FOSSIL MAMMALIA. 81 



served, is smooth and vertical. Each superior maxillary hone contains the sockets 

 of five teeth, occupying an antero-posterior extent of three inches seven lines, (PI. 

 XXII and XXIII. fig. 3). The posterior alveolus is situated just behind the trans- 

 verse line, extending across the anterior boundary of the orbits ; the remaining 

 sockets of the molar series extend forwards three inches in front of the orbits. In 

 the Megatherium, the roots of the five superior molars are all situated behind the 

 anterior boundary of the orbit : in the Orycteropus, on the contrary, the grinders 

 are all placed in advance of the orbit ; so that the Scelidothere resembles that species 

 more than the Megathere in the relative location of the teeth. The palatal inter- 

 space between the roots of the last molar tooth of each series is eleven lines ; the 

 palate gradually though slightly widens, as it advances forwards : the posterior 

 margin of the palate is terminated by an acute-angled notch. In the breadth 

 of the bony palate the Scelidothere is intermediate between the Megathere and 

 Orycterope. 



The anterior of the upper molars is represented at fig. 3, 4, and 5, PI. XXL, and 

 at 1, fig. 3, PI. XXIII.; it corresponds closely in form and size with the opposite 

 molar below ; the base of the triangle given by its transverse section is turned 

 inwards and obliquely forwards. 



The second molar of the upper jaw, also presents in transverse section a 

 triangular form, with the angles rounded off; but the inner side of the tooth is 

 traversed by a longitudinal groove. The largest diameter of the transverse 

 section, which is placed obliquely as regards the axis of the skull, measures ten 

 lines and a half; the opposite diameter of the tooth is six lines. 



The third and fourth molars present the same form and size, and relative 

 position as the second. 



The fifth molar is the smallest of the series ; its transverse section gives an 

 inequilateral triangle, with the corners rounded off; the broadest side is turned 

 outwards, and is slightly concave ; the antero-posterior diameter of this tooth 

 is seven lines ; the transverse four lines. The length of the teeth in the upper 

 jaw is about two inches and a half. 



It is almost superfluous to observe that the teeth of the Scelidothere, as 

 in other Bruta, are without fangs, and have their inserted base excavated by 

 large conical cavities, for the lodgment of a persistent pulp. The tooth is com- 

 posed of a small central body of coarse ivory or 'dentine,' traversed by medullary 

 canals, which at the periphery of the coarse dentine anastomose by loops, 

 from the convexity of which the calcigerous tubes are given off which form 

 the fine dentine: the layer of this substance, which immediately surrounds the 

 coarse dentine, is about one line and a half in thickness, and the whole is 

 invested with a very thin coating of cement. The teeth of the Scelidothere thus 



M 



