Bones discovered in a cave at Kirkdale, in Yorkshire. 193 
down and worn completely smooth, whilst the opposite side 
and ends of the same bone are sharp and untouched ; in the 
same manner as the upper portions of pitching stones in the 
street become rounded and polished, whilst their lower parts 
retain the exact form and angles which they possessed when 
first laid down. This can only be explained by referring the 
partial destruction of the solid bone to friction from the con- 
tinual treading of the hyaenas, and rubbing of their skin on the 
side that lay uppermost in the bottom of the den. In many of 
the smaller and curved bones, also, particularly in those of 
the lower jaw, (see Plate XIX. fig. 1 and 2.) the convex sur- 
face only is uniformly that which has been worn down and 
polished, whilst the ends and concave surface have suffered 
no kind of change or destruction, (Plate XIX. fig. 3 and 4,) : 
and this also admits of a similar explanation ; for the curva- 
ture of the bone would allow it to rest steady under constant 
treading only in this position ; as long as the concave surface 
was uppermost, pressure on either extremity would cause it 
to tilt over and throw the convex side upwards ; and this 
done, the next pressure would cause its two extremities to 
sink into any soft substance that lay beneath, and give it a 
steady and fixed position. Such seems to have been the pro- 
cess by which the curved fragments I allude to, have not 
only received a partial polish on the convex side only, but 
have been submitted to so much friction, that in several in- 
stances more than one-fourth of the entire thickness of the 
bone, and a proportionate quantity of the outer side of the 
fangs and body of the teeth, have been entirely worn away. 
(See Plate XIX. fig. 1.) I can imagine no other means than 
the repeated touch of the living hyaenas’ feet and skin, by 
MDCCCXXII. C C 
