NO. 2127. 



OSTEOLOGY OF THE8CEL0SAURUS—GILM0RE. 



605 



of the distal row as in all other orthopodous dinosaurs. Viewed 

 from the external side this bone is crescentic in outline. 



The external tarsal of the distal row articulates with the outer 

 haK of the proximal end of metatarsal IV 

 while the inner element completely covers the 

 upper end of metatarsal III and extends part 

 way over metatarsal IV. The extension of this 

 carpal bone over the joint between metatarsals 

 III and IV, and its notched distal surface for 

 the more perfect articulation with metatarsal IV 

 is the most perfect mechanical joint yet observed 

 in the Dinosauria. It is an advance in the spe- 

 ciahzation of the tarsus over any of the earher 

 known members of this group and is admirably 

 adapted to resist the strains which come upon 

 the foot. 



Metatarsus. — The metatarsus consists of five 

 metatarsals, of which three are large and sup- 

 port functional toes. Metatarsal I is reduced 

 and metatarsal V is vestigal. 



The proximal ends of the three median meta- 

 tarsals are in the closest apposition, their shafts 

 being closely applied to one another for more 

 than haK their lengths. 



The proximal and distal ends of the metatar- 

 salia II, III, and IV are stout, with deep pits for 

 the attachment of lateral ligaments. 



The relative lengths of the metatarsalia are 

 remarkably simdar to those of HypsilopJiodon Ztu^SZI^ZIZ 

 and Camptosaurus , as is shown in the following lectus gh-more. type. 



- 11 . Cat. No. 7757, U.S.N.M. 



^^"^®- i NAT. SIZE. Shown 



as found in situ. a, 

 astragulus; c, calca- 

 neum; F, distal end of 

 fibula; r, DISTAL row of 

 tarsals; Ti, distal end 



OF tibia; I, II, III, AND 

 IV, DIGITS ONE TO FOUR. 



It will be observed that metatarsal III is the longest and heaviest. 

 The first is about half the length of the third and the fifth is less than 

 one-fourth the length of the same element. Digits II, III, and IV 

 carried all of the weight. Digit I would scarcely have touched the 

 ground, and was doubtless fast becoming functionless. It articulates 

 rather loosely with metatarsal II, lying in a shallow depression on 

 the inner proximal side of this metatarsal, as shown in figures 14 

 and 15. 



