582 UNGULATES. 



successor below the level of the second and fourth of the large 

 grinders, and especially the non-development of the last grinder 

 will betray the fact that the young Horse has not passed his 

 third year. The incisors give evidence with which it is still more 

 difficult to tamper without detection. The first permanent incisor 

 as above stated, takes its place before the end of the third year; 

 and should its growth have been accelerated by extraction of its 

 predecessor the strong * mark' on the third deciduous incisor will 

 indicate the deception. The second incisor (fig. 6, i 2) pushes out 

 its predecessor between three and a half and four years. The 

 small persistent canine, or ' tusk' contrary to the usual rule, next 

 follows, its development having received no check by the retention 

 of its rudimental predecessor : its appearance indicates the age of 

 four years ; but it sometimes makes its appearance earlier, rarely 

 later. The third incisor pushes out the deciduous one about the 

 fifth year, but is seldom completely in place before the Horse is 

 five years and a half old.(l) The third premolar is then usually 

 on a level with the other grinders. 



213. Toxodon. — This extinct genus of large pachydermal Quadru- 

 peds is represented by two species, both equalling the Hippopotamus 

 in size, whose remains have been discovered by Mr. Darwin and 

 M. de Angelis in the recent tertiary deposits of South America. 

 In both, the teeth consist of molars and incisors, separated by a long 

 diastema, or toothless space. In the upper jaw the molars are 

 fourteen in number, there being seven on each side ; the incisors four, 

 which differ in their proportions in the two species. In the Toxodon 

 platensis the outer or second incisor is very large, and the inner one 

 small, in each intermaxillary bone. In the lower jaw there are six 

 incisors and twelve molars. 



The general form and nature of the teeth are indicated by the 

 sockets, and the structure of the grinders is exhibited in a broken 

 molar, the last in the series on the left side of the skull of the 

 Toxodon platensis, discovered by Mr. Darwin ; and by another perfect 



(1) Upon the rising of the third permanent incisors or ' corner nippers' the 'colt' becomes 

 a ' horse', and the ' filly' a ' mare', in the language of the dealers. For the subsequent changes 

 ic the character of the teeth, see the descriptions of the Plate 136. 



