Webster's New World Medical Dictionary

pronation 1
Rotation of the arm or leg inward.
In the case of the arm, the palm of the hand faces
posteriorly when it is pronated.
2
The correspon-
ding motion in the foot with the sole down. See also
Appendix B, “Anatomic Orientation Terms.”
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pronation
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pronator foot type
A type of foot that rolls far
inward during the weight-bearing phase of the
stride. This type of foot is characterized by a very
low or flat arch. Heavier people often have feet of
this type.
prone
With the front or ventral surface down-
ward (lying face down), as opposed to supine. See
also Appendix B, “Anatomic Orientation Terms.”
pronucleus
A cell nucleus with a haploid
(halved) set of chromosomes—23 chromosomes
in humans—that results from division (meiosis) of
a germ cell. The male pronucleus is the sperm
nucleus after it has entered the ovum at fertilization
but before fusion with the female pronucleus.
Similarly, the female pronucleus is the nucleus of
the ovum before fusion with the male pronucleus.
prophylactic 1
A medication or treatment given
to prevent development of disease.
2
A drug or
device for preventing pregnancy, particularly a
condom.
prophylactic cranial irradiation
Radiation
therapy to the head that is intended to prevent can-
cer from spreading to the brain.
prophylaxis
The prevention of disease.
propositus
See 
proband.
proprioception
The ability to sense stimuli aris-
ing within the body regarding position, motion, and
equilibrium. Even if a person is blindfolded, he or
she knows through proprioception if an arm is
above the head or hanging by the side of the body.
The sense of proprioception is disturbed in many
neurological disorders. It can sometimes be
improved through the use of sensory integration
therapy, a type of specialized occupational therapy.