the ovary and the uterus.
2. The ovary.
3. The body of the uterus.
4. The uterine canal.
5. The urinary bladder represented as empty.
6. The entrance of the ureter.
7. The pubic bone.
8. The urethra.
9. The vagina.
10. The common external opening or vulva.
11. The rectum and anus.]

[Illustration: FIG. 10.--THE LUNGS AND WINDPIPE. Parts of the lungs
have been removed to show the branching of the air tubes or bronchi
which pass into them. All the tubes and the surfaces of the lungs
communicate with the inner surface of the body through the larynx.]

The nervous system (Fig. 8) represents one of the most important of
the enclosed organs. It serves an important function, not only in
regulating and coördinating all functions, but by means of the special
senses which are a part of it, the relations of the organism as a
whole with the environment are adjusted. It consists of a large
central mass, the brain and spinal cord, which is formed in the embryo
by an infolding of the external surface, much in the same way that a
gland is formed; but the connection with the surface is lost in
further development and it becomes completely enclosed. Connected with
the central nervous mass, forming really a part of it and developing
from it, are the nerves, which appear as white fibrous cords and after
dividing and subdividing, are as extremely fine microscopic filaments
distributed to all parts of the body. By means of the nerves all