. The development of the chick; an introduction to embryology. Birds -- Embryology. ax. Mes. 'S^. /^ Mes. N ^ Fig. hb. â Transverse section through the head immediately behind the optic vesicles; stage, 10 s. Ao., Aorta, ax. Mes., Axial mesoblast. Ect., Ectoderm. Ent., Entoderm. F. B., Fore-brain. Mes., Mesoderm, or. pi., Oral plate, p'a. c, Periaxial cord. p. C. Parietal cavity. Pr'a., Proamnion. Ph., Pharynx, v. Ao., Ventral aorta. axis. It is identified by these writers with the permanent neuro- pore of Amphioxus. However, this is open to question. Poste- riorly the closure of the ne
. The development of the chick; an introduction to embryology. Birds -- Embryology. ax. Mes. 'S^. /^ Mes. N ^ Fig. hb. â Transverse section through the head immediately behind the optic vesicles; stage, 10 s. Ao., Aorta, ax. Mes., Axial mesoblast. Ect., Ectoderm. Ent., Entoderm. F. B., Fore-brain. Mes., Mesoderm, or. pi., Oral plate, p'a. c, Periaxial cord. p. C. Parietal cavity. Pr'a., Proamnion. Ph., Pharynx, v. Ao., Ventral aorta. axis. It is identified by these writers with the permanent neuro- pore of Amphioxus. However, this is open to question. Poste- riorly the closure of the neural tube proceeds much more rapidly, though, of course, it is not fully completed until after the disap- pearance of the primitive streak. ^â F. '^-^-;§_?& mmiSif^^^^^s& ^ ^mmmmm^ ?^3£Ect. ^®l«5;i?'- A'U Fig. 56. â Early stage of the neural folds. Transverse section through a 4-5 s embryo between the last somite and the anterior end of the primitive streak. Ect., Ectoderm. Ent., Entoderm, n. F., Neural fold. N'ch., Noto- chbrd. med. pi., Medullary plate. Mes., Mesoderm. The question as to the position of the anterior end of the original neural axis is one of great morphological significance. Accompanying the closure of the neural tube in this region the. 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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