CHAP, x.] THE DEVELOPMENT Off THE CAT. 



347 



omv), and which, as it were, lay the foundation of the future portal 

 and hepatic veins. Before entering the incipient auricular end of the 

 primitive heart, these omphalo-meseraic veins first unite into a common 

 trunk and then dilate into a venous chamber, which hears the name 

 of sinus venosus (Fig. 156, 8), and opens directly into the heart. 



Fig. 156. DIAGRAM OF FCETAL ARTERIES AND 

 VEINS. VERY EARLY CONDITION. THE 

 ARTERIES AND VEINS OF ONE SIDE ONLY 

 ARE REPRESENTED TO AVOID CONFUSION. 



S. Sinus venosus. 



A. Auricle. 



V. Ventricle. 



Jj. Btilbus arteriosus. 



L. Liver. 



1, 2, 3, 4. Aortic arches. 



a. Dorsal aorta. 



oma. Omphalo-meseraic artery to umbilical 



vesicle. 



ua. Umbilical artery (to allantois). 

 ila. Iliac artery to incipient hind-limb, 

 ca. Caudal artery. 

 omv. Omphalo-meseraic vein. 

 uv. Umbilical vein. 

 dv. Ductus venosus. 

 liv. Hepatic vein. 

 ilv. Iliac vein. 

 vci. Inferior vena cava. 

 pc. Posterior cardinal vein, 

 oc. Anterior cardinal vein. 

 dc, Ductus Cuvieri. 



Fig. 157. DIAGRAM OF THE FCETAL CIRCULA- 

 TION THROUGH THE HEART AND AORTA. 



CONDITION OF HEART AND GREAT VESSELS 

 AT BIRTH. 



RA. Right auricle. 



LA. Left auricle. 



RV. Eight ventricle. 



LV. Left ventricle. 



A 1 . Great aorta. 



A 2 . Second aortic arch (afterwards pulmonary 

 artery). 



pa, pa. Incipient branches to lungs. 



da. Ductus arteriosus, which at first places the 

 two aortic arches in direct communication. 

 The arrows indicate the course of the blood, 

 one going directly from the right to the 

 left auricle through the foramen ovale of 

 the as yet incomplete inter-auricular 

 septum. 



Soon two elongated venous trunks make their appearance heneath, and 

 parallel to, the primitive vertebral column (ac and pc), each such 

 vein sending down a branch, called a ductus Cuvieri (dc), to the 

 sinus venosus. That part of each of these two trunks which runs 

 backwards from the head end of the embryo to its ductus Cuvieri, 

 is called an anterior cardinal vein. That part of each of these 

 trunks which runs forwards from the hinder part of the embryo to 

 the ductus Cuvieri of such trunk is called a posterior cardinal vein, 

 which ultimately become the azygos vein. Before the commence- 



