THE TEETH OF GET ACE A. 307 



into their composition, and forming as much as half the 

 bulk of the tooth. 



The Orycteropus, or Cape Ant-eater, the peculiarities of 

 whose teeth have already been alluded to, has about twenty- 

 six teeth in all ; the true ant-eaters are edentulous. The 

 teeth of some of the gigantic extinct Edentates were a little 

 more complex in form and structure ; thus the teeth of the 

 Glyptodon were divided by longitudinal grooves, which in 

 section rendered it trilobed ; and the teeth of the Mega- 

 therium were likewise marked by a longitudinal furrow. 



In their persistent growth, uniformity of shape, and 

 absence from the inter-maxillary bone, they strictly con- 

 formed with the teeth of recent Edentata. 



THE TEETH OF CETACEA. 



No cetacean is known to develop more than one set of 

 teeth, and these, when present in any considerable numbers, 

 closely resemble one another in form. 



They are usually composed of hard dentine, with an in- 

 vestment of cement; after the attainment of the full 

 dimensions of the tooth what remains of the pulp is very 

 commonly converted into secondary dentine ; tips, and even 

 entire investments of enamel, are met with in many of the 

 order. 



The dentine of many Cetaceans, e. g. of the sperm whale, 

 is remarkable for the very numerous interglobular spaces 

 which it contains ; these are clustered in concentric rows, 

 so as to give rise to the appearance of contour lines. The 

 cement is often of great thickness, and the lacunae in it are 

 very abundant ; its lamination is also very distinct. 



In the dolphin the teeth are very numerous, there being 

 about 200 ; they are slender, conical, slightly curved in- 



x 2 



