Part 17 (1/2)

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 pa.s.sing into this duct?

[Ill.u.s.tration: Fig. 62. A portion of the small intestine, lacteal vessels, mesenteric glands, and thoracic duct. 1, The intestine. 2, 3, 4, Mesenteric glands, through which the lacteals pa.s.s to the thoracic duct.

5, 6, The thoracic duct. 7, The point in the neck where it turns down to enter the vein at 8. 9, 10, The aorta. 11, 12, Vessels of the neck. 13, 14, 15, The large veins that convey the blood and chyle to the heart. 16, 17, The spinal column. 18, The diaphragm, (midriff.)]

Explain fig. 62. What is said respecting the mesenteric glands?

_Observation._ The mesenteric glands, which are situated between two layers of serous membrane (mesentery) that connects the small intestine with the spinal column, occasionally become diseased in childhood, and prevent the chyle from pa.s.sing to the thoracic duct.

Children thus affected have a voracious appet.i.te, and at the same time are becoming more and more emaciated. The disease is called mesenteric consumption.

254. The LIVER, a gland appended to the alimentary ca.n.a.l, is the largest organ in the system, and weighs about four pounds. It is situated in the right side, below the diaphragm, and is composed of several lobes. Its upper surface is convex; its under, concave. This organ is retained in its place by several ligaments. It performs the double office of separating impurities from the venous blood, and of secreting a fluid (bile) necessary to chylification. On the under surface of the liver is a membranous sac, called the _gall-cyst_, which is generally considered as a reservoir for the bile.

[Ill.u.s.tration: Fig. 63. The under surface of the liver. 1, The right lobe. 2, The left. 3, 4, Smaller lobes. 10, The gall-bladder, or cyst, lodged in its depression. 17, The notch on the posterior border, for the spinal column.]

_Observation._ A good idea of the liver and intestines can be obtained by examining these parts of a pig. In this animal, the sacs, or pouches, of the large intestine are well defined.

255. The PANCREAS is a long, flattened gland, a.n.a.logous to the salivary glands. It is about six inches in length, weighs three or four ounces, and is situated transversely across the posterior wall of the abdomen, behind the stomach. A duct from this organ opens into the duodenum.

254. Describe the liver. 255. What is said of the pancreas?

256. The SPLEEN, (milt,) so called because the ancients supposed it to be the seat of melancholy, is an oblong, flattened organ, situated in the left side, in contact with the diaphragm, stomach, and the pancreas. It is of a dark, bluish color, and is abundantly supplied with blood, but has no duct which serves as an outlet for any secretion. Its use is not well determined.

[Ill.u.s.tration: Fig. 64. The pancreas with its duct, through which the pancreatic secretion pa.s.ses into the duodenum.]

257. The OMENTUM (caul) consists of four layers of the serous membrane, which descends from the stomach and transverse colon. A quant.i.ty of adipose matter is deposited around its vessels, which ramify through its structure. Its function is twofold in the animal economy. 1st. It protects the intestines from cold. 2d. It facilitates the movements of the intestines upon each other during their vermicular, or worm-like action.

258. Every part of the digestive apparatus is supplied with arteries, veins, lymphatics, and nervous filaments, from the ganglionic system of nerves.

256. Why is the spleen so called? What is peculiar to this organ? 257.

Of what is the omentum composed? What is its use? 258. With what is every part of the digestive apparatus supplied?

CHAPTER XIV.

PHYSIOLOGY OF THE DIGESTIVE ORGANS.