The development of the human body; a manual of human embryology . eters.) 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 t
The development of the human body; a manual of human embryology . eters.) 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 andunite to form an extensive blood space completely sur-rounding the embryonic vesicle. Into this blood spacethe vessels of the uterine walls open, and into it also theirregular processes of the trophoblast project, formingwhat are termed the chorionic villi, the space itself beingknown as the intervillous space (Fig. 66, B).. ON Fig. 67.—Two Villi from the Chorion op an Embryo op 7 mm. These villi may at first be developed over the wholesurface of the chorion or they may be limited to a broadband situated at what may be termed the equator of theovum; but whichever arrangement occurs, only those de-veloped from that portion of the chorion to which thebelly-stalk is attached undergo further elaboration inlater stages, the rest gradually disappearing or remainingonly as minute rudiments. It is customary, consequently, 144 THE DEVELOPMENT OF THE HUMAN BODY.
Size: 1567px × 1595px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
