720 



UTEEOGESTATION. 





pass from one extreme branch of tlie villi to another, within the fibrous 

 core of which they are situated, and SchriJder van der Kolk has 

 described also a tiner superficial network of capillaries distributed 

 below the epithelial covering of the stems and larger branches of the 

 villi. By artificial injections fluids can be made to pass with perfect 

 precision from the umbilical arteries through the capiharies of the 

 villi into the veins, or in the reverse direction from the veins into the 

 arteries. Nor does there ever occur, except from visible accidental 

 rupture of the vessels, either extravasation of the injected material into 

 the intervening tissue, nor any escape into the maternal sinuses. 



Fig. 523. Fig. 523.— Small Portion of Tla- 



CENTA SHOWING THE FcETAL ViLLI 



Slightly Magnified (from Leish- 

 man after Weber). 



The uterine blood-passages, 

 on the other hand, are of the 

 nature of irregular spaces, into 

 which the maternal blood is 

 poured directly by numerous 

 small coiled arteries which, as 

 shown by the Hunters, pierce 

 the external decidua at the uterine surface of the placenta, and open 

 into these blood-spaces without the intervention of any capillary sub- 



Tl'j. 524. Fig. 524. — Chorionic Villits from: the Pla- 



centa AT THE Twelfth Week. Enlarged 

 ISO Diameters (from Leisliman after Ecker). 



From a to h, the epithelial coveriDg is left 

 entire ; from a to a it ha.s been removed and 

 tlie fibrons core with the capillary blood-vessels 

 is shown. 



division. The result of artificial in- 

 jection of the blood-vessels in the 

 pregnant uterus equally demonstrates 

 the nature of the circulation in the 

 maternal part of the placenta, for it 

 is easy to show by this method, that 

 a fluid thrown into the uterine arteries 

 fills at once all the maternal blood- 

 spaces of the placenta, surrounding 

 everywhere the chorionic or foetal 

 villi, and returns thence into the 

 uterine veins b_y a number of slanting 

 venous channels, the ntero-jilaccntal 

 sinuses, provided with delicate coats, 

 which issue from the placenta at its 

 uterine surface by piercing the decidua serotiua, and which are most 

 numerous towards the circumference of the organ, where they are in com- 

 munication with the so-called circular vein or circular sinus previously 

 referred to. Some of these veins may even be traced for some distance 

 into the placenta, in the septa of decidual substance, which are pro- 



