198. The erect attitude lessens the exhaustion of the muscles. A person whose position is erect will stand longer, walk further, and perform more labor, than an individual whose position is stooping, but equal in all other respects. The manly port in an erect attitude, depends chiefly upon the action of the muscles of the back; and it follows that the fewer the muscles in a state of tension, the less the draught upon the nervous system, and the less its exhaustion. Another advantage which attends the erect position is, the trunk and head are balanced upon the bones and cartilages of the spinal column. If the body slightly incline forward, the muscles attached to the posterior side of the spine, by a gentle contraction, will bring it to the perpendicular, and even incline it backward. This is immediately removed by a slight contraction of the muscles upon the anterior side of the spinal column.
199. In the erect position, there is a constant slight oscillation of the body backward and forward, like the movement of a pendulum; while, in the stooping posture, the muscles on the posterior side of the spinal column are kept in a state of continued tension and contraction, to prevent the body from falling forward. This enfeebles the muscles of the back, and exhausts the nervous energy, while the erect position favors their development and power, because there is an alternate contraction and relaxation of the muscles. Again, in the stooping position, the lower limbs are curved at the knee. In 97 this attitude, there is a constant tension of the muscles of the lower extremities, which produces muscular exhaustion.
198. Why will a person who stands erect walk further, and perform more labor, than if he assumed the stooping posture? 199. Why are the muscles of the back so soon exhausted in the stooping position?
Fig. 48. 1, A perpendicular line from the centre of the feet to the upper extremity of the spinal column, where the head rests. 2, 2, 2, The spinal column, with its three natural curves. Here the head and body are balanced upon the spinal column and joints of the lower extremities, so that the muscles are not kept in a state of tension. This erect position of the body and head is always accompanied with straight lower limbs.
Fig. 49. 1, A perpendicular line from the centre of the feet. 2, Represents the unnatural curved spinal column, and its relative position to the perpendicular, 1. The lower limbs are curved at the knee, and the body is stooping forward. While standing in this position, the muscles of the lower limbs and back are in continued tension, which exhausts and weakens them.
What is represented by figs. 48 and 49?
200. When it is necessary to call into action a part of the muscles of the system in the performance of any duty, as those of the lower limbs in walking, if the muscles of other parts are in a state of inaction, the influence of the nervous system can be determined in an undivided manner upon those parts of the lower limbs in action; hence they will not so soon become wearied or exhausted, as when this influence is divided between a greater number of muscles. In performing any labor, as in speaking, reading, singing, mowing, sewing, &c., there will be less exhaustion, and the effort can be longer maintained in the erect position of the body and head, than in a stooping attitude.
Experiment. Hold in each hand a pail of water or equal weights, in a stooping posture, as long as it can be done without much suffering and injury. Again, when the muscular pain has ceased, hold the same pails of water, for the same length of time, in an erect posture, and note the difference in the fatigue of the muscles.
201. If the stooping posture is acquired in youth, we are quite certain of seeing the deformed shoulders in old age. Hence the importance of duly exercising the muscles of the back, for when they are properly developed, the child can and will stand erect. In this attitude, the shoulders will be thrown back, and the chest will become broad and full.
202. Pupils, while standing during recitations, often inadvertently assume the attitude represented by fig. 49, and it is the duty of teachers to correct this position when assumed. When a child or adult has contracted a habit of stooping, and has become round-shouldered, it can be measurably, and generally, wholly, remedied by moderate and repeated efforts to bring the shoulders back, and the spinal column in an erect 99 position. This deformity can and should be remedied in our schools. It may take months to accomplish the desired end, yet it can be done as well under the direction of the kind instructor, as under the stern, military drill sergeant, who never fails to correct this deformity among his raw recruits.
200. What suggestion when it is necessary to call into action a part of the muscular system? Give the experiment that illustrates this principle. 201. Why should a child he taught to stand erect? 202. How can round shoulders acquired by habit be remedied?
Fig. 50.
