Journal of morphology . ion of theoriginally simple cavity into two nearlyequal parts gradually becomes more andmore distinct, and here, as in othermammals, the sacculus is from the firstdevoted to the production of an exten-sive cochlea, so that almost before it isformed its ventral region is bent andmoulded into the cochlear pocket, whosegrowth from this time on is rapid in aventral direction, spirally along a dorso-ventral line. The anterior and posteriordivisions of the auditory vesicle, owingto the twisting of the nerve and revolu-tion of the vesicle, no longer lie along anantero-posterio
Journal of morphology . ion of theoriginally simple cavity into two nearlyequal parts gradually becomes more andmore distinct, and here, as in othermammals, the sacculus is from the firstdevoted to the production of an exten-sive cochlea, so that almost before it isformed its ventral region is bent andmoulded into the cochlear pocket, whosegrowth from this time on is rapid in aventral direction, spirally along a dorso-ventral line. The anterior and posteriordivisions of the auditory vesicle, owingto the twisting of the nerve and revolu-tion of the vesicle, no longer lie along anantero-posterior axis, but move nearlythe one above the other along a verticalaxis, so that they are commonly describedas the upper and lower chambers of theear. The two divisions of the auditoryganglion belong exclusively to their re-spective auditory chambers, and as theseparation progresses a median raphesprings into the vesicle cavity much as it is seen to do in the adultMyxine and especially Petromyzon (utriculo-saccular septum).. Cut 2^. — The left internal ear from a human embryo, 13 mm. long, about the fifth week of development. After W. His, Jr. a Anterior canal. am Ampulla. (/ Ductus endolymphaticus. h External canal. / Lagena. / Posterior canal. J Sacculus. ti Utriculus. 2o8 AVERS. [Vol. VI. About the fifth week the parts of the adult ear are all wellmarked out. The two primary canals, anterior and posteriorverticals, inclose between them an angle of i6o° and open intothe utriculo-sacculus by a short common tube, while all threepresent the S-shaped curvings so characteristic of the canals inmany fishes. The horizontal canal remains still a shallow groovein the utricular wall. The nerve end organs of the utriculus lie very close together,and at this time one cannot distinguish separate nerve fibres of the utricular branch spring from the whole sur-face of the utricular ganglion and pass in the form of a loosebundle to the inner face of the utriculus, its sense organ
Size: 1091px × 2290px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorwistarin, bookcentury1800, bookdecade1890, bookyear1892
