Question

Which of the following examples represents a bony joint, or synostosis?

A. Cranial sutures form as a synostosis when the baby's fontanels close.
B. A synostosis develops at the ends of the tibia and fibula to help hold them together.
C. When the two maxillary bones unite to form the anterior two thirds of the hard palate, a synostosis develops.
D. A synostosis occurs in the jaw when a child's second set, or permanent teeth come in.
E. An infant is born with right and left mandibular bones, but they soon fuse into a single bone.

Answer 1

The correct example of a bony joint, or synostosis, is when the cranial sutures of a baby's skull close as the fontanels ossify and fuse the bones together.

Step-by-step explanation:

The correct answer to which example represents a bony joint, or synostosis, is: A. Cranial sutures form as a synostosis when the baby's fontanels close.

A synostosis is a type of joint where the bones are fused completely by bone tissue, resulting in an immobile joint. During the development of a child, the fontanels—which are broad areas of connective tissue—provide flexibility and space for the growth of the skull and brain. As the child grows, these fontanels begin to narrow, and the connective tissue ossifies into bone, turning the fibrous joints into bony joints or synostoses. This process is evident when the cranial sutures in a baby's skull close as the fontanels become ossified and the suture lines eventually disappear, leaving a continuous bony structure.

This is different from other fibrous joints, such as syndesmoses (like the tibia and fibula connection) which are bound by connective tissues but allow for some movement, or gomphoses (like teeth in their sockets), which are peg-like structures held in place by the periodontal ligament. Therefore, option A is a direct example of synostosis where the fontanels close to form the adult skull, illustrating the transition from a fibrous joint to a bony joint.