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brane, which is richly supplied with blood vessels. ated in front of the ear; the submaxillary, within
This membrane is called the mucous membrane, the angle of the lower jaw; and the sublingual,
and from it is secreted by the glands which it con under the tongue. The mouth in most animals is
tains a viscid substance called mucus. If the provided with hard tissues—teeth, beaks—for the
finger be thrust into the back of the mouth, and subdivision of food before it is swallowed. Vege-
the mucous membrane gently scraped, the fluid table feeders, eating tough grains, roots, and fibres,
which will adhere to the finger is seen to be viscid : have large molar or grinding teeth, while the car-
it is secreted by the glands of the mouth. Not nivora have these same teeth modified so as to
only mucus, but many other substances useful in present a cutting edge, with which and their
digestion are fornied by little glands in the mucous pointed canines meat is torn and cut into
membrane, so that the whole digestive system is pieces, which are then swallowed (see TEETH).
bathed during digestion with fluid having a diges. The mucous membrane of the mouth is covered
tive action on the food. In addition there are externally by the muscles of the cheek and
other glands, such as the salivary, the liver, and lips. Into its cavity the muscular tongue projects.
the pancreas, which we may look upon as glands On looking into the mouth with a looking-glass,
of the mucous membrane which have enormously one sees back into the throat. The entrance to
developed. To so great an extent have they in the throat will be observed to be bounded at the
creased in size that they have got far outside the sides by two muscular curtains passing downwards
digestive system, and have become situated in neigh- obliquely to the sides of the root of the tongue.
bouring parts of the body, only connected with the These are termed the anterior pillars of the fauces,
digestive system by their ducts or elongated mouths. and behind them, one on each side, are masses of

lymphoid tissue, subject to enlargement, called
the tonsils. Above, another curtain hangs down.
It is called the soft palate, and separates the mouth
from the hinder part of the nasal cavity. Project-
ing from its centre is a little cone called the uvula
(fig. 1). The cavity of the pharynx, or the interior
of the throat, is another cavity lined by mucous
membrane, with muscular walls. These muscles
constrict it (constrictors). Below, the cavity passes
into the gullet or csophagus, and in front of this
tube runs the windpipe which communicates with
the pharynx through
the farynx, or organ

of voice. Food will
TONGUE

pass through the
pharynx into

the
gullet; and air, dur-
ing respiration, passes
through the pharynx
on into the larynx

and windpipe; a
h

valve, called the epi.
glottis, partly closes
the aperture of the
larynx. The pharynx
is common, therefore,
both to the digestive
system and the re-
spiratory passages.
Above, the pharynx

communicates, as beFig. 1.-Section through Mouth, Nose, &c. :

fore described, with

the mouth and also a, sphenoid bone; b, Eustachian tube; c, soft palate ; &, uvula;

with the nose. One e, nasal passage; J, upper jaw; g, lower jaw; h, epiglottis ;

h m, mouth.

can demonstrate this

latter fact by drawing Through these ducts their secretions, like that smokeinto the mouth, of the microscopic mucous gland, pour into the and expelling it by cavity of the digestive system. Outside the mucous the nostrils. This coat we have the muscular coat, the function of communication is which is to move the food onwards in its course, closed during the act

le and to mix it with the digestive juices. In the of swallowing, and mouth, throat, and the upper part of the gullet, also during the singthe muscles which move the food onwards, as in ing of pure

vowel swallowing, are, when examined by the microscope, sounds, such as ā, ou, Fig. 2.- Human Alimentary seen to be transversely striped, and like other striped and the closure is

Canal: muscles their contraction is rapid. In other parts effected chiefly by the a, qesophagus; \, stomach ; €, carof the digestive system, however, the muscular coat elevation of the soft

diac orifice; d, pylorus; e, small

intestine; S, biliary duct; g, panconsists of smooth muscle, and like all other palate, which acts as creatic duct; h, ascending colon; smooth muscles this coat contracts slowly. On à valve. The pharynx i, transverse colon; j, descendthis account the food rapidly swallowed passes communicates in ad ing colon; k, rectum. very slowly along the rest of the digestive system. dition with the mid

