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/lit29465/896/
886 
TEETH. 
gigantic Salamander and of the Alligator ; and 
the outer surface of the bones was strongly 
sculptured, as in the Crocodilian family, but 
of a relatively larger and coarser pattern. 
The upper jaw contains a single row of small 
teeth, about sixty in number, anterior to which 
are three or four large conical tusks. The 
bases of the serial teeth project directly from 
the outer wall of the shallow socket, there 
being no alveolar ridge external to it. The 
second large anterior tusk is three times the 
size of the first of the serial teeth, and the 
size of these teeth gradually diminishes as 
they are placed further back ; the length of 
the common-sized teeth being about two lines, 
and the greatest breadth one-third of a line. 
The apical two-thirds of each tooth is smooth, 
but the basal third is fluted and anchylosed 
to the outer wall of the socket. The osseous 
roof of the mouth is principally composed of 
a pair of broad and flat bones, homologous 
with the divided vomer in Batrachia, but of 
much greater relative extent, approaching, in 
this respect, those of the Menopome, and de¬ 
fending the mouth with a more extensive 
roof of bone than exists in any Lacertian 
reptile ; physiologically, therefore, the La¬ 
byrinthodon, in this part of its structure, 
comes nearest to the Crocodile ; but the 
structure itself, morphologically, is essen¬ 
tially Batrachian.* In the Menopome-}- and 
gigantic Salamander, a row of small teeth ex¬ 
tends transversely across the anterior extre¬ 
mity of the vomerine bones ; and the occur¬ 
rence in the Labyrinthodon of a similar row, 
consisting in each palatine bone of three 
median small teeth and two outer larger ones, 
marks most strongly its Batrachian nature ; 
and from the outermost tooth a longitudinal 
row of small and equal-sized teeth is con¬ 
tinued backward along the exterior margin of 
the palatine bone. The whole of this series 
of palatal teeth is nearly concentric with the 
maxillary teeth. 
In Lacertine reptiles the examples of a 
row of palatal teeth are rare, and, when pre¬ 
sent, it is short, and situated towards the 
back of the palate, upon the pterygoid bones, 
as in the Iguana and Mosasaur.j; In Batra- 
chians the most common disposition of the 
palatal teeth is a transverse row placed at the 
anterior part of the divided vomer, as in Frogs, 
the Menopome and gigantic Salamander, and 
at the posterior part in certain toads. In the 
Amphiume, on the contrary, the palatal teeth 
form a nearly longitudinal series along the 
outer margin of the palatine bones. The 
Labyrinthodon combines both these disposi¬ 
tions of the palatal teeth. The lower jaw, 
like the upper, contains a series of small 
teeth, with a few larger tusks anterior to them, 
the serial teeth are long and slender, gradually 
diminishing in size towards the anterior por¬ 
tion of the jaw ; the largest fossil portion 
which I have obtained presents a linear series 
of not less than fifty sockets, placed alter- 
* Odontography, pi. 63. A, fig. 3. 
f lb. pi. 62. figs. 1 & 2. 
X lb. pi. 68. 
nately, one nearer the inner, the next nearer 
the outer side of the jaw. The sockets of 
the teeth are shallower than in the upper 
jaw ; the outer wall is more developed than 
the inner, and the anchylosed bases of the 
teeth more nearly resemble, in their oblique 
position, those of existing Batrachia. With 
regard to the modification of the microscopic 
structure of the teeth, I may observe that, 
between the apex and the part where the 
inflected vertical folds of the cement com¬ 
mence, the tooth resembles, in the sim¬ 
plicity of its intimate structure, that of the 
entire tooth of ordinary Batrachia and most 
reptiles ; and in the lower or basal half of the 
tooth the labyrinthic structure above de¬ 
scribed commences, and gradually increases 
in complexity. 
In the genus JDeirodon*, the teeth of the 
ordinary bones of the mouth are so small 
as to be scarcely perceptible ; and they appear 
to be soon lost, so that it has been described 
as edentulous, and has been called “ Anodon.” 
An acquaintance with the habits and food 
of this species has shown how admirably 
this apparent defect is adapted to its well¬ 
being. Its business is to restrain the undue 
increase of the smaller birds by devouring 
their eggs. Now if the teeth had existed 
of the ordinary form and proportions in the 
maxillary and palatal regions, the egg would 
have been broken as soon as it was 
seized, and much of the nutritious contents 
would have escaped from the lipless mouth 
of the snake in the act of deglutition ; but, 
owing to the almost edentulous state of the 
jaws, the egg glides along the expanded 
opening unbroken ; and it is not until it has 
reached the gullet, and the closed mouth 
prevents any escape of the nutritious matter, 
that the egg becomes exposed to instruments 
adapted for its perforation. These instruments 
consist of the inferior spinous pocessess (hyp- 
apophyses) of the seven or eight posterior cer¬ 
vical vertebrae, the extremities of which are 
capped by a layer of hard cement, and pene¬ 
trate the dorsal parietes of the oesophagus. 
They may be readily seen, even in very 
small subjects, in the interior of that tube, 
in which their points are directed backwards. 
The shell being sawed open longitudinally 
by these vertebral teeth, the egg is crushed 
by the contractions of the gullet, and is 
carried to the stomach, where the shell is 
no doubt soon dissolved by the acid gastric 
juice. 
In the Boa Constrictor, the teeth are 
slender, conical, suddenly bent backwards 
and inwards above their base of attachment ; 
the crown is straight or very slightly curved, 
e. g. in the posterior teeth. The inter¬ 
maxillary bone supports four small teeth ; 
each maxillary bone has eight much larger 
ones, which gradually decrease in size as they 
are placed further back. There are eight 
or nine teeth of similar size and proportions 
in each premandibular bone. These teeth 
* The Coluber scaber of Linnæus ; an arboreal 
serpent of South Africa.
        

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