Eustathius applies a series of formal manipulations to justify this derivational descriptive etymology by which the skull is the summit. Through shortening (κάρᾰνον) and syncope (κρανον) he obtains a *κράνον, from which he derives κρανἰον. The οὗ προϋπάρχειν means that κράνον comes first in the derivation chain, between κάρηνον and κρανἰον. Eustathius does not notice that in fact κρᾱνἰον has a long ᾱ, as do ὠλέκρανον and ἐπίκρανον, therefore the first step, shortening, cannot account for the forms unless a re-lengthening is assumed. But the etymology was designed at a time when phonemic vowel quantity was lost. On the other hand, κρᾰ́νος "helmet" has a short ᾰ