74 



SEVENTH LECTURE. 



disregarding the most acute-angled ramifications and looped 

 communications, is on the whole regular. They are, in gen- 

 eral, perpendicular to the surface of the pulp cavity and 

 therefore vertical on the vertex of the crown, oblique on its 

 marginal portions, horizontal over the neck and fang, and at 

 the apex of the latter reassuming an obliquely descending 

 direction. A transverse section shows them radially 

 arranged. By more careful examination, however, we 

 meet with a number of smaller interesting variations (Koll- 

 man). 



Filled with air they appear dark, saturated with fluid as 

 transparent, readily disappearing canals. The condition 

 of the lacunae of bone is, therefore, repeated here. An 

 elastic, calcified parietal layer, like that of the bone, is 

 also not wanting in the dentinal canals. They are now- 

 much more easily recognized with the greater diameter of the 

 tubuli. 



Our dentinal canals open internally into the central cavity. 

 The latter may be very well compared to a Haversian canal 

 of the bone. 



The fang is covered by cement, as we have already 

 remarked. This (a), is a thin layer of bone substance, 

 increasing downwards towards the apex of the root, gen- 

 erally without lamellar structure, but with delicate bone cor- 

 puscles. 



A portion of the lacunae of the latter communicate with the 

 dentinal tubuli which have entered the cement or — more cor- 

 rectly said — pass over into the latter. At the margin of the 

 bone covering and the dentine, numerous spaces occur, the 

 so-called interglobular spaces (b), which may be mistaken for 

 bone corpuscles. 



Let us leave the enamel covering of the crown for the 

 present, and turn to the contents of the dental cavity, the 

 pulp. 



In the progressing bone, as the previous lecture taught, the 

 ruptured cavities were filled with unripe tissue, on the surface 

 of which the osteoblasts appeared. Now the tooth pulp pos- 