Fig. 50. A proper position in sitting.
203. The child should be taught to sit erect when employed in study or work. This attitude favors a healthy action of the various organs of the system, and conduces to beauty and symmetry of form. Scholars are more or less inclined to lean forward and place the elbow on the table or desk, for support 100 and this is often done when their seats are provided with backs. Where there is a predisposition to curvature of the spine, no position is more unfavorable or more productive of deformities than this; for it is usually continued in one direction, and the apparent deformity it induces is a projection of the shoulders. If the girl is so feeble that she cannot sit erect, as represented by fig. 50, let her stand or recline on a couch; either is preferable to the position represented by fig. 51. In furnishing school-rooms, care should be taken that the desks are not so low as to compel the pupils to lean forward in examining their books.
203. Why should the erect attitude be assumed in sitting?
204. The muscles, when exhausted, cannot endure continued effort. When the energies of the muscular system have been expended by severe and long-continued exercise, or the brain and nervous system prostrated by protracted mental effort, the muscles are unfitted to maintain the body erect in standing or sitting for a long time, as the nervous system, in its exhausted state, cannot supply a sufficient amount of its peculiar influence to maintain the supporting muscles of the body and head in a state of contraction. Hence, a child or adult, when much fatigued, should not be compelled to stand or sit erect in one posture, but should be permitted to vary the position frequently, as this rests and recruits both the muscular and the nervous system.
205. A slight relaxation of the muscles tends to prevent their exhaustion. In walking, dancing, and most of the mechanical employments, there will be less fatigue, and the movements will be more graceful, when the muscles are slightly relaxed. When riding in cars or coaches, the system does not suffer so severely from the jar if there is a slight relaxation of the muscles, as when they are in a state of rigid contraction.
Experiments. Attempt to bow with the muscles of the limbs and trunk rigid, and there will be a stiff bending of the body only at the hip-joint. On the other hand, attempt to bow with the muscles moderately relaxed; the ankle, the knee, and the hip-joint will slightly bend, accompanied with an easy and graceful curve of the body.
206. The muscles when relaxed, together with the yielding character of the cartilage, and the porous structure of the ends of the bones that form a joint, diffuse or deaden the force of 102 jars, or shocks, in stepping suddenly down stairs, or in falling from moderate heights. Hence, in jumping or falling from a carriage, or any height, the shock to the organs of the system may be obviated in the three following ways: 1st. Let the muscles be relaxed, not rigid. 2d. Let the limbs be bent at the ankle, knee, and hips; the head should be thrown slightly forward, with the trunk a little stooping. 3d. Fall upon the toes, not the heel.
204. When are the muscles unfitted to maintain the system erect either in standing or sitting? What is necessary when this condition of the system exists? 205. Why should the muscular system be slightly relaxed in walking, &c.? Give illustrative experiments. 206. What is the reason that we do not feel the jar in falling from a moderate height?
Experiments. Stand with the trunk and lower limbs firm, and the muscles rigid; then jump a few inches perpendicularly to the floor, and fall upon the heels. Again, slightly bend the limbs, jump a few inches, and fall upon the toes, and the difference in the force of the shock, to the brain and other organs, will be readily noticed.
207. The muscles require to be educated, or trained. The power of giving different intonations in reading, speaking, singing, the varied and rapid executions in penmanship, and all mechanical or agricultural employments, depend, in a measure, upon the education of the muscles. In the first effort of muscular education, the contractions of the muscular fibres are irregular and feeble, as may be seen when the child begins to walk, or in the first efforts of penmanship.
208. Repetition of muscular action is necessary. To render the action of the muscles complete and effective, they must be called into action repeatedly and at proper intervals. This education must be continued until not only each muscle, but every fibre of the muscle, is fully under the control of the will. In this way persons become skilful in every employment. In training the muscles for effective action, it is very important that correct movements be adopted at the commencement. 103 If this is neglected, the motions will be constrained and improper, while power and skill will be lost.
