558 DR DAVID HEPBURN ON THE 



verge in a bipenuate manner to a common tendon of insertion. Quain* says each 

 dorsal muscle arises " from both of the metacarpal bones between which it is placed, 

 but most extensively from that supporting the finger upon which it acts." This 

 description is endorsed by the other authorities mentioned. 



Third. — Each palmar muscle possesses one head of origin, and, according to Quain, it 

 arises " from the corresponding lateral surface of the body of the metacarpal bone of 

 the finger on which it acts," — a statement which closely resembles what is given by other 

 authors. 



Fourth. — As regards the functions performed by these muscles, one may say that 

 there is unanimity of opinion so far as the movements of Abduction and Adduction are 

 concerned. Both of these movements take place in the radio-ulnar or horizontal plane 

 around an antero-posterior axis with reference to an imaginary line bisecting the middle 

 digit, and being prolonged upwards to the wrist, — the dorsal muscles being the Abductors 

 and the palmar muscles the Adductors. In addition to these actions, however, various 

 writers t claim that the interosseous muscles assist the Extensors and Lumbricales in 

 producing flexion of the first and extension of the second and third phalanges. 



It is important to note that flexion of the first phalanges takes place around a radio- 

 ulnar axis, which is at right angles to the axis in which abduction and adduction occur ; 

 and further, that the latter movements are regarded as of primary importance, while 

 flexion is referred to as a secondary action dependent upon their mode of insertion. Now, 

 although we are familiar with movements occurring at an articulation around axes at 

 right angles to each other, as, for example, at the radio-carpal joint, yet such movements 

 are produced by combinations of muscles which individually usually act in opposition to 

 each other ; and it is rather startling to find that the power of producing movements in 

 two directions at right angles to each other is claimed for an individual muscle. 



Turning now to my own dissections of these muscles, it is necessary to observe that 

 the shaft of each metacarpal bone, with the exception of that for the pollex, is described 

 as prismatic, and regarded as presenting a dorsal surface of triangular outline (having 

 the apex towards the carpal end, while the base is directed towards the phalanges), and 

 two lateral surfaces which are separated from each other on the palmar aspect by a 

 smooth ridge occupying the proximal two-thirds of the shaft, but in the distal third of 

 the shaft this smooth ridge bifurcates and leaves a small triangular area towards the 

 head of the metacarpal bone. Muscular fibres do not arise either from the larger 

 dorsal triangular area or from the smaller palmar one. The lateral surfaces are there- 

 fore prolonged to both the dorsal and palmar aspects of the shaft, and it is from them 

 that the dorsal and palmar muscles take origin. If we now examine a,nj lateral surface 

 which, according to current descriptions, accommodates the entire origin of a palmar 

 interosseous muscle, and one head of a dorsal interosseous muscle, we shall find the area 



* Loc. cit. 



t (1) Quain, loc. cit. (2) Gray, loc. cit. (3) Duchenne, Physiologic des Mouvements, quoted by Gray and Quain. 

 ( I C let, and (Jour, of Anat. and Phys., old series, i. 85). 