Having shown that the digestive system is a muco dle ear by the Eustachian tubes, and this may muscular tube, we may now consider it more in be rendered evident if the mouth and nose be detail. The mouth (figʻl, m) is lined with mucous closed, and a violent expiratory effort made at membrane, and into it is poured the secretion of the same time. As the pressure of air within the three pairs of salivary glands—the parotids, situ- | throat is increased, the Eustachian tubes which

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DIGESTION
previously were collapsed now become distended, layer-submucous coat-is the muscular coat. This
and a little wave of air at high pressure is forced is similar to that of the rest of the alimentary
into the middle ear, causing a buzzing sound. canal, except that there are in addition to the
Occasionally the middle ear communicates with circular and longitudinal fibres, many oblique
the external air through congenital or acquired fibres. The circular fibres are
apertures in the membrana tympani. In these very thick indeed at the pyloric
cases smoke may be propelled from the throat out aperture, forming a circular
of one or both ears.

sphincter band, which contracts
The gullet or esophagus (figs. 1, 2, and 3) is a and keeps back the food in the
long tube passing from the pharynx to the stomach. stomach until gastric digestion
Its mucous coat is loaded with very large mucous is nearly completed.
glands, which secrete a quantity of very viscid The food, now called the

Its muscular walls contain striped fibres chyme, passes into the small
in the upper, unstriped in the lower part. The intestine, a tube some 20 feet
stomach itself is a greatly dilated part of the long. This tube, besides the
digestive system. Its shape is indicated in the fig. muscular and mucous coats,
It may be said to consist of two parts, even in the possesses in addition an
human subject; a inore complex arrangement is ternal coat of loose fibrous
found in many animals, such as the ruminants. tissue, covered by a single layer
The large dilated portion into which the gullet of flat epithelial cells. This
opens is termed cardiac, and the opening the coat is prolonged into, and
cardiac or oesophageal opening. The narrow part helps to form the mesentery,
opening into the duodenum is the pyloric part, membrane connecting the
and the opening the pyloric opening. The intestine with the abdominal
whole is lined with mucous membrane, which, walls, which are lined with a
in the empty stomach, is thrown into projecting similar fibro-epithelial coat.
folds or ruga, but these folds are effaced when This membrane is called the
the organ is distended with food (fig. 3). In the peritoneum, and is sometimes B, cardiac gland from

inflamed (peritonitis ) as a result the middle of the of cold, injuries, &c. The sinall

stomach, intestine is somewhat arbitrarily

magnified about 156

diameters: a, wall divided into three portions—the

of the tube, lined upper (duodenum), the middle with large oval nuc(jejunum), and the lower

leated cells; b, the b (ileum). In all parts the mus

same cells isolated ;

C, nucleated cells of cular coat is similar to that of

epithethe rest of the digestive system.

lium, nccupying the The mucous coat contains glands

tubes; d, blind exvery like the pyloric glands of

tremity of the tube. the stomach, called Lieberkühn's follicles. These, however, rarely branch. They secrete the intestinal juice. In the duodenum, one finds in addition highly-branched glands called Brunner's. These extend right down

into the submucous coat. Little is known conFig. 3.-Section of the Stomach : a, ducts of liver; U, pylorus; C, bile duct; d, pancreatic duct; submucous coats, and generally involving both

cerning their function. In both the mucous and e, cardiac orifice.

layers, are found masses of tissue-lymphoid. membrane are innumerable glands, which secrete These are termed solitary glands, but it must

similar to that found in a lymphatic gland (fig. 6); the digestive juices of the stomach (fig. 4). If the be understood that they do not secrete any surface of the inembrane be examined with a strong juice concerned in digestion.

Their function is pocket-lens, the apertures of these little glands may probably connected with the blood and the bloodbe seen. They run down from the surface into the corpuscles. Collections of these solitary glands, deeper parts of the mucous membrane. They are lined by secreting cells. The greater number of glands situated in mucous membranes have the simple structure diagrammatically represented in fig. 4. Each gland has a inouth or short duct lined by cells.

Below this the little tube is lined by cells which secrete the juice peculiar to the gland. This secreting part sometimes branches. Outside the gland blood-capillaries ramify, which supply the gland with nourishment, enabling it to manufacture the substances which it secretes. The gastric juice is acid, and the chief acid secreted is hydrochloric acid.

