# The cranium, and how the face ages
Head size and shape by sex, the cephalic index, how the vault changes with age and its genetics, then site-specific bone resorption and the facial fat compartments. Every figure attributed.
*Figure: A scale from 160 to 215 mm. Bands: 165 to 210, 95% range, 165-210 mm. Marks: Female 180 at 180; Male 195 at 195.* Head length (g-op): the female and male means in a 95% range.
## The cranium - the container
*Figure: Range strips on one scale from 48 to 64 cm, each with a mean tick, a solid band at plus or minus one standard deviation and a pale band at plus or minus two. Female 54.2 ± 2.4; Male 56.3 ± 2.6.* Head circumference by sex, adults.
Landmarks: `g` glabella · `op` opisthocranion (back of skull) · `eu` euryon (widest point of the vault) · `v` vertex (top)
Everything else on this page hangs off the braincase. The skull is effectively two modules welded together: the **neurocranium** (the vault that houses the brain) and the **viscerocranium** (the face). They grow on different schedules and are modular to a real degree - a large vault with a modest face, and the reverse, both occur naturally. Head *shape* is captured by a single ratio, the cephalic index.
| Measure | Female | Male | Notes |
|---|---|---|---|
| Head length (g-op) | 180 mm | 195 mm | 95% range 165-210 mm; US & British adults[5] |
| Head breadth (eu-eu) | 136-150 mm | 140-155 mm | varies by population and by method[6][7] |
| Head circumference | 54.2 ± 2.4 cm | 56.3 ± 2.6 cm | n≈2,508 adults; overall 55.3 ± 2.7 cm[8] |
| Endocranial volume | ≈ 1,130 cm³ | ≈ 1,260 cm³ | very wide individual spread[11] |
| Vault sex dimorphism | males ≈10-15% larger brain volume · ≈12% larger intracranial space | survives adjustment for body height[9][10] | |
*Head dimensions, adults*
### Head shape - the cephalic index
Head breadth ÷ head length × 100 sorts skulls into three classic forms. It is the most useful single knob for how a face *reads*, because the vault underneath sets the outer limit the face has to fit inside.
| Index (F / M) | Class | Meaning |
|---|---|---|
| < 75 / < 75.9 | Dolichocephalic | long-headed, narrow - face reads long and slim |
| 75-83 / 76-81 | Mesaticephalic | medium - the common case in most samples |
| > 83 / > 81.1 | Brachycephalic | short-headed, broad - face reads wide and flatter |
*Cephalic index classes[12]*
Distribution is population-specific and not a fixed marker: one 600-skull Indian study found dolichocephaly dominant (47.2%), a Tharu-community study found dolichocephaly in 44.4% of males, and Korean children were mostly mesocephalic (43.2%).[13][14] Boas showed head shape shifting measurably within one generation of migration, so treat it as a soft prior, never a hard category.
### Sex and size in the vault
- **Males are larger in essentially every cranial region**, and the most dimorphic spots are the glabella and mastoid process - the same brow region the brow section covers.[2]
- **Brain volume** averages roughly 10-15% larger in males, and intracranial space about 12% larger - a difference that persists after adjusting for body height.[9][10]
- **Head circumference is a usable proxy for brain volume** in this context: it correlates with measured brain volume (ρ = 0.47) and with height (ρ = 0.39), and differs reliably between the sexes.[8]
- **Bone thickness runs the other way.** Females carry *greater* cranial vault cortical thickness than males, and a greater age-related increase in it.[18]
### The vault keeps changing with age
The adult skull is not finished. Geometric-morphometric work on head CT across ages 20-100 found significant shape change with age in **almost every region in males** (all but the posterior cranial fossa), and in females mainly in the **anterior and middle cranial fossae**.[17] The pattern is localised compression of the inner frontal and posterior parietal regions with relative expansion of the inferior parietal and temporal regions - which loosely tracks where the brain's grey matter thins.
| Change | Female | Male |
|---|---|---|
| Vault shape change with age | anterior + middle fossae | nearly all regions |
| Cortical thinning of inner/outer tables | −36 to −60% (20→100 yr) | not significant |
| Full vault thickness (diploë) | slight increase with age in both sexes | |
*Ageing of the cranial vault and tables[17][18]*
Practical read: the brow and forehead stay put or thicken, while the midface and orbital rim resorb around them (the ageing section). That contrast is a large part of why an older face looks like the face slid down inside a stable skull.
### Genetics of the vault
Cranial vault shape is highly heritable and overwhelmingly polygenic, like the face - but with a different lead actor.
