110 



553. The dental pavement of the under jaw of an JEtobates; two of the teeth or 



dental plates have been detached from the anterior worn end, to show their 

 chevron-shape and the grooved basis by which they adhere to the mandibular 

 cartilage. Hunterian. 



554. A portion of the mandible, with the dental pavement, of the jfitobates an- 

 gustm. Mm. Brit. 



555. Portions of the upper and lower jaws, with their dental pavements, of an JEto- 



bates. Hunterian. 



556. A portion of the dental pavement of the lower jaw of a large Eagle Ray 



(j&obates). 



The pores visible on the posterior fractured surface are the orifices of the medullary ca- 

 nals of the minute denticles, the aggregate of which denticles composes each of the transverse 

 dental plates : the antero-posterior parallel grooves on the under or attached surfaces of these 

 plates are well seen in this large specimen, together with the canals continued upwards from 

 the posterior part of the grooves, which canals lead to a continuous transverse channel run- 

 ning along the back part of the grooved basis of the tooth. The vessels and nerves of the 

 denticles pass out of the canal by the pores with which it is perforated. By this arrange- 

 ment the delicate vascular matrix is effectually defended from the superincumbent pressure 

 which is transmitted by the margins of the longitudinal lamellae beneath the dental canal 

 upon the jaw-bone. 



Hunterian. 



557. The dental pavement of the lower jaw of a large ^Etobates. Hunterian. 



558. The dental pavement of the lower jaw of an ^tobates. Mm. Brit. 



559. The dental pavement of the lower jaw of an ^Etobates. Mm. Brit. 



560. Two of the chevron-shaped dental plates of the mandibular pavement of an 



^Etobates. Hunterian. 



