8 A MANUAL OF DENTAL ANATOMY. 



pointed out, the armadillo has a bilobed tooth germ, the 

 one cusp predominating over the other. But I do not think 

 that we have at present the data upon which to cer- 

 tainly determine the fundamental form of the mammalian 

 tooth. 



There is evidence that all the teeth in the jaw of a 

 mammal may have been derived from a single form; in 

 other words, marked though the distinction between in- 

 cisors, canines, bicuspids, and molars seems to be at first 

 sight, a closer inspection reveals various gradational or 

 transitional characters linking them together, though there 

 are gaps in the chain not bridged over by forms known to us. 

 This may be seen by a careful study of the human teeth, as 

 I shall endeavour to show; but it is much more conspi- 

 cuously seen in an extinct animal (Homalodontotherium, 

 an extinct ungulate from Patagonia, described by Professor 

 Flower, Philos. Trans. 1874), which apparently possessed 

 the fall typical number of mammalian teeth, viz., forty-four. 

 The point in which its dentition is chiefly instructive is that 

 the teeth, in close juxtaposition one with another, present 

 an exceedingly perfect gradation of form from the front to 

 the back of the mouth, no tooth differing markedly from 

 its neighbour, though the difference between, say, the first 

 incisor and first molar, is exceedingly great. In Professor 

 Flower's words, " it is only by the analogy of other forms 

 that they can be separated into the groups convenient for 

 descriptive purposes, designated as incisors, canines, premo- 

 lars, and molars." 



In viewing the gradational characters which do exist be- 

 tween the various human teeth, it must not be forgotten 

 that some links in the chain have dropped out and are 

 absent. Mention has already been made of the full typical 

 number of mammalian teeth being 44, i.e. 



I. c. Imxn, = 44. 



