70 THE ANATOMY OF THE HORSE. 



is lined with a very rough skin, having its points facing back- 

 ward ; thus serving to aid the palate in retaining whatever 

 substance may have entered the mouth to be masticated. 



The front of the mouth is formed partly by the teeth and 

 partly by the lips, the upper of which is the prehensile organ 

 in the horse, as by means of this he is able, when feeding 

 off the ground, to gather the grass together in sufficient 

 quantities for a bite ; to turn over the hay in his rack ; and 

 even nicely to select certain portions as well as to reject 

 others. The lips also are the principal seat of feeling in the 

 animal, a fact apparently wtII known to man, as he selects 

 this part on which to apply that torturing instrument — the 

 twitch. 



On the side of the upper part of the head, behind the 

 place where it is connected by a joint with the lower jaw, is 

 a small projecting canal, which is the opening to the internal 

 ear (Skel. l) ; but as this organ, as well as its outward ap- 

 pendage, belongs to another part of our subject, we must 

 at present do no more than allude to them. 



THE TEETH. 



The substances which enter into the formation of tooth are 

 bone, enamel, and crusta petrosa. These three are perfect 

 when the tooth enters the mouth, and lay one under the 

 other. The crusta petrosa is the outer covering, of a dark 

 colour and tolerable thickness. It was formerly mistaken for 

 tartar, covering and dirtying the teeth ; but that it is not 

 tartar is shown by its always covering young teeth, and 

 being absent from the fi*ont of old horses when the attrition 

 consequent upon gathering the food has worn it off; there- 

 fore whiteness in teeth is no sign of youth in the horse. 

 The crusta petrosa is a dark, tough, and highly organized 

 substance, covering the whole of the fang, and following 

 the enamel wherever it bends or dips into the windings upon 

 the table of the tooth. 



The enamel lies next under the crusta petrosa, and con- 

 sists of a thin layer of very brittle unorganized and crys- 

 talline substance ; it principally coats the crown of the 

 tooth, being very thin up the fang, which it only partially 

 envelops. 



The main bulk of the tooth consists of bone, which is 



