What are the Muscles?

Bundles of thin fleshy fibres, or threads, fastened to the bones of
animals, the contraction and expansion of which move the bones or
perform the organic functions of life.

_Organic_, relating to organs or natural instruments by
which some process is carried on.

_Functions_, employments or offices of any part of the body.

_Contraction_, drawing in or shortening.

_Expansion_, extending or spreading out.


What is Twilight?

The light from the first dawning of day to the rising of the sun; and
again between its setting and the last remains of day. Without
twilight, the sun's light would appear at its rising, and disappear at
its setting, instantaneously; and we should experience a sudden
transition from the brightest sunshine to the profoundest obscurity.
The duration of twilight is different in different climates; and in
the same places it varies at different periods of the year.

_Instantaneously_, done in an instant, in a moment's time.

_Obscurity_, darkness, want of light.