966 PRACTICE OF AGRICULTURE. Part III. 



In the ox it is wanting ; in the dog and cat, as requiring numerous motions in their iimbs, it is, on the 

 contrary, perfect. 



6328. The tarsus, or hock oftht horse (10, 10), is a striking instance of the perfect mechanism displayed 

 in the bony structure of this admired animal. It is formed by an assemblage of six bones, and sometimes 

 of seven ; while in the ox, sheep, and deer, there are seldom more than five. Between these bones there 

 is little motion, yet there is sufficient to give a spring to the parts, and to preserve the joints from the 

 effects of shocks, &c. As the human anatomy is generally received as the standard of comparison, we 

 must, in order to a proper consideration of the hock, consider it as the instep and heel ; and all the parts 

 beyond it as the foot. The human tarsus, and that of some beasts, as the monkey and some varieties of 

 the bear, makes a right angle with the tibia in standing or walking; but, in the horse, the hock makes 

 an open angle with the tibia, and is far removed from the ground. In him, and the greater number of 

 quadrupeds, all the bones, from the hock downwards, are much elongated, and form a part of the upright 

 pillar of the limb. In the horse, therefore, the point of the hock is the true point of the heel, and, as in 

 the human figure, the great twisted tendons of the gastrocnfemii muscles are inserted into it: but the 

 appellation of tendo Achilles would be too forced here A broad hock, as already observed in the exterior 

 conformation, may be now still more plainly seen to be very important to strength and speed ; for the 

 longer the calc^neum or heel bone of the hock, the longer must be the lever that the muscles of the thigh 

 act by ; and a very slight increase or diminution in its length must make a very great difference in the 

 power of the joint. It is by this tendon acting on this mechanism, that, when the animal has inclined 

 the angle between the canon and the tibia, or, in other words, when the extremities are bent under him 

 in the gallop or trot, he is enabled to open it again. The bones of the hock, like those of the knee, are 

 united together by strong ligamentous fibres ; and it is to an inflammation of those uniting the calc^neum 

 and cuboid bones, that the disease called curb is to be attributed ; and to a similar inflammatory affection 

 of the ligaments in the front of the hocks, that spavins of the first stage are owing : in the latter stages 

 the periosteum and bones themselves become affected. The remainder of the bones below do not dififer 

 so essentially from the corresponding bones in the fore extremities as to need an individual description. 

 It may, however, be remarked, that the hinder canon or shank bone is longer than the fore, and that the 

 pastern is also the same, but is less oblique in its situation ; by which wise provision the horse is enabled 

 to elevate and sustain his body entirely on his hinder parts without danger; which would not have been 

 the case if the obliquity of those parts had been considerable. 



ScJBSECT. 4. General Functions of the Bony Skeleton. 



6329. The skeleton of the horse must be considered as a mechanism of admirable wisdom and contrivance, 

 which having considered in detail, we offer the following summary of its functions generally as a whole. 

 It will be found to present nearly a quadrilateral figure, having an inclined cylinder resting on four sup- 

 porting pillars. The spinal column, as the inclined cylinder, serves as a base for the soft parts, and is 

 found not truly horizontal, but dipping downwards over the fore legs ; by which the propelling force of 

 the hinder extremities is relieved by the maximum of strength thus transferred. The increased weight 

 of the hinder part of the cylinder is admirably counterpoised by the head and neck, which are projected 

 forwards ; by these means leaving the line of direction near the centre of the whole. The length of a 

 cylinder may be such as not to support its own weight ; Nature, therefore, has limited the length of the 

 spines of animals : hence, ceteribus paribus, a long-backed horse must be weaker than a short one ; and 

 thus, likewise, small horses can carry proportionably more than larger ones. The four pillars which 

 support this cylinder are not perpendicular partially ; but they are so totally : for a perpendicular drawn 

 from their common centre of gravity will be found to fall nearly in their common base, by which means 

 they are supported as firmly as though their individual axes had been in a line perpendicular to the 

 horizon. Had they been perpendicularly opposed to each other, there could have been but little elas- 

 ticity, and consequent ease in motion ; every exertion would have proved a jar, and every increased effort 

 would have produced luxation or fracture. To increase our admiration of this mechanism, we need only 

 turn our attention to the contra-disposition of these angles in the fore and hinder supporting pillars. 

 Had these angles presented themselves in the same direction, the body must have been precipitated for- 

 ward or backward ; but each offering a counteraction to the other, the body is firmly sustained within them. 



6330. The bony masses are operated on by muscles, for this deviation from a perpendicular direction in 

 the various bony portions of the limbs must necessarily have powers to correct it, which is effected by the 

 muscles ; and wherever the angles are found most extensive, the muscles will be found proportionally 

 strong and large. This muscular exertion, to counterbalance the angular inclination, occasions fatigue ; 

 as the set of muscles immediately employed becoming weary, the animal is obliged to call another set into 

 action, which change is necessarily more or less frequent as the animal is weaker or stronger. 



6331. The extent of the action of the bony portions of the extremities is the produce of the length and 

 direction of the various parts entering their composition, and of the different angles they are capable of 

 forming ; as progression itself is effected by these angles closing, and suddenly extending themselves 

 again. The force of the action arises from the direction of the component parts of the ankles, in combin- 

 ation with the agency of the muscles. The repetition of the action is dependent on the muscles alone ; 

 but as the original action arose out of the length and direction of the parts, so it will be evident that in 

 every subsequent repetition, it will be more or less extensive, as these are more or less perfect in their 

 formation, even though the muscular exertions should be the same; thus, some strong animals cannot 

 move so fast as others with less strength, as the cart-horse and racer, or greyhound and mastiff 



6332. The bony mechanism of the fore and hinder extremities presents sotne differences. That of the fore 

 limb may be said to exhibit altogether a different character. The fore-leg bones are much less angular, 

 and appear framed purposely to receive the weight imposed on them by the impulse of the hinder limbs. 

 This weight they are destined to sustain, until the elevation is forced on them by the tendency the general 

 inclined mass has to meet the ground, or to find its common centre in the earth. The fore extremities, 

 under this view of the matter, could not have been placed with equal wisdom in any other situation, nor 

 have taken any other form. The hinder extremities having less weight on them, and at no time bearing an 

 increase of pressure, as the fore do by the impetus communicated from behind, are much more angular; 

 and their angles, by being thrown into a backward direction, afford the necessary impetus for the projection 

 of the body forward. This important operation of impelling the mass being almost wholly dependent on 

 the hind extremities, as that of sustaining it is principally confined to the fore extremities ; so the former 

 are also much stronger in point of muscular apparatus ; by which their angles can be advantageously 

 opened and closed with superior effect in progression. 



Sect. IV. Anatomy and Physiology of the soft Parts. 



633S. IFe sJiall include under appendages to bone, the muscles and tendons, blood- 

 vessels, absorbents, nerves and glands, integuments, head, ear, eye, nose, mouth, neck, 

 chest, abdomen, organs of generation, and the foot. 



SuBSECT. 1. Appendages to Bone, the Muscles, and Tendons. 



6334. The appendages to bone are cartilages or gristle, periosteum, medulla or marrow, ligaments, and 

 synovia or joint oil. 



