333 Royal Tiistitution. 



blade is trilobate, but both the anterior and posterior smaller lobes 

 are notched, and the internal tubei'cle, which is relatively larger than 

 in the permanent sectorial, is continued from the base of the middle 

 lobe, as in the deciduous sectorial of the Dog and Hysena ; it thus 

 typifies the form of the upper sectorial, which is retained in the per- 

 manent dentition of several Yiverrine and Musteline species. The 

 third or internal fang of the deciduous sectorial is continued from 

 the inner tubercle, and is opposite the interspace of the two outer 

 fangs. The Musteline type is further adhered to by the young Feline 

 in the large proportional size of its deciduous tubercular tooth. In 

 the lower jaw, the first milk-molar is succeeded by a tooth which 

 answers to the third lower premolar in the Dog and Civet. The 

 deciduous sectorial, which is succeeded by the premolar, answering 

 to the fourth in the Dog, has a smaller proportional anterior lobe, 

 and a larger posterior talon, which is usually notched ; thereby 

 approaching the form of the ])ermanent lower sectorial tooth in the 

 Mustelida;. The last tooth which is functionally analogous to the 

 carnassial above, is the first of the true molar series, and is the 

 homotype of the little tubercular tooth above. 



The true nature of the dentition of the Lion and other Felines, 

 as determined by the above pha^i^omena of development, is : — 



. 3—3 1—1 3—3 1—1 .... ,1 , ,, o • 



I. o~y (^- jziT> P- 5Zl2' ^'^^' TUT • sigmiying that there are 3 m- 



cisors, 1 canine, 3 premolars, and 1 molar, on each side of the 

 upper jaw, and the same, with the exce})tion of a small premolar, 

 on each side of the lower jaw. The teeth, Avhich are the seat of 

 the sectorial or carnassial modifications, are not homologous or 

 homotypal in the two jaws. 



In the genus Ursus the dentition was, in like manner, shown to 

 , . 3—3 1—1 4--4 2—2 ,„ 



In the Hog, four deciduous molars are succeeded by four 

 premolars, vertically ; and three molars are developed in hori- 

 zontal succession behind these, the dental formula being : — 

 . 3_3 i_i 4_4 3— 3_ .. 

 *• 3—3' ^' 1—1' P' 4—4' ''"" 3—3 ~ 



This number of teeth is never surpassed in the Diphyodont series ; 

 and the Lecturer regarded it as the typical dentition. It is, however, 

 rarely maintained in existing species, but appears to have been much 

 more common in extinct Mammalia, especially those from the most 

 ancient tertiary epochs ; illustrations of which were given in the 

 Hycenodon and Hyopotamus, and examples cited in the extinct 

 genera Chceropotamus, Anthracotherium, Hyracotherium, Oplothe- 

 rium, Merycopotamus, Hippohyus, Aaoplotherium, Pulceotherium, 

 and Paloplotherium. In the three latter genera, Professor Owen 

 had determined the nature of the molar series to be the same as in 

 the Hog, by specimens showing the deciduous dentition. 



In the hoofed quadrupeds with toes in uneven number {Perisso- 

 dactyld), whose premolars, for the most part, repeat both the form 



