VI.] GENERAL VIEW OF INTERNAL SKELETON. 233 



We have, secondly, the fibula ; the calcaneum ; the cuboid ; 

 the fourth and fifth metatarsals ; and the annexed digits 

 forming the bi-digital series. 



24. In man, however, the ulna takes part in the limb joint, 

 while the fibula does not. As we have found, however, this 

 difference may disappear, for in some animals the fibula does 

 articulate with the femur. 



Again, in man the ulna has a large proximal process the 

 olecranon while his fibula has nothing of the kind. An 

 olecranon-like fibular structure may, however, be developed, 

 as we have seen, in the Ornithorhynchus. 



In man and in most animals there is a patella in the leg, 

 but no analogous ossicle at the elbow-joint Sometimes, how- 

 ever (as in the Wombat), there is a distinct ossicle above the 

 olecranon on the extensor side of the elbow-joint. 



25. Again, the leg in man does not articulate with the tarsus 

 in the same manner as the arm does with the carpus the 

 ulna, unlike the fibula, not entering directly into such union. 

 But the ulna may articulate with the carpus directly, even in 

 man's own order. 



The scaphoides and lunare are often together represented 

 by a single bone which seems to answer to the astragalus, 

 especially since the latter may be represented by two bones, 

 as in the Salamander. 



The os calcis is furnished with a great tuberosity of which 

 there is no representative in the carpus, but then this pro- 

 cess is not constant, as it is entirely wanting in Lizards. 



The naviculare seems to have no representative in the 

 human carpus, but even in most Apes there is an extra carpal 

 the os intermedium, or centrale. 



The cuboides and unciforme of man may each be repre- 

 sented by two bones in other animals, so that their cor- 

 respondence in unity is confirmed by a correspondence in 

 duplicity. 



The trapezium of man differs from his ento-cuneiforme in 

 that it has a saddle-shaped surface for the pollex ; but in 

 Lemur the latter bone has a surface of that shape for the 

 hallux. 



26. The first digit is opposable in man's hand, but not in 

 man's foot. 



In Cheiromys and many Marsupials it is opposable in the 

 foot, and not in the hand. 



In man the digits of the hand are longer than those of the 

 foot, but in Macroscelides those of the foot are the longer. 



