Cephalic Index

What is a Cephalic Index?

Cephalic index is given as the percentage of breadth to length in any of the skulls. The index is determined by measuring the diameters of the skull. The distance between the glabella (the midpoint between the brows) and the most projecting point on the back side of the head is used to calculate the skull length. The breadth of the skull is given as the distance between the most projecting points at the sides of head, generally a little above and behind the ears.

Range of Cephalic index

The cephalic index is given as the breadth, which is multiplied by 100 divided by the length. An index of below 75 means that the skull is narrow and long when seen from the top; such types of skulls are known as dolichocephalic and they are typical of Australian aborigines and the native southern Africans. An index of ranging 75 - 80 means that the skull is approximately oval; such skulls are known as mesaticephalic and are typical of the Chinese and Europeans. A skull, which holds an index of about 80 is short and broad, and is known as brachycephalic; such skulls are quite common among the Andaman Islanders and Mongolians.

Historic Use in Anthropology

Early Anthropology

In the early twentieth century, anthropologists used to calculate the cephalic index (cephalic index calculator) to categorise the human population. Now, it is primarily used to describe the individuals' appearances and for estimating the fetuses age for obstetrical and legal reasons.


Anders Retzius (1796–1860), a Swedish professor of anatomy, invented the cephalic map, which was first used in physical anthropology to classify ancient human remains found in Europe. This theory became more closely associated with the racial anthropology development in both 19th and early 20th centuries, when the prehistorians attempted to use ancient remains to model population movements in terms of the racial categories. Also, the Carleton S. Coon used the index in the 1960s.

Indices

Cephalic indices can be grouped as in the below table:


Females

Males

Scientific term

Meaning

Alternative Term

< 75

< 75.9

dolichocephalic

'long-headed'


75 to 83

76 to 81

mesaticephalic

'medium-headed'

mesocephalic; meso cranial

> 83

> 81.1

brachycephalic

'short-headed'

brachycranic


Technically, the measured factors can be defined as the maximum width of the bones, which surround the head above the supramastoid crest (it means, behind the cheekbones), and the maximum length from the very easily noticed part of the glabella (between the eyebrows) to the very easily noticed point at the back side part of the head.

Controversy

Giuseppe Sergi challenged the cephalic index's utility, claiming that cranial morphology was a better way to model racial ancestry. In addition, Franz Boas analysed the children of immigrants to the United States between 1910 and 1912, finding that the children's cephalic index differed significantly from that of their parents, suggesting that local environmental factors had a major impact on cephalic head shape growth.


Boas also argued that the cephalic index was useless for defining race and mapping ancestral populations if craniofacial features were too malleable in a single generation. Scholars like Earnest A. Hooton continued to argue that both heredity and environment were involved. But, Boas did not himself claim it was completely plastic.


In 2002, Jantz and Sparks re-evaluated some of Boas' original data using modern statistical techniques, concluding that the shape of the head had a "relatively large genetic component." The new study, according to Columbia University's Ralph Holloway, raises concerns about whether differences in skull shape have "adaptive significance" and whether "normalising selection may be at work on the trait, where both hyper brachycephaly and hyper dolichocephaly are at a small disadvantage in terms of selection."

Modern Use in Animal Breeding

The cephalic index can be used in the categorisation of animals, especially in the breeds of cats and dogs.

Brachycephalic Animals

Relatively, a brachycephalic skull is short and broad (typically having the breadth at least 80% of the length). Some dog breeds, such as the pug, are known as "Extreme Brachycephalic." Due to the health issues brachycephaly is regarded as torture breeding, often, as it leads to the Brachycephalic airway obstructive syndrome.

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List of Brachycephalic Dogs

  • American Bulldog

  • Affenpinscher

  • Boxer

  • Boston Terrier

  • Brussels Griffon

List of Brachycephalic Cats

  • British Shorthair

  • An Exotic Shorthair

  • Exotic Shorthair

List of Brachycephalic Pigs

  • Middle White

List of Brachycephalic Rabbits

  • Lionhead rabbit

  • Jersey Wooly

  • Lop rabbit

Mesaticephalic Animals

Mesocephalic Labrador Retriever

A mesaticephalic skull consists of intermediate width and length. These mesaticephalic skulls are not markedly dolichocephalic and brachycephalic. When dealing with animals, especially dogs, the more common and widely used term is "mesaticephalic," which refers to the ratio of the head to the nasal cavity. This group is exemplified by the breeds mentioned below.

List of Mesaticephalic Canines

  • Alaskan Malamute

  • African Wild Dog

List of Mesaticephalic Cats

Note: Almost all the felines are known to be mesaticephalic

  • American Bobtail

  • American Shorthair

FAQs (Frequently Asked Questions)

1. Why Do Human Skulls Represent Much Variation in Shape?

Answer: Culture and environment practices play an important role in shaping our heads. Genes regulate the process of unfolding of growth and skull development. However, genes do not define the shape of the skull.

2. What is Dolichocephalic?

Answer: “The cephalic index or the cranial index is given as the ratio of the maximum width (BPD or biparietal diameter, side to side) of the head of an organism (either animal or human) multiplied by 100 divided by its maximum length (OFD or occipitofrontal diameter, front to back). Also, the index is used to categorize animals, especially cats and dogs.”

3. Why are Human Skulls Weak?

Answer: The skull is not all that weak. It is strong enough that the huge majority of us do not crack our heads before reproduction, which is all nature cares about, even though for the first 20 years of life, it is not yet in its hardheaded, closed form.

4. Why are Human Skulls Hard and Strong?

Answer: Because when a skull is mushy and soft, heavy objects, which fall or bump into on top of the head, often, would crush whatever happened to be inside.