534 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



slightly downward projection. Other conspicuous 

 characters are the relatively large orbits (as compared 

 with those of Brontotherium) , the bridge over the 

 infraorbital foramen, the steep slope of the occipital 

 vertex (contrast Brontotherium). Additional features 

 of advancing age are the development of the marked 

 supraciliary expansion of the lateral frontal parietal 

 crest (Nat. Mus. 1220), the obliteration of the suture 

 between squamosal and malar. 



Horns. — The distinctive characters of the horns are 

 not only the connecting crest, which, as shown in the 

 section, is situated very far back, but the normal 



triangle with the external angle at the vertex. (See 

 figs. 399, 444, 445.) The skull has other distinctive 

 features: First, we observe the width of the bridge 

 over the infraorbital foramen; as in the Palaeosyopinae 

 and also in the related Brontops phylum this bridge 

 extends into a thin plate anteriorly, so that the fora- 

 men is distinctly seen on the side of the face, whereas in 

 Brontotherium and Megacerops the malar bridge is 

 narrow and convex and the foramen is not seen in 

 side view. This elongate condition of the infraorbital 

 canal and breadth of the malar bridge is correlated 

 with the dolichocephaly existing throughout the 



A 



B 



Figure 444. — Sections and contours of skulls of Menodus giganteus and M. varians 



M. giganteus: A, Am. Mus. 505, cf (neotype), and B, Yale Mus. 12010 (type of Brontotherium ingens); relatively long-pointed horns witli a prominent 

 anterior swelling suggestive of the accessory hornlet in Diploclonus, horns trihedral in hasal section, connecting crest near the plane ot the posterior 

 face of the horns, nasals long and wide, zygomata little expanded. C, M. varians, Yale Mus. 12060 (type); horns thiclser (especially at the top), basal 

 section widely trihedral, nasals broad and thicli, zygomata somewhat expanded. One-ninth natural size. 



direction, which is chiefly outward and slightly up- 

 ward. A very distinctive character in front view is 

 the straight inferior contour of the horn (see fig. 442); 

 all members of the Brontotherium and Megacerops 

 series have a curved or convex lateral inferior contour 

 as seen from in front. Correlated with the lesser 

 strain of the horns and the great breadth of the 

 anterior nares the maxillary pillars on either side of 

 the anterior nares are much thinner than in the stout- 

 horned species. The basal horn section as compared 

 with that of M. trigonoceras has already been described 

 and is very distinctive; briefly it consists of an isosceles 



skull. In the midline of the parietal crest there is 

 observed a median ridge clearly shown in the section, 

 there is also occasionally a conspicuous knob in the 

 midparietal region. In the occipital region we observe 

 a mastoid foramen; the postglenoid and paroccipital 

 processes are proportionately narrower and deeper 

 than in the Brontotherium series, another fact in keep- 

 ing with the dolichocephalic structure of the skull. 

 Again there is narrower contact between the post- 

 glenoid and post-tympanic, a more open auditory 

 meatus, and a wider space behind the ear than in the 

 brachycephalic types. 



