skct. 152] VILLI OF THE SMALL INTESTINE. 325 



follicles, the so-called solitary and Peyerian glands, and, in the 

 submucous tissue of the duodenum, the glands of Brunner. 



The mucous membrane consists of a more homogeneous or 

 indistinctly fibrous areolar tissue (especially at the innermost part) 

 and possesses, except where certain glands are situated, but little 

 submucous tissue, on which account it is pretty firmly connected 

 with the muscular coat. Upon the inner surface of the mucous 

 membrane there is a cylindrical epithelium, of which we shall 

 speak further/when treating of the villi; whilst externally, towards 

 the submucous tissue, the membrane is limited by a layer of longi- 

 tudinally and transversely arranged smooth muscular fibres, dis- 

 covered by Brucke, which, measures at the most 0*017 7"' in 

 thickness, and on account of its being often but slightly developed, 

 is not always readily recognisable in man. 



§ 152. The villi of the small intestines (villi intestinales) are 

 small -whitish elevations of the innermost parts of the mucous 

 membrane, visible to the naked eye, which, seated upon or between 

 the folds of Kerkring, are so closely arranged throughout the whole 

 small intestine, from the pylorus to the sharp border of the 

 valvula Baultiui, as to give the mucous membrane its well-known 

 velvet-like appearance. They are most numerous (50 to 90 in a 

 square line) in the duodenum and jejunum, less frequent in the 

 ileum (40 to 70 in a square line). In the duodenum they are 

 lower and broader, like folds and laminae, and measure ^"' to J"' 

 in height, J'" to ^'", or even g"' in breadth. In the jejunum, they 

 mostly appear conical but compressed, frequently, also, leaf-shaped 

 or cylindrical, clavate or filiform, which three last- mentioned forms 

 preponderate in that part of the intestine. The length of these 

 villi is from V" to £'" '; the breadth, \'" to -J/', or even J/'j the 

 thickness in the fiat ones, -£>$". 



The villi consist of an interior part, belonging to the mucous mem- 

 brane, and an epithelial investment. The former, or the villus, in 

 the stricter sense of the term, corresponds in its contour to the 

 whole villus, and consists merely of a solid process of the proper 

 mucous membrane, provided with blood-vessels and lymphatics and 

 smooth muscles. Its matrix, beset with a variable number of 

 I roundish nuclei and cells, like that of the mucous membrane 

 in general, is a more homogeneous, seldom a fibrillated areolar 

 tissue, without any intermixture of elastic fibres, but mostly 

 containing numerous small round cells as well as free nuclei, 



