336 THE THIGH AND LEG. [CHAP. 



bone, and in an adult Fin Whale (JBal&noptera muscitlus), 

 sixty-seven feet long, this was found to be only repre- 

 sented by an oval nodule of cartilage about the size of a 

 walnut. 1 Even this is wanting in some species of the group, 

 as B. ro strata and B. boreal is. 



No trace of any structure representing the skeleton of 

 the hind limb, beyond the pelvis, has yet been detected in 

 any of the Odontocetes. 



In none of the existing SIRENIA are there any rudiments 

 of the hind limb proper, but the extinct Halitherium had an 

 ossified femur, articulated to a well-defined acetabulum in 

 the pelvis. 



In the terrestrial and fossorial EDENTATA the femur is 

 generally short and broad. There is a third trochanter in 

 the Armadillos and Orycteropus, and a sharp ridge along 

 the whole external border in Myrniecophaga. The fibula is 

 as long as the tibia. In the Armadillos these bones are 

 commonly ankylosed together at each extremity, but curve 

 away from each other at the middle, leaving a wide inter- 

 osseous space. In the Anteaters they are both nearly 

 straight and parallel. 



In the Sloths the femur is long, slender, ard flattened 

 from before backwards. There is no third trochanter ; the 

 head is large and globular, and placed near the middle of 

 the proximal end of the shaft, with the axis of which it 

 more nearly coincides than in most Mammals. The tibia 

 and fibula are complete, and more nearly equal in size than 

 in most Mammals. They are both curved, so as to be 

 separated considerably in the middle part of the leg. The 

 lower end of the fibula has a conical prominence which 

 . turns inwards, and fits into a depression on the outer side 



1 " Proceedings of the Zoological Society, 1865," p. 704. 



