Ch. 5 Notes - Fingerprints (Pg. 1)

1. Fingerprints

   1. The study of fingerprints for identification purposes is known as dactylography or dactyloscopy.

   2. your fingers, toes, feet, palms, and lips are covered with small ridges that are raised portions of the skin, arranged in connected units called dermal, or friction, ridges,

   3. ridges help us grip objects

   4. fingers accumulate natural secretions and dirt. when the ridges press against things, they leave a mark or impression called a fingerprint.

      1. A ridge appears dark on a fingerprint image; a valley appears light.

2. Formation of Fingerprints

   1. Fingerprints begin forming near the 10th week of pregnancy when the fetus is about 3 inches long.

      1. inner layer - dermis

      2. outer layer - epidermis

      3. basal layer in between

   2. in a fetus, the basal layer cells grow faster than the layers above and below it so it collapses and folds to form intricate shapes.

   3. fingerprint residue originates from glands in the subcutaneous skin. Apocrine and eccrine glands are commonly referred to as sweat glands.

      1. apocrine glands are associated with hair follicles.

      2. Eccrine glands are primarily located on the ridges of the hands and feet

3. Fingerprint patterns

   1. two things a forensic examiner looks for on a fingerprint are the presence of a core and deltas.

      1. the core is the center of a loop or whorl

      2. A triangular region located near a loop is called a delta

   2. There are 3 specific classes for all fingerprints based on their visual pattern: arches, loops, and whorls

Arch: Have ridges that enter from one side of the fingerprint and leave from the other side with a point in the center. population - 5%

Loop: Have ridges that enter from either the right or the left and exit from the same side they enter. Population - 65%

Whorl: have at least one ridge that makes a complete circuit. Looks like a bull’s-eye with two deltas. population - 30%