n's _Apologia
pro vita sua_. (See APOLOGETICS.)

APONEUROSIS ([Greek: apo], away, and [Greek: neuron], a sinew), in
anatomy, a membrane separating muscles from each other.

APOPHTHEGM (from the [Greek: apophthegma]), a short and pointed
utterance. The usual spelling up to Johnson's day was _apothegm_, which
Webster and Worcester still prefer; it indicates the pronunciation--i.e.
"apothem"--better than the other, which, however, is more usual in
England and follows the derivation. Such sententious remarks as
"Knowledge is Power" are apophthegms. They become "proverbs" by age and
acceptance. Plutarch made a famous collection in his _Apophthegmata
Laconica_.

APOPHYGE (Gr. [Greek: apophugae], a flying off), in architecture, the
lowest part of the shaft of an Ionic or Corinthian column, or the
highest member of its base if the column be considered as a whole. The
apophyge is the inverted cavetto or concave sweep, on the upper edge of
which the diminishing shaft rests.

APOPHYLLITE, a mineral often classed with the zeolites, since it behaves
like these when heated before the blowpipe and has the same mode of
occurrence; it differs, however, from the zeolites proper in containing
no aluminium. It is a hydrous potassium and calcium silicate,
H7KCa4(SiO3)8 + 4-1/2(H2O). A small amount of fluorine is often present,
and it is one of the few minerals in which ammonium has been detected.
The temperature at which the water is expelled is higher than is usually
the case with zeolites; none is given off below 200 deg., and only about
half at 250 deg.; this is slowly reabsorbed again from moist air, and is
therefore regarded as water of crystallization, the remainder being
water of constitution. When heated before the blowpipe, the mineral
exfoliates, owing to loss of water, and on this account was named
apophyllite by R.J. Hauy in 1806, from the Greek [Greek: apo], from, and
[Greek: phullon], a leaf.

[Illustration: FIG. 1.]

[Illustration: FIG. 2.]

Apophyllite always occurs as distinct crystals, which belong to the
tetragonal system. The form is either a square prism terminated by the
basal planes (fig. 2), or an acute pyramid (fig. 1). A prominent feature
of the mineral is its perfect basal cleavage, on which the lustre is
markedly pearly, presenting, in white crystals, somewhat the appearance
of the eye of a fish after boiling, hence the old name fish-eye-stone or
ichthyophthalmite for the mineral.