cranial changes Flashcards
what is the main change in the skull from apes to hominins?
the main change was due to bipedalism which changed the foramen magnum
what is the foramen magnum
it is the hole in the base of the skull where the spinal cord passes
where is the foramen magnum located in apes?
in the back/ rear of the skull
where is the foramen magnum located in hominins?
underneath the base of the skull
why does the skull balance on top of the spinal column for hominins?
they require less muscular energy to support the skull over the centre of gravity.
why do apes require lots of energy to support the head?
they require large neck muscles which prevents the head from dropping forward. the strong neck muscles attach to a large nuchal crest on the skull
do humans have a nuchal crest?
no
why did the skull need to adapt to when the brain size increased?
the cranium showed greater roundness as there was an increase of the forehead as the cerebrum developed
why did prognathism of the jaw decrease?
the extent of protrusion of the jaw decreased and facial angle became flatter with an increased steepness in the angle of the forehead to accommodate a larger brain.
what is the brow ridge?
This is a bony ridge located above the eye sockets. Its purpose is to reinforce the weaker bones of the face (reduces vertical stress). In Apes they are much larger due to the tremendous strain put on the cranium by their temporal (jaw) muscles. Without this reinforcement the eye sockets would collapse. The brow ridge was one of the last traits to be lost in the path to modern humans
what is the saggital crest?
The Sagittal Crest is a ridge of bone running lengthwise along the midline of the top of the skull. The presence of this ridge of bone indicates that there are exceptionally strong jaw muscles. The sagittal crest serves primarily for attachment of the temporalis muscle, which is one of the main chewing muscles. It is absent or greatly reduced in most Hominins (with the notable exception of the Paranthropus genus).
why did chins appear in h.sapiens ?
for an increase in jaw stability
what is the zygomatic arch?
These are a bony arch just behind the cheeks. They provide a gap for the temporal muscles to pass through (see above). They are much larger in apes to accommodate much larger temporal muscles.
what is the nuchal crest?
This is the area where the neck muscles attach onto the back of the skull, to keep it balanced on the spinal column / looking forward.
