OSSEOUS SYSTEM OF MAMMALIA 103 



anterior row, supporting the phalanges, viz., a cuboid, and three cunei- 

 form bones : behind the latter is a large os naviculare ; between which 

 and the tibia and fibula, is the astragalus (being articulated to both) ; on 

 the outside of the astragalus is placed the os calcis, of considerable size, 

 articulated both to the astragalus and the fibula. Resting partly on it, but 

 chiefly on the os naviculare, and lower extremity of the tibia posteriorly, 

 as a supplemental os calcis, is a large round bone, superior in size to the 

 os calcis, and supporting another, but smaller, which forms the base of a 

 powerful spur (in the male), bending upward and inward : this latter 

 bone, in the spurless female, is merely rudimentary. Meckel states, that 

 the two-toed Ant-eater has nine tarsal bones ; the Marsupials and Car- 

 nivora have usually seven. 



In the Aii the anterior bones of the tarsus are anchylosed together, 

 and with the metatarsal ; the astragalus and os calcis being alone distinct. 

 In the Rodentia the number of tarsal bones is augmented by the division 

 of the os naviculare, or scaphoid bone, into two portions ; and often, also, 

 by the presence of a long compressed supplemental bone, along the inner 

 side of the tarsus, as in the Beaver : this bone is, however, wanting in the 

 Hamster, the Squirrel, the Cavy, and the Porcupine : nevertheless, a 

 division of the second cuneiform bone, in the latter, renders the number 

 nine. In the Hare, the tarsus consists of six bones only. The arrange- 

 ment of the phalanges and of the metatarsal bones is analogous to those 

 of the metacarpal bones and phalanges of the anterior limbs. 



With respect to the metatarsus, in the solipedous Pachydermata, and 

 in the ruminants, it agrees with the metacarpus : in the former it is accom- 

 panied by two rudimentary stylets. In the Pachydermata, generally, and 

 in all other orders, the number of metatarsal bones is the same as that 

 of the toes ; but they are by * no means of equal size and volume. 

 Where the toes are short and feeble, the metatarsal bones will be feeble 

 also, as is seen in the outer toe of the Armadillo. In the Kangaroo, the 

 two first, or internal metatarsal bones, are remarkable for their slender- 

 ness and close approximation to each other ; each bears a small toe, and 

 both are joined together as far as the claw. The third metacarpal bone 

 is very robust and large, and sustains a strong elongated toe, armed with 

 a hoof-like nail. The fourth metacarpal bone is short, and, though far 

 inferior in bulk to the third, exceeds the first and second both together. 

 In the Opossum, the first metatarsal bone stands apart from the others, 

 and is flattened : in its situation, and in its opposableness to the foot, 

 this bone, and the two phalanges which it bears, represent a thumb. 

 In the Helamys, a rodent of South Africa, the first metatarsal is blended 

 with the first cuneiform bone of the tarsus. It is, however, in the 

 Gerboa, that the metatarsus is most remarkably modified. In this spe- 

 cies (Dipus Sagitta) the toes are three ; but the metatarsus consists 



