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XV. On the Osteology of the Marsupialia. (Part IV.) Bones of the Trunk and Limbs, 

 Phascolomys. By Professor Owen, C.B., F.B.S., F.Z.S. 



Read 3rd December, 1872. 



[Plates LXIX. to LXXIV.] 



The endeavour to restore the lost species of Wombat presumes a power of recognizing 

 the bones or portions of bones when discovered in a fossil state '; and this can only be 

 acquired by a knowledge of the characters of the corresponding bones of the existing 

 species. 



Such knowledge has been imparted, in reference to the skull of Phascolomys, in my 

 former Papers ; I propose to make the remainder of the skeleton the subject of the 

 present ' Part,' in which the descriptions and figures are limited to those bones of the 

 trunk and limbs yielding satisfactorily distinctive and determinative characters subser- 

 vient to the above-deiined aim. 



Vertebral Column. — The general characters of the vertebral column in the genus 

 Phascolomys are defined in my first memoir'. The annular atlas is there shown, from 

 a specimen (of Phascolomys vombatus) in the Museum of the Eoyal College of Surgeons 

 of England, to have the lower part of its ring " completed by dried gristly substance," 

 not, as in some kinds of Kangaroo, by " extension of ossification from centres in the 

 superior laminae "^ The term ' neurapophysis ' had not then been proposed for these 

 vertebral elements, nor had I, in 1838, satisfied myself that the 'centrum' of the atlas 

 was the ' odontoid process ' of the succeeding vertebra. It is further remarked that 

 " the transverse processes are grooved merely by the vertebral arteries," and that " the 

 atlas presents only the perforation on each side of the superior [now called ' neural '] 

 arch'". 



These general characters of the atlas of the bare-nosed Wombat of Tasmania are 

 repeated in that of a not fully grown specimen oi Phascolomys platyrhinus (PI. LXIX. 

 figs. "3 & 4) ; but in the atlas of an older and larger specimen of that species ossification 

 has extended into the sclerous representative of the pleurapophysis, and has converted 

 the vertebrarterial notch into a foramen on both sides (as indicated by the dotted line, 

 pl,m fig. 3, PI. LXIX.). 



The same bony circumscription obtained on the right side in the atlas of a Phasco- 

 lomys latifrons (PI. LXIX. figs. 1 & 2, ^ /), The first cei-vical nerve, in both species, 



' " On the Osteology of the MarsupiaKa " (Part I. 1838), Trans. Zool. Soc. vol. ii. p. 379 et seq. 

 ' lb. ib. p. 394. I have since seen the atlas of an old male Macropus nifus, incomplete below. 

 ' Tom. cit. p. 394. 



