714 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



SECTION 4. MUSCLES OF THE LIMBS OF THE EOCENE 

 TITANOTHERE PALAEOSYOPS (SUBGRAVIPORTAL 

 TYPE) 



The limb bones of the middle Eocene titanothere 

 Palaeosyops are so much like those of existing tapirs 

 (Tapirus) that it is highly probable that the positions 

 and courses of the muscles were also essentially smiilar, 

 the differences being chiefly due to the more robust 

 development of certain muscles ia Palaeosyops. Both 

 animals are tetradactyl-tridactyl. Tapirus is typically 

 mediportal; Palaeosyops is subgraviportal. 



In the following study Murie's description (1872.1) 

 of the myology of the tapu- and Windle and Parson's 

 studies (1901.1; 1903.1) on the muscles of the ungu- 

 lates were constantly used, and comparisons were 

 made with the myology of other mammals, especially 

 the horse, as figured by Schmaltz (1909.1). 



tendon of the trapezius, which covered the 

 shoulder muscles of the neck and back. To the lower 

 border of the spine was attached a slip of the deltoid, 

 which lay outside the broad infraspinatus muscle. 



The infraspinatus muscle passed downward below 

 the spine and above the teres minor, which in turn was 

 probably attached to the ridge for the teres minor, 

 obliquely traversing the lower third of the postspinous 

 fossa. Above and behind this streak, near the angle 

 of the scapula, is a rough streak which is probably for a 

 second slip of the deltoid. 



Along the axillary border and running below into a 

 rugose axillary prominence, as well as into a curved 

 area behind the ridge for the teres minor, is the origin 

 of the long head of the triceps, the largest muscle of 

 the forearm. The posterior angle of the scapula is 

 roughened for the teres major. 



Serraius cervicis 

 [Levaior- scan.) 



PecioraliS 

 profundus 



Tr-apezius 



Pectoralis profundus 

 Delioideus 



■Biceps 



Coraco brach-ial, 



Cap-ui 

 lonp'um. 

 Triceps 



Figure 652. — Right scapula of a lower Oligocene titanothere (Broniotherium cf. B. gigas), showing the principal 



muscle attachments 

 A', inner side; A', outer side. (Compare flg. 623.) 



MUSCIES OF THE FOKE LIMB 



[See PI. XLIV, A] 

 MUSCULAR ATTACHMENTS OF THE SCAPULA 



The large scapula is about •j-Vo" ^-s long as the 

 humerus and afforded a broad base for the massive 

 shoulder muscles. The superior border is roughened 

 for the rhomboideus; the anterosuperior continuation 

 of this roughening may have given attachment to the 

 serratus cervicis (levator scapulae) subclavius and, in 

 its antero-inferior part, to the pectoralis profundus 

 (pars ascendens). 



The coracoid process gave origin anteriorly to the 

 single-headed biceps and inferiorly to the coracobra- 

 chialis. 



The supraspinous fossa and its muscle area for the 

 supraspinatus are broad and well defined, and the same 

 is true of the postspinous fossa, which is the area 

 chiefly for the infraspinatus. The spine of the scapula 

 is reflected and bears a'prominent tuberosity for the 



The medial or internal surface of the scapula in its 

 upper third bears a large triangular roughening for the 

 serratus magnus; below this nearly the whole surface 

 was filled by the subscapularis. 



Near the axillary border the medial surface is raised 

 into a long, gently convex eminence or column running 

 parallel and internal to the postspinous fossa and 

 culminating above in the surface for the serratus. 

 This subscapular column greatly strengthens the blade 

 against the pull of the serratus, infraspinatus, sub- 

 scapularis, and caput longum of the triceps. 



MUSCULAR ATTACHMENTS OP THE HUMERUS 



The great tuberosity, expanded into a broad flange, 

 gives insertion on its anterior hook to the supraspina- 

 tus; a branch of this muscle forks over the biceps and 

 is inserted into the lesser tuberosity. The superior and 

 external surfaces of the great tuberosity form the 

 insertion area for the infraspinatus. The bicipital 

 groove is filled by the single-headed biceps. 



