346 



axato:my of verteeeates. 



maxillarv bones, and encroaches a little upon the palatines. In 

 Mange's Dasyure there are two large ovate apertures crossing 



the palato-maxillarv sutures se- 

 parated from each other by a 

 broad plate of bone : posterior to 

 these are two apertures of sunilar 

 size and form, which, being situ- 

 ated nearer the mesial line, are 

 divided bv a narrower osseous 

 bridge ; each posterior external 

 angle of the bony palate is also 

 perforated by an oval aperture. 

 In the Yiverrine Dasyure the 

 two vacancies which cross the 

 ])alato-maxillary suture are in the 

 form of longitudinal fissures, cor- 

 responding to the fourth and fifth 

 grinders : the posterior margin of 

 the bony palate has four small 

 apertiu'es on the same transverse 

 line. 



Since the defective condition 

 of this ])art of the cranium is one 

 of the characteristics of the skull 

 of the Bird, it might be ex- 

 pected that some approximation 

 would be made to that structure 

 in the animals which form the 

 transition between the Placental 

 and Oviparous Vertebrates. We 

 have already noticed the large vacuities which occur in the bony 

 palate of nearly all the Marsupials : but this imperfectly ossified 

 condition is most remarkable in the Perameles lagotis, in which, 

 fig. 222, the bony roof of the mouth is perforated by a wide oval 

 space extending from the second premolars to the penultimate 

 molars, exposing to view the vomer and the convolutions of the 

 inferior spongy bones in the nasal cavity. The pterygoids, fig. 

 220, 24, long maintain their individuality ; and repeat the connec- 

 tions they present in Birds. 



The parietes of the cranial cavity are remarkable for their 

 thickness in some of the ^larsupial genera. In the Wombat the 

 two tables of the parietal bones are separated posteriorly for the 

 extent of more than half an inch, the interspace being filled with 



Perameles lagotis. 



