344 THE ANATOMY OP VEETEBRATED ANIMALS. 



eacli foot — the tliird — much longer and largei* than the 

 rest. The latter are represented only by their metacarpal 

 or metatarsal bones, the inner and outer toes being absent, 

 or represented by mere ossicles (as rudiments of their meta- 

 carpals or metatarsals) in all existing EquidcB. But, in the 

 extinct Sipparion, the second and fourth digits were com- 

 plete, though small and like dew claws ; while the mio- 

 cene Anchitherium, which most nearly approaches the 

 Palceotheridoe, has the lateral toes much larger, and taking 

 their shai'e in supporting the weight of the body. 



See page Zib. ' 



Fig. 94. -A, right fore foot of a Horse. I.Radius. 2. Groove in the 

 front face of the radius. 3. Scaphoides. 4. Lunare. 5. Cunei- 

 forme. 6. Pisiforme. 7. Magnum. 8. Unciforme. 9. Metar.ar- 

 pale, zVV. 10. Metacarpale, j'd. 11. Sesamoid bones in the ligaments 

 at tlie back of the metacarpo-phalangeal articulation. 12. Proximal 

 phalanx (fetter bone). 13. Middle phalanx (coronarj'). 15. Distal 

 phalanx (coffin bone). 14. Sesamoid bone in the tendon of theyfezor 

 perforans (called " navicular " by Veterinarians). 



B, left hind foot of a Horse. 1. Tibia. 2. Calcaneum. 3. Astragalus. 

 4. Cuboid. 5. Navicular, or scaphoid. 6. Ectocuneiform. 7. Me- 

 tatarsale, Hi. 8. Metatarsale, iv. 9, 1 1, 12. Phalanges. 10, 14. Se- 

 samoids. 

 . 3'3 1*1 4*4 3*3 



The dental formula is i. -— c. v.in. — t m. tt^- The 



33 A'l-^ 4*4 3*3 



tooth here counted as the first premolar may be a milk tooth, 

 as it appears to have neither predecessor nor successor, and 

 soon disappears. 



The molar teeth present an outer wall, which is bicrescentic 

 in transverse section; and two inner ridges, which are 

 curved more or less inwards and backwards, and coiTespond 

 respectively with the anterior and the posterior crescents of 

 the outer wall. The valleys may be more or less com- 

 pletely filled up with cement, which also coats the tooth. 

 The incisors are similar in form in each jaw, and in Equus 

 and Hipparion their crowns present a wide and deejD median 

 cavity, formed by a fold of the enamel. 



These are the distinctive characters of the Equidce. It 

 may be useful to add some special details respecting the 

 anatomy of the Horse as a familiar example of the peris- 

 sodactyle group. 



