THE DENTAL TISSUES. 105 



The pulp may be described as being made up of a mucoid, 

 gelatinous matrix, containing cells in abundance, which are 

 especially numerous near to its periphery. In it some 

 fibrous connective tissue is discoverable, though this is not 

 abundant until the period of degeneration has set in. Nerves 

 and vessels also ramify abundantly in it. 



The cellular elements of the pulp are arranged, as seen. 

 in transverse sections, in a direction radiating outwards from 

 the centre ; this is most marked in the highly specialised 

 layer of cells which form the surface of the pulp, and are 

 termed odontoUasts. 



The odontoblast layer, sometimes called the membrana 

 eboris, because it usually adheres more strongly to the 

 dentine than to the rest of the pulp, and is therefore often 

 left behind upon the dentine when the pulp is torn away, 

 consists of a single row of large elongated cells, of darkish 

 granular appearance, with a large and conspicuous nucleus- 

 near to the end farthest from the dentine. 



The sharp contours which the odontoblasts possess in 

 pulps which have been acted on by chromic acid, alcohol, 

 or even water, are absent in the perfectly fresh and unaltered 

 condition, and it is believed that they have no special in- 

 vesting membrane. They are furnished with three sets of 

 processes. The dentinal process (which is equivalent to the 

 dentinal fibre) enters the canal in the dentine, and the in- 

 dividual odontoblast may be furnished with several dentinal 

 processes. By means of lateral processes the cells communi- 

 cate with those on either side of them, and by means of 

 their pulp processes with cells lying more deeply; these 

 deeper cells again are to some extent intermediate in size 

 between the odontoblasts and the internal cells of the pulp. 

 The membrana eboris covers the surface of the pulp like 

 an epithelium. The odontoblasts vary much in form at 

 different periods ; in the youngest pulps, prior to the forma- 

 tion of dentine, they are roundish, or rather pyriform j 



