GLANDS OF THE SMALL INTESTIKTE. 363 



tides, and the central lacteal becomes filled ■with them. According to 

 our own observations, the amoeboid lymph-corpuscles contained in the 

 meshes of the retiform tissue, and which also extend amongst the 

 columnar epithelium cells of the surface, become filled with fat globules 

 during digestion : and we think it probable that these cells may serve 

 as carriers of fatty matters into the lacteal, just as the white blood- 

 corpuscles are known to convey minute solid particles out of the blood 

 vessels and into the lymphatics. Other authorities are of opinion that 

 the fat is conveyed into the lacteal through the branched cells of the 

 retiform tissue. 



With reference to the presence of fat in the epithelium-cells of the intestine, 

 it must be borne in mind that, as pointed out by Vu'chow, the columnar epithe- 

 limn of other parts, the bile-ducts and gall-bladder, for example, also becomes 

 filled with fatty particles during digestion (although at a somewhat later stage) ; 

 and in these cases the fat cannot have entered the cells by a jirocess of dkect 

 absorjition, but must have been elaborated and deposited within the cells them- 

 selves, probably serving for their nutrition. 



The muscular tissue within the villus was discovered by Brilcke: it 

 consists of a thin stratum of plain fibre-cells disposed longitudinally 

 around the lacteal ; on being stimulated in animals, they produce au 

 obvious retraction of the villus. 



This muscular tissue is a prolongation from the muscularis mucosas : the fibre- 

 cells at the sides and towards the end of the villus pass from the lacteal to be 

 attached to the basement membrane ; usually tlieii' attachment to this is forked, 

 a connective tissue corpuscle filling up the interval (AVatney).* 



Two kinds of small secreting glands open on the inner surface of the 

 intestine, viz., the crypts of Lieberkiihn, and Brunner's glands, the 

 last being peculiar to the duodenum. In addition to these, numerous 

 lymphoid nodules are found, which are cither scattered and isolated 

 (solitary glands) or collected into patches (Peyer's glands). 



The crypts of Lieberkuhn, the smallest but most numerous of these 

 glandular structures, are found in every part of the small intestine, 

 opening between the villi (fig. 257, g). They consist of minute tubes, 

 closed at theii- attached extremity, and placed more or less perpendi- 

 cularly to the surface, upon which they open. They appear to be 

 analogous to the tubuli of the stomach, but are not so thickly set, and 

 are hardly ever divided. Similar tubules also occur throughout the 

 whole mucous membrane of the large intestine. The crypts of Lieber- 

 kiihn vary in length from the .>jyi\\ to the -J^th of a line, and their 

 diameter is about -^-^ih. of a line. The walls of the tubes are thin, 

 formed of the l^ascmcnt membrane, lined with a columnar epithelium 

 (fig. 259), whicli, as elsewhere, possesses the thickened border. 



Brunner's glands are small rounded compound glands, first pointed 

 out by Brunner, which exist in the duodenum, where they are most 

 numerous at the upper end, in general occupying thickly a space ex- 

 tending a little way from the pylorus. A few of them are said also to 

 be found quite at the commencement of the jejunum. They are im- 

 bedded in the submucous coat, and may be exposed by dissecting off the 

 muscular coat from the outside of the intestine. In structure they 

 resemble the small glands wliich are found in various parts of the 

 lining membrane of the mouth and elsewhere, each consisting of a 



* Proceedings of the Royal Society, No. 152, 1874, and Centralblatt, f. d. med. Wiss. 

 48, 1874, where also will be found other facts having reference to the structm'e of the 

 villi and the absorjjtion of fat. 



