354 



ANATOMY OF VERTEBRATES. 



incisors at the seventh year, and in the third or outer incisors at 

 the eighth year, in the lower jaw. It remains longer in those of the 

 upper jaw, and in both the place of the ( mark ' continues for some 

 years to be indicated by the dark-coloured cement or osteo-dentine. 

 The canines are small in the stallion, less in the gelding, and 

 rudimental in the mare. The unworn crown is remarkable for 

 the folding in of the anterior arid posterior margins of enamel, 

 which here includes an extremely thin layer of dentine. The 

 upper canine is situated in the middle of the long interspace be- 

 tween the incisors and molars : the lower canine, fig. 280, c, is 

 close to the outer incisor, as in the Ruminants, but is better dis- 

 tinguished by its cuspidate form. 



The most obvious character by which the horse's molars may 

 be distinguished from the complex teeth of other Herbivora cor- 

 responding with them in size, is the great length of the tooth 

 before it divides into fangs. This division, indeed, does not 

 begin to take place until much of the crown has been worn away; 

 and thus, except in old horses, a considerable portion of the whole 

 of the molar is implanted in the socket by an undivided base. 

 This is slightly curved in the upper molars. It provides for mas- 

 tication during a longer life than in the cow. 



The following is the average course of development and suc- 

 cession of the teeth in the Equus Caballus : — The summits of 

 the first functional deciduous molar 1 (' first grinder' of veterinary 

 authors) are usually apparent at birth; the succeeding grinder 2 

 sometimes rises a day or two later, sometimes together with the 



first. Their appearance is speedily 

 followed by that of the first decidu- 

 ous incisor, fig. 282, d l (' centre 

 nipper' of veterinarians), which usu- 

 ally cuts the gum between the third 

 and sixth days ; but occasionally pro- 

 trudes at birth. The second deciduous 

 incisor, ib. d 2, appears between the 

 twentieth and fortieth days, and about 

 this time the rudimental molar, 3 

 comes into place, and the last de- 

 ciduous molar 4 begins to cut the gum. 

 About the sixth month the inferior 

 lateral or third incisors, ib. d 3, with 

 the deciduous canine make their appearance. The lower minute 

 canine is shed about the time that the 



282 



Deciduous incisors of l-year old Colt. 

 Lower jaw. 



The homologue of d fig,2 . 287. 



Ib. d 3. 



contiguous 

 8 Ib. d l. 



incisor is in 



Ib. d 4. 



