76 Mr Buchanan on the Organs of Hearing and Vision. 
apex in these cases invariably pointed towards the vestibule ; 
indeed this position seems to be general, whenever the form of 
the caliber approaches towards an oval. 
Seeing, then, that the caliber of these canals is uniformly 
circular in the young, of whatever class or species, and that, in 
the adult, one or more of the canals are generally more or less 
of an oblong figure, according to the age of the subject ; and that 
this elongation of the parietes of the canal does not diminish the 
original diameter, and also that the caliber of the membranous 
semicircular canals in the old, as well as in the young, is cir- 
cular, and always continues so when in a healthy state, notwith- 
standing any alteration which may take place in the form of the 
caliber of the osseous or cartilaginous canals ; may it not be in- 
ferred from these circumstances, that the oblong figure of the 
caliber is caused by the vibratory action of the membranous tubes 
exciting absorption of part of the cartilaginous or osseous parie- 
tes of the canals in which they are inclosed, and that, by the con- 
tinuance of this excitement, the oval form of the caliber is gra- 
dually increased ? 
This view of the subject will receive additional confirmation, if 
we take into account the myriads of vibrations which the mem- 
branous 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 me- 
tropolis, or the more peaceful calm of rural solitude ! 
Such are the dimensions of the cast, taken with the greatest 
care, which will be sufficient to demonstrate the superior mag- 
nitude of the cavities to those of the human ear ; and the follow- 
ing account of the contents of the vestibule and canals, the re- 
sult of a series of dissections of the membranous parts and nerves 
in various species of the squalus, will, I hope, tend to place Com- 
parative Anatomy, as regards these organs, in a more advantage- 
ous point of view, than usually esteemed by many of the pro- 
fession *. 
* The Plate explanatory of the structure above described, will be given in the 
next number of Journal.— Ed. 
( To he continued. ) 
