686 MK. F. G. PAESONS ON THE [Junel6, 



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 

 disc, and it is interesting to notice that, if the two parts of the 

 bone bad been separated here, the anterior would have corresponded 

 very closely to the odontoid bone of Ornithorhynclms. In the older 

 specimen of Petrogale with which I compared vaj 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 vertebi-al formula :— C. 7, T. 13, L. 6, S. 2, 

 C. 24. 



The spines of the cervical vertebrte are short, and the neck is 

 kept in an extended position by the very strong ligamentasubflava. 

 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 7tb C. to the long 1st T. There are 

 thirteen ribs, all of which excejjt the first articulate with two 

 vertebral centra, and all of which are supported by a 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 common hgament, 

 and is more closely attached to the jjosterior 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 ia 

 median and has no separate centre of ossification. 



The lumbar transverse or costal processes have a sharp curve 



