OF THE MARSUPIALIA. 397 
rus three are anchylosed together, although two only join the zlium. In the Wombat 
the transverse processes of the numerous anchylosed vertebre are remarkable for their 
length: those of the first four are directed outwards, and are confluent at their ex- 
tremities ; the remaining ones are turned in a slight degree backwards, and very 
nearly reach the tuberosities of the ischia, behind which they gradually diminish in 
size, and disappear in the three last caudal vertebra. 
The transition from the sacral to the caudal vertebre is very obscure in the Wombat ; 
if we limit the sacral to the three which join the ilium, then there remain twelve 
vertebrae for the tail. The spinal canal is complete in all but the last three, which 
consist only of the body. There are no inferior spines ; and as only the six posterior 
vertebrze, which progressively diminish in length, extend beyond the posterior aperture 
of the pelvis, the tail is scarcely visible in the living animal. In the Koala the tail 
is also very short. In the Cheropus it would seem to be wanting. In one species of 
Perameles I find eighteen caudal vertebrz, in another twenty-three. 
In two species of Potoroo there are twenty-four caudal vertebre, but the relative 
length of the tail differs in these by one-third, in consequence of the different length of 
the bodies of the vertebre. In the Hypsiprymnus ursinus there are more than twenty- 
six caudal vertebree. In the great Kangaroo there are twenty-two caudal vertebre ; in 
Bennett’s Kangaroo there are twenty-four caudal vertebre. In the Phalangista Vulpina 
there are twenty-one caudal vertebre. In the Petawrus macrourus I find twenty-eight 
caudal vertebre ; in Pet. Taguanoides there are twenty-nine, while in the Pet. sciureus 
there are but twenty. In both these species the bodies of the middle caudal vertebre 
are remarkably long and slender. In the Dasywrus Maugei I find twenty caudal ver- 
tebree. 
In the Didelphys cancrivora there are thirty-one, in the Virginian Opossum there are 
twenty-two caudal vertebrz : in the latter species the spinal canal is continued along the 
first six ; beyond these the superior spinous processes cease to be developed, and the 
body gives off above only the two anterior and two posterior oblique processes, which 
are rudimental, and no longer subservient to the mutual articulation of the vertebre. 
The transverse processes are single on the first five caudal vertebrz, and are nearly the 
breadth of the body, but diminish in length from the second caudal, in which they are 
generally the longest. In the other vertebra a short, obtuse, transverse process is de- 
veloped at both extremities of the body, on either side, so that the dilated articular 
surfaces of the posterior caudal vertebre present a quadrate figure. 
In most of the Marsupials which have a long tail this appendage is subject to pres- 
sure on some part of the under surface. In the Kangaroo this must obviously take place 
to a considerable degree when the tail is used as a fifth extremity to aid in supporting 
or propelling 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 acrutch, in locomotion, as in the Kangaroos. In the 
