66 



BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 



ened rugose surface described above. Tbe pointed ends would be directed back- 

 ward and outward as in TracTiodon (fig. 34). Although these bones were found 



widely separated in the quarry and 

 none of the three can be definitely as- 

 sociated with any of the surro undin g 

 specimens, yet a comparison of these 

 elements with those of Trachodon (com- 

 pare figs. 33 and 34) show such close 

 general resemblances that there ap- 

 pears to be but little doubt of their 

 correct identification. 



Among the predentate dinosaurs, 



sternal elements were first discovered 



in Trachodon (Claosaurus) by Marsh, 



later in Triceratops by Brown, 1 and 



That they are present in all members 



Fig. 33.— Diagram showing probable mannes. of articu- 

 lation OF StEGOSAURUS STERNAL BONES. J NAT. SIZE. 



a. Anterior ends; p, posterior ends; r, sternal rib. 



quite recently by Gilmore 2 in Thescelosaurus 

 of this group is likely. 



Measurements of sternal bones. 





No. 761S. 



No. 7619. : No. 7620. 



i 





mm. 



170 

 S6 



mm. mm. 



17S 1 156 



65 



Greatest transverse width, proximal end 





Shoulder Girdle. 



Scapula. — The scapula is comparatively short, and when not flattened by post- 

 mortem causes the inner surface 

 is concave from end to end, ren- 

 dering it conformable to the con- 

 vex curve of the body wall when 

 articulated. This curvature of 

 the scapula also tends to throw 

 the articulated coracoid well in 

 front on the chest, as in Thescelo- 

 saurus, TracTiodon, Camptosaurus, 

 and Triceratops. 



There are seven scapulae in 

 the National Museum collections 

 all showing a downward curve of 

 the bone proximo-distally (pi. 21, 

 fig. 3), and not straight, as Marsh 

 has represented this element in 

 S. ungulatus. In this respect 

 they approach the scapula of Ankylosaurus, as figured by Brown. 



1 Bull. Amer. Mus. Nat. Hist., vol. 22, 1906, pp. 297-300. 

 ■' Smiths Misc. Coll., vol. 61, No. 21S4, 1913, p. 4. 

 s Bull. Amer. Mus. Nat. Hist., vol. 24, p. 196, fig. 15. 



Fig. 34. — Left sternal bone of Trachodon annectens (Marsh). 

 £ Nat. size, a, Seen from above; &, seen from below. After 

 Marsh. 



