Hair Morphology

Introduction to Hair Morphology in Wildlife Crime Scene Investigation

  • The section focuses on the morphology of hair as it relates to wildlife crime scene investigation.

Hair Structure

  • Follicles: Hairs grow out of pits in the skin called follicles.

  • Root: The base of the hair that is embedded into the skin.

  • Shaft: The portion of the hair that emerges from the skin's surface.

  • Sebaceous Gland: Often situated next to the follicle; secretes oily substances that lubricate and condition the hair.

Erector Pili Muscle

  • Function: A small involuntary muscle located next to the follicle.

  • Effect on Hair: Contraction causes hair to stand up or become more perpendicular to the skin.

  • Goosebumps: The pulling action of the muscle also causes skin to form bumps, a phenomenon commonly known as goosebumps.

Composition of Hair Shaft

  • The shaft is primarily composed of a protein called keratin.

Hair Shaft Structure

  • Cuticular Scales:   - Outer layer made of dead, transparent cells.   - Arranged in distinctive patterns, often overlapping.

  • Cortex:   - Thick layer beneath the cuticular scales, can exhibit pigmentation.

  • Medulla:   - Central area of the hair, made up of large cuboidal cells with potential air pockets.   - The arrangement, thickness, color of the cortex, and the distribution of colored medulla cells are diagnostic of species.

Microscopic Examination of Hair

  • Hair analysis often requires the use of a microscope to inspect the cortex and medulla.

  • Observation of Cuticular Scales:
      - Typically requires embedding a hair in ethyl acetate, allowing it to harden, then removing the hair to examine the impressions.

Hair Development Process

  • Hair grows from the papilla, and besides that point of generation, it consists of dead cornified cells.

  • The hair shaft projects above the skin, while the root is embedded in the skin.

  • Root Bulb:
      - The lower end of the root expands to form the bulb, which is rounded.   - Contains keratin as the main protein, melanin as the primary pigment, and trace quantities of metallic elements absorbed from the environment.

  • Cell Formation:
      - New cells are formed in the bulb area, stick together, harden, creating a strand of hair.

  • As new hardened cells continue to attach from below, the hair is gradually pushed up and out of the skin.

  • Eventually, the hair enters a resting state in the follicle before being sloughed off.

Types of Mammalian Hair

  • There are four main types of hair in mammals:   1. Vibrissae (Whiskers):      - Specialized hairs that provide tactile sensation.      - Rich in nerve endings, allowing for sensitive touch detection.      - Typically found around the nose, above the lips, and on parts of the face.      - Thicker and stiffer compared to other hair types.      - The term comes from the Latin word "Vibrio".      - Species-specific arrangement in a grid-like pattern, visible in species like walruses.

  2. Overhairs:      - Longest hairs on a mammal's coat, sparsely distributed.      - Less useful for species identification due to lack of distinguishing features when heavily pigmented.

  3. Guard Hairs:      - Form the outer layer of the coat.      - Long and coarse, tapering to a point, protecting underfur from environmental factors.      - Can vary in morphology based on body region and age (immature vs. mature).      - Some can develop into defensive spines, as seen in porcupines.

  4. Underfur (Undercoat):      - Comprises short, fine, fluffy hairs that sit close to the skin.      - Not ubiquitous in all mammals; found in those who require insulation.      - Hairs are often crimped, enhancing their ability to trap air for insulation through interlocking mechanisms.