REPORT ON THE MARSUPIALIA. 53 



The remaining three dorsal interossei (fig. 2, cP to d 5 ) cannot be properly studied 

 unless we throw forward both the plantar and intermediate muscles. They are then 

 seen to be prismatic, one-headed muscles, lying in the interosseous spaces, but only 

 reaching for a short distance upwards between the bones ; indeed they are more plantar 

 than dorsal in their relation to the metatarsus. They spring from the bases of the 

 metatarsal bones, and are inserted so as to abduct the toes from a line drawn through 

 the medius. The second and third, therefore, are appropriated by the medius, whilst the 

 fourth is set aside for the annularis. They correspond, therefore, in their insertions with 

 the same muscles in the human hand. 1 



Dasywrus viverrinus (PI. XI. figs. 5-6). 



The foot of this animal is long and narrow. The hallux is very rudimentary, consisting 

 merely of a short metatarsal, which is only evident in the undissected condition of the pes 

 as a slight protuberance on its inner margin. The other four digits are well developed, 

 and of nearly equal length. 3 The metatarsal bones are placed in such close apposition 

 that when the foot is viewed from its dorsal aspect, not a single intrinsic muscle is appa- 

 rent. They are all crowded into the sole, but, in spite of this, they exhibit in a marked 

 manner the typical trilaminar disposition, each of the four well-developed toes being pro- 

 vided with three separate intrinsic muscles. 



Plantar layer (fig. 5, p 1 to p 5 ). — In this layer we find four muscles which act 

 so as to draw the digits into which they are inserted towards a line drawn through the 

 medius. They are — 



1. Adductor hallucis (y* 1 ). 



2. Adductor indicis (/r). 



3. Adductor annularis (p 4 ). 



4. Adductor minimi digiti (p) 5 . 



The adductor indicis and adductor minimi digiti are. the most strongly marked. 

 They together constitute an exceedingly thin triangular sheet of fibres which lies superficial 

 to the other muscles. This muscular sheet takes origin by its apex which is tendinous, 

 in the middle line of the foot, from the ligaments which bind the metatarsus to the 

 tarsus. Its base arches over the bases of the annularis and medius, and it is inserted by 

 its anodes into the index and minimus — in the case of the former into the outer sesamoid 

 bone at its base, and in the case of the latter, into the inner sesamoid bone. The 

 separation of the two muscles is indicated by a faint fibrous raphe which traverses the 

 triangular muscular sheet from the apex to the centre of its arched base. 



The adductor annularis is a minute fusiform fleshy slip which arises from the deep 

 surface of the raphe which separates the two preceding muscles. The muscular sheet com- 



1 In the feet of the small female Thylaciih e slight tendency to fusion between the flexores breves, and the dorsal 

 interossei was exhibited. In the large male, however, they were <[iiitr distinct. 



- In Wuterhouse's well-known work upon .Mammalia, an excellent figure of this foot is given in vol. i. pi xii. 



fia l. 



