The velum with its uvula comes into contact below with the upper part of the back of the tongue, and with a sort of gristly, lid-like process connected with its base, the epiglottis (e).

Behind the partition thus formed lies the cavity of the pharynx, which may be described as a funnel-shaped bag with muscular walls, the upper margins of the slanting, wide end of which are attached to the base of the skull, while the lateral margins are continuous with the sides, and the lower with the floor, of the mouth. The narrow end of the pharyngeal bag passes into the gullet or œsophagus (b), a muscular tube, which affords a passage into the stomach.

There are no fewer than six distinct openings into the front part of the pharynx-four in pairs, and two single ones in the middle line. The two pairs are, in front, the hinder openings of the nasal cavities; and at the sides, close to these, the apertures of the Eustachian tubes (g). The two single apertures are, the hinder opening of the mouth between the soft palate and the epiglottis ; and, behind the epiglottis, the upper aperture of the respiratory passage, or the glottis.

14. The mucous membrane which lines the mouth and the pharynx is beset with minute glands, the buccal glands; but the great glands from which the cavity of the mouth receives its chief secretion are the three pairs which, as has been already mentioned, are called parotid, submaxillary, sublingual, and which secrete the principal part of the saliva (Fig. 41).

Each parotid gland is placed just in front of the ear, and its duct passes forwards along the cheek, until it opens in the interior of the mouth, opposite the second upper grinding tooth.

The submaxillary and sublingual glands lie between the lower jaw and the floor of the mouth, the submaxillary being situated further back than the sublingual. Their ducts open in the floor of the mouth below the tip of the tongue. The secretion of these salivary glands, mixed with that of the small glands of the mouth, constitutes the saliva-a fluid which, though thin and watery, contains a small quantity of animal matter, called Ptyalin, which has certain very peculiar properties. It does not

act upon proteid food-stuffs, nor upon fats; but if mixed with starch, and kept at a moderate warm temperature, it turns that starch into grape sugar. The importance of this operation becomes apparent when one reflects that

A dissection of the right side of the face, showing a, the sublingual; b, the submaxillary glands, with their ducts opening beside the tongue in the floor of the mouth at d; c, the parotid gland and its duct, which opens on the side of the cheek at e

starch is insoluble, and therefore, as such, useless as nutriment, while sugar is highly soluble, and readily oxidizable.

15. Each of the thirty-two teeth which have been mentioned consists of a crown which projects above the gum, and of one or more fangs, which are embedded in sockets, or what are called alveoli, in the jaws.

The eight teeth on opposite sides of the same jaw are constructed upon exactly similar patterns, while the eight teeth which are opposite to one another, and bite against one another above and below, though similar in kind, differ somewhat in the details of their patterns.

The two teeth in each eight which are nearest the middle line in the front of the jaw, have wide but sharp and chisel-like edges. Hence they are called incisors,

or cutting teeth. The tooth which comes next is a tooth with a more conical and pointed crown. It answers to the great tearing and holding tooth of the dog, and is called the canine or eye-tooth. The next two teeth have broader crowns, with two cusps, or points, on each crown, one on the inside and one on the outside, whence they are termed bicuspid teeth, and sometimes false grinders. All these teeth have usually one fang each, except the bicuspid, the fangs of which may be more or less completely divided into two. The remaining teeth have two or three fangs each, and their crowns are much broader. As they crush and grind the matters which pass between them they are called molars, or true grinders. In the upper jaw their crowns present four points at the four corners, and a diagonal ridge connecting two of them. In the lower jaw the complete pattern is five-pointed, there being two cusps on the inner side and three on the outer.

The muscles of the parts which have been described have such a disposition that the lower jaw can be depressed, so as to open the mouth and separate the teeth; or raised, in such a manner as to bring the teeth together; or move obliquely from side to side, so as to cause the face of the grinding teeth and the edges of the cutting teeth to slide over one another. And the muscles which perform the elevating and sliding movements are of great strength, and confer a corresponding force upon the grinding and cutting actions of the teeth. In correspondence with the pressure they have to resist, the superficial substance of the crown of the teeth is of great hardness, being formed of enamel, which is the hardest substance in the body, so dense and hard, indeed, that it will strike fire with steel (see Lesson XII.). But notwithstanding its extreme hardness, it becomes worn down in old persons, and, at an earlier age, in savages who live on coarse food.

