16 DEVELOPMENT. 



of connexion between those parts, either as elastic Ugaments, or by 

 continuous ossification. 



Here we have the second step in the development of the mammalian 

 tooth represented, viz : the imbedding of the pulp in a follicle of the 

 mucous membrane ; but the eruptive stage of the tooth takes place 

 without any previous inclosure of the follicle and pulp in the sub- 

 stance of the jaw. 



In the Batistes, Sparoids, Sphyrana, Scarus, and many other fishes, 

 the formation of the teeth presents all the usual stages which 

 have been observed to succeed each other in the dentition of the 

 highest organized animals : the papilla sinks into a follicle, becomes 

 surrounded with a capsule, and is then included in a closed alveolus 

 of the growing jaw, where the development of the tooth takes place, 

 and is followed by the usual eruptive stages. 



The development of the dental pulp in fishes, prior to the deposi- 

 tion of the calcareous particles in it, corresponds in the main with the 

 process described by Purkinje and Raschkow in the mammalia. The 

 pulp-substance, or contents of the memhrana propria remain, in fishes, 

 for a longer period in a fluid or semi-fluid state, and the granules or 

 nucleated cells which are first developed, float loosely or in small 

 aggregated groups in the sanguineo-serous fluid : they first attach 

 themselves to the inner surface of the memhrana propria, if these be 

 not originally developed from that surface, and the whole of the con- 

 tents of the growing pulp becomes soon after condensed by the nu- 

 merous additional granules which are rapidly developed in it after it 

 has become permeated by the capillary vessels and nerves. The ar- 

 rangement of these particles into linear series, or fibres, is first ob- 

 servable at the superficies of the pulp to which the fibres are vertical : 

 and, at this period, ossification has commenced in the dense and 

 smooth memhrana propria of the pulp : it is thence continued centri- 

 petally in the course of the above-mentioned lines, towards the base 

 of the pulp, either regularly progressive, as in the incisors of the 

 ^ar^wsand Balistes, or radiating, as in Sphyrcena and (if we may judge 

 by a posteriori observation of the structure of the fully developed teeth) 

 in most other fishes, from the various centres formed by the persistent 

 capillaries of the pulp, around which the cells or granules become 



