706 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



In preparation for this work and as a part of our 

 studies of the muscular anatomy of the entire titano- 

 there skeleton, Gregory and Christman made a 



form, muscle form, and external appearance were 

 observed not only by this means but in living rhinoc- 

 eroses, tapirs, and other animals in the New York 



comparative study of the head muscles of the tapir, | Zoological Park and elsewhere. These observations 



were gradually applied to the study of 

 the muscular anatomy of the heads of 

 titanotheres ; and the probable location 

 of the bony areas of muscular origin 

 and insertion were determined and illus- 

 trated in the series of diagrams here 

 presented. 



Next a series of reconstructions of 

 the skulls of five Eocene and Oligocene 

 titanotheres was carefully made. Each 

 model in this series forms a synthesis 

 of the best-preserved specimens of parts 

 of the skull of the species it represents, 

 for no one fossil skull is perfectly pre- 

 served. In these models also the distor- 

 tion and crushing of the originals were 

 corrected. The muscles of the jaw, 

 neck, and face were modeled first upon 

 one side, and after the models had been 

 photographed in this stage the other 

 side was modeled. 



The general shape of the muscles of 

 the jaw and neck in recent perissodactyls 

 is plainly indicated by the form and 

 extent of the temporal fossae, lower 

 jaw, and occiput, and our models of 

 titanothere heads are doubtless fairly 

 accurate in these parts. The precise 

 shape of the nose and lips is more diffi- 

 cult to determine, but the models here 

 figured represent the result of a series of 

 carefully considered hypotheses based 

 upon a wide range of comparative ana- 

 tomical facts. 



In this series of restorations we have 

 taken into account the origin, evolution- 

 ary trend, and systematic relations of 

 all the animals studied. First we con- 

 sidered the structure, the habits, and 

 the probable appearance of the earliest 

 known and generalized members of the 

 titanothere group and of the related 

 families of perissodactyls — the earliest 

 "tapirs," "rhinoceroses," "horses, "etc. 

 Second we studied the diverse and highly 

 specialized end members of these fami- 

 lies, and third we studied the interme- 

 diate types. In the order Perissodactyla 

 unusually complete material for such 

 study is available. We know the skull and the den- 

 tition of many genera of primitive lower Eocene 

 perissodactyls; we know the features of a still greater 

 number of their divergent descendants in the middle 



Figure 643. — Facial musculature and nasal cartilage of a lower Oligocene titano- 

 there {Brontotherium plaiyceras) 

 Ai, Superficial layer of muscles; A2, relations of nasal chamber and surrounding muscles to skull. One- 

 sixth natural size. 



horse, elephant, and other mammals, as elaborately 

 figured by Boas, Murie, Schmaltz, and others. Obser- 

 vations were also made of freshly dissected heads of 

 horses and zebras. The correlations between bone 



