e
visceral or ventral tube, as it contains the viscera, or general
organs of the body, as the alimentary canal, the heart, the lungs, the
sympathetic nervous system, and other organs.

The more detailed study of the body may now be begun by a description of
the skeleton or framework which supports the soft parts.

Experiments.

For general directions and explanations and also detailed suggestions for
performing experiments, see Chapter XV.

Experiment 1. _To examine squamous epithelium._ With an ivory
paper-knife scrape the back of the tongue or the inside of the lips or
cheek; place the substance thus obtained upon a glass slide; cover it
with a thin cover-glass, and if necessary add a drop of water. Examine
with the microscope, and the irregularly formed epithelial cells will be
seen.

Experiment 2. _To examine ciliated epithelium._ Open a frog's
mouth, and with the back of a knife blade gently scrape a little of the
membrane from the roof of the mouth. Transfer to a glass slide, add a
drop of salt solution, and place over it a cover-glass with a hair
underneath to prevent pressure upon the cells. Examine with a microscope
under a high power. The cilia move very rapidly when quite fresh, and
are therefore not easily seen.

For additional experiments which pertain to the microscopic examination of
the elementary tissues and to other points in practical histology, see
Chapter XV.

[NOTE. Inasmuch as most of the experimental work of this chapter
depends upon the use of the microscope and also necessarily assumes a
knowledge of facts which are discussed later, it would be well to
postpone experiments in histology until they can be more
satisfactorily handled in connection with kindred topics as they are
met with in the succeeding chapters.]

Chapter II.

The Bones.

27. The Skeleton. Most animals have some kind of framework to support
and protect the soft and fleshy parts of their bodies. This framework
consists chiefly of a large number of bones, and is called the
skeleton. It is like the keel and ribs of a vessel or the frame of a
house, the foundation upon which the bodies are securely built.

There are in the adult human body 200 distinct bones, of many sizes and
shapes. This number does not, however, include several small bones found
in the tendons of muscles and in the ear. The teeth are not usually
reckoned as separate bones, being a p