1632 A MANUAL OF ANATOMY 



this reticulum are occupied by Wharton's jelly, which is composed of 

 connective tissue, pervaded by a gelatinous fluid. 



The external epithelial covering of the cord consists of ectoderm, 

 and at the placental end of the cord this ectoderm is continuous 

 with that of the amnion. 



In early foetal life one or more loops of intestine protrude into the 

 umbilical cord for a short distance, but this condition is of tem- 

 porary duration. 



The Uterine Mucosa. 



The uterine mucosa, or mucous membrane of the cavity of the 

 body of the gravid uterus, having undergone hypertrophy, is known 

 as the membrana decidua. It consists of three parts — namely, 

 decidua vera, decidua capsularis, or reflexa, and decidua basalis, or 

 serotina. 



The ovum, after entering the cavity of the body of the uterus, 

 becomes embedded in the uterine mucosa, the lining ciliated colum- 

 nar epithelium of this part having disappeared, as well as the base- 

 ment membrane and some of the superficial cells of the corium. 

 The mucosa thus becomes excavated at the place where the ovum 

 sinks into it, and the connection between the two is established 

 through means of the fixation or root villi of the chorion frondosum. 

 The usual site of attachment of the ovum is the upper part of the 

 posterior uterine wall, close to the fundus uteri. 



The decidua vera represents the greater part of the uterine 

 mucosa or membrana decidua. It lines the cavity of the body of 

 the uterus, except where the ovum is attached, and it has no direct 

 connection with the ovum. 



The decidua capsularis, or reflexa, is derived from the margins of 

 the excavation formed at the site of attachment of the ovum, and 

 it invests the ovum in the form of a capsule. . This maternal envelope 

 lies outside the chorion leve, but does not encroach upon the chorion 

 frondosum. It is at first separated from the decidua vera by a 

 space. As, however, the embryo increases in size the decidua 

 capsularis, or reflexa, comes into contact with, and joins, the 

 decidua vera, one deciduous membrane being thereby formed, and 

 the cavity of the body of the uterus being obliterated. 



The decidua basalis, or serotina, is that portion of the uterine 

 mucosa which forms the floor of the excavation formed at the site 

 of attachment of the ovum. It corresponds to the region of the 

 chorion frondosum, with which it becomes incorporated, and it 

 gives rise to the maternal part of the placenta, as distinguished from 

 the ffjeial part. 



Structure of the Decidua Vera. — ^The mucosa which forms the 

 decidua vera has undergone certain modifications in structure, 

 (i) It has become very much thickened, and the covering layer of 

 ciliated columnar epithelium has disappeared. (2) The uterine 

 glands have undergone enormous development, and are now much 

 elongated, dilated, and tortuous. (3) In the interglandular spaces 



