Royal Institution. 331 



an uninterrupted line marked ''Cuvier" was made to intersect the 

 teeth in each jaw of the Carnivora, called by that great anatomist 

 " carnassieres :" those anterior to them being the teeth which he 

 called **fausses molaires ;" those behind being the " tuberculeuses." 

 Most zoologists, both at home and abroad, have adopted the Cuvierian 

 system of formulising the molar teeth. Prof. De Blainville, however, 

 abandoned that classification of the molar series, without assigning 

 his objections to it ; and proposed another, in which he divides the 

 series into " avant-mol aires," " principales," and " arriere-molaires ;" 

 he exemplifies this division by the human dentition, in which the 

 five grinders on each side of both jaws are formulised as *' two 

 avant-molaires, one principale, and two arriere-molaires." The teeth 

 regarded by De Blainville as the homologues of these, were indi- 

 cated in the diagram above referred to by a dotted line intersecting the 

 ** dent principale " in each species. 



Truly homologous teeth are determined, like other parts, by their 

 relative position, by their connexions, and by their development. The 

 teeth of one side of the jaw repeat, are answerable to, or are homo' 

 types i of the teeth on the other side ; and those in the upper jaw 

 usually correspond, in like manner, to those in the under jaw. 



Those teeth which are implanted in the premaxillary bones, and in 

 the corresponding part of the lower jaw, are called " incisors," what- 

 ever be their shape or size. The tooth in the maxillary bone, which 

 is situated at, or near to, the suture with the premaxillary, is the 

 " canine," as is also that tooth in the lower jaw which, in opposing 

 it, passes in front of its crown when the mouth is closed. The first- 

 formed incisors and canines are deciduous ; they are succeeded and 

 displaced vertically by the permanent incisors and canines. With 

 regard to the other teeth, their true nature and homologies, about 

 which the difference of opinion has chiefly prevailed amongst anato- 

 mists, are determinable not by shape or size, or by relative position 

 to the zygoma, but by developmental characters exclusively. The 

 first set are the " deciduous molars ;" the teeth which displace and 

 succeed them vertically are the "premolars;" the more posterior 

 teeth, which are not displaced by vertical successors, but succeed 

 each other horizontally, are the " molars," properly so called. 



The phsenomena of the development and succession of the teeth 

 were then explained and illustrated in examples of Carnivorous, Her- 

 bivorous, and mixed-feeding species of Diphyodont Mammalia. 



Genus Felis. — In the Cat, the deciduous incisors begin to appear 

 between two and three weeks old ; the canines next, and then the 

 molars follow, the whole being in place before the sixth week. After 

 the seventh month they begin to fall in the same order; but the 

 lower sectorial molar and the tubercular tooth above, appear before 

 the deciduous molars are shed ; they do not push out any predeces- 

 sors, and have no successors ; they are, therefore, true molars. The 

 first deciduous molar in the upper jaw is a very small and simple 

 one-fanged tooth ; it is succeeded by the corresponding tooth of the 

 permanent series, which answers to the second premolar of the Hysena 

 and Dog. The second deciduous molar is the sectorial tooth ; its 



