14 THE ANATOMY OF THE HORSE. 



vessels ; but as it passes downwards, it recedes from them, and passing 

 under cover of the scapulo-ulnaris, it reaches the space between the 

 olecranon and the inner condyle. Thence it descends to the back of the 

 fore-arm, where it will subsequently be dissected. At present it is seen 

 to give off only one branch, which disappears within the superficial 

 pectoral muscle, and afterwards becomes distributed to the skin of the 

 fore-arm (Plate 5). 



The ]\Iedian Nerve (Plates 5 and 6) is formed by the union of two roots. 

 The anterior of these comes from the 6th, 7th, and 8th cervical, while 

 the posterior is derived from the 8th cervical and the 1st dorsal. These 

 roots gives off some pectoral twigs, and then unite by forming a loop in 

 which the axillary artery rests. The nerve then descends in front of 

 the axillary ai'tery and its brachial continuation, and will afterwards be 

 seen to accompany the posterior radial artery. The following branches 

 of the nerve may be found at present : — 



The Nerve to the Biceps and Coraco-humeralis comes off close below the 

 union of the two roots of the median, or from the anterior root above 

 the point of union. It passes betw^een the upper and lower insertions 

 of the coraco-humeralis, supplying that muscle and terminating in the 

 biceps. 



Jftisculo-ciiianeous branch. — This is given off from the median about 

 the middle of the humerus ; and passing underneath the biceps, it 

 divides into a muscular branch for the brachialis anticus, and a cutane- 

 ous branch for the front of the fore-arm. 



Directions. — The muscles of this region should now be examined in 

 the order of their description. 



The Latissimus Dorsi (Plates 5 and 6). The insertion of this muscle 

 into the inner tubercle of the humerus is here seen. About an inch or 

 two from its termination the tendon gets a twist which alters the direc- 

 tion of its surfaces, and brings it to be inserted in front of tlie termina- 

 tion of the teres major on the same tubercle. 



Action. — The muscle is a flexor and an inward-rotator of the shoulder- 

 joint 



The Teres Major (Plate 5). It ai-ises from the dorsal angle of the 

 scapula, and from an aponeurosis between it and t' subscapulars. It 

 is inserted into the internal tubercle of the humerus, its terminal tendon 

 resting in the twist formed by tlie tendon of tlie latissimus dorsi muscle. 



Action. — It is a flexor and an inward-rotator of the shoulder. 



The Scapulo-Ulnaris (Plate 5). This is a thin, flat muscle which 

 rests on the inner surface of the triceps, and is provided, in front and 

 above, with a thin, transparent tendon. It arises from the posterior 

 border of the scapula, and is inserted into the posterior border of the 

 olecranon, and into the fascia of the foi-e-arm. At its lower extremity 

 the muscle covers the ulnar vessels and nerves. 



