562 DR DAVID HEPBURN ON THE 



flexors, and each becomes either the radial or ulnar head of the short flexor muscle of 

 a specific digit. 



According to current descriptions there are three palmar interosseous muscles in 

 Man's hand, and they occupy the second, third, and fourth inter-metacarpal spaces 

 respectively. In the Gibbon, Orang-utan, and Gorilla a similar number has been 

 described ; # but in the Chimpanzee I have recorded the presence of three additional 

 muscles belonging to this series, making a total of six, so disposed as to place two in each 

 of the second, third, and fourth inter-metacarpal spaces ; while D wight,! in his recent 

 dissection, has described a total number of seven. He says : — " The smallest of these is 

 the first. It arises from the radial side of the metacarpal bone of the index, internal to 

 the belly of the dorsal." . ..." I have called it a palmar interosseous, because it seems 

 to me a distinct muscle ; still its mode of termination gives support to those who would 

 call it a part of the first dorsal." 



Whatever may be said concerning the supposed incomplete condition of the short 

 flexor stratum in Man's hand, it must be quite evident that, so far as the Chimpanzee's 

 hand is concerned, there is no occasion to distinguish between short flexors and palmar 

 interosseous muscles, because between them the stratum is completed, and each digit 

 possesses its short flexor muscle presenting a radial and an ulnar head of origin. It 

 must now be abundantly clear that the four palmar slips of muscle, which I have 

 described as capable of being dissected in the human hand, in addition to the three palmar 

 interosseous muscles already accepted, produce a condition exactly parallel to that seen 

 in the Chimpanzee's hand ; but, instead of considering them merely as so many additions 

 to the group of palmar interosseous muscles, my opinion is that the nomenclature should 

 be amended so as to conform to accepted facts of comparative anatomy, and that the 

 general term " Short Flexors of the digits " should supersede the present use of " Palmar 

 Interosseous." Thus, each digit would present its short flexor, consisting of a radial and 

 an ulnar head, while the entire series would resemble the dorsal stratum in occupying 

 interosseous positions, with the exception of those portions on the radial and ulnar borders 

 of the hand, viz., radial head of Flexor brevis pollicis and ulnar head of Flexor brevis 

 minimi digiti. In each case, the short flexor would be distinguished by the distinctive 

 name of the digit on which it acted. In this way we should recognise M. flexor brevis 

 'pollicis as consisting of the Radial and Ulnar heads at present described. 



M. flexor brevis indicis consists of a radial head, separable from the Abductor 

 indicis, and an ulnar head (First Palmar Interosseous). The insertions of these two 

 portions are found in opposite sides of the base of the first phalanx of the index 

 digit. 



M. flexor brevis rnedii digiti consists of a radial head, separable from Abductor 

 medii digiti (radiad), and an ulnar head, separable from Abductor medii digiti (ulnad). 

 These are inserted into opposite sides of the base of the first phalanx of the middle 

 digit. 



* Hepburn, loc. cit. t Dwight, loc. cit. 



