HINGED TEETH OF THE COMMON PIKE. 5 



If we compare the fully tleveloped hinged tooth with an 

 anchylosing tooth of the same fish which has not as yet 

 advanced to complete calcification, the true nature of this 

 curious bundle of elastic strings is at once apparent. 



It has already been mentioned that in the case of a tooth 

 destined to be attached by anchylosis an outer cap of hard 

 dentine is formed upon the surface of the pulp after the ordi- 

 nary fashion of dentine formation, but that the tooth is then 

 completed by a different process, rods of calcification shooting 

 down through the pulp, and by their increase in size oblite- 

 rating all central pulp chamber, while by their extension 

 downwards to, and final blending with, the bone they fix the 

 tooth in place. 



Arrest the progress of calcification in these rods at a stage 

 when they are not thick enough to collectively block up and 

 obliterate the pulp cavity, and we have the elastic bands 

 of the hinged tooth ; in fact, the same structure which is 

 made use of to rigidly fix the one is, by arrest of its develop- 

 ment at a certain point, made to do duty as an elastic spring 

 in the other. 



During the period of their active development osteoblast- 

 cells thickly and regularly coat each one of the rods ; whilst, 

 in places, these osteoblast-cells are elongated instead of being 

 spherical (o, fig. 6). But in a completed tooth these osteo- 

 blast-cells have vanished ; the rods, if examined tolerably 

 high up within the dentine cap, are calcified ; they are quite 

 rigid, brittle, breaking with a sharp fracture, and no cell 

 structures are to be distinguished. The space between the 

 parallel rods is not, however, empty, but the sole remainder 

 of the cellular vascular pulp is a filmy, cobwebby-looking 

 tissue, equally impossible to describe and to draw. I have 

 attempted to delineate this web in fig. 7, but no drawing 

 can convey any idea of its exquisite delicacy and filmy 

 transparency. 



The nature of the attachment of one of the rods to the bone 

 of the jaw is shown in fig. 6; its relation to the dentine cap 

 is sufficiently indicated in figs. 4 and 5. In many places 

 bundles of parallel fibres may be found springing from the 

 same eminence of bone {i, fig. 8), and these in their further 

 development would coalesce into a single thicker rod. Thus 

 the development of the osteo-dentine in this situation would 

 seem, so far as it goes, to confirm Von Ebner's view as to 

 the fibrous basis of all bone ; but I have not been successful 

 in demonstrating this fibrous structure at a period subsequent 

 to full calcification. 



There is little to be said as to the structure or the develop- 



