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rameles ; in a greater degree in the Kangaroos and Potoroos ; and 

 gives off a distinct and strong obtuse process in the Wombat, 

 which not only extends outwards but is curved forwards. In the 

 Potoroos the symphysis of the ischia or the lower part of what is 

 commonly called the symphysis pubis, is produced anteriorly. The 

 length of this symphysis, and the straight line formed by the lower 

 margin of the ischia, is a characteristic structure of the pelvis in most 

 of the Marsupiata. 



" The marsupial bones are elongated, flattened, and more or less 

 curved, expanded at the proximal extremity, which sometimes, as in 

 the Wombat, is articulated to the ptibis by two points ; they are rela- 

 tively longest, straightest, and most slender in the Perameles; flattest, 

 broadest, and most curved in the Koala. They are always so long 

 that the cremaster muscle winds round them in its passage to the 

 " testicle or mammary gland ; and the uses of these bones immediately 

 relate to those muscles. 



" With reference to the interesting question — What is the homo- 

 logy or essential nature of the ossa marsupialia ? I have, on a pre- 

 vious occasion, discussed that problem before the Zoological Society, 

 and have not found reason to change the opinion I offered in 1835 * ; 

 viz. that they belong to the category of the trochlear ossicles, com- 

 monly called, sesamoid, and are developed in the tendon of the exter- 

 nal oblique which forms the mesial pillar of the abdominal ring, as the 

 jiatella is developed in the rectus femoris. They are not, however, 

 merely subservient to add force to the action of the ' cremasteres,' 

 but give origin to a great proportion of the so-called ' pyramidales.' 



" The osteogenesis of the marsupial pelvis derives some extrinsic 

 interest from the not yet forgotten speculations which have been 

 broached regarding the analogies of the marsupial bones. ITiese 

 have been conjectured to exist in many of the placental Mammalia, 

 with a certain latitude of altered place and form, disguised, e. g. as the 

 bone of the penis in the Carnivora, or appearing as the supplemental os- 

 sicles of the acetabulum, which exist in the young of many of the Ro- 

 dentia. In the os innominatum of the immature Potoroo, the curved 

 prismatic ilium contributes to form by the outer part of its base the 

 upper or anterior third of the acetabulum ; the rest of the circumfe- 

 rence of this cavity is completed by the ischium and pubis, excepting a 

 small part of the under or mesial margin, which is formed by a distinct 

 ossicle or epiphysis of the ilium, analogous to that described by 

 Geoffroy St. Hilaire as the rudimental marsupial bone in the rabbit. 

 Now here there is a co-existing marsupial bone : but besides the five 

 separate bones just mentioned, there is a- sixth distinct triangular os- 

 sicle, which is wedged into the posterior interspace of the ischio-pubic 



* See the abstract of a Paper on the analogy of the Danyurus, Proc. Zool. 

 Soc, January 1835, in which the discussion of the question of the marsupial 

 bone is abridged in the following words : " and Mr. Owen stated it to be his 

 opinion, that the marsupial bones are essentially ossifications of the tendons 

 of the external abdominal muscle which constitute the internal or mesial 

 pillars of the abdominal rings." The same hypothesis is again advanced in 

 the account of the anatomy of the Wombat. Pro. Zool. Soc. 18oG, p. 19. 



