IN THE GENUS SQUALUS. 
155 
which causes it to form an acute angle, anterior and supe- 
rior to the entry of the tube into the sac. 
The perpendicular part of the canal is very large as it 
descends to and from this common aperture, being nearly 
six or seven times larger than any part of the tube^ and is 
separated (below the opening) from the sac by a slight 
cartilaginous septum, which runs inwards, and then up- 
wards, and assists to form the division between the fora- 
men oblongatum and the foramen rotundum. 
When the tube is nearly within a line of being on a 
level with the floor of the vestibule, it describes a gentle 
curve, running backwards, and contracts in a little space 
to within one-half of the size of the longitudinal part. 
The perpendicular part of the tube, and its curvature, to 
where it contracts, is very thin, delicate, and transparent, 
and is closely attached to the cartilaginous parietes ; but 
becomes tough and strong when it emerges into the en- 
larged cavity, where, in the space of a line and a half, it gra- 
dually increases, and forms a globular expansion that has 
been denominated the Ampulla, and which is the largest 
in the organ. It then contracts, and forms a strong, tough, 
membranous tube, which runs backwards, upwards, and 
forwards, so as to describe an irregular circle, until it ar- 
rives at the superior part of the vestibule (directly above 
the anterior parts of the great sac), to the roof of which^ as 
formerly mentioned, it is firmly attached. 
The other two canals arise from the spherical sac, which 
gives to the parts a somewhat clustered and irregular ap- 
pearance, owing to the ampulljs of Jhe anterior and hori- 
zontal canals being situate close to the sac ; and this is ren- 
dered still more so, by the great quantity of nerves with 
which the expansions of the tubes are surrounded. 
The anterior canal emerges from the upper part of the 
spherical sac, and, running upwards nearly a line, dilates 
