1885.] 



MR. J. B. SUTTON ON HYPERTROPHY. 



441 



the dorsum of the beak ; and from the smooth appearance of the 

 anterior border and inner surface of each shaft, it is evident that 

 they must have rubbed against each other, or against the beak 

 during the movements of tlie lower jaw in the act of opening the 

 mouth." 



Besides this specimen, Prof. Turner also received the skull and 



Fig. 8. 



A magnified vertical transverse section through the summit of the shaft of the 

 tooth of the adult Mesoplodo'n layardi. The tooth is made up of the 

 following tissues, from above downwards : a. cement ; h, vaso-dentine ; 

 e. a layer of more opaque modified vaso-dentine ; d, dentine ; e, modified 

 vaso-dentine of the centre of shaft. (After Turner.) 



parts of the skeleton of an immature Mesoplodon layardi, which en- 

 abled him to determine the nature of the various parts of this strange 

 tooth. Each tooth in this immature specimen was two inches from 



