HIPPOPOTAMUS TEETH OR TUSKS. 273 



the outer side, deeply furrowed in the centre on the inner side, and ridged 

 longitudinally, more especially on that portion of the tusk which is coated 

 with the enamel. The canines of the lower jaw are considerably larger, are 

 very much curved, like the tusks of a boar, and in shape somewhat 

 elliptical ; they are also ridged after tbe same fashion as those in the upper 

 jaw. 



Both the incisors and canines of this animal, although popularly 

 called teeth, are virtually tusks ; for they are uninterrupted in their growth, 

 are formed on cores, and consequently hollow for a considerable portion of 

 their length. 



The canine teeth, or tusks, of the hippopotamus, are primarily composed 

 of the two substances known as dentine, and enamel; the first-named 

 forming the principal body of the tusk, whilst the enamel is merely an 

 external shield, or tooth armour, of a denser and more durable material ; 

 and described as sufficiently hard to strike fire when contused with steel. 



The enamel is not continuous throughout the entire circumference of 

 these tusks, but only to the extent of from one-half to two-thirds of the 

 whole, and occurs on such portions, as apj)ear to be the most exposed to 

 injury : lengthwise, the enamel extends from end to end, and is formed anew, 

 in conjunction with the dentine, as the tusk grows. In thickness, the enamel 

 varies from l-32nd to l-16th part of an inch, according to the size 

 of the tusk. • River-horse, or hippopotamus teeth, contain less organic 

 matter (33-00) than either elephant ivory, or the tusk of the walrus, 

 in which substances, the organic elements amount to about 44-00 and 

 38-00 per cent, respectively. The chemical composition of these teeth, 

 as well as the essential difference between their dentine and enamel, 

 is advantageously illustrated in the following analyses by Thomson. 



Hippopotamus Teeth. 



Constituents. Enamel. Dentine. 



Organic Matter 4-102 33'41 



Phosphate of Lime 83-630 55-90 



Fluoride of Calcium 0-850 



Phosphate of 'Magnesia T19 



Carbonate of Lime 10-620 9-14 



Chloride of Sodium ) 



Chloride of Potassium J °' 80U °' 36 



Total 100-002 100-00 



Sp. gr. of the dentine, 1-866. 



A mere glance at the foregoing table, is sufficient to discover the more 

 prominent qualities of the teeth now under consideration. The larger pro- 

 portion of mineral matter in this dentine, coupled with great density of 

 formation, renders it both harder, and less liable to receive stains, than other 

 bone substances ; whilst, to the smaller amount of organic matter, and the 

 almost entire absence of oily particles, the delicate and superior whiteness tf 



T 



