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plete in iiU but the lašt three, \vhich consist ouly of the body. 

 There are no inferior spines ; and aiš only the six posterior vertebrčie, 

 which progres&ively diminish inlength, extend beyond the posterior 

 uperture of the pelvis, the tail is scarcely visible in the living animal. 

 In the Koala the tail is also very short. Inone species of Perameles 

 I tind eighteen caudal vertebrse, in another twenty-three. 



" In t\vo species of Potoroo there are twenty-four caudal verte- 

 bra;, but the relative length of the tail differs iu these by one-third, 

 in consequeuce of the greater length of the bodies of the vertebrse. In 

 the GreatKangaroD there aret\venty-two, while inBennett'sKangaroo 

 there are twenty-four caudal vertebrse. In the Phalangista vulpina 

 there are t\veuty-one caudal vertebrse. In the Pe taurus macrurus I 

 find twenty-eight caudal vertebra?, while in the Ptt. sciureus there 

 are but twenty. The bodies of the middle caudal vertebrse, in both 

 these species, are remarkably long and slender. In the Dasyurus 

 Maugei I find twenty caudal vertebrse. 



" In the Virginian Opossum there are t\venty-t\vo caudal vertebrse ; 

 the spinal canal is continued along the first six, beyond these the 

 superior spinous processes cease to be developed, aud the body gives 

 ofF above only the tvvo anterior and two posterior oblique processes, 

 \vhich are mdimental, and no longer subsen'ient to the mutual arti- 

 culation of the vertebrce. The transverse processes are single on 

 the first five caudal vertebrse, and are nearly the breadth of the body, 

 but diminish in length from the secoud caudal, in \vhicli thej"^ are 

 generally the longest. I u the other vertebrse a short obtuse trans- 

 verse process is developed at both extremities of the body on either 

 side, so that the dilated articular surfaces of the posterior caudal 

 vertebrse present a quadrate figure. 



" Iu most of the RIarsupials, which have a long tail, this appendage 

 is subject to pressure on some jjart of the under surface. I n the 

 Kangaroo this mušt obviously take place to a considerable degree 

 ■vv'hen the tail is used as a fifth extremity to aid in supporting or pro- 

 pelliug the body. In the Potoroos and Perameles the tail also 

 transmits to the ground part of the superincumbent pressure of the 

 body by its under surface, when the animal is erect ; but it is not 

 used as a crutch i n locomotion, as in the Kangaroos. In the Pha- 

 langers and Opossums the tail is prehensile, and the vessels situated 

 at the under surface are liable to compression A\hen the animal 

 hangs suspended by the tail. To protect these vessels, therefore, 

 as well as to afFord additional attachment to the museles ■svhich execute 

 the various movements for \vhich the tail is adaptcd in the above-men- 

 tioned Marsupiata, ^'-shaped bones, cr inferior arches Ųtd-mapojjhy- 

 ses) are developed, of vaiious fonns aud sizes, and are placed oj)posite 

 the articulations of the vertebrse, analogous to the situation of the 

 superior arches in the sacral regionof the spine in Birds, and in the 

 dorsal region of the spine in the Chelonian Reptiles. 'llie two crura 

 of the subvertebral arch embrace and defend the blood vessels ; aud 

 the 2)rocess continued from their point of uniou ])resents a variety 

 of forms in different genera. In the \'^irginian OĮ)ossum and \'ul- 

 piue Phalanger they are simplc. about a quarter of an iuch ia 



