54 Messrs. Embleton and Atthey on the 



bottom of the alveoli, and gradually become continuous with, 

 and ancliylosed 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 surface 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 

 appears structureless. 



The internal structure of the teeth has been carefully drawn 

 by Mr. Dinning in Plate VII., in which fig. 2 shows a per- 

 pendicular 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 longitudinal and slightly converging pillars or 

 lines lying on each side of the pulp-cavity are the converging 

 plates of dentine, the plicte, seen in the transverse section, 

 fig. 5. These plates or lines represent the labyrinthodont ar- 

 rangement of the constituents of the tooth ; and their upper 

 terminations show the distance to which that peculiar struc- 

 ture extends — namely, 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, in- 

 terlocked 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 VII., 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, are parts 

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

 a thin plate of enamel, and encloses the small prolongation of 

 the pulp-cavity. 



Fig. 4 of the same Plate is a transverse section near the top 

 of the wider part of the pulp-cavity, and above the cessation 

 of the radiating branches of the pulp-cavity ; the aiTangement 

 of the dentine is still peculiar. 



In Plate VII., fig. 5 represents a transverse section of a 

 maxillary tooth (marked in Plate V., left side of figure, 



( 



