THE FETLOCK JOINT. 33 



moid joint a convex surface glides upon a concave surface (the 

 two surfaces being more or less adapted one for the other). 



To facilitate this backward and forward movement it is 

 necessary that the surfaces be smooth, and that they be 

 lubricated. Both requirements have been provided for in the 

 most complete manner. The articular surfaces are covered by 

 cartilage, which, whilst very smooth, possesses a certain elas- 

 ticity. The lubricating fluid is supplied by a peculiar secreting 

 membrane, which we shall consider later. 



The horse's foot presents the following joints : — (1) the fetlock 

 joint ; (2) the coronet joint ; (3) the pedal joint. The ligaments 

 are shown in figs. 21 to 23, to which the under-mentioned 

 letters refer. 



1. The Fetlock Joint. 



In this joint the lower end of the metacarpus forms the 

 upper articular surface. The upper end of the suffraginis bone 

 and the anterior surfaces of the sesamoid bones are so combined 

 that the articular surface of the suffrag^inis forms the anterior, 

 the sesamoid bones the posterior, portion of the lower articular 

 surface. To attain the necessary strength, this joint is provided 

 with numerous strong ligaments. 



{a) All the bones which contribute to the formation of the 

 fetlock joint are enclosed by a synovial membrane (fig. 10, e). 

 This surrounds the lower end of the great metacarpus and the 

 upper end of the suffraginis bone throughout their entire extent, 

 but in the case of the sesamoid bones is only inserted around the 

 articular borders. Behind, a portion extends between the great 

 metacarpus and the superior sesamoidean ligament : its walls 

 are very thin. Anteriorly, however, between the metacarpus 

 and suffraginis bones the walls are thick, and are attached 

 at either side to the lateral ligaments. Another part of this 

 capsule closely surrounds the flexor tendons. 



(h) The great metacarpus and suffraginis bones are con- 

 nected by an inner and an outer lateral ligament. Each of these 

 consists of a comparatively weak, superficial layer, which arises 

 from the lateral surface of the lower end of the metacarpus 

 and extends to the middle of the suffraginis bone, and of a 

 deeper, short but very strong, layer, whicli arises from the 



c 



