THE LOWER JAW. 135 



treatment ; or a few mashes, and gentle alteratives, will relieve the animal. 

 A few slight cuts across the bars with a lancet or penknife, and taking cari.- 

 to avoid the principal artery and the vein of the palate, the situation of 

 which has just been pointed out, will relieve the indamnialion, and cause 

 the swelling to subside ; indeed, this scarification of the burs will seldom 

 do harm, although it is far from being so necessary as is supposed. To the 

 brutal custom of the farrier, who sears and burns down the bars with a 

 red-hot iron, we do most peremptorily object. It is torturing the horse 

 to no purpose ; and it is rendering that part callous, on the delicate sensi- 

 bility of which all the pleasure and safety of riding and driving depend. 

 It may be prudent in case of lampas to examine the grinders, and more 

 particularly the tushes, to see whether either of them is endeavouring to 

 make its way through the gum. If with the gum-lancet, or penknife, two 

 incisions across each other be made on the tooth, the horse will experience 

 immediate relief. 



THE LOWER JAW. 



The posterior or lower jaw may be considered as forming the floor of the 

 mouth (a, p. 63, or w, p. 68). The body or lower part of it contains the 

 under cutting teeth and the tushes ; the sides are two flat pieces of bone, 

 containing the grinders. On the inside, and opposite to a, p. 63, is a hole 

 through which blood-vessels and nerves enter to supply the teeth, and some 

 of which escape again at another hole on the outside, and near the nippers. 

 The branches are broader and thinner, rounded at the angle of the jaw, 

 and terminating in two processes. One, the coracoid, from its sharpness or 

 supposed resemblance to a beak, passes under the zygomatic arch, (see p. 

 63,) and the temporal muscle, arising from the whole surface of the pari- 

 etal bone (see p. 70), is inserted into it, and wrapped round it ; and by its 

 action, principally, the jaw is moved, and the food is ground. The other, 

 the condyloid, or rounded process, is received into the glenoid (shallow) cav- 

 ity of the temporal bone, at the base of the zygomatic arch, and forms the 

 joint on which the lower jaw moves. This joint is easily seen in the cut 

 at page 63 ; and being placed so near to the insertion of the muscle, or the 

 centre of motion, the temporal muscle must act with very considerable 

 mechanical disadvantage, and must possess immense power. 



This joint is admirably contrived for the purpose which the animal 

 requires. It will admit freely and perfectly of the simple motion of a 

 hinge, and that is the motion of the jaw in nipping the herbage and seizing 

 the corn. But the grass, and more particularly the corn, must be crushed 

 and bruised before it is fit for digestion. Simple champing, which is the 

 motion of the human lower jaw, and that of most beasts of prey, would very 

 imperfectly break down the corn. It must be put into a mill; it must be 

 actually ground. 



It is put into a mill, and as perfect a mill as imagination can possibly 

 conceive. 



The following cut represents the glenoid cavity in a carnivorous, or flesh- 

 eating, and herbivorous, or grass-eating animal, viz : the tiger and the 

 horse : the one requiring a simple hinge-like motion of the lower jaw to 

 tear and crush the food : the other a lateral or grinding motion to bring it 

 into a pulpy form. First examine this cavity in the tiger, represented at 

 B. At the root of the zygomatic process, D, is a hollow with a ridge along 

 the greater part of the upper and inner side of it, standing to a considerable 

 height, and curling over the cavity. At the lower and oooosite edge of 



