THE FORM OF THE HUMAN STOMACH 497 



The position of the pylorus could not be determined with cer- 

 tainty in the 10-mm. embryo (fig. 5); and Tandler (1900) states 

 that in an embryo of 11 mm. the pylorus is not marked. At 

 14.5 mm., " where the stomach passes into the duodenum, there- 

 fore at the place of the future pylorus" he saw u a considerable 

 thickening of the epithelium." The epithelial proliferation, 

 which Tandler describes, is seen throughout the upper part of 

 the duodenum. It is not evident that he recognized the local 

 swelling, chiefly on the upper side of the digestive tube, which is 



A. du. 



rr~*~~^>-^ P- py- 



Fig. 11. Frontal section through the pylorus of a 19-nim. embryo, H. E. C. 

 828, section 330, X 40 diam. A.du., antrum duodenale. B.om., bursa omentalis. 

 P.py., pars pylorica. T.musc, tunica muscularis. 



shown in figures 6 to 8. This swelling, which distinctly marks the 

 position of the pylorus when the muscle-layers are still undiffer- 

 entiated, and scarcely to be recognized, is apparently the duo- 

 denal antrum of Retzius. In a frontal section through the pars 

 pylorica of a 19-mm. embryo, it appears as shown in figure 11. 

 At this stage the musculature of the pars pylorica is considerably 

 thicker than that of the duodenum, but in this it conforms to the 

 shape of the epithelial tube. In figure 9 the duodenal antrum is 

 seen to be smoother than the more distal part of the duodenum, 

 recalling the statement of Retzius that here, in the adult, the 

 valvulae are absent and the villi are short. In this embryo the 



