412 



TITANOTHERES OP ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



the articular facets for the condyles of the jaw. The 

 postglenoid processes are narrow and tuberous; the 

 glenoid facets are not transverse in position but 

 directed obliquely forward, as if their outer borders 

 were drawn out anteriorly by a stretching of the skull. 

 In M. manteoceras these glenoidal facets are more 

 directly transverse. The whole basicranial region is 



Vplam.ms.plj 



VlpfJUJO 



Figure 347. — Skull of Dolichorhinus hyo- 

 gnathus 



Palatal view. One-fourth natural size. Am. Mus. 1S51 

 (type of Telmaiotherium cornutum Osborn). Supple- 

 mentary details from Am. Mus. 1845. Both specimens 

 from White Kiver, Uinta Basin, Utah; Uinta B 2. 



correspondingly elongate, the bridge of bone separat- 

 ing the foramen ovale and the foramen lacerum medium 

 now measures 42 millimeters as compared with 27 in 

 M. petersoni or 17 in the brachycephalic LimnoTiyops 

 laticeps. 



The anterior aspect of the skull (fig. 348) exhibits 

 the extraordinarily long premaxillo-maxillary rostrum, 

 which extends horizontally backward into the floor of 



the narial chamber, the total length being 144 milli- 

 meters. The infraorbital shelves are well shown. 

 The infraorbital foramina are deep and narrow; the 

 nasals are vertically decurved at the sides, so that 

 they form three sides of a square. The projection of 

 the nasal horns, although the animal is a female, is 

 admirably illustrated. 



The lateral aspect of the skull (fig. 349) shows that 

 the midcranial concavity characteristic of Manteo- 

 ceras and the Oligocene titanotheres is replaced in 

 this species by the prominent frontoparietal convexity, 

 the lowest point of the cranium in the upper profile 

 being above the orbits between the horns. The suture 

 between the maxillary and the nasals is similar in 

 form to that in related species, the nasofrontal junc- 

 tion being above the orbit. The failure of the frontals 

 to send forward a spur overlapping the enlarged nasals 

 is well shown. A broadly concave space (68 mm.) 

 separates the narial notch and the orbit, and the 

 infraorbital foramen issues 33 to 40 millimeters in 

 front of the orbit. The maxillaries contribute to the 

 anterior portion of the infraorbital process, the chief 

 convexity being formed by the malars. Below the 

 orbits the malars are gently concave, as in the related 

 species of this genus. Other characteristic dolicho- 

 cephalic features are the limited vertical extent of the 

 zygomatic portion of the squamosal, the great fore 

 and aft thickening of the postglenoid processes, and 

 the widely open external auditory meatus. 



The occipital view (fig. 348), best shown in Am. Mus. 

 1845, is highly characteristic. The height of the occi- 

 put, 142 millimeters from the basioccipital to the 

 supraoccipital crest, approximately equals the width 

 across the middle of the occiput. Above the foramen 

 magnum two prominent ridges diverge and terminate 

 in tuberous convexities in the upper lateral portions 

 of the crest. 



The interior structure of the skull, including that of 

 the narial and cranial cavities, is shown in Figure 254. 



Dentition in general. — The grinding teeth are more 

 or less perfectly preserved in most of the crania and 

 jaws; three specimens afford a complete knowledge 

 of the upper and lower cutting teeth. 



Incisors. — The superior series has a semicircular 

 arrangement (Am. Mus. 1851); the median pair are 

 separated by a considerable diastema (12 mm.). The 

 incisors increase in size regularly from i^ to i'. They 

 exhibit convex anterior faces, more flattened posterior 

 faces, with a median convex ridge. The posterior 

 cingulum rises to form a distinct cup in i^ less marked 

 in i^ and i'. P is fully incisiform (in contrast to its 

 caniniform shape in the contemporary Telmatherium) ; 

 it exhibits a narrow antero-external cingulum besides 

 the postero-internal, obliquely sloping cingulum; it 

 differs from other incisors in its more elevated crown. 

 A narrow diastema (9 mm.) separates i' from the 

 canine. 



