252 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



could obtain access; the following are the results of our 

 investigation. 1 



Teeth of the Lower Jaw. The lower tooth (Lign. 50 and 

 52, 3, 4,) is curved with the concavity outwards, or towards 

 the external alveolar parapet ; the upper and lower limbs, 

 corresponding respectively to the wedge-shaped crown, and 

 elongated taper fang, are not separated by a constriction 

 or neck, but are flattened in opposite directions. In the 

 upper moiety of the coronal segment, it is compressed trans- 

 versely with an outer convex, and a flat inner aspect, and 

 gradually increases downwards in width and thickness, from 

 the broad-rounded eccentric apex to its greatest longitudinal 

 diameter. It continues to expand transversely while decreas- 

 ing in breadth, and subconcave planes replace, the serrated 

 edges at which the surfaces meet above ; it obtains its greatest 

 thickness where the tooth bends and forms the fang, which 

 diminishes rapidly in both diameters, and the lateral facets 

 are brought in contact below, and obliterate the inner sur- 

 face ; in fully formed teeth when a successional germ is not 

 developed, the fang terminates in a point. 2 



The enamelled surface is divided into two unequal chan- 

 nelled areas by a primary longitudinal ridge ; commencing 

 at the apex, it intersects the long diagonal, and terminates 

 behind the lower angle. 



The relative width and depth of the longitudinal grooves, 

 and the prominence of the intervening ridges, vary in different 

 specimens. The serrations are produced by small mammil- 

 lated ridges, separated at slight intervals ; the inner edges of 

 the anterior apical ones are prolonged downwards, and those 

 on the posterior margin are abraded, apparently by absorp- 

 tion, during the upward growth of the germ. The inner 

 convex surface of the fang is in apposition with the outer 

 alveolar parapet. The lateral planes converge inwards, and 

 are grooved longitudinally ; they extend as high as the obtuse 

 angle of the crown, and leave between them, as they diverge 

 in their ascent, an unenamelled triangular space on the inner 



1 The details of this examination are given by Dr. Melville in the 

 memoir referred to, " Philos. Trans." 1848, pp. 191 195. 



2 "Philos. Trans." 1841, Plate VII. figs. 1, 2. A specimen of this 

 kind is placed on the middle shelf of Wall-case C. 



