The sagittal plane is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and divide it into two equal parts (mid-sagittal), or away from the midline and divide it into unequal parts (para-sagittal).
Mid-sagittal section of a human skull, by Leonardo da Vinci, c. 1489
Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, the face of a human being has a plane of symmetry down its centre, or a pine cone displays a clear symmetrical spiral pattern. Internal features can also show symmetry, for example the tubes in the human body which are cylindrical and have several planes of symmetry.
A selection of animals showing a range of possible body symmetries, including asymmetry, radial, and bilateral body plans
Illustration depicting the difference between bilateral (Drosophila), radial (actinomorphic flowers) and spherical (coccus bacteria) symmetry
Lilium bulbiferum displays hexamerism with repeated parts arranged around the axis of the flower.
Apple cut horizontally showing that pentamerism also occurs in fruit
