Archive image from page 121 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 102 THE DEVELOPMENT OF THE CHICK stage that the former closes completely (cf. Fig. 64). The final point of closure at the anterior end, known as the neiiropore, is supposed by some to be a point of great morphological signifi- cance, and to mark the extreme anterior end of the original neural axiMes. â Ent. \'- ' £ >i< Fig. 55. â Transverse section through the head immediately behind the optic vesicles; stage, 10 s. Ao., Aorta,
Archive image from page 121 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 102 THE DEVELOPMENT OF THE CHICK stage that the former closes completely (cf. Fig. 64). The final point of closure at the anterior end, known as the neiiropore, is supposed by some to be a point of great morphological signifi- cance, and to mark the extreme anterior end of the original neural axiMes. â Ent. \'- ' £ >i< Fig. 55. â Transverse section through the head immediately behind the optic vesicles; stage, 10 s. Ao., Aorta, ax. Mes., Axial mesoblast. Ect., Ectoderm. Ent., Entoderm. M. A., Mandibular arch. M. B., Mid-biain. 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. .iL'.atif ..'oV VT'', 5 V< â ?' Wm0§siM â F. SlC- m&mm 'fcA A'hA. 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- chord. 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
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