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 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 pa.s.sage or leave it free.

237. The SALIVARY GLANDS are six in number; three on each side of the jaw. They are called the _pa-rotid_, the _sub-maxil-la-ry_ and the _sub-lingual_.

[Ill.u.s.tration: 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 _frnum lingu_, (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 frnum lingu. 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.

[Ill.u.s.tration: Fig. 59. A side view of the face, oesophagus, and trachea.

1, The trachea (wind pipe.) 2, The larynx. 3, The oesophagus. 4, 4, 4, The muscles of the upper portion of the oesophagus 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 upper portion of the spinal column. It extends from the base of the skull to the top of the _trache-a_, (windpipe,) and is continuous with the oesophagus.

From the pharynx are four pa.s.sages; 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 OESOPHAGUS 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 oesophagus, called the _cardi-ac_ orifice; the other connected with the upper portion of the small intestine, called the _py-loric_ 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 _rug_, (folds.) The stomach is provided with a mult.i.tude of small glands, in which is secreted the gastric fluid.

_Ill.u.s.tration._ 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 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 pa.s.sages leading from it. 242. Give the structure of the oesophagus. 243. Where is the stomach situated?

How many coats has it? Describe them. What article prepared for food does the stomach resemble?

[Ill.u.s.tration: Fig. 60. The inner surface of the stomach and duodenum. 1, The lower portion of the oesophagus. 2, The opening through which the food is pa.s.sed into the stomach. 8, The stomach. 9, The opening through which the food pa.s.ses 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 pa.s.s into it. _a_, _b_, _c_, The three coats of the stomach.]

244. The INTESTINES, or alimentary ca.n.a.l, 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-denum_, the _Je-junum_, and the _Ile-um_. The large intestine is about five feet in length, and is divided into three parts, namely, the _Cc.u.m_, the _Colon_, and the _r.e.c.t.u.m_.

(Appendix D.)

245. The DUODENUM is somewhat larger than the rest of the small intestine, and has received its name from being in 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 pa.s.ses 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 pa.s.sing 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 _villous_ coat.

249. The Cc.u.m is the blind pouch, or cul-de-sac, at the commencement of the large intestine. Attached to its extremity is the _ap-pendix verm-i-formis_, (a long, worm-shaped 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 cc.u.m.

250. The COLON is divided into three parts--the _ascending_, _transverse_, and _descending_. The ascending colon pa.s.ses 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 _sigmoid flexure_.

[Ill.u.s.tration: 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 cc.u.m. 6, The ascending colon. 7, The transverse colon. 8, The descending colon. 9, The sigmoid flexure of the colon. 10, The r.e.c.t.u.m.]

250. Describe the course of the divisions of the colon. Explain fig.

61.

251. The r.e.c.t.u.m 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 cc.u.m 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 pa.s.s between the membranes of the _mesen-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 pa.s.sing 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 pa.s.ses 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 oesophagus. At the lower part of the neck, it makes a sudden turn downward and forward, and terminates by opening into a large vein which pa.s.ses 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.