403 



follows the original direction, and opens into the ascending- or interior 

 vena cava, very near to the spot where this vein pours its contents into 

 the right auricle of the hearfc 



CCX. The arterial blood which flows along the umbilical vein, acquires 

 the properties of venous blood, and combines with hydrogen and carbon, 

 and parts with its vivifying qualities, in flowing along the vessels of the 

 mother and the tortuous vessels of the placenta. It parts with these 

 principles, and again becomes vivified* by circulating through the liver, 

 which, at this period of life^ fulfils the function which, after birth, is com- 

 mitted to the lungs. Hence the liver and brain form the greatest part of 

 the weight of a new born child. The former alone occupies the greatest 

 part of the abdomen. It acquires this bulk, by assimilating to itself the 

 hydrogen and carbon of the umbilical blood. Its substance is adipose, 

 oily^ and contains these two principles, in a considerable proportion. 

 The secretion of the bile and that of the fat, the only secretions that are 

 manifestly carried on in the foetus, may besides supply, very well, the 

 want of respiration*. 



The blood conveyed by the umbilical vein into the lower vena cava, and 

 deposited by that vein into the right auricle, does not unite with that 

 which is brought by the descending cava, from the upper parts, for as 

 was observed elsewhere, the orifices of these two vessels not being di- 

 rectly opposed to each other, the columns of blood which flow in them do 

 not meet each other. That which is brought by the lower cava, passes 

 through the foramen ovale, towards which the mouth of that vessel is 

 turned; it passes into the left auricle, thence into the left ventricle, with- 

 out circulating through the lungs, which containing no air and being dense 

 and indurated, could not have received it ; the contractions of the left 

 ventricle send it into the aorta, the force of its impetus is broken, by 

 striking against the great arch of this artery. It enters into the vessels 

 which arise from it, and these convey it directly to the brain and upper 

 parts. This blood is the most pure, the most oxygenated, and that which 

 comes most immediately from the placenta ; it has not yet circulated in 

 the body of the foetus, with the exception of a very small quantity brought 

 from the pelvis and lower parts, for, the blood which comes from the 

 abdominal viscera, is purified in passing through the liver. The other 

 parts of the body receive, on the contrary, blood very imperfectly oxy- 

 genated, since the very inconsiderable quantity which the contractions 

 of the left ventricle of the aorta have not been able to send into the ves- 

 sels arising from the arch of this vessel, mixes with the venous blood 

 which is brought by the ductus arteriosus, immediately below this cur- 

 vature. Hence the growth, which is always relative, not only in respect 

 to the quantity, but likewise to the vivifying qualities of arterial blood, 

 is much more rapid, before birth, in the upper parts, so that the brain 

 alone constitutes the greatest part of the body, and the shoulders, the 

 chest, and the upper extremities, are developed, in a much greater de- 

 gree than the abdomen, and especially than the pelvis and lower extre- 

 mities. 



The blood which is brought by the descending cava, from the upper 

 parts of the body of the foetus, passes into the right ventricle which forces 

 it into the pulmonary artery ; this vessel sends only two small branches to 

 the lungs, and terminates, by a vessel called the ductus arteriosus, into 



* See APPENDIX, Note 1 1, 



