. Text-book of embryology. Embryology. 130 EMBRYOLOGY OF THE LOWER VERTEBRATES ch. shadows the anterior vertical semicircular canal (as) and a little later a similar bulging more ventral, in position—the horizontal canal (). The lagena also is foreshadowed by a slight downward bulging of the floor of the otocyst. With further development the posterior vertical canal rudiment appears also as a bulg- ing of the otocyst wall continuous with that which will form the anterior canal (Fig. 72, C-F, ). The three canal rudiments come to project more and more prominently, the recess assumes the tu
. Text-book of embryology. Embryology. 130 EMBRYOLOGY OF THE LOWER VERTEBRATES ch. shadows the anterior vertical semicircular canal (as) and a little later a similar bulging more ventral, in position—the horizontal canal (). The lagena also is foreshadowed by a slight downward bulging of the floor of the otocyst. With further development the posterior vertical canal rudiment appears also as a bulg- ing of the otocyst wall continuous with that which will form the anterior canal (Fig. 72, C-F, ). The three canal rudiments come to project more and more prominently, the recess assumes the tubular shape of the endolymphatic duct and the lower portion of the otocyst (saccule) with its projecting lagenaf pocket and en- dolymphatic duct be- comes more sharply marked off from the rest of the otocyst (utricle). The pouch-like rudi- ments of the semicir- cular canals, as they come to project more freely from the utricle, assume a flattened form and finally the central portion of the wall on each side bulges in- wards and fuses with that on the other. In this way the central portion of the cavity of each pouch becomes obliterated while the persisting peripheral part takes the form of a curved tube—the definitive canal. At first the space subtended by the canal is traversed by a continu- ous septum formed out of the fused walls but this soon disappears leaving the canal as a. freely projecting arch which opens into the utricle at each end. The ampulla appears at an early stage as a dilatation of the canal rudiment at one end. As will already have been gathered, the three canal rudiments do. :. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original MacBride, E. W. (Ernest William), 1866-1940; Kerr, John Graham, 1869-; Heape, Walter, 1855-1929. London : Macmillan
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Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
