. The anatomy of the human body. Human anatomy; Anatomy. THE COCHLEA. 677 portions of circles ; they are situated within the substance of the base of the petrous portion of the temporal bone, behind the vestibule, into which they open by the five ori- . fices already described. They have been named the great, the middle, and the small semicircular canals ; terms which have caused much confasion, because the differences between them, in regard to length, are not alone sufficient to distinguish them from each other. Their direction forms a much better ground of distinction between them. Two are
. The anatomy of the human body. Human anatomy; Anatomy. THE COCHLEA. 677 portions of circles ; they are situated within the substance of the base of the petrous portion of the temporal bone, behind the vestibule, into which they open by the five ori- . fices already described. They have been named the great, the middle, and the small semicircular canals ; terms which have caused much confasion, because the differences between them, in regard to length, are not alone sufficient to distinguish them from each other. Their direction forms a much better ground of distinction between them. Two are vertical, and one is horizontal: there is an anterior and superior vertical, and a posterior and inferior vertical canal; the horizontal canal is external, and is situated between the . two others. The superior vertical canal {p, figs. 258, 260), which describes two thirds of a circle, is placed at the highest part of the labyrinth, immediately to the outer side of the vestibule. A plane passing through the two branches of this canal would cut the base of the petrous portion almost at a right angle. The convexity of this canal is turned upward, and its concavity downward. In the foetus, its concavity is free, so that it can be seen without any dissection; but in the adult it is filled up with osseous tissue. The anterior and outer extremity {p',figs. 258, 259) of this canal is dilated into an ampulla, and opens separately at the upper and outer part of the vestibule. The poste- rior and inner extremity unites with the corresponding extremity of the inferior vertical canal to form a common canal (a, fig. 260), which opens without any dilatation into the upper and inner part of the vestibule (a', fig. 261). Fig. 260 The inferior vertical canal {q, figs. 258, 260) is placed at right angles to the preceding, and par- allel with the posterior surface of the petrous portion. It commences at the inner and upper part of the vestibule, by the common canal (a. Jig. 260) already described
Size: 1503px × 1661px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., boo, bookcentury1800, booksubjectanatomy, booksubjecthumananatomy
