3B Scientific Gorilla Skull (Gorilla gorilla), male - Manual (Page 2)

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Gorilla 1
Species Gorilla gorilla (Savage & Wyman, 1847)
Subfamily Ponginae Allen, 1925
Family Pongidae Elliot, 1913
Superfamily Hominoidea Simpson, 1931
Infraorder Catarrhina Hemprich, 1820
Suborder Simiae Haeckel, 1866
Order Primates Linnaeus, 1758
The skull of the mature, very large male gorilla presents a very marked relief. The cerebral cranium and the
facial bones (viscerocranium), including the pronounced supra-orbital ridge (torus frontalis), have a rough
appearance and are marked with bumps, ridges, etc., which were formed in response to the requirements
of the masticatory and neck musculature. They are in no way comparable with those of the human.
In the gorilla’s skull too, the disproportionate size of the face/jaw part (the facial bones, i.e. the splanchno-
cranium or viscerocranium) in relation to the cerebral cranium is noticeable. This relationship, however,
only develops in the course of postnatal growth – particularly at the time of the second dentition.
On the sagittal suture, that is down the middle of the skull, a bony sagittal crest (crista sagittalis) develops,
becoming more pronounced towards the back. It is formed from the parietal bones and serves as the
origin of the temporal muscle
2 , which increases in size as it approaches the crest. At the back of the head
(the occiput) the sagittal crest joins the occipital crest, which develops as the neck musculature becomes
stronger.
The occipital condyles of the atlas joint and the great occipital foramen they enclose (foramen occipitale
magnum) are located in the posterior region of the skull. Here too, the obvious contrast with the newborn
or infantile animal is evident.
The sexual dimorphism of the skull appears at first sight more pronounced in the gorilla than with other
Ponginae. As is the case with all primates that have been investigated in this respect, male gorillas display
on average a larger brain volume, larger and differently shaped canine teeth, and a significantly more pro-
nounced skull relief. All mature males at least, as well as almost all mature females, have a sagittal crest.
All adult animals develop occipital crests, due to their “front-heavy” heads.
In general supra-orbital ridges (tori supraorbitales) are formed, which are linked medially by a glabellar
ridge (torus glabellaris) to form a unified brow ridge (torus frontalis). Not unrelatedly, the frontal sinuses are
very pronounced. This development takes place in connection with the formation of the permanent teeth
and then with the wear of the teeth with continuing abrasion from chewing
3 .
The upward branch of the lower jaw (ramus mandibulae) is relatively low. Typical of the Ponginae is the
more or less parallel arrangement of the premolar and molar teeth. In front of them are the incisor teeth.
The sexually differentiated, dagger-like canine teeth extend distinctly beyond the occlusion plane. For this
reason, in the upper jaw between the canine tooth and the first premolar, there is a gap, or diastema, into
which the lower canine tooth engages.
The anterior teeth engage one over the other like shears, which makes it easier to bite off a piece of food,
while the posterior teeth have broad, shallow crowns, suited to grinding; this constitutes – in the case of
the molars – what is known as the dryopithecine pattern, which is also displayed by humans. In the gorilla
too, the enamel shows furrows on the occlusion plane next to the fissures; these are few in number but
characteristic here too.
Since the pioneering studies of E. Selenka around 1900, gorillas have been considered the second-closest
living relatives of humans.