KO. 2127. 



OSTEOLOGY OF THESCEL08AURUS—GILM0RE. 



601 



The metacarpals are much shorter than the metatarsals, the second 

 being the longest of the series, whereas in Camptosaurus and Hypsi- 

 lopTiodon the third is the longest. Metacarpal I is the heaviest of the 

 five, but is more elongate than the homologous bone of the Camptosau- 

 rus fore foot, from which it also differs by being free from the radiale. 

 Metacarpals III, IV, and V are progressively reduced in length, the 

 latter articulating with the iJnare as in HypsilopJiodon. 



Digit I has two phalanges, the terminal one being a short but 

 sharply pointed ungual. Digit II has three phalanges; the terminal 

 is as yet unknown, but well-defined articular facets on the second 

 phalanx, as shown in figure 1 1, indicates that such a bone was present 

 in the complete foot. 



The presence of four phalanges on the third digit is an unusual 

 number and so far as I am aware only found in Thescelosaurus and 

 HypsilopJiodon among the dinosauria.^ Of this feature in Hypsilo- 

 pJiodon Hulke says: 



It is fortunate that the number of phalanges, four, in this toe (Ilird of the manus) 

 is beyond question, because it shows an essential structural difference between the 

 forefoot of Hypsilophodon and that of Iguanodon mantelli, in which, upon the evi- 

 dence of undisturbed specimens in the Brussels Museum, no digit has more than three 

 phalanges. 



The same may be said of the third digit of TJiescelosaurus as com- 

 pared with that of Camptosaurus. 



The ungual of digit III is a small bluntly roimded hoofhke terminal 

 phalanx suggestive of the unguals of the primitive ceratopsian Bra- 

 cJiyceratops . The terminals of digits four and five have been reduced 

 to tiny, rounded bony nodules. 



From the above figures and descriptions of the manus of TJiesce- 

 losaurus it wiU be seen that the fifth digit is becoming atrophied and 

 fast approaching a functionless condition. On account of the manus 

 stdl remaining in the matrix with the palmar side up, it has not been 

 possible to either figure or describe the opposite side. 



Comparative lengths of metacarpals. 



' Since the above was written a description of the new Ceratopsid reptile Leptoceratops gracilis Brown 

 shows that reptile as also having four phalanges on the third digit. Bull. Amer. Mus. Nat. History, vol. 

 33, 1914, p. 571. 



