232 DIGESTIVE SYSTEM. 



which is at first cylindrical and of an uniform calibre 

 (Fig. 64, A). The upper part of this intestine, however, 

 soon dilates (Fig. 64, A, s), and then becomes oblique; 

 so that its lower extremity, which is the least dilated (Fig. 

 64, B, f?), is turned to the right, while the left side becomes 

 anterior. The stomach is thus formed (Fig. 64, C, s, d), and 

 in the same way the pneumogastrie nerve becomes ante- 

 rior as it passes below the diaphragm. The rest of the 

 digestive tube lengthens out, and, consequently, is separated 

 from the vertebral column, and forms a loop : the tube, by 

 means of which the intestine communicates with the umbili- 

 cal vesicle, begins at the summit of this loop (Fig. 64, B, o). 

 The upper branch of the loop is placed anteriorly, and soon 

 exhibits a slight swelling (), which is the first appearance 

 of the caecum and of the ccecal appendix: the remaining 

 portion of the loop forms the large intestine, as far as the sig- 

 moid flexure of the colon (Fig. 64, B, >,/", and C, 5,/', c) ; 

 while the convolutions of the summit and postero-inferior 

 portion of the loop are developed (Fig. 64, B, &), and form 

 the small intestine (C, &). 1 



The epithelium of this part of the digestive tube is colum- 

 nar throughout, and is continued at its two extremities 

 with the pavement epitheliums of the oesophagus and of the 

 skin. It also forms outgrowths on the surface (or phaneres) 

 and in the deeper tissues (or crypts). The former are repre- 

 sented by the villosities, which we shall study in regard to 

 the subject of absorption ; the latter are the various glands 

 of the intestinal tube. Some of these glands are extremely 

 simple, as the follicles or glands of Lieberkiihn, which are 

 only a depression like the finger of a glove (Fig. 65), and 

 are found throughout this portion of the alimentary canal ; 

 in the stomach, however, some of these depressions have a 

 complex structure, and the epithelium of their cascal extrem- 

 ity is no longer columnar ; we have also the peptic glands. 

 Farther on, a still more complex growth gives us glands in 

 clusters, such as the glands of IZrumier, in the duodenum : 

 the pancreas is only a huge gland of this class. Finally, 

 embryology shows us that the liver is itself formed of pouches 

 similar to those of the glands of Lieberkiihn, but very long, 

 and so spacious that between them is found another glan- 

 dular organ, arising from the growth of the coats of the 



1 See K. Vierordt, " Grundriss dcr Physiologie dea Meiischen." 

 Francfort, 18GO, p. 420. 



