370 



THE EVOLUTION OF MAN. 



Fig. 123. — Human embryo of fonr weeks old, opened on the ventral side. 

 The walls of the chest and abdomen have been cut away, so that the contents 

 of the chest and ventral cavities ai'e visible. All tlie appendages (amnion, 

 allantois, and yelk-sac) have been removed, and also the middle portion of 

 the intestine : n, eye ; 3, nose ; 4, upper jaw ; 5, lower jaw ; 6, the second 

 gill-arch, and G" the third; ov, heart (o, right, o', left auricle; v, right, v', 

 left ventricle); b, origin of the aorta; /, liver («, navel-vein) ; e, intestine 

 (with the yelk-artery, cut away at a') ; j', yelk-voin ; m, primitive kidney; 

 t, rudiments of the sexual glands ; r, terminal intestine (with mesentery, z, cut 

 away) ; n, navel-artery ; v, navel-vein ; 7, anus ; 8, tail ; 9, front limb ; 9', 

 hind limb. (After Coste.) 



