292 ANNALS NEW YORK ACADEMY OF SCIENCES 



In brief, the long femur of graviportal animals serves for the attach- 

 ment of long and very massive flexor and extensive muscles inserted at 

 slight angles; it brings the knee joint well down below the belly, and it 

 is further characterized by a very heavy sessile great trochanter and a 

 more or less reduced third trochanter, located far down the shaft; the 

 distal facets, as observed by Osborn, are more or less at right angles to 

 the shaft, so that the femur rests subvertically upon the tibia. 



GEAVIPORTAL AND CURSORIAL TYPES OF PELVIS 



(Figs. 4-6) 



The upper anterior border of the ilium in cursorial animals is con- 

 cave, so that the anterior part of the glutseus medius is produced in front 

 of the ilium and inserted into a long fossa in the posterior end of the 

 fascia covering the longissimus dorsi. 42 The result is that these two 

 muscles apparently pull in tandem, while the subhorizontal position of 

 the pelvis permits the glutgeus medius to be inserted on the great 

 trochanter at an angle approaching a right angle. Thus the powerful 

 and prolonged contraction of the combined glutseus medius and longis- 

 simus dorsi is exerted well across the long axis of the femur, producing 

 a very powerful rotation component. Similarly the subhorizontal posi- 

 tion of the ischium opens out the angles of insertion of the three 

 branches of the biceps and of other extensors and flexors of the thigh. 



In such progressively graviportal lines as the Amynodontinae among 

 the Ehinooeroses, we observe the transformation of the cursorial into 

 the graviportal pelvis by the filling out of the anterosuperior concavity 

 of the ilium, the broadening of the ilium and outward growth of the 

 tuber coxae and the increasing verticality of the whole pelvis. The 

 result of these changes with regard tb the muscles is that the glutseus 

 medius is separated by a wall of bone from the longissimus dorsi, the in- 

 sertion space of the glutseus medius and accessorius is greatly increased 

 and the medius passes down subvertically on to the broad trochanter 

 major of the femur; the angles of insertion of the flexors and extensors 

 also lessen. Such graviportal adaptatibns have taken place independ- 

 ently in many lines of ungulates (Amblypoda, Proboscidea, Titano- 

 theres, Amynodonts, Toxodonts) and also in the ground sloths. 



42 R. Schmaltz : "Atlas der Anatomie des Pferdes." Zweiter Teil : Topographische My- 

 ologie, Taf. 27 u. 28. 4to, Berlin, 1909. 



