718 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



wide ; it is also highly probable that the gluteus medius 

 did not extend over the dorsal edge of the ilium as 

 it does in cursorial animals and therefore was not 

 inserted into the fascia of the longissimus dorsi 

 (Gregory, 1912.1, p. 292). The superior border or 

 crest of the ilium gave attachment to the superficial 

 fibers of the longissimus dorsi and also to the obliquus 

 abdominis externus and obliquus abdominis internus; 

 the outer part of the superior border gave origin to 

 the tensor fasciae femoris and to the inguinal ligament. 

 The gluteus maximus may possibly have barely 

 touched this border. The area for the gluteus mini- 

 mus immediately above the acetabulum is roughened 

 and streaked, probably indicating that the muscle 

 was divided into a number of twisted and parallel 

 strands as in Equus. Immediately in front of the 

 acetabulum is a deep pit for the rectus femoris (the 

 latter, according to Windle and Parsons, homologous 

 with the reflected head of the rectus in man). On 

 the neck of the ilium, on the antero-internal surface, 

 is a pit for the psoas parvus; below this pit the sartorius 

 probably took rise from the fascia of the ilio-psoas. 



The antero-internal surface of the ilium (corre- 

 sponding to the iliac fossa of man) lodges the wide 

 iliacus; between the area for the iliacus and the pit 

 for the psoas parvus is a gently depressed surface 

 homologous with a similar region in the horse and 

 likewise bearing a nutrient foramen (arteria circum- 

 fiexa femoris lateralis. Schmaltz). Dorsomedial to 

 the iliac fossa and below the articular surface for the 

 sacrum the ilium exhibits a flattened elongate surface 

 which as in the horse and tapir probably lodged an 

 anterodorsal extension of the obturator internus. . 



The lower part of the pelvis (that is, the pubis, 

 ischium, and acetabular borders) in a general way 

 gives origin to two principal groups of locomotor 

 muscles — to the abductors of the femur, which are 

 inserted either in the digital (trochanteric) fossa or 

 immediately below it, and to certain flexors of the 

 femur — the ischial head of the biceps femoris ("biceps 

 2"), the semitendinosus, and the semimembranosus. 

 Immediately behind the ischial spine and the area for 

 the gluteus minimus the superior ramus of the ischium 

 is smoothly rounded, this indicating the place where 

 the obdurator internus came over the ridge on its 

 way toward the femur. Immediately below this 

 place, above and behind the acetabulum, is a small 

 roughened area which probably indicates the position 

 of the gemelli (PI. XLIV). 



The ventral border of the symphysis pubis probably 

 gave origin to the closely intermingling adductor 

 magnus and gracilis, while the lower borders of the 

 thyroid (obturator) foramen, as well as parts of the 

 symphysis, gave origin to the obturator externus. 



Near the posterior end of the ischium and on or 

 near the dorsal external border is a long, low promi- 



nence for the true biceps femoris (caput longum of 

 Homo); this contrasts with that of Equus, which has 

 grown outward and downward into a great horizontal 

 flange (the crista tuberis ischii, Schmaltz). Although 

 the bicipital prominence in Palaeosyops and the 

 bicipital flange in Equus are so different in appear- 

 ance that we do not at first recognize their homology 

 with each other, yet they are clearly homologous, 

 because the rhinoceroses Hyrachyus and Caenopus, 

 EoJiippus and other extinct perissodactyls, as well as 

 Tapirus, afford intermediate conditions. Cuvier and 

 Laurillard's plates also show that in many mammals 

 the long head of the biceps femoris arises from the 

 same region we have assigned to it in Palaeosyops. 

 Immediately below the prominence for the biceps 

 femoris is the probable location of the ischial head of 

 the semitendinosus, while below and in front of the 

 latter is the probable origin of the quadratus femoris. 

 The region of the ischial tuberosity very probably 

 served for the ischial head of the semimembranosus. 



The anterior ramus of the pubis probably gave 

 origin to the pectineus; on its anterior border there 

 is little if any iliopectineal eminence, the latter being 

 very prominent in Tapirus and Equus and serving in 

 part for the origin of the pectineus (Schmaltz, 1909.1, 

 Taf. 7, 51). 



The obturator (thyroid) foramen on its inner side 

 and around its border was probably filled by the 

 obturator internus, which also sent forward and 

 upward a -branch lying above and medial to the area 

 for the iliacus. By comparison with Equus and Tapi- 

 rus it seems very probable that in Palaeosyops the 

 obturator internus arose inside the true pelvis, as in 

 the Perissodactyla generally as well as in the Hyra- 

 coidea and the Proboscidea, whereas in the Artio- 

 dactyla it arises outside the pelvis (Windle and 

 Parsons). 



MUSCULAR ATTACHMENTS OF THE FEMUR 



The femur as a whole in Palaeosyops and still more 

 in Oligocene titanotheres is much more elephantine 

 than horselike. The shaft is flattened, the patellar 

 trochlea faces more anteriorly, the limb is straighter 

 at the knee. The long flattened subvertical femur of 

 the graviportal elephant is inclosed in front and at 

 the side by a long vastus externus, of great transverse 

 diameter; the short round femur of Equus and of the 

 kangaroo is covered by a balloon-shaped vastus exter- 

 nus of great anteroposterior diameter. The femur of 

 Palaeosyops has the appearance of having been flat- 

 tened by the pressure of the vastus externus in front 

 and by the lateral strain of the great gluteus maxi- 

 mus along the outer side. The long and transversely 

 wide vastus externus of the femur contributes to the 

 great weight-lifting power and feeble jumping or 

 saltatorial power of the limb; while the balloon- 