This is formed at the cardiac, but not at the pyloric end. The substance called pepsine, which is necessary for digestion, Fig. 5.—The under surface of the Stomach and Liver, is secreted by the whole of the glands. The

which are raised to show the Duodenum and Pancreas : cardiac glands therefore secrete both substances,

st, stomach; p, its pyloric end; 1, liver; g, gall-bladder; d, and they possess two sorts of cells, those which

duodenum, extending from the pyloric end of the stomach to form the hydrochloric acid being bigger and more the front, where the superior mesenteric artery, sm, crosses the granular than the other sort which secrete pepsine. intestines; pa, pancreas; sp, spleen ; a, abdominal aorta. The pyloric glands secreting pepsine have only one kind of cell similar to the pepsine-secreting cell

of forming oblong patches about two inches long, the cardiac end. Outside the vascular and glandu- are called Peyer's patches. These are affected in lar mucous coat, and united to it by a loose delicate | typhoid fever. In addition to the follicles of

columnar

upper parts of the

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Lieberkühn and the glands of Brunner, there are tips, while the rest of the intestine will have pre-
two very important glandular structures, the liver served its ordinary colour. On further examina-
and the pancreas, which pour their digestive juices | tion it will be seen
into the small intestine (fig. 5). The bile, which that the fat has been
is the secretion of the liver, is formed continually taken up in micro-
by that organ, but the amount thus formed is scopic globules by
greatly, influenced by the kind and quantity of the cells covering
food taken. It passes out of the liver by the two | the villi, and that
hepatic ducts, and much of it passes by the cystic they are passing, in
duct into the gall-bladder, where it is stored up. a way which is as

yet not definitely
settled, into the
central lacteal.

The small intes-
tine is a tube of

great importance, -M

and in order to in- Fig. 7.-The Top of a Villus : crease its total area, Fat globules are represented as passthe

ing through one of the epithelial brane is elevated,

cells, F, on through the tissue of

the villus, I, into the central in the upper part,

lacteal, L.
into transverse folds
(the valvulæ conniventes, fig. 8).

The unabsorbed food, mixed with the various secretions we have mentioned, now passes into the large intestine, when both digestion and absorption go on, although to a less extent. The large intestine is only 5 feet in length, but its girth is much greater than that of the small intestine. It commences with the cæcum, a dilated part, into which passes a little blind canal (the vermiform appendix), a large and important structure in some animals. The food remnant (faecal matter) is prevented, under ordinary circumstances, from passing

back into the small intestine, by a double fold of Fig. 6.-Section of Intestinal Mucous Membrane : mucous membrane (the ilio-cæcal valve, fig. 9). L, lacteal in centre of villus; E, epithelium covering villus; The large intestine ascends on the right side (ascendB, blood-vessels represented; F, follicle of Lieberkühn; S, part of a solitary gland; M, muscular fibres.

ing colon), crosses over to the left side (transverse

colon), and descends again (descending colon), and From this the bile passes into the common bile

makes a bend (sigmoid fexure), and finally ter

minates in a somewhat enlarged portion (rectum). duct, which joins the duct of the pancreas, and the two open into the duodenum by a common aperture. The bile is to be looked upon not only as a

b digestive juice, but as a drain or channel of excretion, whereby effete and useless matters are removed from the body. The flow of bile is easily restrained, as by inflammation of the duct, or the presence of a tumour pressing on the duct, or a gall-stone. In this case, the bile already formed is reabsorbed with the blood, through the lymphatics, and we have jaundice due to absorption of the colouring matter of the bile. The secretion of bile goes on before birth; the meconium of infants consisting chiefly of biliary matter. The pancreas is very similar in structure to a salivary gland. It secretes the pancreatic juice which pours with the bile into the digestive system. The mucous membrane of the small intestine contains, in addition to the structures already mentioned, little projections called villi (fig. 6). These are not, to any great extent at least, secretive, but they are im

