GEOWTH AND DEVELOPMENT OF TEETH. 649 



pharyngeal teeth of a Wrasse (Labrus). The base of this tooth is slightly 

 contracted, and is implanted in a shallow circular cavity, the rounded 

 margin of which is adapted to a circular groove in the contracted part 

 of the base ; the margin of the tooth, which immediately transmits the 

 pressure to the bone, is strengthened by an inwardly projecting convex 

 ridge. The masonry of this internal buttress and of the dome itself is 

 composed of hollow columns, every one of which is placed so as to trans- 

 mit in the due direction the superincumbent pressure. 



" In another case, in which long and powerful piercing and lacerating 

 teeth were evidently destined, from the strength of the jaws, to master 

 the death-struggles of a resisting prey, we find the broad base of the 

 tooth divided into a number of long and slender -processes, which are 

 implanted like piles in the coarse osseous substance of the jaw ; they 

 diverge as they descend, and their extremities bend and subdivide like 

 the roots of a tree, and are ultimately lost in the bony tissue. This 

 mode of implantation, which I have detected in a large extinct Sauroid 

 fish (RUzodus), is perhaps the most complicated which has yet been ob- 

 served in the animal kingdom." 



(1773.) For a full account of the growth and development of the 

 teeth of Pishes, we must refer the reader to the same source from which 

 we have extracted the preceding paragraphs ; nevertheless the follow- 

 ing is a brief abstract of Professor Owen's views upon this subject. 



(1774.) In all fishes, the first step in the formation of a tooth is the 

 production of a simple papilla from the surface either of the soft external 

 integument, as in the formation of the rostral teeth of the Saw-fish 

 (Pristis), or of the mucous membrane of the mouth, as in the rest of the 

 class. In these primitive papillae there can be very early distinguished 

 a cavity containing fluid, and a dense membrane (membrana propria) 

 surrounding the cavity (and itself covered by the thin buccal mucous 

 membrane), which gradually becomes more and more attenuated as the 

 papilla increases in size. The pulp-substance, or contents of the mem- 

 brana propria, remains for some period in a fluid or semifluid condition ; 

 granules are ultimately developed in it, which at first float loosely, or in 

 small aggregated groups, in the sanguineo-serous contents of the pulp. 

 These granules soon attach themselves to the inner surface of the mem- 

 brana propria, if they be not originally developed from that surface. 

 The whole of the contents of the growing pulp becomes soon after con- 

 densed by the numerous additional granules which are rapidly deve- 

 loped in it after it has become permeated by the capillary vessels and 

 nerves. The particles become arranged into linear series or fibres an 

 appearance which is first apparent at the superficies of the pulp, to which 

 the fibres are vertical. At this period ossification commences in the 

 dense and smooth membrana propria of the pulp, and is thence con- 

 tinued centripetally in the course of the above-mentioned lines towards 

 the base of the pulp. Lastly, around the capillaries of the pulp the 



