EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



669 



and by the downward and forward projection of the 

 trochlea. In the distal view (fig. 5) we are struck by 

 the great disproportion between the greatly enlarged 

 inner condyle (fig. 5 i) and the much reduced external 

 condyle (fig. 5 e). This asymmetry of the end of the 

 femur is naturally correlated with the asymmetry of 

 the proximal faces of the tibia. The patella measures 

 165 millimeters vertically, 105 transversely, 100 

 anteroposteriorly; it is very stoutly convex. 



Tibia.— The proximal face of the tibia (PI. CCXXI), 

 exhibits an elongate internal facet for the inner 

 condyle of the femur (fig. 5 c) and a shorter external 

 facet for the outer condyle (fig. 5 e). The facets con- 

 verging into the wide and distinctly paired intercon- 

 dylar spines — that is, the internal and external 

 facets — -are entirely separate; the cnemial crest is 

 obtusely rugose (fig. 1). The shaft (fig. 1 a) is tri- 

 hedral in midsection, the transverse diameter being 

 81 millimeters and the anteroposterior diameter the 

 same. Distally there is a shallow trochlea for the 

 astragalus (fig. 6). 



Fibula.— The fibula (PI. CCXXII), articulating by a 

 flat proximal extremity (fig. 8) to the outer face of 

 the tibia, extends into a rounded or subtrihedral shaft 

 to form the external malleolus with facets (fig. 7 t', a, 

 c, and fig. 5 a) for the tibia, astragalus, and calcaneum. 



Pes.— The left pes (PL CCXXVIII, fig. 2) is perfectly 

 preserved except the phalanges. The maximum width 

 of the astragalus and calcaneum combined is 144 mil- 

 limeters, the depth from the top of the astragalus to 

 the extremity of Mts III 320, to the extremity of the 

 phalanx of D. 3 420 (estimated). The calcaneum (PI. 

 CCXXIV) is distinguished by moderate length (230 

 mm.), marked width (85 mm.) of the shaft of the tuber 

 calcis (figs. 1-3), the long axis of which is obliquely 

 transverse. The anterior or astragalar face (fig. 1) ex- 

 hibits tibial (t), fibular (f) (32 mm.), ectal (a) (78 mm.), 

 sustentacular (a') (55 mm.), and inferior (a") (32 mm.) 

 facets, the last being strikingly reduced; distally 

 (fig. 5) the cuboidal facet is divided into two parts, 

 a larger anterior and a very much smaller posterior 

 part; it also shows the ectal (a') and sustentacular (a") 

 calcaneal facets. The astragalus (PI. CCXXIII) is 

 distinguished by the small astragalo-calcaneal inferior 

 facet, the very broad (44 mm.) cuboidal facet (fig. 

 3 c"), the moderate elongation of the neck (fig. 1); 

 the total width of the proximal trochlea (fig. 5) is 112 

 millimeters. The cuboid (PI. CCXXV, figs. 7-12) is dis- 

 tinguished especially by its broad abutment (fig. 12, 

 mt III; 35 mm.) for Mts III; superiorly the cuboido- 

 calcaneal facet (fig. 11; 35 mm.) is double (c, c") 

 and somewhat narrower than the cuboido-astragalar 

 facet (fig. 11a; 36 mm.) ; it unites with the ectocunei- 

 form (fig. 8, ec) by two separate facets, the posterior 

 of which is not represented in the drawing; its maxi- 

 mum vertical depth (fig. 7) is 46 millimeters. The 

 navicular (PI. CCXXV, figs. 1-6) is shallow (fig. 1; 35 



mm.), presenting inferiorly (fig. 6) a broader (42 mm.) 

 ectocuneiform (ec) and a narrower (30 mm.) mesocu- 

 neiform (m) facet. The distinctive feature of the 

 ectocuneiform (PI. CCXXVI, figs. 7-12) is its anterior 

 depth (fig. 7; 27 mm.) and double, internal lateral 

 abutment facets (fig. 8, mt. II; fig. 12, mt. II, mt. II') 

 for Mts II; the mesocuneiform (PL CCXXVI, figs. 1-6) 

 is consequently shallower (fig 2) vertically (20 mm.), 

 measuring superiorly (fig. 5) 35 millimeters (tr.) by 48 

 (ap.). Mts II (PL CCXXVIII), measuring vertically 

 180 millimeters, abuts laterally above, against the ecto- 

 cuneiform, a primitive feature; the shaft with a sharply 

 convex ridge in front is deeply concave behind. Mts 

 III (PL CCXXVIII) , measuring 208 miUimeters verti- 

 cally, is distinguished by its moderately broad (42 mm.) 

 ectocuneiform, an unusually broad cuboidal (35 mm.) 

 facet; the shaft is broadly convex anteriorly and hollow 

 posteriorly. Mts IV (PL CCXXVII, figs. 1-7), measur- 

 ing 170 miUimeters vertically, exhibits a shaft subrec- 

 tangular in section superiorly and flattened and 

 rounded in its middle portion (fig. 7), with a rugose 

 line for muscular attachment, extending obliquely 

 downward and inward across the anterior face (fig. 

 1); the distal face (fig. 6) exhibits the large share 

 taken by the sesamoids (ss) and the limited share 

 taken by the phalanges {pJi). 



Mounted skeleton in the American Museum of Natural 

 History provisionally referred to Brontops 



A mounted skeleton and skull (No. 518) in the 

 American Museum of Natural History is now pro- 

 visionally referred to the genus Brontops. It exhibits 

 many specific if not generic distinctions from the 

 type skeleton of B. robustus just described. Yet the 

 characters of the skull and teeth relate it to Brontops 

 and clearly separate it from either Menodus or 

 Brontotlierium. 



The skeleton is a composite. Its anterior part as 

 far back as the ilium belongs to one individual (Am. 

 Mus. 518) which was discovered by the American 

 Museum expedition of 1892, sent out under the direc- 

 tion of Dr. J. L. Wortman, who was assisted by Mr. 

 O. A. Peterson. It was found near the head of Corral 

 Draw in the Big Badlands of South Dakota. Accord- 

 ing to N. H. Darton, who in 1901 determined the level 

 of this specimen, it was found 32 feet below the 3-foot 

 sUiceous limestone layer at the top of the Titanotherium 

 zone (level Chadron C). Expeditions in two subse- 

 quent years, aided by the Princeton expedition, 

 resiflted in the discovery of the remains of other 

 animals of simUar proportions, which were used in 

 the mounted skeleton — namely, the pelvis (Am. Mus. 

 1065), the left tibia (Am. Mus. 1075), fibula (Am. 

 Mus. 1071), pes (Am. Mus. 1073, 1076), two femora 

 (Am. Mus. 1442, 1443). A few parts in the feet are 

 restored in plaster. The collocation of these hinder 

 parts with the leading specimen is probably not 

 certainly correct. 



