108 SPECIAL HISTOLOGY. 



0*006 — 0*0]'", which is sometimes single, sometimes, especially 

 in the neighbourhood 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 lym- 

 phatics or the nerves in the mucous membrane. The epithe- 

 lium is precisely similar to that of the small intestine, and, at 

 the anus, is separated by a pretty sharp line of demarcation, 

 from the external epidermis. 



§ 157. 



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

 intestine, various as its different structures may afterwards be- 

 come, proceeds 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 membrane, 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 intes- 

 tine, 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 nothing but cells and becomes metamorphosed by their 

 continual multiplication, superficially and perpendicular^, 

 which, according to Remak, takes place by division, in the first 

 place, into the future epithelia ; and in the second, into the 

 glands of the intestine. Of the latter, the Lieberkuhnian 

 follicles are from the first, hollow diverticula of the epithe- 

 lium, 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 diverticula or as solid 

 processes is not yet made out— and form at the commencement 

 a layer completely separated from the fibrous lamina of the 

 intestine j whence, also, the epithelium in their neighbourhood 



