REPORT ON THE MARSUPIALIA 105 



plantar cushion, they have little or no space wherein they can be separated and approxi- 

 mated, and consequently such muscles, had they been present, would have been almost 

 functionless. Another remarkable feature in the foot of this animal is its resemblance 

 to that of the Hyrax in the manner in which the intrinsic muscles derive their nerve 

 supply. The intrinsic pedal muscles are entirely plantar in position. 



The plantar layer consists of a single minute muscle — a transverse adductor of the 

 index — which we may term the transversus indicis (p 2 . t). This muscular slip arises 

 from the head of the fourth metatarsal bone and the fascia covering the flexor brevis 

 annularis, and passes transversely inwards upon the surface of the flexor brevis medii 

 to be inserted into the fibular side of the sesamoid of the index. 



Miall and Greenwood describe also an oblique adductor of the index which they term 

 a " plantar interosseus." According to these authors this muscle " arises from the tarsus, 

 opposite the bases of the third and fourth metatarsals, and is inserted into the fibular 

 side of the base of the second digit." No such muscle existed in the foetus dissected by 

 me, but there was a strong fibrous band having precisely the same attachments, which I 

 have no doubt is its representative (p 2 ). 



Intermediate layer. — This is the only group of intrinsic muscles which is well 

 developed. Each digit, with the exception of the hallux, is provided with a well-marked 

 flexor brevis. These muscles are termed dorsal interossei by Miall and Greenwood. 



The flexor brevis indicis (/ 2 ) is the best marked muscle of the series. It consists of 

 two heads, which arise from the fibrous textures in relation to the tendon of the peroneus 

 longus, and are inserted one into each of the sesamoids on the plantar aspect of the 

 base of the first phalanx of the index. 



The flexor brevis medii (/ 3 ) is also strongly marked, and composed of two heads 

 which arise from the base of the middle metatarsal bone. The inner head also derives 

 numerous fibres of origin from the fibular side of the fibrous cord which represents the 

 oblique adductor indicis. The muscle is inserted in the usual manner into the sesamoids 

 at the base of the medius. 



The flexor brevis annularis (/ 4 ) is more feebly developed. Its two heads are scarcely 

 differentiated from each other, and its fibular slip passes for a short distance forwards 

 into the fourth intermetatarsal space, which suggests the idea that combined with it is 

 the absent fourth dorsal interosseous muscle. Like the preceding muscle it arises from 

 the base of the fourth metatarsal, and is inserted into the sesamoids at the root of the 

 annularis. 



The flexor brevis minimi digiti consists of a single well-marked tibial head (f 5 . t). 

 From its taking a more proximal origin and from the stunted character of the metatarsal 

 bone of the minimus this muscle does not lie in series with the other members of the 

 croup. Indeed, at first sight it is apt to be mistaken for an adductor, and Miall and 

 Greenwood have described it as such. The fact, however, that all the deep branches of 



(ZOOL. CHALL. EXP — PAKT XVI. — 1882.) Q li 



