WILLISl'ON: RESTORATION OF PLATVCOXUS. 



33 



Length of first inferior milk molar 8.5 mm. 



Width of same 5 



Height of crown 5 



Length of second milk molar 10 



Width of same posteriorly 6 



Length of third milk molar 19 



Width of same through first ridge 8 



Width of same through third ridge 9 



Depth of posterior valley 5 



Distance between the apices of the two ]:)Osterior 



outer cusps 6 



Length of first upper milk molar 9 



Width of same over middle of anterior root 6 



Width over middle of posterior root 8 



Length of second upper milk molar 13 



Width of same anteriorly 8 



Width posteriorly 10 



Length of third upper milk molor 13 



Width of same 11 



Length of crown, lower canine 19 



Antero-posterior diameter of same at base 5 



Length of crown, upper canine 25 



Antero-posterior diameter of same at base 7 



Transverse diameter at base 5 



Permanent dentition. 



The unworn first lower molar of the permanent dentition shows a 

 great resemblance in its cusj)s to those of the last milk molar. The 

 cusps are very high, and the valley between the two ridges narrow 

 and deep. The outer and inner margins of the cusps are nearly 

 vertical, and have no ridges whatever at their base, except a very 

 slight one at the inner side of the posterior ridge. The opposed 

 surfaces of the valley are nearly flat. The angular incision of the 

 second pair is behind, and has, on the outer side, a rather prominent 

 sharp ridge. The outer cusps are slightly higher than the inner ones. 

 The secon<l lower molar has the apices of the cusps more approxi- 

 mated transversely, at the expense of the inner surface. The anterior 

 inner cusp sends a ridge downward and outward, on each side of 

 which there is a narrow depression back of a slight tubercle, whose 

 walls have a finely wrinkled appearance. The outer posterior cusp 

 sends a similar but stouter, sharp ridge downward and inward to end 

 in the inner hind margin near its middle, on either side of which the 

 margin slopes rapidly away, enclosing a narrow deep pit, like those 

 in front, and marked in the same way. The valley between the two 

 ridges has a high and narrow transverse ridge in the middle, running 

 from the outer posterior cusp. 



The third lower molar has the cusps yet more approximated trans- 

 versely at their apices, and the ridge across the valley is higher and 



