.354 



PICTURESQUE SKETCHES 



seen in the slope of the back part of the head, 

 which is characteristic of the dinothere, and common 

 to the Cetacea and some of the rodents. A very 

 limited capacity is thus indicated, and the indication 

 is strengthened by the exceedingly small space that 

 there is for the brain. 



The teeth of the Toxodon are very interesting. 

 All the grinding teeth are long and curved; but un- 

 like the case of the guinea-pig, whose teeth, also 

 curved, are directed outwards, the curve is here such, 

 that each two corresponding teeth of the upper jaw 

 bend over to meet each other in the palate and form 

 an arch capable of overcoming immense resistance 

 to pressure. 



The two large incisive teeth, in like manner, bend 

 backwards in their sockets, and extend in an arched 

 form as far as the grinding teeth. The whole of the 

 inside of the upper jaw is thus a vaulted and groined 

 roof of the strongest possible construction ; and as the 

 teeth continued to grow and to be pushed forward 

 during the whole life of the animal, there was a con- 

 stant and continual compensation to meet the effect 

 of the wearing away of the crown of the tooth 

 against opposing teeth of corresponding structure 

 in the lower jaw. The enamel of the teeth is not 

 repeated in distinct folds as in the herbivorous ani- 

 mals of the present day, but the powers of perpetual 

 renovation would amply compensate for this defec- 

 tive quantity of enamel, and enable the animal to 

 grind down vegetable food of the toughest kind, with- 

 out danger of ultimately wearing away the grinding 

 surface. It is evident, however, from the nature of 

 the attachment of the lower jaw, that the motion 



