850 



THE NUTRITION OF THE EMBKYO. 



the liver are developed early, and about the third month bile pigment and 

 bile salts find their way into the intestines. The quantity of bile secreted 

 during mtra-uterine life accumulates in the intestine, and especially in the 

 rectum, forming, together with the smaller secretion of the rest of the canal, 

 and some desquamated epithelium, the so-called meconium. Bile salts, both 

 unaltered and variously changed, the usual bile pigments, and cholesterin, 

 are all present in the meconium. The distinct formation of bile is an indi- 

 cation that the products of foetal metabolism are no longer wholly carried 

 off by the maternal circulation ; and to the excretory function of the liver 

 there are now added those of the skin and kidney. The substances escaping 

 by these organs find their way into the allantois or into the amnion, accord- 

 ing to the arrangement of the foetal mem- 

 [FIG. 230. branes in different classes of animals ; in 



both these fluids urea or allied bodies have 

 been found as well as the ordinary saline 

 constituents ; the latter may or may not 

 have been actually secreted. From the 

 allantoic fluid of ruminants the body allan- 

 toin has been obtained, and human and 

 other amniotic fluids have been found to 



Diagram of the Fcetal Circulation. 1, the umbilical 

 cord, consisting of the umbilical vein and two umbilical 

 arteries, proceeding from the placenta (2) ; 3, the umbi- 

 lical 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, returning the blood from the intestines, and unit- 

 ing with the right hepatic branch ; 8, the right auricle; 

 the course of the blood is denoted by the arrow proceed- 

 ing 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 sub- 

 clavian veins to the superior 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 con- 

 tinuation of the pulmonary artery : the offsets at each 

 side are the right and left pulmonary arteries cut off. 

 The ductus arteriosus joins the descending aorta (18,18), 

 which divides into the common iliacs ; and these into 

 the internal iliacs, which become the umbilical arteries 

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

 the placenta, and the external iliacs (20), which are con- 

 tinued into the lower extremities. The arrows at the 

 termination of these vessels mark the return of the 

 venous blood by the veins to the inferior vena cava.] 



contain urea. It is maintained by some, however, that the fluid in the 

 amnion is secreted by the mother, and that hence the substances present in 

 it are of maternal origin. 



793. About the middle of intra-uterine life, when the foetal circula- 

 tion [Fig. 230] is in full development, the blood flowing along the umbilical 

 vein is carried chiefly by the ductus venosus into the inferior vena cava and 

 so into the right auricle. Thence it is directed by the valve of Eustachius 

 through the foramen ovale into the left auricle, passing from which into the 

 left ventricle it is driven into the aorta. Part of the umbilical blood, how- 

 ever, instead of passing directly to the inferior cava, enters by the portal 

 vein into the hepatic circulation, from which it returns to the inferior cava 



