Prof. Owen on the Labyrinthodon and Cheirotherium. 399 



cess ; while in the Crocodiles the external wall of the intermaxil- 

 lary bone is united by the whole of its outer margin with the 

 maxillary, and is thence continued along the whole outer contour 

 of the intermaxillary bone. Now in the Labyrinthodon the inter- 

 maxillary bone presents the same peculiar modification of the Ba- 

 trachian condition of this bone as in the higher organized Batra- 

 chia, the palatal process of the intermaxillary extending beyond the 

 outer plate both externally and, though in a less degree, internally, 

 where it forms part of the boundary of the anterior palatal foramen, 

 whence the outer plate rises in the form of a compressed process 

 from a longitudinal tract in the upper part of the palatal process ; 

 it is here broken off near its margin, and the fractured surface gives 

 the breadth of the base of the outer plate, stamping the fossil with 

 a Batrachian character conspicuous above all the Saurian modifica- 

 tions by which the essential nature of the fossil appears at first 

 sight to be marked. 



In the anterior frontal bone, Mr. Owen says, there are also indi- 

 cations of Crocodilian structure. Its superior surface is slightly 

 convex, and pitted with irregular impressions ; and from its poste- 

 rior and outer part it sends downwards a broad and slightly con- 

 cave process, which the author considers the anterior boundary of 

 the orbit. This process presents near its upper margin a deep pit, 

 from which a groove is continued forwards ; and in the correspond- 

 ing orbital plate of the Crocodile there is a similar but smaller fora- 

 men. 



From these remains of the cranium of the Labyr. pachygnathus, 

 it is evident, Mr. Owen states, that the facial or maxillary part of 

 the skull was formed in the main after the Crocodilian type, but 

 with well-marked Batrachian modifications in the intermaxillary 

 and inferior maxillary bones. The most important fact which they 

 show is, that this Sauroid Batrachian had subterminal nostrils, 

 leading to a wide and shallow nasal cavity, separated by a broad 

 and almost continuous palatal flooring from the cavity of the mouth ; 

 indicating, with their horizontal position, that their posterior aper- 

 tures were placed far behind the anterior or external nostrils ; 

 whereas in the air-breathing Batrachia the nasal meatus is short 

 and vertical, and the internal apertures pierce the anterior part of 

 the palate. Mr. Owen therefore infers that the apparatus for 

 breathing by inspiration must have been present in the Labyrintho- 

 don as in the Crocodile ; and hence still further, that the skeleton of 

 the Labyrinthodon will be found to be provided with well-developed 

 ribs, and not, as in the existing Batrachia, with merely rudimentary 

 styles. Since the essential condition of this defective state of the ribs 

 of Batrachia is well known to be their fish-like mode of generation 

 and necessary distention of the abdomen, Mr. Owen likewise 

 directs attention to the probability that the generative economy of 

 these fossil reptiles may have been similar to that of existing cro- 

 codiles. 



A fragment of a vertebra presents analogous characters to the 

 vertebra of the L. leptognathus previously noticed. 



