78 Mammalia. Digestive System. 



The Molars are sometimes rootless ; sometimes have short roots, 

 tardily developed; and sometimes ordinary roots soon acquired. 

 These differences in the mode of implantation relate to the differ- 

 ences of diet. Those Eodentia which subsist on mixed food, and 

 which have a tendency to carnivorous habits, or subsist on nutri- 

 tious vegetable substance (e.g. oily kernels) have their Molars, 

 * simplices,' rooted, and with shallow crowns: e.g. most Hystricidae, 

 Muridae, and Sciuridse. Those Rodentia which feed exclusively on 

 vegetable substances, especially on the less nutritious kinds, have 

 their Molars ' complicati,' with incomplete and lately developed roots, 

 and a limited growth of crown ; e.g. Castoridae. Those Eodentia 

 which are strictly herbivorous have their Molars *lamellosi,' and 

 rootless ; e.g. the Leporidte and most Cavidae. The rootless and 

 perpetually growing Molars are always more or less curved. 



Sectorialia. Throughout the Order the Incisors are small, and, 



3 . 3 



except in a few Seals, ~^ in number ; the Canines are long, largely 



o . o 



developed, r-^ in number, the lower passing anteriorly to the 



upper, as usual, when the mouth is closed. The Molars follow the 

 general rule, both as to number and form, in accordance with the 

 variation of diet ; but, in all, the last Premolar [p m 4) of the upper 

 jaw works upon the anterior true Molar {m 1) of the lower jaw, 

 and in the strictly flesh-feeding genera, scissor fashion ; each of these 

 two teeth was denominated by P. Cuvier ' dent carnassiere,' which 

 has been rendered ' dens sectorius,'' the 'sectorial' or scissor tooth; 

 hence the name here given to this Order. A tubercle is generally 

 present at the inner side of the base of the anterior part of the crown 

 of the 'sectorial' tooth; the development of the tubercle bears an 

 inverse relation to the carnivorous propensity of the species. In 

 general the crowns of the teeth of the upper and lower jaws inter- 

 lock. 



Digitigrada. The Incisors have broad and thick creams, shaped as a trefoil in 

 Hysonidae ; indented by a transverse cleft in Felidse ; or with two notches in 

 Canidce ; and are situated in a transverse row ; the exterior Incisors above being 

 larger than the four middle ones. Canines are slightly curved, and have a fang 

 as long or longer (Felidae) than the crown. In all Digitigrada there is a pit 

 internal to the last Premolar of the upper jaw, which receives the crown of the 

 first true Molar of the lower jaw. Both Felidro and HysenidoB have hut a single 

 minute tubercular true Molar on each side of the upper jaw ; and the inferior 

 Molar series are all of the ' sectorial' form, and so set as to shut within the upper, 



