. A laboratory manual and text-book of embryology. Embryology. EARLY HUMAN EMBRYOS AND THEIR MEMBRANES 83 functions performed by the yolk-sac in birds, with a consequent degeneration of the ungulate yolk-sac. In man and Unguiculates, the functions of the allantois are transferred to the chorion and the allantois in turn becomes a rudimentary structure. The Amnion.âThis is formed precociously in Unguiculates and in a manner quite different from its mode of origin in Ungulates and birds. It is assumed that its cavity arises as a split in the primitive ectoderm of human embryos, as in bat embryos
. A laboratory manual and text-book of embryology. Embryology. EARLY HUMAN EMBRYOS AND THEIR MEMBRANES 83 functions performed by the yolk-sac in birds, with a consequent degeneration of the ungulate yolk-sac. In man and Unguiculates, the functions of the allantois are transferred to the chorion and the allantois in turn becomes a rudimentary structure. The Amnion.âThis is formed precociously in Unguiculates and in a manner quite different from its mode of origin in Ungulates and birds. It is assumed that its cavity arises as a split in the primitive ectoderm of human embryos, as in bat embryos (Fig. 71). Later, a somatic layer of mesoderm envelops its ectodermal layer, its component parts then being the same as in birds and Ungulates, an inner layer of ectoderm and an outer layer of mesoderm (Fig. 70 D). It becomes mes am â em. Fig. 72.âSection of embryonic rudiment in Peters' ovum (first week) (after Peters), ect, ectoderm of chorion; mes, mesoderm; am, amnion; em. pi., embryonic plate; , yolk-sac; ent, entoderm; ex. cce., portion of extra-embryonic ccelom limited by a strand of the magma reticulare. a thin, pellucid, non-vascular membrane and about a month before birth is in contact with the chorion. It then contains from one-half to three-fourths of a liter of amniotic fluid, the origin of which is unknown. During the early months of pregnancy the embryo, suspended by the umbilical cord, floats in the amniotic fluid. The embryo is protected from maceration by a white fatty secretion, the vernix caseosa. At birth the amnion is ruptured either normally or artificially. If not ruptured, the child may be born enveloped in the amnion popularly known as a veil or "; The amniotic fluid may be present in excessive amount, the condition being known as hydramnios. If less than the normal amount of fluid is present, the amnion may adhere to the embryo and produce malformations. It has been found, too, that fibrous bands or cords of tissue may exte
Size: 1812px × 1378px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectembryology, bookyear1
