensor suf- 

 fraginis, and the radius and ulna form the boundaries of a somewhat 

 triangular space in which are seen an artery and its accompanying vein. 

 The artery is the interosseous of the forearm, and it rests in the groove 

 formed between the radius and ulna. Extending backwards towards the 

 middle line from the posterior border of the flexor metacarpi externus 

 we find the ulnar accessorius muscle, the posterior border of which is 

 closely related to the ulnar nerve with its accompanying artery and vein. 

 The last mentioned structures lie beneath the deep fascia on the surface 

 of one of the divisions of the flexor perforans muscle. Two other 

 muscles are seen to the inner side of this division of the perforans. 

 The one in the middle line is the flexor perforatus, whilst the one 



