. The development of the chick; an introduction to embryology . ~pr. str. Fig. 59. — Einliryo of 7 s from aliovo drawnill l)alsam with traiismittcd li,iz:ht. x c. Anterior ccrcliral suture, , Ceplialie Mesohlast. F. G., , Nolochord. n. T., Neiu-al tube. , Ojjtic vesicle. Pra., Proanmion. , Primitive streak, s 2, s 7, Second andseventh somites. V. o. m., Omphalo-mes-(nteric vein. HEAD-FOLD TO TWELVE SOMITES 105 parts, sutura neurochordalis sen ventralis and sutura terminalisanterior.) The neiiropore question resolves itself into this: What partof th
. The development of the chick; an introduction to embryology . ~pr. str. Fig. 59. — Einliryo of 7 s from aliovo drawnill l)alsam with traiismittcd li,iz:ht. x c. Anterior ccrcliral suture, , Ceplialie Mesohlast. F. G., , Nolochord. n. T., Neiu-al tube. , Ojjtic vesicle. Pra., Proanmion. , Primitive streak, s 2, s 7, Second andseventh somites. V. o. m., Omphalo-mes-(nteric vein. HEAD-FOLD TO TWELVE SOMITES 105 parts, sutura neurochordalis sen ventralis and sutura terminalisanterior.) The neiiropore question resolves itself into this: What partof the sutura cerebralis anterior is to be called neuropore? Asthe suture extends from near the infundibulum to the pinealregion at least, there is a wide range of choice. However, thereis a point in the suture near its dorsal end where the separationof the ectoderm from the neural tube takes place later thanelsewhere. This may be regarded as the equivalent of theneuropore. The suture is the site of formation of the lami?iaterminalis (Chap. VIII).. PiQ_ 60. — The head of the same embryo frombelow X 30. a. i. p., Anterior intestinal portal. Endc. s.,Endocardial septmn. F. G., Fore-gut. Ht., T., Termination of Notochord. op. Yes.,Optic vesicle, p. C, Parietal cavity. Pra., Pro-amnion. V. o. m., Omjjhalo-mesenteric vein. It will be seen that according to this account most of theprimary fore-brain includes no part of the original floor of theneural tul)e. Primary Divisions of the Neural Tube. The neural tul)e is theprimordium of tlie l)rain and spinal cord. Its cavity becomes theventricles of the brain and the central canal of the cord. There 106 THE DEVELOPMENT OF THE CHICK
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