Complex sentence: Once born (usually within a years time) the Foreman Ovale seals over and it is renamed as the "Fossa Ovalis", the Fossa Ovalis is seen as an embryonic remnant.
Split into simpler sentences: Once born (usually within a year's time) the Foreman Ovale seals over and it is renamed as the "Fossa Ovalis". The Fossa Ovalis is seen as an embryonic remnant.