Molera

A molera is a "hole" in a Chihuahua's head; it is the same as a fontanelle in human babies. Historically, the Chihuahua as developed in Mexico and the United States has displayed a "hole in the head". In times past, this has been accepted as a mark of purity for this dog breed, and it is still mentioned in most Chihuahua breed standards the world over. The bones of the head in all foetuses are not firmly knitted together, but in most mammals, the different bones of the skull join with cartilaginous sutures as the animal matures. The Chihuahuas' moleras vary in size and shape, occurring on the top of the head where the parietal and frontal bones come together.