456 ANATOMICAL AND PATHOLOGICAL OBSERVATIONS. 



of the decidua enlarge, and assume the appearance of sinuses 

 encroaching on the space formerly occupied by the cellular 

 decidua, in the midst of which the villi of the chorion are 

 imbedded. This increase in the calibre of the decidual capil- 

 laries goes on to such an extent, that finally the villi are 

 completely bound up or covered by the membrane which 

 constitutes the walls of the vessels, this membrane following 

 the contour of all the villi, and even passing to a certain 

 extent over the branches and stems of the tufts. Between 

 this membrane, or wall of the enlarged decidual vessels, and 

 the internal membrane of the villi, there still remains a layer 

 of the cells of the decidua. 



From this period, up to the full time, all that portion of 

 decidua in connection with the group of enlarged capillaries 

 and vascular tufts of the chorion, and which may now be 

 called a placenta, is divided into two portions. The first 

 portion of the decidua, in connection with the placenta, or 

 forming a part of it, is situated between that organ and the 

 wall of the uterus. This is the only portion of the placental 

 decidua with which anatomists have been hitherto acquainted, 

 and I shall name it the parietal portion. It has a gelatinous 

 appearance, and consists of rounded or oval cells. Two sets of 

 vessels pass into it from the uterus. The first set includes 

 vessels of large size which pass through it for the purpose of 

 supplying the placenta with maternal blood for the use of the 

 foetus. These may be named the maternal functional vessels 

 of the placenta. The second set are capillary vessels, and 

 pass into this portion of the decidua for the purpose of 

 nourishing it. These are the nutritive vessels of the placenta. 



The account given by Mr. Hunter of the manner in which 

 the functional vessels of the placenta pass through this 

 portion of the placental decidua is still doubted by many, 

 notwithstanding the more recent of Mr. Owen's* dissections, 



* Owen. Palmer s Edition of John Hunter's Works, vol. iv. 



