. A text-book of human physiology . ed above other tones by the sympathetic vibration of the airin the canal, but owing to its highposition in the scale its resonance isof no great consequence from a practi-cal standpoint. A tuning fork allowed to die outuntil the vibrations are just impercep-tible when it is held close to the ear,can be heard again if the handle beplaced between the teeth. In this casethe sound is conducted in part directlythrough the bones of the head to theinternal ear and in part is transmittedfrom the bones to the eardrum andpropagated thence as usual throughthe auditory
. A text-book of human physiology . ed above other tones by the sympathetic vibration of the airin the canal, but owing to its highposition in the scale its resonance isof no great consequence from a practi-cal standpoint. A tuning fork allowed to die outuntil the vibrations are just impercep-tible when it is held close to the ear,can be heard again if the handle beplaced between the teeth. In this casethe sound is conducted in part directlythrough the bones of the head to theinternal ear and in part is transmittedfrom the bones to the eardrum andpropagated thence as usual throughthe auditory ossicles. B. THE MIDDLE EAR 1. Vibrations of the Eardrum.—The tympanic membrane or eardrumis a fibrous membrane mm. inthickness, formed mainly of externalradial and internal circular fibers. Itis obliquely placed across the internalend of the external auditory meatusand is drawn inward at its middle bythe long process of the malleus whichis inserted into its tissue along one ofgiven the form of a shallow, irregular(Fig. 196).. Fig. 196.—Transverse section through the leftauditory canal and tympanic membrane ofman, enlarged four times, after section is taken just behind the handleof the hammer in a plane parallel to thehandle. G, external auditory meatus; C,tympanic cavity; S, the stapes; H, the ham-mer; a ledge projects at L, to which theligaments are attached. Between the longprocess of the anvil and the handle of thehammer the tendon of the tensor tjTiipanimay be seen; LS, ligamentum superior. its radii. In this way the membrane isfunnel with an aperture of about 125° * The small Roman numerals designate octaves. TRANSMISSION OF SOUND IN THE EAR 495
Size: 1538px × 1624px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectphysiology, bookyear1
