At an autopsy, a criminalist collects a hair from the victim's clothing. Microscopic examination reveals: medullary index > 0.5, continuous amorphous medulla, absence of cortical fusi, and scales with a mosaic pattern. This hair is MOST likely from:

• A Caucasian human head hair
• B African (Negroid) human head hair
• C Asian (Mongoloid) human head hair
• D Animal (e.g., cat or dog) hair ✓

Explanation

Human hair has a medullary index (ratio of medulla diameter to hair shaft diameter) < 0.33, typically < 0.3. Animal hairs have a medullary index > 0.5, often with a continuous or fragmented amorphous medulla and distinct scale patterns (e.g., coronal, petal, mosaic patterns depending on species). Absence of cortical fusi (air spaces common in human hair) and a mosaic scale pattern on the cuticle are characteristic of animal hair. Forensic hair examination thus uses medullary index, scale pattern, and cortical features to distinguish human from animal origins before DNA analysis.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

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Written and medically reviewed by the StethoPrep medical team.