REPORT ON THE MARSUPIALIA. 61 



muscle in the Cuscus, and contains a great number of tendinous fibres in its com- 

 position. 



The abductors of the little toe are only two in number — one inserted into the base of 

 the fifth metatarsal, and the other partly into the outer sesamoid bone, and partly into 

 the extensor tendon at the base of the minimus. 



The dorsal interossci are dorsal in position, and can best be inspected upon the dorsal 

 aspect of the foot. The first or abductor indicis agrees in almost every respect with the 

 corresponding muscle in Cuscus. The second, as in Cuscus f is apparently absent, but an 

 examination of the inner head of the flexor brevis medii, shows that it has in reality 

 coalesced with it, as this fleshy slip extends upwards between the metatarsals to the 

 dorsum of the foot, so that when viewed from this aspect it seems to be the absent 

 muscle, whilst viewed from the sole, it gives the observer the impression of its being the 

 flexor. The third is a single-headed prismatic muscle, which takes origin from the dorsal 

 surface of the contiguous bases of the third and fourth metatarsals. At the distal 

 extremity of the interosseous space in which it lies, it ends in a tendon which bifurcatea 

 to be inserted into the adjacent sides of the bases of the first phalanges of the medius and 

 annularis. Clearly, then, it acts as an approximator of these digits. This muscle there- 

 fore corresponds with the same muscle in Cuscus, except in its not being supplied with a 

 separate abducting slip for the medius. The fourth dorsal interosseus is a very remark- 

 able muscle. It is not nearly so dorsal in position as the others, still it can readily be 

 seen between the metatarsals from this point of view. It consists of two well-marked 

 fleshy slips. Of these one arises from the plantar aspect of the base of the metatarsal 

 bone of the minimus, and is inserted into the summit (i.e., centre) of an exceedingly 

 powerful tendinous arch which is attached by its extremities to the adjacent sides of the 

 bases of the proximal phalanges of the annularis and minimus. The second slip springs 

 from the plantar surface of the base of the fourth metatarsal bone, and is inserted into 

 the inner end of the tendinous arch (i.e., that extremity which is fixed to the outer 

 aspect of the root of the annularis). This compound muscle therefore resembles the cor- 

 responding muscle of Cuscus, in so far as it consists of an approximating and an abducting 

 part — the first acting by drawing the minimus and the annularis towards each other, and 

 the second acting by drawing the annularis away from the middle line of the foot. 



Dr. Young, in his able paper upon the intrinsic muscles of the Marsupial hand, 1 

 describes a somewhat similar condition in the manus of the Wallaby. He says : — " The 

 second and third dorsal interossei have a somewdiat remarkable arrangement. On their 

 dorsal aspect they closely resemble the corresponding structures in the human hand. 

 They appear as bicipital muscles, springing from the contiguous surfaces of adjoining 

 metacarpal bones; the fibres converge inferiorly to a common insertion, the plane of 

 which is much more palmar in position than is that of the origin. Turning next to 



1 Journal of Anatomy and Physiology, vol. xiv. p. 154. 



