EAR 



179 



Wurm, Zeitschr. f. tviss. Zoologie, 1885, pp. 107-115, Taf. vii., and 

 pp. 728-730.) 



The middle ear consists of the tympanic cavity, its communi- 

 cation with the cavity of the mouth through the "Eustachian tube," 

 and the sound-conducting apparatus — the " tympanic membrane " 

 and the " columella aui-is." 



The tympanic membrane or drum is thin and stretched across 

 the Avails of the inner end of the auditory meatus, and shuts 

 off the latter from the tymi^anic cavity. This cavity communi- 

 cates with the mouth through a canal — the Eustachian tiibe, Avhich 

 passes between the basisphenoid and basioccipital bones, and 

 opens upon the ventral side of the sphenoid a little behind the 

 latter's articulation with the pterygoid bone. The right and left 



Tb.Eust 



Hind View op the Osseous Auditory Organ of an Owl (J3m6o mdrance). 



About twice the natural size. 



Cd. Occipital condyle ; F.M. Foramen magnum ; L, Lagena ; Pter. Bight pterygoid bone ; 



Q, Quadrate bone ; H, S, Horizontal and Sagittal semicircular canals ; Co, Columella auris, its 



extra-columellar portion continued towards the basis of the quadrate ; Tb.Eust. Eustachian tube. 



canals unite in the middle line into one short membranous duct, 

 which opens in the roof of the posterior part of the mouth cavity. 



The columella is a cartilaginous and partly osseous jointed rod, 

 which fits with its inner slightly-swollen and disk-like end into the 

 " foramen ovale " of the capsule of the inner ear. The outer end 

 of this rod sends out three cartilaginous processes ; the dorsal ^* 

 one is attached to the upper wall of * the tympanic cavity close toM^/^» -^^ .^ 

 the drum ; the outermost process leans against the middle of the ecr\hii*^f^^ 

 drum, and consequently conveys the vibrations of the latter 

 through the Avhole rod into the inner ear ; the venti-al process is 

 directed downwards, and runs out into a thin thread which can be 

 traced between pterygoid and quadrate into the inner corner of the 

 articular portion of the mandible. 





