THE ANATOMY OF A 4.2 MM. HUMAN EMBRYO 



85 



branchial arches. The arrangement is like that of the adult fish which has gill 

 slits, branchial arches, and aortic arches to supply the gills. The descending 



FiG.'91. — Embryos of six to eight weelcs (12.5 to 23 mm.). From His' Normentafel (Keibel and Elze). 

 X 2.5. Stage w{22) marks the transition from embryo to fetus. 



aortse run caudad and opposite the lung buds unite to form a single median dorsal 

 aorta. This, in the region of the posterior Hmb buds, divides into the two um- 



