138 



length where longest, directed obliąuely forM'ards, and diminish in 

 size as they approach the extremity of the tail. In Cook's Phalan- 

 ger I find the hcemapophyses commence between the second and third 

 caiidal vertebrse, increase in length to the fourth, and then pro- 

 gressively diminish to the end of the tail : the penultimate and an- 

 tepenultimate presenting a permanent separation of the lateral moie- 

 ties, and an absence of the spine. 



" In the Potoroos the extremity of the long anterior spines is di- 

 lated, and produced backwards and forvvards ; the posterior smaUer 

 ones becorae expanded laterally, and give oiF similar but shorter pro- 

 cesses from each side, \vhereby the base of the 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 ex- 

 panded, and in sorae jut out into four obtuse processes, two at the 

 sides and two at the interior and posterior surfaces. In a carefully 

 prepared skeleton of Macropus Bcnettii, I found these inferior spines 

 wanting between the lašt nine vertebrse of the tail. In the Petau- 

 rists, Phascogales, and Dasyures, \vhere the tail acts as a balancing 

 pole, or serves, from the long and thick hair \vith which it is 

 clothed, as a portable blanket to keep the nose and extremities 

 warm during ?leep, the subvertebral arclies are also present, but 

 less in number, and of smaUer relative size. They are here princi- 

 pally subservient to the attachment of museles, — their mere mecha- 

 nical office of defending the caudal vessels from pressure not being 

 required. 



"The ribs consist of thirteen pairs, exceptingin the Wombat and 

 Petaurists : the first of these is the shortest, and, except in some of 

 the Petaurists, the broadest. In the Pet. macrurus, the fifth, sixth, 

 or seventh are the broadest, and the ribs generally have, both in this 

 species and in Pet. sciureus, a more compressed form than in the 

 other Marsupials ; but this charactcr does not exist in Petaurus 

 Taguanoides. In the Great Kangaroo they are very slender and 

 rounded, except at the sternal extremities, which are flattened for 

 the attachment of the cartilages. In this species the anterior pairs of 

 ribs articulate directly with the sternum. The cartilages of the other 

 pairs are long and bent towards the sternum, but do not join it ; nor 

 are they confiuent, but have a gliding motion one over the other. 

 In the Opossum there are seven pairs of true ribs, and six which 

 may be regarded as costa nothce. In the Wombat six pairs only out 

 of the iifteen reach the sternum. 



" The sternum consists of a succession of elongated bones, gene- 

 rally six in number, but in the Wombat four. The first bone, or 

 manubriiim sterni, is the largest, and presents in many species a tri- 

 an^^ular shape, from the expansion of its anterior part, and some- 

 times a rhomboidal figure. A strong keel or longitudinal process 

 is given off in many species ft'om the middle of its inferior or outer 

 surface ; the side next the cavity of the chest is smooth and slightly 

 concave. In the Wombat, Phalangers, and others, the keel is pro- 

 duced anteriorly into a strong process, against the sides of -vvhich 

 the clavicles abut : the first pair of ribs joiu the produced anterior 



