394 
the upper jaw of the hare and rabbit, and in Fishes only in the 
lower jaw. 
A fragment of the superior maxillary bone is also described, and 
its chief deviation from the Crocodilian type of structure is the con- 
tinuation of the palatal plate of the intermaxillary bone for about 
an inch to the outer side of the base of the external plate or pro- 
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-lke mode of generation 
