1) Absence of the skull 
Acrania is a rare congenital disorder that occurs in the human fetus in which the flat bones in the cranial vault are either completely or partially absent. The cerebral hemispheres develop completely but abnormally. The condition is frequently, though not always, associated with anencephaly. The fetus is said to suffer from acrania if it meets th...
• (n.) Partial or total absence of the skull. • (n.) The lowest group of Vertebrata, including the amphioxus, in which no skull exists.
(ә-kra´ne-ә) partial or complete absence of the cranium. adj., acra´nial., adj.
A·cra'ni·a noun [ New Latin , from Greek 
Type: Term Pronunciation: ă-krā′nē-ă Definitions: 1. Complete or partial absence of a cranium; associated with meroanencephaly (anencephaly).
acrania A partial or complete absence of the skull.