392 
part of the jaw is the base of the socket of a large tooth. The an- 
terior portion of the jaw being broken off, it is uncertain if the serial 
teeth were continued externally to the anterior tusk, a remarkable 
ichthyic character noticed in another species of Labyrinthodon. 
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. Mr. Owen then describes the micro- 
‘scopic structure of the teeth, and he shows that, between the apex 
and the part where the inflected vertical folds of the cement com- 
mence, the tooth resembles, in the simplicity of its intimate struc- 
ture*, that of the entire tooth of ordinary Batrachia and most rep- 
tiles; and in the lower or basal half of the tooth the structure 
described in the previous memoir commences, and gradually in- 
creases in complexity. From the long and slender character of this 
ramus Mr. Owen shows that the length of the head, as compared 
with the breadth, approximates more nearly to Crocodilian propor- 
tions than to the ordinary Batrachian ones; but that among existing 
Batrachia it resembles most nearly the Amphiume. 
A dorsal vertebra from Coton End, which is next described, pre- 
sents still further evidence of the Batrachian nature of the Laby- 
rinthodon, in having concave but not deep articular cavities at the 
extremities of the body, a condition now known among existing rep- 
tiles only in the Gecko, and in the lower or perennibranchiate divi- 
sion of Batrachians. The body of the vertebra is elongate and sub- 
compressed, with a smooth extended, but not regularly curved sur- 
face, terminating below in a slightly produced, longitudinal, median 
ridge ; and it exhibits the same exceptional condition in the Repti- 
lian class as do the vertebre of existing Batrachians, in having the 
superior arch or neurapophysis anchylosed with the centrum. From 
each side of the base of the neural arch extends obliquely, outwards 
and upwards, the remains of a thick and strong transverse process; 
and from their strength and direction Mr. Owen gathers indications 
of a necessity for an expanded respiratory cavity, and that they 
supported ribs. ; 
A symmetrical bone, resembling the episternum of the Ichthyosau- 
rus, is also described. It consists of a stem or middle, which gradu- 
ally thickens to the upper end, where cross-pieces are given off at 
right angles to the stem, and support on each a pretty deep and wide 
groove, indicating strongly the presence of clavicles, and thus point- 
ing out another distinction from Crocodiles, in which clavicles are 
wanting. 
In concluding the description. of these remains of the Labyrintho- 
don leptognathus, Mr. Owen says, that they prove the fossil to have 
been essentially Batrachian, with striking and peculiar affinities to 
the higher Sauria, leading, in the form of the skull and the sculptu- 
ring of the cranial bones, to the Crocodilian group, and in one part 
of the dental structure, in the form of the episternum, and the bi- 
* See anté, p. 359. 
