THE HORSE. 



55 



" At twenty-one the lateral teeth are also 

 flattened." 



Professor Passini * " systematically di- 

 vides the lifetime of the horse, which he 

 computes at thirty years, into six periods, 

 that take their rise from and are determined 

 by an equal number of changes the teeth 

 naturally undergo, in regular succession. 



" The first period is that during which 

 the animal retains aU or any of his milk 

 teeth ; it extends irom birth to the fifth year. 



" The second period includes the sixth 

 year, and continues so long as the marks 

 remain visible upon the faces of the pos- 

 terior incisors; which is generally about 

 three years. 



" In many instances, however, and espe- 

 cially among horses that have been kept at 

 pasture, the faces of the front teeth, and 

 sometimes those of the middle, are worn off" 

 earlier. 



" The third period is that during which 

 the teeth retain the oval form. As the pits 

 and marks degenerate, the face of the tooth 

 slowly and gradually undergoes a deviation 

 of figure, from that of a pretty regular ellip- 

 sis, whose long to its short axis bears the 

 proportion of six to three, to an irregular 

 one, in which these proportions are as five 

 to four. This period requires, on an aver- 

 age, the space of six years for its comple- 

 tion ; the front teeth enter it in the seventh 

 and conclude it at the expnation of the 

 twelfth ; the middle pass through it one 

 year later ; and the lateral, or side teeth, one 

 year later still. 



" In the fourth period the faces of the 

 teeth assume a circular figure, and hence 

 have been denominated round. At the 

 commencement of this period, the breadth 

 of the face to its thickness is as 5 to 

 4 ; at the conclusion, it measures in an 

 inverse ratio, as 4 to 5 ; about the middle 

 of it, the diameters are equal. This period 

 also endures six years ; so that the front 

 teeth, which enter it in the thirteenth year, 

 complete it by the expu-ation of the 

 eighteenth ; the middle follow one year 

 later ; the lateral, one year later still. 



* See Percivall's Lectures. 



. " During the fifth period, the face of the 

 teeth deviates by slow degrees from the 

 round, and passes into the triangular state. 

 In the beginning, its thickness exceeds its 

 breadth as 5 does 4 ; in the end, as 6 does 

 3. It is the professor's opinion, yet uncon- 

 firmed by experience, that this period, like- 

 wise, on an average, includes a space of six 

 years; the front teeth, therefore, complete 

 it with the twenty-fourth, the middle with 

 the twenty-fifth, and the lateral with the 

 twenty-sixth years. 



" The sixth and last period is one, in the 

 course of which an additional angle is 

 projected from the anterior or inferior part 

 of the tooth ; Pessina distinguishes it by 

 the epithet biangular ; he has never met with 

 a horse that had lost his teeth from age ; 

 but he has seen their faces eUiptrical con- 

 trariwise, looking outwards or forwards. 

 This period is unlimited. 



" In the anterior, or upper jaw, the marks 

 disappear from the front teeth in the course 

 of the ninth year ; from the middle in the 

 tenth; and from the lateral in the elev- 

 enth. 



" What progress these upper teeth have 

 not made in transformation during the 

 second period, equivalent with the poste- 

 rior, they gain it in the third ; notwith- 

 standing the depth of pit, their proportions 

 are then the same. They continue three 

 years longer in the second, and consequently 

 are only three in the third period ; so that, 

 by the twelfth year, the third period is 

 completed by the front upper teeth, and 

 so on. During the fourth, fifth, and last 

 periods, the changes are alike, and equally 

 perceptible in either jaw. 



" So far, th^ upper teeth are entitled to 

 an equal share of our regard; though, in 

 the generality of cases, they need not be 

 inspected. In such a remarkable man- 

 ner the lateral teeth of the upper jaw wear 

 away so that they often appear as if 

 notched or indented. 



" In regard to the tusk or tush, Pessina 

 remarks that he has found the least regu- 

 larity in its changes of any tooth. The 

 very facts that the tushes are not in all 



