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