The Cephalic Index

Skulls that are brachycephalic and dolichocephalic, respectively

The cephalic index, also known as the cranial index, is the source of a series of terms that are really rather commonly used in such things as the world of dog fancy. However, it's likely that a lot of people out there don't actually know that the terms mean. It is a way of looking at the anatomy of the skull. The cephalic index is basically a percentage calculated by comparing the length of the skull to the skull's width. Specifically, it's the width multiplied by one hundred and divided by the length. If the index is seventy-five to eighty, the skull is oval in shape, also known as mesaticephalic or mesocephalic. If the index is less than seventy-five, the skull is long and narrow, also known as dolichocephalic. If the index is more than eighty, the skull is short and broad, also known as brachycephalic. If the index is more than eighty-five, the skull is even shorter and broader and can be called extremely brachycephalic or hyperbrachycephalic. In the past, and indeed currently, these designations have been used to describe different racial designations, which usually share very similar characteristics. Some populations have very long skulls, and thus tend to be dolichocephalic. Others have broad skulls and trend toward brachycephalic. Others are mesaticephalic, and still others are hyperbrachycephalic.

Dolichocephalic, index 64

Mesaticephalic, index 79

Hyperbrachycephalic, index 94

Of course, when looking at humans and the cephalic index designations there is one major characteristic that is lacking and is very important when applying the same terminology to dogs or other domestic animals: muzzle. Humans don't have a muzzle, so the cephalic index is almost entirely based on the shape of the brain case. This is far from true when looking at dogs, since dogs have muzzles. As such, the muzzle plays a major role in determining a dog's cephalic index. Generally, dogs with long muzzles will be dolichocephalic, and dogs with short muzzles will be brachycephalic. However, this is not always the case. For example, there are dogs with fairly moderate muzzles that would be classified as brachycephalic because they have very broad skulls.

Technically brachycephalic

In a series of posts to come, I will be discussing more about the cephalic index in dogs and why it can be so important.

Sources are Scientific Electronic Library Online, Encyclopedia Britannica, Encyclo Online Encyclopedia, . Images are from Wikimedia Commons and are under Creative Commons licenses or are copyright free: one, two, three, four, five, .