OSTEOLOGY OF G.IENIVOKOUS DINOSAURS. 



51 



dimensions. The capitular process is the heavier of the two, and when articulated 

 is directed downward and forward instead of inward almost at right angles to the 

 main part of the bone, as in the proceeding cervical ribs. The vortical supporting 

 lamina of the bone described as strengthening the tubercular process on the rib of 

 cervical eight, on the inner side is here the thin comiecting plate of bone that forms 

 the median part of the anterior entl between the tuberculum and capitulum. The 

 lateral process (fig. 36, A. I. f.) has almost disappeared, and that part remaining 

 is well posterior to the articular processes, where as in the cervical ribs it extends 

 anterior to them. On the internal side the heaviest part of the bone is lightened 

 by deep cavities, as shown in figure 35. The tapering distal extremity is directed 

 backward — a feature that persists in the next three or four rilis of the series. 



Fig. 35.— First thoracic rib, Antrodemus v.u,ens Leidy, No.4734, XJ.S.N.M. ijraER .aspect. Jnat. size, c, capitulum; 



(, TUBERCULUM. 



The next rib back, here considered the second, is of the true thoracic type. 

 The heaviest and strongest part of the rib is in the neighborhood of the tubercle. 

 The process bearing the capitulum is the shortest of any of those present except the 

 first. The pi'ocesses gi'adually lengthen in the posterior members reaching their 

 maximum development h\ the ninth and tenth, which are about subequal. Pos- 

 teriorly they again gradually shorten. They also become progressively more slender 

 from the fifth rib, with a change in direction in relation to the shaft. On the second 

 rib this process is given ofl" at nearly right angles to the main axis of the shaft, but 

 posteriorly it gradually assumes a more upward direction until in the eleventh it 

 reaches an angle of nearly 45° above the horizontal. 



The change in direction of this process is accompanied \ry a change in the curva- 

 ture of the shaft of the rib; so that while the fu-st of the series, when articulated, 