How is this shown by experiment? 207. Upon what do the different intonations of sound or mechanical employments depend? Why are the first efforts in educating the muscles indifferent or irregular? 208. Why is repetition of muscular action necessary? Why is it important that correct movements be adopted in the first efforts of muscular education?
Illustration. If a boy, while learning to mow, is allowed to swing his scythe in a stooping position, twisting his body at every sweep of the scythe, he will never become an easy, efficient mower. Proper instruction is as necessary in many of the agricultural branches as in the varied mechanical employments.
Fig. 52.
Fig. 53.
Fig. 52. An improper, but not an unusual position, when writing.
Fig. 53. A proper position, when writing.
209. Good penmanship requires properly trained muscles. To a deficient analysis of the movements of the arm, hand, and fingers, on the part of teachers and pupils in penmanship, together with an improper position in sitting, is to be 104 ascribed the great want of success in acquiring this art. The pen should be held loosely, and when the proper position is attained, the scholar should make an effort to imitate some definite copy as nearly as possible. The movements of the fingers, hand, and arm, necessary to accomplish this, should be made with ease and rapidity, striving, at each effort, to imitate the copy more nearly.
How is this illustrated? 209. Why have so many pupils failed in acquiring good penmanship?
210. When the arm, hand, and fingers are rigid, the large muscles, that bend and extend these parts, are called into too intense action. This requires of the small muscles, that produce the lateral movements, which are essential to rapidity in writing, an effort which they cannot make, or can with difficulty accomplish.
Experiment. Vigorously extend the fingers by a violent and rigid contraction of the muscles upon the lower part of the arm, and the lateral movement which is seen in their separation cannot be made. But gently extend the fingers, and their oblique movements are made with freedom.
211. An individual who is acquainted with the laws of health, whose muscles are well trained, will perform a certain amount of labor with less fatigue and waste to the system, than one who is ignorant of the principles of hygiene, and whose muscles are imperfectly trained. Hence the laboring poor have a deep interest in acquiring a knowledge of practical physiology, as well as skill in their trade or vocation. It is emphatically true to those who earn their bread by the “sweat of their brow,” that “knowledge is power.”
210. What is said of the lateral and oblique movements of the arm, hand, and fingers in writing? How is this shown by experiment? 211. Why is the study of physiology and hygiene of utility to the laborer?
212. The teeth, in composition, nutrition, and growth, are different from other bones of the body. They vary in number at different periods of life, and, unlike other bones, they are exposed to the immediate action of atmospheric air and foreign substances. The bones of the system, generally, when fractured, unite; but there is never a permanent union of a tooth when broken.
213. The TEETH are attached to the upper and lower jaw-bone, by means of bony sockets, called al´ve-o-lar processes. These give great solidity to the attachment of the teeth, and frequently render their extraction difficult. The gums, by their fibrous, fleshy structure, serve to fix the teeth more firmly in the jaw.
Observation. When a permanent tooth is extracted, these bony processes are gradually absorbed, so that in advanced age there remains only the jaw-bone covered by the lining membrane of the gum. This accounts for the narrow jaw and falling in of the lips in old age. Frequently, a piece of the alveolar process comes out with the tooth when extracted, and the dentist has then the credit of “breaking the jaw.” 106 No great injury results from the removal of the process in this manner.
212. What is said of the teeth? In what respect do they differ from other bones of the body? 213–218. Give the anatomy of the teeth. 213. What confines the teeth in the jaw-bone? What becomes of the socket when a tooth is removed? What effect has this absorption upon the jaw and lips?
214. The teeth are formed in the interior of the jaws, and within dent´al cap´sules, (membranous pouches,) which are enclosed within the substance of the bone, and present in their interior a fleshy bud, or granule, from the surface of which exudes the ivory, or the bony part of the tooth. In proportion as the tooth is formed, it rises in the socket, which is developed simultaneously with the tooth, and passes through the gum, and shows itself without.
Fig. 54.
