OSTEOLOGY 159 



of the acetabulum. This process, however, is undeveloped 

 in animals sufficiently young for the sutures of the innomi- 

 nate to show, and it is not knowTi with certainty whether it 

 more properly belongs with the pubis or ilium. Upon the 

 caudal border of the medial surface of the pubis originates 

 the abductor caudae externus. 



Thus, although there is much variation shown by certain 

 parts of the innominate, these are indi\ddual, and there is no 

 single group character. In addition, there are comparatively 

 few details which are amenable to the influences of but a 

 single muscle. 



POSTEKIOR LIMB 



The true length of the hind limb in a plantigrade mammal 

 is the sum of the length of the femur and the distance from 

 the knee joint to the ground upon which it stands. In a 

 digitigrade type the latter item is also the distance to the 

 ground or to the tip of the toes or hoof. The genus Neotoma 

 is neither plantigrade nor digitigrade. When at rest the en- 

 tire foot is placed upon the ground, but when running, it, 

 hke most rodents, raises the heel smartly. The functional 

 limb length must, therefore, be considered as terminating 

 at some point between the heel and the toe, and it is ob- 

 viously necessary that some arbitrary point be assigned for 

 this; which we can only hope represents the true condition 

 to an approximate extent. In running, the digits may be 

 presumed to play a rather slight part, the "ball" of the foot, 

 at the tarsal terminations, gi\TJig the final impetus to the 

 stride. In such an animal, therefore, that is neither planti- 

 grade nor digitigrade, it seems logical to consider that half 

 the distance from the heel to the end of the longest meta- 

 tarsal bone constitutes the termination of the length of the 

 hind limb from a functional, as opposed to an anatomical, 

 viewpoint. This, it should be mentioned again, is open to 

 the serious objection that it is arbitrary and inaccurate to 



