178 AGE OF THE DOxMESTIO ANIMALS. 



About Three Months. — Sometimes just before and sometimes 

 just after three months from the birth of the animal the fourth 

 (first permanent) molar appears, that of the lower jaw preceding 

 that of the upper by a week or more. 



Three to Nine Months. — During this half-year no characters 

 of substantial value can be found. The incisors during this 

 period attain their full size, and, according to the herbage or 

 other food on which the animal has been fed, more or less wear- 

 ing of the anterior borders of the teeth has taken place. In 

 addition, however, to the general aspect of the animal, it is easy 

 to recognize the difference betweeft the fresher teeth, which have 

 scarcely been worn, of a lamb four to five months of age, and 

 the worn, broken, and loosening ones at eight, nine, or ten months. 



Ni7ie Months. — At nine months the fifth (second permanent) 

 molar makes its eruption. This fixes an important land-mark 

 in the determination of the age of the young animal. 



The fourth and fifth molars are formed of two principal 

 lobes, each with two points of enamel, so that there are four 

 points of enamel ; the internal points are higher on the lower 

 teeth, while the external ones are longer on the upper teeth. 

 These points become used, and as they are worn away the band 

 of central enamel is separated from the outer border of the teeth 

 by a larger area of dentine. 



The character of the points of enamel on these teeth, or 

 the distance of the bands of enamel from the outer border of the 

 teeth, thus indicates whether the animal has just passed nine 

 months or is a year or more old. 



Ten Months. — At about ten months the body of the maxilla 

 is seen to be wider and broader, — due to the development of the 

 permanent pinchers, which press upon the roots of the tempo- 

 rary pinchers, producing absorption, and these latter are found 

 less solidly fixed in their alveolae. 



Eruption of Permanent Teeth. 



One Year to Fifteen Months (Fig. 168, 1). — At this period 

 the permanent pinchers make their appearance. In the more 



