70 THE VOYAGE OF H.M.S. CHALLENGER. 



The other three adductors are inserted respectively into the inner sides of the bases 

 of the first phalanges of the annularis and medius, and into the outer side of the base of 

 the first phalanx of the hallux. 



In the foot of one very large specimen, I found a delicate muscular fasciculus 

 apparently associated with these muscles and inserted into the outer side of the base of 

 the first phalanx of the medius. I could detect no trace of this minute muscle in the 

 other specimens and it is difficult to account for its presence in this individual case. 



In Euge's excellent paper upon the deep muscles of the sole two additional muscles 

 are described as belonging to this group, viz., one inserted into the inner side of the index 

 digit and another inserted upon the outer side of the minimus. I have looked in vain 

 for the first of these, and the deep division of the external plantar nerve afforded me no 

 help in my search. As Ruge has pointed out, this nerve generally runs across the foot 

 between the adductors and the other intrinsic muscles so as to separate this group from 

 the subjacent flexors and abductors. In the Ornithorhynehus I found it impossible to 

 trace this nerve inwards beyond the muscles of the index. It here breaks up into its 

 delicate terminal twigs, in a manner very different from that which is re]n-esented by 

 Euge in fig. 46 of his paper. 



With regard to the extra plantar muscle which he describes for the minimus, I have 

 not the least hesitation in pronouncing this to be the outermost belly of the flexor brevis 

 digitorum. I have undertaken three special dissections with the view of determining 

 this point. The flexor brevis digitorum consists of four fleshy belbes. Of these the two 

 for the index and medius arise from the plantar surface of the long flexor tendon as it 

 enters the sole, whilst the other two (viz., those for the annularis and minimus) spring 

 by a common fleshy origin from the under surface of the outwardly directed tuberosity 

 of the os calcis. They are all inserted into the bases of the first phalanges and also 

 partly into the flexor sheathes of the digits to which they go. 1 The identity of the 

 outermost belly is established (l) by its origin being so far apart from that of the plantar 

 muscles, (2) by its continuity at its origin with the fleshy belly of the flexor brevis 

 digitorum for the annular digit, (3) by its lying superficial to the long flexor tendon of 

 the minimus, (4) and lastly, by its having an insertion similar to that of the other bellies 

 of this muscle. It is quite true, as Euge points out, that it is supplied by a twig from 

 the external plantar nerve, but this of itself is not sufficient to separate it from the 

 muscle to which it so manifestly belongs. 2 



1 Meckel in his great work upon Comparative Anatomy (loc. cit., voL vi. p. 447) holds a different opinion regarding 

 these four fleshy bellies. He looks upon them as being the lumbrical muscles. He says : " Le tendon inferieur produit 

 deux muscles lombricaux alonges, qui se rendent a la premiere phalange des deuxieme et troisieme orteils. Deux 

 muscles sembables, distines aux troisieme (?) et quatrieme orteils, sont fournis, non par ce tendon, mais par le bord 

 externe du tarse." The nerve supply certainly. seems to favour this view. A reference to page 461 of same volume 

 will show that the second " troisieme " in this quotation, should in reality be " cinquieme." 



2 In Cuvier and Laurillard's plates (pi. cclxix. fig. 5) the four fleshy bellies are well figured, and they are all included 

 under the name of " court flechisseur coinrnun." 



