A text-book of veterinary obstetrics : including the diseases and accidents incidental to pregnancy, parturition and early age in the domesticated animals . vum having been lodged in the uterus, and the f/erm-mcmhraTieor blastoderm having divided into two layers—an upper or seroics, and alower or mucous—and between which, at a later period, a vascular layeris developed, another modification occurs by which the outline of theembryo becomes evident. In the centre of the blastoderm, where it is supposed to divide intothese layers, there is observed a clear space which has been designatedthe area
A text-book of veterinary obstetrics : including the diseases and accidents incidental to pregnancy, parturition and early age in the domesticated animals . vum having been lodged in the uterus, and the f/erm-mcmhraTieor blastoderm having divided into two layers—an upper or seroics, and alower or mucous—and between which, at a later period, a vascular layeris developed, another modification occurs by which the outline of theembryo becomes evident. In the centre of the blastoderm, where it is supposed to divide intothese layers, there is observed a clear space which has been designatedthe area jtrolujera or pcllucula, in the centre of which, and in the trans-verse axis of the vitellus, there is going on a multiplication of looselyconnected cells in a small rounded mass, which forms the rjerminativearea, primitive streak, or trace of Von Baer ; while around this anotherspace—the area vasculosa—is developed. The • primitive streak isthe centre where the blastoderm commences to be separated into theexternal and internal layers ; the middle layer, which is to form thefoetal organs, not extending beyond the germinative area or Fig. 42. Blastodkbm and Pkimitivk Thack. a. Vitelline Membrane with iti) <X)iiiiiiencing VilloBities ; h, External (or Serous)Layer of the Bl*«t<xierui ; r. Internal (or Mucouh) Layer ; d, liody of theEmbryo; //, b. Earliest Cephalic and Caudal Elevation of the ExternalLayer. By a proliferation of the elements of the outer and middle layers ofthe blastoderm, the primitive trace increases in surface and thickness,becoming clearly defined and prominent, in the form of a shield, and isnamed the opaque area, which, when it grows transparent in its centre,is named the transparent or pellucid area ; the clear spot, narrowing orconstricting in its middle part, is named the area vasculosa or the middle of this embryonic area appears a dark line, or medianfurrow, duo to changes occurring in the primitive streak ; and b
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishernewyo, bookyear1901