Fig. 54. 1, The body of the lower jaw. 2, Ramus, or branch of the jaw, to which the muscles that move it are attached. 3, 3, The processes which unite the lower jaw with the head. i, The middle and lateral incisor tooth of one side. b, The bicuspid teeth. c, The cuspids, or eye teeth. m, The three molar teeth. A, shows the relation of the permanent to the temporary teeth.
215. The first set, which appears in infancy, is called tem´po-ra-ry, or milk teeth. They are twenty in number; ten in each jaw. Between six and fourteen years of age, the temporary teeth are removed, and the second set appears, called per´ma-nent teeth. They number thirty-two, sixteen in each jaw.
214. Where and how are the teeth formed? Explain fig. 54. 215. What are the first set called? How many in each jaw? The second set? How many in number?
216. The four front teeth in each jaw are called in-ci´sors, (cutting teeth;) the next tooth in each side, the cus´pid, (eye tooth;) the next two, bi-cus´pids, (small grinders;) the next two, mo´lars, (grinders.) The last one on each side of the jaw is called a wisdom tooth, because it does not appear until a person is about twenty years old. The incisors, cuspids, and bicuspids, have each but one root. The molars of the upper jaw have three roots, while those of the lower jaw have but two.
Fig. 55.
Fig. 55. The permanent teeth of the upper and lower jaw. a, b, The incisors. c, The cuspids. d, e, The bicuspids. f, g, The molars, (double teeth.) h, The wisdom teeth.
Observation. The shape of the teeth in different species of animals is adapted to the kind of food on which they subsist. Those animals that feed exclusively on flesh, as the lion, have the cuspids, or canine teeth, largely developed, and the molars have sharp cutting points. Those animals that feed on grass and grain, as the horse and the sheep, have their molar teeth more rounded and flat on the crown. The human teeth are 108 adapted to feed on fruits, grain, or flesh, as they are less pointed than those of the cat, and more pointed than those of the sheep.
216. Give the names of the permanent teeth. What teeth have but one root, or “fang”? How many roots have the molars of the upper jaw? Of the lower jaw? What is said of the shape of the teeth in different species of animals?
217. The teeth are composed principally of two substances—the i´vo-ry and the en-am´el. The internal part of the tooth or the ivory, is harder and more enduring than bone, and forms the body of the tooth. The enamel is remarkable for its hardness, and varies somewhat in color with the age, temperament, habits, and manner of living of different individuals. When any part of the enamel is destroyed, it is never regenerated.
Fig. 56. A side view of the body and enamel of a front tooth.
Fig. 57. A side view of a molar tooth. 1, The enamel. 2, The body of the tooth. 3, The cavity in the crown of the tooth that contains the pulp. 4, A nerve that spreads in the pulp of the tooth. 5, An artery that ramifies in the pulp of the tooth.
218. Each tooth is divided into two parts, namely, crown and root. The crown is that part which protrudes from the jaw-bone and gum, and is covered by the highly polished enamel. The root, or “fang,” is placed in the sockets of the jaw, and consists of bony matter. Through this bony substance several small vessels pass, to aid in the growth and 109 also in the removal of the tooth. There are, beside these vessels, small white cords passing to each tooth, called nerves. (See fig. 57.) When these nerves are diseased, we have the toothache.
217. Give the structure of the teeth. What is said of the enamel? 218. Into how many parts are the teeth divided? Describe the crown. The root. What vessels pass through the bony matter? What is their use?
219. The use of the teeth is twofold. 1st. By the action of the incisors the food is divided, while the molars grind or break down the more solid portions of it. By these processes, the food is prepared to pass more easily and rapidly into the stomach.
220. In the mastication of food there are two movements of the lower jaw—the action by which the teeth are brought together, and the lateral motion. In the former, the food is cut or divided, the jaws acting like shears. This movement is produced by the action of two large muscles situated on each side of the head and face.
