354 THE ANATOMY OF VERTEBEATED ANIMALS. 



no tibialis anticus, peronceus longus, or brevis, nor any tibialis 

 posticus. 



The extensor longus digitorum lias a head whicli arises 

 from the external condyle o£ the femnr ; there is a simple 

 extensor- brevis. 



The flexor hallucis and flexor digitorum perforans 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 

 calcaneum. 



The deciduous or milk dentition of the Horse has the 



following formula : d.i. — - d.c. ^ d.m. -—. It is com- 



^ 3*3 1 — 1 4*4 



plete at birth, with the exception of the oiiter incisors, which 

 appear before the foal is nine months old. The incisors have 

 the same structure as in the adult. The canines and first deci- 

 duous 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 backwards, two concave surfaces separated by a 

 vertical ridge. From the anterior end, and from the middle, 

 of this outer wall, two laminae of the crown pass inwards 

 and backwards, so as to be convex inwards and concave 

 outwards, and thus to include two spaces between them- 

 selves and the outer wall. From the inner surface of the 

 hinder pai't of each of these crescentic laminae a vertical 

 pillar is developed, and the inner stirface of the pillar is 

 grooved vertically. The outer wall, the laminae, and the 

 pillars are all formed of dentine and enamel, thickly coated 

 with cement. The attrition which takes place during mas- 

 tication 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 each, siu'rounded by a band of enamel, and, outside 

 this, by the cement with which the interspaces are filled. 

 The band of enamel is simple and unplaited. The general 

 pattern of the worn surface may be described as consisting, 

 externally, of two longitudinal crescents, one behind the 



