INTRODUCTION. XXVll 



its extent as regards both its shape and structure. The partial 

 application of the enamel in these ' dentes scalprarii' operates in 

 maintaining a sharp edge upon the exposed and worn end of the 

 tooth, precisely as the hard steel keeps up the outer cutting edge of 

 the chisel by being welded against an inner plate of softer iron. 



In the herbivorous mammalia, with the exception of the Eden- 

 tata, vertical folds or processes of the enamel are continued into the 

 substance of the tooth, varying in number, form, extent and direction, 

 and producing, by their superior density and resistance the ridged 

 inequalities of the grinding surface on which its efficacy, in the tritura- 

 tion of vegetable substances, depends. 



In the development of a tooth, composed of the above-mentioned 

 differently organised tissues, a matrix of equal complexity was first 

 recognised to be concerned by John Hunter ; the several parts of this 

 matrix, here termed respectively the * dentinal pulp,' the * enamel 

 pulp,' and the ' capsule ' or ' ccemental pulp,' being first distinctly 

 indicated in the ' Natural History of the Human Teeth.' 



In this otherwise instructive and original treatise the reader will, 

 however, seek in vain for any definite or detailed account of the part 

 which each formative organ plays in the development of its corres- 

 ponding tissue, or of the development of the matrix itself. 



The latter subject has been chiefly elucidated by the observations 

 of Arnold(l), Purkinjeand Raschkow(2), Valentin(3), and Goodsir(4) : 



(1) Salzburg Mediz. Chirurg. Zeitung. 1831, ersterband, p. 226. 



(2) Meletemata circa Mammaliuin Dentium Evolutionem, 4to. 1835. 



(3) Handbucli der Entwickelungsgeschichte des Menschen, 8vo. 1835, p. 482. 



(4) On the Origin and Development of the Pulps and Sacs of the Human Teeth. Edinburgh 

 Medical and Surgical Journal, vol. li, p. 1. 



