520 Mr. Owen on species of 



verse row of palatal teeth, it forms the commencement of a longitudinal row of 

 small and equal-sized teeth, which is continued backward from the large exterior 

 tooth of the transverse row along the outer margin of the vomerine bone ; the 

 whole of the series of palatal teeth thus describe an arch nearly concentric and 

 parallel with the external maxillary series of teeth, and the large tusks occupy 

 the corresponding situations in each row. In the lacertian reptiles the examples 

 of such an inner or palatal row of teeth are very few, and the series, when it 

 does exist, is very short, and is situated towards the back of the palate upon the 

 pterygoid bones, as in the Iguana and Mosasaur. With the Ophidians the com- 

 parison of the present reptile is out of the question ; and their palatine teeth are 

 never arranged transversely to the axis of the mouth. In the Batrachians this is 

 the most common disposition of the palatal teeth ; they form a short transverse 

 series at the anterior part of the divided vomer in the Frog, and at the posterior 

 part of the divided vomer in certain Toads, as Hyladactylus ; the palatal teeth form 

 an extensive transverse row along the anterior margin of the vomer in the Menopome 

 and gigantic Salamander, but are not extended longitudinally. In the Amphiume, 

 on the contrary, the palatal teeth form a nearly longitudinal series along each outer 

 margin of the long and narrow vomerine bone : the extinct Labyrinthodon combines 

 both these dispositions of the palatal teeth. In the Menopome and most other 

 Batrachians the posterior extremities of the maxillary bones are free, and the wide 

 posterior palatal spaces, which are covered by membrane only in the recent animal, 

 are uninclosed externally. In the genus Rana the pterygoid bones extend outwards 

 and forwards so as to touch the palatine and maxillary bones, and circumscribe 

 this aperture, which, however, is of great extent. In the Labyrinthodon the aperture 

 (PI. XLIII. fig. 2, c) is much more completely circumscribed by bone, and, from the 

 greater development of the vomerine bones, its extent is much diminished. In the 

 present specimen the posterior palatal aperture forms a longitudinal ellipse, ten lines 

 in the long and five lines in the short or transverse diameter : it occupies apparently 

 the same relative position as in the Iguana, but a much smaller proportion, if any, 

 of its posterior contour must be completed by the pterygoid bone in the Labyrin- 

 thodon. The anterior transversely produced plate of the vomerine bone has its ex- 

 ternal margin expanded in the longitudinal direction, and abuts by an extensive 

 slightly convex surface against the narrow palatal process of the upper maxillary 

 bone. The anterior and posterior margins of this process of the vomerine bone are 

 concave, the former (PI. XLIII. fig. 2, d) being the posterior boundary of the anterior 

 palatal opening, and the latter the anterior boundary of the posterior palatal opening. 

 What the extent of the anterior palatal orifice may have been, and how far the superior 

 maxillary and intermaxillary bones extended beyond the part of the upper jaw at 

 which the present fossil terminates, is indicated by the length of the lower jaw of 



