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brane, which is richly supplied with blood vessels. ated in front of the ear; the submaxillary, within
lymphoid tissue, subject to enlargement, called
of voice. Food will
pass through the
and windpipe; a
valve, called the epi.
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
DURUM ! 814
sphincter band, which contracts
Its muscular walls contain striped fibres chyme, passes into the small
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
upper parts of the
Lieberkühn and the glands of Brunner, there are tips, while the rest of the intestine will have pre-
yet not definitely
The small intes-
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,
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
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.
Movements of Food in the Alimentary, Canal. ing the commencement of swallowing is almost co-
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.
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-
In any case there is a dis-
Sensory the stomach itself.
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
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).