The morning call. [volume] (San Francisco [Calif.]) 1878-1895, 1895-01-13

which Ii did In very short time. it re-
NAMED permanently in that form during
the animals life. There was a marked
difference, too, between the different
molars. just as there is to-day in man and
the other mammals. Now, however
these have disappeared, the pre-molars
and the true molars being all alike in
the shape and structure of their grinding
surface. Then, ia the prehistoric horse
the whole exposed surface Of the unworn
tooth was covered with enamel. Il had
two nearly transverse. curved ridges, with
shallow valleys between. When the ridges
became worn down the dentine of the in-
terror was exposed and the process of
decay began. Gradually. however, the
valleys between the ridges became filed
up. as they are 10 the modern horse, with
hard substance called cementum; the
crowns of the teeth became longer, the
ridges more elevated and intricately
and very sharp grinding surface. Within
this the enameled surface Is very curiously
lnteTfolded, the folds reaching ia some
places clear to the base of the
crown, while the interstices are filed
and large portion of the surface
covered with the cementum. This gives
very efficacious and durable grinding sur
taee, but even this would not be sufficient
to last out horses lifetime in masticating
the dry, hard food upon which he does his
work for man, and so still another curious
change has taken place. the crown has
continues to lengthen until il is many
times longer than in the primitive horse.
and its form is what is called hypsodont.
The neck of the tooth has disappeared,
and instead Of a root forming the crown
continued down into the socket for con-
siderable distance. The tooth continues
growing until the horse has reached quite
an advanced age, and as the upper sur
face wears away the crown is pushed up,
so that fresh grinding surface is con-
stantly exposed.
This is condition that is still In pro-
cess of evolution. The teeth of the horse
do not grow during his entire lifetime, as
do those OF the rodents, for instance, but
after length is attained, which, under
ordinary circumstances would prove suffi-
eient for the lifetime of the animal, the
crown stops growing. neck is formed,
roots strike down and the tooth is CON-
pIete.
The whole process OF the growth of the
horses teeth is an interesting study 10
evolution. It is quite evident that the
teeth of the ordinary mammal would he of
no use In masticating the comparatively
dry and hard food upon which the horse
subsists. They would be worn out before
the animal was old enough to be of
any use to man. On the other hand.
such teeth would have been more than
useless TO the primitive horse. Even as
1t Is to-day. the renewing process some
times goes on too rapidly for the creatures
comfort. and the teeth grow so long as 10
Interfere with the processes Of mastication.
II then becomes necessary to file them
down. In fact, veterinary dentistry has
grown TO be very important branch OF
horse lore, of late years. The artificial
lie which the horse leads causes him TO be
subject TO almost as many ailments and
diseomforts as is man himself. His teeth
require pulling. filing, sometimes, even,
they are filled. and youngsters on large
breeding farm often become very doeile
under the manipulation of the dentist.
have seen colt open his mouth and stand,
scarcely winciDg, with the stoiclsm of an
Indian, while the doctor pulled a back
molar, big as walnut, from his aching jaw.
MISS RUSSELL