EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



635 



verse extent (170 mm.) of the sacral arcade, the 

 flattened anterior (inferior) faces of the ilia, the vertical 

 keel below the pubo-ischiadic symphysis, the deep 

 acetabular notch. Its graviportal adaptation is indi- 

 cated by the uniformly convex superior border of 

 the broadly expanded ilia, in contrast with the 

 indented border of the pelvis of Limnohyopsf (Am. 



fo&paC 



a 



IB 

 TTialu 



FiGTJHE 556. — Femora and tibiae of 

 Manieoceras manteoceras 



A, Left tibia and distal end of femur, Am. Mus. 

 12204, Bridger D 2, front view; B, left femur and 

 tibia, Am. Mus. 1587, Bridger C or D, front 

 view. One-sixth natural size. 



Mus. 2348) mounted in the skeleton of P. leidyi 

 (see above). 



The femur (Am. Mus. 1587, 12204) is not very well 

 preserved. Its length (400 mm.) is somewhat less 

 than that (435 mm.) of a large Palaeosyops major 

 (Am. Mus. 13116) from Bridger B 3; it is relatively 

 stouter than in the large Mesatirhinus petersoni 



(No. 11659); the third trochanter is large; the distal 

 condyles are more sharply keeled than in Palaeosyops 

 major. 



The tibia (Am. Mus. 1587, 12204) is much shorter 

 (length 265 mm.) than in Palaeosyops major (325 mm.) ; 

 it is somewhat shorter and much stouter than in 

 Mesatirhinus, and the proximal end is relatively 

 broad (87 mm). 



The astragalus (Am. Mus. 1587, 12204) parallels 

 that of LimnoJiyops and Palaeosyops in the following 

 characters: Trochlea broad with very convex tibial 

 keel, neck relatively broad, cuboid facet broad, sus- 

 tentacular facet not very long vertically. It differs, 

 however, from that of the Palaeosyopinae and shows 

 the subfamily kinship with Mesatirhinus in the fol- 

 lowing: Neck not so broad in proportion to the total 

 height, navicular facet deep anteroposteriorly, sus- 

 tentacular facet straight-sided, forming with the 

 cuboid facet a broad L, its internal or tibial edge 



Figure 557. — Left astragalus of Man- 

 teoceras manteoceras 



Am. Mas. 1587; Bridger C or D; front and rear 

 views. One-third natural size. 



set nearly flush with the internal face of the bone; 

 depression on internal face beneath the tibial keel not 

 forming a deep pit; process on internal face near distal 

 end forming a marked protuberance; articular surface 

 of the trochlea extending down antero-internally on 

 to the pedicle of the trochlea. The astragalus is 

 distinguished from that of Mesatirhinus not only by 

 its greater breadth and stoutness throughout, but 

 especially by the greater breadth of the cuboid facet, 

 the more convex tibial keel of the trochlea, the shorter 

 and broader sustentacular facet. Of the two astragali 

 Am. Mus. 12204 is much the smaller and difl'ers 

 from Am. Mus. 1587 in minor details, differences 

 which may be connected with the fact that No. 12204 

 is an old and possibly female animal, whereas No. 1587 

 is a very large young male. 



The rest of the pes is unknown. 



