308 



diastema] tract is more sharply defined, laterally, in the hairy-nosed Wombat. The 

 antorbital vacuity is wider, less slit-shaped, in Ph. latij'rous than in Ph. jiliihjrliiiiiis 

 (PI. XLVI. fig. 1, 121 ) and Ph. vombatus. 



The cerebral cavity in Ph. latifrons (PI. XL1X. fig. 5) is, in length, 3 inches lines, and 

 equals one half the length of the cranium, which is (i inches 9 lines in the specimen figured, 

 the cavity is divided by two vertical ridges into the epencephalic (ep), prosencephala 

 (/;/ ), and rhinencephalic (rh) compartments. These succeed each other lengthwise; but 

 the character is common to the two lower subclasses of Mammalia, in which the 

 cerebrum docs not overlap the cerebellum behind or the rhinencephalon in front. The 

 petrosal (i<i) contributes a vertical surface to the side of the epencephalic compartment, 

 which is overarched by the superoccipital and parietal. The acoustic foramen or fossa 

 is subcircular, and is situated below the horizontal ridge bisecting the cranial surface of 

 the petrosal. The cerebellar pit above the ridge is wider and more shallow than in 

 Thylacinus and most other Marsupials. The ' vagal ' foramen (v) is between the 

 petrosal and the exoccipital. Behind this are the two or three inner orifices of the 

 precondyloid canals ( p). The foramen ovale (ov), 3^ lines in long diameter, perforates 

 the alisphenoid below the tentorial ridge, and opens outwardly anterior to the exca- 

 vation forming the fore part of the tympanic cavity. A groove runs forward from the 

 foramen ovale to the foramen rotundum about 8 lines in advance : at the inner side of 

 this groove the basisphenoid is perforated by the entocarotid. From the inner orifice 

 of this canal a groove runs forward to the common prelacerate and optic fissure (op). 

 The rhinencephalic fossa (rh) is 7 lines in vertical diameter, 5 lines in longitudinal 

 extent. It has a large perforation at its lower and back part leading to the common 

 orbitotemporal fossa ; the floor and fore part of the fossa are perforated by the smaller 

 foramina transmitting the olfactory nerves to the aethmo-turbinals. The nasal or 

 olfactory chamber is divided by the coalesced prefrontals which combine with the 

 vomer to form a vertical septum extending from the rhinencephalic cavity to 8 lines 

 behind the tips of the nasals. The anterior border of the septum is vertical, 1 inch in 

 depth. In Ph platyrhinus the bony septum terminates 14 lines behind the tips of the 

 nasals. The alisphenoid tentorial ridge is less developed in that species. The sethmo- 

 turbinals (e) form a mass about an inch in antero-posterior and less in vertical diameter. 

 The mid turbinal is elongate, developed from a ridge descending from the roof of the 

 nasal cavity, a short distance external to the septum, and defining a longitudinal canal 

 traversing the upper part of the nasal meatus. The preturbinal rises from the side of 

 the floor of the chamber. The septum is continued backward by vertical plates of the 

 palatines to the posterior or internal openings of the respiratory passages of the nasal 

 chamber, at the fore part of the interpterygoid fossa. The frontal is excavated by 

 three sinuses above the rhinencephalic chamber, and forms there the hind part of the 

 olfactory division of the nasal chamber. The roof of the cranium, at the section, has a 

 close cancellous structure 5 lines thick above the prosencephalon, 11 lines thick above 

 the epencephalon. 



