78 PRACTICAL MICROSCOPY. 



THE TEETH. 



A human dentinal tooth is a calcific structure of extreme hardness, 

 and is divided into an exposed crown, a constricted neck, and one or 

 more concealed fangs the latter being inserted into an alveolus, by 

 means of which the whole is firmly connected with the maxilla. 



The central portion presents an elongate cavity (pulp -chamber) 

 containing vascular, nervous, and connective-tissue elements the 

 pulp. 



The pulp-cavity is surrounded by the dentine, which constitutes 

 the major portion of the tooth. 



The crown portion of the dentine is provided with a covering of 

 enamel, while the fang is invested with an osseous cement, the crusta 

 petrosa. 



A thin (one-twenty five thousandth to one-fifty thousandth of an 

 inch) membrane the cuticula covers the enamel in early life, 

 while the crusta receives a periostea! investiture. The vascular and 

 nervous elements of the pulp obtain admission to the pulp-cavity by 

 a perforation or foramen at the apex of the fang, the foramen den- 

 tium. 



The Pulp. The ground-substance, or stroma of the pulp, is a form 

 of primitive connective tissue, gelatinous rather than markedly 

 fibrous. It contains elongate capillary loops, multipolar cells, me- 

 dullated and non-medullated terminal nerve fibrils. 



Surrounding the pulp mass, and next to the dentinal wall of the 

 chamber, we find a single layer of elongate cells odontoblasts. These 

 are in communication, by means of processes, or prolongations, with 

 fibrous elements of the pulp. 



Dentine. The dentinal stroma or matrix is cartilaginous, with 

 calcific elements, and is, next to the enamel, the hardest tissue of the 

 body. The matrix is pierced with the dentinal canals (one-ten thou- 

 sandth to one-twenty thousandth of an inch in diameter) which radiate 

 from their beginning, next the pulp-chamber, toward the outer por- 

 tion of the dentine. These canals branch and anastomose, and are 

 lined with an exceedingly thin dentinal sheath. 



From the outer extremity of the odontoblasts of the pulp numer- 

 ous prolongations are sent which are continued within the dentinal 

 canals as the dentinal fibres. The dentinal canals terminate exteriorly, 

 by very fine lumina, in a system of irregularly formed openings, in- 

 ter globular spaces, which are channeled in the outer part of the den- 



