CHAPTER IX. 



THE RIBS AND STERNUM. 

 (Plates XXXIX, XL, LV, and LVI.) 

 The ribs in tlie Dinocerata present no special characters of importance. 

 Their general features are well shown in the illustrations above cited, 

 especially in the restorations at the end ot" the volume. 



The First Rib. 

 (Plate XXXIX, figures 1-3.) 



The first rib in the Dinocerata has a general resemblance to the 

 corresponding bone in the mastodon. It is, however, proi)ortional]\' 

 shorter, and more flattened at the sternal end. 



This rib presents a well rounded articular face to the first dorsal 

 vertebra, and, confluent with this, on the anterior side of the head, is 

 another strongly convex face, for articulation with a. well develo])ed facet 

 near the posterior margin of the last cervical vertebra. 



The tubercular articulation is but little elevated above the capitular. 

 It is convex from before backward, concave from side to side, and looks 

 almost perpendicularly upward, being directed but very slightly backward. 

 The tubercle of the rib extends outward beyond tlie articular face. 



The shaft is moderately roughened,^ more especially on its anterior, 



or outer, surface. The sternal face is so strongly flattened and expanded 



that the external border of the rib shows only a very moderate degree of 



curvature. The inner border, however, is strongly ciu'ved, mostly in the 



upper half of the bone. 



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