GREGORY, QUADRUPEDAL LOCOMOTION 



289 



1.35. There are also more ratios of intermediate type. Consequently, 

 the tibio-femoral ratios taken alone do not always furnish a sure indica- 

 tion of the mode of locomotion. 



From the viewpoint of adaptation, there are several plausible reasons 

 why the tibia has not shortened to so extreme a degree as has the middle 

 metatarsal. A short tibia implies a low knee joint and a long femur. 

 A long femur, as stated below, is associated with a nearly vertical in- 



lon-ff. dors. 



Fig. 6. — Relations of certain extensor muscles to the pelvis and femur in the. standing 

 pose in (I) a typically cursorial form, the Horse, with relatively wide angles 

 of insertion (a, ft y), and in (II) a typically graviportal form, the Mastodon, 

 with narrow angles of insertion (a', /?', -y'). 



The heavy black lines represent the general directions of the muscles ; the broken lines 

 represent the radii of rotation of the insertion points. 



nominate bone and with narrow angles of insertion of the principal long 

 muscles (Fig. 6). The result of these small angles of insertion is 

 that the long muscles exert a powerful pull in the direction of the shaft 

 of the femur (p. 278 and Fig. 2), an arrangement favorable to the 

 lifting and support of great weight (p. 290). The short tibia and 



