XVI INTRODUCTION, 



diate or inter-tubular tissue ; this he describes as homogeneous and 

 without structure, and as entering into the composition of the dentine 

 in a greater proportion than the tubes themselves. 



The more extensive, varied and minute observations of Professor 

 Retzius led to the discovery of the cells of the intertubular 

 tissue, of the ramuli sent off from the main calcigerous tubes 

 into that tissue, and of the anastomoses of the ramuli with each other, 

 with the intertubular cells, and with the cells at the periphery of 

 the dentine. According to the researches of Dr. Schwann the 

 animal basis of the intertubular tissue possesses a fibrous structure. 



Besides the primary and secondary branches of the calcigerous 

 tubes Retzius first clearly described their curvatures and undulations, 

 which may be defined as follows : as a general rule the dentinal 

 tubes are directed, as affirmed by Leeuwenhoek and Purkinje, from the 

 inner to the outer surface of the tooth, and vertically to those sur- 

 faces ; but in their course the tubes describe two, three, or more 

 curvatures, appreciable by a low magnifying power : these I have 

 termed the ' primary curvatures. '(1) With a higher power, the tubes 

 are seen to be bent throughout the whole of their flexuous course into 

 minute and equal oblique undulations or gyrations, two hundred of 

 which were counted by Retzius in one tenth part of an inch's length 

 of a human calcigerous tube ; these I have termed the ' secondary 

 curvatures' or gyrations. (2) Both the primary and secondary curva- 

 tures of one tube are usually parallel with those of the contiguous 

 calcigerous tubes, and from the radiated course of these tubes they 

 occasion the appearance of lines running parallel with the external 



(1) Trans. Brit. Assoc, vol, vii, p. 148. See Plates 24, fig. 1 ; 64 a, fig. 2 ; 74, fig. 1 ; 94. 



(2) Ibid, p. 141. See Plates 16, fig. 3 ; 24, fig. 2 ; 64 a, fig. 3. 



