312 PROCEEDINGS OF THE ACADEMY OF 



and elsewhere ; the orifice is large, subcircular, and simply a hole 

 without raised brim, pierced in the back upper corner of the bulb. 

 Anteriorly the tympanic bulges so far as to form part of the orbit. 

 "While this special inflation is not otherwise distinguished from the 

 general bulla ossea than by a slight constriction, it is remarkably 

 divided off, above and behind, from the mastoid, by a strong line 

 of impression, of which I shall say more presently. 



Coincidently with the hypertrophy of these otic elements of the 

 temporal, the squamosal is peculiarly reduced in extent, and 

 pushed into the orbit, to which it is almost entirely restricted. 

 It is simply a small irregularly shaped plate of bone lining the 

 back part of the orbit, with a slight spur just exceeding the orbi- 

 tal brim in a little notch between corners of the frontal and pa- 

 rietal bones. The squamosal remains long discrete from all its 

 surroundings. In full-grown though youngish animals the squa- 

 mo-sphenoidal sutures may be readily traced that with the ali- 

 sphenoid just below the glenoid cavit}^ that with orbito-sphenoid 

 within the orbit. The zygomatic 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 the roughened face 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 bone, 

 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 ori- 

 fice 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 uncer- 

 tain of the meaning of this. The end of this ligule or girdle of 

 bone thus encircling the t}^mpanic is in the site of the postero- 

 lateral angle of the skull in Geomyidee, in which such angle is 

 formed by a corner of the squamosal; 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 encroach- 

 ment of the mastoid. Such a view, however, will bear further 



