The osseous structure is peculiarly fitted, by its solidity and hardness, not only to give support to the soft parts, but also to furnish points of attachment to the muscles, by which the different movements are executed. This solid framework of the body is made up of a number of separate pieces, the aggregate of which has been termed " the skeleton" (sceletum, σχελλω, to dry.)
The vertebral column may be considered as the central or fundamental part of the whole, both because it exists in all animals which possess an internal osseous skeleton, and also because the different parts of the osseous system are either immediately or mediately connected with it as a common centre. Thus, on its superior extremity, or apex, it supports the skull; laterally it gives attachment to the ribs, which arch forwards, to form, with the sternum, a bony case for the lodgment of the organs of respiration and circulation, at the same time that they furnish, externally, points of support for the superior extremities: inferiorly the column is immovably connected with the pelvic bones, which are articulated with those of the lower extremity.
When proceeding with the description of the human body, it is usual to consider it as divisible into head, trunk, and extremities, which is sufficient for the purposes of a regional division; but the skeleton must be viewed in a different way, particularly if reference is made to its conformation in the various orders of animals — to its development — and to the subordination of its component parts. The spine being its essential constituent, all the others (the ribs and sternum, clavicle, scapula, and upper extremities, the pelvic bones and lower extremities,) rank as accessories. The sacrum and coccyx are obviously parts of the spine, so likewise are the cranial bones ; for though in outward appearance they differ so much in man and the higher animals from the bones of the spine which are placed beneath them, and with which they are articulated, they still are but modifications of similar organic elements — repetitions, in fact, of like parts, differently developed to suit the peculiar relations into which they enter, and the purposes which they are designed to serve.
The number of pieces which compose the osseous system varies in the different ages of life ; for some, which in the first instance are di- vided into two or more portions, become soldered together as the pro- cess of ossification goes on. But authors are far from being unanimous as to the number of bones which they recognise even in the adult. Do the sesamoid bones form parts of the skeleton, or are they mere accessory structures developed in tendons? Are the teeth, os hyoides, and ossicula auditus, to be enumerated as components or accessories? Monro and Soemmering reckon 260 bones; and Meckel, who takes the number at 253, includes the teeth, patellae, ossa sesamoidea, os hyoides as five pieces, sternum as three, coccyx as four, and the small bones of the ear. If, however, we omit those just named, as being either accessories or connected with special organs, the whole number of pieces found in the ordinary skeleton will be 197, as follow:
The spinal column, properly so called, consists of 24 vertebras, the sacrum and the coccyx - - - - - 26
The skull is made up of eight cranial bones, viz. the occipital, two parietal, two temporal, the frontal, the ethmoid and sphenoid: — and of fourteen facial, viz. two nasal, two lachrymal, two superior maxillary, two malar, two palatal, two turbinated, one vomer, and the inferior maxillary bone - - - - - 22
The ribs are 24 in number (twelve on each side), with the sternum - - - - - - - -25
In the skeleton we recognise two great cavities (which are again variously subdivided) ; one anterior and inferior, comprising the thorax and abdomen; the other posterior and superior, formed by the union of the vertebral canal with the cranial cavity.