Book VII. 



ANATOMY OF THE HOUSE. 



963 



twenty-four grinders, which numbers are equally divided between the two jaws. The teeth are inserted into 

 indentations or sockets between the bony plates of the jaw, called alveoli, by cone-like roots. The bodies 

 of the teeth are principally composed of two substances, one of the nature of common bone, giving bulk 

 and form, and one of extreme hardness, called enamel, placed in man and carnivorous animals wholly 



without the teeth, to give strength and durability; but in the horse and other Granivora, the latter 

 particularly, it is placed in the grinders, in perpendicular plates, within the body of the teeth ; by 

 which contrivance, a rough grinding surface is kept up; for the mere bony parts wearing faster than 

 the lamella; of enamel, it follows that ridges remain to triturate the vegetable matter that passes between 

 the teeth. 



6303. There are two sets of teeth, a temporaneous or milk set, and a permanent or adult set, in which 

 wise provision man and most brutes participate. The milk set are some of them, as the molars, apparent 

 at birth ; there being usually six grinders in each jaw, three on each side in the new-born foal, and which 

 number of this set is never increased. The nippers begin to appear soon after birth, and follow a regular 

 order of succession until the animal is three or four months old ; at which time he begins to require sup- 

 port from herbage as well as milk. The temporaneous set remove gradually one after another ; had they 

 all been displaced at the same time, or even had several of them fallen out together, the animal must 

 have suffered great inconvenience, and perhaps have been starved. This removal, which commences at 

 the age of two years anil a half, and is completed between the fourth and fifth year, is effected by the 

 action of the absorbents on their fangs, and appears to be occasioned by the stimulus of the pressure 

 received from the growing teeth under them. For although these two sets appear with an interval of 

 some years between them ; yet the rudiments of both are formed at nearly the same period, and both 

 sets may be thus seen in a dissected jaw. Regulated by the stimulus of necessity, as soon as the tem- 

 poraneous set falls out, the permanent appears : and that such appearance follows the necessity is 

 evident ; for a premature or accidental removal of the colt's teeth is soon followed by the appearance 

 of the others. Dealers and breeders, aware of this, draw the milk teeth to make their colts appear as 

 horses. It was necessary there should be two sets of teeth ; for, as they grow slowly in proportion to 

 the jaws, had there been but one only, the disproportion of growth between the teeth and jaws must have 

 separated them. 



630* The forms of the teeth vary more than their structure. The incisive or nippers are round, which 

 is favourable for the pressure they undergo ; the upper more so than the lower. On the upper surface a 

 hollow is seen in the young tooth, which, not extending through the whole substance, naturally wears 

 out with the wear of the tooth ; and as a considerable degree of regularity occurs in this wearing away 

 in all horses, it has gradually settled into the general criterion of age. The nippers are not all of them 

 exactly similar ; the corner teeth differ most in being nearly triangular, and in having an internal wall 

 or side, which does not become level with the rest until long after those of the others. The cuspidate 

 tusks or tushes are permanent, appearing at about five years or rather earlier ; those in the front jaw are 

 usually nearer the nippers than those below. Each presents a slight curve, which follows the direction of 

 all the canine or pugnatory teeth of other Mammalia. The pointed extremity wears away by age, leaving 

 merely a buttoned process, which may serve as a guide to the age when a horse is suspected to be Bishoped, 

 as it is called, from a man of that name who was peculiarly dexterous in imitating on old teeth the dis- 

 tinctive cavity of youth. The molar or grinding teeth are stronger in the upper than in the lower jaw ; 

 which was necessary, as they form the fixed point in the process of grinding. The upper surface presents 

 nearly a long square, indented from the alteration of the enamel with the bony portions ; and as the in- 

 terior or upper teeth hang over the posterior, so the ridges of the one set are received into the depressions 

 of the other. 



6305. Wear of the teeth. The teeth, in a state of nature, would probably present a surface opposed to 

 each other for mastication, to the latest period of the most protracted life ; but the removal of the animal 

 from moist food to that which is hard and dry, must occasion an unnatural wear in those organs ; and 

 hence, although the teeth of the horse, even in a domesticated state, are not subject to the caries of the 

 human ; yet the grinders are liable to become thus injured by continued exertion. In the young or adult 

 horse, the upper and under grinders do not meet each other horizontally ; on the contrary, they have 

 naturally an inclination obliquely inwards; and those of the upper jaw present small spaces between each 

 other, while those of the lower are more continuous ; by which means, as the food, particularly its inter- 

 rupted portions, as gTain, becomes ground, it falls within the mouth to be replaced under the grinding sur- 



3 Q. 2 



