684 Mii. F. G. PAitsoNS ON Ti£E [June 10, 



The Osseous System. 



Owen, in his ' Comparative Anatomy of Vertebrates,' has given 

 an excellent account of the Kangaroo's bones, and I only intend to 

 draw attention to certain points which seem to me of special 

 interest. In the first place, the chief characteristics in which the 

 skull of Petrogale differs from that of Macropits are : — 



(1) In Macropus the nasal bones have an eijual breadth in their 

 anterior two-thirds, the posterior third being only slightly broader. 



In Petrogale the nasals are much more slender in comparison and 

 their posterior half is considerably broader than the anterior. 



(2) In Macropus the fronto-nasal sutin-e comes farther back 

 than the most posterior point of the fronto- maxillary in most 

 cases. In Petrogale the condition is reversed. 



(3) In Macropus the zygomatic process of the maxilla projects 

 downwards below tlie cutting-edge of the penidtimate molar. In 

 Petrogale it is seldom much lower than the alveolar margin of the 

 maxilla. I am not inclined to lay much stress on this distinction, 

 since it seems that the processes of the Kangaroo's skull increase 

 with age. 



(4) In my specimen of Petrogale the infra-orbital canal was double 

 on both sides, a condition I have found in two out of five skulls. 



In Macropus the canal is occasionally double on one side, but I 

 have not found it so on both sides once in the thirteen skulls 

 I have had the opportunity of examining. 



(5) In my specimen of Petrogale a Wormian bone {os antiepi- 

 lepiticurii) was present at the junction of the coronal and sagittal 

 sutures (see fig. 1, p. 685). This bone has been described by 

 Gruber and Howes, and I am inclined to regard it as of some little 

 classificatory value '. It occurred twice in the five skulls examined, 

 and I have never seen it in any other Kangaroo. 



(()) In Petrogale the i)ulaiinu process of the palato-bone is only 

 represented by a narrow bridge marldng the posterior boundary of 

 the hard palate. In Macropus the palatine process is complete 

 and the back of the hard palate has no perforation of any size. 



(7) The premaxilla of Petrogale is a larger bone in comparison 

 with that of Macropus, and has not the sharp angle running back 

 between the maxilla and nasal found in the latter. 



(8) The inter-parietal bone of Petrogale has a very different 

 appearance to that of Macropus ; in the latter it is a more or less 

 crescentic bone having a much greater breadth from side to side 

 than from before backward, while in the former its antero-posterior 

 measurement equals its greatest transverse, so that the bone forms 

 either an isosceles triangle or a rough pentagon. 



(9) The paroeeipital processes are better de^'eloped in Macroptus 

 than in Petrogale. 



As special stress is laid on the condition of the centres of 

 ossification of the various bones, it will assist in determining the 

 animal's age if the state of the teeth is noticed here. The antei-ior 



' See the authoi-'s paper on Athcrura africana, V. Z. S. 18U4, p. 677. 



