The primate cranial base: ontogeny, function and - Harvard University

124 YEARBOOK OF PHYSICAL ANTHROPOLOGY [Vol. 43, 2000
Fig. 3. Midsagittal view of nonhuman primate (A) human (B), showing different patterns of drift of
occipital, and position of foramen magnum, relative to overall cranial length in the Frankfurt horizontal.
FM, center of the foramen magnum; OP (opisthocranium) and PR (prosthion) are, respectively the most
posterior and anterior points on the skull in the Frankfurt horizontal. , depository surfaces;
resorptive surfaces.
growth during the neural growth period
(e.g., up to approximately 6 years in humans)
and some additional elongation occurring
through the adolescent growth
spurt (Ashton and Spence, 1958; Scott,
1958; Riolo et al., 1974; Sirianni and Swindler,
1979; Sirianni, 1985). The SOS contributes
to roughly 70% of posterior cranial
base elongation in macaques (Sirianni and
Van Ness, 1978). The rest of posterior basicranial
growth in nonhuman primates occurs
through posterior drift of the foramen
magnum, which has been shown by fluorochrome
dye labeling experiments to migrate
caudally in nonhuman primates through resorption
at its posterior end and deposition
at its anterior end (Michejda, 1971; Giles et
al., 1981). In contrast, the foramen magnum
remains in the center of the human skull
base, roughly halfway between the most anterior
and posterior points of the skull
(Lugoba and Wood, 1990). The posterior cranial
base in H. sapiens still elongates during
postnatal growth, but to a lesser degree
than in nonhuman primates.
Postnatal elongation in the anterior cranial
base is somewhat more complex because
of its multiple roles in neural and
facial growth. The anterior cranial base
(measured from sella to foramen caecum)
elongates in concert with the frontal lobes of
the brain, reaching approximately 95% of
its adult length by the end of the neural
growth period (e.g., 6 years in humans, 3
years in chimpanzees, and 1.2 years in macaques)
(Scott, 1958; Sirianni and Newell-
Morris, 1978; Sirianni and Van Ness, 1978;
Lieberman, 1998). Postnatal anterior cranial
base elongation can occur in the SES (in
the midline), through displacement in the
sphenoid-frontal suture, and through drift
of the anterior margin of the frontal bone. In
humans, however, the SES remains active
and unfused until 6–8 years after birth,
when the brain has completed most of its
growth, but the SES apparently fuses near
birth in nonhuman primates (Michejda and
Lamey, 1971). These differences in the timing
and sequence of synchondroseal activity
and fusion may be related to the different
relative contributions of the lesser wings of
the sphenoid and the frontal to the anterior
cranial floor in humans and nonhuman primates.
Although there is some intraspecific
variation, the lesser wing of the sphenoid in
humans tends to comprise approximately
one third of the cranial floor, extending all
the way to the cribriform plate; in nonhuman
primates, the cribriform usually lies
entirely within the ethmoid (Fig. 4), and the