314 BULLETIN OF THE 



now passes, and among the meshes of which the corpuscles are often 

 entangled, so that the circulation is much less rapid than in the sinus 

 outside. Before this stage is reached the blood of the foetus also be- 

 gins to circulate, and as the outer chamber of the placenta is part of 

 its sinus system, the small corpuscles contained in its blood can be 

 seen passing around the outside of the inner chamber, and thus 

 coming into very close proximity to that of the nurses. Huxley's ac- 

 count of the placental circulation at this period is so good that it will 

 not be out of place here, although he adds very little to the accounts 

 previously published by Sars and Krohn. He says (p. 575), that the 

 placenta " contains two perfectly distinct cavities or sacs ; of these 

 the outer is concave and cup-shaped and envelops the inner, which is 

 subspherical. Now the outer sac is in free communication by a nar- 

 row neck, divided into two channels by a partition, with the dorsal 

 sinus of the foetus ; and the inner sac is in equally free communication 

 by a neck similarly divided, with a short sinus arising immediately 

 behind the heart ; and as there is no communication between the two 

 sacs, it follows that the current of blood in each is perfectly distinct 

 from and independent of that in the other. A more beautiful sight, 

 indeed, can hardly be afforded to the eye of the microscopic observer 

 than the circulation in this organ. The blood-corpuscles of the parent 

 may be readily traced entering the inner sac on one side of the parti- 

 tion, coursing round it, and finally re-entering the parental circulation 

 on the other side of the partition ; while the foetal blood-corpuscles, 

 of a different size from those of the parent, enter the outer sac, cir- 

 culate round it at a different rate, and leave it to enter into the general 

 circulation of the dorsal sinus. More obvious still does the inde- 

 pendence of the two circulations become when the circulation of either 

 mother or fcetus is reversed." 



The following historical sketch of our knowledge of this structure 

 is also taken from Huxley's paper, page 592 : "Cuvier* speaks of 

 finding a fcetus attached to the parent by a pedicle ; and, referring to 

 a figure, he says : ' Ce corps rond [evidently the placenta] seroit-il un 

 organe servant uniquement pendant le temps de la gestation pour 

 etablir l'union entre la mere et son petit et qui s'effaceroit ensuiteT 



Chamissot calls the pedicle of attachment ' pediculus umbilicalis ' ; 

 the placenta, ' globulus opacus.' 



* Ann. Mus. d'hist. nat. 1804, IV. 



t Nova Acta, 1832, XVI. pp. 3G2 - 422. 



