Labyrinthodon /rom Warwickshire. 531 



prised to find other bones of the cranium in the present Batrachian family modified 

 after the same type ; such appears to be the case in the fossil now under consideration, 

 which I regard as an anterior frontal bone, similar in form to that of the Crocodile. 

 It presents a superior, horizontal, expanded and shghtly convex surface, pitted 

 with large irregular impressions, thinning off to a fine edge at the inner side, and 

 sending downwards from its posterior and outer part a broad and slightly concave 

 process, the smooth surface of which strikingly contrasts with the irregularly 

 sculptured one of the horizontal plate. This smooth surface, if I am correct in my 

 idea of the nature of the bone, must form a part of the anterior boundary of the 

 orbit, which it indicates to have been of large size. The posterior margin of the 

 horizontal plate does not extend so far back, or overhang so abruptly the smooth 

 orbital plate, as in the Crocodile. 



The orbital plate is also characterized in the present fossil by a deep pit, from 

 which a groove is continued forwards ; thei'e is a smaller foramen in the corre- 

 sponding part of the smooth orbital plate in the anterior frontal of the Crocodile. 

 The present fragment is two inches and a half in length, and the same in breadth ; 

 the depth of the orbital plate is one inch three lines ; the thickness of the fractured 

 angle of the bone, which would have joined the lachrymal, is three lines. 



Hitherto I have not received any other portions of the cranium of the Labyrin- 

 thodon pachygnathus than those which have been described. They demonstrate 

 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 inter- 

 maxillary and inferior maxillary bones. The most important fact which they make 

 known is, that this Sauroid Batrachian had subterminal nostrils leading to a wide 

 and shallow nasal cavity, extending horizontally backwards, and separated by a 

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

 plainly indicates that their posterior apertures 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, 

 where they are readily closed and opened by the tongue in the act of swallowing 

 the air. 



But breathing by deglutition must have been as difficult, if not as impossible, 

 in the Labyrinthodons as in the Crocodiles ; and we may infer, therefore, that 

 the apparatus for breathing by inspiration must have existed in the one as in the 

 other. The inability to supply air to the lungs by deglutition is compensated for 

 in the Crocodile by the power of dilating the cavity containing the lungs ; which 

 power is given by an apparatus of ribs encompassing the thorax and of their ap- 

 propriate muscles. It may be reasonably anticipated, therefore, that the skeleton 

 of the Labyrinthodon will be found to be provided with well-developed ribs, which, 



