566 



ZOOLOGY 



SECT. 



vertical folds of enamel, the interstices between which may be 

 filled up with cement, and the worn surface of the tooth presenting 

 a pattern of the selenodont type (Fig. 1181, V). In the Camels 

 there are a pair of upper incisors and a pair of large canines in 

 each jaw. 



In the Perissodactyla the molars and pre-molars form a con- 

 tinuous series of large teeth with ridged or complexly-folded 

 crowns, the posterior pre-molars often differing little in size 

 and structure from the molars. In the Horse (Fig. 1193) the 

 formula is — 



• 3 1 4 3 , , 



but the first pre-molar is a small tooth which soon becomes lost, 

 and may belong to the milk-dentition. A fold of the enamel 



jEia 



Fir., lins.— Side view of skull of Horse with the bone removed so as to expose the whole of the 

 teeth, c. canine ; F7\ frontal ; ii. i^. is. incisors ; X. lacrymal ; Ma. ]"ugal ; Mx. maxilla ; 

 ml. liA m3. molars ; ]:^a. nasal ; oc. occipital condyle ; Pa. parietal ; p. ml. situation of the 

 vestigial first pre-molar, which has been lost in the lower, taut is present in the upper jaw ; 

 y)i/i2. yin^, pm^. remaining pre-molars ; PMx. pre-maxilla ; p2^. par-occipital process ; Sq. 

 squamosal. (After Flower and Lydekker.) 



dips downwards {i.e., towards the root) from the extremity of the 

 incisor teeth like the partly inverted finger of a glove ; the 

 canines are small in the female, and may not appear on the sur- 

 face. There is a wide interval in both jaws between the canines 

 and pre-molars. The pre-molar and molar teeth present a com- 

 plicated pattern due to folds of the enamel, which differ in their 

 arrangement in the upper and lower jaws ; their roots become 

 completed only at a late period. 



