146 
ON THE OllGAN OF HEARING 
parts of the tube. This membrane may with propriety be 
termed the membrana vestibuli. The tube then describes 
an angle by running downwards, backwards, and a little 
outwards, until it reaches the foramen oblongatum, to the 
edge of which it is attached, in some subjects more closely 
than in others. 
In young fish of the Squalus canus, the meatus and 
auditory tube are more easily found than in the adult, or 
in some of the other species. In old fish the meatus is 
generally almost obliterated ; the tube and membrana ves- 
tibuli are seen, but indurated and enlarged, so as to be 
scarcely recognisable by the above description. This altera- 
tion of the parts may perhaps be the consequence of dis- 
ease, or the effect of old age. In the ear of the adult of 
the Bdl(jena mysiicetus^ I have frequently found the stapes 
so firmly attached to the foramen ovale, that the union re- 
sembled ossification, and required considerable efforts to 
separate the bone from the foramen the probable cause 
of this adhesion will be pointed out, when describing the 
ear of that animal, so that one fact may, if possible, throw 
light on another. 
The following are the dimensions of the parts in a pre- 
paration of the Squalus canuSy three feet in length. 
Distance between the orifices of the meatus audito- 
rius externus, - - - - - 2^ lines. 
Diameter of the tube at the external orifice, - -^^ih. of a line. 
Bo. do. do. inside of the cuticle, - - - ^ ^o. 
Do. do. do. at the membrana vestibuli, - - 1 line. 
Length of the tube from the orifice to the membrana 
vestibuli, - - - - - -la lines. 
From that membrane to the vestibule, - - 14 do. 
Depression of the cranium, in length about - - 6 do. 
In the species aS*. borealis, or Greenland Shark, the mag- 
nitude of the semicircular canals is such, as to surpass any 
idea which may be formed of the parts from the dissection 
