734 



COMPARATIVE ANATOMY 



The poison fangs of certain serpents are really specialized teeth on 

 the maxillary bones. They may be permanently erect, or turn as on a 

 pivot, so that when the mouth is closed the teeth lie along the roof of 

 the mouth. Vipers and rattlesnakes are examples of this latter type. 

 (Fig. 430.) 



Fig. 431. 



The types shown have been chosen from the principal families of the Carnivora in such a 

 manner as to present a complete view of the changes in dentition in that order. They are : 



P, Proviverra (Cynohyaenodon) Cayluxi (Creodonts) ; V, Viverra (Civets) (Viverridae) ; H, 

 Hyaena crocuta L, (Hyaenidae) ; F, Felis leo L. (lion) (F 'elides) ; M Michairodus cultridens 

 Cuvier (Ancient saber-toothed tiger of the Tertiary age) (F elides) ; C, Canis familiaris L. (com- 

 mon dogs) (Canides) ; U, Ursus arctos, L, (Bears) (Ur sides) . 



Letters used in common for the figures of the groups of teeth : i, incisors ; c, canines ; p, 

 pre-molars ; m., molars ; k, carnivores ; cm, inferior maxillary condyle ; gl, glenoid fossa ; co, 

 occipital condyle. 



I. CREODONTS. Extinct order of the Eocene and of the lower Oligocene ; supposed to be 

 the common stem of all the carnivora. 



Type form: Proviverra (Cynohyaenodon) Cayluxi Filhol, of the phosphorite of Quercy (upper 

 Eocene and lower Oligocene). 



P Right half of the base of the skull seen from below. Below, fragment of the right half 

 of the lower jaw, internal aspect. 



3143 



Complete Dental Formula 



3143 



ance. For example, they are said to be secodont, if used for cutting purposes, such as those of cats ; 

 bunodont, if used for crushing as in man ; lophodont, if they possess well-marked transverse ridges 

 as in the elephant ; and selenodont when they possess longitudinal crescent-shaped crests as in the 

 horse. 



