INCISOR DENTIN OF SICISTA-BETULINA (ZAPOD IDAE, RODENTIA) AS A RECORDING STRUCTURE

Dentin of upper and lower incisors was investigated in 107 birch mice Sicista betulina caught in Karelia, 36 individuals caught in Bialowiez a Primeval Forest, and 36 birch mice caught in Bialowieza and kept in captivity fox the time from 3 days up to 9 months. Age of animals dete rmined by annual bone layers was from less than a year up to 3 years. A normal annual layers of dentin were formed in incisors of birch mice . The hibernation mark was the principal element of each layer. Dentin composed of daily layers formed the intermediate element of each annu al layer. At any given moment, only part of the annual layer can be se en in an incisor due to its permanent growth and wearing. Analysis of distinctness, width, and number of daily layers in different parts of the incisor made it possible to obtain the following information. Erup tion of an incisor and appositional growth of its dentin are correlate d and change in a similar way in different populations and in captive animals. Width of daily layers varied from 6 to 10 mm and the time of incisor complete renovation varied from 60 to 195 days depending on an imal's age and origin. Width and distinctness of daily layers decrease d and time of incisor complete renovation increased depending on the g roup of studied birch mouse in an order: Karelia, Bialowieza Forest (n ature), Bialowieza (captivity). The incisors growth rate appeared to d ecrease with age. In spring, skeleton growth is renewed 5-23 days afte r the end of hibernation. As determined on daily layer's, Karelian bir ch mice arouse from hibernation one and a half month later than Bialow ieza ones. In both populations, males arose two weeks earlier than fem ales. Birch mice kept in winter under room temperature had incisors of the same size as animals in nature. They shown lesser growth Tate of incisors, less distinct daily layers, and great disturbances in dentin calcification. In some individuals of this group the hibernation mark was not formed in dentin, in some of them complex hibernation marks w ere formed possible due to disturbances of hibernation.