THE ALIMENTARY CANAL. 



547 



to the dorsal wall of the body along its whole length, lying 

 immediately ventral to the notochord ; and is hence equal in 

 length to the part of the body in which it lies. During the 

 fourth week, the intestine grows much more rapidly than the 

 body of the embryo, and becomes thrown into loops which pro- 

 ject ventral wards (Fig. 233). A small duodenal loop is formed 

 immediately beyond the stomach, and opposite the bile-duct, 



FIG. 234. Outline figure of the alimentary canal of a Human Embryo, 

 lettered by Professor His, Sch, and estimated as thirty-five days old. 

 The figure is drawn from the right side, and the cavity of the alimentary 

 canal is alone represented, not the thickness of its walls. The curved 

 line bounding the figure on the left is the notochord. (From His.) x 10. 

 An, position at which the anus will be formed. Cc, caecum. CA, notochord. Cl, rectum. 



Ep, epiglottis. HI), basal portion of allantois, which becomes the bladder. Kk, larynx. 



Lbff, bile-duct. Lg, lung. Alg, stomach. N, rudiment of permanent kidney ormetanephros. 



/", pancreas. RT, pituitary body. Sy, clitoro-peiiis. SI, tail. Tr, trachea. Ut, mandible, 



or lower jaw. Zg, tongue. 



Lbg ; and a much larger vitelline loop is formed lower down, from 

 the apex of which the yolk-stalk, Ds, arises. As the intestine 

 lengthens, its attachment to the dorsal wall of the body becomes 

 drawn out into a thin vertical sheet of mesoblast, the mesentery, 

 between the layers of which the blood-vessels of the alimentary 

 canal run, 



N N 2 



