476 DE. H, W. MAEETT TIMS ON THE 



With regard to these smaller cusps it is difficult to express 

 any opinion as to the precise order of evolution, as the results, 

 both palseontological and embryological, are at present somewhat 

 conflicting. 



It will be noticed that I have reserved the term Cone for that 

 which I regard as the representative o£ the Reptilian tooth and 

 to its secondary derivative ; while the term Cusp I have applied 

 to the remainder, all of which I regard as having been developed 

 upon the cingulum. 



Table III. gives the order of evolution of the cones and cusps 

 according to this view, and also the cusps with which they cor- 

 respond, according to the system of nomenclature now in vogue. 

 It will be readily understood that it is impossible fully to deal 

 with this question in a small space, as, from what I have attempted 

 to show above, cusps bearing the same name in different teeth, 

 and even the same teeth in different species, are in reality not 

 homologous. I have therefore confined myself almost entirely 

 to a consideration of the teeth in the Canidse. 



Table III. 



Showing the order of development of the Cusps according to 

 the Theory of Cingulum-cusp Development and the Cusps which 

 they represent in the Upper and Lower Jaws of the Dog. 



1. Primary Cone Paracone, Protoconid. 



'' 2. Anterior Oingulum- Usually remains minute ; Eemains minute in all ex- 

 cusp, forma the Protocone of cept the lower carnassial, 

 the upper premolars. in which it forms the Para- 

 ] eonid. 

 j 2. Posterior Cingulum- Forms posterior part of Minute. Enters into the 

 \^ cusp. the Metacone. formation of the Hypo- 



conid at its posterior part. 



3. Centre - Internal Absent in the premolars. Absent in premolars. Forms 



Cingulum-cusp. Forms the Protocone of Metacoid. 



dpm.4 and the heel of 5^^. 



4. Secondary Cone . . . Anterior part of Metacone Anterior part of the Hypo- 



in the premolars and conid and postero-external 

 almost the entire Meta- cusp of molars, 

 cone in the molars. 



Having thus given a brief outline of what may be termed a 

 Theory of Cingulum-cusp development, it is necessary to ex- 

 amine how far such a theory is borne out by Palaeontology and 

 Embryology. 



(i.) Palceontological evidence. — Starting from the Haplodont 



