pulp-cavity indicated by a dotted line. .
Fig. 2. Tooth of the Gavialis gangeticus :
a, base absorbed and penetrated by, b,
a successional tooth; c, germ of a third
tooth. Fig. 3. Back part of the series of
teeth of the lower jaw of the Alligator
niger, with the inner wall of the alveolar
groove removed showing the absence of
partitions, and the germs of the successional
teeth. Fig. 4. Middle part of the
series of teeth of the same species, exposed
by removal of the outer alveolar wall,
showing the partitions forming here distinct
sockets, from which the teeth are
raised to show the germs of successional
teeth, and the dentiparous cavities, a, a
tooth turned round to show the effect of
the new germ upon its base; b, the shell
of an old tooth and two successors. Fig. 5.
The root of an old tooth of the Black
Alligator, penetrated by its successor.
Fig. 6. Base of the same. Fig. 7. Opposite
end from which the crown has
been broken away, showing the apex of
that of the new tooth. Original.
PLATE 75 A.
Fig. 1.—Skull of an Alligator. Fig. 2.
Skull of a Crocodile. Fig. 3. Skull
of a Gavial. Fig. 4. Skull of a Te-
leosaur. Fig. 5. a, b, two views of a
tooth of the Marmorosaurus obtusus: c,
interrupted ridges of enamel on the base
of the crown, magnified. Fig. 6. a, side
view; b, edge view of the tooth of Hylao-
saurusQ). Fig. 7. a, side view; b, edge
view of the tooth of Cardiodon rugulosus: c,
edge view of a larger tooth of the same
species ; d, surface of the enamel, magnified.
PLATE 76.
Fig. 1.— Side view of the jaws of the Orni-
thorhynchus paradoxus, showing the position
of a the incisive and b the molar
homy teeth. F. Cuvier. Fig. 2. Left
ramus of the lower jaw, showing the
working or free surface of a the incisive,
b the molar tooth. F. Cuvier. Fig. 3.
A diminished view of a transverse slice of
a small portion of the molar tooth of the
Ornithorhynchus, showing the concentric
walls of the canals of the principal tubes,
and the minute pores or cells of the denser
cementing fibrous substance. Fig. 4.
View of the open mouth of a very young
Fin-whale, (Balcenoptera). Brandt and
Ratzeburg. a. The outer vertical margins
of the baleen plates ; the letter is
placed just above the horizontal line, or
‘ bead’ of Hunter, which indicates the
extent to which the cementing substance
descends [in the interspaces of the plates.
b. The inner oblique bristled margins of
the baleen-plates, c. The large tongue.
Fig. 5. A vertical section of four baleen
plates in situ. The transverse bar below
the numeral represents the vascular gum
from which the pulps proceed that penetrate
the base of the plates. Below this
is shown the elastic substance cementing
the plates together; beyond which the
plates project free, and terminate in the
fringe of bristles at c. Hunter. Fig. 6.
A diagram of the matrix of the baleen-
plate. a. Dotted outline of the pulp,
which forms b, the central fibrous part of
the plate; c, the external layers of firm
substance formed by the elastic cementing
material. Fig. 7. A transverse slice of a
portion of a baleen-plate, shewing the
arese of the tubular cavities of the coarse
central fibres, and the outer denser substance.
Heusinger.* Fig. 8. Side view of
the upper and lower molars of the Oryc-
teropus Capensis. F. Cuvier. Fig. 9.
* System der Histologie, 4to. 1822.
Grinding surface of the lower molars of
f the same. F. Cuvier. Fig. 10. A longi-
: tudinal section of the lower molars of the
I same in situ : the section of the middle
I or antepenultimate molar has touched the
| lower end of the outer longitudinal groove, I which might be mistaken for the remnant
I of a central pulp-cavity. Original. Fig.
11. Transverse section of a molar of the
I Orycterope. F. Cuvier.
PLATE 77.
A portion of a longitudinal slice of the base
I of a molar of the Orycteropus, magnified
f 150 linear diameters, a, a. The expan-
I; ded apertures of the pulp-cavities of the
j component denticles. The dark parts of
| the continuation of the pulp-cavities indi-
|i cate the dried remains of the vascular
I- pulp there situated. Original.
PLATE 78.
A portion of a transverse section of a molar
I of the Orycteropus, magnified 500 linear
1' diameters. Original.
PLATE 79.
A section of the tooth of the Mylodon Dar-
I winii showing the dentinal cells, and a
I few vascular canals. Original.
PLATE 80.
■Fig. 1. Transverse section of the five mo-
| lars in situ, of one side of the upper jaw
I of the Scelidotherium leptocephalum. Fig.
| 2. A similar section of the four molars,
I lower jaw, of the same, Jths nat. size.
I Fig. 3. First upper molar. Fig. 4. Its
I grinding surface. Fig. 5. Transverse
I section of the four molars of one side of
1' the lower jaw, in situ, of the Mylodon
| Darwinii: § nat. size. Fig. 6. Trans-
I verse section of a molar of the Megalonyx
laqueatus. (Perhaps another tooth of
the M. Jeffersonii).
PLATE 81.
Fig. 1. Side view of the upper and lower
jaws and teeth of the three-toed sloth,
Bradypus tridactylus. Fig. 2. The same
of the Bradypus torquatus. Fig. 3. The
same of the two-toed sloth ( Choltepus didac-
tylus). Fig. 4. Lower jaw, teeth removed
from left ramus. Fig. 5. Separate
teeth of the same sloth ; e, canine ;
b, first ; c, second ; d, third ; e, fourth
upper molars. De Blainville.*
PLATE 82.
Fig. 1. Longitudinal section of the molar
of Bradypus tridactylus, magn. 250 linear
diameters. Fig. 2. A small portion of the
same, magnified 500 linear diameters.
Original.
PLATE 83.
A section of the upper jaw and five molar
teeth of the Megatherium Cuvieri ; a, cement
; b, vaso-dentine ; c, pulp-cavity ;
d, vacuity at the base which was occupied
by the thick capsule, less than \ nat.
size. Original.
PLATE 84.
Section of part of the molar of the Megatherium,
including the hard dentine c ;
a a', vaso-dentine; b, cement; b], loops of
the vascular canals next the dentine.
Magnified 500 linear diameters. Original.
PLATE 85.
Fig. 1.—Teeth of the great existing Armadillo
(Priodon gig as) ; a, side view of upper
molars ; b, grinding surface ; c, ditto of
lower molars ; d, side view of lower mo-
* Ostéographie des Animaux Vertébrés, 4to, 1839, et seq.