56 Messrs. Embleton and Attliey on the 



into a dark granular-looking layer, which is parallel to the 

 crown and sides, and in some tootlilets double. This layer 

 consists of black lines forming a close network, the meshes 

 of which are minute and look like cells, giving this layer 

 its black and granular aspect. It is usually well defined 

 on its external side ; but towards the pulp-cavity it is in many 

 parts gradually thinned away, and continued, here and there, 

 a good way into the tubular dentine ; in such situations the 

 lines often lose their dark colour, and resemble the tubes of 

 dentine, with which it is not difficult to observe that they are 

 continuous. The dentinal tubules can here and there be seen 

 as black lines approaching the dark network ; some can be 

 observed to divide into two, as is common in human dentine. 

 Many (perhaps all) of the dentinal tubes are thus, as it were, 

 arrested in their straight course by the black layer. 



Beyond this is a narrower and lighter-coloured tract, which 

 forms the external boundary of the crown and sides of the 

 toothlet ; in it numerous closely set straight lines or tubules, 

 mostly pale, but some black, and of the same size as those of 

 the black layer, are visible, passing out of that layer to the 

 exterior surface of the tooth. Thus the whole thickness of 

 the crown of the toothlet is composed of tubular and granular 

 dentine. 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 

 cement 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 

 portion 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 constituents together before coalescence. The straight 

 and short dentinal 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, tlie central band becomes wavy, and then, in most 

 of the long plicce, 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 



