the cutting Teeth of the Rat. 



393 



fully formed, the 

 fang is added. This, 

 at first, consists of 

 a thin lamina of 

 ivory, extending 

 backwards : as the 

 anterior part of the 

 tooth, however, be- 

 comes worn down 

 by mastication, the 

 fangs and alveolar 

 processes are ab- 

 sorbed. Their place 

 is then filled by the 

 next lamina; and, 

 when the last lamina 

 of a grinder has advanced sufficiently to supply the place 

 of its predecessors, the anterior lamina of the next tooth 

 comes forward; and so on in succession. There is never 

 more than one tooth and part of another to be seen at once 

 in the same side of the jaw. (Jig. 51.) 



Should any of your readers wish to see a very full and 

 learned account of this mode of dentition, they will find it in 

 the first volume of Sir E. Home's Comparative Anatomy, from 

 which many of these remarks are taken. 



I am, Sir, yours, &c. 

 January, 1833. C . 



a, The old tooth ; rf, the second grinder, coming forward. 



Another Mention of an Instance of extraordinary Length in 

 the Incisor Teeth of a Rat. — Sir, The instances of extra- 

 ordinary growth of the incisor teeth in rabbits, already regis- 

 tered in Vol. II. p. 134., Vol. III. p. 27., and Vol. VI. p. 21., 

 induce me to mention that an instance of a similar condition 

 has been observed in a rat, as is shown by the following 

 account, copied from the Birmingham Chronicle into the 

 Kaleidoscope, a work published at Liverpool in 1822: — 

 " A rat was, a few days ago, found near this town, the death 

 of which had been occasioned by two teeth in the shape of 

 tusks ; one of which, it appeared, had penetrated the brain." 

 — James Fennell. London, May 20. 1833. 



