Heady Stuff: Understanding the Cephalic Index

A century ago, serious dog people — “cynologists,” to use a phrase common among European fanciers — were well versed in the various numeric values assigned to different aspects of canine conformation, from the body (corporal index) to the chest (thoracic index).

Let’s look at one that has particular relevance to Molossers: the cephalic index.

Calculating Craniums

The word “cephalic” comes from the Greek word, “kephalē,” which means, simply, “head.” And that’s what this index measures — specifically, the relationship between the length and width of the head.

The cephalic index is calculated by taking the maximum width of the head (side to side), multiplying it by 100, and then dividing it by the maximum length of the head (front to back).

The shorter a dog’s head is, the higher its cephalic index will be. And for purposes of comparison, there are three ranges in the cephalic index, which correspond to different head types:

Brachycephalic: “Brachy” is the Greek word for “short,” and that’s what these breeds are: literally, short headed. Brachycephalic breeds, like the Bullmastiff and French Bulldog above, typically have foreshortened muzzles that are around half the length of the skull. They have a HIGH cephalic index. (Definitions of brachycephalic can vary, depending on context. Bullmastiff breeder-judge and frequent MM contributor Helene Nietsch would take us to task for using the B-word in relation to her breed, but according the cephalic index, it is.)

Dolichocephalic: The opposite of brachycephalic, the Greek word “dolichos” meaning “long.” Dolichocephalic breeds, like the Borzoi above, have a LOW cephalin index.

Mesocephalic: These breeds, like these Beagles above, are the middle ground, with muzzles that aren't particularly short or long, and heads that aren't overly wide or narrow. Their cephalic index in the MIDDLE of the brachycephalic and dolichocephalic breeds.

While today’s fanciers don’t speak of dogs in terms of cephalic index, researchers still do, with a number of studies focused on associating this measurement with other values.

A 2024 study out of England that we just reported on associated a high cephalic index with a shortened lifespan.

Another study found a relationship between canine head shape and visual ability: It turns out that in brachycephalic dogs (again, those with short heads and high cephalic-index values, like most Molossers), the retinal ganglion cells in the eyes — which are the first to process visual information — are clustered at the center of their visual field, making it easier to make eye contact and see the gestures of their human companions.

Cephalic index is the ratio of the maximum width of the head (A) multiplied by 100 divided by the head’s maximum length (B). The shorter the head, the higher the cephalic index. Source: “Shorter headed dogs, visually cooperative breeds, younger and playful dogs form eye contact faster with an unfamiliar human,” Scientific Reports, April 2021.

In dolichocephalic dogs (those with long heads and low cephalic index values), those cells instead cluster as a horizontal streak across their line of vision, making it easier to spot prey with their peripheral vision.

These visual tendencies dovetail neatly with the work the different head types evolved to do: In brachycephalic dogs, the shorter head increases biomechanical bite force, making for a more effective guard or fighting dog; it also predisposes the dog to an undershot bite, which is most effective for holding. If the brachycephalic head shape helps a dog read its human handler’s body language, that’s pretty helpful in the midst of its work, as the dog can reconnect more easily with its handler and understand when it is time to relinquish its victim. 

Conversely, in dolichocephalic dogs, the long head contributes to a more aerodynamic silhouette, enhancing speed. Dogs with such elongated heads also tend to have a scissors bite, which enables them to slash and more easily bring down fleet game. In these dogs, the ability to easily scan the horizon increases the opportunity to locate fast-moving prey — to say nothing of their tendency to ignore their handler once that prey has been spotted.

Head Cases

In the first half of the 20th Century, cephalic index was used to describe humans as well, a practice that — perhaps thankfully? — has fallen out of favor.

And, following suit, in the dog world of a century ago, the cephalic index was used as a tool to describe type.

Above: Cephalic index applies to human skulls as well. Below: The children of the Tsar Nicholas II of Russia in June 1917, with loss of hair after fighting measles. From left, Anastasia, Olga, Alexei, Maria and Tatiana, whose skull had the lowest cephalic index.

Italy dog authority Antonio Morsiani was perhaps best known for using the cephalic index to describe the Cane Corso in the breed’s first standard, written in 1987.

Describing the Corso as brachycephalic, Morsiani wrotes that its cephalic index “varies from 64 to 66.”

According to Morsiani, an index higher than 54 was considered brachycephalic; lower than 50, dolcimorphic, and between 50 and 54, mesomorphic.

(The difference between Morsiani’s values and those used in modern study cited above of cephalic-index influence on vision can only be explained by different measurement parameters. Morsiani was either measuring the width using a shorter span, or was measuring the length from a longer point.)

While there isn’t much practical application of the cephalic index in today’s breed standards or discussions of type, it is worth being reminded periodically of the importance of skull dimensions in Molossers. Eye shape and placement, jaw width, brow and cheek development, median furrow — all are impacted dramatically by the width of the skull. And it’s all this interconnectedness between adjacent parts that underlies the details in type between the various Molossers.