JAW OF KITTEN 169 



tend throughout the thickness of the enamel 

 and are generally perpendicular to the surface 

 of the ivory they cover. The cement or bone 

 of the tooth does not differ structurally from 

 ordinary bone, excepting that it rarely contains 

 Haversian canals. 



The photo-micrograph from which the illus- 

 tration (Fig. 52) was taken shows an ampli- 

 fication of 15 diameters ; the focal distance 

 was 50 inches; and the f-inch objective was 

 used. 



In the next illustration (Fig. 53) we have 

 represented a vertical section through the jaw 

 of a kitten. This shows the positions of both 

 the ' milk ' and the ' permanent ' teeth. 



The photograph shows an amplification of 

 26 diameters ; the focal distance was 84 

 inches ; the time of exposure to gaslight was 

 10 minutes; and the objective used was the 

 3j-inch. 



