THE TEETH OF THE HORSE 



|(ni,i.i:( HON IN WAi,:, < Asi:J 



TI 1 I] (IciiImI ;(|)|);ii;it lis of t lie lioisc is one of 1 he iiio>l i iitcic^t iii^ and 

 lii<ilil\' s|)('ciali/('(l ()i-<>;aiis \\v find in natuic. During- the course of 

 (•\-olution tlnoutili in:'ny a^cs, the teeth liave jiradually ^rown 

 inoi'e and more ('onij)le\. t)ecoinin<i constantlx' more |)erfectly adapted to 

 the (•i()j)j)in«»; and ^lindinji of coarse hai'd grasses. They are in fact of 

 such «ii-eat size and iinj)()itance that the wliole skull seems constructed 

 chiefly for theii' lod^inenl and ojx'iation, 1 he custody of the hiain, eyes 

 and ears l)ein«i;, as it were, of secondaiy considei'ation; hence the skull 

 must of necessity he veiy bulky, and in order that the weight may not 

 he unncM-essaiily ^reat, lar<i-e air spaces (sinus(\s) are pi()\'ided, a^^regat- 

 in«i- between two and three times the amount of space occupied by the 

 biain {sjxH'inHMis 51 and 5, on exhibition in wall case). Indeed the skull 

 of the horse is a beautiful design in arches and bi'aces, resulting in a 

 structure of the j>;reatest possible sti'en^lh and utility with a mininnun of 

 w(Uj>ht and mateiial. 



The ethmoids, tlu^ bony framewoi'k of the or<>;an of smell, are also 

 highly developed, with a complicated s\'stem of scrolls presenting an 

 inunense amount of surface to the air that is diawn into the nostiils 

 (specimens 5, 10 and ol). 



STRUCTURE OF THE TEETH 



A\'KRY simple form of tooth is that commonly found amonji; the 

 rei)tiles, a mere i)eglike structure composed of dentine with a veiy 

 much harder covering of enamel on the crown, and a nerve canal in 

 th{^ center. We have selected three incisor t(H^th (Fig. 30) to show ex- 

 ami)les of different degrees of specialization. .4, the tooth of a young 

 cow. is of comparatively sim]:)le foi-m, being somewhat flattened and 

 having a clearly (k^fined line or neck between the crown which is com- 

 ])os(m1 of dentine and completely covered with enamel and the (k^itine 

 I'oot which is without enamel. The nerk, or l)ase of the ci-own, as 

 in most simple teeth, coincides with the line of the gum. In the horse 

 the composition of the teeth is the same except that we have a 

 third el(Mnent known as cement, which begins to be deposited on 

 the sui-face some tinu^ before the erui)tion of the young tooth cover- 

 ing the enamel almost completely. In design it is more complicated. 

 Instead of the plain upj)er boidcM- (Fig. 'M)A) theie is a very deep 

 indentation or folding in of the enamel, somewhat like th(» inverted 

 fingei' of a glove, forming an (Miamel liiUMl cup or cul-de-sac. running far 

 (k)wn into the tooth (Figs. 'M)(' and I)), becoming moic oi' less completely 



