SEVENTH LECTURE. 



DENTINE. — ENAMEL.— LENS TISSUE. 



The tooth as a whole is known to everybody. We distin- 

 guish, (a) the crown, the free part, {b) then a middle portion 

 surrounded by the gum, the neck, and, finally (c), the simple 

 or multiple fang wedged into the alveolus of the jaw. 

 Through the centre of the tooth 

 passes a canal which has a caecal 

 termination above and below, 

 corresponding to the fang ; it is 

 simple or multiple in form, and 

 has a free opening at the apex 

 of the root. This is filled with 

 a soft connective tissue, rich in 

 vessels and nerves, the pulp. 



The chief mass of the tooth, 

 which is limited internally by 

 the cavity, and is covered exter- 

 nally by a thin cortical layer, 

 consists of the so-called tooth- 

 bone or dentine, a modified 

 osteoid tissue. The crown is 

 invested by the enamel, the 

 fang by the cementum ; both 

 substances meet at the neck. 



Let us first of all examine 

 the dentine (Fig. 66, d). It 



contains in a collagenous matrix a still greater quantity of 

 lime salts than the osteoid substance. It is permeated by 

 extraordinarily numerous, very fine canaliculi, O.oon to 0.0023 

 mm. broad, the so-called dentinal canals (e, e). Their course, 

 4 



Fig. 66. — Human tooth-fang d, with ce- 

 ment covering a. At b the granular or 

 Tomes' layer with interglobular spaces ; at 

 c and e the dentinal canals. 



