Prof. Owen on the Labyrinthodon and Cheirotherium. 397 



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 vertebrae 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 sup- 

 ported 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 t» 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- 

 concave vertebrse, to the Ichthyosaurus ; while in the bony palate 

 there is a deviation from the Batrachian character, and a resemblance 

 to the Lacertian type. Another marked peculiarity in this fossil is 

 the anchylosis of the base of the teeth to distinct and shallow sockets, 

 by which it is made to resemble the Sphyraena and certain other 

 fishes. From the absence of any trace of alveoli of reserve for the 



* See antt, p. 317. 



