Osteology of Loxomma AUinanui. 55 



"sectton^^), 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 Lahyrinthodon Jcegeri, figured in Prof, Owen's '■ Palaeon- 

 tology;' from it pass off, radiating towards the periphery, 

 numerous channels, separated from each other by the inwardly 

 projecting plica3 or " infoldings " of the external layers of the 

 tootli. 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 tootli appears in the section to be 

 arranged as a nearly circular series of toothlets or denticles, 

 whose external margins or crowns, rounded but somewhat 

 flattened, constitute the ridges seen on tlie 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 mar- 

 gins, 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 forming the plicee, which divide the radiations of 

 the pulp-cavity from each other ; these plicse are, of course, 

 sections of the vertical plates shown at fig. 2 in Plate VII. 



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

 inner ends, a series of over twenty blunt projections, like radii 

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

 shortest are mere mammillary processes, enclosed between the 

 bases of the longer ones ; and there are others of intermediate 

 but different lengths. They pass in from the periphery at 

 first, for a short distance, straight, but soon form undulating 

 and then zigzag curves, which continue to the end, where, 

 in places, two or more may be seen united. 



Each concavity on the undulating sides of the plica? answers 

 to a secondary offset of the pulp- cavity ; and the dentine par- 

 tially surrounding these little bays is disposed as a secondary 

 toothlet, of which the bay is its })articular pulp-cavity. 



If now with the aid of a ^-inch object-glass (Powell 

 and Lealand's) we look at the dilated end of one of the pri- 

 mary prolongations of the central pulp-cavity, which serves 

 as a pulp-cavity to a toothlet, we see the tubules of the den- 

 tine radiating from its margin through a series of finely 

 arched lines towards the crown and sides of the toothlet ; 

 before, however, reaching the outer borders of these, they pass 



