216 DE. EMBLETOX AND ME. ATXHEY OX THE 



plate of enamel, and encloses the small prolongation of the pulp- 

 cavity. 



Fig. 4 of the same plate is a transverse section near the top of 

 the wider part of the pulp-cavity, and above the cessation of the 

 radiating branches of the pulp-cavity ; the arrangement of the 

 dentine is still peculiar. 



In Plate IV., fig. 5 represents a transverse section of a maxil- 

 lary tooth (marked in Plate II., left side of figure, "section"), 

 made a little below the borders of its alveolus, which are of equal 

 height. In the centre is the somewhat oval pulp-cavity, which 

 is pretty large as compared with that of Ldbyrintlio&on Jozgeri, 

 figured in Prof. Owen's " Palaeontology ;" from it pass off, ra- 

 diating towards the periphery, numerous channels, separated 

 from each other by the inwardly projecting plicae or * ' inf oldings" 

 of the external layers of the tooth. The pulp-cavity and its 

 radiations, being clear and colourless spaces, contrast well with 

 the plicae, which are brownish yellow, the osseous tissue around 

 the tooth being of a lighter yellow. 



The solid part of the tooth appears in the section to be arranged 

 as a nearly circular series of toothlets or denticles, whose exter- 

 nal margins or crowns, rounded but somewhat flattened, consti- 

 tute the ridges seen on the outside of the tooth ; they vary a 

 good deal in size, and in one specimen number forty-one, in 

 another forty-three. The concave internal margins, facing the 

 centre of the tooth, correspond to and embrace the rounded, 

 somewhat expanded ends of the radiations of the central pulp- 

 cavity, each of which serves as the pulp-cavity of a toothlet, 

 whose fangs are on each side of the space : each side of every 

 toothlet is incorporated with that of its next neighbour; and 

 these united are inflected towards the central pulp-cavity form- 

 ing the plica:, which divide the radiations of the pulp-cavity 

 from each other ; these plicae are, of course, sections of the ver- 

 tical plates shown at fig. 2 in Plate IV. 



They vary much in length, the longest forming, by their 

 inner ends, a series of more than twenty blunt projections, like 

 radii of a circle, pointing to the centre of the pulp-cavity ; the 

 shortest are mere mammillary processes, enclosed between the 



