48 



MEMOIRS OP THE CARNEGIE MUSEUM 



The Tibia and Fibula. — These are rather slender bones. The fibula is much the 

 more slender and a little longer than the tibia, since it differs from the same bone in 

 mammals by entering subequally with the tibia into the ectocondylar articulation 

 with the femur, while inferiorly it is produced into an extended external malleolar 

 portion which reaches well below the distal end of the tibia, abuts against the ex- 

 ternal side of the astragalus, having entirely displaced the calcaneum, and reaching 

 almost to the proximal ends of metatarsals four and five. It is subequal in trans- 

 verse diameter throughout, but expanded antero-posteriorly at the extremities, more 

 especially at the proximal end, where it presents a flat internal surface and rather 

 thin anterior edge which fits into the broad groove formed b}^ the recurved cnemial 



18 .19 



Fig. 18. Proximal end of right tibia and fibula of Diplodocus curnegii (No. 94). t, tibia ; /, fibula. 

 One fifth natural size. 



Fig. 19. Distal end of right tibia and fibula of Diplodocus carnegii (No. 94). t, tibia ; /, fibula ; b, 

 surface for metatarsals t. and 11^ a, surface for contact with external side of astragalus. One fifth natural 

 size. 



crest of the tibia, while the flattened proximal surface is closely applied to that bone. 

 A little less than half the distance from the proximal to the distal end there is on the 

 antero-external border of this bone a rather broad rugose area for muscular attach- 

 ment. Distally the fibula is produced below the end of the tibia and expands into 

 a' broad, thick external malleolus which fits into and articulates laterally with the 

 external surface of the astragalus. The proximal end of the tibia is much expanded 

 antero-posteriorly and less so transversely. The shaft is quite slender, but expands 

 again distally so as to entirely cover the superior surface of the astragalus. On its 

 internal and posterior distal extremity it sends downward an internal malleolus 

 which is separated from the main shaft of the bone by a deep groove for the trans- 

 mission of the tendons of the flexor muscles of the foot. This process articulates 



