220 MICROSCOPIC ANATOMY OF THE TEETH 



which these fine branches are continuous. But while these 

 appearances would seem to indicate that there is a direct 

 nerve communication between the pulp and the cement, we 

 cannot definitely prove this until the fibre in this situation 

 is seen to be clearly continuous, since in all metallic im- 

 pregnations deceptive appearances may arise from deposits. 

 It is, however, noticeable that in these fine divisions of the 

 tubes the dotting is uniform and does not show the variation 

 in size of the particles which so often occurs in imperfectly 

 reduced preparations. 



Where the so-called spindles are present in the enamel, 

 especially at the apices of the cusps, fine winding fibres are 

 sometimes seen within them which do not appear with 

 ordinary staining reagents, but these spindles do not appear 

 in the author's preparations to contain definite nerve-end 

 organs as described by Homer (28). It is impossible, how- 

 ever, to speak with certainty on this point, and the spindles 

 being comparatively infrequent a great many teeth should 

 be examined to decide the question. From the preparations 

 already made, however, one would be inclined to consider 

 the penetration of these bodies by nerve fibres more as due 

 to the fact that nerve fibres in the tubes would be likely 

 to penetrate into any open space with which the tubes 

 communicate than as constituting definite nerve-end organs. 



The refraction in these spindles greatly interferes with 

 accurate observation even in thin sections. It is considered 

 by many, as previously stated, that the spindles are inter- 

 prismatic spaces which have remained uncalcified, and the 

 author's own observations on the enamel of marsupials 

 appear to confirm this interpretation of their nature. 



In fig. 137 the mode of distribution of the nerves of the 

 pulp and dentine is represented diagrammatically. 



The mode of distribution of the nerves of the pulp above 

 described appears to be peculiar to the teeth, as such 

 a mode of termination of sensory fibres in ' end cells ' is 

 not met with in other organs. It would appear to show the 

 interposition of a peripheral sensory neuron in the course 

 of the distribution of a sensory nerve, a condition not seen 

 elsewhere in the body. Of the sensory nature of at all 

 events the majority of these nerve fibres there can 



