IN HERBIVOROUS ANIMALS. 
217 
passes that of the lower jaw by some lines. Sometimes, also, the 
lower row passes the upper by the same distance at the temporo- 
maxillary region. 
From this disposition may be presented the deformity which 
will obtain with the increase of age on account of the want of 
friction upon that part of the dental table subtracted from wear. 
The phenomenon which manifests itself under these circumstances 
is identical with that which is so often at the corners of the supe- 
rior jaw, from the age of seven to eight years, that is to say, that 
the part of the table of the first molar teeth, which is submitted to 
the friction, is dug into, whilst the anterior part suffers an indis- 
continued elongation from the want of use. So long as this elon- 
gation does not acquire the height of the inferior first molar, the 
mastication suffers no obstacle ; but if once the exuberance of 
the superior molar becomes such that it can attack the gum in 
front of the inferior and the sharp border of the maxilla, it digs 
into the substance of their tissues, and thus produces intolerable 
pain. 
The same effects manifest themselves under the influence of 
similar causes at the posterior part of the buccal cavity, when the 
difference in the length of the dental rows is in favour of the in- 
ferior arcades. 
D. When one tooth is entirely or in part deficient in one of the 
jaws, either in consequence of fracture, of evulsion, of caries, or 
of an arrestation in its development, the correspondent tooth in 
the antagonist jaw acquires an elongation exactly proportioned to 
the vacuum that it encounters. This void not being complete, as 
in the case of partial fracture, of caries which has destroyed only 
one portion of the organ, or of arrestation of development, the 
exuberant tooth is arrested before the obstacle which it encounters, 
and wears against it ; at the same time that it also wears the 
partially deficient tooth in the approaching of the jaws ; but as the 
healthy tooth — if we may use such an expression — has an advantage 
over the other on account of the greater length that it has acquired, 
and preserving this length in virtue of its growth, which nothing 
arrests, it finishes by shaving, or rather grinding, down to the 
alveole the stump against which it rubs, and often even then it de- 
termines inflammation and tumefaction of the edges of the bone 
which it attacks. 
When there exists a complete void in one of the dental ranks, 
as this void is never obliterated by the approach of the neighbour- 
ing teeth, the tooth which is opposed to it always growing, at 
length finishes by filling it, and then, having once acquired the 
dimensions sufficiently considerable, it imprints itself upon and 
destroys the bone by its friction. 
