Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29465/924/
TEETH. 
914 
ridge, and bounded by an internal belt, the 
cingulum of Illiger: this tooth has a similarly 
shaped, but relatively smaller, crown in Arc- 
tonyx.* The second premolar below (p. 2) 
is commonly the first, through the early loss 
of the minute one in front ; its fangs are 
usually connate, as in its homotype above. 
The third and fourth premolars slightly in¬ 
crease in size, have simple compressed conical 
crowns, and two fangs each. The first true 
molar below (»/. 1) now retains little of its 
sectorial character, the blade being represented 
only by the two anterior small, compressed 
pointed lobes; behind these, the crown ex¬ 
pands into an oval grinding surface, narrower 
in Arctonyx than in Meles, supporting three 
tubercles and a posterior tuberculate ridge : 
it has generally two principal roots and a 
small intermediate accessory fang, as in the 
otter. The second molar (m. 2), which ter¬ 
minates the series below, is of small size, and 
has a rounded flat crown, depressed in the 
centre, and with two small external tubercles; 
its two short fangs are connate. In the 
Labrador Badger, the last premolar has a 
larger relative size, the part corresponding 
with the blade of the sectorial, is sharper 
and more produced, and the internal tu¬ 
bercle has two lobes; the succeeding molar 
tooth is reduced in size, and its crown pre¬ 
sents a triangular form. The first true molar 
below has its sectorial lobes better developed : 
these differences give the North American 
badgers a more carnivorous character than is 
manifested by the Indian or European species. 
Sub-Ursidœ.—In other allied genera, which, 
like the badgers, have been grouped, on ac¬ 
count of the plantigrade structure of their 
feet, with the bears, a progressive approxi¬ 
mation is made to the type of the dentition of 
the Ursine species. The first true molar 
below soon loses all its sectorial modification, 
and acquires its true tubercular character : 
and the last premolar above becomes more 
directly and completely opposed to its homo¬ 
type in the lower jaw. The Racoon ( Procyon f ) 
and the Coati (Nasua) present good examples 
of these transitional modifications ; they have 
the complete number of premolar teeth, the 
3_3 j_1 4,_4 
dental formula being, i. c. ^p. ^ 
2_2 
vi. ~^ : = 40. The development of the in- 
ner part of the crown of the last upper pre¬ 
molar, which constitutes the tubercie of the 
sectorial tooth, now produces two tubercles on 
a level with the outer ones which represent the 
blade; and the opposite premolar below {p. 4), 
which is the true homotype of the modified 
sectorial above, begins to acquire a marked 
increase of breadth and accessory basal tu¬ 
bercles. All the lower premolars, as well as 
the true molars, have two fangs; the three first 
premolars above have two fangs, the fourth 
has three, like the two true molars above. 
The dental formula of the Indian Bentu- 
* See Odontography, pi. 128,fig. 13, m. 1. 
f lb. pi. 129,/^. 7. t lb. pigs. 8—13. 
rong (Arcticlis) and Kinkajou ('Cercolcptes) is 
. 3—3 
3—3’ 
1—I 
=!’*• 
3—3 
3—3 
, m. r 
2—2 
'■ 2—2 
: = 36. 
Phocidœ. — We have seen a tendency to 
deviate from the ferine number of the incisors 
in the most aquatic and piscivorous of the 
Musteline quadrupeds, viz. the sea-otter 
(Enhydra), in which species the two middle 
incisors of the lower jaw are not developed in 
the permanent dentition. In the family of 
true seals, the incisive formula is further re¬ 
duced, in some species even to zero in the 
3_3 
lower jaw, and it never exceeds -—-. All 
the Phocidœ possess powerful canines ; only in 
the aberrant walrus ( Tnchechus) are they absent 
in the lower jaw, but this is compensated by the 
singular excess of development which they 
manifest in the upper jaw. In the pinnigrade, 
as in the plantigrade, family of Carnivores we 
find the teeth which correspond to true mo¬ 
lars more numerous than in the digitigrade 
species, and even occasionally rising to the 
typical number, three on each side ; but this, 
in the seals, is manifested in the upper and 
not, as in the bears, in the lower jaw. The 
entire molar series usually includes five, 
rarely six teeth on each s:de of the upper 
jaw, and five on each side of the lower jaw, 
with crowns, which vary little in size or form 
in the same individual ; they are supported in 
some genera, as the Eared Seals (Otariœ) 
and Elephant Seals (Cystophora*), by a single 
fang ; in other genera f by two fangs, which 
are usually connate in the first or second 
teeth ; the fang or fangs of both incisors, 
canines and molars, are always remarkable 
for their thickness, which commonly sur¬ 
passes the longest diameter of the crown. 
The crowns are most commonly compressed, 
conical, more or less pointed, with the “ cin¬ 
gulum ” and the anterior and posterior basal 
tubercles more or less developed; in a few of 
the largest species they are simple and ob¬ 
tuse, and particularly so in the walrus, in 
which the molar teeth are reduced to a 
smaller number than in the true seals.J In 
these the line of demarcation between the 
true and false molars is very indefinitely in¬ 
dicated by characters of form or position ; 
but, according to the instances in which a 
deciduous dentition has been observed, the 
first three permanent molars in both jaws 
succeed and displace the same number of 
milk molars, and are consequently premolars ; 
occasionally, in the seals with two-rooted 
molars, the more simple character of the 
premolar teeth is manifested by their fangs 
being connate, and in the Stenorhynchus serri- 
dens the more complex character of the true 
molars is manifested in the crown. There is 
no special modification of the crown of any 
tooth by which it can merit the name of a 
* Odontography, pi. 132, fiq. 7. 
f lb. figs. 1—4. 
Î The relation of Trichechus to the Phocidœ is 
analogous to that of Machairodus to the Felidœ, and 
also, in the simplification of the molars, to that of 
Proteles to Canidœ.
        

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