OF DIDELPIIYS VIRGIXIAXA. 67 



cliiefly 1)}' ilie malar, on viewing it from llio ontsido ; bnt the squamous overlapping of the 

 maxillary invades the inner surface of this wall ; the maxillary has greater share in the pro- 

 duction of the anterior, elongated, conical portion of the orbital cavity not occupied by the 

 eyeball. This conical portion is the entranco to the canal whose external a[)orture is the 

 maxillary foramen ; and transmits the superior maxillary division of the trigeminus. The 

 foramen of exit of the nerves that go to the eye are all situated behind the orbital cavity 

 proper; the ductus lachrymalis itself is also outside of the orbit. The palatal foramen, how- 

 ever, is fairly within the orbit ; it is circular, and of large size. 



The glenoid fossa has the peculiar structure tJiat is characteristic of many marsupials, 

 beino" formed at the meeting of three bones — alisphenoid, squamosal, and malar. By far the 

 greater part of it, however, is squamosal. The end of the malar is just nicked to complete 

 the cavity antero-externally ; a long, slender, horizontal, transverse process of the alisphe- 

 noid just touches the malar, and so forms the antero-internal border. The shape of the fossa 

 indicates the nature of the articulation, which is strictly ginglymoid ; there is no convexity 

 of surface in the glenoid, nor such contour as to provide, however imperfectly, for lateral 

 motion of the jaw. The fossa is directly transverse, wider than long, plane from side to 

 side, and very concave antero-posteriorly. The concavity is produced mainly by the wide 

 descending process of the squamosal, which affords an abutment for the mandible, prevent- 

 in ir retraction. Anteriorly, there is only a trace of such a wall. 



The bony palate is of great extent, reaching more than halfway from the incisors to the 

 foramen magnum. It is carried backward beyond the last molars by the palatal process of 

 the palatines, terminating with a thick, directly transverse margin, developing on cither 

 side a stout conical process, whence the sides slope obliquely forward and outward to the 

 last molars. The palate is concave in all directions — most so from side to side, in con- 

 sequence of the well-developed alveolar processes. It is longitudinally divided into 

 halves by a straight line, denoting the apposition of each palatal, maxillary and pre- 

 maxillary with its fellow of the opposite side ; this line is never obliterated by confluence 

 of these pairs of bones. There are ten palatal openings, symmetrically placed in pairs. 

 The incisive foramina are tw^o narrowdy linear apertures, side by side, close to the median 

 line, distinguishing the palatal processes of the premaxillaries from their alveolar portions. 

 The perforations are closed behind by the maxillaries, which, however, take part in their 

 formation by being nicked for about an eighth of an inch. The maxillary apertures, sit- 

 uated opposite the three last molars, are of large size (.G6-.75 of an inch, or more, in 

 length), and narrowly elliptical, or even linear, though their contour is frequently somewhat 

 irregular. The class of osseous perforations to which the present foramina belong is obnox- 

 ious to irregularities of size and shape, and consequently can only be defined in loose terms. 

 Most of the perforation occurs in the maxillaries ; the palatals bound the posterior third or 

 even half Immediately behind these openings there are two smaller (but still large) per- 

 forations in the palatal processes of the palatines, placed close together, and generally pre- 

 senting a four-sided contour. Externally, and a little behind the latter, the same processes 

 of bone are again perforated, this time by oval foramina, situated close by the external bor- 

 der. Finally, there is a minute, circular foramen upon either side, just within the trans- 

 verse, posterior termination of the palate. Notwithstanding these numerous fissures in the 

 osseous roof of the mouth, the palate is much more perfect than that of some other marsu- 



