IN THE GENUS SQUALUS. 
153 
rior part of the sac is kept partially flattened. This liga- 
ment may with propriety be termed the Ligamentum ex- 
tensorum. 
The great sac is chiefly filled with a transparent gelati- 
nous semifluid, of the consistency of the vitreous humour 
in the human eye, and resembles it more than any sub- 
stance which I have seen, and may, from its situation, be 
termed the Sabulous Humour. 
I have not been able to detect any membrane holding 
this humour in separate cells, similar to the membrana hya- 
loides in the human eye. 
There is also a peculiar substance in the lower and pos- 
terior parts of the sac, formed by the termination of the 
filaments of the sabulous plexus, which deserves the most 
careful investigation ; the structure of which shall be de- 
scribed in the account of the distribution of the auditory 
nerve. This substance I have termed the Sabulous Body. 
The inner and anterior parts of the sac are connected with 
a globular membranous cavity, by means of the parts being 
extended so as to form a tube of communication, about two 
lines in length, and a line in diameter. 
This cavity, from its figure, deserves the name of the 
Spherical Sac, is from three to four lines in diameter, — of 
a globular figure, communicating on one side with the 
great sac, and on the other with the ampullae of the ante- 
rior and horizontal canals, and closely attached to the in- 
ferior parts of the cartilaginous cavity in which it is situate. 
In several species of the cartilaginous fishes, the anterior 
canal is given off" by the great sac, and the horizontal or 
external canal is derived from the anterior canal, just before 
the expansion of the anterior ampulla. 
The beginning of both of these canals are in these cases 
firmly connected to the upper part of the spherical sac by 
membranous substance, so that whenever any undulations 
