112 THE ENAMEL. 



large molar, according to the number of processes which they 

 present. Continuous deposition of the bony matter from the 

 membrane of the pulp, unites these points together, and by 

 degrees at different epochs, all the bodies are formed ; the pulp 

 retiring as it were, as the deposition of bone goes on and 

 encroaches upon its cavity, and elongates itself downward, 

 into the shape of the fang. This is finally formed in the same 

 manner as the bodies, and the pulp is completely enclosed in 

 the bony case of the tooth, except at the foramina where the 

 vessels and nerves enter. Where more than one fang exists to 

 a tooth, the lower part of the pulp, is previously divided into 

 an equal number of processes, by little bony partitions which 

 shoot across from the sides of the alveoli. 



Of the Enamel. 



— When the development of the bony shell has fairly begun, the 

 inner layer of the sac becomes thickened and more vascular, 

 receives a greater amount of blood, becomes closely attached to 

 the neck, and forms a loose capsule over the body. From the 

 internal face of this membrane,* is poured out a thickened 

 whitish granular fluid, called by Mr. Goodin the enamel organ 

 which Berzelius considers of the nature of lactic acid ; this is 

 speedily consolidated into a dark chalky substance, deposited 

 first upon the tips of bone, and gradually extending down in 

 layers till it covers the whole crown of the teeth. This is the 

 enamel. It becomes gradually whiter and harder, as though 

 by a more perfect crystallization, but (near to the period at 

 which the teeth are cut,) it is still so soft, as to be frequently cut 

 with the gum lancet. 



* Blake believed that in man, the enamel was formed solely by the inner 

 membrane of the sac. The external contributing nothing to the structure of 

 the teeth. But in graminivorous animals, where the flinty covering of the food 

 they feed on requires a more perfect grinding apparatus, he thought the external 

 membrane performed an important part, in adding another element to the struc- 

 ture of the molar teeth, called by him, crmta petrosa. The cutting teeth are 

 constructed as those of man. In these animals the enamel of the grinders does 

 not form a continuous smooth layer as in man, but passes a little way into the 

 body of the teeth, and is arranged in the form of vertical layers, between which 



