554 



FCETAL CIRCULATION. 



buted byjhe external iliac arteries to the 

 lower extremities ; the greater portion is 

 conveyed by the internal iliac, hypogas- 

 tric, and umbilical arteries to the pla- 

 centa ; the hypogastric arteries proceed- 

 ing from the internal iliacs, and passing 

 by the side of the fundus of the bladder, 

 and upwards along the anterior wall of 

 the abdomen to the umbilicus, where 

 they become the umbilical arteries. 



From a careful consideration of this 

 circulation, we perceive 1st. That the 

 pure blood from the placenta is distri- 

 buted in considerable quantity to the 

 liver, before entering the general circu- 

 lation. Hence arises the abundant nutri- 

 tion of that organ, and its enormous size 

 in comparison with other viscera. 



2dly. That the right auricle is the 

 scene of meeting of a double current ; 

 the one coming from the inferior cava, 

 the other from the superior, and that 

 they must cross each other in their re- 

 spective course. How this crossing is 

 effected the theorist will wonder ; not so 

 the practical anatomist; for a cursory 

 examination of the foetal heart will show, 



1. That the direction of entrance of the 

 two vessels is so opposite, that they may 

 discharge their currents through the 



2. That the inferior cava opens almost 



directly into the left auricle. 3. That by the aid of the Eustachian valve, 

 the current in the inferior cava will be almost entirely excluded from the 

 right ventricle. 



3dly. That the blood which circulates through the arch of the aorta 

 comes directly from the placenta ; and, although mixed with the impure 



* The foetal circulation. 1. The umbilical cord, consisting of the umbilical vein and 

 two umbilical arteries 5 proceeding from the placenta (2). 3. The umbilical vein 

 dividing into three branches; two (4, 4), to be distributed to the liver; and one (5), 

 the ductus venosus, which enters the inferior vena cava (6). 7. The portal vein, re- 

 turning the blood from the intestines, and uniting with the right hepatic branch. 8. The 

 right auricle ; the course of the blood is denoted by the arrow, proceeding from 8, to 9, 

 the left auricle. 10. The left ventricle ; the blood following the arrow to the arch of 

 the aorta (11), to be distributed through the branches given off by the arch to the head 

 and upper extremities. The arrows 12 and 13, represent the return of the blood from 

 the head and upper extremities through the jugular and subclavian veins, to the supe- 

 rior vena cava (14), to the right auricle (8), and in the course of the arrow through the 

 right ventricle (15), to the pulmonary artery (16). 17. The ductus arteriosus, which 

 appears to be a proper continuation of the pulmonary artery, the offsets at each side are 

 the right and left pulmonary artery cut off; these are of extremely small size as com- 

 pared with the ductus arteriosus. The ductu-s arteriosus joins the descending aorta 

 (18, 18), which divides into the common iliacs, and these into the internal iliacs, which 

 become the hypogastric arteries (19), and return the blood along the umbilical cord to 

 the placenta; while the other divisions, the external iliacs (20), are continued into the 

 lower extremities. The arrows at the terminations of these vessels mark the return of 

 the venous blood by the veins to the 'nferior cava. 



J U 



same cavity without admixture. 



