Final answer:
The lambdoid, sagittal, and coronal sutures of the skull begin to ossify and fuse later in life, a process that leads to the gradual disappearance of the suture lines. The exact timing can vary, but this is a normal part of aging.
Step-by-step explanation:
The sutures of the human skull, including the lambdoid suture, sagittal suture, coronal suture, and squamous suture, play critical roles in the development and growth of the skull. The sagittal, coronal, and lambdoid sutures do not fuse until later in life, a process of ossification that causes the suture line to gradually disappear. Newborns and infants have wide areas of connective tissue, known as fontanelles, where these sutures eventually form. These fontanelles allow for the flexibility and growth of an infant's skull. The fusion between the adjacent bones is a synostosis, and it typically occurs predictably as part of the aging process, although the precise timing can vary among individuals.