The head does not literally 'split' as some misinformaed owners may think. The shape or structure of the skull does not change at all, as Caryll has said this ' .
What does it mean when a dog's head splits?
in short no there heads do not split or crack it is simply a line that appears in the middle of the head as the dog matures in to adult hood the line which you see is caused by muscle growth in the dogs head which leaves this indent which to some may appear as if the dogs head has split.
What age do dogs heads split?
Sometime after they are around 6 months old, but usually older, a Staffy puppy's head will “split”. This process is called a lot of things, from spreading to splitting to cracking.