Although the brain, limbs, bones, digestive
tract and lungs have little function in utero,
they will be required in fully operational
form at birth. In anticipation of this, all key
organs are inititiated and developed in a
coordinated way but only so far as it will be
appropriate at birth. Thus the ruminant is
not born with a large functional rumen nor
the ram lamb with horns. The form of the
internalized offspring must also be compatible
with the birth process. It is therefore
inappropriate for fetuses to develop excessively
large heads and shoulders prior to
birth because of the complications that can
arise in expelling the offspring through the
birth canal.