716 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



MUSCULAR ATTACHMENTS OF THE ULNA 



The massive olecranon has a very rough area for the 

 long head of the triceps; to the olecranon were also 

 attached the external (lateral) and medial (internal) 



Figure 654. — Left Tudius oi Bronlops robustus (type), showing probable position 



and attacliments of principal muscles 



Ai, Front view; As, back view; As, inner side view; Ai, outer side view. One oiglitli natural size. 



heads of the triceps, also the fourth head, or "an- 

 coneus." The inner side of the olecranon probably 

 gave attachment to the palmaris longus and to branches 

 of the flexor digitorum profundus and flexor carpi 

 ulnaris. 



The antero-external face of the ulna, together with 

 the adjacent side of the radius, probably lodged 

 the extensor ossis metacarpi pollicis (extensor meta- 

 carpi obliquus), and the rough outer border of the 

 ulna may have been for a slip of the extensor com- 

 munis digitorum. 



The lower end of the ulna, closely appressed to the 

 radius, retained but little independent movement, 

 yet more than in the tapir. To the outer side of the 

 shaft near the lower end was attached the lateral 

 ulnocarpal ligament. Possibly the groove near the 

 end of the ulna, above the cuneiform, lodged the 

 tendon of the extensor digitorum lateralis. 



On the antero-internal edge (or interosseous ridge) 

 of the ulna was stretched the strong interosseous 

 membrane which separated the extensor from the 

 flexor surfaces of the forearm. 



MUSCULAR ATTACHMENTS OF THE CARPUS 



rows moved apart vertically but preserved their 



transverse alinement. 



On the posterior aspect of the carpus the pisiform 



gave insertion superiorly to the flexor carpi ulnaris and 

 possibly also to a slip of the extensor 

 carpi ulnaris, inferiorly to the abductor 

 minimi digiti; it was also no doubt em- 

 braced by the annular ligament. The ex- 

 tensor carpi ulnaris, according to Windle 

 and Parsons (1901.1, p. 700), in most 

 ungulates serves as a powerful flexor of 

 the carpus. According to these authori- 

 ties the slip attached to the pisiform 

 (which appears to the present writer to 

 belong rather to the true flexor carpi 

 ulnaris) is present in Equus and many 

 artiodactyls but is barely or not at all 

 developed in Tapirus, Rhinoceros, Hyrax, 

 Elei^has, Canis, Homo. Hence this 

 pisiform slip may also have been absent 

 in PalaeosyojJS. 



The tuberosities on the posterior aspect 

 of the carpus gave attachment for a set 

 of ligaments radiating from the middle 

 bones (lunar, magnum) to the surrounding 

 elements. The posterior tuberosity of the 



lunar also gave attachment to the interosseus dorsalis 



primus, abductor^minimi digiti, and adductor minimi 



ccip -yried. 



The proximal row of carpals, like those of Equus, 

 was bound together transversely by a series of liga- 

 ments running across the front face of the carpus and 

 connecting respectively with the inner and outer distal 

 portions of the radius. The distal row of carpals 

 was similarly bound together by a second series of 

 ligaments so that during flexion the proximal and distal 



Figure 655. — Left ulna of Brontops robustus (type), showing 



probable position and attachments of principal muscles 



Ai, Front view; A2, inner side view; As, baclc view. One-eightli natural size. 



digiti. The posterior tuberosity of the magnum, the 

 form of which is very characteristic of perissodactyls, 

 gave attachment not oidy to the radiating ligaments 



