Cranial is not the bone itself. It is the adjective for things that belong to the bony box around your brain. Doctors say cranial nerve (a nerve that leaves the brain through holes in that bone), cranial cavity (the space inside it), cranial injury. It is a medical and scientific word; you will not hear it much in the street. If you mean the bone, say cranium or skull. If you mean 'of that bone,' say cranial.

顱的、頭顱的。cranial nerve 台灣醫學上多說「腦神經」，不是字面上的「顱神經」。