. The Journal of comparative neurology and psychology. to this is to be attrib-uted his attitude tow^ard the anterior head cavity as well as his failureto recognize the terminal neural crest and the mesectoderm derivedfrom it. In his figures the primitive optic groove is labelled infun-dibulum, but it is perfectly clear to me that it is the groove relatedto the optic vesicles. See PL 9, Fig. 9, where the groove markedInf. is the base of the optic stalk. In PI. 1, Fig. 15, the referenceline Ent. Zw. passes across the primitive optic groove at the frontand the true infundibular recess near the d
. The Journal of comparative neurology and psychology. to this is to be attrib-uted his attitude tow^ard the anterior head cavity as well as his failureto recognize the terminal neural crest and the mesectoderm derivedfrom it. In his figures the primitive optic groove is labelled infun-dibulum, but it is perfectly clear to me that it is the groove relatedto the optic vesicles. See PL 9, Fig. 9, where the groove markedInf. is the base of the optic stalk. In PI. 1, Fig. 15, the referenceline Ent. Zw. passes across the primitive optic groove at the frontand the true infundibular recess near the deep end of the hypophy-sis. Compare Figs. 23, 24, and 25 of this paper. The terminalridge is especially clear in Dohrns PI. 11, where early stages showits form as well as the early stages of Amblystoma (see below). Johnston, Forehram Vesicle m Vertebrates. 487 c. Roof of the Diencephalon.—In the roof of the interhrain thedevelopment of the vehim transversum, dorsal sac, epiphysis andparaphysis has been well described (Minot, Sterzi) so that I have. Fig. 22. Sqiialus ac, stage M, two sagittal sections near the median 25. In addition to the features shown in earlier figures, the optic chiasma,anterior, posterior and habenular commissures are seen. nothing new to add. I wish only to note that a careful considera-tion of Dr. Neals sections and of the models made from them leadsme to believe that the segmental position of the optic vesicle is 488 Journal of Comparative Neurology and Psychology. practically the same as that of the transverse velum. The velumdoes not become prominent until after the optic vesicle is wellformed (stage K), but in some specimens a slight fold representingit can be recognized in models of embryos as early as 24 somites orearlier. I am inclined to think that the velum represents an infold-ing of the brain wall which is begun early on account of the with-drawal of material from the alar plate to form the optic is the second neuromere wh
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