The provided source material does not contain information regarding a city named Fontanelle in Italy. Instead, it describes a fontanelle as an anatomical feature of the human infant skull.
A fontanelle consists of soft membranous gaps, known as sutures, located between the cranial bones of a fetus or infant. These features allow for the stretching and deformation of the neurocranium during birth and facilitate brain expansion as it grows faster than the surrounding bone. Premature complete ossification of these sutures is a condition referred to as craniosynostosis.