POSTERIOR MEMBER. 253 



subject, or when their limbs get entangled in the traces, when they are down on 

 the ground, or again under the influence of a forcible gliding backward of the 

 foot, etc., may not withstand the strain and may become ruptured. The simul- 

 taneousness which at first existed between the movements of the two above-named 

 segments at once disappears. The flexion of the canon is no more synchronous 

 with that of the thigh ; the former sometimes remains pendulous or swings back- 

 ward, and the tendo Achillis (cord of the hock) becomes relaxed and thrown into 

 folds when the animal walks. As to the position of the limb in station, it is 

 normal. 



This lameness, which must not be mistaken for a symptom of fracture of 

 the tibia, in spite of its appearance, is ordinarily not serious ; it simply incapacitates 

 the animal for his work for six or seven weeks. 



4th. We need only mention, in terminating, the excoriations which are 

 rather frequent upon the legs of kicking horses. They are common on the 

 internal face in those subjects that struggle and kick to disengage themselves 

 when the members have been displaced over the shaft or the pole of the vehicle 

 or the traces of the harness. The presence of these wounds, or their traces on the 

 skin, should be a warning to the intending purchaser of some bad and vicious 

 disposition in the animal which is oifered to him. 



D The Hock. 



Situation ; Limits ; Anatomical Base. The hock, in the 

 horse, is analogous to the knee. It corresponds to the tibio-tarso- 

 metatarsal articulations, supports the bones of the leg, and forms the 

 centre of the chief movements of the foot. 



Functionally, it is, more than any other, a region of dispersion of 

 concussion as well as of propulsion. It is upon this region that the 

 efforts of the extensor muscles which propel the body are concentrated ; 

 it is on this point that the reactions of locomotion bear at the moment 

 when the body, moving with great velocity, and projected forward, 

 strikes the ground ; finally, this is the region on which, in the act of 

 rearing, all the weight of the body presses down with such great force. 



Under these different aspects its study is full of interest, as much 

 in relation to animal mechanics as to that of pathology. 



Let us examine with some detail the parts which compose it. 



The Bones. The tarsus of the horse is composed of six small bones, some- 

 times seven, from a want of fusion of the median and small cuneiforms in one of 

 them. Among these bones there are two whose volume and function are quite 

 peculiar; these are the astragalus and the calcaneus. The first presents a 

 very movable articular trochlea, or pulley, which is opposed to the inferior 

 extremity of the tibia ; the second, more salient and elongated, is situated 

 behind the preceding, continues, by its direction, the canon, and forms a powerful 

 arm of a lever for the extensor muscles of the metatarsus. 



Underneath these two principal bones are found the four othero, flattened 

 from above downward, with numerous facets. They are very solidly united to the 