Observation. The muscles attached to the lower jaw are of great strength; by their action alone, some persons are enabled to bite the hardest substances. By putting the fingers upon the side of the head above and in front of the ears, and upon the face above the angle of the jaw, while masticating food, the alternate swelling and relaxation of these muscles will be clearly felt.
221. The lateral, or grinding movement of the teeth, is produced by the action of a strong muscle that is attached to the lower jaw on the inside.
Observation. Those animals that live solely on flesh, have only the cutting, or shear-like movement of the jaws. Those 110 that use vegetables for food, have the grinding motion; while man has both the cutting and grinding movement.
219–222. Give the physiology of the teeth. 219. Give one of the functions of the teeth. 220. How many movements of the lower jaw in masticating food? What effect has the first movement upon the food? How produced? What is the character of the masticating muscles? 221. How is the grinding motion of the teeth produced? What is said of the movements of the teeth in different animals?
222. 2d. The teeth aid us in articulating with distinctness certain letters and words. An individual who has lost his front teeth cannot enunciate distinctly certain letters called dental. Again, as the alveolar processes are removed by absorption soon after the removal of the teeth, the lips and cheeks do not retain their former full position, thus marring, in no slight degree, the symmetry of the lower part of the face. Consequently, those simple observances that tend to the preservation of the teeth are of great practical interest to all persons.
223. To preserve the teeth, they must be kept clean. After eating food, they should be cleansed with a brush and water, or rubbed with a piece of soft flannel, to prevent the tartar collecting, and to remove the pieces of food that may have lodged between them. Toothpicks may be useful in removing any particles inaccessible to the brush. They may be made of bone, ivory, or the common goose-quill. Metallic toothpicks should not be used, as they injure the enamel.
224. The mouth should be cleansed with pure tepid water at night, as well as in the morning; after which the teeth should be brushed upward and downward, both on the posterior and anterior surfaces. It may be beneficial to use refined soap, once or twice every week, to remove any corroding substance that may exist around the teeth; care being taken to thoroughly rinse the mouth after its use.
225. Food or drink should not be taken into the mouth when very hot or very cold. Sudden changes of temperature will crack the enamel, and finally produce decayed teeth.
222. What is another use of the teeth? 223–232. Give the hygiene of the teeth. 223. How can the teeth be preserved? By what means? 224. How often should they be cleansed? 225. What is said of very hot or cold drinks?
Observation. On this account, smoking is pernicious, because the teeth are subjected to an alternate inhalation of both cold and warm air.
226. The temporary teeth should be removed as soon as they become loose. If a permanent tooth makes it appearance before the first is removed, or has become loose, the milk tooth, although not loose, should be removed without delay. This is necessary that the second set of teeth may present a regular and beautiful appearance.
227. In general, when the permanent teeth are irregular, one or more should be removed. If the teeth are crowded and irregular, in consequence of the jaw being narrow and short, or when they press so hard upon each other as to injure the enamel, remove one or more to prevent their looking unsightly, and in a few months the remaining teeth, with a little care, will fill the spaces.
Observation. When it is necessary to remove a tooth, apply to some skilful operator. It requires as much skill and knowledge to extract teeth well, as it does to amputate a limb; yet some persons, who possess strong arms, will obtain a pair of forceps, or a tooth-key, and hang out the sign of “surgeon-dentist,” although ignorant of the principles that should guide them.
228. It is not always necessary to have teeth extracted when they ache. The nerve, or the investing membrane of the root, may be diseased, and the tooth still be sound. In such instances, the tooth should not be extracted, but the diseased condition may be remedied by proper medication. There are many sound teeth, that become painful, as already mentioned, which are unnecessarily removed.
Why is smoking injurious to the teeth? 226. What remark respecting the temporary teeth? 227. What remarks respecting the permanent teeth? Do those persons that extract teeth require skill as well as knowledge? 228. Why should not teeth be extracted at all times when they are painful?
