480 Intestinal Folds and Villi in Vertebrates 



Whether these depressions and epithelial processes further develop 

 together or whether the epithelial tube later develops in the depths, 

 remains undecided, but it is probable that earlier or later these epithe- 

 lial tubes develop in the depths. 



Patzelt, 82, studied the large intestine; he recognized small eleva- 

 tions of high epithelial cells, the anlages of later villi. Between these, 

 in groups, short broad epithelial cells with basal nuclei, the anlages of 

 the Lieberkiihnen crypts, so that these lie in small depressions between 

 them. Later between the villi, connective-tissue folds are elevated, the 

 villi are in this way bound together so the crypts of Lieberkiihn are 

 formed by elevations of the wall, not at all or but slightly by deep 

 growths. 



Minot, 92, describes the Lieberkiihnen glands as hollow outgrowths 

 of entoderm extending into mesoderm. Kollmann, 98, describes the 

 crypts of Lieberkuhn as developed between the villi, making insinkings 

 into the depths of the mucosa. 



Voigt, 99, has studied the intestine of pig and comes to results con- 

 trary to those of Brand and Patzelt. He describes the intestine at 

 first smooth, then furrows appear which divide the mucous membrane 

 up into more or less isolated elevations and from these elevations villi 

 grow upward, while from the furrows which form a network of con- 

 nected canals, the crypts of Lieberkuhn grow downward as hollow 

 sprouts. Any development of the villus base to form the crypts of 

 Lieberkiihn, as seems possible, does not take place. 



The intestine of the white rat is in some respects rather unfavorable 

 for the study of the crypts of Lieberkiihn, although it is more favorable 

 for the study of the disappearance of villi. 



An embryo of 43 mm. in length has crypts in the lower large intestine 

 while no crypts were made out in the small intestine, although the villi 

 were well formed. About the time of birth crypts begin to make their 

 appearance in the small intestine and beginnings may be made out as 

 little areas which appear like slight thickenings or depressions of epi- 

 thelium, scattered irregularly over the surface of the intestine (Fig. 81). 

 It often happens that on 3 of these crypts begins near a villus base, but 

 this seems to be purely fortuitous (Fig. 83). From birth onward the 

 crypts become more numerous, as do the villi, the latter grow up as 

 little buds of epithelial cells (Fig. 57). The crypts, on the other hand, 

 begin as slight thickenings or slight depressions which vary somewhat 

 in character, but are not sharp depressions at first; later they become 

 more marked and after about five days are like little fiasks with nar- 

 row necks and small lumens (Figs. 83-86). This character they keep 



