56 



PHYSIOLOGY. 



Fi^. 12. 



sively in the absorption v,^ nuirUious materials ; other articles find- 

 ing their way into the circulation through the veins. ' The iacteals 

 commence in the villi of the mucous Hning of the intestinal tube, 

 below the point where the ductus communis choledochus and pan- 

 creatic duct open into the duodenum. Each lacteal tube commences 

 in a single villus, by a closed extremity^ and the trunk that issues 

 from each villus is formed by the confluence of several smaller 

 branches which anastamose freely with each other, forming /oc»/?5 , 

 so' that there is no proper free extremity in any 

 case, nor do the Iacteals ever commence by open 

 orifices wpon the surface of the intestinal canal. 

 (Fig. 12.) 



These loops are imbedded in a mass of cells 

 at the extremity of each villus which select the 

 nutritive elements from the materials of the 

 intestinal canal and when full, yield their con- 

 tents to the absorbent vessels either by burst- 

 ing, or deliquescence. Their place is then sup- 

 plied by fresh cells, and the process is continued 

 so long as there is any nutritive material pre- 

 sent. After this the villi, which were then 

 turgid, become flaccid, and the epithelium, which was removed dur- 

 ing the process of absorption, is again renewed, and the lacteal ves- 

 sels become the lymphatics of the intestinal canal, to effect its inter- 

 stitial absorption. (Fig. 13.) 



* Fig. 13. t 



The villi are also abundantly supplied with blood-vessels, which 

 are supposed to aflx)rd the materials for the development of the cells, 



* Diagram of mucous membrane during digestion and absorption of chyle ; a, a villus, 

 turgid and erect ; its protective epithelium cast off from its free extremity ; its absorbent 

 vesicles, its Iacteals, and its blood-vessels turgid ; 6, a follicle discharging its secreting epi- 

 thelial cells. 



. t Diagram of mucous membrane of jejunum, when absorption is not going on ; a, protec- 

 tive epithelium of a villus; b, secreting epithelium of a follicle ; c, c. c, primary membrane, 

 with its germinal spots or nuclei, d, d; e, germs of absorbent vesicles; /, vessels and Iac- 

 teals of villus. 



