PELVIC LIMBS 735 



VARIATIONS IN FORM AND DEVELOPMENT. 



The posterior-external surface of the head may become almost 

 oval by the rounding of its angles, or may lose the regular pentagonal 

 outline by the prolongation of one of the upper anterior angles. The 

 upper margin may be straight or even produced at the middle (one 

 case in eighty) ; when incised, the posterior part is the smaller, but 

 may be produced upward into a small styloid process ; the anterior 

 part is rarely also produced upward ; its proximal surface carries the 

 facet for the tibia. The posterior-external surface passes through all 

 grades of concavity from almost flat to extreme excavation. Of the 

 two eminences the anterior as a rule is the larger, but the posterior 

 may be greatly extended and continued down the anterior-external 

 border of the Shaft. 



The anterior-internal surface of the head appears to vary in the 

 degree of upward prolongation of the anterior part and in the degree 

 of prominence of the posterior eminence which marks the beginning 

 of the posterior-internal border of the shaft. 



The shaft is apparently subject to slight variation. It is occasion- 

 ally sinuate in the antero-posterior plane. Rarely the anterior- external 

 border is prominent and almost as well marked as the anterior-internal 

 and the posterior-external. The short posterior-internal border is at 

 times very strong and appears as the upward continuation of the 

 posterior-external border, or it may be, absent, the twist of the bone 

 alone indicating its position. 



The outer aspect of the lower extremity exhibits variations in the 

 degree of prominence of the oblique line forming the posterior border 

 of the anterior-external surface. On many bones it is hardly indi- 

 cated, and then the groove for the peroneus is very faint; on other 

 bones it may be so prominent that its beginning at the end of the 

 anterior-internal border of the shaft presents a tubercular enlargement. 

 The malleolar process is always present ; in one specimen examined, it 

 was reduced to a mere tubercle. The variations on the inner aspect 

 are variations in the size and distinctness of the articular facets and 

 in the depth of the pit for the ligament near the lower margin. 



HUMAN FIBULA. 



The fibula in man is relatively shorter and stronger than in the 

 cat (Figs'. 556, 557). 



