In the Dasyurus macrurus I observe a small sesamoid bone wedged in between the as tragalus, tibia, and fibula at the back part of the ankle joint. In the Petaurus taguanoides there is a supplemental tarsal bone wedged in between the naviculare and cuboides on the plantar sur face. In the hand-like foot of the Phalanger the structure of the tarsus is shown in fig. 111 : f is the naviculare, g the internal cuneiform, and h the os cuboides. In the Wombat the sca phoid, cuboid, and three cuneiform bones have the ordinary uses and relative positions.
The analogy of the carpal and tarsal bones is very clearly illustrated in this animal. The anchylosed naviculare and lunare of the hand correspond with the astragalus and navicu lare of the foot, transferring the pressure of the facile :Indus upon the three innermost bones of the second series. The long, back ward-projecting pisiform bone of the wrist closely resembles the posterior process of the as colds; the articular portion or body of the as calcis corresponds with the cuneiforme of the carpus; the large carpal unciprm re presents the tarsal cuboides, and performs the same function, supporting the two outer digits ; the three cuneiform bones of the foot are obvi ously analogous to the trapezium, trapezoides, and os magnum. The internal cuneiform bone is the largest of the three in the Wombat, al though it supports the smallest of the toes. It is of course more developed in the Pedimanous Marsupials, where it supports a large and op posable thumb.
In the Wombat the metatarsals progressively increase in length and breadth from the inner most to the fourth ; the fifth or outermost meta tarsal is somewhat shorter but twice as thick, and it sends off a strong obtuse process from the outside of its proximal end. A correspond ing process exists in the Phalangers (fig. 111). The innermost metatarsal of the Wombat (fig.
105) supports only a single phalanx ; the rest are succeeded by three phalanges each, pro gressively increasing in thickness to the outer most; the ungueal phalanges are elongated, gently curved downwards, and gradually dimi nish to a point.
In the Myrmecobius the tibial or inner most toe is represented by a short rudimental metatarsal bone concealed under the skin. In the Dasyures the innermost toe has two phalanges, hut it is the most slender and does not exceed in length the metatarsal bone of the second toe. In the Petanrists it is rather shorter than the other digits but is the strongest, and in Pctaurus toguanoides the terminal phalanx is flattened and expanded ; the toes are set wide apart in this genus. In the Opossums
and Phalangers the innermost metatarsal bone is directed inwards apart from the rest, and together with the first phalanx is broad and flat. The second phalanx in the Opossums supports a claw, but in the Phalangers is short, trans verse, unarmed, singularly expanded in Ph. Cookii, but almost obsolete in Ph. ursina (fig. 111, 1). In all the preceding genera there are two small sesamoid hones on the under side of the joints of the toes, both in the fore and hind feet.
The commencement of a degeneration of the foot which is peculiar to and highly character istic of the Marsupial animals may be discerned in the Petaurists, in the slender condition of the second and third toes, as compared with the fourth and fifth. In the Phalangers this diminution of size of the second and third toes, counting from the hallux, is more marked. They are, also, both of the same length and have no individual motion, being united to gether in the same sheath of integument as far as the ungueal phalanges, whence the name of Phalangista applied to this genus (fig- 111, 2 and 3).
In the saltatorial genera of Marsupials the degradation of the corresponding toes is ex treme, but though reduced to almost fila mentary slenderness they retain the usual num ber of phalanges, and the terminal one of each is armed with a claw. These claws being the only part of the rudimental digits which pro ject freely beyond the integument, they look like little appendages at the inner side of the foot for the purpose of scratching the skin and dressing the fur, to which offices they are exclusively designed. The removal of the in nermost toe, corresponding with our great toe and the hallux of the Pedimana, commences in the Perameles. In one species I find the metatarsal bone of this toe supports only a single rudimental phalanx which reaches to the end of the next metatarsal bone, and the inter nal cuneiform bone is elongated. In another species the internal toe is as long as the abortive second and third toes, and has two phalanges, the last of which is divided by the longitudinal fissure characteristic of the ungueal phalanges in this genus. In the Perameles lagotis the innermost toe is represented by a rudimentary metatarsal bone, about one-third the length of the adjoining metatarsal.