Linear distance between two points.
arch l. the amount of space required for the permanent teeth as measured from the mesial aspect of the first molar on one side to the mesial aspect of the first molar on the opposite side, as measured through the contact points along an imaginary line of the dental arch.
available arch l. the amount of space available for the permanent teeth around the dental arch from first permanent molar to first permanent molar.
crown-heel l. (CH) l. of an outstretched embryo or fetus from skull vertex to heel. See Streeter's developmental horizon(s).
crown-rump l. (CR, CRL) a measurement from the skull vertex to the midpoint between the apices of the buttocks of an embryo or fetus, that permits approximation of embryonic or fetal age.
greatest l. measurement from the cranial to caudal end of the embryo prior to folding.
required arch l. the sum of the mesiodistal widths of the permanent teeth from first permanent molar to first permanent molar.
resting l. the length at rest from which a muscle develops maximum isometric tension.
spinal l. (SL) a measurement from the distal surface of the embryo where the plane passes through the developing eye (this is the cranial limit of the spinal cord) down to the rump.
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