B_{3} │C_{1} Five toes, nose _Proboscid’eans_ _Digits │ prolonged into a snout with │ nails or │ hoofs_ │ „ │C_{2} Toes odd number, less _E’quines_ │_Ungulates_ │ than five │ │C_{3} Toes even number, upper _Ru’minants_ │ „ │ front teeth lacking, │ „ │ chew the cud │ │C_{4} Toes even number, upper _Swine_ │ „ │ front teeth present, │ „ │ not cud-chewers │ „ │C_{5} All limbs having hands _Quad’rumans_ „ │C_{6} Two limbs having hands _Bi’mans_ =Exercise in Classification=.—Copy the following list, and by reference to figures write the name of its order after each mammal:— Ape (Figs. 405, 406) Rabbit (Fig. 345) Dog (Figs. 356, 408) Hog (Figs. 357, 393) Bat (Figs. 347, 370) Cat (Figs. 337, 348) Armadillo (Figs. 349, 365) Cow (Figs. 344, 386) Walrus (Fig. 340) Monkey (Figs. 352, 401) Horse (Figs. 355, 395) Ant-eater (Figs. 354, 364) Antelope (Fig. 391) Mole (Figs. 367, 368) Beaver (Figs. 372, 373) Duckbill (Fig. 359) Tapir (Fig. 384) Dolphin (Figs. 379, 397) Use chart of skulls and Figs. 381, 382, 395–400 in working out this exercise. Man’s dental formula is (_M_ ⁵⁄₅, _C_ ¹⁄₁, _I_ ²⁄₂)^2 = 32. In like manner fill out formulas below:— Cow (_M_—_C_—_I_—)^2 = 32 Rabbit (_M_—_C_—_I_—)^2 = 28 Walrus (_M_—_C_—_I_—)^2 = 34 Bat (_M_—_C_—_I_—)^2 = 34 Cat (_M_—_C_—_I_—)^2 = 30 Armadillo (_M_—_C_—_I_—)^2 = 28 Horse (_M_—_C_—_I_—)^2 = 40 Whale (_M_—_C_—_I_—)^2 = 0 Am. Monkey (_M_—_C_—_I_—)^2 = 36 Sloth (_M_—_C_—_I_—)^2 = 18 Ant-eater (_M_—_C_—_I_—)^2 = 0 Dog (_M_—_C_—_I_—)^2 = 42 Hog (_M_—_C_—_I_—)^2 = 44 Sheep (_M_—_C_—_I_—)^2 = 32 [Illustration: FIG. 344.—Skull and front of lower jaw of COW. ] [Illustration: FIG. 345.—RABBIT. _A_, _B_, incisors; _C_, molars ] [Illustration: FIG. 346.—WALRUS (see Fig. 341). ] [Illustration: FIG. 347.—BAT. ] [Illustration: FIG. 348.—CAT. ] [Illustration: FIG. 349.—ARMADILLO. ] [Illustration: