FCETAL MEMBRANES. 



121 



From their relation to the ovum and to the uterus, the deciduse (by which is 

 meant the uterine mucosa of pregnancy) have been divided into the decidua 

 parietalis or decidua vera the decidua basalis or serotina, and the decidua cap- 

 sularis or refiexa. 



tro. 



cyt. P.e. 



cap. 



tro. 1 



FIG. 106. Diagram of human ovum of 13-14 days, embedded in the uterine 



mucosa. Bryce and Teacher* 



cap., Capillary; cyt., cellular layer (cyto-trophoderm) ; cp., uterine epithelium; gl., uterine gland; 

 n. z., necrotic zone of decidua (uterine mucosa); P.e., point of entrance of the ovum; try.. 

 syncytium (plasmodium, plasmodi-trophoderm); tro.*, masses of vacuolating syncytium 

 invading capillaries. The cavity of the blastodermic vesicle is completely filled by mesoderm, 

 and embedded therein are the amniotic and entodermic (yolk) vesicles. The natural pro- 

 portions of the several parts have been observed. 



The decidua parietalis is the changed mucosa of the entire uterus with the 

 exception of that portion to which the ovum is attached. The decidua basalis 

 is that portion of the mucosa to which the ovum is attached and which later 

 becomes the maternal part of the placenta. The decidua reflexa is either the 



*The writers have been unfortunate in not having had access to Bryce and Teacher's splendid 

 contribution (T. H. Bryce and J. H. Teacher: An Early Ovum Imbedded in the Decidua. 

 MacLehose and Sons, Glasgow, 1908) in time to incorporate in the text the result of their investi- 

 gation. The ovum in question was found in a piece of membrane expelled during spontaneous 

 abortion which occurred in a healthy young woman ten days after the time of the first Japsed 

 menstrual flow. The age was estimated at thirteen to fourteen days, and the structure was such as 

 to indicate an earlier stage than that of Peters', Jung's, Merttens', Leopold's, or von Spec's embryo, 

 thus making it the youngest human ovum on record. The results of the investigation are important 

 in their bearing not only on the implantation of the ovum in the uterine mucosa but also on the 

 development of the germ layers. 



