Dr. N. Sevcrtzort' on tin M,imui ils of Tud-t'stan. 215 



»*ate(l by tliL'se I'lirrow.s with unitonn ilistinctnosfl. Frequently, 

 t'vom want (>t't<M)(l or tVoiii illness, narrow annulations are formecl 

 round the lu^'n hesidcs those caused hy the annual interruption 

 of their growth in winter, which they much resemble. 



2nd. In addition to these irregular annulations there are 

 other secondary annulations, separating those indicating tlie 

 annual increase of the horns. The furrows formed 1)y these 

 <lifier from those depemlent on the annual increase of the horns 

 in their not l)eing so deep and in their not extending all round 

 the horn. 'riieyare,when present, nearly alwaysdistinguishable. 



3rd. Finally, the rings formed whilst the animal is young 

 are not so distinct as those formed when it is adult, as 

 with .advanced age the rings get thicker. These early 

 rings, in getting towards the end of the horn, sometimes get 

 rubbed oft' and the horn itself gets blunt with advanced 

 age ; this is the case in jiarticular with 0. Polii, because of 

 the inner spiral of the horns getting wider towards the end of 

 the horn ; consequently only the minimum of the animal's age 

 can be fixed — for instance, that the animal is not younger 

 than ten or twelve years, but how much older is doubtful. 

 In specimens which are not above ten years old the age 

 can usually be correctly ascertained, although sometimes this 

 cannot ]>e done without difficulty. Very little confidence can 

 be placed in the determination of an animal's age by the anky- 

 losis of the different bones of its skull, this latter being an 

 uninterrupted process. 



The proportions between the development of the horns and 

 the ankylosis of the skull-bones give also specific characteris- 

 tics which are in most cases constant, althougli some speci- 

 mens of one and the same species difter slightly in that 

 respect ; but this is more or less the case with all mammals. 



In examining the skulls of different species I find that the 

 bones of the skull of an 0. Poh'i about two and a half years 

 old are more firmly ankylosed than those of specimens of 

 O. Karelini CiUil 0. Ifcinsii o( about four and a half or five 

 years of age. The above specimens of O. Polii and (K Karelini 

 are complete, so that the age can be checked by the horns as 

 well as by the general size of the aninnil ; and this shows that 

 O. PoUi has not nearly reached its full size, whilst 0. Karelini 

 lias fully done so ; but notwithstanding this, from the exami- 

 nation of the skull alone, the latter would have appeared to 

 be the youngest. 



It cannot be admitted that O. Karelini and O. Ileinsii 

 grow twice as quickly as 0. Polii, and that at the same time 

 the bones of their skulls ankylose more slowly : the one seems 

 to disprove the other. It is more likely that the parts of 



15* 



