SEXLL AND OTHER BOXES OF LOXOidA. ALLMANKI. 215 



maxilla ; all are expanded at the bottom of the alveoli, and gra- 

 dually become continuous with, and anchylosed to, the bone at 

 that part. 



Each tooth, for about one-fourth of its length above the border 

 of the alveolus, is circular and of uniform diameter ; in the upper 

 three-fourths it is compressed on its inner and outer sides, so 

 that its anterior and posterior edges become sharp and cutting, 

 maintaining at the same time the width of the lower part of the 

 tooth. It is longitudinally grooved all round on its outer sur- 

 face for about one-third of its length from the alveolar border, 

 and is abruptly pointed at the apex. 



Some of the teeth are very slightly curved inwards towards 

 the point. From the apex to within the border of the alveolus 

 the tooth is clothed with a very thin layer of enamel, which ap- 

 pears structureless. 



The internal structure of the teeth has been carefully drawn 

 by "Mr. Dinning in Plate IV., in which fig. 2 shows a perpendi- 

 cular or longitudinal section, in a line with the jaw, of one of 

 the posterior mandibular teeth, at the inner side of its centre, 

 and carried through the contiguous parts of the thin band of bone 

 mentioned as enclosing the lower part of the tooth. The longi- 

 tudinal and slightly converging pillars or lines lying on each side 

 of the pulp-cavity are the converging plates of dentine, the plica:, 

 seen in the transverse section, fig. 5. These plates or lines re- 

 present the labyrinthodont arrangement of the constituents of 

 the tooth ; and their upper terminations show the distance to 

 which that peculiar structure extends ; nanlely, somewhat less 

 than two-thirds of the whole length of the tooth. 



The anchylosis of the tooth to the jaw is also seen in fig. 2 ; 

 the tooth-structures at the base are, every here and there, inter- 

 locked or dovetailed more or less deeply and curiously into the 

 bone, in which they are gradually lost ; but above the base the 

 sides of the tooth keep distinct from the alveolus and are smooth. 



Fig. 3, Plate IV., is a transverse section a little way below 

 the apex ; its outline is fusiform ; and its extremities, one of 

 which is rather more pointed than the other, arc parts of the 

 cutting-edges of the tooth; the dentine is enclosed by a thin 



