IN THE GENUS SQUALUS. 161 
and form a substance of beautiful white particles, similar 
to those of the sabulous body in the great sac, but more 
minute than that substance is, in the young fish. 
Other branches are given off, and distributed on the 
membranous sac itself ; so that, from this circumstance, it 
may be supposed to possess a certain degree of muscularity. 
The whole of the filaments forming the spherical plexus 
unite above the sac, and form a strong nerve, which runs 
upwards, and with a gentle curve inwards, and then rather 
outwards, until it arrives at the upper and rather anterior 
part of the ampulla of the anterior canal, where it enters 
that membranous expansion, on one side, in numerous fila- 
ments. 
This mode of perforation, by only one side of the am- 
pulla, is peculiar to the nerve distributed on the horizontal 
canal. The nerves which supply the ampullae of the ante- 
rior and posterior canals, divide each into two branches, the 
filaments of which perforate the ampullae on opposite sides. 
A fourth branch, by far the most important of the whole, 
if we judge from its size, distribution and termination, en- 
ters the vestibule, and, proceeding outwards, gives off nu- 
merous branches, until it is expanded on the inside of that 
cavity, and forms one of the most beautiful plexus to be 
found in this organ. 
On the first view of the parts, one would be inclined to 
suppose that the plexus arose from a nerve sent to the pos- 
terior canal. Indeed I have dissected several ears where 
the posterior nerve ga\?e off the plexus. But if a prepara- 
tion of the parts in the adult be carefully examined, espe- 
cially when partially dried, it will easily be ascertained, 
that the nerve which is distributed on the posterior am- 
pulla, derives its origin from this branch, which may be 
termed the Sabulous Nerve, from the pecuhar properties 
of its fasciculi. 
VOL. VI. L 
