604 THE DIGESTIVE TRACT. 



cylindrical in shape ; while, where the muscle is extended, the villi 

 are seen as conical or blunt elevations. The villi corresponding 

 to the place of attachment of the mesentery are always the 

 smallest, those on the opposite surface the largest. The lobate 

 form of the short conical villi is due to the contraction of the 

 bundles of smooth muscle-fibers contained in the myxomatous 

 stroma of the villus, as first intimated by Briicke. In 1868 I con- 

 cluded, therefore, that the shape of the villi of the intestine is not 

 fixed, but varies between that of a cylinder and that of a cone, 

 depending on the contraction or extension of the intestinal tube, 

 the peristaltic motion thus producing a continuous change. I also 

 concluded that the muscle-layers of the intestine proper are 

 antagonistic in their action to the muscle-layers of the mucosa ; 

 in other words, when the muscle of the intestine is in the highest 

 degree of contraction, the muscles of the villi, being prolongations 

 of the muscle of the mucosa, are extended, and vice versa. An 

 extended villus has a smooth surface ; the lobation begins as the 

 villus changes its shape from the cylindrical to the conical. In 

 the extended condition of the villi, i. e., when the muscle of the 

 intestine is contracted, the presumed openings at the apices of the 

 villi are gaping and ready to absorb the fat which is present as an 

 emulsion in the considerably narrowed caliber of the intestine, 

 and reduced to extremely small granules, perhaps, by the me- 

 chanical action of the rods of the basal seam of the epithelia. As 

 soon as the contraction of the muscle of the intestine ceases, the 

 contraction of the muscle of the mucosa sets in, the villi become 

 retracted, and the openings at their apices closed. By this proc- 

 ess the absorbed fat will be carried backward into the lymphatic 

 or chyliferous system. Probably there is also an antagonism 

 between the circular and longitudinal layers, both of the mucosa 

 and the intestine. 



The mucosa of the intestine immediately above the muscle 

 is abundantly supplied with lymph (so-called adenoid) tissue, 

 which produces a continuous layer and is accumulated in the 

 solitary follicles and in groups of the aggregated follicles the 

 so-called Peyer's patches. B. Briicke first drew attention to the 

 lymphatic nature of these formations. The solitary follicles 

 appear to the naked eye as flattened protrusions above the level 

 of the mucosa, or as bare spots, or even as shallow depressions. 

 The columnar epithelium covering the surface of the follicle is 

 shorter than the epithelium covering the villi. Villi are wanting 

 in those parts of the mucosa which are furnished with solitary 



