VESTIGIAL STRUCTURES. 97 



fracture as the fibula in its lower fourth. This accident 



* 



is attended with certain peculiarities, and is named after 

 the great surgeon Percival Pott, who first accurately 

 described them. The chief features of Pott's fracture 

 are the following : The fibula, or small bone of the leg, 

 is broken about seven centimetres above the ankle, the 

 tibial malleolus is splintered off, or the deltoid ligament 

 ruptured, and the foot everted. The most frequent 

 cause of this very common accident is a sudden and 

 violent twist of the foot. In order to study thoroughly 

 the conditions which predispose to this accident it will 

 be necessary to briefly review the history of the fibula, 

 and it is a fact of some interest that no one has ever 

 described the occurrence of Pott's fracture in any 

 mammal save man. 



An examination of the hind limb of a menobranchus, 

 or menopoma, will serve to show that the bones of the 

 leg the tibia and fibula are equal in size. In such 

 animals the legs are used chiefly as paddles, enabling 

 them to move freely in water. The descendants of 

 some of these forms changed their mode of life, be- 

 coming semi-aquatic, or entirely terrestrial animals, and 

 began to use their limbs for creeping, crawling, or 

 running habits which led to changes in the bony frame- 

 work. In the case of the leg it is easy to see that it is 

 advantageous for the weight of the body to be transmitted 

 to the ground by one bone rather than two, hence the 

 bone most used increased in size : this enlargement 

 would induce a deviation of blood in favour of the bone 

 most used the tibia to the detriment of the companion 

 bone the fibula, So truly does the fibula obey the law of 



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