1024 



THE ORGANS OF DIGESTION. 



in the axis of the villi, they commence by dilated caecal extremities near to, but 

 not quite at, the summit of the villus. The walls are composed of a single layer 

 of endothelial cells, the interstitial substance between the cells being continuous 

 with the reticulum of the matrix. 



The muscular fibres are derived from the muscularis mucosse, and are arranged 

 in bundles around the lacteal vessel, extending from the base to the summit of the 

 villus, and giving off laterally, individual muscle-cells, which are enclosed by the 

 reticulum, and by it are attached to the basement membrane. 



The blood-vessels form a plexus between the lacteal and the basement mem- 

 brane, and are enclosed in the reticular tissue ; in the interstices of the capillary 

 plexus, which they form, are contained the cells of the villus. 



These structures are surrounded by the basement membrane, which is made 

 up of a stratum of endothelial cells, and upon which is placed a layer of columnar 

 epithelium. The reticulum of the matrix is continuous through the basement 

 membrane (that is, through the interstitial substance between the individual 

 endothelial cells) with the interstitial cement substance of the columnar cells on 

 the surface of the villus. Thus we are enabled to trace a direct continuity between 

 the interior of the lacteal and the surface of the villus by means of the reticular 

 tissue, and it is along this path that, according to Dr. Watney, the chyle passes 

 in the process of absorption by the villi. That is to say, it passes through the 

 interstitial substance between the epithelium cells, through the interstitial sub- 

 stance of the basement membrane, the reticulum of the matrix, and the interstitial 

 substance between the endothelial plates of the lacteal, all which structures have 

 been shown to be continuous with one another, and, being probably semifluid, do 

 not offer any obstacle to the passage of the molecular basis of the chyle. 



Among the structures of the intestinal wall called glands there are two kinds 

 true and false ; the latter belong to the lymphatic system. The true glands 

 are those of Lieberkiihn and Brunner. 



The follicles, crypts, or glands of Lieberkiihn (Figs. 643 and 644) are very 

 numerous, forming an almost continuous layer of tubu- 

 lar depressions throughout the intestines, large and 

 small. They are in every part of the small intestine, 

 opening between the villi (Figs. 640 and 642). Their 

 small circular mouths may be seen by the aid of a 

 lens. They occupy nearly the whole depth of the 

 mucosa, are upon the valvulse conniventes, their blind 

 ends approaching nearly perpendicularly the muscu- 

 laris mucosse. They consist of thin tubes, Avhose 

 walls are made of basement membrane, lined by the 

 columnar epithelium from the free surface. Many 

 of these cells change to spherical secreting cells, some 

 of which become goblet-cells (Fig. 644). They are 

 2 to 3 mm. long and about .04 mm. in diameter. 



FIG. 643. Transverse section 

 of crypts of Lieberkiihn. (Klein 

 and Noble Smith.) 



FIG. 644. Longitudinal section of crypts of Lieberkiihn. Goblet-cells seen among the columnar epithelial 

 cells. (Klein and Noble Smith.) 



The duodenal or Brunner's glands are limited to the duodenum and first part 

 of the jejunum. They are most numerous in the first part of the duodenum, 

 within one or two inches of the pylorus. They are small compound tubular glands, 

 consisting of a number of tubular alveoli opening into a slender duct, much like 



