20 THE ANATOMY OF THE HORSE. 



clothed with muscles, except at the lower third of the inner border of 

 the radius, where the bone is subcutaneous. On the outer side of the 

 front of the elbow-joint a large muscular mass is formed by the extensor 

 metacarpi magnus and the anterior extensor of the digit (extensor pedis). 

 In the living animal (in which it is preferable to study these surface- 

 markings) this is more distinctly visible, and the tendons of these 

 muscles and that of the lateral extensor (extensor sufiraginis) may be 

 distinctly traced. On the inner side of the elbow-joint one may feel 

 the tendon of insertion of the biceps ; and just behind the tendon the 

 posterior radial vessels and the median nerve may be felt as they lie on 

 the bone under cover of the posterior superficial pectoral, and they may 

 be made to roll under the finger. This should be practised, as the 

 posterior radial artery is a convenient vessel at which tq feel the pulse. 

 The internal subcutaneous vein crosses the inner face of the fore-arm 

 obliquely upwards and forwards ; and, in the living animal, pressure at 

 the upper part will distend the vessel and bring it into view. At the 

 outer side of the carpus the prominence formed by the pisiform bone 

 may be seen and felt. On the inner surface of the fore-arm, at its lower 

 third, the skin presents an oval-shaped, horny callosit} 7 , vulgarly termed 

 the chestnut. This is largest in coarse-bred animals. 



Directions. — The skin is now to be carefully removed from the 

 fore-arm and carpus, and the cutaneous nerves and vessels are to be 

 sought. 



Cutaneous Nerves. (1) At the front of the elbow-joint (Plate 8) the 

 cutaneous division of the musculo-cutaneous branch of the median 

 appears from beneath the biceps, and splits into two branches, one 

 accompanying the anterior, the other the internal, subcutaneous vein ; 

 (2) a little way below the elbow, on its inner aspect, the cutaneous 

 branch of the ulnar (Plate 5) appears from beneath the insertion of the 

 posterior superficial pectoral, and divides for the supply of the skin of 

 the back of the fore-arm on both its outer and its inner side ; (3) per- 

 forating the caput medium, or emerging at its lower edge, are some 

 twigs from the musculo-spiral nerve, which are distributed to the skin 

 of the outer side of the fore-arm beneath the elbow ; (4) on the outer 

 side of the carpus (Plate 8) are the ramifications of a cutaneous branch 

 of the ulnar, which comes out between the tendons of the external and 

 oblique flexors of the metacarpus. 



Subcutaneous Veins. — 1. The Median or Internal subcutaneous vein 

 begins at the inner side of the carpus, where 'it continues upwards the 

 internal metacarpal vein. It crosses the fore-arm obliquely upwards 

 and forwards, in company with a cutaneous nerve already described, 

 and divides into the cephalic and basilic veins. The Cephalic vein 

 has already been seen ascending in the groove between the mastoido- 

 humeralis and the anterior superficial, pectoral to terminate in the 



