IN THE GENUS SQUALUS. 
151 
a considerable depressioiij or little pit, in the floor of the 
vestibule, in which this process is situate; so that it is sunk 
beneath the level of the other parts of the sac, and also be- 
low the floor of the cavity. There is, however, sufficient 
space in the fossae to allow of a considerable degree of mo- 
tion in the process, without touching the bottom or sides of 
the depression. 
The form of this process, in various cartilaginous fishes, 
approaches gradually towards that of the shark, according 
to the approximation of their voracious habits. 
Thus, in one species of the Ray, it is continued horizon- 
tally outwards from the end of the sac. In the Thornback 
it is slightly curved, with scarcely any perceptible fossa in 
the young ; while, in the adult, that depression resembles 
the fossa of the young Squalus caninus. I have termed this 
process the angorian appendage^ from its containing the 
cornu angoriana, which will be described in the account 
the distribution and termination of the auditory nerve» 
In the cartilaginous floor of the vestibule, there is 
oblong depression nearly eight lines in length, of which the 
fossa angoriana forms rather more than one-third ; the other 
parts being filled with a semicartilaginous substance, that 
surrounds, and forms a bed for a nerve that shall afterwards 
be noticed. This substance is covered by the membrane 
that lines the vestibule, which dipping downwards into the 
cavity, divides the oblong depression, and in that manner 
forms the inner side of, and lines, the fossa angoriana. This 
great membranous sac measures upwards of eight lines in 
length, and four hnes in diameter, and is, as formerly men- 
tioned, chiefly situate in the interior parts of the vestibule, 
to which it is firmly attached. 
On the anterior side, and close to the cartilaginous sep- 
tum, the sac sends a slender process upwards, which is at- 
tached to the foramen oblongatum, and proceeds upwards. 
