EVOLUTION OF THE SKULL AND TEETH OF EOCENE TITANOTHERES 



411 



the horns are gentle longitudinal valleys separated by 

 median longitudinal convexities; the horn bases thus 

 actually rise decidedly above the surrounding surfaces 

 and overhang the orbits. A biologic fact of interest is 

 that the horns appear to be developed as strongly in 

 the female as in the male skulls and are not at this 

 stage a distinctively sexual character; in none of the 

 crania are they distinctly rugose, as in some of the 

 male crania of M. manteoceras . Under these horn 

 swellings, which are 127 millimeters apart, the nasals 



nent paired eminences, as in Am. Mus. 13164. The 

 extreme elongation of the posterior nares is unique 

 among perissodactyls. The pterygoid plates of the 

 alisphenoid are elongate and depressed on either side 

 of the long and narrow postnarial depression. The 

 palatines do not crowd into the postnarial space as in 

 M. manteoceras. The infraorbital malar plates con- 

 stitute a very prominent shelf, the anterior part of 

 which is shown by the sutures to be composed of the 

 maxillaries. To this prominent infraorbital shelf 



Figure 346. — Skulls of Dolichorhinus 

 One-fourth natural size. A, D. longkcps, Carnegie Mus. 2347 (type), Uinta Basin, Utah, Uinta B 

 B, B. hyognatlius, Am. Mus. 1851, White Eiver, Uinta Basin, Utah, Uinta B 2. 



narrow to 66 millimeters, then broaden again to 76 at 

 the widest point near their extremities. 



Palatal aspect. — As seen from below (fig. 347), the 

 elongation of the palate, in which the palatine and 

 maxillary plates take about equal share, is a most 

 striking feature. The posterior nares open behind 

 . m^. A kind of secondary palatal plate is formed by 

 the backward and upward extension of the dorsal 

 surface of the palatine. In this compressed post- 

 narial chamber the maxilloturbinals appear as promi- 



was probably attached an anterior slip of the masseter 

 muscle, as in many other mammals with weak zygo- 

 mata. Behind these projections the malars are seen 

 to present a long and comparatively narrow edge. 

 The lacrimals are larger and have a broader extension 

 on the face than in any other species. The lacrimal 

 tubercle is preserved in one skull, as in the Palaeosyops 

 series. 



Among the most striking results of progressive 

 dolichocephaly are those seen in the conformation of 



