143 



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

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

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

 Potoroos the symphysis of the ischia or the lower part of \vhat is 

 commonly called the symphysis pubis, is produced anteriorly. The 

 length of this symphysis, and the straight line formed by the lo\ver 

 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 pubis by two points ; they are rela- 

 tivelylongest, straightest, and most slender in the Perameles; flattest, 

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

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

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

 relate to those museles. 



" With reference to the interesting ąuestion — "VVhat 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 * ; 

 vi2. 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 

 ])atella is developed in the rectiis femoris. They are not, hovvever, 

 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 \vhich have been 

 broached regarding the analogies of the marsupial bones. These 

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

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

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

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

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

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

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

 rence of this cavity is completed by the ischium and pubis, exceptino- 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 rudimentai marsupial bone in the rabbit. 

 Now here there is a co-existing marsupial bone : butbesides thefive 

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

 sicle, which is w'edged into the posterior interspace of the ischio-pubic 



* See the abstract of a Paper on the ar.alogy of the Dasyurus, Proc. Zool. 

 Soc, January 1835, in wbich the discussion of tlic ąuestion of the marsupial 

 bone is abridged in the follo\ving \vords : " and Mr. 0\vcn stated it to be his 

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

 of the external abdominal musele \vhich constitutc tlie internai or mesial 

 pillars of the abdominal rings." The šame hypotbesis is again advanccd in 

 the aceount of the anatoniy of the Wombat. Pro. Zool. Soc. 183G, p. -19. 



