PLACENTA. 185 



Each vascular branch, in separating from the outer surface of the 

 chorion, is composed of a single artery and a single vein, which are 

 already twisted in a spiral manner; the trunk soon divides into two 

 branches of each sort, and these again into two others, so that these 

 dycotoraic ramifications go on almost ad infinitum: being pressed 

 together and united to each other by means of the fibrous layer, 

 these divisions and subdivisions constitute a lobe, or cotyledon of the 

 placenta. In ruminating animals, particularly in the cow, these lobes 

 being very remotely separated from each other, form so many dis- 

 tinct placentfe. 



All the vessels of one lobe communicate with each other; but the 

 experiments of Wrisberg, which I have repeated, prove that they do 

 not in general communicate with those of a neighboring lobe. 



479. When any of these lobes separate from the others, and are 

 at some distance from the placental disc, they form a small distinct 

 placenta, and this has assuredly been the reason which has on more 

 than one occasion led to the belief that there were two placentae to 

 one single foetus. Each one unites to those about it, as the different 

 lobules of the same cotyledon are united among themselves, and 

 their adhesion, which takes place in the tliird month, may easily be 

 broken up at full term : being thus disposed, they constitute the 

 parenchyma of the placenta, so that this parenchyma is e-itirely 

 composed of vessels, of solid filaments, of granulations, and a fibri- 

 nous matter which serves as a common bond of union for them, but 

 not of any cellular basis analogous to that of other organs. 



480. MM. Dubois and Biancini state that they have injected the 

 arteries, and probably the veins also, which pass from the uterus to 

 the placenta, and vice versa; Reuss has given a drawing of them, 

 and Albinus had already noticed them; I have vainly sought for these 

 utero-placenfal vessel in a great number of subjects, and the condi- 

 tion of the parts has convinced me that if they do sometimes exist, 

 they are far more frequently wanting. I can assure the reader that 

 whenever I have examined the ovum in the uterus after the third 

 month, its surface, as well as that of the womb, was smooth through- 

 out its whole extent, and that not a single vessel served to maintain 

 the connection between these two parts.* Might not the learned 

 authors whom I have mentioned have been deceived by some ano- 

 maly, some pathological stale, or some false appearances? Could I 



* I have carefully witnessed the anatomical separation of the ovum from the 

 womb at full term, and could never see the smaikst vessel passing from one to 

 the otiier. I do not believe that there is any utero-placental circulation ap- 

 preciable by the senses. — M. 



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