TRANSACTIONS OF SECTION H. 781 



the fingers. In apes, therefore, as in man, these grooves are not acquired after 

 birth, but have an hereditary signification. 



We may now contrast the grooves in the skin of the sole of the human foot 

 with those which we have just described in the palm. For this purpose the foot 

 of an infant must be selected as well as that of an older person in which the toes 

 have not been cramped and distorted by ill-fitting shoes.^ 



The toes are marked ofl" from the sole proper by a deep diagonal depression, 

 which corresponds with the plane of flexion of the first and second phalanges. 

 Behind this depression, and on the sole proper, is a diagonal groove, which com- 

 mences at the cleft between the great and second toes, and reaches the outer border 

 of the foot. It is seen in the infant, but disappears as the skin of the foot becomes 

 thickened from use and pressure. This groove marks the plane of flexure of the 

 first phalanges on the metatarsal bones of the four smaller toes. Associated with 

 its inner end is a short groove which curves to the inner border of the foot, and 

 marks oflPthe position of the joint between the first phalanx and the metatarsal 

 bone of the great toe. The groove indicates the movements of the great toe in 

 flexion, and in adduction to, or abduction from, the second toe. It has sometimes 

 erroneously been regarded as the corresponding groove in the foot to the deep 

 curved groove in the hand, which defines the muscles of the ball of the thumb 

 and is associated with the movement of opposition. This is not its real character,, 

 for the chief joint concerned in opposition is that between the metacarpal bone and 

 the corresponding carpal bone, and not that between the metacarpal bone and 

 the phalanx. In addition, one, or it may be two faint grooves run from 

 within outwards near the middle of the sole. In the infant's foot a groove also 

 extends longitudinally in the centre of the foot. The grooves on the integument 

 of the sole are in harmony with the inner anatomy of the foot, and confirm the 

 statement, already made, that the great toe in man cannot be opposed to the 

 sole, as the thumb can to the palm, for the great curved groove expressing the 

 movement of opposition is wanting. 



In the apes, the condition of the tegumentary grooves in the sole is very 

 difierent from the human foot. In the Anthropoid group, the ball of the great toe, 

 with its muscles, is marked ofi^ by a deep curved groove, which extends from the 

 margin of the cleft between it and the second toe, backwards along the middle 

 of the sole almost as far as the heel. Its depth and extent are associated with the 

 powerful opponent, or grasping action of the hallux. Two other grooves, in front 

 of that just described, pass obliquely across the sole, from the cleft between the 

 hallux and the second toe, and reach the outer border of the foot. They are 

 associated with the movements of the four smaller toes, and their obliquity shows- 

 that, when the foot is used as a prehensile organ, the object is grasped not only by 

 the great toe being moved towards the sole, but by the smaller toes being moved 

 towards the hallux. From these arrangements it is obvious that the pes of the 

 ape is, physiologically speaking, a foot-hand, it is pedimanous. Though anatomi- 

 cally a foot, it can be used not only for support and progression, but for prehen- 

 sion, and, for the latter-named office, the hallux is a more potent digit in the foot 

 than is the poUex in the hand. The external rotation of the thigh at the hip joint,, 

 and the power of rotating the leg inwards on the thigh at the knee joint, contribute 

 to make the foot of the ape a more important prehensile instrument, and enabls 

 the animal to use it more efficiently for this purpose when sitting, than would have 

 been the case if there had been no contributory movements at the hip and 

 knee. 



The power of assuming the erect attitude, the specialisation of the upper limbs 



' These grooves have been described generally by the late Professor Goodsir 

 (Anatomical Memoirs, vol. i. 1868) ; by myself in a lecture on hands and feet, 

 Health Lectures, Edinburgh, 1884 ; and by Mr. Louis Robinson, the last named of 

 whom has called especial attention to their arrangement in the feet of infants 

 {Nineteenth Century, vol. xxxi. 1892, p. 795). The integumentary grooves in both 

 hands and feet of men and apes have also been described and figured in detadl by 

 Dr. Hepburn in Journal of Anat. and Phy$., vol xxvii. 1893, p. 112. 



