Hair Whorls In Dogs – Location, Classification and Directionality

Combing through the literature for neurological development and lateralization one finds the weirdest things; like these two papers on hair whorls in dogs. Both papers are well written and researched and they also contain the kind of dreary detail that only an anatomist could love.

Here is a sample, feel free to skip it:

“Whorl placement in this study was recorded in relation to where the center of the spiral lay. A pair of calipers was used to record the position of the whorl, in millimeters, in relation to bony landmarks within the region. A palpation and hair-cluster technique was used to identify the two focal points from which the distance would be measured; the center of the whorl and the palpable bony landmark. The center of a simple whorl could be determined visually, but palpation and manipulation of the hair-cluster was required to determine the center of a tufted whorl. In this technique, the point at which hair converged over the center of the whorl was located, and the tuft of hair was then held between the index finger and thumb to rotate the hair to expose the center of the tuft. To account for variation in size between different breeds and individual dogs, measurements were also taken to allow whorl distance to be expressed as a percentage distance from a skeletal feature, so position could be standardized and compared between breeds.”1

However since all dog owners like to compare their dog to other dogs, I thought it might be of some interest.

I am going to skip over the methodology and get right to the findings. It could also spur a game of classify the hair whorl (tufted or simple, clockwise or counterclockwise) in your home. You might even have one of those dogs with unusually placed hair whorls.

A simple whorl (A) describes a focal point or center from which the hairs diverge in a flattened swirling pattern, whereas a tufted whorl (B) describes hairs converging from different directions to a central point, forming a tuft.
From Tomkins & McGreevy

• Typical whorls, such as those located on the chest, ischiatic, and brachial axillary regions and the elbows
• Atypical whorls are found in less than 20% of the population
• Atypical whorls are found in the head, cervical regions (dorsal, ventral, and lateral), shoulders, thoracic axillary and ventral abdominal region
• Simple tufts are found in cephalic, cervical, brachial and thoracic axillary, shoulder, and abdominal regions
• 1% of schiatic whorls were tufted
• All elbow whorls were tufted
• 75% of the dogs had chest tufts, 97% simple and 91% of chest whorls were counterclockwise
• 19% of the dog had ventral mandibular (under the jaw) whorls
• Bilateral whorls show opposite rotation
• 5% of the dogs had cephalic whorls

After Tomkin and McGreevy

Check your dog, does he have one of those atypical whorls? And remember the answer for the next installment.

References

Tomkins LM, McGreevy PD. Hair Whorls in the Dog (Canis familiaris). I. Distribution. The Anatomical Record 293:513–518 (2010)

Tomkins LM, McGreevy PD. Hair Whorls in the Dog (Canis familiaris), Part II: Asymmetries. The Anatomical Record 293:513–518 (2010)