- **RUNX2** is the master regulator of calvarial (flat-bone) ossification; it sits at the centre of a network of FGF, BMP/TGF-β, Wnt, Hedgehog and PTHLH signals.[16]
- A multi-ancestry GWAS of 3D vault shape (6,772 children) found **30 genome-wide loci explaining ≈1.31%** of global vault shape variation; a pleiotropy-informed re-analysis raised that to **120 loci**.[15][16]
- **≈60% of vault loci overlap facial loci**, and the frontal region shares signal with both face and brain - which is exactly why head shape and face shape are not independent variables.[15]
- **Cephalic index specifically** has been associated with loci near **SOX9** and **SOX11**. The old textbook candidate FGFR1 did not replicate.[15]
## Ageing - bone, fat & cartilage
*Figure: Horizontal bars grow from a zero line, one per row. Orbital aperture area, by the 7th decade: +15-20%; Maxilla height: -8 to -15%.* Orbits widen, the maxilla shortens.
Ageing is not a uniform deflation or a uniform droop. It is **site-specific bone resorption** under a set of **independently-deflating fat compartments**, and the two interact.
### The skeleton
| Region | Change | Effect on read |
|---|---|---|
| Orbital aperture | +15-20% area by 7th decade | deeper-set eyes, tear troughs, lid droop |
| Maxilla | −8 to −15% height | midface flattening, reduced upper-lip support |
| Piriform aperture | enlarges; lower rim recedes most | nose appears longer, tip support weakens |
| Mandible | angle +3-7° | square jaw → rounded, receding |
*Skeletal change with age[1][3]*
Site-specific resorption is heaviest in the orbit, piriform aperture and maxilla; postmenopausal changes are accelerated in women in the orbit, while men show more mandibular remodelling.[3]
### The fat compartments
Facial fat is **partitioned by septal walls into discrete compartments**, not spread as a uniform pad - the core insight from Rohrich & Pessa’s cadaver work.[4] Ageing is compartment-specific deflation, so each pocket should be modelled as its own volume that shrinks and repositions independently.
| Layer | Compartments | Aging behaviour |
|---|---|---|
| **Superficial** - visible contour | nasolabial · medial cheek · middle cheek · lateral temporal-cheek · jowl · infraorbital | temporal-cheek hollows; nasolabial fold deepens; jowl descends |
| **Deep** - structural support | deep medial cheek · suborbicularis oculi (SOOF) · buccal | deflation → pseudo-descent of the whole cheek (“pseudoptosis”) |
*Facial fat compartments and their ageing behaviour*
> **Key insight, kept from the draft.** Fat deflates *and* retaining ligaments (zygomatic-cutaneous, orbitomalar, mandibular) slacken; the result looks like tissue sliding downward even where little has moved. Model the compartments independently, then let a light downward “rail” through the ligament lines produce the descent illusion.
## Sources
1. Shaw & Kahn / Pessa: *Changes in the Facial Skeleton With Aging.*
2. Quantitative Analysis of Male Versus Female Frontal Bone and Orbital Skeletal Morphology.
3. Facial bone aging: an update and literature review (orbital enlargement, maxillary height loss, mandibular angle increase).
4. Rohrich & Pessa (2007). *The Fat Compartments of the Face.* Plast Reconstr Surg.
5. Head length norms by population (Hong Kong / British / US / Japanese). Online Anthropometry reference.
6. Cranial anthropometry in 600 North Indian adults (head breadth M 139.5 / F 136.19 mm).
7. Anthropometric data: head breadth percentiles (Roy Mech).
8. Microcephaly measurement in adults (n=2,508; head circumference M 56.3 ± 2.6 / F 54.2 ± 2.4 cm; correlation with brain volume and height).
9. Are sex differences in human brain structure associated with sex differences in behavior? (male brains 10-15% larger).
10. Males and females differ in specific brain structures (intracranial volume ~12% larger in males, n>14,000). University of Cambridge.
11. Brain size - endocranial volume (≈1,260 cm³ men / ≈1,130 cm³ women).
12. Cephalic index - dolichocephalic / mesaticephalic / brachycephalic classification.
13. Cephalic Index in the Indigenous Tharu Community (dolichocephaly 44.4% of males).
14. Establishment of Cephalic Index using cranial parameters (dolichocephalic 47.2%).
15. Joint multi-ancestry and admixed GWAS of human cranial vault shape (30 loci; ≈1.31% of vault shape variance; SOX9/SOX11 for cephalic index; 60% overlap with facial loci). *Nature Communications* 2023.
16. Enhanced insights into the genetic architecture of 3D cranial vault shape using pleiotropy-informed GWAS (120 loci; RUNX2). *Communications Biology* 2025.
17. Evaluation of morphological changes in the adult skull with age (cranial fossae shape change; males across nearly all regions).
18. Evaluation of skull cortical thickness changes with age and sex (female cortical thinning 36-60%; greater vault thickness in females). *JBMR* 2015.
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First published 2026-10-02, updated 2026-10-18. Web page: https://www.mackenziebowes.com/research/facial-character-parameters/cranium-and-ageing Part of [Facial parameters for character work: the dials that carry a face, and how far they travel](https://www.mackenziebowes.com/research/facial-character-parameters).