SYNOPSIS OF THE PRINCIPAL GROUPS. 119 
There are fifteen orders: 
Edentata. No median incisors; teeth with- 
out enamel; toes with powerful claws. 
Sirenia. No hind legs, but a horizontal cau- 
dal fin; fore limbs converted into paddles ; 
nostrils on the snout; jaws with molar teeth. 
Cetacea. No hind legs but a horizontal cau- 
dal fin; fore limbs converted into paddles ; 
nostrils on the top of the head; no molars 
in the jaws. 
Ungulata. Toes enclosed in hoofs; never 
more than four toes; no clavicles; placenta 
non-deciduate; molar teeth with dentine, 
enamel, and cement. 
Dinocerata. No upper incisors; upper ca- 
nines very lone: fore feet with five toes (ex- 
tinct). 
Tillodontia. Two long incisors, and small 
canines in each jaw ; feet plantigrade (extinct). 
Toxodontia. Molars strongly convex outside, 
and concave inside; small canines in the 
lower jaw, none in the upper; six incisors in 
the lower jaw, four in the upper (extinct). 
Hyracoidea. ‘Toes enclosed in hoof like nails, 
the hind inner toe with a claw; two incisors 
in each jaw, no canines, no clavicles ; placenta 
deciduate. 
Proboscidea. ‘Two tusk-like incisors in the 
upper jaw, none in the lower ; no canines. 
Carnivora. Canines well developed in both 
jaws; molars with sharp edges, and covered 
with enamel ; no clavicle. 
