3-6. SPLIT LINES
There are specific lines of tension or stress that varies from one area of the body
to the next. The dense FCT of the dermis tends to be oriented along these lines. If a
blunt probe is inserted into the dermis, the FCT fibers will separate to form a split. The
lines of splits, or split lines, follow the lines of tension in the local area.
The surfaces of the palms, soles, and digital pads of the hands and feet are
thrown up into ridges and grooves. The patterns formed by these ridges and grooves
are called dermatoglyphics. These dermatoglyphics are used as a means of
identification, both by law enforcement agencies and by hospitals for newborns. We
often refer to such procedures as fingerprinting or foot-printing.
The body is jointed to allow motion. To facilitate motion of the joints, the skin
develops natural creases. These creases are in relationship to the joints, but not
exactly opposite to the joints.
As the continuous covering of the body, the integument proper, or skin, is
everywhere. However, the actual thickness of the dermis and/or epidermis varies
considerably from very thin to very thick. For example, the thickest skin is located
across the back between the shoulders.
The integument proper of humans has some type of coloration (pigmentation).
This coloration is because the presence of special chemicals called pigments. Black,
red, and yellow are the most common colors of these pigments.
a. Development. Special cells are located in the dermis, just below the basal
layer of the epidermis. These special cells provide the precursors of the pigments to the
basal cells. As these basal cells migrate to the surface, the precursor materials are
gradually converted into the actual pigments or colors.
b. Genetic Control. Genes control the type of color for each individual. There
are various genes (sometimes multiple genes) for each color.
(1) When these genes are absent, the individual is an albino. There is a pink
glow to the skin and eyes that is produced by the red color of the blood shining through
the clear layers of the skin. There is also a whiteness of the skin produced by the