374 ANATOMY OF VERTEBRATES. 



In the great extinct sabre-toothed Tiger, Machairodus, fig. 293, 

 vii., the series is still further reduced by the loss of p 2, in the 

 upper jaw. 



In the common Cat, the deciduous incisors, d i, begin to 

 appear between two and three weeks old ; the canines, d c, next, 

 and then the molars, d m, 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, m l , 

 and its tubercular homotype above, m l, appear before d 2, 

 d 3, and d 4 fall. The longitudinal grooves are very faintly 

 marked in the deciduous canines. The first deciduous molar, 

 m 2, in the upper jaw is a very small and simple one-fanged 

 tooth ; it is succeeded by the corresponding tooth of the perma- 

 nent series, which answers to the second premolar, p 2, of the 

 Hyaena and Dog. The second deciduous molar, m 3, is the 

 sectorial tooth ; its blade is trilobate, but both the anterior and 

 posterior smaller lobes are notched, and the internal tubercle, 

 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 Hyaena ; it thus typifies the form 

 of the upper sectorial, which is retained in the permanent den- 

 tition of several Viverrine 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, d 4. In the lower jaw, the first milk-molar, d 3, is suc- 

 ceeded by a tooth, p 3, which answers to the third lower pre- 

 molar in the Dog and Civet. The deciduous sectorial, d 4, 

 which is succeeded by the premolar, p 4, answering to the fourth 

 in the Dog, has a smaller proportional anterior lobe, and a 

 larger posterior talon, which is usually notched; thereby ap- 

 proaching the form of the permanent lower sectorial tooth in the 

 MustelidcB. 



When the premolars and the molars are below their typical 

 number, the absent teeth, as a rule, 1 are missing from the fore- 

 part of the premolar series and from the back-part of the molar 

 series. The most constant teeth are the fourth premolar and the 

 first true molar ; and these being known by their order and mode 

 of development, the homologies of the remaining molars and pre- 

 molars are determined by counting the molars from before back- 



1 In some instances the first premolar or first milk-molar remains, of small size, 

 when p 2 and p 3 are lost. 



