FCETAL MEMBRANES. 135 



them are known as placenta duplex. Placenta triplex and up to placenta septu- 

 plex have been described. When one or more placental lobules develop at a 

 little distance from the main placental mass but connected with the latter by 

 blood vessels, the result is the not uncommon placenta succenturiata. Placenta 

 spuria is applied to such an accessory lobule when it has no vascular connection 

 with the main placenta and consequently no function. 



Anomalies of the placenta associated with multiple pregnancies and with 

 anomalies of the foetus will be found under their respective heads. 



Anomalies of the cord are for the most part dependent upon anomalies of 

 the fcetus and of the placenta. 



PRACTICAL SUGGESTIONS. 



The early formation of the foetal membranes can be studied most conveniently in chick 

 embryos of the second and third days of incubation. At the beginning of the second day the 

 amniotic folds are beginning to develop and show very clearly. Further development can be 

 followed in successive stages up to the end of the third day, when the amnion and chorion 

 form complete sacs (Figs. 94 and 96). 



Remove the embryo from the egg, fix in Zenker's or Perenyi's fluid, section tranversely in 

 paraffin, and stain with Weigert's haematoxylin and eosin. Much time can be saved by 

 staining in toto with borax-carmin (see Appendix). 



After the amnion and chorion have grown dorsally they can be seen, if the egg is opened 

 carefully, as a thin semi-transparent veil over the embryo, and sometimes the dorsal line of 

 fusion can be made out. (See Fig. 94.) 



In transverse sections of embryos of the second day the anlage of the allantois can be 

 seen as a ventral evagination from the caudal end of the gut. (See Fig. 99.) 



The later stages of the membranes in the chick can be studied macroscopically after 

 carefully turning the contents of the egg into a dish of warm salt solution. 



The lack of knowledge concerning the early formation of the fcetal membranes in Mammals, 

 especially in man, is due chiefly to the difficulty in procuring embryos in early stages. In 

 later stages the membranes can be clearly seen and their relations ascertained when the 

 uterus is opened. A careful dissection of the uterus and membranes of some Mammal 

 (the dog, for example) is very instructive. Occasionally human embryos are obtained in 

 which the membranes can be studied. (See Figs. 117 and 118.) 



For the study of the relation between the chorion and uterus, the gravid uterus of the 

 pig furnishes excellent material. The relation is very simple, yet gives a clue to the much 

 more complicated conditions in higher forms. Fix pieces of the uterine wall with the chorion 

 in situ in Zenker's fluid, cut sections vertical to the surface, and stain with Weigert's haema- 

 toxylin and eosin. (See Fig. 102.) 



In man the relations between the chorion (placenta) and uterus are extremely complicated 

 and it is difficult even to interpret the structures seen in section. Up to the end of the third 

 month, in cases of spontaneous abortion, the membranes usually come away intact with the 

 villi projecting from the chorion. For study of the histological structure of the chorion by 

 itself, cut pieces from the wall of the vesicle, fix in Orth's fluid, cut sections vertical to the 

 inner surface, and stain with haematoxylin and eosin (see Appendix). The villi of course are 

 cut at various angles, but their structure shows very clearly. (See Fig. 109.) Similar technic 

 can be used for study of later stages of the chorion frondosum or foetal placenta. In the 



