560 DR DAVID HEPBURN ON THE 



of Palmar Interosseous muscles from three to seven. Now, various forms of increase 

 in the number of Palmar Interosseous muscles have been recorded, and in Professor 

 Macalister's * great work on muscular abnormalities there are references to each of the 

 four longitudinal bundles I am describing. The point of distinction is, that Professor 

 Macalister records as abnormalities, structures which I desire to show are constantly 

 present and capable of more or less easy separation in every hand. The fact that 

 under certain circumstances these muscles are so distinct that they have been observed 

 and noted as abnormalities shows that I am not introducing an unknown element into 

 the human hand, although I claim its constant presence as the normal condition. 



From this standpoint the questions naturally arise : what position should be assigned 

 to this series of Palmar Interosseous muscles ?, and what nomenclature is most applicable 

 to their description ?, both of which questions can only be answered by reference to the 

 facts of comparative anatomy. Our knowledge of the comparative anatomy of the 

 intrinsic muscles of the manus is principally based upon Professor Cunningham's 

 Challenger Report. t These muscles are divided into three strata, viz., Dorsal, Inter- 

 mediate, and Palmar. Considered according to the actions performed by them, they 

 are Abductors, Short Flexors, and Adductors respectively. In the human hand the 

 Dorsal or Abductor stratum consists of six muscles, of which the Medius digit possesses 

 two in virtue of its being situated in the middle line of the hand. With the exception 

 of the Abductor pollicis (brevis) and the Abductor minimi digiti, the other members 

 of the group are interosseous in position, and each is bipennate in the arrangement of 

 its fibres. 



The Palmar Stratum consists of Adductors of the various digits. Their principal 

 source of origin is the middle line of the hand, but the individual muscles of this 

 stratum are subject to much variation, both as regards number and size, in different 

 animals. In the case of Man, only one member of this group is present, namely, the 

 Adductor pollicis, which, however, has become so specialised that it is usually observed 

 and described in two portions, called Obliquus and Transversus respectively. The full 

 number of muscles belonging to this group is four, and these may be seen in the Gibbon,\ 

 in which the Pollex, Index, Annularis, and Minimus digits are so provided. This 

 entire group has been termed " Contrahentes digitorum."§ 



The Intermediate Stratum embraces a series of muscles, situated for the most part 

 between the dorsal and palmar strata, and acting as short flexors of the various digits. 

 They are generally regarded either as derived from or as producing the members of the 

 dorsal stratum by a process of cleavage or segmentation. Each member of this stratum 

 consists of two separate portions or heads of origin, which are associated with both 

 lateral surfaces of the shaft of the metacarpal bone which carries the digit upon which 



* Macalister, " Muscular Anomalies in Human Anatomy," Trans. Roy. Irish Acad., vol. xxv., Science. 

 t Cunningham, " Challenger" Reports, Zoology, v. 



% Hepburn, " Comparative Anatomy of the Muscles and Nerves of the Superior and Inferior Extremities of the 

 Anthropoid Apes," Journ. Anat. and Phys., vol. xxvi. 



HaIiFORD, Lines of Demarcation between Man, Gorilla, and Macaque, Melbourne, 1864. 





