September 2, 1897J 



NATURE 



431 



arms, or who have accidentally lost them in early life, who have 

 trained themselves to hold a pen, pencil, brush, or razor with 

 the foot, and to write, draw, paint, or even shave. But. in 

 these cases the object is held between the hallux and the toe 

 lying next to it, and not grasped between the great toe and the 

 sole of the foot by a movement of opposition. 



If we compare the anatomical structure of the human foot 

 with that of the foot of the ape, though the bones, joints, and 

 muscles are essentially the same in both, important differences 

 in arrangement may be easily recognised, the value of which 

 will be better appreciated by first glancing at the thumb. Both 

 in man and apes the thumb is not tied to the index digit by an 

 intermediate ligament, which, under the name of " transverse 

 metacarpal," binds all the fingers together, and restricts their 

 separation from each other in the transverse plane of the hand. 

 The great toe of the ape, similarly, is not tied to the second 

 toe by a " transverse metatarsal ligament," such as connects to- 

 gether and restricts the movements of its four outer toes in the 

 i transverse plane of the foot. The hallux of the ape is therefore 



I set free. It can, like the thumb of man and ape, be thrown 



' into the position of opposition and be used as a prehensile digit. 



Very different is the case in the human foot, in which the hallux 

 is tied to the second toe by a continuation of the same transverse 

 metatarsal ligament which ties the smaller toes together. Hence 

 it is impossible to oppose the great toe to the surface of the sole 

 in the way in which the thumb can be used, and the movements 

 of the digit in the transverse plane of the foot are also greatly 

 restricted. 



The development of a connecting transverse band, for the re- 

 striction of the movements of the great toe in man, is not the 

 only anatomical structure which differentiates it from the hallux 

 of an ape, or the thumb in the hand. In the manus both of 

 man and apes the joint between the metacarpal bone of the 

 thumb and the bone of the wrist (trapezium) is concavo-convex, 

 or saddle-shaped, and permits of a considerable range of move- 

 ment in certain directions, and notably the movement of oppo- 

 sition. A joint of a similar configuration, permitting similar 

 movements, is found in the pes of the ape between the meta- 

 tarsal of the hallux and the tarsal bone with which it articulates. 

 In the foot of man, on the other hand, the corresponding joint 

 is not saddle-shaped, but is almost plane-surfaced, and conse- 

 quently the range of movement is slight, and is little more than 

 the gliding of one articular surface on the other. 



One of the chief factors in the production of the movement 



of opposition in the manus of man and apes is a special muscle, 



the opponens poUicis, which, through its insertion into the shaft 



of the metacarpal bone of the thumb, draws the entire digit 



I across the surface of the palm. In the foot of the Anthropoid 



apes there is not complete correspondence in different species in 



the arrangement of the muscles which move the great toe. In 



the Orang the abductor hallucis, in addition to the customary 



insertion into the phalanx, may give rise to two slips, one of 



which is inserted into the base and proximal part of the first 



metatarsal bone, and the other into the radial border of its shaft 



for a limited distance ; these slips apparently represent an im- 



i perfect opponens muscle, which acts along with the adductor 



I and short flexor muscle of the great toe. In the other Anthro- 



p)oid apes, the muscle seems to be altogether absent, and the 



power of opposition is exercised solely by the adductor and the 



flexor brevis hallucis, the inner head of the latter of which is 



remarkably well developed.^ In the human foot there is no 



opponens hallucis, and the short flexor of the great toe is, in 



relation to the size of that digit, comparatively feeble, so that 



no special provision is made for a movement of opposition. 



I The character and direction of the movements of the digits 



\ , both in hand and foot are imprinted on the integument of palm 



and sole. In the palm of the human hand the oblique direction 



\ of the movements of the fingers towards the thumb, when bent 



I in grasping an object, is shown by the obliquity of the two great 



\ grooves which cross the palm from the root of the index to the 



' root of the little finger. The deep curved groove, extending to 



the wrist, which marks off the eminence of the ball of the 



thumb from the rest of the palm, is associated with the opponent 



action of the thumb, which is so marked in man that the tip of the 



thumb can be brought in contact with a large part of the palmar 



surface of the hand and fingers. Faint longitudinal grooves 



in the palm, situated in a line with the fingers, express slight 



1 For a comparative description of the muscles of the hand and foot of 

 the Anthropoid apes consult Dr. Hepburn's memoir in Journal of A naionty 

 and Physiology, vol. xxvi. 



NO. 1453, VOL. 56] 



folds which indicate, where the fingers are approximated to or 

 separated from each other, in adduction and abduction. In 

 some hands a longitudinal groove marks off the muscles of the 

 ball of the little finger from the rest of the palm, and is asso- 

 ciated with a slight opponent action of that digit ; by the com- 

 bination of which, with a partial opposition of the thumb, the 

 palm can be hollowed into a cup — the drinking-cup of Diogenes. 



These grooves are present in the infant's hands at the time of 

 birth, and I have seen them in an embryo, the spine and head 

 of which were not more than 90 mm. (three and a half inches) 

 long. They appear in the palm months before the infant can 

 put its hand to any use ; though it is possible that the muscles 

 of the thumb and fingers do, even in the embryo, exercise some 

 degree of action, especially in the direction of flexion. These 

 grooves are not therefore acquired after birth. It is a question 

 how far the intra-uterine purposeless movements of the digits 

 are sufficient to produce them ; but even should this be the case, 

 it is clear that they are to be regarded as hereditary characters 

 transmitted from one generation of human beings to another. 

 They are correlated with the movements of the digits, which 

 give the functional power and range of movement to the hand 

 of man. 



In the palm of the hand of the Anthropoid apes grooves are 

 also seen, which differ in various respects from those in man, and 

 which are characteristic of the group in which they are found. 

 In these animals the palm is traversed by at least two grooves 

 from the index border to that of the minimus. In the Gibbon 

 they are oblique, but in the Gorilla, Chimpanzee, and Orang 

 they are almost transverse, which implies that in flexion the 

 fingers do not move so obliquely towards the comparatively 

 feeble thumb as they do in man. The curved groove which 

 limits the ball of the thumb is present, but on account of the 

 less development of that eminence, it is not so extensive as in 

 man. The longitudinal grooves in the palm are deeper than in 

 the human hand, and in the Gorilla and Orang a groove 

 differentiates the eminence associated with the muscles of the 

 little finger from the adjoining part of the palm. The character 

 and direction of these grooves are such as one would associate 

 with the hand of an arboreal animal, in which the long fingers 

 are the chief digits employed in grasping an object more or less 

 cylindrical, like the branch of a tree, and in which the thumb 

 is a subordinate digit. I have not had the opportunity of 

 examining the palm of the embryo of an Anthropoid ape, but 

 in that of an embryo Macaque monkey I have seen both the 

 groove for the ball of the thumb which marks its opposition, 

 and the transverse and longitudinal grooves in the palm which 

 are correlated with the movements of 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 off 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 commences 

 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 pres- 

 sure. 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 off the 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 m 

 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 



1 These grooves have been described generally by the late Prof. 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 special attention to their .-irrangement in 

 the feet of infants (Nineteenth Century, vol. xxxi., 1892, p. 795)- The in- 

 tegumentary grooves in both handsand feet of men and apes have also been 

 described and figured in detail by Dr. Hepburn in Journal of Anat. and 

 Phys., vol. xxvii. 1893, p. 112. 



