. The American journal of anatomy . sociation tracts. Thislayer, striking in sections on account of the dearth of nuclearmaterial, forms a brilliant background which permits one to readilyoutline the nuclei wandering over its surface later. From the embryological series of this laboratory definite evi-dences of the migration leading up to the formation of pontinenuclei appear in an embryo of 23 mm. (Mall Collection No. 382).Fig. 2 was drawn from a wax-plate reconstruction of the rhomb-encephalon of this embryo. Here the degree of medullarydevelopment corresponds pretty accurately to that of th
. The American journal of anatomy . sociation tracts. Thislayer, striking in sections on account of the dearth of nuclearmaterial, forms a brilliant background which permits one to readilyoutline the nuclei wandering over its surface later. From the embryological series of this laboratory definite evi-dences of the migration leading up to the formation of pontinenuclei appear in an embryo of 23 mm. (Mall Collection No. 382).Fig. 2 was drawn from a wax-plate reconstruction of the rhomb-encephalon of this embryo. Here the degree of medullarydevelopment corresponds pretty accurately to that of the 22 just described. The behavior of the cells lining the ven-tricular cavity deserves particular attention, inasmuch as they fur-nish the neuroblasts for the future pontine nuclei. The ependymacovering the floor of the fourth ventricle over the basal and alarplates has lost all signs of the great activity which it showedduring the formation of the tegmental structures. The cells DEVELOPMENT OF THE NUCLEI PONTUS IN MAN 31. Fig. 2 Ventro-lateral view of a wax-plate model of the rhombencephalon of a23 mm. embryo. X 18. (No. 382). 32 CHAKLES K. ESSICK composing it are sharply marked out into a definite lamina andonly after searching through many microscopic fields is one ableto detect evidences of cell division. In marked contrast to thisinactive region, the lip-plate which makes up the caudal wall ofthe lateral recess and the roof of the fourth ventricle just behindit, is found busily engaged in producing new elements. The fur-row formed by the attachment of the roof plate to the medulla,contains great numbers of karyokinetic figures in every high powerfield of the microscope and in this neighborhood the ependymalzone is not so sharply differentiated into such a thin layer as coversthe medullary floor nearer the midline. Its cells are more closelypacked, its nuclei take on a deeper stain, and the line of demarca-tion from the subjacent tissue is partly destroyed by the
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1912
