lyo 



THE ENTODERMAL CANAL AND THE BODY CAVITIES 



toneal cavity from left to right (cf. Fig. 138). The change in position progresses 

 rapidly and is already completed early in the second month (12 to 15 mm.). 

 The rotation of the stomach explains the asymmetrical position of the vagus nerves 

 of the adult organ, the left nerve supplying the ventral wall of the stomach, orig- 

 inally the left wall, while the right vagus suppHes the dorsal wall, originally the 

 right. 



Gastric pits are indicated in 16 mm. embryos, and, at 100 mm. (C R), gland cells of the 

 gastric glands are differentiated. These undoubtedly arise from the gastric epitheUum 

 (Lewis). The cardiac glands are developed early (91 mm. (C R) fetuses), and, according to 

 Lewis, there is no "evidence in favor of Bensley's conclusion that the cardiac glands are 

 decadent . fundus glands.'' 



Pharynx 

 Root of longuc 

 Thyreoid 

 Tip of tongue 



Rathlie's pocket 

 Trachea 

 Stomach 



Liver 



Dorsal pancreas 



Hepatic diverli- 

 culnm 



Yolk-stalk 

 Allanlois 

 Mesonephric duel 

 Clooea 



Hind-gut 



Fig. 177. — Median sagittal section of a 5 mm. human embryo to show the digestive canal (modified 



after Ingalls). X 14. 



At 10 mm. the stomach wall is composed of three layers: the entodermal epithelium, a 

 thick mesenchymal layer, and the peritoneal mesothelium. At 16 mm. the circular muscle 

 layer is indicated by condensed mesenchyma. At 91 mm. (C R) the cardiac region shows a 

 few longitudinal muscle fibers, which become distinct in the pyloric region at 240 mm. (C R). 



In 17 mm. embryos the stomach has reached its permanent position, the cardia having 

 descended through about ten segments, the pylorus through six or seven. 



Intestine. — In 5 mm. embryos (Fig. 177), the intestine, beginning at the 

 stomach, consists of the duodenum (from which are given ofif the hepatic diver- 

 ticulum and dorsal pancreas), and the cephalic and caudal limbs of the intestinal 

 loop, which bends ventrad and connects with the yolk stalk. Caudally the intes- 



