MARSUPIALIA. 



279 



another twenty-three. In two species of Po- 

 toroo there are twenty-four caudal vertebrae, 

 but the relative length of the tail differs in 

 these by one-third, in consequence of the 

 different length of the bodies of the vertebras. 

 In Hypsiprymnus ursinua there are more than 

 twenty-six caudal vertebra. In the great Kan- 

 garoo there are twenty-two caudal vertebrae. 

 In Bennett's Kangaroo there are twenty-four 

 caudal vertebrae, whicli are remarkable for their 

 size and strength. In the Phetlangista vulpina, 

 there are twenty-one caudal vertebra?. In the 

 Petaurus macruriis I find twenty-eight caudal 

 vertebrae, while in the Pet.sciureus there are but 

 twen ty ; the bodies of the midd le caudal vertebrae 

 in both these species are remarkably long and 

 slender. The Myrmecobius has twenty-three 

 caudal vertebrae. In the Dasyurus Maugei I 

 find twenty caudal vertebrae ; in Didelphis can- 

 crivora there are thirty-one ; in the Virginian 

 Opossum there are twenty-two caudal vertebrae. 

 In the latter species the spinal canal is con- 

 tinued 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 vertebrae. The 

 transverse processes are single on the first five 

 caudal vertebrae, and are nearly the breadth of 

 the body, but diminish in length from the 

 second caudal, in which vertebras they are gene- 

 rally the longest. In the other vertebrae 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- 

 tebrae 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 (Jig. 103,) this must obviously take place 

 to a 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- 

 coots 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 (haemapophyses) 

 are developed, of various forms and sizes, 

 and are placed opposite the articulations 

 of the vertebrae, a situation which is analo- 



Fig. 103. 



104. 



gous to that of the superior arches in the 

 sacral region of the spine in Birds, and in 

 the dorsal region ot 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 Phalauger I find the 

 haemapophyses commence between 

 the second and third caudal ver- 

 tebra, 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 (Jig. 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- f f f ' In , a , carefully prepared 

 dal vertebra, skeleton of Macropus Bennettu 

 in the Museum of the Zoological 

 Society, I found these inferior spines want- 



Macroptu elegans. 



