34 STRUCTURE AND ECONOMY OF THE HORSE. 



in shape, having a number of protuberances for the attachment 

 of muscles. Its lower end articulates with the tibia, forming 

 Avhat is commonly termed the stifle joint, and which corresponds 

 anatomically with the human knee. As an additional security, 

 and to ward off concussion, there are two elastic substances, 

 called from their shape the semilunar cartilages, interposed be- 

 tween the bones which form this joint. In front we find a small 

 bone called the patella, or knee-pan, which performs the office of 

 a pulley, receiving from above the tendons of the strong extensor 

 muscles of the thigh, and firmly fastened by equally strong liga- 

 ments to the upper and front part of the tibia. In all animals 

 the length of the femur depends on that of the metatarsus : in 

 horses and cattle the latter is very long, and the former short ; 

 whilst in man and in many animals we discover an opposite 

 arrangement. In man the leg is formed by two bones, the tibia 

 and the Jibula, both of which enter into the composition of the 

 joint, and thus afford a considerable extent of motion in every 

 direction. In horses, however, the fibula is altogether small and 

 unimportant, the leg being almost entirely formed by the tibia, 

 which in the horse is much longer than the femur, and its lower 

 end communicates with the tarsal joint, or, as it is commonly 

 tei'med, the hock. The tibia extends obliquely backwards from 

 the stifle joint, whilst the femur extends from above in a contrary 

 direction, thus forming an angle which is more or less acute in 

 different animals, being in speedy animals much more acute than 

 in slower ones. 



The hock is composed of no less than six bones, but the 

 motion of the joint is almost entirely confined to the upper bone, 

 the astragalus, which articulates with the tibia. In the human 

 subject, the tarsus rests on the ground, and the various bones 

 which compose it, constructed in the form of an arch, form a 

 very important spring, to which very much of the elasticity of 

 the foot is owing. Man is the only animal whose heel rests on 

 the ground ; but there are many who tread on the various pha- 

 langes, whilst the horse treads entirely on the last toe. Thus, 

 Avitli the long metatarsal bone, which closely resembles the meta- 

 carpus in the fore extremity, the hock is elevated considerably 

 from the ground in a similar manner to the knee, but, unlike 

 this joint, it forms an angle from the metatarsus, extending for- 

 wards under the body of the horse. The upper joint of the 

 hock possesses a very considerable extent of motion in a forward 

 direction, but none laterally ; and the joint is accordingly con- 

 structed on the principle of the hinge, and secured from dislo- 

 cation by means of two condyles, or rounded prominences, on 

 the upper part of the astragalus, which fit into corresponding 

 depi'cssions in the tibia, and receive between them also a ridge 

 in the middle of the tibia. 



