Anatomy of Fibula. 359 



the position of the Hallux and the loss of power of adduction 

 we have an impairment of the mobility of the foot, the diminish- 

 ed call for work resulting in lessened extent and variety of 

 muscular activity and subsequent changes in the bones of the 

 leg. 



In the upper limb associated with the adduction of the 

 thumb we have the movements of pronation and supination, 

 and for this, two forearm bones are necessary. In the Koala 

 and Lemur with great mobility of the feet, the uses of which are 

 almost, if not as great as those of the hand, we find both bones 

 of the leg, namely, the Tibia and Fibula well developed and in 

 the Koala little distinguishable in size, and both entering into 

 the formation of the ankle and knee-joints ; but in man and 

 the Kangaroo, where the erect position predominates and sup- 

 port only is requisite, the question of the utility of a second 

 bone in the leg is raised. 



Hence a comparison is necessary, the basis of which de- 

 pends on the mobility or otherwise of the ankle-joint which 

 is itself a natural association of an approximating Hallux. 



Before entering into this consideration a brief review may 

 be made of the Fibula as occurring in man. Although the Tibia 

 — the companion bone in the leg — is the longest and largest 

 in the skeleton excepting the Femur, the Fibula is on the other 

 hand, in proportion to its length, the most slender of all the 

 long bones. Its upper end forms no part of the knee-joint, 

 its chief function being to increase the surface for muscular 

 attachment, while at the lower end it supports the outside of 

 the ankle-joint. It may, though rarely, be completely absent, 

 an instance of which Hughes reported at a recent meeting of 

 the Intercolonial Medical Congress. In some instances the upper 

 and lower ends may be distinct, the shaft having disappeared, 

 being represented but by a thickening of the interosseous mem- 

 brane connecting the two ends. In fact congenital absence 

 of part of the bone is more frequent than that of the 

 whole bone, which when present causes great disability of the 

 foot and difficulty of ambulation, not on that account only but 

 owing to its frequent association with an imperfect develop- 

 ment of the tarsal bones and an absence of one or more of the 

 four outer toes. 



