REPORT ON THE MARSUPIALIA. 09 



fifth metatarsal bone. From the distal end of this, two small fleshy bellies proceed, and 

 these are inserted into the sesamoid bones at the base of the first phalanx of the minimus. 

 A few short oblique fleshy fibres are observed upon the outer surface of the tendinous 

 part of the flexor brevis minimi digiti. These probably represent the abductor minimi 

 digiti. 



The flexor brevis annularis is a strongly developed muscle, which lies upon the 

 plantar surface of the fourth metatarsal, and takes origin from the base of the fifth 

 metatarsal bone. Its two heads do not separate from each other until the muscle reaches 

 the metatarsophalangeal joint. They are then inserted into the sesamoid bones at the 

 base of the annularis. 



Two delicate fleshy slips which lie upon the plantar surface of the attenuated 

 metatarsals of the index and medius, and are inserted into the inner sesamoids of these 

 toes, in all probability represent the inner heads of the flexor brevis indicis, and flexor 

 brevis medii respectively. 



Dorsal layer. — The members of this group have disappeared. Traces of two, however, 

 are to be found. The abductor minimi digiti is evidently represented by the short fleshy 

 fibres which are found adhering to the outer surface of the fibrous part of the flexor 

 brevis minimi digiti. The fourth dorsal interosseous muscle is present in the form of 

 strong aponeurotic fibres which bind the fourth and fifth, metatarsal bones together. 



Nervous arrangements. — All the muscles are supplied by the external plantar nerve. 



MONOTREMATA. 



Ornithorhynchus paradoxus (Duck-mole) (PI. IX. fig. 5). 



The intrinsic muscles in the pes of this animal present a very compHcated arrangement, 

 and the following account of their disposition is the result of the dissection of both feet 

 of four specimens. The plantar layer is always quite distinct, but a considerable degree 

 of fusion usually exists between the members of the intermediate and dorsal layers. 



Plantar layer. — This group is composed of four muscles, arranged so as to adduct 

 the toes towards the index or second digit. They are — 



1. The adductor minimi digiti. 3. The adductor medii. 



2. The adductor annularis. 4. The adductor hallucis. 



All these have a common origin from the plantar surface of the external and middle 

 cuneiform bones. 



The adductor minimi digiti is the largest of the series, and is placed very obliquely 

 in the sole. It is chiefly inserted upon the tibial aspect of the base of the first phalanx 

 of the minimus, but it also sends a slender fleshy process forwards upon the inner aspect 

 of the digit, so as to gain attachment to the second phalanx. 



