The adult human body contains 206 bones, but this number changes throughout life. Newborn infants have significantly more bones than adults. This difference in skeletal structure serves important biological purposes, facilitating both the birthing process and rapid early development.
The Infant Skeleton
An infant’s skeletal system differs from an adult’s in bone number and composition. Newborns typically have between 270 and 300 bones, nearly 100 more than the adult count of 206. This higher number is due to many smaller, separate bone segments and a greater proportion of cartilage.
Many infant “bones” are cartilage, a flexible connective tissue. This cartilage is softer and more pliable than mature bone, allowing for flexibility. The infant skull, for example, is not a single, fused structure but comprises several separate bony plates connected by fibrous fontanelles, or “soft spots.” These fontanelles and the cartilaginous nature of bones contribute to the higher count.
The Journey to Adulthood
The transition from an infant’s skeletal structure to an adult’s involves bone development and fusion. As a baby grows, initial cartilage is gradually replaced by bone through ossification. This hardening begins in the womb and continues throughout childhood and adolescence.
Beyond ossification, many smaller, separate bones present at birth begin to merge. This fusion occurs in parts of the body, including the skull, spine, and pelvis. For instance, multiple skull plates, initially separated by fontanelles, gradually grow together, with fontanelles closing to form strong, fused cranial bones. This ongoing process typically reduces the bone count to 206 by the late teens or early twenties.
Why the Difference Matters
The unique skeletal composition of infants offers significant biological advantages. A primary reason for the higher number of bones and flexible cartilaginous structures in newborns is to facilitate childbirth. Separate, unfused skull plates and fontanelles allow the infant’s head to compress and reshape as it passes through the narrow birth canal, reducing injury risk for both mother and baby.
This adaptable skeletal structure is essential for an infant’s rapid growth and development. The fontanelles and flexible sutures in the skull provide necessary space for the brain, which grows quickly during infancy, to expand without restriction. This flexibility also allows for the continued development of the entire skeletal system as the child grows, providing the necessary framework to support increasing body size and mobility.