Fig. 8.-Small In Fig. 9.-Cæcum inflated, dried, testine distended

and opened to show the arrangeportant absorbants. This property they share

and hardened by ment of the valve : with the whole of the digestive system, through

alcohol, and laid a, termination of the ileum; b, ascendany part of which, and especially through the walls

open

show ing colon; c, cæcum ; d, a transof the stomach and small intestine, digested matter the valvulae con

verse construction projecting into

niventes. passes into the numerous blood-capillaries which

the cæcum ; ef, lips of the valve

separating the small from the large form everywhere a dense network. The villi are

intestine; y, the vermiform appenpeculiar, however, for each one contains, in addition to blood vessels, a small lymph-vessel or lacteal. Nearly all the fat absorbed by the diges The anal aperture is closed by muscles, an internal tive system is taken up by the little cells of the sphincter of non-striped, and an external of striated villi, and passes on into the lacteals, and thence fibre. The mucous membrane of the large intestine to the blood (fig. 7). If some osmic acid, which differs from that of the small intestine in containblackens fat, be poured into the intestine of a milk ing no villi, or Brunner glands. Lieberkühn's and rabbit, killed during active digestion, and if the solitary glands are present, but the aggregation of villi be examined with a microscope, they will the latter into Peyer's patches is nowhere to be be seen to have been blackened, especially at their found.

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Movements of Food in the Alimentary, Canal. ing the commencement of swallowing is almost co-
When food is taken into the mouth it is at once incident with the passage of food down the gullet,
swallowed, unless it is in the solid form. In this which produces a very audible sound. Following
case it is chewed or masticated; the use of which the propulsion of the food downwards, there is
is to divide the solid fragments taken into a con a wave of contraction, which, commencing in the
venient size for swallowing, for which purpose it, in pharynx, travels downwards through the gullet.
addition, is inixed with the viscid saliva and juices This, however, is comparatively slow. It is seen
of the mouth. The chewed food, moreover, is more then that swallowing is not due to the falling of
easily digested, inasmuch as the gastric and other liquids down the throat. A horse drinks up
juices can act more readily upon finely divided hill, and the jugglers, or indeed any one, can
than upon larger masses of fool. Many animals drink or swallow with the head vertically down-
can hardly be said to masticate; such are the wards.
carnivora (dog, cat, &c.), and they are not pro When the food has reached the back of the
vided with grinding teeth. In most animals living mouth, the rest of the act of swallowing occurs
on vegetable food, which frequently consists of irrespective of the action of the will. The nerves,
hard grains, roots, and fibres, large flat grinding which commence in the mucous membrane of the
molars are found. In these animals, not only is pharynx and gullet (sensory branches of vagus),
the food finely divided in the mouth, but the food, carry impressions to the brain, which disengage of
largely consisting of starch, is partially digested by themselves the appropriate muscular movenients
the saliva. In mastication, the head is firmly fixed without necessarily involving either the will or con-
by the powerful muscles of the neck, while the sciousness. Thus, in alcoholic stupor, or fainting
lower jaw is moved upon the upper. The lower from drowning, in both of which conditions con-
jaw is approximated to the upper by powerful sciousness is suspended, food and liquid placed at
muscles (the temporal, masseter, and internal ptery- the back of the month are at once swallowed.
goids), which pass upwards, and are attached to There is a possibility that during swallowing
the side of the head and face. Their contraction the food may go the wrong way–i.e. it may pass
may be felt by placing the hand in front of the ear into the larynx and windpipe. It will be seen
and voluntarily contracting the jaws. The lower from the diagram that the food in its passage to
jaw is depressed by muscles which pass down the the gullet must actually pass over the aperture of
front of the neck. Most of these spring from the the larynx. It is prevented from passing into it
hyoid bone, which may be felt deep in the tissues by the elevation of the larynx (this can be felt by
of the neck above the Adam's apple. Rotating the hand placed on the throat), which pushes its
movements and those of protrusion and retraction aperture against and under the back of the tongue,
of the jaw are produced chiefly by the action of the which at the same time is pushed backwards. In
pterygoid muscles. It is obvious that during masti- addition, there is a valve called the epiglottis,
cation the food would naturally tend to escape from which is pushed down over the larynx by the move-
between the grinding surfaces of the teeth, and ment just described, and by muscular fibres, which
would collect within the mouth and outside the act upon it for that especial purpose.

