34 COMPARATIVE ANATOMY 



and probably representative of the metatarsal. This is suc- 

 ceeded by a flat crescentic piece representing a phalanx. The 

 first toe is generally called a supplemental toe, and, as we have 

 already seen, the innermost of the longer toes is usually 

 reckoned as the hallux or great toe. There are five fairly 

 long metatarsals in the foot, and to these succeed the 



Fig. 4. 



A, Femur of the Frog. /, proximal; d, distal articulating surfaces; s, 

 shaft. By Tibio-fibula, seen from below. ^, proximal ; d, distal 

 articulating surfaces ; t, tibial half of the bone separated by a groove 

 fromy^ the fibular half C, The right ankle and foot of the Frog, seen 

 from below. This figure is drawn to a smaller scale than A and B. 

 a, astragalus ; c^ calcaneum ; / — V, the five principal digits ; X, the 

 minute accessory digit. (All the figures after Ecker.) 



phalanges of the toes. The first and second toes have two 

 phalanges, the third three, the fourth four, and the fifth three. 



It is obvious that the fore and hind limbs are built on 

 essentially the same plan. The humerus of the arm has its 

 analogue in the femur of the leg. The radius and ulna are 

 represented respectively by the tibia and fibula in the leg. 

 The wrist corresponds to the ankle, and the bones of hand 

 and foot are very similar. Paired structures, which are 

 repeated in this way, are said to be serially homologous, but 



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