THE MOST PRIMITIVE KNOWN REPTILE. 



283 



The tibiale is a small squarish bone with rounded edges and 

 corners. It has a somewhat definite edge towards the inter- 

 medium. 



The intermedium is a well-formed bone with a cylindrically 

 concave ventral surface. Towards the tibia and fibula it has 

 well -formed edges, which are separated proximally by a smooth 

 well-rounded notch of considerable breadth. It articulates with 

 both tibiale and fibulare, the faces towards those bones being- 

 separated distally by a small smooth notch. 



Text-figure 12. 



Seymouria bayloriensis Broili. — Right hind leg of my skeleton, X f . 



The bones are represented as they lie in the matrix. The dotted part of the fibula is 

 exposed on the lower surface of the block and. is represented as seen through 

 it and its distal end beyond the line which crosses it is drawn reversed from 

 the bone of the left side. 



* The fibulare is a small rounded bone resembling the tibiale in 

 general characters. It is separated from the intermedium by a 

 definite layer of matrix. 



The only other tarsal preserved is a small rounded element 

 above the upper end of the 3rd metatarsal. 



In text-fig. 12 I have represented the right femur, tibia, fibula, 

 and proximal tarsals in the position in which they lie in the 

 matrix. The part of the fibula indicated in dotted lines is 

 exposed on the other side of the block, and the distal strip of the 

 fibula about 1 mm. wide is restored from the bone of the left 

 side, as the right bone is slightly weathered here. 



In text-fig. 13 I have restored the tarsus by moving up the 

 fibula into contact with the proximal tarsals, the resulting 

 accuracy of fit is good evidence for the reliability of the figure. 



This leg differs from Prof. Williston's figure somewhat in the 

 shape of the lower end of the fibula, and much more importantly 

 in showing the clearest evidence of an intermedium. There is no 



