340 THE EVOLUTION OF MAN. 



the inner stratum, on the contrary, innumerable minor 

 glands develop from the intestinal-glandular layer. These 

 are the peptic glands, which supply the most important 

 digestive fluid — the gastric juice. At the lower extremity 

 of the pouch of the stomach a valve develops, which, as 

 the pylorus, separates the stomach from the small intestine 

 (Fig. 275, d). 



The disproportionately long middle intestine, or small 

 intestine, now develops below the stomach. The develop- 

 ment of this section is very simple, and is essentially caused 

 by a very rapid and considerable longitudinal growth. 

 Originally this section is very short, straight, and simple ; 

 but immediately below the stomach a horseshoe bend, or 

 loop, begins to appear at a very early period in the intestinal 

 canal, simultaneously with the separation of the intestinal 

 tube from the yelk-sac and with the development of the 

 mesentery. (Cf. Plate V. Fig. 14, g, and Fig. 136, vol. i. p. 381.) 

 Before the abdominal wall closes, a horseshoe-shaped loop of 

 intestine (Fig. 136, m) protrudes from the ventral opening of 

 the embryo, and into the curve of this the yelk-sac or navel- 

 bladder opens (n). The thin, delicate membrane which 

 secures this intestinal loop to the ventral side of the vertebral 

 column, and occupies the inside of this horseshoe curve, is 

 the first rudiment of the mesentery (Fig. 286, g). The most 

 prominent part of the loop into which the yelk-sac opens 

 (Fig. 287, x), and which is afterwards closed by the intestinal 

 navel, represents that part of the small intestine which is 

 afterwards called the crooked intestine (ileum). Soon a 

 very considerable growth of the small intestine is observ- 

 able ; and in consequence, this part has to coil itself in many 

 loops. The various parts of the small intestine which we 



