Anatomy oj Fihula. 365 



In the Baboon the outer Malleolus ax-ticulates with the outer 

 facet on the Astragalus, there being a marked ridge separating 

 the upper and the outer surfaces not met with in the Lemur. 

 There is more marked differentiation between the Tibia and 

 Fibula than in the Lemur, and the Fibula is more rounded. 

 There is not the lipping at the outer Tuberosity for easy 

 articulation, as in the Lemur, although some movement is 

 allowable ; but the bones are much more firmly attached. 



Conclusions. 



That the Fibula is undergoing marked evolutionaiy changes 

 is undeniable, and no doubt the condition in the Kangaroo 

 points the way. Possibly the absence of the Fibula with loss of 

 the outer toes seen occasionally in congenital cases in mian 

 serves as an indication of ultimate destination ; though ob- 

 viously here Nature creates a condition for which the erect 

 position has not yet educated itself. Processes of this charac- 

 ter are slow and gradual, as seen in the Marsupial, where, as 

 in the Kangaroo, by a fusion to the Tibia, and so a broadening 

 of its surface and streng-ihening the outer ankle, the bone 

 still performs a function. In the oases of congenital absence 

 of the bone it would be interesting to know had the Fibula 

 really disappeared or was there a fusion to the Tibia, and so 

 a broadening of its sui'face? In man the marked contrast be- 

 tween the relative size of Tibia and Fibula, and the fact that 

 the latter has been pushed from the knee-joint, and partakes 

 little in the formation of the ankle-joint are indications of its 

 retrogression. The shaft of the bone is- undoubtedly thinning, 

 and scarcely do we find two bones alike in size, whilst at the 

 same time the Tibia is uniformly broad and compact. From 

 previous considerations one would naturally expect changes to 

 occur at the lower third of the bone, and thinning is in my 

 experience most marked here, of which the so-called congenital 

 fractures must be regarded as advanced evidences. Probably 

 these cases of so-called fractures are best undetected as the ques- 

 tion may be raised of reconstituting the Fibula, i.e., a bone be- 

 coming obsolete in the animal economy. One might expect a 

 better residt to be obtained if the ends projecting undei* 



