. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine . Fig. 83.—Diagram of the foetal membranes ofthe Virginian opossum (Haddon, after Os-born). Two villi are shown greatly processes of the cells, which have beenexaggerated, doubtless correspond to thepseudopodia described by Caldwell, al,allantois; am, amnion: , sinus termi-nalis; <«.z, subzonal membrane; r. villi onthe subzonal membrane in the region ofthe yelk-sac; ijs. yelk-sac. The vascularsplanchuopleure (hypoblast and mesoblast)is indicated by the black line. 82 C
. A text-book of comparative physiology for students and practitioners of comparative (veterinary) medicine . Fig. 83.—Diagram of the foetal membranes ofthe Virginian opossum (Haddon, after Os-born). Two villi are shown greatly processes of the cells, which have beenexaggerated, doubtless correspond to thepseudopodia described by Caldwell, al,allantois; am, amnion: , sinus termi-nalis; <«.z, subzonal membrane; r. villi onthe subzonal membrane in the region ofthe yelk-sac; ijs. yelk-sac. The vascularsplanchuopleure (hypoblast and mesoblast)is indicated by the black line. 82 COMPARATIVE PHYSIOLOGY. a characteristic body, allantoin, related to uric acid, urea,etc. Certain bodies, being probably inspissated allantoic fluid,have been termed hippomanes. They may either float freein the fluid or be attached to the allantois by a slender pedicle. The relation of the parts described above will become clearerafter a study of the accompanying cuts and those of precedingpages, in which the allantois is Fig. 84.—Exterior of chorial sac; mare. (Chauveau.) A, body; B. C. cornua. The Placenta.—This structure, which varies greatly in com-plexity, may be regarded as the result of the union of structuresexisting for a longer or shorter period, free and largely inde-pendent of each other. With evolution there is differentiationand complication, so that the placenta usually marks the sitewhere structures have met and fused, differentiating a new or-gan; while corresponding atrophy, obliteration, and fusion takeplace in other regions. All placentas are highly vascular, all are villous, all dis-charge similar functions in providing the embryo with nourish-ment and eliminating the waste of its cell-life (metabolism).In structural details they are so different that classifications ofmammals have been founded upon their resemblances and dif-ferences. They will now be briefly described. In marsupials the yelk-sac is both large and vascular; theallantois sma
Size: 2150px × 1163px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1890
