218 DR. EMBLEI0X AXD MR. ATTHEY OX THE 



granular or nodular layer corresponds to that seen and often 

 figured as commonly existing in the fang and other parts of the 

 human tooth, and which is commonly black, but at times light- 

 coloured. 



In the tooth of Loxomma nothing like an external layer of ce- 

 ment is anywhere visible. 



If we examine in any of our sections one of the grooves on the 

 exterior of the tooth, we find it filled with a wedge-shaped por- 

 tion of osseous tissue ; but this does not pass beyond the bottom 

 of the groove : the sides of the groove are formed by the adjacent 

 borders of two toothlets ; these approach each other at an acute 

 angle, coalesce, and the resultant band passes inwards to the 

 interior of a plica, being somewhat narrower than its constitu- 

 ents together before coalescence. The straight and short den- 

 tinal tubes, some pale, others black, are very distinctly seen on 

 the margins of the groove. 



The black granular layer of each of the two toothlets is bent 

 inwards, and passes into the plica, one on each side of the now 

 central band, which is of light colour, and forms, as it were, the 

 core of the plica. At first, for a short distance, straight, the 

 central band becomes wavy, and then, in most of the long plica:, 

 zigzag ; and from each of the angles a straight process is given 

 off laterally, and ends in a blunt point, which partially separates 

 two secondary toothlets. The concavities of these undulations 

 and zigzags correspond to the concavities of the borders of the 

 plica, and therefore to the secondary pulp-cavities before men- 

 tioned. 



The granular layer accompanies everywhere on each side the 

 sinuosities of the central band and its processes, and holds the 

 same relation to the tubular dentine of the secondary toothlets 

 as it does to the same tissue of the toothlets of the exterior of 

 the tooth ; and it can anywhere be seen that the dentinal tubules 

 have a similar course through that layer to the central band. 



On scrutinizing closely the pale central band of a plica with 

 a one-eighth -inch object-glass, the tubules of dentine are clearly 

 seen at its margins ; many of them end there, or perhaps are 

 cut off, whilst others mostly, but not always or everywhere, 



