AETIODACTYLA. 445 



enamel of the front and middle incisors show complete 

 rings. Tushes quite out of gum. 



10. At six years. — Inner edge of corner incisors worn flat, 



central enamel in complete ring. Tables of front 

 incisors oval. The cement of the front incisors has 

 nearly gone. 



11. At seven years. — The posterior edge of the lower corner 



incisor is well in advance of that of upper jaw, giving 

 the upper incisor a hook-like projection. 



12. At eight years. — Lower incisors with obHque direction. 



A yellow transverse line — the dental star — is well 

 marked in the front incisors. 



13. At ten years. — Tables of front and middle lower incisors 



become rounded and the central enamel triangular. 

 The front incisors also have become longer and nar- 

 rower, and more or less triangular in shape. This 

 becomes more and more advanced with age. 



14. At thirteen years. — Central enamel has nearly gone from 



lower incisors. 



15. At ttventy-one years. — The middle and corner incisors 



converge inwards. 

 16 At thirty years. — The incisors are in nearly a straight 

 line, and the tables are broadest from the front to 

 the back. 



Section 2. Artiodactyla. 



Toes even in number, either two or four. The functional 

 axis passes between the third and fourth toes. Dorso-lumbar 

 vertebrse nineteen, and there is no third trochanter to the 

 femur. The horns when present are always supported on 

 bony cores or projections from the frontal bones of the skuU 

 (fig. 215, 3). The stomach is (with the exception of one group) 

 more or less complex, there being several divisions, some of 

 which are probably dilatations of the oesophagus ; the caecum is 



