EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



601 



tinctive motions of the fore limbs as follows: (a) The 

 great tuberosity of the humerus expands into a broad, 

 elevated plate; the deltoid crest descends into a dis- 

 tinct tuberosity; the supinator crest secondarily 

 increases in size and prominence. Of the above 

 characters the platelike great tuberosity (fig. 510) is 



Primitively (Eotitanops iorealis) the deltoid tuber- 

 osity of the humerus is near the upper part of the 

 shaft; secondarily it is extended downward. Prim- 

 itively the great tuberosity is a sessile prominence 

 divided by a shallow median notch; secondarily it 

 becomes very prominent and platelike and is divided 



fo.intei^v. 



E4 



FiGUKE 508. — Atlas of Eocene titanotheres 



A, Palaeosyops rohustus, Am. Mus. 1580, upper Bridger; B, Telmatherium ullimum, Am. Mus. 2060 (type), Uinta C; C, Mesatirhinus megarhinus. Am. 



Mus. 1523, upper Bridger; D, DoUchorhinus sp., Am. Mus. IS44, Uinta C. A-D, Dorsal views. E, Manieoceras manteoceras, Am. Mus. 12204, upper 



Bridger: Ei, Dorsal view; Ej, ventral view; Ej, anterior view; Ei, posterior view. One-third natural size. The arrows indicate the course of the first 



spinal nerve and vertebral artery. 



the most distinctive, (b) Distally the radio-ulnar 

 articulation (rotula and capitellum) is decidedly 

 asymmetric; this asymmetry persists in the titano- 

 theres; its significance is fully explained on page 602. 

 (c) The ectocondylar or supinator crest is already quite 

 prominent, (d) The entocondyle is less prominent. 



by a very deep median notch. Primitively the ecto- 

 condylar crest, which is small, is distinctly defined, 

 rising somewhat on the shaft (Eotitanops); second- 

 arily it rises and widely expands. A distinctive fea- 

 ture of the humerus as compared with that of the 

 Hyracodontidae and Amynodontidae is the prominent 



