You folks are making it too difficult.
The fetal skull is comprised of many bones of two basic developmental
types: membraneous and endochondral. These bones form "plates" separated
by soft connective tissues that grow as the brain grows but eventually fuse
when the brain reaches "adult" size. For more details read on.
Much of the base of the vault is endochondral in origin and is formed as
bone cells invade and replace the cartilage template. Examples include the
occipital and sphenoid bones. These are complex structures. The fetal
occipital consists of pairs of basioccipital, exoccipital,
supraoccipital...yada, yada that eventual fuse into one nifty bone. The
holes (foramen and fissures) form as blood vessels and nerves grow and
there are complex chemical signallings involved.
The membraneous bone form as bone cells invade and ossify membranes. At
birth the paired frontal, parietal, and temporal bones are separated by
considerable distances and can be manipulated. As the brain increases in
size the membranes increase in surface area and only by the mid to late
teens do the bones fully fuse.
rlh
At 5:56 AM +0000 5/30/99, Ian at dragoncon.net.deletethis wrote:
>On 28 May 1999 12:56:40 GMT, didier at Glue.umd.edu (Didier A. Depireux)
>wrote:
>>Ian at dragoncon.netdeletethis wrote:
>>: On 27 May 1999 15:17:23 GMT, didier at Glue.umd.edu (Didier A. Depireux)
>If I remember correctly the skull is not only pliant at a young age,
>but there is a gap at the top of the skull. This is only slowly filled
>in over time, I don't know how quickly. But possibly this does allow
>the brain to have some determinism, some room to manoeuver.
>>However, I suspect that both the skull and brain size are
>predetermined by genetics to be a neat fit. As you know the brain
>doesn't completely fill the cranial cavity, and even the surrounding
>fluid is at relatively low pressure. I would have thought that if one
>or the other was the restrictive factor then the space would be
>completely filled.
>>Ian
Richard Hall, Associate Professor of
Comparative Animal Physiology
Division of Sciences and Mathematics
University of the Virgin Islands
St. Thomas, USVI 00802
340-693-1386
rhall at uvi.edu
