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



From the above examples it is seen that very much the same functions may be per- 

 formed by different feet by a great diversity of arrangements of the intrinsic pedal 

 muscles. In the animals that we have compared, however, we must remember that we 

 have only looked at the feet from one point of view, viz., that which bears chiefly upon 

 the special mode of life adopted by the animal. We must not lose sight of the fact that 

 the difference in structure in feet, which we might expect to find similar, may be due to 

 many circumstances that we have not taken into account. The offices and duties re- 

 quired of the foot are very numerous and very diverse, and we cannot therefore classify 

 them arbitrarily into burrowing, aquatic, terrestrial, and arboreal. 



Dr. Young is of opinion that "the differentiation and development of the flexores 

 breves" is for the purpose of providing for the maintenance of a "continuous and powerful 

 flexion of the digits, without at the same time interfering with the free movements at the 

 wrist." I am rather inclined to believe that the part which all the intrinsic muscles have 

 to play is the production of the more rapid and precise movements of the digits, move- 

 ments which could not be produced by muscles which arise in the forearm or in the leg, 

 and which are inserted into the digits by means of long tendons. In a general sense, 

 Dr. Young is decidedly correct in the observation which he makes, that those digits "which 

 are endowed with the most independent powers, have invariably the most distinctly 

 differentiated muscular arrangements; hence, even when the whole of the digits are 

 supplied with the "typical" complement of muscles, the first and fifth are very commonly 

 more favoured than the rest." 



One cannot examine a large number of different Mammalian feet without being struck 

 by the decided ordinal distinctions which the intrinsic muscles exhibit in their disposition. 

 In Marsupialia, we have the tendency to the trilaminar disposition. In Monotremata 

 there is the marked development of the adductors and the primitive condition of these 

 as regards their insertion with reference to the middle line of the foot. In Carnivora the 

 prominent feature is the coalescence (or shall we say the non-separation V) of the flexores 

 breves and dorsal interossei with the frequent development of an opponens minimi digiti 

 from the plantar layer. In the Solidungula and Buruinantia, the flexores breves are con- 

 verted into the suspensory ligament. In Eodentia there is the pre-eminence of the 

 intermediate layer of the flexores breves. In the Quadrumana the muscles of the hallux 

 are inordinately developed, and the adductor hallucis becomes split up into an oblique 

 and transverse portion. In Homo and his more immediate allies of the Quadrumanous 

 order, viz. the Gorilla and Orang, there is the loss of the plantar muscles, with the excep- 

 tion of the adductor hallucis and the loss also of certain of the heads of the flexores breves 

 so that the remainder take on the function of the absent adductors. In the Edentata, 

 which is composed of so many diverse forms, there is apparently no feature peculiar to all. 



Nerve arrangements. — At the outset of this chapter upon the intrinsic pedal muscles 

 we referred to the view which is held by certain anatomists, that the relationship between 



