406 MAMMALIAN ANATOMY 



cementum. Where the fangs join the crown is a faint constriction, 

 the neck. 



The crown as a whole is conical in shape, but strongly compressed 

 from side to side. It is limited at its base by a well-marked ridge 

 of enamel, the cingulum, 1 which completely encircles the tooth above 

 the neck and thus protects the edge of the surrounding gum. The 

 base of the crown is broader behind than in front ; the outer side 

 is usually more convex from before backward than the inner side. 

 The cingulum rises in front and behind and arches over the interval 

 between the two fangs. The central triangular elevation of the crown 

 is known as the principal cusp, or protoconid ; its inner and outer 

 surfaces, sometimes called the lingual (tongue) and buccal (cheek) 

 surfaces respectively, are both convex from before backward ; the 

 inner surface is usually marked by a vertical median ridge. The 

 outer surface is more convex from above downward than the inner 

 surface. The crown presents sharp anterior and posterior borders. 



The posterior border is interrupted a little below the middle by a 

 transverse notch, which produces a second smaller cusp, the posterior 

 basal cusp, or metaconid. Behind this cusp is a second transverse 

 incision, beyond which the cingulum is elevated into a small cusp 

 known as the talon, or heel. 



The anterior border is more vertical ; it is notched at its lower 

 end to produce a small anterior basal cusp which sometimes is 

 merely an elevation of the cingulum. The inner side of the crown 

 exhibits depressions below the notches which define the middle central 

 cusp. 



The length of the fangs is slightly greater than the height of 

 the crown ; the antero-posterior diameter of both and the transverse 

 diameter of each are less than the diameters of the crown at its base. 

 The fangs are oval in cross-section, and their tips, although often 

 enlarged, are smaller than their bases ; of the two the anterior is 

 usually the smaller. 



The tooth is formed of a peculiar hard tissue, the dentine, which 

 encloses a pulp cavity filled with the dental pulp supplied by vessels 

 and nerves through the foramina in the apices of the roots. The 

 dentine is covered on the crown with enamel, and on the roots with 

 bone-like cementum. While a tooth is growing, the pulp cavity 



1 A girdle. 



