32 THE ANATOMY OF THE HORSE. 



Directions. — The student must now pursue the dissection of the 

 following mxiscles which have already been dissected in the fore-arm, 

 viz., the extensor pedis and extensor suflfraginis on the front of the 

 limb, and the superficial and deep flexors behind. In addition to these, 

 there are the lumbrioales and interossei muscles, which entirely belong 

 to this region; and, as they are of small size and might easily be 

 overlooked, their dissection must be first undertaken. 



The LuMBEiCALES Muscles (Plate 9) receive their name in the human 

 hand from their resemblance to a common earthworm. In the horse 

 they are of small bat very variable .size. Frequently they contain but 

 little muscular tissue, but now and again a subject is met in which 

 they are very distinct. They are two in number, one being placed on 

 each side of the deep flexor tendon, above the fetlock. The fibres of 

 the small muscular belly arise from the side of the deep flexor, and 

 terminate in a small tendon which is lost in the tissue beneath the 

 horny spur of the fetlock. 



The Interossei Muscles (Plate 9). These are the representatives 

 of the muscles which, in the human hand, fill up the interspaces of the 

 metacarpal bones, and give lateral movement to the fingers. In the 

 horse they are two in number, and they are extremely rudimentary. 

 Each is to be sought to the inner side of the small metacarpal bone of its 

 own side, between that bone and the edge of the suspensory ligament. 

 Each has at its upper end a small muscular belly taking origin from 

 the neighbourhood of the head of the small metacarpal bone. It is 

 succeeded by a long, slender, nerve-like tendon, which at the fetlock 

 blends with the band sent from the suspensory ligament to the extensor 

 pedis tendon, or with the connective-tissue on the side of the joint. 



The interossei and lumbricale muscles are of great interest to the 

 comparative anatomist, but, from their small size, they can have no 

 appreciable efifect on the movements of the digit. 



The Ttndon of the Extensor Suffbaginis (Plate 7) is to be followed 

 from the point below the carpus to which it has already been dissected. 



The flat tendon, after crossing the carpus, descends to the outer side 

 of the anterior surface of the large metacarpal bone. As it passes over 

 the fetlock-joint it becomes somewhat broader, and its play over the 

 anterior ligament of the joint is facilitated by means of a small synovial 

 bursa. Immediately below the joint it is inserted into the fore part of 

 the upper end of the first phalanx. In the region of the metacarpus 

 the tendon receives on each side a reinforcing band. The outer band 

 comes from the external side of the carpus ; the inner is detached from 

 the extensor pedis tendon. 



Action. — The muscle is primarily an extensor of the digit on the 

 metacarpus. When contraction is carried beyond this it extends the 

 metacarpus on the fore-arm. 



