A molera's a "hole" in a Chihuahua's head; it's 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's still mentioned in most Chihuahua breed standards the world over. The bones of the head in all foetuses aren't firmly knitted together, but in most mammals, the different bones of the skull join with cartilaginous… (More on Molera)