391 
most 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, Short, and situated towards the back of the palate, upon the 
pterygoid bones, as in the Iguana and Mosasaur. In Batrachia the 
most common disposition of the palatal teeth is a transverse row 
placed at the anterior part of the divided vomer in Frogs, the Meno= 
pome 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, as already shown, combines both these 
dispositions of the palatal teeth. The posterior palatine apertures 
are more completely circumscribed by bone than in most Batrachi- 
ans, occupying the same relative position as in the Iguana. The 
posterior margin only of one of the anterior apertures is exhibited 
in this specimen, but from its curve Mr. Owen infers that the two 
apertures were not confluent, as in the Crocodile, the Freg, or the 
Menopome, but that they were distant, as in the Iguana. . 
From the physiological condition of the nasal cavity Mr. Owen 
is disposed to believe that the Labyrinthodon differed from the Ba- 
trachians and resembled the Saurians, in having distinct’ posterior 
nasal apertures surrounded by bone, and that its mode of respiration 
was the same as in the higher air-breathing reptiles. In the shed- 
ding and renewal of the maxillary and the transverse palatal teeth, 
Mr. Owen shows that the process took place alternately in each 
row, as in many fishes, whereby the dental series is always kept in 
an efficient state. 
The author then diterbes a portion, sixteen inches long, of the 
left ramus of an under jaw from the Warwick sandstone, and con- 
sidered to belong to the same species as the bone just described. It 
is slender and straight, and the symphysial extremity is abruptly 
bent inwards, and it presents, Mr. Owen says, almost as striking a 
Batrachian character as any of the bones just mentioned. The an- 
gular piece is of great breadth, extending on both sides of the jaw, 
and is continued forward to near the symphysis, forming the whole 
of the inferior part of the jaw, and extending upon the inner as far 
as upon the outer side of the ramus, the inner plate performing the 
function of the detached os operculare in the jaw of Saurians. ‘The 
dentary bone is supported upon a deep aud wide groove along the 
upper surface of the angular piece, which also projects beyond the 
groove, so as to form a strong convex ridge on the external side of 
the jaw, below the dentary piece. This character, which in the 
large bull-frog (Rana pipiens) is confined to the posterior part of the 
maxillary ramus, is in the Labyrinthodon continued to near the an- 
terior extremity. The teeth are long and. slender, gradually dimi- 
nishing in size towards the anterior portion of the jaw, and the 
fragment presents a linear series of not less than fifty sockets, placed 
laternately a little more internally; and at the anterior inflected 
2k 2 
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