another twenty-three. In two species of Po- 
_ toroo there are twenty-four caudal vertebra, 
but the relative length of the tail differs in 
_ these by one-third, in consequence of the 
_ different length of the bodies of the vertebrae. 
In Hypsiprymnus ursinus there are more than 
_ twenty-six caudal vertebre. In the great Kan- 
roo there are twenty-two caudal vertebre. 
n Bennett’s Kangaroo there are twenty-four 
_ caudal vertebra, which are remarkable for their 
size and strength. In the Phalangista vulpina, 
there are twenty-one caudal vertebre. In the 
Petaurus macrurus 1 find twenty-eight caudal 
_ vertebra, while in the Pet. sciureus there are but 
_ twenty ; the bodies of the middle caudal vertebra 
_ in both these species are remarkably long and 
_ slender. The Myrmecobius has twenty-three 
caudal vertebre. In the Dasyurus Maugei I 
' find twenty caudal vertebre ; in Didelphis can- 
_ erivora there are thirty-one; in the Virginian 
Opossum there are twenty-two caudal vertebre. 
In the latter species the spinal canal is con- 
‘tinued along the first six; beyond these the 
_ Superiorspinous 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 ofthe vertebre. The 
transverse processes are single on the first five 
caudal vertebre, and are nearly the breadth of 
the body, but diminish in length from the 
second caudal, in which vertebre they are gene- 
rally the longest. In the other vertebre a short 
| obtuse process is developed at both extremities 
of the body on either side, so that the dilated 
"articular surfaces of the posterior caudal ver- 
tebre present a quadrate figure. 
In most of the Marsupials which have a long 
tail, this appendage is subject to pressure on 
some part of the under surface. In the Kanga- 
roo (fig. 103,) this must obviously take place 
_ toa considerable degree when the tail is used 
as a fifth extremity, to aid in supporting or pro- 
pelling the body. In the Potoroos and Bandi- 
' €oots 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 in 
locomotion as in the Kangaroos. In the 
-Phalangers and Opossums the tail is pre- 
hensile, and the vessels situated at the 
under surface are liable to compression 
when the animal hangs suspended by the 
tail. To protect these vessels, therefore, as 
well as to afford additional attachment to 
‘the muscles which execute the various 
| movements for which the tail is adapted in 
_ the above mentioned Marsupials, V-shaped 
bones, or inferior arches (hzemapophyses) 
_ are developed, of various forms and sizes, 
and are placed opposite the articulations 
' of the vertebrae, a situation which is analo- 
—, 
Fig. 103. 
bn igs ae alii > 
MARSUPIALIA. | 
279 
gous to that of the superior arches in the 
sacral region of the spine in Birds, and in 
the dorsal region of the spine in the Chelonian 
Reptiles. The two crura of the sub-vertebral 
arch embrace and defend the bloodvessels, and 
the spinous process continued from their point 
of union presents a variety of forms in different 
genera. 
: In Cook’s Phalanger I find the 
Fig. 104. hemapophyses commence between 
oun the second and third caudal ver- 
tebre, increase in length to the 
fourth, and then progressively 
diminish to the end of the tail; 
the penultimate and anteepnulti- 
mate presenting a permanent sepa- 
ration of the lateral moieties, and 
an absence of the spine (fig. 104.) 
In the Virginian Opossum and 
Vulpine Phalanger they are sim- 
ple, about a quarter of an inch in 
length where longest, and directed 
obliquely forwards, and diminish 
in size as they approach the extre- 
mity of the tail. In the Potoroos 
the extremity of the long anterior 
spines is dilated and produced 
both backwards and forwards; the 
posterior smaller ones become ex- 
panded laterally, and give off 
similar but shorter processes from 
each side, whereby the base of 
support is extended. In the Great 
Kangaroo the spine of the first 
subvertebral arch only is simple 
and elongated, the extremities of 
the others are expanded, and in 
some jut out into four obtuse pro- 
cesses, two at the sides, and two 
at the anterior and posterior sur- 
Terminal cau. *°°S- In a_ carefully prepared 
dal vertebra, Skeleton. of Macropus Bennettii 
in the Museum of the Zoological 
Society, I found these inferior spines want- 
