58 Royal Society. 



No. of grinding 

 Phase. 



I, 



). of grinding 

 teeth. Kinds of teeth. 



4_4 ' \ d 3, d 4, m 1 , m 2. 



1L 6-6 yiz Jp2,p3,p4> 9 ml, m2,m3.- 

 5_5 * \ jt? 3, p 4. m 1 , m 2, m 3. 



jjj 5-5 . fp3,p4;ml,m%m 3. 

 4Z4 * \jt? 4, m 1, m 2, m 3. 



4—4 

 IV. viz. » 4, ml, m 2, m 3. 



4-4 r 



V. — viz [ p S 'P 4 '' m 2 > m 3 ' 

 3-3 ' \ p 4, m 2, m 3. 



VI. ?Z? viz. » 4, m 2, m 3. 

 3-3 



VII. -^- viz. » 4, m 3. 



2-2 ■* 



VIII. — viz. m 3. 



These observations prove that, contrary to the opinion of Home 

 and Cuvier, the Wart-hogs have deciduous teeth, succeeded verti- 

 cally by premolar teeth; in the Phacochcerus jEliani, at least, 

 three deciduous teeth are, in some individuals, succeeded by as 

 many premolar teeth ; and, as a general rule, two deciduous teeth 

 are displaced vertically by two premolars. The first true molar is 

 remarkable for its unusually early development, which is followed 

 by an unusually early abrasion and expulsion, when its place is ob- 

 literated by the second true molar being pushed forwards into con- 

 tact with the last premolar. This tooth is as remarkable for its 

 longevity, and remains after the wearing away and shedding of the 

 second true molar, when the last true molar advances into contact 

 with the last premolar, and the place of both the previously inter- 

 vening true molars is obliterated. This unusual order of shedding 

 of the molar teeth has given rise to the idea of the last large and 

 complex true molar of the Phacochcerus being the homologue of 

 both the last and penultimate grinders of the common Hog, which 

 the author's observations refute ; and he, also, is able to point out, 

 by re-examination of the original specimen figured by Home in the 

 Phil. Trans., the source of the erroneous idea that the common Hog 

 had an additional true molar behind the large one symbolised by 

 m 3, in the author's system of dental notation. 



The nature and signification of the symbols proposed are ex- 

 plained and illustrated by a series of drawings. One of the fruits 

 of the determination of the homology of a part is the power of gi- 

 ving it a name, and signifying it by a symbol applicable co-exten- 

 sively w T ith such homology. The limits are shown within which 

 the homologies of individual teeth can be determined : they present 



