35G 



Genus Piiascolomys. 

 Osteology of the existing Species. 



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. Contributions thereto, in reference to the skull of Piiascolomys, have been 

 made in a preceding section (p. 305) ; the remainder of the skeleton is the subject of 

 the present one, 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-defined aim. 



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

 Piiascolomys are defined in pp. 297-299. The annular atlas was first recognized, in 

 a specimen of Piiascolomys vombatus in the Museum of the Iloyal 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" 1 . 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" 2 . 



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

 peated in that of a not fully grown specimen of Piiascolomys platyrhinus (PI. XCVIII. 

 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, 

 pi, in fig. 3). 



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

 lomys latifrons (PI. XCVIII. figs. 1 & 2, pi), The first cervical nerve, in both species, 

 perforates obliquely the neurapophysis (at c \, figs. 1 & 3), the aperture within the 

 neural canal being above the articular concavity (z 1 , z') for the occipital condyle. 



The transverse diameter of the atlas is less in proportion to its vertical one in Piiasco- 

 lomys latifrons (ib. figs. 1 & 2) than in Piiascolomys platyrhinus (ib. figs. 3 & 4) ; the 

 cups for the condyles (fig. 1, z', z') are less turned outward, and the diapophyses (ib. d, d) 

 are more tuberous in Piiascolomys latifrons;, in Piiascolomys platyrhinus (figs. 3 & 4, d, d) 

 they are flattened below as well as above. The articular surfaces for the odontoid are 

 more oblong and more nearly transverse in Piiascolomys latifrons (fig. 2, z*,z ] ), and their 



1 " On the Osteology of the Marsupialia " (Part I. 1838), Trans. Zool. Soc. vol. ii. p. 394. I have since seen 

 the atlas of an old male Macropus rufus, incomplete below. * Tom. cit. p. 394. 



