Cephalic Index (Cranial Index / Breadth Index)

Definition

The cephalic index (CI) - also called the breadth index - is a numerical ratio used to classify skull shape based on the proportional relationship between head width and head length.

Formula

CI = (Maximum Transverse Breadth x 100) / Maximum Anteroposterior Length

Landmark Measurements

Length (anteroposterior): Distance from the glabella (midpoint between brows) to the external occipital protuberance
Breadth (transverse): Greatest diameter across the skull, measured above the mastoid process
Best measured with sliding calipers (not a measuring tape); an osteometric board can be used as an alternative

Classification

Skull Type	Cephalic Index	Description	Typical Race
Dolichocephalic	70 - 74.9	Long-headed (narrow)	Aryans, Negroes/Blacks
Mesaticephalic	75 - 79.9	Medium/oval-shaped	Europeans, Chinese
Brachycephalic	80 and above	Round/short-headed	Mongolians

Related Skull Indices

Two additional indices are used alongside CI for racial identification from skeletal remains:

Height Index (HI): (Height of skull x 100) / Length of skull
- Height = tip of mastoid process to bregma
Nasal Index (NI): (Width of nasal aperture x 100) / Height of nasal aperture

Index	Blacks	Europeans	Mongols
CI	70-74.9	75-79.9	80+
HI	72	71	75
NI	55	46	50

Clinical / Obstetric Use

In fetal medicine (prenatal ultrasound), the cephalic index is calculated as:

CI = (Biparietal Diameter x 100) / Occipitofrontal Diameter

Normal range: 0.70 - 0.86
High CI = brachycephaly (short, wide head)
Low CI = dolichocephaly (long, narrow head)

This helps distinguish normal fetal skull shape from abnormalities such as craniosynostosis.

Uses

Forensic anthropology - helps estimate race/ancestry from skeletal remains
Physical anthropology - used historically in the study of human population variation
Obstetrics/fetal medicine - prenatal assessment of fetal head shape on ultrasound
Craniosynostosis surgery - monitors head shape before and after surgical correction

Sources: P C Dikshit Textbook of Forensic Medicine and Toxicology; Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology; Creasy & Resnik's Maternal-Fetal Medicine; Encyclopaedia Britannica

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