Illustration. Dr. H. M., of Belfast, Me., related to me that an individual in that vicinity had his teeth, (all of them sound,) on one side of the lower jaw, extracted by an ignoramus of a “tooth-puller,” and this without any relief from pain. The disease was tic douloureux, which was relieved by Dr. M.
229. The preservation of the teeth requires that they be frequently examined. When a part of the enamel is removed, and a small portion of the body of the tooth has become carious, in many instances such teeth may be preserved from further decay by having them filled or “plugged” with gold foil. All amalgams, pastes, and cheap patent articles for filling, should be avoided, if you would preserve both the teeth and the general health.
230. The practice of cracking nuts with the teeth, or of lifting heavy bodies, and the constant habit of biting thread, should be avoided, as they finally destroy the enamel.
231. All acidulated drinks and mineral waters, that “set the teeth on edge,” are injurious. All tooth-powders and washes that contain any article that is acid, corrosive, or grinding, should be banished from the toilet. Tobacco is not a preservative of the teeth. It contains “grit,” which wears away the enamel; beside, when chewed, it debilitates the vessels of the gums, turns the teeth yellow, and renders the breath and the appearance of the mouth disagreeable.
232. Healthy persons have generally sound teeth, while feeble persons have decayed teeth. For this reason, we should try to learn and practise the few simple rules that promote health.
Give an illustration of the removal of sound teeth. 229. How may decaying teeth be preserved? What should be avoided in the filling of teeth? 230. What practices should also be avoided? 231. What is said of acidulated drinks? What effect has the chewing of tobacco upon the teeth? 232. What is one reason for preserving health?
233. From the earliest existence of the human system to the last ray of life, change is impressed upon it by the Giver of this curious fabric. New atoms of matter are deposited, while the old and now useless particles are constantly removed. The material necessary to sustain the growth of the body in early life, and also to repair the waste that is unceasing to animal existence, is the food we eat.
234. Food, animal or vegetable, contains most of the elements of the different tissues of the system, yet it must undergo certain essential alterations before it can become a part of the body. The first change is effected by the action of the Digestive Organs.
235. The DIGESTIVE ORGANS are the Mouth, Teeth,[7] Sal´i-va-ry Glands, Phar´ynx, Œ-soph´a-gus, (gullet,) Stom´ach, In-tes´tines, (bowels,) Lac´te-als, (milk, or chyle vessels,) Tho-rac´ic Duct, Liv´er, and the Pan´cre-as, (sweetbread.)
233. What is impressed upon the human system from its earliest existence? What maintains this change? 234. Has animal or vegetable food any resemblance to the different tissues of which it finally forms a part? By what organs is the first change in the food effected? 235–258. Give the anatomy of the digestive organs. 235. Name them. 236. Describe the mouth.
MOUTH is an irregular cavity, which contains the instruments of mastication and the organs of taste. It is 114 bounded in front by the lips; on each side by the internal surface of the cheeks; above, by the hard palate (roof of the mouth) and teeth of the upper jaw; below, by the tongue and teeth of the lower jaw; behind, it is continuous with the pharynx, but is separated from it by a kind of movable curtain, called the soft palate. This may be elevated or depressed, so as to close the passage or leave it free.
237. The SALIVARY GLANDS are six in number; three on each side of the jaw. They are called the pa-rot´id, the sub-max´il-la-ry and the sub-lin´gual.
Fig. 58.
Fig. 58. A view of the salivary glands in their proper situations. 1, The parotid gland. 2, Its duct. 3, The submaxillary gland. 4, Its duct. 5, The sublingual gland, brought to view by the removal of a section of the lower jaw.
238. The PAROTID GLAND, the largest, is situated in front of the external ear, and behind the angle of the jaw. A duct (Steno’s) from this gland opens into the mouth, opposite the second molar tooth of the upper jaw.
237. How many glands about the mouth? Give their names. What does fig. 58 represent? 238. Describe the parotid gland.
239. The SUBMAXILLARY GLAND is situated within the lower jaw, anterior to its angle. Its excretory duct (Wharton’s) opens into the mouth by the side of the fræ´num lin´guæ, (bridle of the tongue.)
