. The development of the chick; an introduction to embryology . t 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 plat
. The development of the chick; an introduction to embryology . t 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 tive .streak, l)ut tliis j)art becomes distinct as the primitive streaksplits into its derivatives. It is therefore only when the latteris entirely used up that the entire length of the medullary plateis established. However, long l^efore this time the greater por-tion has become converted by folding into the neural tube, aprocess that proceeds in general from in front backwards. Thus ■^^
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