144 ANATOMY AND DISEASES 01< THE NOSE AND MOUTH. 



So great is the conformity between the structure of the animal and his destination, 

 that a tolerable student in comparative anatomy, by a mere inspection of the glenoid 

 cavity, would at once determine whether the animal to which it belonged was car- 

 nivorous, and wanted no lateral motion of the jaw ; or omnivorous, living occasionally 

 on all kinds of food, and requiring some degree of grinding motion; or herbivorous, 

 and needing tlie constant use of this admirably-constructed mill. 



At g, p. 125, is represented the masse.ter muscle, an exceedingly strong one, con- 

 stituting the cheek of ihe horse — arising from the superior maxillary under the ridge 

 continued from the zygomatic arch, and inserted into the lower jaw, and particularly 

 round the rough border at the angle of the jaw. This acts with the temporal muscle 

 in closing the jaw, and in giving the direct cutting or champing motion of it. 



Within the lower jaw, on either side, and occupying the whole of the hollowed 

 portion of them, and opposite to the masseters, are the pterygoid rniiscles, going from 

 the jaws to bones more in the centre of the channel, likewise closing the mouth, and 

 also, by their alternate action, giving tliat grinding motion which has been described. 

 The space between the branches of the lower jaw, called the channel, isof consider- 

 able consequence. It may be a little too wide, and then the face will have a clumsy 

 appearance : but if it is too narrow, the horse will never be able to bend his head 

 freely and gracefully ; he will be always pulling or boring upon the hand, nor can ho 

 possibly be well reined in. 



The jaws contain the teeth, which are the millstones cmploj-ed in comminuting the 

 food. The mouth of the horse at five years old contains i'crty teeth, viz. six nippers 

 or cutting teeth in front, a tush on each side, and six molars, or grinding teeth, above 

 and below. They are contained in cavities in the upper and lower jaws, surrounded 

 by bony partitions, to which they are accurately fitted, and by which they are firmly 

 supported. For a little way above these bony cavities, they are surrounded by a hard 

 substance called the gum, so dense, and adhering so closely to the tceih and the jaws 

 as not to be separated without very great difficulty — singularly compact, that it may 

 not be wounded by the hard or sb.arp particles of the food, and almost devoid of feel- 

 ing, for the same purpose. 



Seven or eight months before the foal is born, the genns or beginnings of the teeth 

 are visible in the cavities cf the jaws. The tooth grows, and 

 presses to the surface of the gum, and forces its way through it ; 

 and, at the time of birth, the first and second grinders have 

 appeared, large compared with the size of the jaw, and seemingly 

 filling it. In the course of seven or eight days the two central 

 nippers are seen as here represented. They likewise appear to 

 be large, and to fill the front of the mouth ; although they will 

 afterwards be found to be small, compared with the permanent 

 t^eth that follow. In the course of the first month the third 

 grinder appears above and below, and, not long after, and gener- 

 ally before six weeks have expired, another incisor above and 

 below will be seen on each side of the two first, which have now 

 considerably grov/n, but not attained their perfect height. The 

 second cut will represent the appearance of the mouth at that time. 

 At two months, the central nippers will have reached 

 their natural level, and between the second and third 

 month the second pair will have overtaken them. They 

 will then begin to wear awa}' a little, and the outer edge, 

 which was at first somewhat raised and sharp, is brought 

 to a level with the inner one, and so the mouth continues 

 until some time between the sixth and ninth month, when 

 another nipper begins to appear on each side of the two 

 first, making six above and below, and completing the 

 colt's mouth ; after which, tlie only observable difference, 

 until between the second and third year, is in the wear of 

 these tt^eth. 



The term m'pper is familiar to the horseman and the tat- 

 riei;, and much better expresses the action of thrse teeth 

 than the word incisor or cutter, which is adopted by ar.ato- 



