526 SPECIAL HISTOLOGY. 



times single, sometimes, especially in the neighborhood of the solitary 

 follicles, multiple. 



From these vessels wider venous trunks arise and penetrate deeply 

 between the glands, which are themselves surrounded by a dense network 

 of fine capillaries derived immediately from the arteries (Fig. 205). 

 Nothing is known of either the lymphatics or the nerves in the mucous 

 membrane. The epithelium is precisely similar to that of the small 

 intestine, and, at the anus, is separated by a pretty sharp line of demar- 

 cation, from the external epidermis. 



157. Development of the intestinal canal. The entire wall of the 

 intestine, various as its different structures may afterwards become, pro- 

 ceeds from two points of development: viz. in the first place from the 

 inferior lamina of the germinal membrane (mucous layer of Pander and 

 Baer; mucous tunic, Reichert; glandular layer or intestinal glandular 

 layer, of Remak), which is not the foundation of the whole mucous mem- 

 brane, but only of the intestinal epithelium and of the intestinal glands ; 

 and 2, from the middle layer of the germinal membrane (vascular lamina, 

 Pander, membrana intermedia, Reichert), which gives rise, in addition 

 to many other parts (muscles, bones, nerves, heart), to the vascular and 

 nervous fibrous coats of the intestine, as well as to the vessels, nerves, 

 and coats of the intestinal glands. 



The inner layer or the epithelial tube consists from first to last of no- 

 thing but cells and becomes metamorphosed by their continual multipli- 

 cation, superficially and perpendicularly, which, according -to Remak, 

 takes place by division, in the first place, into the future epitlielia ; and in 

 the second, into the glands of the intestine. Of the latter, the Lieber- 

 kiihnian follicles are from the first, hollow diverticula of the epithelium, 

 whilst the salivary and Brunner's glands arise, like the sudoriparous 

 glands, as solid processes, which only subsequently acquire cavities and 

 become branched. The gastric glands and those of the large intestine 

 also certainly arise from the primitive epithelial tube whether as diver- 

 ticula or as solid processes is not yet made out and form at the com- 

 mencement a layer completely separated from the fibrous lamina of the 

 intestine; whence, also, the epithelium in their neighborhood appears 

 much thicker than it subsequently is. At a later period, delicate vas- 

 cular processes grow from the fibrous layer between the glands, until at 

 length both layers, intimately united, constitute the proper mucous mem- 

 brane. Similar and more considerable processes of the fibrous layer 

 form the villi, whilst the muscular and serous tissues are developed from 

 its external portion. 



The examination of the intestinal mucous membrane presents greater 

 difficulties than that of other parts. The epithelium is usually in a good 



