780 REPORT— 1897. 



into the radial border of its shaft for a limited distance; these slips apparently 

 represent an imperfect opponens muscle, which acts along with the adductor and 

 ehort flexor muscle of the great toe. In the other Anthropoid apes, the muscle 

 eeems 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. 



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

 which cross the palm from tlje root of the index to the root of the little finger. 

 The deep curved groove, extending to the wrist, which marks ofl' 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 

 Ibrouglit 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 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 ofi" the muscles of the ball of the little finger from the rest of the palm, and 

 is associated with a slight opponent action of that digit ; by the combination 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 

 suflicient 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 com- 

 paratively 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 dierits 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 



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

 Anthropoid apes consult Dr. Hepburn's memoir in Jonrnal of Anatomy and Physiology, 

 vol. xxvi. 



