720 



TITANOTHERES OF ANCIENT "WYOMING, DAKOTA, AND NEBRASKA 



MUSCULAR ATTACHMENTS OF THE PATELLA 



The more or less pear-shaped patella (morphologi- 

 cally the sesamoid of the quadriceps femoris) is on the 

 whole more elephantine than horselike, in correlation 

 with the straighter limb. It differs from that of 

 Tapirus in having the dorsal prominence for the 

 rectus sessile instead of hooklike; the upper surface is 

 anteroposteriorly deep and fiat; the lower end for the 



lexlj 



Ai 



A2 



A3 



(AJi.) 



A4 



<^^, 



Figure 658. — Left fibula and left tibia of Broniops robustus (type), showing 

 probable position and attachments of principal muscles 



Ai, Fibula, outer side; Ai, inner side; A3, rear view; A 

 view; B3, outer side; Bi, inner side. 



I, front view. Bi, Tibia, front view; B 

 One-eightb natural size. 



ligament of the patella is prolonged and pointed; 

 the inner side is not produced. Correlated with the 

 latter structure is the small size of the inner patellar 

 keel on the femur, this keel not being globose above, 

 as it is in Equus and to a less extent in Tapirus. All 

 this implies that, unlike Equus, Pdlaeosyops could not 

 rest the patella on top of the inner patellar keel of the 

 femur but stood with straighter limb. 



MUSCULAR ATTACHMENTS OF THE TIBIA 



The tibia is rather similar to that of Tapirus. On 

 the cnemial crest the surface for the ligamentum 

 patellae (which was probably tripartite, as in the 

 horse) faces more upward than in Tapirus, in correla- 

 tion with the straighter limb, but is otherwise similar. 

 The cnemial crest is somewhat less reflected than 

 it is in Tapirus. It terminates above in a supero- 

 external tuberosity, which not only 

 gave origin to a part of the liga- 

 mentum patellae but probably also 

 gave insertion to some of the deeper 

 strands of the biceps femoris (ischial 

 head). Immediately postero-external 

 to this bicipital tuberosity is a large, 

 deep vertical groove for the tendon 

 of the extensor longus digitorum. 

 The tendon is attached to the femur 

 immediately above the groove. 



Immediately below the extensor 

 groove and behind the cnemial crest 

 is the fossa for the tibialis anticus, 

 covering the inner face of the tibia 

 but not defined below and nowhere 

 as sharply defined as in Tapirus. 

 The front of the cnemial crest served 

 chiefly for the inferior prolongation 

 of the ligamentum patellae, but the 

 lower end of the crest bears a promi- 

 nent scar, into which was inserted a 

 deep strand of the semitendinosus 

 which passed across the inner face 

 of the tibia on its way to the fascia 

 of the shank. 



On the inner surface of the tibia, 

 behind the cnemial crest, the area, 

 for the gracilis is not defined, but 

 no doubt that muscle was inserted 

 in this region. The inner tuber- 

 osity, a low prominence behind the 

 middle line on the proximal border, 

 together with the pit behind it, pos- 

 sibly gave insertion to a deep slip of 

 the semimembranosus and also to the 

 ligamentum collaterale tibiale. 



Most of the inner or medial sur- 

 face of the tibia was free of muscular 

 attachments (planum subcutaneum. 

 Schmaltz). Distally the inner face 

 bears near the front border a sharply flattened promi- 

 nence for the ligamentum collaterale breve running 

 obliquely to the astragalus and calcaneum. Some dis- 

 tance behind this prominence is a vertical groove for the 

 flexor longus digitorum. The back of the tibia below 

 the popliteal notch is taken up by a wide and deep 

 fossa for the popliteus. This muscle may also have 

 extended around on to the inner surface of the tibia. 



