Head. (Showing the dorsal and the ventral tubes.)

A, the cranial cavity;
B, the cavity of the nose;
C, the mouth;
D, the alimentary canal represented as a simple straight tube;
E, the sympathetic nervous system;
F, heart;
G, diaphragm;
H, stomach;
K, end of spinal portion of cerebro-spinal nervous system.
]

We may say, then, that the body consists of two tubes or cavities,
separated by a bony wall, the dorsal or nervous tube, so called
because it contains the central parts of the nervous system; and the
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.