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Mr. C. S. Tomes on Vascular Dentine. 



[Mar. 8, 



dentine is sudden, and the tooth is easily broken off at this point. 

 When the greater part of the length of the root has been formed the 

 manner of calcification again changes, this time not so abruptly, till near 

 to the end of the root the dentinal pulp becomes converted into osteo- 

 dentins, which is quite indistinguishable from and blends insensibly with 

 the surrounding coarse bone by which the tooth is fastened into the 

 socket; there is, in fact, no reason for calling it any thing else than 

 coarse bone, except the fact that it is the product of calcification of a 

 dentinal pulp. In this case a single dentinal pulp forms first hard 

 dentine, secondly vaso-dentine, and at last osteo-dentine. 



Another variety of complex dentine is brought about by foldings and 

 subdivisions of the formative pulp : both vaso-dentine and osteo-dentine 

 are formed by the calcification of simple pulps ; but in many instances 

 the odontoblast-bearing surface of the pulp is itself complicated in form, 

 and a dentine arranged as it were round many pulp-chambers is the 

 result. 



For this no better name than plici-denti^ (also a term already in use) 

 suggests itself : it is to be seen in its simpler form at the base of the 

 teeth of Lepidosteus, in greater complexity at the base of the teeth of 

 Varanus, and in exceeding complexity in the teeth of Labyrinthodonts. 



The author would distinguish, therefore : — 



(i) Hard unvascular dentine, the characters of which are sufficiently 



known. 



(ii) Vaso-dentine, which is developed from odontoblasts after the 

 manner of dentine, but contains an anastomosing network of 

 canals modelled around and containing capillaries. 



(hi) Plici-dentine, developed from odontoblasts, but from a complicated 

 pulp, so that it is more or less divided up into distinct systems 

 of dentinal tubes. 



(iv) Osteo-dentine, developed from osteoblasts, like bone, and quite 

 unlike dentine ; permeated by a system of large canals, which do 

 not contain, or have any special relation to, blood-vessels. 



The author lays no stress on the characters formerly given as distinc- 

 tive of osteo-dentine (i. e. a laminated arrangement of the matrix and the 

 presence of lacunae), because (i) lamination of the matrix is not unknown 

 in vaso-dentine, (ii) lacunas are very frequently absent from bone in 

 fishes, and very frequently from osteo-dentine, so that these characters, 

 as those who have tried to apply them have found, are not useful in 

 practice. 



The attachment of the teeth of the hake is so peculiar as to merit a word 

 of notice : the inner and longer of the two rows of teeth are set upon elastic 

 hinges, which allow of their being bent inwards towards the throat, but 

 cause them at once to spring back into the upright position when pres- 

 sure is taken off them. This arrangement, shared by the angler, was 

 hardly to be expected in one of the Gadidae; but the author has found in 