240. The SUBLINGUAL GLAND is elongated and flattened, and situated beneath the mucous membrane of the floor of the mouth, on each side of the frænum linguæ. It has seven or eight small ducts, which open into the mouth by the side of the bridle of the tongue.
Observation. In the “mumps,” the parotid gland is diseased. The swelling under the tongue called the “frog” is a disease of the sublingual gland.
Fig. 59.
Fig. 59. A side view of the face, œsophagus, and trachea. 1, The trachea (wind pipe.) 2, The larynx. 3, The œsophagus. 4, 4, 4, The muscles of the upper portion of the œsophagus forming the pharynx. 5, The muscle of the cheek. 6, The muscle that surrounds, the mouth. 7, The muscle that forms the floor of the mouth.
239. The submaxillary. 240. The sublingual. What observation respecting these glands? What does fig. 59 represent?
241. The PHARYNX is a membranous sac, situated upon the 116 upper portion of the spinal column. It extends from the base of the skull to the top of the tra´che-a, (windpipe,) and is continuous with the œsophagus. From the pharynx are four passages; one opens upward and forward to the nose, the second leads forward to the mouth, the third downward to the trachea and lungs, the fourth downward and backward to the stomach.
242. The ŒSOPHAGUS is a large membranous tube that extends behind the trachea, the heart, and lungs, pierces the diaphragm, and terminates in the stomach. It is composed of two membranes—an internal, or mucous, and a muscular coat. The latter is composed of two sets of fibres; one extends lengthwise, the other is arranged in circular bands.
243. The STOMACH is situated in the left side of the abdomen, immediately below and in contact with the diaphragm. It has two openings; one connected with the œsophagus, called the car´di-ac orifice; the other connected with the upper portion of the small intestine, called the py-lor´ic orifice. It is composed of three coats, or membranes. The exterior or serous coat is very tough and strong, and invests every part of this important organ. The middle, or muscular coat is composed of two layers of muscular fibres, one set of which is arranged longitudinally, the other circularly. The interior coat is called the mucous, and is arranged in ru´gæ, (folds.) The stomach is provided with a multitude of small glands, in which is secreted the gastric fluid.
Illustration. The three coats of the stomach anatomically resemble tripe, which is a preparation of the largest stomach of the cow or ox. The outer coat is smooth and highly polished. The middle coat is composed of minute threads, which are 117 arranged in two layers. The fibres of these layers cross each other. The inner coat is soft, and presents many folds, usually named “the honey-comb.”
241. Describe the pharynx and the passages leading from it. 242. Give the structure of the œsophagus. 243. Where is the stomach situated? How many coats has it? Describe them. What article prepared for food does the stomach resemble?
Fig. 60.
Fig. 60. The inner surface of the stomach and duodenum. 1, The lower portion of the œsophagus. 2, The opening through which the food is passed into the stomach. 8, The stomach. 9, The opening through which the food passes out of the stomach into the duodenum, or upper portion of the small intestine. 10, 11, 14, The duodenum 12, 13, Ducts through which the bile and pancreatic fluid pass into it. a, b, c, The three coats of the stomach.
244. The INTESTINES, or alimentary canal, are divided into two parts—the small and large. The small intestine is about twenty-five feet in length, and is divided into three portions, namely, the Du-o-de´num, the Je-ju´num, and the Il´e-um. The large intestine is about five feet in length, and is divided into three parts, namely, the Cæ´cum, the Co´lon, and the Rec´tum. (Appendix D.)
245. The DUODENUM is somewhat larger than the rest of the small intestine, and has received its name from being in 118 length about the breadth of twelve fingers. It commences at the pylorus, and ascends obliquely backward to the under surface of the liver. It then descends perpendicularly in front of the right kidney, and passes transversely across the lower portion of the spinal column, behind the colon, and terminates in the jejunum. The ducts from the liver and pancreas open into the perpendicular portion, about six inches from the stomach.
