DENTINE 261 



a tree, spreading out on every side towards the circum- 

 ference. In some sharks, and in the Pike, a more regular 

 arrangement of these medullary spaces is seen at the 

 periphery, giving this layer more the appearance of ortho- 

 dentine ; but the tubes do not enter at their bases into a pulp 

 cavity, but are continuous with the main branches of the 

 medullary system in the centre of the tooth as in Lamna 

 (fig. 164). 

 If treated with alcoholic fuchsin (allowed to penetrate by 



FIG. 163. Dentine of incisor of Cynomys (Prairie Marmot) 

 showing vascular loops. ( x 350.) 



capillary attraction) the structure of an osteodentine tooth 

 is beautifully brought out, the stain penetrating into 

 the very finest divisions of the branching processes, which 

 resemble the canaliculi of bone (fig. 165). 



In some examples of osteodentine the resemblance of the 

 tissue to bone is much more marked than in the specimens 

 shown in the illustrations, and traces of lamination are seen. 

 ' The similarity of the channels of the pulp in osteodentine 

 to Haversian canals in bone is in some respects close ; so 

 similar, that when teeth consisting of osteodentine become, 

 as in many fish they do, anchylosed to the subjacent bone, 



