COMPOSITION AND DEVELOPMENT OF TEETH. 



179 



whilst in another it was 28. The following analyses afford a more particular view of the 

 components of each substance: 



Molars of Mult Man. 



Phosphate of Lime, with traces of fluate of lime 

 Carbonate of Lime ..... 

 Phosphate of Magnesia ..... 



Other Salts .- 



Chondrine ....... 



Fat 



10000 



100-00 



Incisors of Ox. 



Dentine. 



Phosphate of Lime, with trace of finale 

 of lime ...... 



Carbonate of Lime 

 Phosphate of Magnesia 



Salts 



Chondrine 



Fat 



59-57 

 7-00 

 099 

 0-91 



30-71 

 0-82 



IIIIHIO 



Enamel. 



81-86 

 9-33 

 1-20 

 0-93 

 6-66 

 0-02 



100-00 



Cement. 



58-73 



7-22 



0-99 



0-82 

 31-31 



093 



100-00 



213. The Dentine and its modifications, the Enamel, and the Cementum, 

 originate in three distinct structures ; which may be termed respectively, the 

 dentinal-pulp, the enamel-pulp, and the capsule or cemental-pulp ; the whole 

 forming the " matrix" from which the entire tooth is evolved. The Dentinal 

 pulp is always the first-developed part of the matrix ; and it makes its appear- 

 ance in the form of a papilla, budding out from the free surface of a fold or 

 groove of the mucous membrane of the mouth. This may be converted into 

 dentine, without ever becoming inclosed within a capsule; as we see in the 

 Shark, whose dentition never advances beyond this papillary stage. The 

 dentinal pulp consists of a mass of nucleated cells, imbedded in a semi-fluid 

 granular blastema, and the whole inclosed in a dense structureless pellucid 

 membrane. This substance is copiously supplied with blood-vessels, origin- 

 ating in a trunk that enters the base of each papilla; the branches ramify and 

 diverge in their progress through the pulp ; and at last they form a capillary 

 network, which terminates in loops near the apex of the pulp (Fig. 82). 

 These vessels are accompanied by nerves; which also have looped termina- 

 tions. The following is the substance of the account given by Prof. Owen, 

 of the conversion of the dentinal pulp into dentine; based upon his observa- 

 tion of this process as it occurs in the foetal Shark. The primary cells, which 

 are smallest at the base of the pulp, and have large simple sub-granular nuclei, 

 soon fall into linear series, directed towards the periphery of the pulp ; and 

 those which are nearest to the periphery become closely aggregated, increase 

 in size, and present a series of important changes in their interior (Fig. 83, a). 

 A pellucid point appears in the centre of the nucleus ; and the latter increases 

 in size, and becomes more opaque around it. A division of the nucleus in 

 the course of its long axis is next observed (b] ; and in the larger and more 

 elongated cells, still nearer the periphery of the pulp, a further subdivision of 

 the nuclei is observed, in a transverse as well as a longitudinal direction (c, c), 

 the subdivisions becoming elongated, with their long axes vertical, or nearly 

 so, to the surface of the pulp. The subdivided and elongated nuclei become 

 attached by their extremities to the corresponding nuclei of the cells in ad- 

 vance; and the attached extremities become confluent (</); so that lines or 



