246 



HISTOLOGY 



In the later stage (Fig. 241, C) both the fore-gut and hind-gut have 

 greatly elongated; together they form a loop of intestine extending out 

 into the cavity of the umbilical cord. Near the bend in this loop the 

 yolk-sac is still attached to the intestine by a stalk; the sac itself has been 

 cut away in the figure. In addition to the pharynx already described, the 



al 



FIG. 241. STAGES IN THE DEVELOPMENT OF THE DIGESTIVE TUBE. A. Rabbit of nine days. B. Man 



2.15 mm. (after His). C. Pig. 12 mm. D. Man, 17.8 mm. (after Thyng). E. Man, about five months. 

 a., Anus; al., allantois; bl., bladder; cae., bulb of the colon; cl., cloaca; du., duodenum; 1. i., large intestine; 



oe., oesophagus; p., penis; pe., perineum; ph., fore-gut; r., rectum; s. i., small intestine; St., stomach; 



u. c., umbilical cord; ur., urethra; ura., urachus; u. s., urogenital sinus; v. p., vermiform process: 



y. s., yolk-sac; y. St., vitelline duct within the yolk-stalk. 



fore-gut has given rise to an expanded portion or stomach. Between the 

 stomach and pharynx it remains tubular and becomes the oesophagus; 

 posterior to the stomach it is likewise tubular and there it forms a part 

 of the small intestine. The first portion of the small intestine is called the 

 duodenum, and is followed by the jejunum which passes without demarca- 

 tion into the ileum. The ileum includes the portion to which the yolk- 

 stalk is attached, and terminates at a bulbous enlargement (Fig. 241, C, 

 cae) which gives rise to the cacum and -vermiform process. This bulbus 

 coli (Johnson) marks the beginning of the large intestine or colon, and 

 the caecum and vermiform process are parts of the large intestine. Toward 

 the cloaca the colon becomes the rectum, and near its termination it forms 

 an elongated bulbous enlargement, the bulbus analis. As shown by F. P. 



