Title: THE ANATOMICAL OBSERVATION OF THE ROUND WINDOW WITH A SPECIAL EMPHASIS TO ENDAURAL SURGERY
Abstract: With the purpose to clarify the positional relationship between the round window and its: surrounding, the author used 10 ears obtained from autopsy cases of Japanese adults (male and female).After exposing the antrum, the tympanic attic, and the mastoid cells by operation, the- layer of the external auditory canal skin and the tympanic membrane were removed.Then arranging the axis of Zeiss' otomicroscope in parallel with the anterior wall of the external audi- tory canal, pictures were taken by a camera attached to the microscope in the following four steps.Namely, (1) the view where the bridge is left, (2) the view exposing the niche of the- round window, (3) the view exposing the round window, and (4) the view exposing the stapes and the prominentia canalis facialis, after removing the malleus and the incus.The detailed' measurement on the position of the round window was made utilizing those photographs. For the convenience of the practical use of otomicroscope, the area of fossula fenestrae coch- leae (the niche of the round window) should be taken into consideration in establishing the- optimal spot or line as the standard for the measurement.In this way, it has been found that in, actual practice the stapedial muscle tendon and the prominentia canalis facialis show the most serviceable standards.Therefore, based on these standardized lines, the measurement has been carried out.As the result, the niche of the round window can be exposed to be seen by biting posteriorly about 2 mm of the posterior wall of the external and tory canal.The niche of the round window is located at the uppermost hollow posterior to the line drawn perpendicular to the point where- the stapedial muscle tendon is attached to the stapes.As for the membrane of the round window, draw the line parallel with the stapedial muscle- tendon at the upper edge (tangential point) of the niche of the round window, and from this- tangential point the resection is proceeded perpendicularly toward the tendon up to the mid-point between the stapedial muscle tendon and the upper edge of the niche.From here the resection is made anteriorly along the line projecting toward the prominentia canalis facialis at the angle- of 60°, and stop the resection at the intersection of this line and the line drawn perpendicular from the point of the stapedial muscle tendon attachment to the stapes, and then the membrane of the round window is exposed fairly well.Moreover, in the case which possesses no muscle tendon due to the loss of the stapes, draw a line at the upper edge of the niche in parallel with the line connecting the inferior edge of the niche, and locate the point about 0.5mm upward on the line drawn at right angle to this line at the upper edge of the niche, and through this point: draw a straight line with about 60° angle to the line of the facial canal.By removing the upper edge of the niche up to this imaginary line, a portion of the round window can be exposed.