222 THE FCETUS. 



patic veins, which, as in the adult, proceed to open into the vena 

 cava a little above the ductus venosus. 



568. Course of the blood. From the above arrangement of the 

 circulatory organs, it is evident that the course of the fluids must be 

 much more complicated than in the adult. From the smaller branches 

 of the umbilical vein, the blood passes into the larger ones, and soon 

 afterwards into the great trunk of that vessel, it then passes along the 

 cord through the umbilicus, and divides beneath the liver into two prin- 

 cipal currents, one of which follows the venous canal so as to go and be 

 mixed with the blood of the inferior cava, while the other proceeds 

 along the umbilical branch of the vena portae, to be ramified in the 

 right lobe of the liver, and taken up by the hepatic veins, which pour 

 it into the trunk of the cava as it passes through the diaphragm. 

 There it forms three columns; that of the venous canal, that of the 

 hepatic veins, and that which is brought by the cava from the lower 

 half of the body, which unite, and together enter the right auricle, 

 thence passing through the foramen ovale into the left auricle; from 

 the latter, the blood falls into the corresponding ventricle, which 

 forces it along the aorta towards all parts of the body, but chiefly to 

 the head and upper extremities, by means of the brachio-cephalic 

 trunk, the left carotid, and the subclavian. 



569. After losing among the tissues the nutritive principles with 

 which it was charged, the blood is brought back by the jugular and 

 the axillary veins to the subclavians, and thence to the superior cava, 

 which also receives that of the azygos; the superior cava carries it to 

 the right auricle, the auricle to the right ventricle, and the latter to 

 the pulmonary artery, which directs only two small columns of it 

 to the lungs, and causes the rest of it to pass through the arterial 

 duct to the descending aorta, where it meets with a part of what the 

 left ventricle had already expelled. That portion which reaches the 

 primitive iliacs is in part distributed to the lower extremities by the 

 external iliacs; but by far the largest portion of it returns along the 

 umbilical arteries, through the cord, and at last to the placenta, from 

 whence it set out. 



570. In the heart. Haller, Wolf, Sabattier, MM. Portal, Riche- 

 rand, &c., supposed that the blood of the two venae cavae does not 

 mix at all in the right auricle, that that of the ascending or inferior 

 cava passes entirely to the left, and that of the superior cava entirely 

 into the right ventricle. 



571. Bicliat was opposed to this view of the subject, and M. 

 Magendie does not adopt it; it is difficult, say they, to understand 

 how two columns of fluid can pass into the same cavity without being 



