358 MICROSCOPIC ANATOMY OF THE TEETH 



this band is not shown, and this observation led the author 

 to examine these hinged teeth in fresh specimens and in 

 decalcified serial sections in order to make clear the mean- 

 ing of this appearance in the ground section. A fresh 

 specimen of this fish of unusually large size was examined, 

 and it was found that a probe could be passed through to 

 the pulp at the centre, but met with resistance to the right 

 and left of this position, showing that the tooth lies free 

 upon the bone only in the middle line of the pedestal. Teeth 

 were decalcified and examined in a series of sections from 

 one side of the tooth to the other. These preparations 

 showed that there is a band of fibrous tissue attached to 

 the tooth and bone on either side of the central opening. 

 On dividing the anterior bands in the fresh tooth, the tooth 

 resumed its position when depressed almost as well as when 

 these bands were entire, but it was unsteady on the pedestal, 

 and easily displaced laterally. Division of the posterior 

 hinge entirely prevented the return of the tooth to the up- 

 right position. The function of this anterior hinge would 

 thus appear to be the increase of the resiliency of the 

 whole structure and the prevention of lateral displace- 

 ment. In the figure in Tomes's Dental Anatomy, the section, 

 presumably a ground one, had been taken through the 

 centre of the longitudinal axis, and the anterior hinge con- 

 sequently is not shown. In Plate VI B a diagrammatic draw- 

 ing of the bone of attachment is shown, the tooth having 

 been removed. The upper part of this diagram represents 

 the elevated pad of bone or pedestal, and it is seen that the 

 pulp cavity is prolonged forward, forming a semicircular 

 hollow at the posterior margin of the pedestal. The two 

 bands which make up the anterior hinge reach from each 

 side only as far as this depression. The ridge of bone at r 

 is at a considerably lower level than the pedestal, and the 

 larger posterior hinge is attached to it, encircling the posterior 

 half of the tooth and bone. 



The structure of the posterior or principal hinge is shown 

 in fig. 238, photographed from a decalcified section. The outer 

 border of the dentine on the inner side of the tooth is con- 

 tinued downwards to its attachment to the bone, as is well 

 shown at k in fig. 238 and in Plate VI. This portion of the 



