File:Streeter1917-fig07.jpg

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Fig. 7 Median view of reconstruction of the left membranous labyrinth and the periotic spaces in a human fetus 85 mm CR length

(Carnegie Collection, No. 1400-30) enlarged 9 diameters.

The oval indentation in the proximal end of the scala tympani corresponds to the fenestra cochleae. This space extends along the cochlear duct about the same distance as the scala vestibuli; the two however do not communicate with each other as yet. The peripheral border of the scala tympani is characterized by sacculations corresponding to spaces that are coalescing with the main space. This indicates the direction of the growth of the scala at this time.


The scala tympani, as can be seen in figure 7, extends downward on the basal side of the cochlear duct along its first two turns. This corresponds to about the same linear dimension as that of the scala vestibuli. In its proximal portion it shows a greater area in cross section than the latter, but further toward the apical region it is about the same size and in some places it is even smaller. The peripheral margin of the scala tympani is distinctly more irregular than the central margin. This irregularity is due to spaces along the margin that are actively coalescing with the main space, but in which the fusion is not yet complete. The irregularity of this margin is thus an indication of the direction of the expansion of the scala. As the diameter of the whole cochlear mass increases it is evident that the main growth of the scala must radiate outward in a peripheral direction. This is accomplished by the continual assimilation of new reticular spaces along this margin. At the proximal end of the scala tympani can be seen an oval depression which corresponds to the fenestra cochleae (rotundum) and with which it stands in intimate relation.


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Reference

Streeter GL. The development of the scala tympani, scala vestibuli and perioticular cistern in the human embryo. (1917) Amer. J Anat. 21: 300-320.


Cite this page: Hill, M.A. (2024, February 20) Embryology Streeter1917-fig07.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Streeter1917-fig07.jpg

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