490 



COMPAEATIVE ANATOMY. 



With regard to the toes, we find five to be the dominant number 

 in the Ecptilia ; it is in Birds only that they fall to four, or three, or 

 even to two (Struthio). The phalanges of the 

 toes generally increase in number from within 

 outwards; there are two on the hallux and five 

 on the fourth toe. This holds for the Saurii, 

 Crocodilini, and Aves. There are not so many 

 in the Amphibia or Chelonii. Amongst the 

 Eeptilia the limbs are reduced in the snake-like 

 Lizards, and in all Ophidii, among which the 

 Peropoda only are provided with any rudiments 

 of them at all. 



Gegenbaur, C, Uiitersucliungen zur vergleich. Anat. I. 

 Leipzig, 1864. 



§ 369. 



The special differentiations in the skeleton of 

 the hind-limb of Birds and "Reptiles do not re- 

 semble those which are seen in the MammaHa. 

 As a rule it is less altered than the fore-limb. 

 In the Perissodactyla, many Rodents, etc., the 

 femur is distinguished by the possession of a 

 third trochanter. The tibia is the most im- 

 portant bone of the leg ; the fibula is often rudi- 

 mentary, especially in the Ungulata. In the 

 Artiodactyla the distal end remains ; it is articu- 

 lated to the tibia and to the tarsus (astragalus), 

 and appears to enter into the composition of the 

 latter. In some (as in Rodents and Insectivora) 

 the tibia and fibula are complete, and are fused 

 together. 



The tarsus is the most characteristic part ; it is attached by two 

 pieces to the leg, but, as a rule, only one of these forms the ankle- 

 joint. The process on the second bone (calcaneum), of which there 

 were indications in the Crocodilini, is still more developed. The 

 centrale remains separate, but passes to the inner edge of the foot, 

 where it forms the navicular. In some of the Prosimige it unites 

 with the calcaneum to form a long process (Macrotarsi). Of the 

 five distal bones the two outer ones are always replaced by the 

 cuboid, while the three inner ones generally remain distinct (cunei- 

 form). When the number of toes is diminished, these latter bones 

 are often reduced ; they may even fuse with the metatarsus, as in 

 Bradypus. The cuboid also may be united to the navicular 

 (Ruminantia) . 



In addition to its primitive function as an organ of support 

 and of movement, the foot may be developed into a grasping organ; 

 when this happens, the foot comes to resemble in many points the 

 end of the fore-limb, or hand. But in all essential points of 



Fig. 275. Hinder ex- 

 tremity of Bnteo 

 vulgaris, a Femur. 

 b Tibia. V Fibula, 

 c Tarso-metatarsus. 

 c' The same ^^iece 

 isolated, and seen 

 from in front, d d' 

 d" d'" Four toes. 



