40 



MEMOIRS OF THE CARNEGIE MUSEUM 



plates. They are regularly but very gently concave superiorly and convex inferiorly. 

 Contrary to Marsh I have interpreted the thick, narrow, rugose extremities of these 

 bones as the posterior and the thin, broadly expanded extremities as the anterior. 

 I believe these bones to have been closely applied and firmly united by cartilage 

 throughout three fourths of their total length as indicated by the long, straight, 

 rugose margin which extends from the thickened extremity throughout three fourths 

 the total length of tlie bone and Avhich I have interpreted as the inner margin of 



each sternal. The outer margin of each 

 sternal is then slightly emarginate, thin and 

 smooth, while anteriorly they are broadly 

 pointed and rugose. Thus the sternum of 

 Diplodocus may be considered as composed 

 of two broad plates of bone arranged one 

 on' either side of the median line, with their 

 longer axes parallel Avith the longitudinal 

 axis of the skeleton. These bones were 

 firmly united by cartilage throughout three 

 fourths of their length. They are contracted 

 and thickened posteriorly where they pre- 

 sent a broad rugose surface for the attach- 

 ment of the cartilaginous xiphisternum and 

 sternal ribs. Anteriorly they expand into 

 broad thin plates with rugose anterior margins by means of which they were attached 

 to the coracoids and thus Avith the scapular arch possibly without the intervention 

 of ossified clavicles or interclavicles. Taken together the sternals of Diplodocus Avould 

 thus form a shall oav, raft-like sternum, the individual elements of Avhich have a 

 certain resemblance to those found in Iguana, in Avhich animal, hoAA^ever, they are 

 separated throughout a considerable portion of their length by the interclavicle and 

 are contracted both anteriorly and posteriorly. The connection betAA^een the ribs and 

 sternum Avas chiefly posterior and not lateral as in the Ratitte, and doubtless took 

 place through Avell-developed cartilaginous or imperfectly ossified sternal ribs and 

 xiphisterni. In Fig. 12 the sternal bones are shoAvn in their relative positions to one 

 another as here interpreted. 



11 Marsh places the narrow thick ends of these bones as anterior in Brontosaurus, while in Morosaurus 

 he considers the narrow extremities as posterior. I believe the latter the correct interpretation, since it does 

 not appear possible that the coracoids conld have approached sufficiently close to one another to have articu- 

 lated with the narrow tliickened extremities which seem so well adapted for the support of the sternal ribs 

 and xiphisterni. 



Fig. 12. Superior view of pair of Jsterual 

 bones of Dlplodocus carnegii (No. 84). a, ante- 

 rior ends ; p, posterior ends ; c, c, surface for 

 attachment of coracoids. About one eleventh 

 natural size. 



