v . ] SKELE TON OF L WER LIMB. 20 7 



as in the Seals. It may be, on the contrary, enormously pro- 

 duced, as in the Horse. 



It may have appended to it an elongated ossification which 

 in parts enters upon the tendo Achillis, as in Bats, and this 

 may be of great breadth as well as length, as in Noctilio 

 leporinus. 



The end of the os calcis is broad, bifid, and incurved in 

 the Ornithorhynckus and Echidna. 



In that man's ankle-joint is situated between the leg-bones 

 and the tarsus, it agrees with the same part not only in the 

 whole of his own class, but also in Batrachians. It may be, 

 however, that the joint by which the foot moves upon the leg 

 is not so situated. This is the case in all Birds, where motion 

 takes place not between the tarsus and the tibia, but between 

 the proximal and the distal parts of the tarsus, the ankle-joint 

 being in them an inter-tarsal one, with the proximal part of 

 the tarsus anchylosed to the tibia, and its distal part to the 

 metatarsus. 



A similar joint exists in Crocodiles, though the proxi- 

 mal part of the tarsus is firmly attached to the leg-bones 

 but by fibrous tissue, and not by anchylosis. 



Much more mobility than obtains in man may exist even 

 in Mammals, between the proximal and distal parts of the 

 tarsus, as in the Orang, and especially in Galago. 



The leg, instead of being set on the foot vertically, as in 

 man, may be applied obliquely, as e.g. in the Orang and Potto. 



There was, doubtless, in the Ichthyosaurus a limitation of 

 motion between the bones of the hind limb, similar to that 

 which we find in the existing Cetacea between the bones of 

 the fore limbs. 



The naviculare, or scaphoid, may anchylose with one of 

 the distal row of tarsal bones, as in the Ox and Deer, where 

 it unites with the cuboid. 



Instead of being situate as in man, it may be central and 

 distinct, as in Salamandra and other Tailed-Batrachians, and 

 as in Chelydra and Chameleo. It may be very short and 

 very wide transversely, as in the Horse. 



Its tuberosity may be much produced, as in Hylobates. The 

 articular surfaces for the cuneiforme may be remarkably 

 convex, as in Loris. 



The naviculare may be greatly produced, as is the case in 

 Galago and Tarsius. 



18. The BONES OF THE SECOND ROW are far less con- 

 stant and never so large and conspicuous as are those of the 



