556 UNGULATES. 



(PI. 140, fig. 2, m 3) does not come into place until all the 

 deciduous teeth have been shed ; it is the last molar : the cavity 

 in the lower jaw figured by Home, ' Lectures on Comparative 

 Anatomy,' Vol. ii, PI. 27, fig. 3, as " a new cell formed for a 

 succeeding tooth," is a medullary cell of the osseous tissue, not 

 a closed alveolus with a tooth-germ. 



In the Phacochere the first small and simple equivocal 

 premolar is not developed in either jaw. The three deciduous 

 molars are present in the upper jaw, but only two, the second 

 and third, in the lower jaw, of a young Phacochcsrus Mliani 

 with the deciduous incisors still retained, and the second 

 true molar not yet protruded : nor is there any trace of an 

 alveolus of the first deciduous molar of the lower jaw, which 

 may, therefore, be transitorily manifested, ' en germe' and never 

 functionally developed. With this reduction in number, the 

 deciduous dentition of the Phacochere, nevertheless, departs much 

 less from the typical characters of the Suidae than does the 

 dentition of the adult. The three milk molars of the upper jaw 

 present the same degree of increase of size, as do the three true 

 molars of the Wild Boar. But the first is much more simple, has 

 a compressed crown three lines long, supported by two fangs : the 

 second milk-molar has a triangular crown broadest behind, and is 

 supported by one anterior and two posterior fangs ; the third is 

 subtetragonal, wuth a grinding surface of six lines by four lines, 

 •with a central enamel island, surrounded by six somewhat larger 

 islands; it is implanted by four fangs. The same cause, viz. the 

 large matrix of the tusk, w^ould seem to have drawn off the 

 supply from the first and second premolars, and to have prevented 

 their development; the third and fourth premolars, which have 

 been above described in the ^lian Phacochere are more simple, 

 especially the fourth, than the teeth which they displace. The 

 last deciduous molar in the lower jaw (PI. 141, fig. 1, c? 3) very 

 closely resembles in size and shape the corresponding tooth in the 



late, in the upper jaw ; but with regard to the lower jaw, he says ' peut-etre meme n'est-elle 

 jamais remplacee en has,' (Ossemens Fossiles, 4to. 1822, torn, ii, pi. 1.) I have not, hitherto, 

 found a successor to the small tooth in question, unless the above-cited Indian Wild Boar be 

 regarded as an instance, but aa this tooth/) 1' has not displaced p \, it seems rather to be an 

 a noma lous or supernumerary premolar. 



