The elements of embryology. / By M. Foster ... and Francis M. Balfour.

  • Michael Foster
Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: The elements of embryology. / By M. Foster ... and Francis M. Balfour. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

    81/336 page 55
    THE PROTOVERTEBR^. nil.] 1 but clear fluid; and transverse sections sliew that they are , due to breaches of continuity in the mesoblast only, the ^epiblast and hypoblast having no share m the matter, ihe T first transverse lines which appear are two m number, one a I little behind the other, about opposite the spot where the 1 medullary folds first coalesced to form the neural tube, ihe 1 longitudinal lines begin at about the same place and run thence i backward, parallel to the notochord, as far as the closure ot :the medullary canal extends. Behind the first two transverse ; lines other parallel transverse lines in course of time make 1 their appearance. . Thus each vertebral plate appears in surface views to be cut up into a series of square plots, bounded by transparent lines. Each square plot is the surface of a corresponding . cubical mass (Fig. 13, P. v., Fig. 20, P. v.). The two such Fig. 13. /jyc rPr ,1, / / \C7p 'jio \i3c -^rp Tbansvebse Section through the Dorsal Region of an Embryo of the Secokd Day. (Copied from His), introduced liere to illustrate the forma- tion of the protovertebrse, and the cleava^'e of the mesoblast. The provertebrffi appear irregularly quadrate; they wouM have been more distinctly square, had tlie section been one of the first day. before the appear- ance ot the primitive aortse, and of the rudimenta of the Wolffian ducts: com- pare Fig. 20. t ITT liC J 4- M. medullary canal. Pv. pmtovertebra. w. rudiment of Wolffian duct. A. epiblaat. C. hvpoblast. Ch. notochord. Ao. aorta. £0. splanch- nopleure. (/^^ f^CtcU>-fe^^^'^ ca<^c^ - cubical masses first formed, lying one on either side of the notochord beneath, and a little to the outside of the medul- lary folds, are the first pair of protovertebrce. Behind this first pair, but otherwise similarly situated, a second and thurd pair make their appearance during the first day.
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