. Elementary text-book of zoology. MAMMALIA. 513 Turning to the dentition there are sufficiently obvious differences. In the ox there are no incisors nor canines in the upper jaw, their place being taken by a horny pad. In the mandible there are three pairs of chisel-shaped incisors and a pair of canines which resemble incisors in shape and size. In the horse, on the other hand, there are three pairs of incisors in both upper and lower jaw which are of a pecuhar shape. They have their terminal surface pushed in as a deep pit, partially filled with cement. On being worn flat the surface of the
. Elementary text-book of zoology. MAMMALIA. 513 Turning to the dentition there are sufficiently obvious differences. In the ox there are no incisors nor canines in the upper jaw, their place being taken by a horny pad. In the mandible there are three pairs of chisel-shaped incisors and a pair of canines which resemble incisors in shape and size. In the horse, on the other hand, there are three pairs of incisors in both upper and lower jaw which are of a pecuhar shape. They have their terminal surface pushed in as a deep pit, partially filled with cement. On being worn flat the surface of the tooth presents two con- centric circles of enamel, the inner circle becoming narrower with age. The canines are small and pointed Fjg. 352.—Upper Jaw (left-half) and are only rarely pre- ^^ young (A) and Old Horse (B). sent m the female. As regards the molar series we have seen that there are considerable resemblances in the two types, and in each there are six functional teeth on each side, of which three are premolars and three are molars. Here the resemblances end. In most horses there is, at least in the adolescent stage, a very small first premolar in each upper jaw, which usually falls out at maturity. Thus the full dentition of a young horse may be given as pg., but that of a mature mare is ^^. The dentition of the ox is |2a. 3033 . 3133 Though the patterns of the enamel in the molars have a general resemblance, a little study shows that they are derived from different types. The horse starts from the simple bilophodont type, found in the tapir, consisting of a pair of transverse ridges: this is further complicated, as in the rhinoceros, by a junction of the two ridges and by their bending into a crescentic outline: in the horse these ridges are still further twisted, the multiplication of enamel ridges being the end in view. M. 34. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration an
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