686 MR, F. G. PARSONS ON THE [June 16, 
dorsal surface of the body of the axis, a line of cartilage was seen 
running transversely across just behind the level of the anterior 
articular facets ; this evidently corresponded to an inter-vertebral 
dise, and it is interesting to notice that, if the two parts of the 
bone had been separated here, the anterior would have corresponded 
very closely to the odontoid bone of Ornithorhynchus. In the older 
specimen of Petrogale with which I compared my own there 
was no indication of this separation, but in the disarticulated 
skeleton of a young Labillardiere’s Wallaby the two parts of the 
axis were quite separate. 
Fig. 2. 
| | 
Axis of Petrogale. 
A, line of union of two parts. 
The following is the vertebral formula :—C. 7, T. 13, L. 6, S. 2, 
C. 24. 
The spines of the cervical vertebre are short, and the neck is 
kept in an extended position by the very strong ligamenta subflava. 
The transverse process of the 6th cervical vertebra has a very 
prominent ventral tubercle, which forms quite an antero-posterior 
ridge. 
The thoracic spines are long, there being quite a sudden 
transition from the short 7th C. to the long Ist T. There are 
thirteen ribs, all of which except the first articulate with two 
vertebral centra, and all of which are supported by « transverse 
process. They are divided into 7 vertebro-sternal, 3 vertebro- 
costal, and 3 vertebral. 
On the ventral side of the body of the 1st lumbar vertebra and 
just to the right of the mid-ventral line there is a single triangular 
bone fastened by its base to the centrum, while its apex projects 
ventrally ; it seems to be developed in the anterior commonligament, 
and is more closely attached to the posterior than to the anterior 
part of the vertebra. From its unilateral position I regard it as 
one of a pair of hypapophyses or intercentra which has worked 
forwards from the ventral side of the disc and which may possibly 
be homologous with the projection from the ventral side of the 
centrum of the 1st lumbar in the Hare, although that process is 
median and has no separate centre of ossification. 
The lumbar transverse or costal processes have a sharp curve 
