. The bird, its form and function . -large size and protected by a movable flap of skin whichmay serve to aid in focussing the sounds from below—a very useful function to an owl at night, silently wing-ing its way over field and meadow in search of mice andother terrestrial prey. A rather singular fact is that inmany owls the two ear-openings are unlike, one beinglarger and of a different shape from the other, and thisasymmetry extends even to the form of the skull itself. The Senses 21 7 Two membranes are stretched across the ear-tube,and between these a tiny bone, the columella, is sus-pende
. The bird, its form and function . -large size and protected by a movable flap of skin whichmay serve to aid in focussing the sounds from below—a very useful function to an owl at night, silently wing-ing its way over field and meadow in search of mice andother terrestrial prey. A rather singular fact is that inmany owls the two ear-openings are unlike, one beinglarger and of a different shape from the other, and thisasymmetry extends even to the form of the skull itself. The Senses 21 7 Two membranes are stretched across the ear-tube,and between these a tiny bone, the columella, is sus-pended, taking the place of the chain of three bones inthe ear of a mammal. When sound-waves strike againstthe outermost membrane, or drum of the ear, vibrationsare transmitted by the little bony suspension bridge tothe inner membrane, and this in turn troubles the fluid. Fig. 1)7. -External car of Rarrod Owl. which fills the inner ear. The hair-like endings of thenerve of hearing are affected by the vibrations of thefluid and thus is hearing accomplished. Rather say,thus the disposition of the physical components of theear may be explained; but Jiow anything more than themonotone of a sea-shells cavity is translated to the brain,no one can say. The fluid contained in three semicircular canals, situ- 21 8 The Bird ated in the inner ear—whicli occupy the three planes ofspace,—exercises a most important function, that of equi-libration. They have been compared to the glass tubefilled with water and a shifting bubble of air, by centringwhich a surveyor knows his instrument is perfectly these canals be injured or cut, the bird loses allcontrol of his actions; if a certain one of the three canalssuffers, the bird moves its head rapidly sideways andspins around in a circle; if another of the trio is by anaccident severed, the motion of the head
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Keywords: ., bookauthorbeebewil, bookcentury1900, bookdecade1900, bookyear1906
