156 Dr. D. C. L. Fitzwilliams on the 



be said to exist. The tliumb is sliort in comparison witli tlie 

 rest of the hand ; it extends slightly beyond the level of tlie 

 nietacarpo-phalangeal joint of the second digit, but not as far 

 as the web between the second and third. In man the thumb 

 reaches to the level of the proximal interphalangeal articu- 

 lation of the index, while the interphalangeal joint of the 

 thumb is on a level with the metacarpo-phalangeal joint of 

 the second digit. 



The web of the gibbon's thumb is very small, not reaching 

 halfway down the first metacarpal bone. This gives rise to 

 an appearance as if the palm and the thumb sprang separately 

 from the region of the wrist. In marked contrast to this, the 

 webs of the fingers are much more extensive than those of 

 man, and reach nearly halfway down the elongated proximal 

 plialanges, thereby lengthening the palm at the expense of 

 the fingers. This extensive webbing prevents separation of 

 the fingers to any great extent. As in man, the third digit 

 is the longest. The fingers are placed parallel to one another, 

 but show slight ability to oppose the thumb. 



The positions of the deep creases of the skin are as follows : — 



1. In front of the wrist there is a deep transverse crease 

 due to the flexion of this joint. 



2. From just below the midpoint of the wrist-crease another 

 starts, and runs downwards and outwards into the deep cleft 

 which intervenes between the thenar eminence and the rest of 

 the palm. This crease and cleft are caused by the adduction 

 of the thumb. In man tlie great development of the thumb- 

 muscles has filled out the cleft and increased the web, while 

 the upper limit of the crease curves outwards round the theucir 

 eminence well below the creases of the wrist. 



3. Starting from the same point as the preceding, a crease 

 passes downwards and inwards to the inner margin of the 

 palm, just above its centre. The causation of this line is not 

 very evident, as the muscles of the hypothenar eminence are 

 small. Of such a crease little or no trace is to be found in 

 the human hand : but in the foot of the ape a very similar 

 marking is found in front of the outer part of the heel, the 

 jjart which corresponds to the hypotlienar eminence of the 

 hand (see PI. V. fig. 1, 13). 



4. In common with the two preceding yet another crease 

 starts and runs longitudinally down the palm to the root of 

 the third digit. 



5. Parallel and to the outer side of the last-mentioned 

 crease is a shorter crease which ends at the cleft between the 

 second and third digits. These creases result probably from 

 the contraction of the contrahentcs and ))alniar interosseous 



