EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



673 



sternal, measures 94 millimeters anteroposteriorly and 

 65 transversely; the succeeding sternal measures 

 85 millimeters anteroposteriorly and 48 transversely. 



The scapula is perfectly preserved on both sides. 

 (The scapulae are placed too low on the side of the 

 thorax; cf. corrected placing 

 in fig. 606.) It exhibits a 

 vertical diameter of 657 milli- 

 meters, as compared with 

 690 millimeters in B. robustus 

 (type). Its maximum hori- 

 zontal diameter is 572 mil- 

 limeters. The postspinous 

 fossa is much more expanded 

 than the prespinous fossa, the 

 posterior border presenting a 

 concave backward and up- 

 ward surface to the thick- 

 ened rugose suprascapular 

 border, which rises with a 

 convex arch to a point in 

 front of the spine, at the 

 same time thinning gradu- 

 ally; the anterior border is 

 extremely thin in the mid- 

 section, forming a deep rec- 

 tangle, passing below into 

 the coracoid process; the di- 

 ameter of the glenoid border 

 is 160 millimeters. The tu- 

 berous elevated apex of the 

 spine is considerably below 

 the center of the scapula, in 

 contrast with that in Palaeo- 

 syops major, which is above 

 the center; the spine is still 

 more elevated at this point 

 than in B. rohustus. 



The proportions of the 

 bones of the fore limb are 

 indicated by the relative 

 lengths of the humerus (550 

 mm.), radius (460), and lu- 

 nar to tip of middle digit 

 (365). 



The humerus is 50 milli- 

 meters shorter than that of 

 Marsh's type of B. rohustus. 

 Its greater tuberosity and 

 deltoid crest are substan- 

 tially similar to those in the type of B. rohustus 

 (PI. CCV); its lesser tuberosity is much more 

 prominent than in that type. These tuberosities, 

 together with the great supinator crest, indicate 

 an enormous development of the supraspinatus, infra- 

 spinatus pectoral, subscapularis, deltoid, and other 



muscles. The anterior trochlea of the humerus, as 

 in that of B. rohustus, presents a decided upward 

 extension of the internal face, correlated with the 

 elevation of the internal half of the radius. This 

 is a distinctive character of the titanothere forearm. 



Figure 608. — Scapulae of Oligocene titanotheres 



A, Brontops robuDtus, Yale Mus. 12048 (type); B, Brontops, Am. Miis. 518; C, AUops crassicornis, British Mus. 5743 M; 



D, Menodus Irigonoceras, Munich Museum. One-eighth natural size. 



The proportions of the radius may be judged from the 

 total length (460 mm.) as compared with the total 

 proximal breadth (165 mm.) and the distal breadth 

 (162 mm.), figures which should be contrasted with 

 those of the radius of Menodus giganteus. The prin- 

 cipal characters are the elevation of the inner side of 



