Collier's New Encyclopedia (1921)/Fin
FIN, the organ by which locomotion
is effected in a fish. As a rule fins
consist of a membrane supported by rays.
Of these organs the two pectoral fins, so
called from being situated on the breast,
where they are just behind the branchial
aperture, are modifications of the
anterior limbs in other vertebrata. The
ventral fins, so called from being, as a
rule, situated on the belly, correspond to
the hind limbs in other vertebrata. Often
there are also one or more dorsal fins
on the back, two anal fins near the anus,
while the tail is technically called the
caudal fin. In carpentry, a tongue on
the edge of a board. In commerce, a
blade of whalebone. In machinery, a slip
inserted longitudinally into a shaft or
arbor, and left projecting so as to form
a guide for an object which may slip
thereon, but not rotate; a spline or
feather. In molding, a mark or ridge
left in casting at the junction of the
parts of the mold.