. The development of the chick; an introduction to embryology . m an entire mount in balsam bytransmitted light. a. (. v., Amnio-cardiac vesicle, a. o., In-ner margin of Area opaea-. Fct., , Fntoderm H. F., Head-fold. ,First intersomitic furrow, med. Medullaryj)late. Mes., Mesoderm, n. Neural groove,pr. gr., Irimitive gr()o\(\ Iia, jiioanmion. in the next chapter. At the 12 s stage one such place of contactis already formed, lying a sliort distance in front of the thickenedectoderm destined to form the auditory j^it. HEAD-FOLD TO TWELVE SOMITES 95 Andther place
. The development of the chick; an introduction to embryology . m an entire mount in balsam bytransmitted light. a. (. v., Amnio-cardiac vesicle, a. o., In-ner margin of Area opaea-. Fct., , Fntoderm H. F., Head-fold. ,First intersomitic furrow, med. Medullaryj)late. Mes., Mesoderm, n. Neural groove,pr. gr., Irimitive gr()o\(\ Iia, jiioanmion. in the next chapter. At the 12 s stage one such place of contactis already formed, lying a sliort distance in front of the thickenedectoderm destined to form the auditory j^it. HEAD-FOLD TO TWELVE SOMITES 95 Andther place of fusion between the fore-gut and the ecto-derm IS the so-called oral plate (pharyngeal membrane), whichoccupies a mid-ventral position at the extreme anterior paiietal cavities meet posterior to the oral ])late (Figs. 67and 75). Transverse sections show the oral plate to be depressedbeneath the level of the ventral surface of the head at the stage of10 somites (Fig. 55), a condition that increases, as development /Tff. _;,»*£»■. <^.. Fig. 49. — Metlian sagittal section of tlie head at the stage of 4 s. a. i. p., Anterior intestinal portal. F. G., Fore-gut. Ect., , Entoderm. H. F., head-fold. Mes., Mesoblast. n. F., Neural fold,or. pL, Oral plate. proceeds. l)y the formation of the cranial flexture, and by the up-growth of the tissues behind and at its sides; thus will ])e estal)-lished a deep depression lined by ectoderm, the floor of which isformed by the oral i:)late, and which is destined to form a largepail of the mouth. The depression is known as the stomodsBum. III. Origin ob the Nkural Tube The Medullary Plate. The medullary plate is the i:)rimordiumof the central nervous system. At the time of formation of thehead-fold it is broad in front and narrower posteriorly, endingopposite the posterior end of the j^rimitive streak. Its centralportion is not a separate plate of cells in the region of the priini- 96 THE DEVELOPMENT OF THE CHICK tiv
Size: 1937px × 1290px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookiddevelopm, booksubjectbirds
