Answer
The number of usually assigned the adult vertebral column is 206. However this number may vary.-- some bones ar missing in some individuals.
At birth the infant usually has 270 bones. But later in development and maturation some bones fuse to form a single structure. For example in the infant the ilium, ischium and pubis are three distinct bones. Nevertheless, by mid adolescence these three bones will have fused to form a single coxal, or hip bone on each side. Similarly , in infants there are distinct right and left mandibular processes separated by fibro- cartilage. By but age 2 years, the right and left process fuse, and the right and left mandibles become one bone. The intervening cartilaginous line between the two halves of the bone can still be traced in adults; however, this is not considered to be a real symphysis
Work Step by Step
Additional bones can also form de novo after birth. Two examples of this kind of bone are sesamoid bones, and wormian (sutural bones).
The patella is the largest sesamoid bone. Babies are not born with bony kneecaps. They are patches of soft cartilage in the tendon of the quadriceps femoris. muscle of the thigh. These patches of grow, and by age 5 years they join to form a soft knee cap. Growth and ossification goes on into adolescence and beyond. It is believed that stress exerted by the pull of the muscle on the quadriceps tendon promotes the development off the patella. Smaller sesamoid also occur in the hand at several locations; for instance adjoining the metacarpo-phalangeal joints of the middle and ring finger i.e. digits III and IV.
So-called Wormian or sutural bones develop in some suture joints; for example Wormian bobes are often found in the interparietal suture.
