The development of the human body; a manual of human embryology . unt of torsion from the move-ments of the embryo in the later stages of development andmay even be knotted. The greater part of its substanceis formed by the mesoderm, the cells of which becomestellate and form a reticulum, the meshes of which areoccupied by connective-tissue fibrils and a mucous fluidwhich gives to the tissue a jelly-like consistence, whenceit has received the name of Whartons jelly. 142 THE DEVELOPMENT OF THE HUMAN BODY. The Chorion.—The umbilical cord, or, more properly,the belly-stalk, places the body of the
The development of the human body; a manual of human embryology . unt of torsion from the move-ments of the embryo in the later stages of development andmay even be knotted. The greater part of its substanceis formed by the mesoderm, the cells of which becomestellate and form a reticulum, the meshes of which areoccupied by connective-tissue fibrils and a mucous fluidwhich gives to the tissue a jelly-like consistence, whenceit has received the name of Whartons jelly. 142 THE DEVELOPMENT OF THE HUMAN BODY. The Chorion.—The umbilical cord, or, more properly,the belly-stalk, places the body of the embryo in commu-nication with the wall of the embryonic vesicle, and thiswall, termed the chorion, is in contact with the walls of theuterus and becomes specially modified to produce the con-nection between the embryo and the maternal tissueswhich is characteristic of all the higher mammalia. It iscomposed of two layers, an outer ectodermal trophoblastlayer and an inner chorionic mesoderm. In the earlieststages it may be presumed that the trophoblast is com-. Fig. 66.—Two Diagrams Illustrating the Formation of Chorionic Villi. Bl, Blood-space; ca, maternal capillary; en, endothelium; fi, fibrin;Is, intervillous space; M, chorionic mesoderm; sp, stratum spon-giosum; Sy, syncytium; TV, trophoblast; v, villus.—(Peters.) paratively thin, as in the bats ovum, and later becomesa stout layer many cells thick. In the Peters embryo,whose ovum measures only about i mm. in diameter, ithas already become quite thick and contains numerousblood lacunas arranged as a network throughout its sub-stance. These lacunae seem to have been produced byblood extravasated from the maternal vessels penetratinginto the substance of the trophoblast and breaking it upinto irregular bands and processes (Fig. 66, A), this beingpossible from the fact that even at this early stage the THE CHORION. 43 ovum is completely embedded in the mucosa of theuterus. In later stages the lacunae increase in size and
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
