614 



DEVELOPMENT 



[CHAP. XLIII. 



supplies successive generations of cells as the old ones are gra- 



dually removed. 



The wall of the venous sinus of the mother, reflected from 



tuft to tuft, forms numerous 

 tubular processes, passing in 

 various directions amongst 

 them ; thus connecting the 

 several tufts with each other, 

 and forming a sort of support- 

 ing framework for the entire 

 organ. The tubular prolonga- 

 tions, of course, contain cells 

 of the decidua in their inte- 



Relation between the foetal and maternal vessels ; j v fu 



after Dr. Reid. Foetal tuft dipping into dilated venous *lOr, &ntt DV their 



sinus. 1. Curling artery of uterus. 2. Uterine rein. f__ 



3. Sinus. 4. Vessels of fetal tuft, composed of a small tace 

 branch of artery and rein. 



C11T . 

 SUr- 



nous sinuses of the mother. 



fig. 289. 



are 



lining membrane of the ve- 

 Dr. J. Reid has shown that the foetal 

 tufts often dip quite in- 

 to the uterine sinuses. 

 Weber has made 

 some beautiful injec- 

 tions of the foetal 

 tufts, which demon- 

 strate very satisfacto- 

 rily the highly tor- 

 tuous nature of the 



Uterine sinuses and foetal tufts. After Dr. Reid. 1. Curling .,, , 



artery of the_ uterus. 2. Uterine sinus, into which a tuft is pro- Capillaries, and show 



4. Foetal vessels branching. , , J , 1,1 



that the convoluted 



longed. 3. Foetal tuft. 4. Foetal vessels branching. 



capillary vessel may make many turns from one foetal loop into 

 another, before it opens into one of the branches of the umbilical 

 vein. Dr. Reid describes the blood brought by the curling arteries 

 of the uterus as being poured " into a large sac formed by the 

 inner coat of the vascular system of the mother," from which the 

 blood is carried back by the veins. The researches of Dr. J. Reid 

 agree with those of Weber; but Eschricht holds, that in man the 

 arrangement is essentially the same as in animals ; and that the 

 capillaries of the placenta of the human foetus are brought into 

 relation with the capillaries only of the mother. In many animals, 

 the maternal and foetal portions of the placenta can be very readily 

 separated from each other ; but in man this cannot be done without 

 tearing the vessels. 



The formation of the placenta commences in the human subject 



