13G THE VOYAGE OF H.M.S. CHALLENGER. 



exhibited. The branch in question comes from the superficial division of the external 

 plantar, but it is joined at its point of bifurcation by a large twig from the deep division. 



Very few cases occur in which the plantar nerves deviate from the ordinary course. 

 In the Ornithorhynchus we find the external plantar entering the foot upon the outer 

 side of the os calcis, apart from the internal plantar. Again, in the Echidna the internal 

 plantar gives off a branch which enters the foot by a similar route and replaces the super- 

 ficial part of the external plantar nerve. 



So constant, indeed, are these nerves in their relations that Euge has been induced to 

 make the generalisation that all those muscles which lie superficial to the deep division 

 of the external plantar nerve are contrahentes. So far as I am aware this rule fails to 

 apply to the foot in only two cases, viz., the Dasyurus viverrinus and Dasyurus hallucatus, 

 in both of which the nerve passes under cover of one of the abductors of the minimus. 

 The great objection to this method of classifying the adductors, however, is that it is 

 incapable of being extended to the hand. In the Manus the deep division of the ulnar 

 nerve passes inwards under cover of the flexor brevis minimi digiti, and also under (or 

 through) the opponens minimi digiti, both of which, therefore, according to this generalis- 

 ation would be looked upon as contrahentes or adductores. 



Intrinsic muscles of the human hand. — The fact that abduction and adduction takes 

 place in the human hand with reference to the middle digit constitutes the chief 

 difference between the disposition of the intrinsic muscles of the Manus and pes in Man. 

 The descriptions given of the short muscles of the thumb in works upon human anatomy 

 are very misleading and at variance with the homologies of these muscles. The nerve 

 supply is of itself sufficent to lead us to suspect this. In these text-books a single adductor 

 pollicis and a flexor brevis pollicis, consisting of a superficial, and deep head, are described. 

 The adductor and the deep head of the flexor draw their nerve filaments from the deep 

 division of the ulnar, whereas the superficial head of the flexor is supplied by the median 

 nerve. Bischoff many years ago pointed out the fallacy of this description, and insisted 

 that the so-called adductor pollicis is in reality the adductor transversus (the homologue 

 of the transversalis pedis), and that the so-called deep head of the flexor brevis is the 

 adductor obliquus. These two muscles, which form a continuous muscular stratum, are 

 separated from each by the entrance into the palm of the radial artery. But an inner or 

 deep head of the flexor brevis is also present. This muscular slip, however, is not always 

 described, and when it is noticed it has a different name applied to it, viz., the " interosseus 

 volaris primus " of Henle. I entirely agree with Bischoff in his views upon the short 

 muscles of the thumb ; indeed, I had arrived at similar conclusions before I read his paper 

 upon this subject. From a number of dissections made by Mr. Sheridan Delepine in the 

 Practical Anatomy Rooms of the Edinburgh University, I am led to believe that the 

 minute inner head of the flexor brevis pollicis is a constant muscular slip. It is quite 

 invisible from the palmar aspect of the hand, and is best exposed from the dorsal aspect 



