518 Mr. Owen on species of 



longitudinal impressions or smaller grooves, which converge anteriorly. The upper 

 surface of the nasal bone is impressed by elUptical and oblong pits, the intervening 

 ridges of which form an irregular open network. The preceding sculpturing of the 

 nasal and maxillary bones resembles that of the corresponding bones in the Croco- 

 diles, but presents a relatively larger and coarser pattern ; and when it is remem- 

 bered that analogous sculpturing characterizes the crania and other bones of certain 

 species of fishes, the ribs and sternum of the Trionyx and the jugal bones of the 

 Spotted Cavy among Mammalia, much importance need not be attached to this 

 indication of the Saurian affinities of the present extinct reptiles. 



The affinity of the Labyrinthodon to the Crocodile is more essentially shown by 

 the broad and entire upper jaw, which deviates widely from the Batrachian condi- 

 tion of the same part. 



In both the caducibranchiate and perennibranchiate species the upper maxillary 

 bones present the form of slender elongated styles, attached only by a slightly ex- 

 panded anterior extremity, from which they project backwards and generally ter- 

 minate in a free and disengaged point : the external surface rises nearly vertically 

 above the alveolar margin, and is not extended horizontally over the upper surface 

 of the skull, but a very wide interval is left between the maxillary and nasal bones ; 

 and while the maxillary bones thus form so small a proportion of the upper wall of 

 the nasal cavity, their palatal processes contribute as little to the formation of the 

 floor of the same cavity. In the Crocodiles, on the contrary, the palatal processes 

 of the maxillary bones extend horizontally inwards and meet at the middle line of 

 the roof of the mouth, and thus form an unbroken floor to the nasal cavity. In 

 the present fossil we have already seen that the superior maxillary extends inwards 

 to the nasal bone, forming with it a continuous strong bony roof over the nasal 

 cavities. The whole of the under surface of the fossil was covered with the sand- 

 stone matrix, but the fractured margin, opposite the alveolar border, exhibited the 

 edge of a thin plate of bone, uninterrupted in the longitudinal extent, and forming 

 the floor of a wide and shallow nasal cavity ; thus affording a strong indication that 

 the Labyrinthodon breathed air like the higher reptiles. That the bony palate 

 extended as far in the transverse as in the longitudinal extent was indicated by the 

 projecting base of a fractured conical tooth, twice the size of the large anterior fang 

 of the maxillary series, and situated internal to the anterior small serial teeth. 

 Although the Labyrinthodon resembles the Crocodile in the character of the bones 

 forming the upper surface of the maxillary part of the cranium, and in the inter- 

 ception of a wide and shallow nasal cavity between two horizontal plates of bone, 

 yet the main evidence of its affinity to the higher Saurian was to be derived from 

 the condition of the bony palate, first in regard to the bones composing it, and, 

 secondly in their relation to the dental system. 



In Crocodiles, the floor of the nasal cavity is chiefly formed by the maxillary 



