Recently the mechanism of the transmission of sound in the middle ear has been mechanically clarified with the progress of audiology.
Together with this, however, one must make clear the biological conditions under which the middle ear sufficiently performs its function.
As the first step of the studies from this standpoint, the functional structure of the Eustachian tube and its surrounding tissues has been investigated on the cadavers of adults macroscopically and microscopically. The macroscopic study was particularly complemented by the roentogenograms and molds of the tubes of the cadavers.
Thus, it was able to demonstrate the findings in three dimensions objectively. The results obtained were as follows
1. On six cadavers X-ray figures of the tubes filled with the contrast medium by horizontal, vertical and sagittal projection were taken and measured, and the courses of the tubes were also examined.
The tubes of the cadavers appeared as dense, homogeneous shadows in all of the three projections. On the other hand it has been reported that on the living subjects a thin, dense filament and a broader and fainter band are observable in the inferior view (Aschan 1952).
It is inferred that this difference is dependent on the degree of dilation of the tubal lumens, and that the tubal lumen of the living subject is more dilated than that of the cadaver owing to the pressure given to introduce the contrast medium.
2. In order to resolve the question about twisting of the tubal lumen besides its bend, the mold of the tube was made with methacrylic methyl ester, by which it was able to save artificial products in making it. It became clear from the mold that there was no distinct twisting of the lumen and that the long axis of the cartilaginous portion slightly declined posteriorly against that of the osseous portion. These findings might be explained in terms of the dislocation of the anterolateral wall due to the contraction of the tensor veli palatini muscle caused by rigor mortis.
The mold simultaneously made of the fossa of Rosenmueller demonstrated that it reached the middle part of the cartilaginous portion.
3. In the structure of the tube and its surrounding tissues the relation between the tube and its related muscles is the most complicated and unintell igible.
So the three-dimensional relation was examined through the roentogenogram, on which the tube was visualized by filling it with Moljodol and the muscles, by bordering them with fine fuses.
As the result, it was ascertained that the tensor veli palatini muscle arose from the lateral lamina of the tubal cartilage and the membranous lamina in the upper half of the cartilaginous portion and ran apparently laterally to the tubal lumen to reach the hamulus of the pterygoid plate, and that the levator veli palatini muscle arose from behind the tubal lumen and came to touch its bottom below the middle of the cartilaginous portion.
4. In serial sections the difference between the cartilaginous and osseous portions was more clearly shown by the shape of the tubal lumen than by the compos ition of the tubal wall.
This boundary, however, did not always accord with the isthmus anatomical isthmus (Miner).
After such morphological classification of the cartilaginous and osseous portions was decided, classification from the functional point of view should be made into the mobile and non-mobile portions.
5. From the histological investigation the differences concerning the shape of the tubal lumen, the shape and structure of the tubal cartilage and the construction of the tubal wall by glandular and fatty tissues were found out even in the cartilaginous portion.
Consequently it is necessary to divide the cartilagenous portion into two parts ? the upper and lower half - and consider the physiology and pathology of those parts from different standpoints.
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