202 



THE NATURE BOOK 



more favourable. He will only be checked 

 when co\-er fails him, and it would appear 

 to be Nature's design that he himself 

 should be responsible for the failure of 

 co\-er. Once he has abandoned the marsh- 

 land he has brt)ken the law of the wild, 



(grinding teeth at the back) there is a 

 toothless gap which is termed the tliastema. 

 In many instances the furred borders of 

 the lips curl in so as partially to fill this 

 gap. and it has been suggested that this 

 fur insertion may save the animal the dis- 



and his extermination is dependent solely comfort of swallowing material which it 

 on the speed with which his furred and intends merely to gnaw, 

 feathered enemies can assemble. Some such provision would l)e almost 



essential to the true Mice, and 

 1 - 3 to the Red - backed Meadow 



Mouse, while even the Short- 

 tailed Meadow Mouse may, on 

 occasion, gnaw without the wish 

 to feed ; in dressing his own fur, 

 lor instance, or in nest-building. 

 It ma}' be mentioned that in 

 nest-building. Meadow Mice con- 

 struct the soft hning of their 

 nests by biting grass stems into 

 short lengths of an inch or less. 

 1 hey soften these short lengths 

 b\' j)ulling them between their 

 teeth, and, as the grass has a 

 tendency to split apart in this 

 process, they can deal with a 

 large mass of material m a very 

 short time. 



If reference be made to the 

 illustrations on this page, it will be 

 seen that the molar teeth of mice 

 (they have three molars on each 

 side of their upper and lower 

 jaws) present peculiar and some- 

 what intricate patterns. The 

 type of molar found in the true 

 ^lice is shown in Fig. i ; that of 

 the Red-backed IMeadow ]\h)use 

 in Fig. 3. and that of the Short- 

 tailed Meadow Mouse in Fig. 3. 

 It will be seen that the first 

 ty})e differs materially from the 

 other two. In this " bunodont " 

 type of dentition (which we 

 ourselves ]iossess) the grinding 

 surface of each tooth consists of 

 several small hillocksof enamel ar- 

 ranged in more or less parallel rows — three 

 rows in this case of the uj^per teeth, and 

 two of the lower. Such teeth are adapted 

 for masticating fish, flesh, fowl, or good 

 red herring, and, of course, any kind ot ' 

 soft vegetable in addition. In the Meadow 

 Mice the molars arc far more highly 

 specialised. Their surfaces present a zig- 

 zag series of rough triangles. The sides 



PHOTO-MICKOGKAFHS OF THE GRINDING SURFACES OF 

 THE LEFT UPPER AND LOWER MOLAR TEETH OF 



(1) The Long-tailed Field Mouse: bunodont type. 



(2) The Red-backed Meadow Mouse. Teeth rooted. Prismatic 



spaces 5, 4, 5 ; 7, 3, 3. 



(3) The Short-tailed Meadow Mouse. Teeth not rooted. Prismatic 



spaces 5, 5, 6 ; 7, 5, 3. 



The most obx-ious adaptations of the 

 Meadow Mouse to his marshy surroundings 

 are to be seen in his fur and in his giiiid- 

 ing teeth. 



In a previous article I referred to the 

 peculiarities of the incisors (front teeth) 

 of Rodents. The entire absence of canines 

 (dog teeth) is characteristic of the order, 

 and between the incisors and the molars 



