528 MONOGUAPnS OF NOUTIi AMERICAN RODEXTIA. 



process of the squamosal is of peculiar character; instead of a slender curved 

 spur reaching around to grasp the malar, there is a short abrupt heel appressed 

 against the tympanic, and to tlie roughened dice of this heel the clubbed end 

 of the needle-like malar is affixed. The relation of the parts is such that the 

 zygoma appears to articulate behind with the tympanic — it actually has an 

 abutment against that hone, though no real articulation with it. 



From the lower back edge of the squamosal, a curious thread of bone 

 starts off and occupies the deep groove already mentioned as separating the 

 tympanic from the mastoid. No break from the squamosal can be seen in 

 this thread, which curls around the orifice of the meatus, still in the groove 

 mentioned, and ends by a slightly enlarged extremity below and behind the 

 meatus, exactly in the position of an ordinary "mastoid process". I am 

 uncertain of the meaning of this. The end of this ligule or girdle of bone 

 thus encircling the tympanic is in the site of the postero-lateral angle of the 

 skull in Geomyidce, in which such angle is formed by a corner of the squamo- 

 sal ; and the inference is self-suggestive that this delicate bony strap may 

 really be squamosal — an edge of the squamosal persisting in situ after the rest 

 of that bone has been crowded down into the orbit by the encroachment of 

 the mastoid. Such a view, however, will bear further scrutiny. Even if a 

 slender spur of actual squamosal does run out into the tympano-mastoid 

 groove, it does not follow that the whole of the fold in this groove is squamo- 

 sal ; and certainly the enlarged extremity of this ridge, behind the meatus, 

 has every appearance of an ordinary mastoid process. 



Next after the squamosal, the occipital bone suffers most from the 

 enlargement of the otic elements; it is singularly restricted in extent, and 

 presents itself in unique shape, compressed between the swollen mastoids. 

 All the lateral occipital suturation is with the mastoid, excepting the basi- 

 occipital. The occipital lies in three planes, nearly at right angles with each 

 other. The basioccipital is horizontal, as usual, upon the floor of the skull; 

 the exoccipitals, with probably part of the supraoccipital, are perpendicular 

 behind ; the rest of the supraoccipital is horizontal again, on top of the skull. 

 The basioccipital is wedge-shaped, and offers nothing very peculiar, except- 

 ing its entire disconnection from the petrosals, between which it lies; its 

 sphenoidal articulation is just behind the joined apices of the petrosals. 

 Exoccipitals appear as a pair of flaring flange-like processes, just outside the 

 condyles, appressed against the otic capsules. The foramen is very large, 



