. Outlines of zoology. s are arranged in patchesto which branches of the auditory nerve are distributed. With thesesensory patches calcareous concretions (otoliths) are associated, exceptin the cochlea of Mammals. The fact that lime salts are often deposited in the skin, and that theear-sac arises as an insinking of epiblast, may perhaps shed some lighton the origin of otoliths. 494 STRUCTURE OF VERTEBRATA. The parts which we have so far considered constitute together themembranous labyrinth of the ear. Round about them the mesoblast(mesenchyme) forms a two-layered envelope. Its inner layer di
. Outlines of zoology. s are arranged in patchesto which branches of the auditory nerve are distributed. With thesesensory patches calcareous concretions (otoliths) are associated, exceptin the cochlea of Mammals. The fact that lime salts are often deposited in the skin, and that theear-sac arises as an insinking of epiblast, may perhaps shed some lighton the origin of otoliths. 494 STRUCTURE OF VERTEBRATA. The parts which we have so far considered constitute together themembranous labyrinth of the ear. Round about them the mesoblast(mesenchyme) forms a two-layered envelope. Its inner layer to produce a fluid, the perilymph, which bathes the wholeouter surface of the membranous labyrinth. Its outer layer forms afirm case, the cartilaginous or bony labyrinth, surrounding the internalear. The membranous labyrinth itself contains another fluid, theendolymph. With regard to the function of the parts of the ear, the semicircularcanals are believed by many to be concerned wiih the appreciation of a. Fig. 263.—Diagram showing the ear and related partsin a young cat. P., Pinna; Sg.^ squamosal: ^ external auditory meatus; T.,tympanum; M.^ malleus; /., incus; .5^, stapes abutting on foramenovale; 5., bulla of tympanic tone ; i>., a_ septum in the bulla; ,eustachian tube leading from the tympanic caviiy to the back of themouth ; , basi-occipital: C, cochlea ; .S., sacculus ; U., utriculus ;, ductus endolymphaticus; N., auditory nerve; , semi-circular canal; PE., periotic bone. change in the direction or velocity of movement. How far the ears ofInvertebrates ( Crustacea and MoUusca) are adapted for any functionexcept this, is still doubtful, and we can hardly see that any otherwould be of much use to purely aquatic animals. It seems likely atany rate that the primitive function of the ear was the perception ofvibrations, and that from this both the sense of hearing and the senseof equilibration have been differentiated. It is in acco
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
