28 

 tion, is obvious, so is it tlie more strange that the 

 thick coating of the crusta petrosa around the molars 

 should by authors have been mistaken for an accu- 

 mulation of tartar. The mistake was certainly extra- 

 ordinary, as the crusta petrosa in the horse's tooth is 

 of physiological importance, and will presently be 

 shown to merit the attention of the pathologist. I 

 am aware, when making this statement, that contra- 

 diction is offered to the opinions of many and deser- 

 vedly esteemed authorities ; and while I regret the 

 necessity of differing with such writers, I also lament 

 that my opinion as to the supposed use of the outer 

 membrane of the newly-developed organ, does not 

 coincide with theirs. The nature of this treatise will 

 not allow me to enter into the subject of the deve- 

 lopment of the teeth ; but I may here say, that the 

 outer membrane has been generally stated to secrete 

 the enamel. It is that membrane which, thickening 

 with the growth of the tooth, becomes the crusta 

 petrosa; but with regard to its secretive powers, I do 

 not imagine it is endowed with any function of that 

 description, or that it is in any way concerned in the 

 production of the enamel. My reasons for making 

 such and so bold an assertion are well considered, 



