262 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



Measurements of Specimen, Cat. No. 5818, U.S.N.AI. 



mm. 

 Greatest length of right tibia 531 



Greatest diameter of proximal eml 222 



Greatest diameter of distal end 90 



The fibula. — The fibula of No. 1877, Yale Museum, is a slender 

 bone, being somewhat shorter than the tibia. It has a flattened shaft 

 above, which is subcylindrical below, with flattened expanded ex- 

 tremities. The face of the proximal end which was applied to the 

 tibia is concave antero-posteriorly, while the outer surface is convex. 

 The articular surface of this end is nearly straight antero-posteriorly, 

 but roughened and gently rounded transversely. The expansion of 

 the upper end takes place more especially toward the anterior border 

 which overhangs considerably the constricted shaft. As with the 

 tibia, planes passed through the longer axes of the expanded articular 

 ends would cut one another at nearly right angles. Internally the 

 distal extremity is plain and was closely applied to the opposing 

 flattened surface of the outer anterior face of the tibia. The articular 

 end is roughened and concave and viewed from below is semicircular 

 in outline. The shaft has a small medullary cavity. The distal end 

 articulates closely with the upper surface of the calcaneum. 



THE HIND FOOT, 



The astragalus. — The astragulus, although closely applied, was 

 not ankylosed to the tibia, even in adult individuals. Its upper 

 surface is the counterpart of the inner articular surface of the tibia. 



The upper surface (see a, fig. 34) is deeply concave from front 

 to back and divided by a ridge, which marks out two portions cor- 

 responding to the inner and part of the outer tibial malleolus. These 

 two surfaces meet one another at an obtuse angle. The distal sur- 

 face is convex antero-posteriorly, with a broad, shallow deprassion 

 medially, making this surface slightly concave transversely. The 

 anterior margin is a thickened lip. The posterior margin is stout, 

 and viewed from above, terminates in a heavy, angular, posterior 

 point. The inner end is comparatively thin and probably non- 

 articular, although a prominently developed projecting loiob on 

 the antero-internal angle appears to have been closel}'^ apposed to 

 the distal inner surface of the fibula. The anterior half of the 

 external depression of the dorsal surface is nonarticular and did 

 not come in contact with the tibia, but formed the walls of an open- 

 ing leading down between this bone and the os calcis. The outward 

 knob-like projection overlaps the outer surface on the distal part 

 of the tibia. On the anterior internal surface, just below the supe- 

 rior border, is an elongated pit. 



There is no ascending process on the astragulus of (Uimptosaurus. 



