a surface of wide extent, comprising in the male the urethra, a long
canal which opens into the bladder, and is continuous with ducts that
lead into the genital glands or testicles. The internal surface of the
bladder is extended by means of two long tubes, the ureters, into the
kidneys, and receives the fluid formed in these organs. In the female
(Fig 9) there is a shallow external orifice which is continued into
the bladder by a short canal, the urethra, the remaining urinary
surface being the same as in the male; the external opening also is
extended into the short, wide tube of the vagina, which is continuous
with the canal of the uterus. This canal is continued on both sides
into the Fallopian tubes or oviducts. There is thus in the female a
more complete separation of the urinary and the genital surfaces than
in the male. Practically all of the waste material of the body which
results from cell activity and is passed from the cells into the fluid
about them is brought by the blood to the kidneys, and removed by
these from the blood, leaving the body as urine.


[Illustration: FIG. 8.--A LONGITUDINAL SECTION THROUGH THE MIDDLE OF
THE BODY SHOWING THE EXTERNAL AND INTERNAL SURFACES AND THE ORGANS.

1. The skull.
2. The brain, showing the convolutions of the gray exterior in which
the nerve cells are most numerous.
3. The white matter in the interior of the brain formed of nerve
fibres which connect the various parts of this.
4. The small brain or cerebellum.
5. The interior of the nose. Notice the nearness of the upper part of
this cavity to the brain.
6. The hard or bony palate forming the roof of the mouth.