518 CHORDATA. 
by a great and equal reduction of the second and fifth 
digits, leaving the third and fourth of equal size. Meta- 
carpals three and four fuse together to form the so-called 
“cannon-bone,” which still, however, bears distally the two 
functional digits (three and four) and two small vestigial 
digits (two and five). The former carry the two paired 
Fig. 358.—Tue Lerr PEs Fig. 359.—RiGHT Pes oF Horse 
OF AN OX x }. (Zquus Caballus x 3). 
(Ad nat.) (Ad nat.) 
Calcaneum. 
~Calcaneum, 
Astragalus. 
: Cuboid. 
Naviculo- 
cuboid. Cuneiform. 
c b 3rd Metatarsal. 
annon bone 
(Metatarsals 
3 and 4). 
Digit: } 
hoofs, which appear superficially like a “‘cloven” hoof, and 
the latter also bear small hoofs or horny nodules. In the 
horse the same derivation from the pentadactyle type can be 
traced, but the weight is borne predominantly on the third 
digit. Thus the first and fifth disappear altogether, the 
