CHAPTER VIII 



THE MUSCULAR ANATOMY AND THE RESTORATION OF THE TITANOTHERES « 



By William K. Gregory 

 SECTION 1. MUSCLES OF THE FACE AND JAW 



The skeleton of Eocene titanotheres resembles 

 that of other perissodactyls in so many points that 

 the general position and course of the principal 

 muscles may be inferred by comparison with the 

 musculature of existing perissodactyls — the horses, 

 tapirs, and rhinoceroses. 



and Windle and Parson's work on the muscles of the 

 Ungulata (Windle, 1901.1, 1904.1) were also con- 

 sulted. Other authorities referred to are Cuvier, 

 Cunningham, Ellenberger, Haughton, Schmaltz, Still- 

 man, and Weisse. (See Bibliography, p. 802.) 



A study of existing musculature enabled the writer 

 (Gregory, 1920) to infer the general anatomy of the 



Figure 640. — Heads of four titanotheres 



Representatives of the four principa genera of lower Oligocene time, restored by Charles R. Knight under the direction of the author. 

 A, Brontops roiusius; B, Menodus gigantms; C, Megacerops copei; D, Brontotherium platyceras. About one-seventeenth natural size. 



The facial muscles of the horse, of the tapir, and 

 of many other mammals have been described and 

 superbly figured in a great monograph by J. F. V. 

 Boas and S. PauUi (Boas, 1908.1). The facial muscles 

 in the Sumatran rhinoceros have been briefly described 

 and figured by Beddard and Treves (Beddard, 1889.1). 

 Murie's dissection of the Malayan tapir (1872. 1) 



" The conclusions here presented are the results of studies made in 1912, 1917, 

 and 1918 (Gregory, 1920.1). The drawings from which the figures were reproduced 

 were made by Erwin S. Christman. 



facial muscles in the extinct Tertiary ancestors of the 

 tapirs, horses, and rhinoceroses and especially the 

 Eocene and Oligocene titanotheres. 



In the Eocene titanotheres, such as Manteoceras 

 (fig. 641), the smooth anterosuperior border of the 

 premaxillae and the adjacent region of the maxillae, 

 as well as the front end of the lower jaw, doubtless 

 lay beneath the orbicularis oris muscle, which sur- 

 rounded the mouth. This muscle in ungulates,' 



703 



