Final answer:
The vertebral column starts with around 33 vertebrae in a baby and fuses down to 26 bones in an adult. Growth plates in the bones allow for length growth until they are replaced by bone by age 18 to 25.
Step-by-step explanation:
A baby back plate, also known as the vertebral column or spinal column, starts out with approximately 33 vertebrae in infancy. As we age, these vertebrae undergo a fusion process. By adulthood, the vertebral column comprises 26 bones: the 24 vertebrae, the sacrum (composed of 5 vertebrae fused into one), and the coccyx (typically 3-4 vertebrae fused into one).
In addition to the structural changes in the vertebrae, as babies and children grow, they have areas called growth plates in their bones. These cartilaginous zones allow for the elongation of bones throughout childhood and adolescence. Once a person reaches the age of about 18 to 25, the cartilage in the growth plates is completely replaced by bone, ending the bone growth in length.