746 



TIT.\NOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



LENGTH OF ILIUM AND OF ISCHIUM AND RATIO OF acetabulum, the length of the ischium, and the ratio 



THESE LENGTHS TO TOTAL LENGTH OF OS INNOMI- of these lengths to that of the OS innominatum in 



NATUM certain mediportal, cursorial, and graviportal types 



The absolute length of the ilium measured from the are shown in the following table : 



middle of the superior crest to the center of the 



Lengths of ilium and of ischium and their ratio to length of os innominatum in certain Perissodactyla and 



Artiodactyla 



[Measurements in millimeters; ratios in percentage] 



Length of 

 OS inno- 

 minatum 



PERISSODACTYLA 



Tapirus terrest ris, j uvenile (mediportal) 



Tapirus terrestris, adult (mediportal) 



Tapirus indicus (mediportal) 



Equus caballus (cursorial) 



Rhinoceros (Opsiceros) bicornis (graviportal) 



Manteoceras manteoceras (Am. Mus. 2358) (graviportal) 



ARTIODACTYLA 



Tragulus (subeursorial) 



Sus (subeursorial) 



Cervulus 



Auchenia lama (cursorial) 



Dicotyles (subeursorial) 



Hippopotamus amphibius (graviportal) 



Camelus dromedarius, juvenile (cursorial) 



323 

 358 

 427 

 480 

 530 

 425 



111 

 263 

 158 

 275 

 213 

 670 

 337 



This table shows that we can not at present estab- 

 lish any law or make any deduction as to these ratios 

 with reference to speed and weight, but it brings out 

 two facts of interest: First, the ilium as compared 

 with the ischium is proportionately longer in the Peris- 

 sodactyla than in the Artiodactyla; second, the ilium 

 of the titanotheres is proportionately longer than in 

 other Perissodactyla. 



The true cursorial, mediportal, and graviportal 

 indices are obtained by dividing the entire length of 

 the pelvis (from crest of ilium to extremity of ischium) 

 by the entire breadth (across the widest part of Uium). 

 In the graviportal type the pelvis is short and broad; 

 in the cursorial type it is long and narrow. 



RATIOS OF LENGTH OF SCAPULA AND ILIUM TO THAT 

 OF HUMERUS AND FEMUR, RESPECTIVELY 



From the constancy of the limb-segment ratios in 

 graviportal and cursorial forms it was expected that 

 somewhat similar ratios would be discovered between 

 the arch elements and the proximal limb segments. 

 For example, in the graviportal Proboscidea the ilium 

 shortens and expands while the femur lengthens; 

 conversely in the cursorial Equidae the scapula 

 lengthens while the humerus shortens. 



To ascertain whether there is any law underlying 

 these allometric changes Gregory made a test series 

 of comparative measurements and obtained the fol- 

 lowing ratios, expressed as percentages (scapula -?- 



humerus = scapulohumeral ratio ; ilium -J- femur = ilio 

 femoral ratio) : 



Ratio of length of scapula and ilium to length of humerus and femur 



Phenacodus primae vus (primitive) 



Phenacodus wortmani (primitive) 



Coryphodon lobatus (graviportal) 



Mastodon americanus (graviportal, rectigrade) _ _ 



Elephas indicus (?) 



Elephas africanus (graviportal, rectigrade) 



Toxodon (graviportal, digitigrade) 



Palaeosyops leidyi (mediportal to graviportal) _ _ 

 Palaeos3'ops major (mediportal to graviportal) _ _ 

 Brontotherium gigas (mediportal to graviportal) _ 



Hyrachyus agrarius (cursorial) 



Hyracodon nebrascensis (cursorial) 



Amynodon intermedins (mediportal) 



Metamy nodon planif rons (graviportal) 



Teleoceras f ossiger (graviportal) 



Rhinoceros indicus (graviportal) 



Mesohippus (cursorial) 



Hypohippus (cursorial) 



Neohipparion (cursorial) 



Equus scotti (cursorial) 



Equus caballus (cursorial) 



Hippidion (subeursorial) 



Cervus megaceros (cursorial, heavy-bodied) _ . 



Bison bison (cursorial, heavy-bodied) 



Camelus arabicus (cursorial, heavy-bodied) __. 

 Antilocapra (cursorial) 



Scapulo- 

 humeral 

 ratio 



109 

 104 



150 

 107 



121 

 114 



118 

 108 

 120 

 131 

 118 

 120 

 132 

 140 

 140 

 113 

 112 



Ilio- 

 femoral 

 ratio 



74 

 66 

 66 

 52 



73 

 61 

 78 

 74 

 60 

 66 

 77 

 75 

 60 

 77 

 83 



