EVOLUTION OF THE SKELETON OF EOCENE AND OLIGOCENE TITANOTHERES 



685 



The manus of Menodus (Am. Mus. 1079, fig. 614), 

 fortunately associated with the pes above described, 

 is no less readily distinguished in all its parts from 

 the type of Brontops robustus. Its most striking dis- 

 tinctions lie (1) in the high, narrow proportions of the 

 manus as a whole, but especially of the carpus; (2) in 

 the extreme displacement illustrated especially in the 

 broad abutment of the lunar on the uncifoi'm with the 

 correspondingly reduced narrow oblique lunar magnum 

 facet; and (3) in the small simple form of the magnum 

 which readily distinguishes it from that of Brontops. 

 The proportions are shown in the following measure- 

 ments: Proximal breadth of carpus, 155 millimeters, 

 as compared with length from lunar to extremity of 

 D. 3, 340 millimeters; thus the carpus is relatively 

 narrower from side to side and deeper anteroposte- 

 riorly in proportion to its length than that of Brontops. 



The extreme displacement of the carpus is first 

 noticed in the relatively wide extension of the scaphoid 

 on the magnum, in the correspondingly small weight 

 the lunar transmits to the magnum, as compared with 

 its broad surface resting on the unciform. The an- 

 teroposterior measurement of the radial face of the 

 lunar (73 mm.) decidedly exceeds its transverse 

 measurement (59 mm.), whereas in Brontops rohustus 

 (type) the anteroposterior and transverse measurements 

 of the radial facet of the lunar are subequal. The 

 radial face of the scaphoid measures 55 millimeters 

 transversely by 59 anteroposteriorly. The cuneiform 

 is wanting in this specimen. The trapezoid, which 

 exhibits no face for a trapezium facet, measures 28 

 millimeters vertically, 38 transversely, 48 antero- 

 posteriorly. The magnum measures 25 millimeters 

 vertically by 54 transversely ; it is of simpler and more 

 quadrate form than in Brontops owing to the oblique 

 ectal facet for the lunar above and the unciform below. 

 The unciform is decidedly broad, constituting one of 

 the most characteristic features of the Menodus carpus 

 with its broad abutment against Mtc III, measuring 

 transversely 82 millimeters. The metacarpals are 

 elongate but not extremely so, the vertical measure- 

 ments through the middle of the shaft being, Mtc II, 

 196 millimeters; III, 199; IV, 188; V, 172. The shafts 

 are relatively much more slender than in Brontops 

 rohustus. Mtc III exhibits a short, broad process 

 abutting against the unciform, like that seen in Bron- 

 tops. 



Mounted skeleton in the State paleontologic collection at Munich 



This specimen (fig. 616, B) from the Hat Creek bad- 

 lands of Nebraska comprises the greater part of the 

 skeleton. It was presented to the Museum by Com- 

 merzienrath Th. Stiitzel in 1897. The skull is a typical 

 Menodus trigonoceras. (See p. 528.) The limbs are 

 notably slender and elongate, in comparison with those 

 of Brontops, Allops, and Brontotherium, the apparent 

 slenderness of the limbs having been increased by 

 crushing. The following description is based on the 

 observations of the author and of Dr. Ernst Stromer 

 von Reichenbach. 



Mounting. — The skeleton as mounted has the 

 scapulae placed too low on the sides of the thorax, 

 the curvature of the backbone is not quite correct, the 

 intervertebral spaces are not wide enough, so that the 

 backbone is somewhat too short. Certain parts of 

 the skeleton are more or less restored in plaster, 

 especially the symphysis of the lower jaw, the outer 

 side of the first three right upper premolars, the middle 

 of the upper border of the occiput, both wings of the 

 atlas, the spinous process of the atlas, the posterior 

 half of the tail, the greater part of the left ilium, both 

 hind feet (except the upper and lower ankle bones 

 and the second right metatarsus). 



Dimensions. — The total length of the skeleton from 

 the tip of the nasals to the drop of the tail is estimated 

 at 3 meters. The height at the withers, to the tip of 

 the second dorsal spine, is 2.28 meters. 



Figure 617. — Left astragalus of Menodus giganteus 

 Am. Mus. 505, Chadron. Front and rear views. One-third natural size. 



Vertebrae. — The vertebral formula of the specimen 

 as mounted is cervicals 7, dorsals 17, lumbars 3, 

 sacrals 4(?), caudals 21 (restored). 



As compared with Brontops robustus (type) the 

 spine of the atlas is higher and its lateral process 

 thicker, the spine of the axis is longer and lower, the 

 centra of the cervical vertebrae are longer and their 

 spines lower, except the spine of C. 7, which is higher; 

 the spines of the first two dorsals are subequal in 

 height and of fairly uniform diameter from base to 

 summit; the spines of the dorsals D. 4 and D. 5 are 

 straight, less concave anteriorly; the parapophyses 

 appear to be lower. The spine of the third dorsal 

 (D. 3) is the highest; behind that the spines decrease 

 gradually in height to the caudals; all appear thin 

 transversely and relatively high as compared with 

 those of B. robustus. The spines of D. 1-D. 4 are 

 remarkably thin and lack the deep posterior grooves, 

 except at the base. The articular facets of the pre- 

 zygapophyses in the third cervical vertebra present 

 upward and somewhat inward; in the succeeding ver- 

 tebrae they gradually turn more strongly inward, 

 especially in the midthoracic vertebrae. On the last 

 dorsal and first lumbar the articular processes are 

 weaker than usual. The last dorsal bears a shallow 

 facet for the tubercle of the rib. The lumbar vertebrae 

 bear flattened diapophyses just above the base of the 

 neural arches. In D. 1 and D. 2 the posterior zyga- 

 pophyses are nearly horizontal. 



