Medulla
Definition
The central canal of the hair shaft, which may be continuous, interrupted, fragmented, or absent. Medullary pattern and the medullary index (medulla diameter divided by shaft diameter) assist in species attribution and, to a lesser extent, human hair comparison.
- Location
- Central canal of the hair shaft
- Pattern types
- Continuous, interrupted, fragmented, absent
- Medullary index
- Medulla diameter divided by shaft diameter
- Primary use
- Species attribution
- Secondary use
- Aid in human hair comparison
Common questions
How does medullary pattern help distinguish human hair from animal hair?+
Most human head hair has a discontinuous or absent medulla and a medullary index below about one-third of the shaft diameter, while many animal species show a continuous medulla occupying half or more of the shaft with a distinctive internal structure. This contrast makes medulla examination one of the first screening steps in hair comparison.
Can medullary pattern alone identify a specific animal species?+
Not by itself with full confidence. Medulla structure narrows the range of likely species and is a strong indicator, but examiners typically combine it with scale pattern, cuticle structure, and overall hair morphology to reach a species-level conclusion, since some species share similar medullary appearances.
Why is medulla examination less useful for individualising human hair to a specific person?+
Because human medullas are often fragmented or absent altogether, and even when present the pattern shows limited variation between individuals compared to cuticle scale detail and pigment distribution. Analysts rely more heavily on those other microscopic features, and increasingly on mitochondrial DNA, to individualise human hair evidence.
Related terms
- Cortex
- The middle, and largest, layer of the hair shaft. It contains cortical cells, pigment granules (melanin), and cortical fusi (air spaces). The...
- Cuticle
- The waxy, polymer layer covering the outer surface of leaf epidermal cells. It protects against water loss and herbivory but, forensically, it...
- Follicular Tag
- Translucent sheath tissue adhering to the root of a forcibly pulled hair. Contains nucleated epithelial cells from the inner root sheath and...
- Medullary Index
- The ratio of the medulla diameter to the total hair shaft diameter. In companion animal hair identification, a medullary index above 0.5...
- Anagen
- The active growth phase of the hair cycle, lasting two to six years in scalp hair. During anagen the root matrix is...
- Anagen / Catagen / Telogen
- Hair growth phases. Anagen is the active growing phase (about 85 percent of scalp hairs), catagen the brief transition, telogen the resting...
- Cortical Fusi
- Air-filled spaces within the cortex of the hair shaft, most common near the root end. Their size, shape, and distribution are minor...
- Mitochondrial DNA (mtDNA)
- DNA located in mitochondria rather than the cell nucleus. Present in hundreds to thousands of copies per cell, making it recoverable from...
- Natural Fibre
- Fibre of biological or mineral origin. Animal (wool, silk, cashmere, mohair, alpaca), vegetable (cotton, jute, flax, hemp, sisal, coir) or mineral (asbestos;...
- Synthetic Fibre
- Fibre manufactured from regenerated cellulose (rayon, acetate) or polymer chemistry (nylon, polyester, acrylic, polypropylene, spandex, kevlar). Identified by birefringence, FTIR and pyrolysis...
- Telogen
- The resting phase of the hair cycle, lasting two to four months in scalp hair. The root forms a club-shaped, non-pigmented bulb....
Explained in these topics
- Hair Anatomy and the Growth Cycle
- Hair and Fibers: Nature, Types, Structure and ExaminationCentral canal of the hair shaft. Classified as continuous, interrupted, fragmentary or absent. Pattern is species-diagnostic.
- Hair Examination and MicroscopyThe central canal of the hair shaft, which may be absent, fragmented, interrupted, or continuous. Human hair typically has an absent or fragmented medulla; mos...