276 ELEMENTARY ANATOMY. [LESS. 



section of the tooth presents such a complex series of radiat- 

 ing contorted lines as to have obtained for the animals their 

 name, and for the kind of tooth the epithet Labyrinthic. 



A third kind of complex tooth is presented by one Mammal 

 only, though certain Fishes present a more or less similar 

 structure. The animal referred to 

 is the Cape Ant-eater (Orycteropus\ 

 which possesses the only really com- 

 pound teeth found amongst Beasts. 

 Each tooth is cylindrical in shape, 

 and apparently simple, but when 

 cut transversely exhibits a number 

 FIG. 254.-THE AARPVARK, of minute apertures, as does a cut 

 OR CAPE ANT-EATER. cane. Each of these apertures is the 



(prycteropus). ,orifice of a pulp-cavity cut across, 



and from each of these cavities 



minute dentinal tubuli radiate in every direction, so that 

 the tooth is really made up of a number of very elongated 

 and slender denticles anchylosed together into one solid 

 mass. 



FIG. 255. TRANSVERSE SECTION OF A TOOTH OF Orycteropus, showing the 

 numerous denticles, each with its pulp-cavity. 



True teeth do not co-exist with a horny beak in any 

 known Mammal. They did so, however, in some of those 

 extinct flying Reptiles the Pterosauria, and also the extinct 

 Reptiles Dicynodon had a tooth which grew from a perma- 

 nent pulp on each side of the head, though tlie jaws seem to 

 have been furnished with a horny beak. 



34. Enderonic calcifications which can hardly be called 

 teeth may occur further back in the alimentary canal than 

 anything we have yet met with. In a little African Serpent, 

 Rachiodon^ certain bony processes which depend from the 

 ventral surface of the backbone penetrate the gullet and are 

 tipped with a kind of enamel. These cesophageal * teeth per- 



1 (Esophagus is the name of the passage which leads from the "back of the 

 mouth (or pharynx) to the stomach. 



