. The Journal of comparative neurology and psychology. FiG. 28. Amblystoma p., a little more advanced thau the one shown inFig. 27. Parasagittal section through the optic ridge. X •^^•. rpo. Fig. 29. Amblystoma p., of about the same stage as that in Fig. 28. Modelof the right half of the brain seen from the medial surface, x 40. necting the optic vesicles (Fig. 25). This is the primitive opticgroove as described in Squalus. The model of this stage shows asecond angle at the front of the neural tube, separated from the Johnston, Forehrain Vesicle in Vertebrates. 493 primitive o
. The Journal of comparative neurology and psychology. FiG. 28. Amblystoma p., a little more advanced thau the one shown inFig. 27. Parasagittal section through the optic ridge. X •^^•. rpo. Fig. 29. Amblystoma p., of about the same stage as that in Fig. 28. Modelof the right half of the brain seen from the medial surface, x 40. necting the optic vesicles (Fig. 25). This is the primitive opticgroove as described in Squalus. The model of this stage shows asecond angle at the front of the neural tube, separated from the Johnston, Forehrain Vesicle in Vertebrates. 493 primitive optic groove by the terminal ridge. This is a pit formedin the lower part of the nenropore and is the terminal pit (Fig. 25).From the earliest stages after the formation of the neural plateand folds, the region from which the hypophysis will be formed canbe accurately located. In a median sagittal section of any stageup to the time when the hypophysis is invaginated, a slight reen-trant angle is seen between the terminal ridge and the preoral ento-derm. The ectoderm of this angle will form the hypophysis. Whenthe neuropore closes this hypophysial ectodenn is slightly thickenedand
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