Molera

A molera is a "soft spot" on the top of a Chihuahua's skull; it is the equivalent to the bregmatic or anterior fontanelle in human babies, but unlike most mammals, a Chihuahua's fontanelle persists into maturity. Historically it has been very common amongst Chihuahuas and was regarded as a mark of purity for this miniature dog breed. It is still mentioned in many Chihuahua breed standards; however, it is considered a fault in European countries because of concern that this might reflect underlying malformations such as hydrocephalus and ventriculomegaly, Chiari-like malformation and syringomyelia. Fontanelles are fibrous, membrane-covered gaps that lie between the skull bones and at the intersection of the cranial sutures. The cranial sutures are the junctions between cranial bones. The fontanelles serve as the major sites of bone expansion during post-natal skull growth which accommodates the enlarging brain. The Chihuahua likely has a molera because of neuroparenchymal disproportion. This is likely because there is premature closure of the skull base cranial sutures. To accommodate the developing brain there is increased growth of the skull bone in a parallel plane giving the dog a characterised domed or "apple-headed" appearance.

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