SKELETON OF LOWER LIMB. 



211 



In such cases a separation of the lower end of the bone 

 into articular condyles for the different digits indicates the 

 composite nature of the bone. 



There may be but four metatarsals well developed, as in 

 the Dog ; or but three, as in Rhinoceros ; or two, as in the 

 Hog and Proteus ; or but one, as 

 has been mentioned, in the Horse 

 and Chan'opus. 



They may be anchylosed to- 

 gether at their proximal ends, 

 as in the Three-toed Sloth. 



The metatarsals never seem 

 to decrease in size from the first 

 to the fifth, but often, as in man, 

 from the second to the fourth. 

 They may increase in size from 

 the first to the fifth, as in the 

 Great Ant-eater and the Orni- 

 thorhynchus. 



The two central ones may 

 greatly exceed the lateral ones, 

 as in the Hog ; or the first and 

 fifth may greatly exceed in size 

 the three central ones, as in the 

 Seal. 



The second metatarsal is 

 never exceptionally reduced, 

 while the other four all remain 

 well developed. 



The metatarsals are never 

 enormously elongated like the 

 metacarpals of Bats. 



All may be extremely short 

 and stunted, as in the Land Tor- 

 toises and Ichthyosaurus. 



The number five is never 

 increased (except by monstrosity) in any known Verte- 

 brates. 



The vertical line of bilateral symmetry in the foot may 

 pass (as in the Ox and Sheep), so as to have the third meta- 

 tarsal on one side of it and the fourth metatarsal on the other; 

 or it may (as in the Horse and Rhinoceros) pass through the 

 middle of the third metatarsal. 



The latter symmetry may prevail where there are four 



P 2 



FIG. 182. BONES OF RIGHT PES 

 OF JERBOA (Dipus /Egyptius}. 



a, astragalus; c, calcaneum ; cb, 

 cuboides ; c' 2 , meso cuneiforme ; 

 c 3, ecto-cuneiforme ; //. ///. 

 and 7K, second, third, and 

 fourth digits. 



(From Flowers "Osteology") 



