The bones contain more earthy matter in their composition than any other part of the human body, being firm, hard, and of a lime color. They compose the skeleton or frame work, and, when united by natural ligaments, form what is known as the _natural_ skeleton; when they are wired together, they are called an _artificial_ skeleton. The number of bones in the human body is variously estimated; for those regarded as single by some anatomists are considered by others to consist of several distinct pieces. There are two hundred distinct bones in the human skeleton besides the teeth. These may be divided into those of the Head, Trunk, Upper Extremities, and Lower Extremities. [Illustration: Fig. 10. The bones of the skull separated. _1_. Frontal, only half is seen. _2_. Parietal. _3_. Occipital, only half is seen. _4_. Temporal. _5_. Nasal. _6_. Malar. _7_. Superior maxillary (upper jaw). _8_. Lachrymal. _9_. Inferior maxillary (lower jaw). Between _4_ and _6_ a part of the sphenoid or wedge-shaped bone, is seen. Another bone assisting to form the skull, but not here seen, is called the _ethmoid_ (sieve-like, from being full of holes), and is situated between the sockets of the eyes, forming the roof of the nose.] THE BONES OF THE HEAD are classed as follows: eight belonging to the Cranium, and fourteen to the Face. The bones of the Cranium are the _occipital_, two _parietal_, two _temporal, frontal, sphenoid_, and _ethmoid_. Those composing the face are, the two _nasal_, two _superior maxillary,_ two _lachrymal_, two _malar_ two _palate_, two _inferior turbinated, vomer_, and _inferior maxillary_. The cranial bones are composed of two dense plates, between which there is, in most places a cancellated or cellular tissue. The external plate is fibrous, the internal, compact and vitreous. The skull is nearly oval in form, convex externally, the bone being much thicker at the base than elsewhere, and it is, in every respect admirably adapted to resist any injury to which it may be exposed, thus affording ample protection to the brain substance which it envelops. The internal surface of the cranium presents eminences and depressions for lodging the convolutions of the brain, and numerous furrows for the ramifications of the blood-vessels. The bones of the cranium are united to one another by ragged edges called _sutures_, which are quite distinct in the child but which in old age are nearly effaced. Some authorities suppose that by this arrangement the cranium is less liable to be fractured by blows; others think that the sutures allow the growth of these bones, which takes place by a gradual osseous enlargement at the margins. The bones of the _Face_ are joined at the lower part and in front of the cranium, and serve for the attachment of powerful muscles which assist in the process of mastication. Although the soft parts of the face cover the bony structure, yet they do not conceal its principal features, or materially change its proportions.