Complex sentence: The mortarboard may also have been influenced by practices in Islamic madrassas or other Islamic customs believed to be when one are graduating they wore a skull cap and a Koran placed on top of their head tighten to the skull cap.
Split into simpler sentences: The mortarboard may also have been influenced by practices in Islamic madrassas or other Islamic customs. It is believed that graduates wore a skull cap with a Koran placed on top of their head, tightened to the skull cap.