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



These all lie upon the same plane and constitute an exceedingly thin but distinct 

 muscular stratum. 



The adductor hallucis arises from the plantar fascia and the ligaments over the bases 

 of the second and third metatarsal bones. Narrowing as it passes downwards and inwards, 

 it is inserted into the outer aspect of the base of the first phalanx of the hallux along 

 with the tibial head of the flexor brevis hallucis. 



The adductor minimi digiti is a slender and thin muscle which takes origin from the 

 fibrous structures in relation to the base of the fourth metatarsal bone, and also from a 

 short tendinous intersection which separates it from the muscular slip to the annularis 

 which lies along its inner margin. It is inserted into the tibial side of the base of the 

 first phalanx of the minimus. 



The adductor medii et indicis is a broad, quadrate, continuous sheet of muscular fibres 

 placed over the second and third metatarsal bones and the muscles in connection with 

 them. It springs from the proximal two-thirds of a strong tendinous raphe, which 

 stretches from the base of the fourth metatarsal to the base of the first phalanx of the 

 annularis. It likewise derives fibres from the ligaments in relation to the bases of the 

 second and third metatarsal bones. From this wide origin the fibres are directed towards 

 the roots of the middle and inner digits, and as they approach these they diverge slightly 

 so that the inner fibres pass to be inserted into the tibial aspect of the base of the proximal 

 phalanx of the index, whilst the outer fibres go to their insertion into the fibular side of the 

 corresponding phalanx of the medius. At the roots of these toes a few fibres pass trans- 

 versely, and form a slightly arched bundle which runs directly from one digit to the other. 



This muscle is undoubtedly modified in accordance with the syndactyle nature of the 

 digits into which it is inserted, and its actions are in consequence varied. 



The fourth muscular slip which belongs to this layer arises from the fibular side of 

 the fibrous raphe, and from a tendinous intersection which separates it from the adductor 

 minimi digiti. It is inserted into the outer side of the first phalanx of the annularis, and 

 must therefore exercise an abducting influence upon this toe. It is difficult to account 

 for the presence of such a distinct abductor in this layer. 1 In all probability, however, it is a 

 portion of the adductor minimi digiti which has shifted its insertion to the adjacent digit. 

 In support of this view we may mention that where there is a median raphe it is the custom 

 for the adductor of the minimus to arise from the greater or indeed the entire extent of 

 its fibular margin {i.e., Thylacine, Dasyurus, Cvscus, Vulpine Plialanger), whereas in 

 this case it is shut out from the raphe by the muscular slip in question. 



Intermediate layer (figs. 2, 3,/ 1 toy 5 ). — The usual five muscles are found entering into 

 the composition of this layer. With the exception of the flexor brevis minimi digiti each 

 of these muscles consists of two slips. 



1 By referring to Plate II., fig. 3, a somewhat similar slip will be seen in the manus of the Cuscus in connection 

 with the index digit. 



