the body of the stomach. They rest upon the muscularis mucosa, and are simple tubular glands, often branched. They contain two distinct kinds of cells-the chief or central cells which, small and prismatic, line the principal part of the tubule and secrete pepsin; and the parietal or acid cells, which occur at irregular intervals along the membrana propria and outside of the chief cells. The parietal cells appear to secrete the acids of the gastric juice. (3) The pyloric glands, occurring in the pyloric part of the stomach, and distinguished from the preceding by numerous turns and divisions of the tubules and by entire absence of the parietal cells. In addition, the mucous membrane of the stomach contains closed follicles similar in structure to that of the solitary follicles of the intestine.

In

The mucous membrane of the intestine presents numerous elevations, the intestinal villi,- which consist of a prolongation of the tunica propria, smooth musclefibers, a capillary network with small meshes, and also, as a rule, one, or rarely several, central chyle vessels. the duodenum the villi are broad and leaf-like. Two kinds of epithelium cover the villi-the epithelial cells proper, of cylindric form and provided with a distinct cuticular border on their free surface, the nucleus lying in the inferior half of the cells; between these occur the second kind of cells, the goblet cells.

The glands of the small intestine are formed by the simple tubular depressions, or Lieberkühn's crypts, between the villi, and they are lined with cylindric cells and goblet cells. Between the epithelial cells of the villi and of the crypts migratory leukocytes are found in varying numbers.

In the duodenum there occur also branched tubular glands of Brunner, which pierce the muscularis mucosa, and are lined with darkly granular, cylindric cells.

The large intestine is devoid of villi; the crypts of Lieberkühn are larger and contain numerous goblet cells.

The commonest change of the thyroid is an increase in volume, called goiter or struma, which may depend on various histologic processes. From embryonal remnants of epithelial cells, which are not arranged as tubules, there may develop solid columns and loops the ends of which are expanded, but in which the amount of colloid usually is slight. This is generally called adenoma of the thyroid, or parenchymatous goiter. At other times the preexisting tubules increase both in length and breadth at the same time as the amount of colloid greatly increases. This is known as colloid goiter.

The colloid material is secreted by the cells, which may also change directly into colloid material; in that case there appear in the cells small, glistening drops of colloid substance which gradually coalesce to form larger masses, crowding the nucleus and obscuring the cell outline. When such changes occur over a considerable part of an acinus, the colloid material lies in direct contact with the connective tissue. Desquamated epithelial cells, or fragments of such, are often found in the colloid material. If the epithelial cells do not degenerate, the constantly increasing mass of colloid flattens the cells more and more. The colloid contents of the lymph-vessels are also often much increased. The great dilatation of adjacent follicles may lead to their confluence with lymph-vessels, whereby larger cystic spaces filled with colloid material are produced (cystic goiter). Hemorrhages may render the contents rusty red or brownish in color, and mixed with blood pigment (hemorrhagic goiter). The surrounding stroma often proliferates, sometimes in the form of papillary ingrowths into the follicular spaces, the epithelium of which is lifted up and carried inward.

Among the frequent degenerative changes in the fibrous tissue of a goiter may be mentioned hyaline changes, which are among the more common. Broad, glistening, homogeneous bands without nuclei are then formed between

the gland spaces; the hyaline changes frequently occur in an extensive degree in the walls of the blood-vessels, whose lumen often appears greatly narrowed.

Calcareous salts are frequently deposited in goiters, so that very hard and extensive calcification results (calcareous goiter). Goiter is also accompanied with telangiectatic dilatations of the blood-vessels, leading to formal cavernous spaces (vascular goiter).

Carcinoma is the most frequent tumor in the thyroid gland; sarcoma is more rare, and osteosarcoma sometimes

occurs.

III. THE DIGESTIVE ORGANS.

The oral cavity is lined by a mucous membrane composed of a squamous, stratified epithelium and tunica propria. The latter rises up into papillæ of varying heights, some being very high. The basal layer of the epithelium is cylindric, then comes the stratum Malpighii with its prickle cells, which become flatter and flatter toward the surface. The tunica propria, which is composed of connective tissue, elastic fibers, and fine vessels, contains lymphocytes, scattered either diffusely or accumulated in follicular masses. Below, the tunica propria merges gradually into the submucous coat, which contains the glands. The glands are compound, tubulo-acinous, mucous glands; the ducts, lined principally with flat cells, empty upon the surface of the mucous membrane; not infrequently, small accessory glands empty into the main ducts. In several places occur striped muscles under the oral mucosa.

The bulk of the tongue consists of striated muscles, the bundles of which interlace in various directions. A median septum divides the muscular mass into a right and a left half. The musculature is surrounded by a submucous coat, which contains numerous mucous and serous glands, some of which extend into the muscles. The papillæ, formed by the tunica propria, are more or less complicated. In man four general types are distinguished: (1) The filiform papillæ, which are cylindric elevations with numerous dichotomous branches at the free end; (2) the fungiform papillæ, situated on a broad base and covered by numerous secondary papilla; (3) the circumvallate papillæ, especially large