In forensic hair examination using light microscopy, which feature MOST reliably distinguishes human head hair from animal (canine) hair?
- A Presence of melanin granules in humans only
- B Uniform cortex with medulla index less than 0.33 in human hair vs. medullary index greater than 0.5 in dog hair ✓
- C Absence of a cuticle in human hair
- D Cross-sectional shape — humans have always circular, dogs always triangular cross-sections
Correct answer: B. Uniform cortex with medulla index less than 0.33 in human hair vs. medullary index greater than 0.5 in dog hair
Explanation
The medullary index (diameter of medulla / diameter of hair shaft) is a key differentiating criterion. Human hairs have a medullary index <0.33 (narrow medulla or absent) with a continuous, uniform cortex and ovoid cuticular scales. Animal hairs (including canine) typically have a medullary index >0.5 and may show a continuous, ladder, or vacuolated medulla. Both humans and animals have melanin granules and cuticle scales. Cross-sectional shape varies by body region and race in humans and is not the most reliable single criterion.
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.