200 



the Wombat and Koala. The entocarotids entering the suture between the basi- and 

 alisphenoids, usually pierce the basisjiheuoid and enter the cranial cavity close together, 

 behind the sella, this pituitary fossa being obvious though not bounded by a posterior 

 clinoid late. The petrosal in the Thylacine, Kangaroo, Koala, and Phalanger is im- 

 pressed above the meatus auditorius internus by a deep, smooth, round pit, which 

 lodges the lateral appendage of the cerebellum. The corresponding pit is shallower in 

 the Dasyures, and scarcely marked in the Wombats. 



In the Kangaroos and Phalangers a thin ridge of bone extends for the distance of one 

 or two lines into the periphery of the tentorial process of the dura mater ; and two sharp 

 spines are sent down into it from the upper part of the cranium in Phalangista vulpina. 

 The tentorium is supported by a ridge of bone in the Thylacine ; but it is not completely 

 ossified in any of the Marsupialia. The rhinenccphalic is separated by an obtuse ridge 

 from the prosencephalic division of the cranial cavity. Both primary divisions, with 

 the epencephalic one for the cerebellum and medulla oblongata, succeed one another 

 longitudinally in the Lyencephala as in the Lissencephala ; this character would not 

 distinguish an Australian murine species from a marsupial one. 



The olfactory chamber is the largest in the skull, and is divided by a prefrontal bony 

 septum, continued in some to near the anterior aperture. A longitudinal ridge projects 

 downward from the inside of each of the nasal bones, and is continued posteriorly into 

 the a?thmoturbinals, which extend into the part of the olfactory chamber outside of and 

 partly surrounding the rhinencephalic one. The convolutions of the mid turbinals are 

 extended chiefly in the axis of the skull ; the processes of the subturbinals are arranged 

 obliquely from below, upward and forward. They are extremely delicate and numerous 

 in the Dasyures and Phalangers, but become more simple in the Kangaroo, Koala, and 

 Wombat. The chamber communicates freely with large frontal and maxillary sinuses, 

 and finally terminates by wide apertures behind the bony palate. 



The angle of the jaw is bent inward in the form of a process, encroaching in various 

 shapes and various degrees of development in the different marsupial genera upon the 

 interspace of the rami of the lower jaw. In looking down upon the lower margin 

 of the jaw, we see, therefore, in place of the margin of a vertical plate of bone as in 

 most Placentalia, a more or less flattened surface extended between the external ridge 

 and the internal process or inflected angle. In the Opossums this internal angular 

 process is triangular and trihedral, with the point slightly curved upward. In the 

 Dasyures it has a similar form, but the apex is extended into an obtuse process. In 

 the Thylacine the base of the inflected angle is proportionally more extended. In the 

 Bandicoots the angle of the jaw forms a still longer process ; it is of a flattened form, 

 extended obliquely inward and backward, and slightly curved upward. In the Potoroos 

 and Phalangers the process is broad, with the apex slightly developed, bounds the lower 

 part of a wide and deep depression on the inside of the ascending ramus. In the 

 Kangaroos the internal margin of this process is curved upwards, so as to augment the 

 depth of the internal depression above mentioned. The internal angular process arrives 



