v.] SKELETON OF LOWER LIMB. 199 



shows a predominance of size, like that of the radius in the 

 arm over the ulna, and this to a yet greater degree. Thus 

 while, like the radius, it never aborts though its fellow may 

 do so, it never in existing animals even becomes the subordi- 

 nate bone of the two, as is the case in the radius compared 

 with the ulna in Birds. Yet in length it may be exceeded by 

 the fibula, as e.g. in the Ornithorhynchus ; and a certain slight 

 subordination appears to have existed in the extinct Reptiles 

 Ichthyosaurus and Plesiosaurus. Moreover, the two bones 

 are developed equally in certain existing Reptiles with rudi- 

 mentary limbs, e.g. Seps and Ophiodes, and in Batrachians 

 also. 



In its elongated figure the tibia of man agrees with the 

 same bone as generally developed, and it never becomes in 

 any existing species so relatively short and thick above as 

 does the radius in Cetacea. Such is the case only in the 

 extinct Plesiosaurus and Ichthyosaurus. 



The relation which it bears to the femur is less constant 

 than that which the radius bears to the humerus. We have 

 seen that where in Vertebrates above Fishes the humerus is 



FIG. 170. SIDE VIEW OK BONES OF POSTERIOR EXTREMITY OF GREENLAND 



RIGHT WHALE (Batana mysticctits . 



i, ischium ;./, femur ; t, accessory ossicle, probably representing the tibia. 

 (From Eschricht and Reinfuirdt.) 



represented by a bone or cartilage, the radius is also developed. 

 But in Megaptera longimana and Balcunoptera musculns we 

 have a rudimentary representative of the femur, but none 

 whatever of the tibia ; while in Balcena mysticetus and in Boa 

 constrictor there is a tolerably large ossicle representing the 

 femur, but only a minute rudiment representing the tibia. 



