顱骨 is read as ろこつ (rokotsu) and means skull.
ろこつ
rokotsu
ずこつ
skull
ほね
bone
てっこつ
steel frame
がいこつ
skeleton
broad
げんこつ
(clenched) fist
せぼね
spine
なんこつ
cartilage
いこつ
remains (of war dead)
じんこつ
human bones
はっこつ
white (bleached) bone
さんこつ
scattering of ashes (cremated remains)