3^0 



THE EVOLUTION OF MAN 



two shallow transverse indentations of the circumference 

 appear, which externally mark the three sections (Figs. 307, 

 308). The anterior section, vhich is turned toward the 



e r 



Fig. 307. — Heart of an embryouic Eabbit, from beliind : a, yelk-veins ; 

 h, auriculae; c, auricle (atrium) ; d, ventricle; e, artery-stalk; /, base of the 

 three pairs of arterial arches. (After Bischoff.) 



Fig, 308. — Heart of the same embryo (Figf. 307), from the front : r, 

 yelk- veins ; a, auricle ; ca, auricular canal ; J, left ventricle ; r, right 

 ventricle ; ta, arterj^-stalk. (After Bischoff.) 



Fig. 309.— Heart and bead of an embryonic Dog, from the front : 

 a, fure-brain ; h, eyes ; c, mid-brain ; d, primitive lower jaw ; e, primitive 

 upper jaw ; /, gill-arches ; g, right auricle ; h, left auricle ; i, left ventricle ; 

 A-, right ventricle. (After Bischoff ) 



Fig. 310. — Heart of the same embryo, from behind : a, entrance of the 

 yelk-veins ; h, left auricular process ; c, right auricular process ; d, auricle ; 

 e, auricular canal ; /, left ventricle ; g, right ventricle ; h, artery-stalk. 

 (After Bischoff.) 



ventral side, and from which the aortal arches spring, 

 reproduces the arterial stalk (hidhus arteriosus) of the 

 Selachii. The central section is the rudiment of a simple 

 chamber, or ventricle (ventiiciihis) ; and the posterior 

 section, the one turned toward the dorsal side, into which 

 the yelk-veins open, is the rudiment of a simple auricle 



