CONTENTS. 



PAGES. 



Introduction 63-65 



Methods 65-68 



Vascular system of the chick 68 



General account of the vascular system of the chick up to stage of 14 somites 68-77 



Origin of the cardinal veins 77-80 



Vascular system of the brain and the primary head-vein 80-93 



Development of the spinal arteries 94-96 



The vascular system in young pig embryos 97 



The form of the heart 97-99 



Ventral branches of the aorta, including the allantoic arteries and the subintestinal artery 99-105 



The umbilical vessels 105-106 



Neural branches of the aorta and the primary head-vein 106-1 13 



The cardinal veins in the pig 114 



Nephritic vessels in the pig 1 14-124 



62 



