The molera, or fontanel, is a “soft area” on the top of the Chihuahua’s skull. It is analogous to the bregmatic or anterior fontanelle in newborn humans, but unlike most mammals, the fontanelle of the Chihuahua survives into adulthood. It was once thought to be a sign of purity for the Chihuahua breed and was highly popular among them.

 

 

Fontanelles are fibrous, membrane-covered spaces at the junction of the cranial sutures and between the skull’s bones. The intersections of the cranium (or skull) bones are known as the cranial sutures. It is still mentioned in many Chihuahua breed standards; however, in European nations, it is regarded as a defect due to worries that it may be a sign of underlying defects such as hydrocephalus, ventriculomegaly, Chiari-like malformation, and syringomyelia.

The principal areas of bone growth during post-natal skull growth, which accommodates the growing brain, occur at the fontanelles. Due to a relatively large brain for the skull, the Chihuahua most likely has a molera. This is probably due to the cranial sutures at the base of the head being prematurely closed (brachycephaly due to craniosynostosis). The skull bone grows more rapidly on a parallel plane to support the growing brain, giving the dog its distinctive domed or “apple-headed” appearance.