4P4 Sir Everard Home on the placenta . 
The lungs are the last parts of the embryo that are com- 
pletely formed. As soon as this happens, the blood that cir- 
culates through the lungs must greatly diminish the supply 
of blood to the placenta ; the consequence of which will be, 
that the small terminal arteries of the foetal portion will be- 
come contracted ; which cannot happen to any great degree 
without producing more or less of a separation of the placenta 
and chorion, and this will be followed by the expulsion of 
the young. That very slight disturbance at this period brings 
on labour, is well known, from the number of children pre- 
maturely born, that are with difficulty kept alive till the circu- 
lation through the lungs becomes complete : they are called 
blue children. 
I shall not carry these observations farther at present, and 
shall conclude them with a specimen of a new mode of 
classing animals, upon the principles laid down respecting 
the difference in structure of the placenta. 
It will have the advantage, that the characters are fixed, 
and therefore the arrangement will never require to be 
changed : and there is a circumstance in its favour — it places 
the human species in an order separate from all inferior 
animals, the place undoubtedly assigned for mankind by the 
Almighty Creator. 
Class I. 
includes all animals in which the ovum becomes attached to 
the womb of the mother. 
Ova with adherent chorions. 
7 Orders. 
1. Lobulated placenta. Vide Plates XLII. and XLIII. 
One genus ; one species ; Man. 
