COXCLUSlOX AS TO THE PLACENTA. 723 



he cliilers therefore from Sharpey in regarding the crypts as of new formation 

 and independent of the glands. He is thns led to the general conclusion that m 

 no kinds of placenta do the uterine glands form an essential part of the placental 

 structm'e, and that the uterine crypts which receive the fcetal processes are 

 essentially interglandular in their origin. Nevertheless Turner recognises the 

 existence in all placentas of uterine structiu'al elements of a cellular nature, which 

 he regards as descendants of the epithelial or subepithelial tissue of the uterine 

 mucous membrane, and to which he attributes, as others have done, glandular 

 functions in the preparation of the matter which is absorbed as nourishment by 

 the blood-vessels of the foetal \'illi. Further observations will be requhed to 

 detennine in how far these views admit of application to the stractiu-e of the 

 full}'- formed human placenta. (See also Tm'ner's Memoir on the Placentation of 

 Seals. Trans. Roy. Soc. of Edinbm-gh. Vol. xxvii.. 1875.) 



With respect also to the relation of the uterine glands to the penetration of the 

 decidua by the viUi in the fonnation of the human placenta, further observations 

 are stiU requii-ed. As iireviously stated, anatomists have failed to trace the villi into 

 the dilated parts of the enlarged glands, and Kolllker after a careful examination 

 of the whole subject, comes to the conclusion (Lectures, p. 1G2) that the villi in 

 becoming involved in the decidua have no pennanent connection with the glands. 

 He affirms indeed that the glands soon shrmk over the whole extent of the 

 decidua. beg'uining to do so as early as in the second month of j^regnancy, and 

 have in great measiu-e disappeai-ed before the chorionic villi are fully connected 

 with the uterine membrane. Reichert. however, in his recent description of an 

 early human o\Tim affirms that commencing villi actually enter the mouths of 

 uterine glands, and he has given a diagrammatic representation of the pro- 

 longation of the tubes of the uterine glands through the decidua to the surface 

 of the membrane, and the small marginal villi of the o\Tim as actually within 

 tenninal portions of the glands, the cavities of which have undergone some 

 degree of ramification. Fui-ther observations will, however, be necessary for the 

 confirmation of a statement so much at variance with the results of most other 

 observers. 



General conclusion- — In recapitulation of the preceding description 

 it may be stated that the human placenta is an organ which is formed 

 by the conabination of two different structural elements ; of which one 

 is derived from the foetus or its membranes, and the other from the 

 uterus. The foetal part consists of the developed vascular villi of the 

 chorion, continues to grow and extend itself with the foetus during 

 the whole of uterogestation, and is the seat of a complete circulation of 

 the foetal blood through the capillary ramifications of the umbilical 

 arteries, veins, and capillaries. The uterine element of the placenta 

 originates in a part of the decidua, which is produced by increased 

 growth and transformation of the lining membrane of the uterus and 

 its blood-vessels. "With the hypertrophied structure so produced the 

 villi of the foetal chorion at first interpenetrate, so that in the earlier 

 stages of placental formation the uterine and fcetal elements are for a 

 time separable, and may still be distinguished fi-om each other, at the 

 period even when they have become more intimately united. But in the 

 progress of development the uterine elements are so much modified, and 

 finally so completely attenuated or removed, that they almost entirely 

 disappear ; and as along with them the walls of the blood-vessels are 

 either thinned out to the last degree, or are entirely absorbed, there 

 remain only the vascular spaces through which the maternal blood 

 flows. A doubt, however, may still exist as to whether these spaces 

 are, or are not, entirely deprived of any uterine enclosure. 



The maternal blood is introduced into these spaces directly by the 

 small coiled uterine arteries, without capillary intervention, and after 



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