Ancestry: Cranium

Ancestry refers to a pattern of genetic descent of an individual, and can be assessed by analyzing various features of the skeleton. Cranial features are often the most useful for determining ancestry.  (Keep reading below for more information about the use of ancestry in forensic anthropology.)

Bones of the Face

Orbit Shape

The shape of the orbits, or the eye sockets, among the different races varies. In general, Caucasian orbits are triangular, African orbits are rectangular, and Asian orbits more rounded or oval.

Zygoma

Another characteristic in the nasal/orbital region that can be assessed is the zygomatic bone, or the cheek bone, whose arch shape can vary.  In Caucasians and Africans, the shape is receding, while in Asians the arch is more flared.  The Asian skull has a wider zygomatic bone than parietal bone measurement.  This gives the appearance of the “higher cheek bones” associated with Asian and Native American peoples.

Additionally, a feature located on the zygomatic bone known as the zygomaticomaxillary suture can be shaped differently among biological races as well.  In Caucasians and Africans, the suture is generally curved in a “S” shape, whereas in Asians it is more angled (“Z” shaped) from eye orbit to cheek.

Nasal aperture

The nasal aperture among the different races is shaped differently.  In general, Caucasians have narrow, slightly pointed nasal openings, Africans have wide nasal openings, and Asians have intermediately shaped nasal openings.

Nasal sill

The nasal sill, that is the location on the skull where the vertical maxillae create a sharp ridge separating the nasal cavity from the maxillae, is a useful feature as well. If this nasal sill ridge is high, it is scored as “deep” and, if it is shallow, it is accordingly scored as “shallow.” If the ridge is lacking entirely, then it is scored as “blurred.” Furthermore, a smooth curve leading from the maxillae into the nasal aperture without interruption is known as “guttered.” With those distinctions in mind, it can be determined that, in general, Caucasians have deep nasal sills, Africans have guttered nasal sills, and Asians have blurred nasal sills.

Nasal overgrowth

Nasal overgrowth, that is the projection of the nasal bones slightly beyond the maxillae, can be noted as either present or absent among different races. This overgrowth is present in Asians, but it is absent in Caucasians and Africans.

Nasal spine

The nasal spine of a human specimen can vary depending on the amount of projection it exhibits. In Asians and Africans, the spine is small, whereas in Caucasians the spine is relatively larger.

Prognathism

The level of prognathism exhibited by a cranium can be scored as “large”, “medium, or “absent,” depending upon the amount of alveolar projection in the maxillary region.  Africans typically have a large amount of prognathism, while Asians have a medium amount.  In Caucasians, this feature is generally scored as absent.

Ascending ramus

In Caucasians and Africans, the ascending ramus is generally “pinched” (narrowed at about the midpoint) and “slanted” at an angle greater than 90 degrees. However, in Asians the ramus is more wide with a fairly uniform width and it is oriented vertically with the posterior border near 90 degrees.

Mandibular lower border

The mandibular lower border feature of the oral region can be used in ancestry determination.  This can be scored as “straight”, as “rocker” in which the manicle is more rounded on the bottom, or as “undulating” in which there is a deviation of the border upwards from the plane surface in the vicinity of the anterior border of the ascending ramus. This upward deviation of the border is most easily seen by placing the mandible on a flat surface.  Furthermore, with undulation, the body of the mandible thins greatly near the location of M2.  In Africans and Asians, this border is generally straight, while in Caucasians it is typically undulating.

Bones of the Brain Case

Metopic Suture

The frontal bone is a paired bone that fuses during the second or third year of life.  The suture where the two frontal bones fuse together is called the metopic suture.  However, 10% of the population maintains an unfused frontal bone throughout life.  These individuals are said to have a “persistent metopic suture” or “metopism” resulting in a paired frontal bone.  Metopism is a non-metric genetic trait and is considered a type of morphological variation as opposed to pathological.

Palate

Palate shape of the mouth can be scored as “parabolic” if it is narrower and tapering, “elliptic” if it is wider and smoothly curving, or “hyperbolic” if it is approaching a more rectangular shape. Caucasians generally have a parabolic shape; Africans a hyperbolic shape; and Asaisn an elliptical shape.

Palatine Suture

The shape of the palatine suture can be used to determine ancestry.  The shape of this suture is scored as a “straight” or can be scored as “bulging” if the central portion sweeps forward at the point of the suture’s intersection with the intermaxillary suture.  In Caucasians and Africans this suture is bulging, while in Asians it is typically straight.

External Auditory Meatus

The external auditory meatus, or the area of the skull around the ear, is an outgrowth of the ectotympanic bone, is either described as “round” or as “elliptic” when it is more vertically oriented. The meatus is typically rounded in both Caucasians and Africans, whereas in Asians it is generally more elliptical.

Wormian bones

Wormian bones are clearly defined small bones islands formed by the complexities of sutural coursing, particularly exhibited by the lamboidal and sagittal sutures.  This feature is generally absent in Caucasians and Africans, while in Asians it is present.

Inion hook

The inion hook is defined as an inferior projection of the external occiptal protuberance.  This feature is generally absent in Caucasians and Africans, whereas it is present in Asians.