Identifier: veterinaryobstet00will (find matches)
Title: Veterinary obstetrics, including the diseases of breeding animals and of the new-born
Year: 1909 (1900s)
Authors: Williams, Walter Long, 1856-
Subjects: Veterinary obstetrics
Publisher: Ithaca, N.Y. : The author
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries

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eventually filled with fluid. (See Figs. 74, 75.) Tracing the allantois from its origin in the hind gut, there isa slight constriction which is to constitute the urethra, followedby a dilation from which the urinary bladder is to develop, thenan elongated, narrow tube, the urachus, which extends from thefundus of the urinary bladder out through the umbilicus andalong in the umbilical cord across the amniotic cavity. In structure, the inner layer of the allantois is of hypoblastderived from the inner layer of the hind gut, while the externallayer consists of mesoblast, \\\ which the allantoic vessels areformed to constitute the va.scular layer. In all our domestic animals, the allantois constitutes a greatsac, which is filled with a liquid, the allantoic fluid, which con-sists largely of the secretions from the kidneys, augmented per-haps by transudation from the blood vessels of the walls ofthe sac itself. The allantoic fluid contains albumin, grape sugar 23 354 Veterinary Obstetrics
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Rent in the Wallof the Ovum. Fig. 73. A, Embryo of the horse in its membranes. 4.2 cm. in its greatest diameter. Twenty-eight days after fecundation.B, The same seen from the other side. (Bonnet). The Chorion 355 and urea aud is, consequently, similar in character to the amnioticfluid, except that no meconium can reach this cavity since onlythe urinary tract communicates with it. In the fetus the urinary secretions may pass either backwardthrough the urethra into the amniotic cavity or forward throughthe urachus into the allantoic cavity and, consequently, throughthis tract the two cavities communicate throughout intra-uterineexistence. In the human embryo there is virtually no allantoicsac except for a very brief time early in pregnancy, the walls ofthe allantois soon coming in immediate contact. Collectively, these membranes, with the addition of the vesti-gial remains of the vitelline sac, constitute the fetal membranes,or after-birth. The Chorion. The external or vascular layer of

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