530 dr. G. e. dobson on the [June 20, 



the lines of flexion indicating the position of the joints of the toes, 

 and the longitudinal cleft dividing the heel to the groove along which 

 the tendons of the flexor muscles enter the sole of the foot ; but the 

 great depth and extent of these grooves evidently allow of very free 

 motion in the sole during flexion and adduction, the importance of 

 which will be seen when we investigate the mechanism on which the 

 adhesive power of the foot depends. 



There is nothing therefore in the structure of the sole of the foot 

 alone which can explain the extraordinary power of clinging to 

 smooth surfaces which we know the species of Hyrax possess. 



In dissecting the flexor muscles of the forearm the comparatively 

 very large size of the palmaris lonyus is particularly noticeable (Fig. 

 B, P. I). This muscle, arising from the internal condyle of the 

 humerus and from the intermuscular fascia, forms a broad and strong 

 tendon which, passing into the sole of the foot, spreads out into the 

 palmar fascia, which contains a fibro-cartilaginous disk. From the 

 superficial and deep palmar fascia, and from this fibro-cartilaginous 

 disk, arises a very peculiar muscle (first described by Messrs. Murie 

 and Mivart*), the Jiexor brevis manus (Fig. B, F.b.m), which is 

 inserted by three tendons into the second, fourth, and fifth toes. The 

 tendon going to the second, or inner toe, is inserted on the inner side 

 of the tendon of the Jiexor profundus, while that going to the fifth or 

 outer toe is inserted on the outer side of the tendon of the same muscle; 

 the middle tendon forms, with the corresponding tendon of the 

 Jiexor sublimis, the perforated tendon of the fourth toe; and as this 

 toe is so much longer than the second and fifth toes, the positions of 

 the insertions of the three tendons of the Jiexor brevis manus occupy 

 nearly the same line across the foot. 



If we take a line drawn along the middle of the fore foot from the 

 centre of the carpus to the extremity of the third toe as the centre 

 line of the foot, we 6nd the insertions of t\\e Jiexor brevis manus on 

 either side of this line, two of the three tendons being inserted at 

 points on opposite sides of the foot furthest from the centre. The 

 action of this muscle must therefore be, not only to flex the outer 

 and inner toes, but also to rotate them slightly and draw inwards 

 both sides of the foot towards the centre line. In this action the 

 tendency to cup the sole of the foot is evident. Further, as the 

 Jiexor brevis manus arises from the palmar fascia, it follows that this 

 muscle can only act effectively when its point of origin is fixed ; and 

 this is accomplished by the action of the strong palmaris longus, 

 which, as we have seen, terminates in the palmar fascia. In the co- 

 ordinate action of these two muscles on such a foot provided with a 

 soft elastic sole and united toes we have, I believe, all that is neces- 

 sary to produce the remarkable power of adhesion of the foot to anv 

 smooth surface on which it may be placed, which has been observed 

 in most species of Hyrax. 



The palmaris lonyus, in fixing the palmar fascia, removes the 



* L. c. p. 341. Messrs. Murie and Mivart (with the sanction of the Council of 

 the Society) have kindly permitted me to make use of one of the wood blocks 

 (Fig. B) from which the illustrations accompanying their paper were printed. 



