AND FAMILY DISPENSATORY. 
es tne ur cose aero tae ae 
siiciy alonds< hte teaeemes nas ) 4 artery, and scaves a paffage into the 
continually moves out of the final a brill ; ‘“e oe ar nes aes body, 
ricle and right ventricle, into the pulmona os Setar aile “whan zn A ghee 
4g | ry artery, in a continued and forcible 
fiream. The blood carried by this artery into the lungs, and diftributed by its 
branches through the whole fubftance thereof, is firft admitted into the extremities 
of the pulmonary vein, called arteria venofa; whence, paffing into four large veffels 
which unite together, it is brought to the left /inus venofus, or trunk of the pulmbiary 
_ vein; by the force of whofe mufculous ftructure it is driven into the left ventricle, 
which on this occafion is relaxed, and by that means prepared to receive it. Hence, 
as before, it is driven into the left ventricle, which is relaxed by the fame means ; 
_and the valvule mitrales opening, admit it into the left ventricle, and hinder its re 
flux into the pulmonary vein. From hence it is forced into the aerta; at whole 
orifice there are three femilunar valves, which alfo prevent a reflux by clofing the 
fame. And thus is circulation effected ; all the blood fent into the lungs, and re- 
ceived in the arteria venofa, finus venofus, left auricle and ventricle, being here con- 
tinually propelled into the aorta, whofe ramifications are fpread throughout all the 
reft of the body, with a violent motion. Thus is all the blood, in its return from 
every part of the body, internal and external, and from every part of the heart and 
its auricles, impelled into the right ventricle; out of that into the lungs; thence 
into the left ventricle, and thence through the whole extent of the body; and thence 
again brought back to the heart. 
In a fetus, the apparatus for the circulation is fomewhat different from that 
above defcribed. The /eptum which feparates the two auricles of the heart, is 
pierced through with an aperture, called the foramen ovale; and the trunk of the 
~ pulmonary artery, a little after it has left the heart, fends out a tube in thedefcending 
aorta, called the communicating canal. The blood in the lungs of the fetus has 
~ none of the advantages of air or refpiration; which yet being neceffary, nature, it 
is fuppofed, takes care that it receives a portion of air, mixed together with its mo- 
ther’s blood, and tranfmitted to it by the umbilical vefféls, to be diffufed through 
the body. This is confirmed hence; that, by conftringing the navel-ftring very 
tight, the child dies like a man ftrangled, which appears to be owing to nothing 
but the want of air. Add to this, that, as foon as the mother ceafes to refpire, the — i 
Setus expires. | | “fa . ee 
As to the velocity of the circulating blood, and the time wherein the ¢ 
is completed, feveral computations have been made. By Dr. Keill’s acco 
blood is driven out of the heart into the aorta, with a velocity which would casry 
33. BeOS o Ee oe ee ee 
105 
