. The development of the chick; an introduction to embryology. Birds -- Embryology. ^^^^^^^ ^cl ^o/r?J/es. O 6^ ^.?>;^: yT^/. 6"ce/ Fig. 57. — Later stage of the neural folds. Section through the head of an embryo of 2-3 s; corresponding to about the future mid-brain region. Coel., Coelome. g. C, Germinal cells, med. pi., Medullary plate. Mes., Mesoblast. n. F., Neural fold. n. Cr., Neural crest. N'ch., Notochord. som. Mes., Somatic layer of mesoblast. spl. Mes., Splanchnic layer of mesoblast. anterior end rapidly grows forward beyond the anterior end of the fore-gut. The floor of the
. The development of the chick; an introduction to embryology. Birds -- Embryology. ^^^^^^^ ^cl ^o/r?J/es. O 6^ ^.?>;^: yT^/. 6"ce/ Fig. 57. — Later stage of the neural folds. Section through the head of an embryo of 2-3 s; corresponding to about the future mid-brain region. Coel., Coelome. g. C, Germinal cells, med. pi., Medullary plate. Mes., Mesoblast. n. F., Neural fold. n. Cr., Neural crest. N'ch., Notochord. som. Mes., Somatic layer of mesoblast. spl. Mes., Splanchnic layer of mesoblast. anterior end rapidly grows forward beyond the anterior end of the fore-gut. The floor of the neural tube does not, however, take part in this extension, the consequence being that the sum- mits of the neural folds form arching knees extending in front of the original anterior end of the medullary plate (Figs. 51 and 52). The extreme anterior end of the neural tube formed in this way has a ventral as well as a dorsal defect, and when it closes there is a ventral as well as a dorsal suture. The ventral end of this suture marks the original anterior end of the me- dullary plate, and this lies at the stage of 10 somites a short distance in front of the ante- rior end of the oral plate in the region of the future re- cessus opticus (Fig. 62). (Go- ronowitsch calls the anterior fissure, sutura cerchralis ante- rior; His divided it into two. Fig. 58. — Ventral view of the head region of an embryo of 5 somites, drawn in balsam with transmitted light. X 30. a. c. v., Amnio-cardiac A-esicle. a. i. Anterior intestinal jiortal. F. G., Fore-gut. My'c, Myocardium. N'ch., Notochord. n. F., Neural fold. s 2, s 4, Second and fourth Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lillie, Frank Rattray, 1870-1947. New York, Holt
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