'ig. 32. Designation of teeth 



A. Lower jaw of colt 9 months and 12 days old, miirked to show designation of deciduous teeth 



B. Lower jaw of horsi 5 years old marked to show designation of permanent teeth 



In works on comparative anatomy and zoology the teeth are ex- 

 pressed by initial letters and numbers in fractional form ; the numerator 

 denotes the number of upper teeth, and the denominator the number of 

 lower teeth of each class, running back from the median line in front, 

 and considering only one side of the skull. For instance the typical 

 mammahan milk dentition is as follows, all being deciduous teeth: in- 

 cisors three, canine one, molars four, which would be expressed d. i. t, 

 d. c. \ d. VI. '\. The permanent dentition would be i. f , c.l, p. 7n . ^, and m . i 

 — forty-four teeth in all. The human subject having only thirty-two 

 permanent teeth, would be expressed i. f , c. i, /;. m. 1, and m. 1. 



The teeth are numbered from the median line, hence when indicating 

 a certain tooth /. t would be read, lower incisor three; p. m. - upper pre- 

 molar four; lower deciduous canine is expressed d. c.-^. Figure 32 shows 

 the designation of deciduous and permanent teeth. A is the lower jaw of 

 a colt nine months and twelve days old, in which the deciduous dentition 

 is all in use, and though the eruption of the molars has not yet begun, the 

 development of one at least is well under wa^^ In B, a horse about five 

 years old, the permanent teeth are all in place. It must be borne in mind 

 that when a subject has a reduced dentition the teeth are numbered not 

 necessaril}^ as they appear in the jaw, l^ut according to what is l)elieved 

 to be their true relation in the typical dentition, having forty-four teeth. 

 For instance, in the human subject where there are but two premolars 



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