16. When solid food is taken into the mouth, it is cut and ground by the teeth, the fragments which ooze out upon the outer side of their crowns being pushed beneath them again by the muscular contractions of the cheeks and lips; while those which escape on the inner side are thrust back by the tongue, until the whole is thoroughly rubbed down.

While mastication is proceeding, the salivary glands pour out their secretion in great abundance, and the saliva mixes with the food, which thus becomes interpenetrated not only with the salivary fluid, but with the air which is entangled in the bubbles of the saliva.

When the food is sufficiently ground it is collected, enveloped, in saliva, into a mass or bolus, which rests upon the back of the tongue, and is carried backwards to the aperture which leads into the pharynx. Through this it is thrust, the soft palate being lifted and its pillars being brought together, while the backward movement of the tongue at once propels the mass and causes the epiglottis to incline backwards and downwards over the glottis and so to form a bridge by which the bolus can travel over the opening of the air-passage without any risk of tumbling into it. While the epiglottis directs the course of the mass of food below, and prevents it from passing into the trachea, the soft palate guides it above, keeps it out of the nasal chamber, and directs it downwards and backwards towards the lower part of the muscular pharyngeal funnel. By this the bolus is immediately seized and tightly held, and the muscular fibres contracting above it, while they are comparatively lax below, it is rapidly thrust into the esophagus. By the muscular walls of this tube it is grasped and propelled onwards, in a similar fashion, until it reaches the stomach.

17. Drink is taken in exactly the same way. It does not fall down the pharynx and gullet, but each gulp is grasped and passed down. Hence it is that jugglers are able to drink standing upon their heads, and that a horse, or ox, drinks with its throat lower than its stomach, feats which would be impossible if fluid simply fell down the gullet into the gastric cavity.

During these processes of mastication, insalivation, and deglutition, what happens to the food is, first, that it is reduced to a coarser or finer pulp; secondly, that any matters it carries in solution are still more diluted by the water of the saliva; thirdly, that any starch it may contain begins to be changed into sugar by the peculiar constituent (ptyalin) of the saliva.

18. The stomach, like the gullet, consists of a tube with muscular walls composed of smooth muscular fibres,

and lined by an epithelium; but it differs from the gullet in several circumstances. In the first place, its cavity is greatly larger, and its left end is produced into an enlargement which, because it is on the heart side of the body, is called the cardiac dilatation (Fig. 42, b). The opening of the gullet into the stomach, termed the cardiac aperture, is consequently nearly in the middle of the whole length of the organ, which presents a long, convex, greater curvature, along its front or under edge, and a short concave, lesser curvature, on its back or upper contour. Towards

its right extremity the stomach narrows, and, where it passes into the intestine, the muscular fibres are so disposed as to form a sort of sphincter around the aperture of communication. This is called the pylorus (Fig. 42, d).

The mucous membrane lining the wall of the stomach is very delicate, and multitudes of small glands open upon its surface. Some of these are simple, but others (Fig. 43) possess a somewhat more complicated structure, their blind ends being subdivided. It is these glands, and more especially the more complicated ones, the socalled peptic glands, which, when food passes into the stomach, throw out a thin acid fluid, the gastric juice.

When the stomach is empty, its mucous membrane is pale and hardly more than moist. Its small arteries are then in a state of contraction, and comparatively little blood is sent through it. On the entrance of food a nervous action is set up, which causes these small arteries to dilate; the mucous membrane consequently receives a much larger quantity of blood, it becomes very red, little drops of fluid gather at the mouth of the glands, and finally run down as gastric juice. The process is very similar to the combined blushing and sweating which takes place when the sympathetic in the neck is divided. Pure gastric juice appears to consist of little more than water, containing a few saline matters in solution, and its acidity is due to the presence of free hydrochloric acid; it possesses, however, in addition a small quantity of a peculiar substance called pepsin, which seems to be not altogether dissimilar in chemical composition to, though very different in its effects from, ptyalin (§ 14).

Thus, when the food passes into the stomach, the con

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