. The Journal of comparative neurology and psychology. of the lips of the neuropore from below upward and thereforethe last point of the neuropore to remain open is a point in thedorsal seam of the neural tube some distance removed from theanterior border of the neural plate. This part of the seam of closurewhich represents the length of the neuropore is what is called the 480 Journal of Comparative Neurology and Psychology. lamina terminalis. This is not very long in the embryo of 17somites, but grows distinctly in length as the forebrain apparent great thickness of the lamina ter
. The Journal of comparative neurology and psychology. of the lips of the neuropore from below upward and thereforethe last point of the neuropore to remain open is a point in thedorsal seam of the neural tube some distance removed from theanterior border of the neural plate. This part of the seam of closurewhich represents the length of the neuropore is what is called the 480 Journal of Comparative Neurology and Psychology. lamina terminalis. This is not very long in the embryo of 17somites, but grows distinctly in length as the forebrain apparent great thickness of the lamina terminalis in Fig. 3 isof course due to the persistence of the fusion of ectoderm and brainwall at this time. The primitive optic groove is deeper and-sharperin outline than in the last stage. The relations in an embryo of 24 somites are shown in Fig. 16representing the medial view of a model of the right half of thehead. In this is seen the depression of the primitive optic grooveuntil its wall comes into contact with the ectoderm and cuts off the Fig. 16. Squaliis ac, 24 somites, medial aspect of a model of the right halfof the head. X ^^ front part of the preoral entoderm as before described. The lens-shaped space in front of the primitive optic groove is filled chieflyby mesectoderm from the terminal part of the neural crest. Thelamina terminalis is marked by a small triangular pit above, theneuroporic recess, and by a rounded shallow pit below. This pitoccupies the lower portion of the neuropore space and may thereforebe called the terminal pit. The optic vesicle is now stalked and thecavity of the stalk is seen near the base of the brain. It is notice-able that this cavity no longer communicates directly with the primi-tive optic groove. It seems equally closely related to the terminalpit. Between the two pits the brain wall is somewhat thickened. Johnston, Forcbrain Vesicle ni Vertebrates. 481 This thickening corresponds to the anterior border of the neural plateand t
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