The Washington times. [volume] (Washington [D.C.]) 1902-1939, 1928-02-16
Mysteries of Life
Expeunded By
Philosopher
By George A. Dorsey,
Phi. D., LII. d.
CHAPTER ".

TH e function of the renal
: organs or kidneys is to pre-
serve certain constancy in the
blood stream and to eliminate
certain noxious elements from
the body. TO perform this double
function. three types of kidneys
have been evolved. The develop
Ing human embryo, as well as
snbroyos Of other mammals. re-
l1earses this story. all three types
appearing in prenatal life.
4 The alimentary canal appears
first as closed tube within the
body. ftsopens later at each end,
the upper opening becoming part
OF the mouth cavity. Below this
opening foEaf crevices appear which
represent the internal arrange
merlt Of the fish.like-gill-clefts.
Below these crevices a single sac
like structure appears; this di'
vides, and by further subdivisions
becomes the right and left lung.
From the region of the crevlces
oJitgrowths of the alimentary canal
develop into thyroid, epithyroIu'
and thymus glands. From the
extreme upper end of the en-
bryonic canal develops a portion
Of another important gland, the
fituitary., The stomach at first
is merely an enlargement of the
canal Just below the stomach
two outgroWths of the canal de-
velop into the important glands
of digestion, pancreas and liver.
without further details OF fetal
development it will be worth while
to recall certain variations in the
systems Of digestion, respiration
and circulation. which are signlfl-
cant in light of our animal ances-
tors.
Our dentition is as well adapted
for spinach as for beefsteak,, spe-
cializeds for neither. Our front, or
incisor, teeth are only fair cutters:
our bicuspids, or premolars,, are
not strong enough to crunch bones;
our grinders, or nolars,. are not
very good rniIlstones. Our snarl-
ing muscle discloses no such ca
mines as the nesh.eaters stab and
tear their prey with. Our teeth
are on the go. A perfect "civil-
: Jed set is rare. In hundreds of
skulls collected in New Guinea
there was not one imperfect set
all strong sound, beautifully
aligned.
Man. apes, and old World mon
KEYS have 80 teeth, eight on eight
side of each jaw: two fncisors,
one canine; two bicuspids, three
molars. Mans mammalian ances-
tors had "A teeth; three incisors,
one canine, three bicusipids, four
nIOfars
Variation rules. Often there is
ONLY enc incisor, an inherited con-
dition, there may be three incis-
ors. The canine is rarely absent,
but 1T may be a tiny stump; more
often it is .over-deyeloped. disfig-
uring the face. A third bicuspid
In not rare. A fourth molar is
more rare, but frequent enough
to be suggestive. The third molar.
or wisdom tooth, Is d.. bad lot
among 4eI1ites-jaws too short; it
comes in at any angle. varies in
It's cuspss often is a mere stump,
often never, erupts at all.
Most fishes have teeth in the
roof OF the mouth as well as in
the Jaws proper. They do not oc-
eur in sets but are endlessly
shed and reproduced. In the fish
embryo the dental germs appear
before the jawbones; in the human
ennbryo also. In the infant's
mouth Is a ridge with from five
+ Eo seven pairs of cross ridges:
they are even more pronounced in
the fetus. They disappear with
age Apes have ten pairs of these