EMBRYOS OF THIRTY -EIGHT DAYS. 



151 



liver, into the extra-embryonic coelom of the umbilical cord is a constant phenom- 

 enon. It begins at a somewhat earlier stage and continues for a considerable 

 period. This curious condition has been observed in many different kinds of mam- 

 mals in the corresponding stage. Later on, the viscera are entirely withdrawn from 

 the umbilical cord and the cavity itself is wholly obliterated. The umbilical cord 

 is a hollow prolongation of the body-wall or somatopleure of the embryo, and the 

 amnion springs from its distal end. The yolk-stalk is very long and narrow. Its 

 entodermal cavity is obliterated. It is the representative of the original broad con- 

 nection between the yolk-sac and the entodermal cavity of the embryo, although 

 it is now only a small appendage of a loop of the intestine. It bears the blood- 



FIG. ioo. HUMAN EMBRYO OF 10.0 MM. SERIES 

 1000. X 5 diams. (Compare Fig. 99.) 



FIG. 101. HUMAN EMBRYO OF 11.5 MM. 



SERIES 1006. X 5 diams. 



vessels which run from the embryo and ramify upon the yolk-sac. On the caudal 

 side of the umbilical cord we find the tissue of the original body-stalk in which 

 run the allantoic vein and the two allantoic arteries which ramify upon the 

 chorion. 



Embryos of Thirty-eight Days, 16 mm. in a chorionic vesicle of 45 by 40 mm. 

 The age of this specimen (Fig. 103) is known by estimate only. This stage repre- 

 sents the transition of the embryo to the fetus, because after the fortieth day the 

 form is distinctly human. The head has risen considerably, and the back has 

 straightened still more, the rectangular neck-bend thus becoming emphasized. The 

 body has become still more protuberant on the ventral side, and in side views the 

 arms reach to the outline of the body. In the anterior limb we note the first indi- 

 cations of the five digits and of the separation of the upper and lower arms. To 



