http://www.anatomics.com/products/cranial-implants/acrylic/
http://www.girlgeniusonline.com/comic.php?date=20071005
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1. To allow liquid/air-bubbles past for easier installation, to be covered-over by another layer later.
2. For attaching the Meninges?
3. Screw holes?
http://www.anatomics.com/products/cranial-implants/acrylic/