66 



BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 



ened rugose surface desci'ibed above. The pointed ends would be directed back- 

 ward and outward as in Trachodon (fig. 34). Altliougb these bones were found 



widely separated in the quarry and 

 none of the three can be definitely as- 

 sociated with any of the surrounding 

 specimens, yet a comjjarison 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 jjredentate dinosaurs, 



sternal elements were first discovered 



in Trachodon (Claosaurus) by Marsh, 



later in Triceratops by Bro%vn,^ and 



That they are present in all members 



Fig. 33.— Diagkam showing probable manner op articu- 

 lation OF STEGOSAUEUS sternal bones. J NAT. SIZE. 



a. Anterior ends; p, postekioe ends; t, sternal eib. 



quite recently by Gilmore ^ in Thescelosaurus. 

 of this group is likely. 



Measurements of sternal bones. 



Greatest length 



Greatest transverse width, proximal end . 



No. 7618. 



No. 7619. 



No. 7620. 



170 

 S(i 



mm. 

 178 



156 

 65 





Shoulder Girdle. 



Scapula. — The scapula is comjjaratively 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 cuiwature of 

 the scapula also tends to thi'ow 

 the articulated coracoid well in 

 front on the chest, as in Thescelo- 

 saurus, Trachodon, Camptosaurus, 

 and Triceratops. 



There are seven scapulae in 

 the National Museum collections 

 all showing a downward curve of 

 the bone proximo-cUs tally (pi. 21, 

 fig. 3), and not straight, as Marsh 

 has represented tliis element in 

 S. ungulatus. In this respect 

 they approach the scapula of Arvkylosaurus, as figured by Brown 



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

 i NAT. SIZE, a, Seen from above; 6, seen from below. After 



M.ARSH. 



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



2 Smiths Misc. Coll., vol. 61, No. 2184, 1913, p. 4. 



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