If the gums. This is prevented, however, by the muscles epiglottis be destroyed, as by ulceration, gun-shot placed in the substance of the cheeks (buccinators) wounds, &c., it is necessary for the patient to have and lips (orbicularis oris). These keep the cheek the food he takes carried over the aperture of the and lip walls closely opposed to the outside of the larynx into the gullet by a feeding-tube. It is teeth. On this account food will only escape from obvious that one cannot speak with the larynx between the grinders into the interior of the mouth, shut, and with the larynx open we cannot safely from which it is collected and pushed back between swallow. Food is prevented from passing into the the teeth by the muscular tongue.

nose by the elevation of the soft palate which meets The very complex muscular movements just the constricting pharynx, and shuts off the cavity described result from very perfectly co-ordinated of the nose like a valve (fig. 1). nervous impulses, which pass from the brain to the The walls of the stomach and intestine are, like muscles, and cause and regulate their contractions. the gullet, provided with muscular fibre. An exOne can masticate at will—that is to say, one can ternal layer passes in the length of the gut, and consciously cause the muscles to contract. In within this is a circular layer. These muscles, order that the mastication may be effective, how- unlike the muscles of the limbs, contract slowly on ever, it is necessary not only to know the sizes, but stimulation, and they are outside the domain of also to be aware of the ever-changing positions of voluntary action. During digestion they contract the particles of food. This is effected by sensory peristaltically, urging the food towards the rectum. nerves, which pass to the brain froin the mucous The peristaltic waves may begin in any part of the membrane of the mouth. Although mastication is gut and pass slowly downwards, followed at vary; frequently voluntary, yet, like most other volun- ing intervals by other waves. It is probable that tary actions frequently, performed, it can be per- what is called antiperistaltic waves may occasionformed reflexly. In this case the sensory impulses ally occur, tending to bring the food back towards pass from the mucous membrane to the brain, and the mouth, for bilious matter is frequently vomited, initiate appropriate motor impulses which pass to the bile having in all probability passed upwards the muscles, without exciting attention and special into the stomach by antiperistalsis from the duovolition in their passage.

denum. As a result of mastication, the food is gathered Eructations are frequently caused by antiperisin the form of a round moist bolus on the upper talsis, and by a movement of this kind food is surface of the tongue (see fig. 1). It is now ready to brought back into the mouth for further chewing be swallowed. In the first place, it is pushed back in the ruminants (sheep, oxen, &c.). The peristalsis wards by the tongue, and seized by muscles, many is particularly active during digestion, and is proof which are attached to the hyoid bone, which can duced in great part by the food stimulating the be felt to move during their contraction. According mucous membrane. If a portion of the intestine or to the inost recent investigation, the bolus is pro the stomach be removed from the body, peristalsis pelled with great rapidity through the pharynx and may continue or may be produced artificially, espegullet into the stomach. If the finger be placed cially by irritating the mucous membrane. In the upon the hyoid bone, or Adam's apple, and the ear body the canal is under the influence of additional placed against the upper third of the back of a

nerves (vagus), through which fibres the digestive patient, the inovement of the hyoid bone indicat

processes are chiefly regulated among themselves.

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The peristalsis in the stomach is combined by parts. The psalterium (maniplies), so called from irregular churning movements.

the lamellated appearance of its mucous membrane, The act of vomiting is a reflex nervous act. It communicates with the last division, the rennet can be excited by stimulating the branches of the stomach (abomasum, fig. 11). vagus nerve, which are distributed to the stomach, Fluid passes either into the first, second, or third as when indigestible and irritative food is taken ; or parts of the stomach, and thence on into the fourth. emetics, such as mustard, hot water, or a hot Solid matter, such as grass, roots, &c., passes either saline solution, tartar emetic, ipecacuanha, sulphate into the paunch or reticulum. This is mixed with of zinc, and alum are administered. By tickling the saliva swallowed with it, and in addition it is the back of the throat with a feather, the glosso- mixed with juices formed by the mucous membrane pharyngeal nerve is stimulated, and vomiting may of these cavities. When the animal has finished readily be produced. It is of frequent occurrence feeding, it lies down and rumination commences. when painful irritation of the uterine nerves in preg Due in part to the contraction of the abdominal nancy, of the nerves of the liver and kidneys during muscles and diaphragm, the food is propelled in the

