256 



THE EVOLUTION OF MAN. 



Fio. 53. 



in A- a 



Fig. 54. 



Fig. 55. 



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

 nir, medullary tube; x, chorda; na, nose; au, eyes; g, ear-vesicle; md, 

 mouth; k, gill-body; A.s, 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; //, testicles; c, body-cavity 

 (visceral cavity); m^, muscles; Ih, leather-skin {coriuiv); oh, outer-skin 

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



Fig. 53. — Same as above, viev^ed from the ventral side. 



