428 HARRIS HAWTHORNE WILDER ON 



The teeth are pleurodont, i. e., situated upon the inner side of the tooth-bearing 

 ridge, and possess a root and a crown, the di\asion between the two being coincident topo- 

 graphically with the edge of the bone upon the outside of a row of teeth. Thus the root, 

 which is formed simply of bone substance, and is unprotected by enamel, is guarded by 

 the ridge of bone, while the enameled crowns project beyond this protection. The root 

 is made of a hard bony substance or dentine, and is directly continuous with the bone 

 which bears it, arising from it ])y two lateral supports, which leave between them the 

 characteristic hollow seen in all of the figures that represent teeth as seen from the inner 

 aspect. Each hollow is really a foramen, which forms the entrance to the pulp canal of 

 the crown and serves in life to transmit the special nerves and blood vessels which supply 

 the tooth. The crown is in the shape of a slender cone, with a tip that is often set off a 

 little from the rest by a slight .constriction. The apex is pointed and slightly recurved, 

 and is colored at the very point a deep amber color, similar to that found upon the 

 exposed outer surface of the incisors of beavers and many other rodents. 



Comparison of Nomenclature. 



That the numerous authors who have written upon the Urodele skull have not been 

 in accord with regard to the nomenclature of the elements concerned is to be expected 

 when we consider both the time covered by their investigations, and the fact that grounds 

 for an accurate homologizing of the parts have been sadly lacking, especially pre^dous to 

 the epoch making years of the '60's and '70's. An attempt to arrange the synonyms 

 used by various authors in designating the parts of the skull of Necturus and a few allied 

 forms is given in the following table. The two last columns give respectively the terms 

 used in this work and the abbreviations by which they are designated in the figures. 



