90 



§ XVIII. Physiological Deductions. 



From the shape of a tooth may be inferred its work; a pointed one to pierce, a tren- 

 chantone to cut, a broad knobbed or ridged crown to bruise. But the kind of substances to 

 l>c pierced, cut, or ground demands other considerations than that of mere shape to deter- 

 mine. The chief of these is the kind of teeth with which the piercers, the cutters, or the 

 pounders may be respectively associated, more especially the first two. If the Palaeontologist 

 has no other part of the skeleton than a jaw with teeth to work from, the guiding principle of 

 correlation is correspondingly limited in its applicability. Cuvier's choice of tooth or class 

 of teeth as being of highest correlative value, or as throwing most light on the food and habits 

 of an unknown and extinct Mammal, still commends itself to my experience as the best. 



Guided by his rule,' my first attention was paid to the molar teeth of Plagiavlax. 

 These are too few, too small, and occupy too short a space in the dental series to 

 perform the effective kind and amount of mastication required for the preparatory act of 

 digestion of vegetable substances. 



Known only as they exist in the lower jaw, the analogy of Tlujlacoleo teaches that they 

 would not be in greater, were more likely to be in less number, in the upper jaw ; accordingly, 

 the inference of their functional relations to food may be legitimately drawn. 



Every known instance of a like condition of tubercular molars points to the 

 modifications of the rest of the dental series for predatory life and animal diet. And this, 

 as regards the mandibular dentition of Plagiaulax, we have seen to be the case in every 

 species and variety. 



A pair of teeth, placed favorably at the fore part of the jaw, manifest the length, strength, 

 sub-compressed, sub-recurved, pointed form of the laniaries of the Carnivore, and suggest 

 the application to seizing, piercing, lacerating, slaying. The major part of the alveolar 

 tract is occupied by teeth of the trenchant carnassial or shear-blade type. 



There are few instances in which the sagacity of Cuvier in directing primary attention 

 to the ' dents molaires ' is better exemplified than by the small extinct Mesozoic Marsupial 

 under consideration. 



The Musk-deer has a pair of canines almost as formidable for lethal purposes as the 

 upper ones of Machairodus. The Gorilla has canines in shape and proportion like those 

 of the ordinary large Carnivora ; the Baboon adds to them the secondary feline characters 

 of longitudinal grooves and the trenchant ridge ; but the tyro taking these teeth only for 

 his guide or basis of physiological reasoning would be led astray. 



The light-giving teeth in each case, by their massive cubical crowns, complex 

 configuration and structures, number, and large proportion contributed by them to the 



1 " La premiere chose a. faire dans 1'e'tude d'un animal fossile est de reconnoitre la forme de ces dents 

 molaires ; on determine par la s'il est carnivore ou herbivore." — Cuvier, ' Recherches sur les Ossemens fos- 

 siles,' 4to (1822), torn, iii, p. 1. 



