[1] Fontanelles allow for stretching and deformation of the neurocranium both during birth and later as the brain expands faster than the surrounding bone can grow.

This pulsating action is how the soft spot got its name – fontanelle is borrowed from the old French word fontenele, which is a diminutive of fontaine, meaning "spring".

In fact, although they may colloquially be called "soft-spots", the membrane covering the fontanelles is extremely tough and difficult to penetrate.

Increased cranial pressure in infants may cause the fontanelles to bulge or the head to begin to enlarge abnormally.

[2] One of the more serious problems that can affect canines is known as an "open fontanelle", which occurs when the skull bones at the top of the head fail to close.

In many young dogs the skull bones are not fused at birth, but instead will close slowly over a three- to six-month period.

In these cases, however, the dog's owners need to be very careful, since any injury or bumps to the animal's head could cause significant brain damage, as well as conditions like epilepsy.

The American Kennel Club breed standard states that the skull of the Chihuahua should be domed, with or without the molera being present.