Final answer:
Fontanelles are vital for the flexibility of the fetal skull during childbirth and for the postnatal growth of the skull and brain. They allow the skull bones to move and change shape as the infant's head passes through the birth canal and enable the skull to expand as the brain grows.
Step-by-step explanation:
Function of Fontanelles in the Fetal Skull
The fontanelles are expanded areas of fibrous connective tissue found in the fetal and newborn skull. They play a critical role in both childbirth and infant development. During childbirth, the flexibility provided by the fontanelles allows the bony plates of the skull to move and change shape, enabling the child's head to pass more easily through the birth canal. This flexibility can sometimes cause a newborn's head to appear temporarily misshapen.
After birth, the fontanelles are crucial for the continued growth and expansion of the skull as the brain enlarges. The largest fontanelles, the anterior and posterior, allow for the rapid development of the infant's skull and brain. The fontanelles gradually decrease in size and ossify as the skull bones grow, transforming into narrower fibrous joints called sutures. By about two years of age, fontanelles are typically closed as part of normal development.
It is important to note that the cranial bones arise from mesenchyme during embryonic development, through a process known as intramembranous ossification. While the bones grow, the large areas of connective tissue between them – the fontanelles – remain, eventually becoming the sutures that continue to allow for growth during childhood.