The Axial Skeleton
Within the framework of the axial skeleton lie all the most vital organs of the body. People have gone on living with the loss of a hand or a leg – indeed, with the loss of any or all of their limbs. But nobody can live without a brain, a heart, a liver, lungs, or kidneys – all of which are carried within the framework of the axial skeleton.
The bones of the skull have as their most important function the protection of the brain and sense organs. There are also, of course, the jawbones that support the teeth and gums and which enable us to bite and chew our food.
Most of the skull appears to consist of a single bone – a hard, unbroken dome. Actually, the brain cage or cranium consists of eight individual platelike bones which have fused together in the process of growth. At birth, these bones are separated, causing the soft spots or fontanelles we can readily feel on a baby’s brain enlarges, the bones grow along along their edges to fill in the fontanelles, finally knitting together in what are called suture lines, somewhat resembling inexpertly mended clothes seams. Along the suture lines, the skull bones continue to grow until the individual’s mature skull size is reached.
The hardest substance in the human body is the enamel that covers the exposed surface of a tooth. Below the gum, the tooth’s outside surface is composed of somewhat softer cementum is a bonelike substance called dentin, which covers the soft interior of the tooth called pulp. Pulp is serviced by blood vessels and nerves through the root or roots of the tooth. The passageway of nerves and blood vessels that lead up through the tooth from the gum sockets is called root canal. Tooth and gum are stuck to each other by a tough, adhesive tissue called periodontal (or peridental – “surrounding the tooth”) membrane.