256 



THE EVOLUTION OF MAN. 



au 



9 



Jls 



*9 



i; h% -ma C 

 ins 



Fig. 53. 



471 S I 



Fig. 54. 



Fig. 55. 



Fig. 52. — The ideal Primitive Vertebrate type, seen from the left side : 

 rnr, medullary tube ; oc, chorda ; na, nose ; au, eyes ; g, ear-vesicle ; md, 

 mouth; fc, gill -body ; ks, gill-openings; kg, gill-arches; ma, stomach; I, 

 liver ; d, small intestine ; af, anus ; v, intestinal vein ; hz, heart ; a, body, 

 artery ; n, primitive kidney canal ; e, ovary ; h, testicles ; c, body-cavity 

 (visceral cavity); ms, muscles; Ih, leather-skin (corium); oh, outer-skin 

 (epidermis) ; /, skin-fold, acting as fin. 



Fig. 53. — Same as above, viewed from the ventral side. 



