804 DR. J. MURIE ON PHASCOLOMYS PLATYRHINUS. [JuUC 27, 



Cervical Vertebr<x. — It has been remarked by Prof. Owen* that in 

 the Koala and Wombat the body of the atlas remains permanently 

 cartilaginous. This observation appears not to be exceptional in the 

 case of Phascolotmjs platyrhinus and P. latifrons, where the bony 

 rino- is incomplete in both. In the specimens examined by me of 

 P. platyrhinus the bony separation was as much as 0'4 of an inch, 

 and in P. latifrons, as in P. ivombat, about 0-3". 



The first cervical vertebra in P. platyrliinus, besides slightly larger 

 dimensions, has a sensibly higher arched lamina than either P. 

 wombat or P. latifrons, and there is the rudiment of a neural 

 spine. The breadth from before backwards of the neural arch is 

 usually greatest in P. latifrons ; but this is not constant. The 

 transverse processes seem also relatively longer and broader in P. 

 platyrhinus, although this may only appear to be so from the gene- 

 rally increased size of the vertebrae. They, however, are flatter in 

 P. latifrons, in this respect approaching to the shape found in the 

 Koala. 



The greatest diameter to the tips of the transverse processes in the 

 specimens compared respectively measured 2""6 in P. j^^ofyrhinus 

 and 2"*2 in P. wombat and P. latifrons. 



The antero-posterior diameter of the body of the axis in P. lati- 

 frons is comparatively greater than in either P. platyrhinus or P. 

 wonbat. 



In P. platyrhinus, however, the perforated transverse processes 

 extend considerably beyond the body, whereas they are short in P. 

 wombat and P. latifrons, where they barely reach outside the ante- 

 rior articulating surfaces. 



The peculiar feature of the neural spine of the axis in P. latifrons 

 is its possessing only in a slight degree the anterior projection, which 

 is strongly marked in P. platyrhinus, and even relatively more so 

 in P. wombat. The superior border from this to the summit of the 

 spine is also very perpendicularly inclined in its arch in P. latifrons ; 

 and both behind and before the neural spine and laminae there are not 

 such deep concavities as in the two other species. In this manner 

 the neuial spine has a sharper and half-crescentic form, distinguish- 

 ing it from the other species. 



The two specimens of P. platyrhinus examined varied, inasmuch 

 as one had a spine of the shape attributed to P. latifrons ; the other 

 reverted to what is found in P. wombat — namely, where the spine is 

 derived from broad laminae whose anterior and posterior edges are 

 deeply concave. 



In the succeeding cervical vertebrae P. wombat has the neural spine 

 of the fourth slightly longer than those of the third, fifth, sixth, and 

 seventh, which last are all about equal in length. In P. platyrhinus 

 the third cervical has only the rudiment of a spine, which is bifid 

 and corresponds to a tubercle on the posterior arched concavity of 

 the neural spine of the axis. The four cervical vertebrae posterior to 

 the third have their spines nearly alike in length ; the seventh, how- 

 ever, is perceptibly the longest. In P. latifrons the seventh neural 

 spine is by far the longest (with the exception of that of the axis) ; 



* Op. cit. p. 394. 