244. Explain fig. 60. What is the length of the small intestine, and how is it divided? What is the length of the large intestine? Give its divisions. 245. Describe the duodenum.
246. The JEJUNUM is continuous with the duodenum. It is thicker than the rest of the small intestine, and has a pinkish tinge.
247. The ILEUM is smaller, and thinner in texture, and somewhat paler, than the jejunum. There is no mark to distinguish the termination of the one or the commencement of the other. The ileum terminates near the right haunch-bone, by a valvular opening into the colon at an obtuse angle. This arrangement prevents the passing of substances from the colon into the ileum. The jejunum and ileum are surrounded above and at the sides by the colon.
248. The small intestine, like the stomach, has three coats. The inner, or mucous coat is thrown into folds, or valves. In consequence of this valvular arrangement, the mucous membrane is more extensive than the other tissues, and gives a greater extent of surface with which the aliment comes in contact. There are imbedded under this membrane an immense number of minute glands, and it has a great number of piles, like those upon velvet. For this reason, this membrane is sometimes called the vil´lous coat.
249. The CÆCUM is the blind pouch, or cul-de-sac, at the commencement of the large intestine. Attached to its extremity is the ap-pend´ix verm-i-form´is, (a long, worm-shaped 119 tube.) It is from one to six inches in length, and of the size of a goose-quill.
What important ducts open into it? 246. Describe the jejunum. 247. The ileum. 248. What is said of the coats of the intestines? Why is the mucous membrane sometimes called the villous coat? 249. Describe the cæcum.
250. The COLON is divided into three parts—the ascending, transverse, and descending. The ascending colon passes upward from the right haunch-bone to the under surface of the liver. It then bends inward, and crosses the upper part of the abdomen, below the liver and stomach, to the left side under the name of the transverse colon. At the left side, it turns, and descends to the left haunch-bone, and is called the descending colon. Here it makes a peculiar curve upon itself, which is called the sig´moid flex´ure.
Fig. 61.
Fig. 61. 1, 1, The duodenum. 2, 2, The small intestine. 3, The junction of the small intestine with the colon. 4, The appendix vermiformis. 5, The cæcum. 6, The ascending colon. 7, The transverse colon. 8, The descending colon. 9, The sigmoid flexure of the colon. 10, The rectum.
250. Describe the course of the divisions of the colon. Explain fig. 61.
251. The RECTUM is the termination of the large intestine. The large intestine has three coats, like the stomach and small intestine. The longitudinal fibres of the muscular coat are collected into three bands. These bands are nearly one half shorter than the intestine, and give it a sacculated appearance, which is characteristic of the cæcum and colon.
252. The LACTEALS are minute vessels, which commence in the villi, upon the mucous surface of the small intestine. From the intestine they pass between the membranes of the mes´en-ter-y to small glands, which they enter. The first range of glands collects many small vessels, and transmits a few larger branches to a second range of glands; and, finally, after passing through several successive ranges of these glandular bodies, the lacteals, diminished in number and increased in size, proceed to the enlarged portion of the thoracic duct, into which they open. They are most numerous in the upper portion of the small intestine.
253. The THORACIC DUCT commences in the abdomen, by a considerable dilatation, which is situated in front of the lower portion of the spinal column. From this point, it passes through the diaphragm, and ascends to the lower part of the neck. In its ascent, it lies anterior to the spine, and by the side of the aorta and œsophagus. At the lower part of the neck, it makes a sudden turn downward and forward, and terminates by opening into a large vein which passes to the heart. The thoracic duct is equal in diameter to a goose-quill, and, at its termination, is provided with a pair of semilunar valves, which prevent the admission of venous blood into its cylinder.
251. What is said of the arrangement of the fibres of the muscular coat of the large intestine? 252. What are the lacteals? Give their course from the mucous coat of the intestine to the thoracic duct. 253. Describe the course of the thoracic duct. How is the venous blood prevented from passing into this duct?