THE MUSCULAR ANATOMY AND THE RESTORATION OF THE TITAN OTHERES 



705 



inserted on the rather small coronoid process. The 

 internal and external pterygoids were as well developed 

 as in other perissodactyls. They doubtless assisted 

 greatly in oblique and lateral movements of the 

 mandible in feeding. 



As thus interpreted, the Eocene titanotheres differed 

 from the tapirs in having the upper branch of the 

 maxillolabialis placed more directly anteroposteriorly 

 instead of having it run more obliquely upward and 

 forward over the nasal cartilage. This arrangement is 

 clearly implied by the shape of the nasals 

 which are not pointed and retracted as in the 

 tapir but long and distally spreading. Thus 

 the shape of the nasals in Manteoceras proves 

 that this animal could not have had a pro- 

 boscis. Both branches of the maxillolabialis 

 in Eocene titanotheres probably occupied their 

 primitive position, immediately in front of the 

 orbit, as shown by the raised preorbital border 

 and by the depression in front of it. 



In Oligocene titanotheres the great deep- 

 ening and shortening of the preorbital part of 

 the skuU was accompanied by corresponding 

 changes in the facial muscles. The area for 

 the nasal chamber and for the dorsal branch 

 of the maxillolabialis was greatly increased 

 transversely but shortened anteroposteriorly, 

 the muscle being bounded postero-externally 

 by the sharp external ridge running down from 

 the horn to the front end of the zygomatic 

 arch. The inferior branch of the maxillo- 

 labialis may well have covered the region below 

 the infraorbital foramen, and probably its pos- 

 terior tendon was attached to the rough surface 

 below the orbital rim, along with the anterior 

 end of the fascia of the masseter. 



The progressive abbreviation of the nasals 

 in certain phyla, Brontops, Allops, Megacerops, 

 together with the great widening of the area 

 of origin of the maxillolabialis and the narrow- 

 ing of the end of the lower jaw, points to the 

 progressive development of an enormous nasal 

 chamber and highly protrusile lip-nostril com- 

 plex of great vertical thickness. 



In the Menodus phylum, on the other hand, 

 the persistently wide nasals and the general 



configxiration of the face are somewhat more 



suggestive of the rhinoceroses; probably these ,,/////^''i0' 



cursorial titanotheres were more square-lipped Figure 642. — Facial musculature and nasal cartilage of a lower Oligocene 



and the upper lip was less pendulous. titanothere {Menodus giganteus) 



In Eocene titanotheres the masseter and Ai, superficial layer of museles; A2, relations of nasal chamber and surrounding muscles to 



its fascia extended over the whole lower 



skull. One-sixth natural size. 



border and part of the inner side of the malar, 

 as indicated by the presence of deep scars in this 

 region, analogous to similar scars among other 

 perissodactyls. The masseter was inserted along 

 the outer rim of the expanded angle of the 

 mandible. 



In Oligocene titanotheres the masseter was relatively 

 of enormous size. The temporal muscle doubtless 

 filled a great part of the temporal fossa and was 



SECTION 2. RESTORATIONS OF THE HEADS OF 

 TITANOTHERES 



Preliminary restorations of the heads of a series of 

 eight Eocene and Oligocene titanotheres were made 

 some years ago by Charles R. Knight under the direc- 

 tion of Professor Osborn (figs. 220, 640). Afterward it 

 was felt that the mouth and nose of these models called 

 for further study, and a series of life-size head models 

 was projected. 



