210 LABYRINTHODONTS. 



situated on the outer part of this expanded extremity of the vomer in 

 the present species of Labyrinthodon. The corresponding part of the 

 vomer in the Menopome and gigantic Salamander supports a trans- 

 verse row of small teeth ; and the large tooth of the Labyrinthodon 

 is the outermost of a similar transverse row of teeth extending, five in 

 number, across the anterior expansion of each lateral moiety of the 

 vomer, the three median teeth being small and equal, the two outer- 

 most much larger. In the present fossil these teeth appear to have 

 been alternately shed ; that is the first, third, and fifth, counting 

 outwards from the middle line are in place ; the second and fourth 

 are indicated by their empty sockets. This is analogous to the 

 condition of the maxillary series of teeth ; it is a course or order 

 of shedding and renewal which is common in many fishes, where 

 these processes succeed each other frequently and quickly, and by 

 which the dental series is always kept in an efficient state. The 

 outermost or fifth tooth is placed behind, as well as to the outer side 

 of the socket of the fourth displaced tooth ; and while it terminates 

 the transverse row of the vomerine teeth, it forms the commencement 

 of a longitudinal row of small and equal-sized teeth which is continued 

 backward along the outer margin of each vomerine bone (fig. 3 c) ; 

 the whole of the vomerine series of teeth thus describes a curve, 

 nearly concentric and parallel with the external maxillary series of 

 teeth ; and the large fangs occupy corresponding situations in both 

 the outer and the inner row of the teeth of the upper jaw. 



In the Saurian reptiles, the examples of such an inner or 

 palatal row of teeth are comparatively 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, aporo- 

 mera and mosasaur. In the Ophidians, the inner rows of teeth 

 are situated on the palatine and pterygoid bones, and are never 

 arranged transversely to the axis of the mouth. In the Ba- 

 trachians this is the most common disposition of the palatal 

 teeth ; they form a short transverse series at the posterior 

 part of the divided vomer in the frog, and at the anterior part 

 of the vomer in the menopome and gigantic salamander ; in the 

 amphiume, the palatal teeth form a nearly longitudinal series, along 



