OSTEOLOGY OF THE ARMORED DINOSAURIA. 



89 



Fig. 52.— Right hind foot op Stegosaurus sp. Cat. no. 

 4280, U.S.N.M. About } nat. size. Drawn articulated. 

 s, Sesamoid; t, tuberosity; I, n, III, digits one, two, 

 and three. Ungual on digit III probably pertains to 



DIGIT ONE. 



The slightly concave proximal articular surface does not reach the back but the 

 bone develops a strong, roughened, overhanging tuberosity for ligamentary attach- 

 ment. The shaft is constricted, the 

 distal end about evenly expanded, 

 with broad, shallow median groove. 

 The distal articular surface extends 

 well up on the anterior face of the 

 shaft, as it does in all three metatar- 

 sals. On the external side of the 

 anterior surface, below the center, a 

 vertically elongated, tuberosity with 

 roughened surface is developed, as 

 shown in figure 52, t. 



Metatarsal III has an irregularly 

 rounded proximal end, with slightly 

 concave, roughened articular surface. 

 The shaft is constricted in all diame- 

 ters, but more especially the trans- 

 verse. 



The distal end has two surfaces 

 which meet at an obtuse angle on 

 the internal third of this end. The 

 rounded internal surface articulates with the first phalangial, while the external 

 surface turns somewhat backward, remaining free. 



Metatarsal IV consists of a small, slightly flattened element, 

 with rounded distal and a pinched-off proximal end, the latter 

 without articular surface. If my interpretation of the respective 

 ends is correct, then this digit would have one or more phalanges; 

 but on the other hand, if they have been reversed it would repre- 

 sent all that remains of this digit. The upper end is somewhat 

 roughened, as shown in figure 53. 



Phalanges. — The complete phalangial formula of the hind foot 

 of Stegosaurus is unknown. The partially articulated foot (No. 

 4280) shown in plate 21, figure 1, has the proximal row of pha- 

 langes of digits I, II, and III preserved in their proper relations to 

 the metatarsals, and is the only specimen in the collection in the 

 United States National Museum furnishing positive evidence as 

 to their proper arrangement. 



The proximal phalanges in all of the digits are short and 

 broad, relatively much heavier than those of the manus. Their 

 proximal ends are shallowly concave from above downward and 

 slightly roughened. Their distal ends are convex from above downward, with a 

 broad, concave transverse median depression. 



The proximal phalanx of digit I is a short, broad bone which articulated with 

 a broad , depressed . hoof-like ungual (fig. 54) with roughened surface, which in life was 



cc 



Fig. 53. — Vestigal 

 metatarsal of 

 Stegosaurus sp. 

 Cat. No. 7419, 

 U.S.X.M. Natural 



SIZE. a, ARTICULAR 

 end; 6, PINCHED OFF 

 PROXIMAL END. 



