52 AFRICA
continues even more deeply and extensively on inter-
nal aspect of suture. Just above notch is a more
obliquely oriented, thinner accessory notch, which
also continues internally for some distance. Bone
above notches angles medially more sharply than does
the essentially vertical plane of squamosal.
Internally, petrosal broad and flat, with minor
oblique elevation over region of anteriorly oriented
superior semicircular canal. Beneath this area is a hori
zontal eminence incompletely closed off below (prob-
ably corresponds to inferior semicircular canal). No
superior petrosal sinus, but a sharp angulation in that
region between superior and medial surfaces of pet-
rosal. Area of subarcuate fossa closed over and slightly
depressed. Very large upper part of single sigmoid si-
nus preserved. Traces of posterior branch of middle
meningeal artery, which emerges from foramen (spin-
osum?) lying at juncture between squamosal and pet-
rosal portions of temporal (foramen not contained in
sphenoid). Area of jugular foramen broken, but its
location is indicated internally by sigmoid sinus.
Inferior portion of petrosal broken away, exposing
two (possibly three) air chambers separated by parallel
thin septa at right angles to long axis of petrosal. In
line with bony septum between the most lateral and
adjacent chambers is an elevation on the ectotympanic
tube that appears to be part of vaginal process. On in-
ternal side of this process, on axis of middle chamber,
is a relatively broad, shallow vertical depression. This
depression is in line with peak of vaginal process (pos-
sibly reflecting presence of styloid process). A major
opening lies medial to this depression (in line with
third air chamber and internal to medial portion of
vaginal process); it conducts to interior through a long,
bony tube that emerges through the superior surface of
the petrosal lateral and slightly anterior to the internal
auditory meatus. Homologies of this structure uncer-
tain. If it were a stylomastoid foramen, it would be
highly unusual in size and medial position relative
both to peak of vaginal process and to mastoid region
itself (in hominoids, stylomastoid foramen typically
lies lateral to peak of vaginal process and associated
styloid process). More likely, the canal represents an
extremely small conduit for the internal carotid artery
that has been displaced far from the jugular vein.
Internal orifice of canal oriented superoanteriorly.REFERENCESDeino, A. and A. Hill. 2002. “Ar/”Ar dating of Chemeron
Formation strata encompassing the site of hominid KNM-
BC 1,Tugen Hills, Kenya.J. Hum. Evol. 42: 141-151.
Hill, A. et al. 1992. Earliest Homo. Nature 355: 719-722.
Martyn, J. 1967. Pleistocene deposits and new fossil locali-
ties in Kenya. Nature 215: 476-480.
Sherwood, R. et al. 2002. The taxonomic status of the
Chemeron temporal (KNM-BC 1). J. Hum. Ewol. 42:
153-184.Repository
National Museums of Kenya, P. 0. Box 40658, Nairobi,
Kenya.