NECTURITS MACULATUS. 



417 



process is in the form of a flattened splint and is superposed npou the dorsal surface 

 of the anterior end of the frontal, lying in a shallow groove formed for its reception. 

 This is the only contact between the premaxillar}' and any of the other bones of the 

 skull ; but the extreme tips of the rostral cartilages may touch its ventral surface, and 

 the two premaxillaries almost touch each other at their antero-internal angles. 



2. THE PALATO-PTEKTGOiD ARCii. Tlils arch in Urodeles consists typically of three 

 dermal elements, vomer, palatine, and pterygoid, but owing to fusion or loss of one or 

 more of the elements, it usually appears in a modified form. In some Urodeles the first 

 two of the typical elements fuse and form a Ijroad vomero-palatine, while in others, as is 

 the case in Necturus. the vomer is distinct and the second and third elements fuse to form 

 a palato-pterygoid. Usually in the vicinity of the pterygoid there is a part of the primitive 

 cartilaginous palato-pterygoid arch around which the dermal bones may be supposed to 

 have originated, and this is denominated the " cartilaginous pterygoid." In a few cases 

 (Desmognathus, Batrachoseps) the osseous pterygoid fails, leaving the vomero-palatine 

 as the sole dermal representative of the arch. 



a. Vomer. — The main portion of this bone is somewhat triaiigular in shape and 

 forms the extensive, flattened palatine portion. Added to this upon its outer border 

 appears the alveolar portion, set at right angles to the main part and .slightly curved. 

 The palatine portion forms the greater part of the anterior third of the roof of the mouth 

 but the two bones do not meet in the mid- 



dle line. The inner Ijorders, forming the 

 longest side of the triangle, are quite near 

 one another anteriorly but diverge jjosteri- 

 orly, and in the space thus left appears the 

 parabasale, which also extends along the 

 dorsal side of the palatine process of the 

 vomer, thus doubling the bony roof of the 

 palate over a large extent of the anterior 

 surface. The parabasal does not, how- 

 ever, extend anteriorly as far as the voni- 

 erine teeth, and there is thus left a consid- 

 erable interval, bounded by the above 

 mentioned teeth, the inner borders of the 

 vomers, and the anterior border of the 

 parabasal, where there is no bony roof. 

 This opening is nearly square, and through 

 it, in the prepared skull, there may be 



X \/. f»frf ,....._ 





X P?T. 



VENTRAL. 



Fig. 17. Two views of right vomer. 



DORSAL. 



X 3. Contact sur- 

 faces with otlier bone.s are designated by an x. 



