CHAP. VII.J THE CONNECTIVE TISSUES. 289 



pound is then deducted from the total weight of phosphoric acid, 

 the difference being calculated as calcium phosphate. The amount 

 of calcium in this compound is calculated and deducted from the 

 total amount of calcium found. Thus is found the calcium which 

 exists in other states of combination than as phosphate, viz. as 

 carbonate, chloride and fluoride. The whole of the carbon dioxide 

 found is assumed to have been derived from the decomposition 

 of calcium carbonate, so that the amount of the latter is easily 

 calculated. The chlorine found is calculated as present in calcium 

 chloride. By deducting then the calcium in combination with 

 phosphoric and carbonic acids and with chlorine from the total 

 quantity of calcium found, the amount of calcium present as CaFl 2 is 

 obtained. 



SECT. 5. TOOTH. 



A tooth is a composite organ presenting for examination several 

 tissues; of these, three constitute the hard portion of the tooth, viz. 

 enamel, dentine, and crusta petrosa or cementum. In the interior 

 of the tooth is the so-called pulp cavity, which lodges the pulp, 

 which consists of a framework of connective tissue, to which are 

 distributed blood-vessels and nerves, and whence proceed processes 

 which are prolonged into the dentinal tubules. 



Although two only of the hard tissues of tooth viz. dentine and 

 crusta petrosa belong to the group of connective tissues, the enamel, 

 which is a modified epithelial structure, will also, for reasons of 

 expediency, be considered in this place. 



Dentine. 



Dentine, or ivory, constitutes the chief part of the teeth. On 

 making a longitudinal section through a tooth it will be found 

 that the pulp cavity is bounded on all sides, except where the 

 cavities of the fangs open into it, by dentine ; the same tissue forms 

 the body of the crown (which is only covered by an external layer of 

 the harder enamel) and nearly the whole thickness of the fang or 

 fangs. 



Dentine Dentine is distinctly mesoblastic in its origin, being 



mesobiasticin formed through the agency of certain cells, termed 

 ' odontoblasts,' which are modified connective-tissue 

 corpuscles arranged circumferentially over the surface of the papillary 

 protrusions which rise from the connective tissue of the buccal meso- 

 blast so as to meet and indent the downward dipping epiblastic 

 cells which give rise to the enamel organ. 



G. 19 



