EVOLUTION OP THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



679 



hooklike process for the msertion of the supraspinatus 

 muscle; this process is much less expanded than in 

 B. rohustus. The deltoid tuberosity, on the lower 

 outer part of the deltopectoral crest, is also less devel- 

 oped than in B. robustus. The circumference of the 

 humerus at the nan'owest part of the shaft is 230 

 millimeters. The middle of the shaft is rather slender, 

 but the proximal end is wide. The rugosity for the 

 brachialis anticus, on the anterior face, is prominent. 



The radius is only 360 millimeters in length, as 

 compared with 495 in Brontops robustus (type) and 

 525 in Menodus trigonoceras. The ratio of the length 

 of the radius to the basilar length of the skull, in per 

 cent, is as follows: Allops marshi, 53; Brontops 

 robustus (type), 64.8; Menodus trigonoceras, 75. 



The ulna also is short, 475 millimeters in length, 

 as compared with 680 in Brontops robustus (type) and 

 595 in Menodus trigonoceras. The olecranon is long 

 and less expanded than in B. robustus (type). 



The manus is small, measuring only 142 millimeters 

 across the proximal carpals as compared with 200 in 

 Brontops robustus (type). At the same time it is 

 relatively wider than that of Menodus trigonoceras, 

 which has about the same absolute width (149 mm.) 

 but a far longer median metacarpal. The carpals 

 present nothing remarkable. The combined trans- 

 verse width of the scaphoid and lunar is 95 milli- 

 meters; that of the cuneiform 49. The depth of the 

 carpus from the top of the lunar to the summit of 

 Mtc III is 63 millimeters. The median metacarpal 

 (Mtc III) is relatively and absolutely short and wide, 

 155 millimeters in length as compared with 225 in 

 Brontops robustus (type) and 233 in Menodus tri- 

 gonoceras. 



Hind limb. — The hind limb is quite short, the length 

 of the limb from the head of the femur to the ground 

 being only 1,150 millimeters (estimated), even with 

 the limb fully extended. 



The crest of the ilium is relatively narrow, measuring 

 530 millimeters in width. 



The femur (length 590 mm.) is relatively shorter 

 than in Brontops robustus (type), the ratio of the 

 length of the femur to the basilar length of the skull, 

 in per cent, being as follows : Allops marsJii, 90; Brontops 

 robustus (type), 107; Menodus trigonoceras, 100.4. 

 The circumference of the shaft of the femur is 210 

 millimeters. 



The tibia is short (length 350 mm.), the compara- 

 tive ratios of the length of the tibia to the basilar 

 length of the skull, in per cent, being as follows: 

 Allops marshi, 53; Brontops robustus (type), 56; 

 Menodus trigonoceras, 60. 



The pes is small, the length of the calcaneum being 

 only 147 millimeters as compared with 230 in Brontops 

 robustus. The width of the tarsus across the navicular 



and cuboid is 90 millimeters, the width of the astraga- 

 lus 70, and that of the cuboid 42. The tuber calcis is 

 oval in section. The facet for the fibula on the calca- 

 neum is prominent. 



Allops crassicornis (referred) 



An incomplete skeleton in the British Museum 

 (5743 M) belongs with the skull described in Chapter 

 VI. The poster anial skeleton is represented by the 

 atlas, axis, two cervicals, two dorsals (all more or less 

 crushed or imperfect), the right humerus, radius, 

 and manus (lacking cuneiform and two distal rows 

 of phalanges), the left femur, tibia, and astragalus, 

 the right pes (lacking meso- and entocuneiform and all 

 the smaller phalanges), the right and left patellae. 



Vertebrae. — As compared with B. robustus the trans- 

 verse processes of the atlas were proportionately 

 smaller, projecting less, rounded instead of truncate 

 distally; the facets for the occipital condyles were less 

 oval in shape and tapering more at the bottom; in top 

 view the atlas lacks the median groove in the neural 

 arch seen in B. robustus. In the inferior view there is 

 a decided median process from the posterior haemal 

 surface. 



Measurements of the atlas 



Millimeters 



Extreme width 275 



NTeural arch, maximum anteroposterior 87 



■ Width across cotyli 180 



In comparison with B. robustus (type) the verte- 

 brarterial foramen of the atlas is larger, the dorsal 

 expansion of the neural arch is lighter, the odontoid 

 less spout-shaped, the condyles for the atlas more ver- 

 tical, narrower transversely and deeper vertically; on 

 the inferior surface the haemal ridge seems more pro- 

 nounced. 



Measwfiments of the axis 



Millimcteis 



Width across cond^des (estimated) 180 



Odontoid to posterior border of centrum 93 



Fore limb. — The scapula is well preserved, 570 milli- 

 meters in length and 290 in width, less expanded 

 laterally than in B. robustus. The humerus (length 

 450 mm.) is slightly longer than that of the Field 

 Museum specimen of A. marshi (425). The circum- 

 ference of the shaft measures 225 millimeters. The 

 radius is similar to that of A. marshi, its length being 

 350 millimeters, circumference of shaft 160, breadth of 

 distal end 120, of proximal end 117, least width of 

 shaft 48. The manus is noteworthy for the wide dis- 

 placement of the scaphoid on the magnum, of the 

 lunar o n the unciform, so that there is only a very 

 narrow lunar-magnum facet. Perhaps in correlation 

 with this character the median metacarpal (Mtc III) 

 appears to be relatively somewhat wider than in typi- 

 cal Oligocene titanotheres. 



