150 
ON THE ORGAN OF HEAHING 
tion, if we take into account the myriads of vibrations which 
the membranous tubes perform in a few years. But how 
much the more immense must be the number performed by 
those of the aged, whether the person has frequented the 
busy haunts of the metropohs, or the more peaceful calm 
of rural solitude. Such are the dimensions of the cast, 
taken with the greatest care, w^hich will be sufficient to de- 
monstrate the superior magnitude of the cavities to those 
of the human ear ; and the following account of the con- 
tents of the vestibule and canals, the result of a series of 
dissections of the membranous parts and nerves in various 
species of the Squalus, will, I hope, tend to place compara- 
tive anatomy, as regards these organs, in a more advanta- 
geous point of view, than usually esteemed by many of the 
profession. 
When the ear of the shark is dissected immediately after 
t])8 animal is killed, the appearance of the parts, to the 
young anatomist, is novel and unique. The transparency 
of the cerulean cranium, membranous canals and sac, and 
liquor contained, forms a most beautiful preparation, and, 
at the same time, an elegant and useful view of the mem- 
branous parts of the organ of hearing. The cavity of the 
vestibule is chiefly occupied by a large membranous sac, 
wliich, in the young recent subject, is thin, delicate, and 
transparent. This sac is of an irregular triangular figure, 
the body running horizontally outwards ; while the parts 
next to the brain shoot up considerably beyond it, and are 
lost in the anterior and posterior canals. The body of the 
sac runs outwards until within tv/o lines of the extremity 
of the vestibule, when it terminates in a remarkable process 
that descends nearly two lines downwards and forwards, 
below the base of the sac, and there turns inwards, and 
sometimes slightly upwards. Immediately below there is 
