The nasal bones vary in their form and rela tive size in the different genera; they are longest and narrowest in the Perameles, shortest and broadest in the Koala. Their most charac teristic structure is the expansion of their upper and posterior extremity, which is well marked in the Wombat, Myrmecobius, Petaurists, Phalangers, Opossums and Dasyures.
In the Potoroos the anterior extremities of the nasal bones converge to a point which pro jects beyond the inter-maxillaries. In some Petaurists and Perameles the corresponding points reach as far as the inter-maxillaries, and in a skull of the Perameles lagotis I have found the bony case of the nasal passages to be further increased by the presence of two small rostral bones, resulting, as in the Hog, from ossification of the nasal cartilage.
The inter-maxillary bones always contain teeth, and the ratio of the development of these bones corresponds with the bulk of the dental apparatus which they support. They are con sequently largest in the NVombat, where they extend far upon the side of the face and are articulated to a considerable proportion of the" nasal bones, but do not, as in the placental. Rodentia, reach the frontal or divide the maxillary bone from the nasal. They pre-, sent a somewhat lower degree of development in the Koala, but both in this species and in the Wombat they bulge outwards and thus remarkably increase the transverse diameter of the osseous cavity of the nose. Neither in Hypsiprymnus nor Macropus do 1 find the incisive palatal foramina entirely in the intermaxillary bones, as is described by the author of the text in Pander and D'Alton's Shekte der Bottelthiere ; a small proportion of their bony circumference is due to the anterior extremity of the palatal process of the maxil lary: the same structure obtains in the Wom bat, Koala, and Opossums. In the Dasyures and Phalangers a greater proportion of the posterior boundary of the incisive or anterior palatal foramina is formed by the maxillaries; in the Petaurists they are entirely surrounded by the maxillary bones, while in the Perameles they are, on the contrary, entirely included in the intermaxillaries. They always present the form of two longitudinal fissures : the Myrme cobius agrees with the other Marsupials in this structure.
The superior maxillary bone in the Wom bat sends upwards a long, narrow, irregular nasal process, which joins the frontal and nasal bones, separating them from the inter maxillaries ; the part of the maxillary bone which projects into the temporal fossa behind the orbit presents two or three smooth tuberosi ties, formed by the thin plate of bone covering the pulps of the large curved posterior grinders.
The corresponding part in the Perameles lagotis is perforated by numerous minute apertures like a cribriform plate, and this structure is presented in a-slighter degree in the Potoroos and Ursine Dasyure. The antorbital foramen does not present any marked variety of size, which is generally moderate. It is much closer to the orbit in the carnivorous Marsu pialia than in the corresponding placental quadrupeds. It is relatively largest in the Ursine Dasyure. It presents the form of a vertical oblique fissure in the Wombat. I have observed it double in the Kangaroo. The chief differences in the maxillary bones, indepen dently of the teeth and their alveoli, are pre sented by the palatal processes, the modifica tions of which we shall consider in conjunction with those presented by the palatal processes of the palatal bones. The perforations and vacuities of the bony palate deserve, indeed, particular attention, as they are often specific and of consequence in the determination both of recent and fossil species.
In Phalangista Cookii, in Petaurus f laviven ter, and Paramus sciureus, in Marropus major, and some other great Kangaroos the bony palate is of great extent and presents a smooth surface, concave in every direction towards the mouth ; it is pierced by the two posterior palatine foramina at the anterior external angles of the palatine bones, either within or close to the transverse palato-maxillary sutures. Behind these foramina, in the Kangaroo, there are a few small irregular perforations. The bony palate is similarly entire in the Hypsiprymnus ursinus. In Maeropus Bennettii there are four orifices at the posterior part of the bony palate. The two anterior ones are situated upon the palato-maxillary suture, and are of an ovate form with the small end forwards. The two posterior foramina are of a less regular form and smaller size. In the Brush Kangaroo ' ( Maeropus Cuv.) the posterior palatal foramina present the form of two large fissures placed obliquely and converging posteriorly.