fibrous tissue, the skin, tendons, and ligaments.] so strong that the
bones are sometimes broken without injuring the fastenings.

II. CLASSIFICATION OF THE BONES.

For convenience, the bones of the skeleton are considered in three
divisions: the _head_, the _trunk_, and the _limbs_.

1. THE HEAD.

THE BONES OF THE SKULL AND THE FACE form a cavity for the protection of
the brain and the four organs of sense, viz.: sight, smell, taste, and
hearing. All these bones are immovable except the lower jaw, which is
hinged [Footnote: A ring of cartilage is inserted in its joints, something
after the manner of a washer in machinery. This follows the movements of
the jaw, and admits of freer motion, while it guards against dislocation.]
at the back so as to allow for the opening and shutting of the mouth.

THE SKULL is composed, in general, of two compact plates, with a spongy
layer between. These are in several pieces, the outer ones being joined by
notched edges, sutures (su'tyurs,), in the way carpenters term
dovetailing. (See Fig. 4.)

FIG. 4.

[Illustration: _The Skull._--1. _frontal bone;_ 2, _parietal bone;_
3, _temporal bone;_ 4, _the sphenoid bone;_ 5, _ethmoid bone;_ 6,
_superior maxillary (upper jaw) bone;_ 7, _malar bone;_ 8, _lachrymal
bone;_ 9, _nasal bone;_ 10, _inferior maxillary (lower jaw) bone._]