38 



Plate XII. fig. 2, i,ii,iii,iv), shows that three of those teeth were rightly so referred; 

 but that the small molar alluded to at p. 342, op. cit., does not belong to the lower 

 jaw, which has only four teeth in each ramus. 



The first molar (Plate XVI. and XII. fig. 2, /) is 8 inches in length, with a 

 pulp-cavity of 5 inches in depth; it presents a curve, with the convexity forwards, 

 which is more marked than in any of the upper molars. The anterior surface is so 

 much less convex transversely than in the first upper molar, that the transverse sec- 

 tion presents a tetragonal rather than a semicylindrical figure ; the anterior side, 

 however, being only three-fourths the breadth of the posterior one, by which the first 

 lower molar may be distinguished from all the tetragonal teeth of the upper jaw. 

 Both the inner and outer sides are slightly concave transversely, the posterior side is 

 moderately convex. The posterior ridge has a base twice as thick as the shorter 

 anterior ridge. The greatest transverse breadth of the crown is 2 inches, the great- 

 est fore and aft breadth is 1 inch 7 lines. 



The second molar (Plates XVI. and XII. fig. 2, ii) is the largest, at least the 

 broadest transversely, of those of the lower jaw. ft is 9 inches in length, with a 

 minor curvature, convex forward. The anterior side is the broadest, being more 

 extended inward than the posterior side: its transverse diameter is 2 inches 3 lines, 

 the fore and aft diameter of the crown is 1 inch JO lines: the base of the hinder 

 eminence in the latter diameter exceeds that of the front eminence chiefly by the 

 greater extent of dentine exposed. 



The third molar (Plates XVI. and XII. fig. 2, Hi) is of the same length as the 

 second, but has its two diameters more nearly equal, the transverse section being 

 nearly square, the anterior division being rather the broadest transversely, and of 

 equal thickness from before backwards. Both this and the preceding tooth are con- 

 vex transversely before and behind, concave at the sides. 



The last lower molar (Plates XVI. and XII. fig. 2, iv), with an equal antero- 

 posterior diameter to the preceding, is shorter and narrower transversely, especially 

 in regard to its posterior division, which is more rounded, or convex transversely, 

 behind, than in any of the antecedent teeth. The hinder slope of the hinder ridge 

 is more nearly horizontal, and those towards the middle of the tooth are less deep: 

 the modification of the grinding surface of this tooth relating to the flatter surface 

 of the fifth molar above, and its greater antero-posterior extent as compared with its 

 breadth compensating for the absence of a fifth molar in the lower jaw. The grind- 

 ing surface of the four lower molars equals that included between the anterior ridge 

 of the first molar and the posterior ridge of the last molar in the upper jaw. 



Each molar has its base undivided, but excavated by a deep conical pulp-cavity 

 (Plate XVII. fig. 2,p,p), from the apex of which cavity a fissure is continued to the 

 middle of the grinding surface of the tooth, where it is more conspicuous in the upper 

 (Plate XV.) than in the lower molars. Plate XVII. fig. 2, exhibits a longitudinal 

 section of the five molars of the upper jaw, in situ. The central axis of vaso-dentine 

 (v) is surrounded by a thin layer of true or hard dentine (d), and this is coated by 



