u6 GROWTH 



The next figure (62) shows a lateral view of three later hu- 

 man embryos, all magnified to the same scale. Figure 62A repre- 

 sents an embryo 4.2 mm. (% inch) long with the yolk sac (ys) 

 and the connecting stalk (cs) for the attachment of the embryo. 

 Note the relatively large head region, and the ventral curvature 

 of the body axis. His ascribed this characteristic curvature to the 

 resistance of the amniotic folds, which tend to prevent the direct 

 elongation of the body; but the relative overgrowth of the 

 neural tube and dorsal region seems to be the most important 

 factor in producing this flexure, as was noted by Merkel. 36 The 



CS-'"' 



A. 4.2 mm. 



•i '■-^:r 



-l--- u 



£>. 11 mm. C. 16 mm. 



Figure 62. Later stages of the human embryo, lateral view, magnified 4 diameters. 

 From His." I, first branchial groove (external ear); U, upper limb; L, lower limb; *, 

 tail region; h, heart region; Umb, umbilical cord. 



A. Embryo 4.2 millimeters long, ys, yolk sac; cs, connecting stalk. 



B. Embryo 11 millimeters long (crown-rump length). 



C. Embryo 16 millimeters long (crown-rump length). 



