Hemangiomas18 (he-MAN-jee-OH-mas), or birthmarks, are patches of discolored skin caused by benign tumors of the dermal blood capillaries. Capillary hemangiomas (strawberry birthmarks) are bright red to deep purple and are slightly swollen; they usually disappear in childhood. Cavernous hemangiomas (port wine stains) are flat, are duller in color, and last for life.
Freckles and moles are tan to black aggregations of melanocytes. Freckles are flat melanized patches that vary with heredity and exposure to the sun. A mole (nevus) is an elevated patch of melanized skin, often with hair. Moles are harmless and sometimes even regarded as "beauty marks," but they should be watched for changes that may suggest malignancy.
The skin is also marked by many lines, creases, and ridges. Friction ridges (fig. 6.2b) are the markings on the fingertips that leave oily fingerprints on surfaces we touch. Friction ridges are characteristic of most primates. They help prevent monkeys, for example, from slipping off a branch as they walk across it, and they enable us to manipulate small objects more easily. Friction ridges form during fetal development and remain essentially unchanged for life. Everyone has a unique pattern of friction ridges; not even identical twins have identical fingerprints.
Flexion (palmar) creases are the lines of the palms formed after birth by repeated closing of the hand. Similar flexion lines form in other places such as the wrist and elbow (see fig. B.8 in atlas B).
Before You Go On
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