93 COMPARATIVE ANATOMY. 



The dentition of the Mole is that of the'typical formula ; 

 small as this skull is, it contains 44 teeth. 



Notice the large tympanic bones, indicating its acuteness of 

 hearing, its powers of vision being very feeble. 



The Rodents are divided in the table into two classes 



Non-claviculata 



Claviculata. 



The most striking characteristic, as you may' see in this 

 squirrel's skull, is the peculiar formation of the incisor teeth. 



They are made like a chisel, having a hard plate of enamel 

 in front, which is kept constantly sharp by use. 



As these teeth would soon wear away, if not renewed, they 

 keep continually growing from the roots throughout life. 



As a consequence of this, if a rodent receives an injury 

 misplacing one of its incisors, the opposing tooth continues 

 growing in a circular direction until it penetrates the skull 

 into the brain and causes death ; showing us the" way in which 

 nature provides for the termination of the^. existence of an 

 animal, whose powers of feeding are considerably impaired. 



Instances of rabbits and hares that have thus perished are 

 by no means uncommon. 



The two succeeding classes the Marsupialia and Monotre- 

 mata, I will pass over, as they are entirely unrepresented in 

 Great Britain, and I have no specimens to show you. 



And now I beg to hand over to the custody of the society 

 this small but fairly representative series of mammalian skulls, 

 hoping that the members of our rapidly increasing body will 

 add to its number more specimens to fill up the gaps and 

 render the collection more complete. 



Above all things, I hope that these specimens may be 

 placed in a museum, so that they may be accessible to all for 

 the purposes of study. 



I hope that, if I have been unable to avoid technical lan- 

 guage, I have yet made clear to all of you the^broad dis- 

 tinctions wherein one class of animals differ from another. 



The subject may seem at first to be dry bones, but when 

 we begin to realise how much those dry bones tell us ; the 

 mill of the horse grinding the com ; the incisor of the 

 squirrel drilling a hole in the nut ; the tusk of the boar 

 tearing up the ground for food ; the tuberculated teeth of 

 the mole piercing the insect ; the scissorlike teeth of the cat 



