302 THE ANATOMY OF YERTEBRATED ANIMALS. 



tensors of the carpus are also present, l^he flexor perforatus 

 has only a single tendon, which splits, and is attached, as 

 usual, to the sides of the middle phalanx. The flexor per- 

 forans also has only a single tendon, which pierces the 

 former, and is inserted into the lesser sesamoid and the distal 

 phalanx. 



The interossei of the third digit are represented only by 

 the ligaments which connect the greater sesamoid bones with 

 the metacarpal, and in which a few muscular fibres are some- 

 times found. There are said to be two others, one for each 

 lateral metacarpal, and a lumhricalis. 



In the hind-limb, tlie femoral muscles are in the Horse 

 the same as in Man, but enormously developed. There is 

 no tibialis anticus^ peroncieus longus^ or brevis^ nor any tibialis 

 posticus. 



The extensor longus digitorum has a head which arises 

 from the external condyle of the femur; there is a simple ex- 

 tensor brevis. 



l^he flexor hallucis and flexor digitorum per for ans unite 

 into the single perforating flexor tendon for the distal phalanx ; 

 while the perforated tendon is the termination of that of the 

 plantaris^ which passes over a pulley furnished by the cal- 

 caneum. 



The deciduous or milk dentition of the Horse has the fol- 

 lowing formula : d.i. ^3 d.c. 1^ d.tn. ~^. It is complete at birth, 

 with the exception of the outer incisors, which appear before 

 the foal is nine months old. The incisors have the same struct- 

 ure as in the adult. The canines and first deciduous molars 

 are simple and very small, the canines being smaller than the 

 molars. In the upper jaw, the other deciduous molars all have 

 the same structure. The outer wall of the tooth is bent in 

 such a manner as to present, from before backward, two con- 

 cave surfaces separated by a vertical ridge. From the anterior 

 end, and from the middle, of this outer wall, two laminae of 

 the crown pass inward and backward, so as to be convex in- 

 ward and concave outward, and thus to include two spaces 

 between themselves and the outer wall. From the inner sur- 

 face of the hinder part of each of these crescentic lamina a 

 vertical pillar is developed, and the inner surface of the pillar 

 is grooved vertically. The outer wall, the lamina?, and the 

 pillars, are all formed of dentine and enamel, thickly coated 

 with cement. The attrition which takes place during mastica- 

 tion wears down the free surfaces of all these parts, so as, in 

 the long-run, to lay bare a surface of dentine in the middle of 



