256 



nerve. It is sometimes a complete loramen, separate from the other ; 

 sometimes only a deep notch in the lower border of the main opening-; 

 and this difference may be observed on the two sides of the same skull. 

 I am ready to believe that this lesser opening, giving passage to the su- 

 perior maxillary nerve, is the true "anteorbital" foramen itself; for it 

 seems to correspond to the lower part of the large slit in Muridw, which 

 is walled in by the maxillary lamina, and it is formed by a little plate 

 of bone, which rises as a ridge from the alveolar portion of the jaw, and 

 bends over to abut against the main wall of the maxillary. la cases in 

 which this plate fails to reach the main wall of the maxillary, so that 

 only a notch and not a foramen results, the correspondence of the whole 

 opening with the pyriform slit of the Muridm is very evident, aud the 

 relation of the parts is fully established, though the shape is quite 

 different. 



The contour of the parts surrounding the foramen is such, that the 

 zygomatic process of the maxillary stands out from the bone at right 

 angles at a point scarcely above the level of the alveoli. The anterior 

 root of the zygoma is hence notably depressed in position : there being 

 no forward-upward reach of the lower border of this arch, so evident in 

 Muridce. The zygoma, in fact, is nearly horizontal in all of its length 

 along the under side ; but anteriorl}^ the upper edge rises prominently, 

 in consequence of the unusual extension of the malar up the maxillary, 

 already mentioned. The malar runs all the wa}- up to the lachrymal 

 bone, affording a circumstance I have not seen elsewhere, and which I 

 believe to be very rare, namely, a lachrymo-malar suture. This ascend- 

 ing spur of the malar is, moreover, expanded into a rather broad lamina, 

 partly defending the orbit, thus supplying a wall that, in most cases, is 

 afforded by expansion of the zygomatic process of the maxillary ; the 

 latter being in this case of styloid character. In its continuity, the 

 malar is a slender rod ; behind, it underlaps a short spur of the squamo- 

 sal with simple squamous suture. 



The general shape of the orbit is much the same as in Mus. In both, 

 the squamosal forms much of the posterior orbital wall ; the orbito-sphe- 

 noid being correspondingly reduced. The autero-exterior corner of the 

 parietal reaches to the brim of the orbit. 



The rostral portion of the skull bears to the rest about the same pro- 

 portion as in Mus, and is equally attenuate anteriorly, though thicker at 

 the base, and consequently more tapering. The ends of the nasals pro- 

 ject conspicuously beyond the plane of the incisors ; behind, these bones 

 terminate opposite the ends of the iutermaxillaries ; the suture of the 

 frontal with each of them, as well as with the maxillaries, being nearly 

 in one transverse jagged line. The intermaxillaries develop a strong 

 alveolar plate, separating the superior incisors for nearly half their 

 length ; this, with the projection of the nasals and backward set of the 

 much-curved teeth, results in a snout strikingly like that of the 

 Saccomyidcv. The feeble retreating under jaw, densely hairy upper lip, 

 and small nasal pads, bear out this resemblance in tne external physi- 

 ognomy. 



As in Mus, the interorbital constriction is moderate, being about as 

 wide as the rostrum at base ; aud there is no trace of postorbital 

 processes. The parietals are nearly square, though somewhat emargi- 

 nate in front, to correspond with the convexity of the frontal. There is 

 little, if any, dipping-down of a postero-exterior angle, so well exhibited 

 in Mus. The interparietal is of a large size transversely, though narrow 

 in the other direction ; it reaches across the whole width of the com- 

 bined parietals, bounding them both posteriorly, as it is itself bounded 



