DIGESTIVE TUBE. 



231 



similar to that of a gland : these prolongations are filled with 

 epithelial detritus, the odor of which is often very offensive. 

 The epithelium of the remaining portions of the buccal 

 cavity is simple, but not less important on that account. We 

 shall find that it forms a considerable part of the structure 

 of the papilla? of the tongue, the organs of the sense of 

 taste. It is this which, when covered with calcareous sub- 

 stances, changes into enamel, a layer of prismatic elements 

 forming a resisting covering for the surface of the teeth ; and, 

 by a similar transformation, produces whalebone or fins in the 

 young cetaceans. Finally, we have seen that the salivary 

 glands are the seat of deep and more or less considerable 

 giowths of this epithelium. 



m. 



SUB-DIAPHRAGMATIC PORTION OP THE DIGESTIVE 

 TUBE. 



THE sub-diaphragmatic part of the digestive tube proceeds 

 from the internal or mucous fold of the blastoderm by means 

 of the folding in which the body of the embryo undergoes 



'Fig. 64. Formation of the intestinal tube.* 



at the two extremities and at the sides. Its primitive cavity 

 is divided in two : on the one side the umbilical vesicle (see 

 farther on, Embryology), and on the other a middle tube, 



* A, B, C, Different degrees of development of the stomach and of the con- 

 volutions of the intestine, properly so called, s, Stomach. /, S iliac, o, Om- 

 phalo-mesentevic.tube. 6, Pouch from which tta ca?cum is afterwards formed, 

 c, Colon, k, Convolutions of the small intestine. 



