70 



BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 



The posterior convex side of the head of the radius fits nicely into the radial groove 

 on the anterior face of the ulna. On the front of the shaft a shallow groove passes 

 diagonally downward across the front of the bone and doubtless marks the course 

 of one of the larger tendons. It is clearly shown in pi. 20, fig. 4 A. In immature 

 specimens this groove is very indistinct. 



The heavy expanded distal end is triangular in outline with the apex of the 

 triangle directed outward. This end of the radius of specimen No. 4937 is divided 

 into two unequal faces, which meet one another at an obtuse angle. The larger 

 one articulates with the radiale, but the smaller looks inward and backward and 

 probably represents the attachment of the heavy ligaments which bound the joints 

 together. This conclusion is further strengthened by comparing the surfaces of 

 the two faces, the. latter being roughly pitted and lacking the finish of the former. 



Measurements of radii. 



Greatest length 



Greatest width proximal end - 



Greatest width distal end 



Least width ot shaft 



S. stenaps, 



type No. 



4934. 



mm. 

 384 



84 



S. sulcatum, 



type No. 



4937. 



mm. 

 463 

 147 

 158 

 67 



Forefoot. — A complete fore foot of Stegosaurus is as yet unknown, though a 

 considerable number of supplementary specimens give a fairly good idea of its struc- 

 ture, but it yet remains to definitely determine the pha- 

 langial formula. 



In young animals the proximal row of the carpus is 

 composed of four bones, but in the adult three of these 

 consolidate to form a single element on the ulnar side. 

 The distal segment of the carpus remains unossified. The 

 digitigrade foot was large, and possessed five well-devel- 

 oped digits which were doubtless inclosed in a muscular 

 mass, the only external evidence of the digits being the 

 flattened hoof-like nails on the first and second toes. 



Carpus. — In Stegosaurus only the proximal row of the 

 carpus is ossified. This row as now definitely determined 

 is composed of the radiale, intermedium, ulnare, and pisi- 

 form. It is only in young specimens that these elements 

 are found separate. In old animals the intermedium, 

 ulnare, and pisiform become ankylosed to form a single element, and in adults where 

 the sutures have become obliterated the carpus would appear to consist of the two 

 block-like bones shown in figure 38, 2, ul + in+p, and r. In the collections of the 

 United States National Museum, however, we are fortunate in having preserved in 

 situ the radiale, intermedium, and ulnare of one individual (No. 7401, fig. 37) and 

 the intermedium, ulnare, and pisiform of a second specimen (No. 7403, fig. 36). 



Fig. 36. — Carpus of Stegosaurus 

 sp. Juvenile. Cat. no. 7403, 

 U.S.N.il. i NAT. size. A, Front 

 and B, top views, in, Inter- 

 medium; p, PISD70RM; Ul, ULNARE. 



