CARNIVORA. 891 



as to the definition of terms. The meaning of the word sectorial is in this 

 connection important, since there are so many transitional forms between 

 the sectorial and tubercular tooth. A sectorial tooth, then, of the upper jaw 

 is one which has at least two external tubercles, which are the homologues 

 of the median and posterior lobes of the sectorial of the cat. By the flat- 

 tening and emargiuation of their continuous edges, the sectorial blade is 

 formed.^ One or two interior and an anterior lobe may or may not exist. 

 In the genera of the Procyonidce, except in Bassaris, the two external 

 tubercles do not form a blade. The inferior sectorial tooth differs from the 

 tubercular only in having an anterior lobe or cusp, which belongs prim- 

 itively to the interior side. The inferior sectorial teeth with large heels, as 

 in Vivei'ridse and Canidte, I have called tubercular sectorials. The secto- 

 rial blade is formed by the union and emargination of the edges of the an- 

 terior and the principal external cusp. This blade is not well developed in 

 the genus Cynogale and still less in the Procyonidce and Ursidce. 



In looking for causes in explanation of the modifications of structure 

 cited, one can easily discover that there is a close relation between the 

 arrangement of the teeth and the mechanical laws involved in the perform- 

 ance of their function, that of seizing an active prey and of cutting up their 

 carcasses into pieces suitable for swallowing. It is obvious that in the lat- 

 ter case the flesh-teeth bear the resistance, and the masseter muscle is the 

 power, and that the nearer these parts are together the better is the function 

 performed. As a matter of fact, the sectorial teeth in modern Carnivora are 

 placed exactly at the angle of the mouth, which is nearly the front border 

 of the masseter muscle. 



Both the muscle and the teeth have, however, moved forwards in con- 

 nection with the shortening of the jaw behind. This has been due to the 

 necessity of bringing the power (masseter) nearer to another point of resist- 

 ance, viz, the canine teeth. In the early carnivores (as Hycenodontidce) the 

 long jaws supported more numerous teeth (^) than in any modern families, 

 and the fissure of the mouth was probably very wide. The canine teeth 

 were evidently very ineffective weapons. The animals probably only 

 snapped with their jaws, and did not attempt to lacerate or hold on, as do 



'See "On the origin of the specialized teeth of the Carnivora," American Naturalist, 1879, p. 171. 



