THE INTESTINES. 



95 



Fig. 210. 



be different in the broad and foliaceons forms (see Mikr. 



Anat., ii, 2, p. 160). 



In addition to these organs, the villi also contain, as Briicke 



discovered a short time ago, a 



thin layer of longitudinal smooth 



muscles situated more centrally 



round the lacteals; these, however, 



are not always distinct in man. 



They produce contractions of the 



villi (fig. 210), which are very 



evident immediately after death, 



and which, according to Briicke, 



are also perceptible in the liv- 

 ing animal. They have, in all 



probability, an important influ- 

 ence over the propulsion of the 



chyle and of the venous blood 



in the villi — always supposing that there is no objection to 



the assumption that they perform repeated contractions during 



life. Nothing is known of nerves in the villi. 



The epithelium of the villi and of the rest of the surface of 



the mucous membrane, although it is very intimately united 



with the deeper-seated parts during life, only becoming de- 

 tached accidentally or by disease, separates very readily in 

 the dead subject, and can only be observed in perfectly fresh 

 portions of intestine. It consists everywhere of a simple layer 

 of cylindrical cells slightly narrowed below, of 001 — 0*01 2'" in 

 length and 0003 — 0-004'" in breadth, whose contents are 

 usually nothing but fine granules and an oval, clear, vesicular 

 nucleus, provided with one or two nucleoli. During life, these 

 cells, which agree in all their chemical characters with the 

 deeper cells of the oral epithelium, are so intimately united, 

 that even after death their contours, in a longitudinal view, are 

 at first either not at all, or only indistinctly distinguishable, 

 though on the surface they have the appearance of a beautiful 

 mosaic. The cylinders only become quite distinct when they 

 are either spontaneously or artificially detached, a process 

 which usually takes place in such a manner that they hang 

 together in continuous portions, all the cells covering a villus 

 Fig. 210. Two intestinal villi of the Cat, contracted, x 60. 



