ANATOMY OF A 17.8 MM. HUMAN EMBRYO 43 



the umbilical coelom. The lumen of the du(xlenum, beginning 

 somewhat cephalad of the duct of the dorsal pancreas and ex- 

 tending caudad to the duodenal diverticulum above mentioned, 

 is subdivided into two or three parts by a proliferation of the 

 epithelium in a manner similar to that already described by 

 Tandler ('00) in a human embryo of 14.5 mm. This observa- 

 tion has been confirmed by Forssner ('07), Johnson ('10) and 

 Lewis ('12). Beyond this proliferation the lumen of the small 

 intestine is either a small cylindrical passage or a slight slit. 



The yolk-stalk has a lumen for a short distance beyond its 

 connection with the epithelium of the intestine. It then becomes 

 a cord of degenerating cells, showing here and there traces of a 

 lumen. Whether the yolk-stalk is still connected with a rudimen- 

 tary yolk-sac could not be determined as these parts were cut 

 away in the embryo. 



The lumen of the colon as it leaves the caecum, is a very small 

 cylindrical passage, but as it nears the rectum, it becomes a 

 transversely directed slit (corresponding to the shape of the 

 intestine which is compressed dorso-ventrally) . 



The cephalic portion of the rectum is a little larger in diameter 

 than the colon, while the terminal part is more attenuated. The 

 latter is circular in transverse section and the lumen is reduced to 

 a very small cylindrical passage, which, however, does not connect 

 with the shallow external depression (An.) between the protrud- 

 ing genital folds. 



Liver. The liver (see plates 1, 2 and 4, Hepar) occupies the 

 greater part of the cephalic and ventral regions of the abdominal 

 cavity. The right lobe is much the larger, and extends from the 

 cephalic end of the abdominal cavity on the right, caudad to a 

 point on a level with the crossing of the duodenum by the colon. 

 It is joined to the dorsal abdominal wall on the right of the 

 dorsal mesogastrium, at the ventral region of the right supra- 

 renal gland, by the plica venae cavae of Ravn ('89) (caval mes- 

 entery) . 



The caudate lobe is located between the caval mesentery and 

 the lesser omentum. It projects somewhat toward the left 

 into the bursa omentalis. The position of the quadrate lobe 



