THE TEETH, THE TONGUE. 45 
What is the structure of enamel ? 
It is composed of elongated, hexagonal prisms, set vertically. These 
prisms are marked by slight transverse shadings. 
What is the structure of dentine ? 
It is composed of a hard, calcareous material resembling bone, but 
having no lacunze or Haversian canals. It is pierced everywhere by 
fine canaliculi radiating out from the central cavity of the tooth. This 
cavity contains the tooth pulp. Along the sides of this pulp cavity lie 
round or oval cells which send branches into the canaliculi in the 
dentine and also into the pulp. They are the analogues of bone cells, 
and are called dentine cells or odontoblasts. 
Describe the tooth pulp. 
It is a soft, vascular tissue containing nerve fibres and irregular- 
shaped and branching cells. 
What is the cement or crusta petrosa ? 
It is a layer of lamellated bone having lacune and canaliculi but no 
Haversian canals. This layer surrounds the root of the tooth. 
THE TONGUE. 
What is the structure of the tongue ? 
In great part it is composed of striated or voluntary muscle fibres. 
It is covered with mucous membrane, the surface of which, as in the 
rest of the mouth, is covered with stratified epithelium. The free 
surface of the tongue is covered with small papille called conical and 
Jiliform papillz. Scattered here and there are larger or fungiform 
papilla. Near the base of the tongue there are twelve or thirteen 
large papillee arranged in a V shape and called circumvallate papille. 
Between the superficial muscular fibres, small tubular glands may be 
seen, running to the surface of the tongue. 
Describe these different papille. 
The fungiform papille are capped with stratified epithclium, while in 
the filiform variety the papilla: are fringed with fine filaments springing 
from the epithelial cells covering them. The circumvallate papille 
project above the mucous surface of the tongue and are surrounded by 
a groove. They are covered by stratified epithelium. 
What are taste buds ? 
They are small, oval clusters of epithelial cells situated in the 
covering of the sides of the circumvallate papillae. These taste buds 
