The name Marsupial indicates what is perhaps the most salient character of this order. The pouch in which the young are carried is almost universally present. It is less developed {123} on the whole in the Polyprotodont forms, such as the Thylacine, Dasyures, etc., but is found in so many of them that the two divisions of the Marsupials, the Diprotodonts and the Polyprotodonts, cannot be raised to distinct orders on this and other grounds. The marsupial pouch of the Marsupials must not, as has been already pointed out, be confounded with the pouch of the Monotreme mammals. Distinct teats are found in the marsupium of the Marsupials, while there are none in the mammary pouch of the Monotreme, the pouch itself indeed representing an undifferentiated teat, of which the walls have not closed up. The pouch opens forward in the Kangaroos, and backwards in the Phalangers and in the Polyprotodonts. Its walls are supported by a pair of bones diverging from each other in a [70]-shaped manner; these are cartilaginous and vestigial in the Thylacine. They {124} are the precise equivalents of similar bones in the Monotremata. It has been held, but apparently erroneously, that these bones are mere ossifications in the tendons of the external oblique muscle of the abdomen, or of the pyramidalis of the same region; and vestiges have been asserted to exist in the Dog. Such bonelets are undoubtedly present in the Dog; but it seems clear from their development in Marsupials, as structures actually continuous with the median unossified portion of the symphysis pubis, that the "marsupial bones" belong to that part of the skeleton, and that they correspond with the epipubis of certain amphibians and reptiles. The pouch, it may be remarked, exists in a rudimentary form in the males of many Marsupials. [Illustration] FIG. 60.--Ventral surface of innominate bone of Kangaroo (_Macropus major_). x 1/3. _a_, Acetabulum; _ab_, acetabular border of ilium; _is_, iliac surface; _m_, "marsupial" bone; _pb_, pubic border; _pt_, pectineal tubercle; _s_, symphysis; _si_, supra-iliac border; _ss_, sacral surface; _thf_, thyroid foramen; _ti_, tuberosity of ischium. (From Flower's _Osteology_.) [Illustration] FIG. 61.--Mammary foetus of Kangaroo attached to the teat. (Nat. size.) (From Parker and Haswell's _Zoology_.)