IN THE GENUS SQUALUS. 
147 
of the organ in the human subject. The superior size of 
the parts may be estimated from the dimensions of a cast 
of the left ear of that animal now before me, which I took 
a few hours after it was killed.* 
The entrance of the meatus internus is about three lines 
in diameter, and situate in the inferior part of the organ. 
It runs downwards, and a little outwards, about two lines 
and a half ; then contracts suddenly, and runs horizontally, 
outwards, nearly a line, when it enters the vestibule, paral- 
lel with the floor of that cavity. The vestibule is large, of 
an irregular triangular figure ; the apex of which may be 
said to be directed towards the brain, while the base runs 
horizontally outwards and backwards. The circumference 
of the greatest diameter of the vestibule is twenty-five lines, 
and the height of the cavity, from the highest to the lowest 
points, twenty- two lines. On the inside of the superior 
part of the external angle of the vestibule, is a longitudinal 
ridge, which, in the sketch of the cast, is seen as a depres- 
sion ; and on the floor there is a correspondent ridge on the 
opposite side, that runs upwards on the parietes next to 
the brain, until it arrives at the top of the cavity, where it 
unites, and forms a septum, which separates the foramen 
oblongatum from the foramen rotundum. The floor of the 
vestibule is more tough and hardened than any other part 
of the labyrinth, particularly that which is directly under 
the sabulous body, where it has a white, scaly, opaque ap- 
pearance, approaching towards ossification. The whole of 
the vestibule is lined with a reflection of the dura mater, 
which is closely attached to its parietes, where it is con- 
siderably less dense than in the inside of the cranium, — 
* See Plate I. figs. 1. and 2., where the parts are shewn oi' the na- 
tural size. 
If 2 
