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V 11, —Sketches of the Compcirative Anatomy of the 
Organ of Hearing, founded chiefly on the Ear 
of the Squalus. 
By Thomas Buchanan, C. M. 
Member of the Wernerian Natural History Society, Author of the 
' Illustrations of Acoustic Surgery,' &c. &c. 
{Read I9th November 1825.) 
The organ of hearing in the Shark tribe varies con- 
siderably from that of the human subject. We find nei- 
ther ossicula auditus, tympanum, eustachian tube, nor 
cochlea, — but, as if to compensate for the want of parts so 
essentially necessary to the perfect ear, the semicircular ca- 
nals are of almost incredible extent. The cranium being com- 
posed of semi transparent cartilaginous substance, of a 
beautiful coerulean hue, the whole of the organ can be dis- 
tinctly seen, by merely removing the cuticle, and some of 
the surrounding parts. When the cranium is divested of 
the common integuments, a considerable depression is seen 
in the coronal and posterior portion, which, in the living 
subject, is occupied by a kind of spongy, elastic, cellular 
membrane. This depression is of a heai't-like figure, the 
apex pointing forwards, with a roundish process in the pos- 
terior part, which causes a partial division of this portion 
of the cavity. 
