138 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



expanded anteroposteriorly, so that the distal articular surface somewhat 

 resembles an italic letter L, with the intercondylar groove in front deep, 

 the popliteal groove shallow. In front, the outer border is convex to the 

 articular surface for the fibula, and the articular surface as a whole is directed 

 ventrad at an angle of about forty-five degrees from the long axis of the 

 femur, and also outward at an angle of about twenty degrees; the articular 

 surface also extends proximad on the ventral side so as to permit a con- 

 siderable degree of flexion, while complete extension would have been impos- 

 sible. The considerable depth of the pelvic symphysis raised the acetabular 

 surface some distance from the ground, and doubtless the knee was con- 

 stantly flexed to a considerable extent. 



"The tibia is preserved in the matrix in articulation with both the 

 femur and tarsus, but rotated somewhat upon its outer side. Its proximal 

 extremity is much expanded, anteroposteriorly, and also somewhat from 

 side to side. Its articular surface for the femur is slightly concave, sloping 

 obliquely backward and outward from the long axis. Its proximal part 

 in front is broad for the insertion of the stout muscles of the intercondylar 

 groove, while a large surface posteriorly also gave insertion to the flexor 

 muscles. The middle of the shaft of the bone is slender, and nearly circular 

 in cross-section, from which place the bone becomes gradually broader to 

 the distal end, which is thickened and broader from side to side than from 

 before back. The outer border of the bone, as a whole, is nearly straight, 

 or gently concave; the inner border is deeply concave. 



"As already stated, the fibula was dislodged from its position. Lying 

 close by the inner side of the tibia is a flattened bone, imperfect at one side, 

 which is evidently the distal extremity of a fibula. The part preserved is 

 remarkably broad, much thinner on its outer side, thickened, shaft-like 

 on the inner, where it is broken oif. Distally it shows two thickened, appa- 

 rently articular borders separated by a thinner, non-articular margin. 



"The tarsus and foot lie almost perfectly in position, the tibiale slightly 

 turned outward by the rotation of the tibia, and the fifth toe partially 

 turned under the fourth and third. Lying as they do upon the sides of the 

 fourteenth, fifteenth, and sixteenth vertebrae, the bones are somewhat 

 uneven, because of the rugosities. There are twelve tarsal bones, three in 

 the proximal, four in the middle, and five in the distal row, a number found 

 by Baur in Archegosaurus, but otherwise unknown among air-breathing 

 vertebrates. Of the proximal row, the tibiale is elongate, a little broader 

 proximally, with a thickened, rounded internal margin, articulating proxi- 

 mally with the tibia, distally with the first centrale, and internally with 

 the second and third centralia. The intermedium is large, with a thickened, 

 oblique face for union with the fibula proximally, a free rounded border 

 opposite the distal part of the tibia, articulating distally with the large 

 centrale, and externally with the fibulare, leaving, however, a small open- 

 ing for the passage of vessels. The fibulare is elongate anteroposteriorly, 

 and is rather broad; it articulates proximally, on the upper side, with the 

 fibula, internally, above, with the intermedium, distally with the fourth 

 and fifth distalia, and between them and the intermedium with the large 

 centrale. The proximal centrale is one of the largest bones of the tarsus; 

 it is somewhat broader on the inner than on the outer end, articulating 

 proximally with the intermedium, internally with the tibiale, externally 

 with the fibulare, and distally with the two outer centraha. The innermost 



