File:Bartelmez1923 fig02.jpg

Fig. 2. A reconstruction of a four—somite embryo

(H279, U. of C. Coll.; Carnegie 3709); magnified 200 diameters and reduced one half in reproduction. The plane of section is indicated by the position of section 54 which was shown as figure 1 in my 1922 paper.

camn-e., neurenteric canal; ch., chorda; disc.o£., otic disc; mom. cl., cloacal membrane (the entoderm has shrunken away from the cctoderm) ; mem. ph., pharyngeal membrane; mesen., midbrain; ph., pharynx; pr.ac.fac., acoustic0-facial primordium; prosen., forebrain; rh.A, rh.B, first and second hindbrain segments; rh..C'1 and 7'h.C'2 have resulted from the division of rh.C’ in the previous embryo; rh.B is identical with the definitive fourth rhombomere, rh.C'; with the fifth.

Figure 2 gives the relations in a four-somite embryo (H279, U. of C. Coll.; Carnegie 3709) in which abundant mitoses are to be seen, although the specimen underwent great shrinkage during dehydration. It belongs to a group which includes that just described as well as Wilson’s ‘H3’ (’14) and ‘Klb’ (Keibel and Elze, ’O8, Normentafel No. 3). Forebrain, midbrain, and three hindbrain subdivisions were clearly visible in the gross specimen when studied in 80 per cent alcohol. It will be seen in the figure that the forebrain has begun to grow forward beyond the pharynx and that it is relatively longer than in the previous case. The midbrain is wedge—shaped. There are clear signs of differentiation in the hindbrain in that there are four segments and a ganglionic anlage. The first segment (rh.A) is still small and inconspicuous, whereas the second (rh.B) has acquired new characters which distinguish it for the rest of our period. The enlargement is sharply marked off by constrictions fore and aft, and corresponding to it there is a dip in the floor. Ventrally the neural groove is enlarged in the manner typical for neuromeres, but dorsally the folds approach one another only to diverge again at the dorsal edge where they are thickened. The thickening is the acoustico-facial primordium (pr.ac.fac.). These relations may be seen in figure 1 of my 1922 paper. The level of that section is indicated in the present figure 2, where it will be seen that the plane of section passes obliquely through the otic segment (rh.B) and the two succeeding segments. The latter two (rh.C1 and rh.C2) correspond in position to the third hindbrain segment of the previous specimen (rh.C). It may be that that segment has divided, but it is possible that H279 is an individual in which the segmentation of the nervous system is particularly pronounced.

Online Editor Embryo H279 (University of Chicago Collection) became Carnegie Collection Embryo no. 3709, 4 somite embryo corresponds to Carnegie stage 10 in Week 4.

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Reference

Bartelmez GW. The subdivisions of the neural folds in man. (1923) J. Comp. Neural., 35: 231-247.

Cite this page: Hill, M.A. (2024, April 27) Embryology Bartelmez1923 fig02.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Bartelmez1923_fig02.jpg

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