75 
Organs of Hearing and Vision. 
The extremities of these canals, adjoining to the vestibule, 
are considerably enlarged, so as to have a similar appearance to 
that which in the human subject is termed the Ampullae ; where- 
as the proper ampullae of these cartilaginous canals are situated 
at a considerable distance from the vestibule, and are of an ob- 
long figure. 
The Posterior canal is the largest, and measures fifty-three 
lines , or nearly five inches and a-half in length, and two lines 
by two and three quarters in diameter. It runs in a longitudi- 
nal direction from and to the vestibule, and, when viewed inter- 
nally, has the appearance of a circle attached to the ampulla of 
the external canal. 
The circumference of the ampulla is sixteen lines, and the 
average circumference of the other parts of the tube eight lines 
and three quarters. 
The External canal is the next in size, and measures thirty-six 
lines in length and seven lines in circumference. The ampulla 
of this canal, at its greatest circumference, measures only ten 
lines and a-half. 
The canal runs in a diagonal direction, the one extremity aris- 
ing from the superior and posterior parts of the vestibule ; and 
the other from a globular space communicating with the inferior 
and anterior parts of that cavity. 
The Anterior canal, although the smallest of the three, is yet 
of considerable size, measuring thirty- one lines in length, and 
from five to seven lines in circumference. 
These canals are partially flattened, so that if any of them 
were divided at a little distance from the ampullae, the section 
would be of an oval figure, with the apex pointing inwards. 
In a considerable number of preparations now before me is 
one of an elephant (the animal has apparently been of great 
age), where the caliber of the canals, one in particular, is ex- 
tremely oblong. 
When dissecting the organ of hearing in various animals, as 
well as in the human subject, I have found the caliber of the 
canals in children, young animals, and birds, to be circular, and 
in the adult ear, one or more of the semicircular canals slightly 
flattened ; and this oblong form of the caliber increased consi- 
derably in aged persons, in whom it is seldom wanting. The 
