_24′_, Lingual surface of crown; _24″_, masticatory surface. The crown
is clearly marked off from the rounded root by a neck. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The =deciduous incisors= differ from the permanent set chiefly in being
much smaller. The crowns are narrower and diverge more.
The =canines= are absent (unless the fourth incisors be considered to
represent them).
[Illustration:
FIG. 286.—SKULL OF OX TWO YEARS OF AGE, SCULPTURED TO SHOW THE
EMBEDDED PARTS OF THE TEETH.
_11–4_, Permanent incisor teeth, the third and fourth not erupted;
_Di.3, 4_, third and fourth deciduous incisors; _P1–3_, upper
permanent premolars, only first erupted; _Dp.2, 3_, deciduous
premolars; _M1–3_, molars.
]
The =cheek teeth= (Fig. 286) resemble those of the horse in number and
general arrangement. They are, however, smaller, and also differ in the
fact that they progressively increase in size from before backward. This
feature is so marked that the first tooth is quite small, and the space
occupied by the first three (_i. e._, the premolars) is only about
one-half of that required for the posterior three (_i. e._, the true
molars). The enamel folds stand out even more prominently in relief on
the masticatory surface than in the horse. The occurrence of wolf-teeth
is rare.
The formula of the deciduous teeth is:
( 0 0 3 )
2 ( Di — Dc — Dp — ) = 20
( 4 0 3 )
TABLE OF AVERAGE PERIODS OF ERUPTION OF THE TEETH
IN THE OX
│
TEETH │ ERUPTION
│
_A._ _Temporary:_ │
First incisor (Di 1) │Birth to 3 weeks.
Second incisor (Di 2) │ „
Third incisor (Di 3) │ „
Fourth incisor (Di 4) │ „
──────────────────────────────┼──────────────────
First cheek tooth (Dp 1) │Birth to 3 weeks.
──────────────────────────────┼──────────────────
Second cheek tooth (Dp 2)│Birth to few days.
Third cheek tooth (Dp 3) │ „
──────────────────────────────┼──────────────────
│
_B._ _Permanent:_ │
First incisor (I1) │1½ to 2 years.
Second incisor (I2) │2 to 2½ years.
Third incisor (I3) │3 years.
Fourth incisor (I4) │3½ to 4 years.
First cheek tooth (P1) │2 to 2½ years.
Second cheek tooth (P2) │1½ to 2½ years.
Third cheek tooth (P3) │2½ to 3 years.
Fourth cheek tooth (M1) │5 to 6 months.
Fifth cheek tooth (M2) │1 to 1½ years.
Sixth cheek tooth (M3). │2 to 2½ years.
The eruption of the permanent teeth is subject to great variation. The
above figures are the average of observations of improved breeds under
favorable conditions.