TISSUES OF THE BODY. 



2G3 



Larger globules of dentine may make their appearance internally on the 

 boundary wall of the cen- 

 tral cavity of the tooth, 

 communicating to it here, 

 as has been very well said, 

 a "stalactitic" appearance. 

 In the crown we may fre- 

 quently recognise concen- 

 tric tracings running more 

 or less parallel to the sur- 

 face, probably pointing to 

 a kind of lamination 

 which may hereafter find 

 its explanation in histo- 

 genesis. These are the 

 so-called " contour-lines " 

 of Oioen. 



We have already re- 

 marked that dentine may 

 be regarded as a species of 

 bone. Comparative his- 

 tology also teaches us that 

 the osseous tissue of many 

 bony fishes supplies inter- 

 mediate forms bet ween bone 

 and dentine, and that in 

 no inconsiderable number 

 of these the latter appears 

 in the place of osseous 

 tissue (Koelliker) (3). 



REMARKS. 1. Beside the 

 German works of Henle, Ger- 

 lach, and Koelliker, com p. Todd 

 and Bowman (Vol. 2). Fur- 

 ther, E. Owen Odontography, 

 etc. Vol. 1 ; Loud. 1840-45. 

 J. Tomes A Course of Lectures 

 on Dental Physiology and Sur- 

 gery. Lond. 1848; andPhilos. 

 Transact, for the year 1856, 

 p. 515. Beale. The struc- 

 ture of the simple tissues. 2. 

 In the many-pointed crowns of tho back teeth the direction of the canaliculi is the 

 same as if every knob were the crown of a simple tooth. Between the many roots on 

 the so-called alveolar surface, as Purkinje has very happily named this part, the 

 perpendicular course of the middle portion of the crown is again re-established. 3. 

 Subsequently to Queckett's having directed attention to this in certain fishes 

 (Catalogue of Surgeons of England, Vol. 2), the above-mentioned German investigator 

 proved the frequent and extensive occurrence of this interesting relation. 



Fig. 254. Premolar tooth of the cat (after Waldeyer). 1, 

 enamel with cross and parallel streaks; 2, dentine with 

 so-called lines of Schreger; 3, cement; 4, periosteum of 

 alveolus; 5, bony tissue of the lower jaw. 



The pulpa dentis is the unossified remainder of the papilla existing in 

 the embryonic tooth (see below). It is a kind of undeveloped soft con- 

 nective-tissue, possibly belonging to the mucous or gelatinous species, 

 containing numerous cellular elements of elongated or round form. The 

 intermediate substance, which is not rendered clear by acetic acid, is 

 18 



