Asymmet´rical, a. Uneven; disproportionate as to opposite, as right and left, parts.

Asym´metry, n. Disproportion of duplicate parts or organs, or of those which are repeated on opposite sides of a plane or axis.

At´avism, n. Reversion, or tendency to revert, to characters of ancestral stock.

At´las, n. First cervical vertebra, articulating with the occipital bone.

Atres´ia, n. Closure.

At´rophy, n. See Hypertrophy.

Atten´uate, a. Growing gradually slenderer toward an extremity; or, narrowly produced for a long distance; in neither case necessarily sharp-pointed, which would be rather acuminate.

Attyp´ical, a. Of particular character acquired in specialization from a common type.

Auche´nium, n. Lower back part of neck; the scruff. (50.) (Little used.)

Au´ral or Auric´ular, a. Pertaining to the ear.