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 
8 