the passage of a hepatic or form of rounded pellets from the paunch and retirenal stone, or indeed when culum up into the mouth. The pellets are there irritation of

any sensory thoroughly masticated, and are returned in a pulpy nerves takes place. Nerve condition to the stomach. Now, however, the food impulses may pass to the passes into the psalterium, and finally into the brain through any one of rennet stomach. It will be seen, therefore, that these channels (fig. 10), or the consistency of the food determines into which may be excited in the brain part of the stomach it passes. The walls of the itself by the sight or smell | stomach near the gullet are thrown into two folds or even the thought of any. thing disgusting, and they

produce, if the person be con-
-5 scious, a feeling of nausea.

In any case there is a dis-
charge of nerve-impulses,
which, as a result of this
stimulation, passes to the
glands of the mouth through
the chorda tympani nerve,
and produces a rapid flow

b
of saliva. In addition, motor
nerves carry impulses to the
muscular walls of the ab-

Id
domen, and to the walls of
Fig. 10.

Sensory the stomach itself.
Nerves concerned in
Vomiting:

result of the muscular conNerves come to vomiting

traction which follows, the centre V, through spinal contents of the stomach are cord SC, from pharynx propelled upwards into the P, lungs L, gall bladder mouth. Just before vomitG, stomach S, kidney K, intestine I, and bladder ing an inspiration generally

occurs, and the aperture of

the larynx (glottis) is closed. The diaphragm—the muscle which separates the

Fig 11.-Compound Fig. 12.- Alimentary thorax from the abdomen—then becomes pressed

Stomach of Ox:

Canal of Fowl: down upon the abdominal contents, and assists in

0, cesophagus; b, rumen, or a, oesophagus; b, crop; C, pro

paunch; c, reticulum,' or ventriculus, the act of vomiting. Cases in which irritating or

or secreting

second stomach; d, omasun, stomach; d, gizzard, or tripoisonous substances are swallowed are so frequent, or third stomach ; e, abom turating stomach; é, intesthat every one should be aware that a large quan asum, or fourth stomach tinal canal; f, two long

s, the duodenum.

cæcal tubes indicating the tity of hot liquid, especially if it contain much salt,

commencement or some mustard, forms a safe and speedy emetic.

of large intestine. Ice is a valuable sedative, and often prevents vomiting. The undigested food when it reaches or lips which, when in contact, form a tube leading sensory, nerves which carry impulses to the brain tube the masticated and fluid food can pass. The and spinal cord. A feeling of distension results, mouthfuls of grass which are first swallowed pass and voluntary contraction of the abdominal muscles between their lips, and find their way at once into and of the diaphragm—an inspiration usually the paunch or reticulum. taking place-expels the undigested matter. This In the bird some interesting modifications in the yoluntary effort is aided by the contraction of the structure of the alimentary canal are seen (fig. 12). bowel itself, and by the relaxation of the band of The gullet at about the middle of its course is

promuscular fibres (sphincters) which, during the in- vided with a pouch or crop. Into this the food tervals between evacuations, remain contracted. passes, and is bathed by a secretion formed by its

In many animals, such as the sheep, ox, and glands. It is then propelled onwards into a dilated camel, the stomach consists of several cavities com cavity, the proventriculus, and is acted on by digesmunicating with one another. In the ox and sheep tive juices." Thence it passes into the gizzard. This both the cardiac and the pyloric portions are each cavity is provided with muscular walls of enormous subdivided into two compartments,

The cardiac thickness in the case of birds that are vegetablepart consists of a very dilated cavity, the paunch feeders. It is lined by thick and corneous epithe(rumen), into which the food is passed as soon as lium, and in its interior are generally found pieces swallowed. In addition there is a smaller part, the of stone, chalk, &c. The gizzard is a powerful reticulum (honeycomb), so called from the folds of mill, which grinds the food into a soft pulp, upon lining mucous membrane which intersect, forming which the digestive juices can readily act (see A reticulum. The pyloric half is divided into two | BIRD).

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