Final answer:
The soft spots in a fetal skull, responsible for flexibility during birth and allowing skull growth postpartum, are called fontanelles. They are areas of fibrous connective tissue that help in shaping the head during birth and provide space for the brain to grow.
Step-by-step explanation:
The "soft spots" in a fetal skull are composed of fibrous connective tissue and are known as fontanelles. Fontanelles serve as broad areas that form fibrous joints between the bones of the skull in a newborn. They are crucial during childbirth and for the early growth of the infant's brain.
The largest fontanelles on the fetal skull are the anterior (frontal) fontanelle, located at the front top part of the skull, and the posterior (occipital) fontanelle, situated at the back of the head. These areas permit the skull bones to move and overlap slightly during birth, aiding the baby's head to pass through the birth canal. As the child grows, these fontanelles also accommodate the expanding brain before they eventually close as the connective tissue ossifies, reducing to a narrow layer called sutures.
The process of ossification ultimately leads to the fusion of bones at the sutures, a process called synostosis. Examples include the fusion of frontal and maxillary bones into a single bone and the late-life fusion of sagittal, coronal, and lambdoid sutures.