EAR 179 
Wurm, Zeitschr. f. wiss. 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 auris.” 
The tympanic membrane or drum is thin and stretched across 
the walls of the inner end of the auditory meatus, and shuts 
off the latter from the tympanic cavity. This cavity communi- 
cates with the mouth through a canal—the Eustachian tube, which 
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 
Hinp VIEW OF THE OssEOUS AUDITORY ORGAN OF AN Owt (Bubo indranee). 
About twice the natural size. 
Cd. Occipital condyle; F.47. Foramen magnum; L, Lagena; Pter. Right 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. £ust. 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 
« seinen 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 to 
the drum; the outermost process leans against the middle of the 
drum, and consequently conveys the vibrations of the latter 
through the whole rod into the inner ear; the ventral 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. 
