382 



THE EVOLUTION OF MAX. 



Fig. 313 



Fig. 314. 



Fig. 311.— Heart of a human embryo of four weeks ; 1, from the front; 

 2, from the back ; 3, open, and with the upper half of the auricle removed ; 

 a', left auricular process ; a", riii^ht auricular process ; v', left ventricle ; 

 v", right ventricle ; ao, artery-stalk ; c, upper hollow vein (vena cava) {cd, 

 right, cs, left) ; s, rudiment of the partition, between the chambers. (After 

 Koelliker.) 



Fig. 312. — Heart of a human embryo of six wepk«, from the front: 

 r, right ventricle ; t, left ventricle ; s, furrow between the two ventricles ; 

 to, artory-stalk ; af, furrow on its surface; at the right and left are tht 

 two large auricular processes of the heart. (After Ecker.) 



F[G. 313. — Heart of a human embryo of eight weeks, from behind 

 a', left auricular process ; a", right auricular process ; v', left ventricle 

 v", right ventricle ; cd', right upper vena cava ; cs, left upper vena cava 

 ci, lower vena cava. (After Koelliker.) 



Fig. 314.— Heart of human adult, perfectly developed, irom the front, in 

 its natural position : a, right auricular process (below it, the right ventricle) ; 

 h, left auricular process (below it, the left ventricle) ; C, upper vena cava ; 

 V, lung-veins ; P, lung-artery ; d, Botalli's duct ; A, aorta. (After Meyer.) 



right ventricle, and the aorta-trunk, which opens into the 

 left ventricle. Not until all these partitions are complete, 

 is the lesser, or luno'-circulation, entirelv distinct from the 



