Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 3: Ins-Pla
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29464/275/
true molar has cut the gum: the succeeding 
true molar is soon afterwards extruded; and 
I have seen a skull of an old Macropus major 
in the Museum at Leyden, in which the 
grinders were reduced to two on each side of 
each jaw by this yielding of the anterior ones 
to the vis a tergo of their successors. 
The general form of the body in the Ma- 
cropodidœ is that of an elongated cone, the 
broad and stout haunches forming the base, 
and the produced tapering muzzle the apex. 
The proportions of the body are, however, re¬ 
duced by so elegant a gradation that they are 
justly considered as among the most picturesque 
of quadrupeds. The hinder extremities are al¬ 
ways longer and stronger than the fore ones, but 
in various proportions ; the difference being least 
• .1 1 ___1 T~> _ i__r.^/4 4*-» oontmn nf 
MARSUPIALIA. 267 
differs more from the Koala than the latter does 
from either the Phalangers or Kangaroos. 
The dental system presents the extreme de¬ 
gree of that degradation of the teeth, interme¬ 
diate between the front incisors ànd true molars, 
which we have been tracing from the Opossum 
to the Kangaroos : not only have the function¬ 
less premolars and canines now totally disap¬ 
peared, but also the posterior incisors of the 
upper jaw, which we have seen in the Potoroos 
to exhibit a feeble degree of development as 
compared with the anterior pair ; these in fact 
are alone retained in the dentition of the present 
group, the representative of which possesses 
the fewest teeth of any Marsupial animal. The 
dental formula of the Wombat is thus reduced 
both in number and kind to that of the true 
in the arboreal Potoroos, and in that section of Rodentia.* 
the genus represented by the Hypsiprymnus 2 . canineS; 2; premolars, Lui; 
myosurus of Van Dieman s Land. The tail is 2 0 1 — 1 
very long in all the species, but is strongest in ^^ 
the great kangaroos, which make use of it as a molars, —-—- = 24. 
kind of crutch or fifth extremity in their slower 4 4 
modes of progression. In the Potoroos the The incisors moreover are true dentes scalpra- 
tail is more slender, and in these and some of r«, with persistent pulps, but are inferior, espe- 
the smaller species of kangaroo it is bent be- cially in the lower jaw, in their relative length 
1 '' 1 and curvature to those of the placental Glires; 
they présenta subtriedral figure, and are traversed 
by a shallow groove on their mesial surfaces. 
The spurious molars present no trace of that 
compressed structure which characterizes them 
in the Koala and Kangaroos, but have a wide 
oval transverse section ; those of the upper jaw 
being transversed on the inner side with a 
slight longitudinal groove. The true molars 
are double the size of the premolars : the su¬ 
perior ones are also traversed by an internal 
longitudinal groove, but this is so deep and 
wide that it divides the whole tooth into two 
prismatic portions, with one of the angles 
directed inwards. The inferior molars are 
in like manner divided into two triedral 
portions, but the intervening groove is here 
external, and one of the facets of each 
prism is turned inwards. All the grinders 
are curved, and describe about a quarter 
of a circle : in the upper jaw the con¬ 
cavity of the curve is directed outwards ; 
in the lower jaw, inwards. The false and 
true molars, like the incisors, have per¬ 
sistent pulps, and are consequently devoid 
of true fangs, in which respect the Wom¬ 
bat differs from all other Marsupials, and 
resembles the extinct Toxodon, the denti¬ 
gerous Bruta, and herbivorous Rodentia. 
I may add that the Wombat deviates from 
the other Marsupials in the number of its ribs ; 
as these are very constant in the rest of the order, 
the difference in the Wombat, which has 15 
pairs, instead of 13 or 12, is the more deserving 
neath the body when the animal reposes. 
Tribe V. RHIZOPHAGA. 
In this tribe, the stomach is simple in out¬ 
ward form, but complicated within by a large 
cardiac gland ; and the cæcum, which is short 
and wide, with a vermiform appendage. 
Genus PHASCOLOMYS, (fig. 93.) 
In its heavy shapeless figure, large trunk, 
and short equably developed legs, the Wom¬ 
bat offers as great a contrast to the Kangaroos as 
Fig. 93. 
Phascoltmysfusca, Geoff, one-half nat. size. 
does the Koala, which it most nearly resembles 
in its general outward form and want of tail. 
But in the more important characters afforded 
by the teeth and intestinal canal, the Wombat 
succeeded in the vertical direction by a permanent 
spurious molar, as in the Halmaturi, it was dis¬ 
placed by the trite molars, which are developed 
from behind forwards. 1 have however detected the 
crown of the permanent spurious molar in the jaws 
of the 3Iacropus major in a concealed alveolus, and 
have observed it completely formed and in place 
in an individual which had nearly attained its full 
size.— See F. Cuvier’s account of the Halmatwrus 
Thetis in the “ Histoire des Mammifères,” folio. 
* In all the placental Rodents, which have more 
than three molars in each lateral series, the addi¬ 
tional ones are placed at the anterior part of the 
row, and are subject to displacement by a perma¬ 
nent successor in the vertical direction, and conse¬ 
quently are essentially “ premolars,” or spurious 
molars ; the Wombat strikingly manifests its mar¬ 
supial character in having four true molars on each 
side of both jaws.
        

Nutzerhinweis

Sehr geehrte Benutzer,

aufgrund der aktuellen Entwicklungen in der Webtechnologie, die im Goobi viewer verwendet wird, unterstützt die Software den von Ihnen verwendeten Browser nicht mehr.

Bitte benutzen Sie einen der folgenden Browser, um diese Seite korrekt darstellen zu können.

Vielen Dank für Ihr Verständnis.