PART II.

               Outlines of Anatomy and Physiology.

                                CHAPTER I.

                             THE SKELETON.

THE anatomy and physiology contained in this and the following
chapters is merely intended to convey a general knowledge of the
animal's structure, the position of the various organs and their
functions, sufficient for the reader unacquainted with these subjects
to recognize the structures probably affected in such injuries or
diseases as may come under his observation.

External form is dependent upon an internal basement structure.
This consists of a number of definitely but diversely shaped masses
of a hard substance called bone. This basement structure is known
as the skeleton. The bones entering into its formation are of
various forms and sizes, depending on the uses for which they are
intended. They are divided into four classes : long, short, flat and
irregular. The first named are situated in the limbs ; they have a
shaft and two extremities. Examples :—Arm bone (humerus), thigh
bone (femur). The scapula or shoulder blade, pelvis, and frontal
bones of the head are examples of flat bones. The bones of the
vertebral column are examples of the irregular type of bones, and
those of the knee and hock are short bones. Bone is a tough, hard,
elastic substance consisting of animal matter impregnated with
earthy salts. The earthy salts may be removed from the bone by
immersion in dilute hydrochloric acid ; the figure of the bone remains
unchanged, but instead of being hard, it will be found to resemble
cartilage or grizzle, and may be twisted in any direction. The
composition of bone is as follows :—

The ends of the bones are constructed in different ways to
permit of more or less motion. In some parts there is a ball and
socket arrangement ; in others, hinge-like joints, and so on.