122 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Tol.YI. 



and average diameter of .5 of a millimetre. Above and midwaj^, later- 

 ally, the borders of the foramen are encroached upon by the petrosal on 

 either side, giving it rather a constricted appearance ; from these points, 

 as we follow the posterior moiety of the foraminal periphery, we find it 

 to be grooved, each groove ending posteriorly within a millimetre of each 

 other, in a minute foramen that traverses the internal table of the cra- 

 nium upwards, outwards, and forwards for a short distance, thence to 

 arch around, as a sinus, the epencephalic fossa, meet in the longitu- 

 dinal sinus coming from above. This arrangement obtains in the Cor- 

 vidce, and some other families, where it is more strongly marked. The 

 diapophyses of the occipital vertebrae are in a i^laue but a little lower 

 than the basi-si)henoid ; theyform, as is quite common, the horizontal 

 floor of the cavity of thaotocrane, and blend with the surrounding bones. 

 A moderately well-marked "cerebellar prominence " occupies its usual 

 site in the middle line ; no openings or foramina are ever to be discovered 

 either at its summit or laterally, as seen in some other birds {Anatidcey 

 Strigidce). It divides the shallow temporal fossae that slope away from 

 it on either side, and varies somewhat in size in different individuals. 

 From the ui)per region of the ear and the superior boundaries of the tem- 

 poral fossae to the line of that psuedoarticulation, the frouto-mandibu- 

 lar, this bird's cranium is remarkably smooth, and of a clear white, and, 

 owing to the extraordinary amount of diploic tissue, possessing a ]}q,- 

 culiar translucency . The median furrow is only well marked as it passes 

 between the orbits ; the superior ijeripheries of these cavities, as con- 

 stituting one of the boundaries of the surface under consideration, are 

 sharp at first, rounding as they iuclude tlie lachrymals, and entirely de- 

 void of any notches or indentations. As is usual, all sutural traces are 

 absent (PL lY. Fig. 25). The transverse line of the fronto-mandibular 

 juncture is slightly concave backwards along its middle third, the extremi- 

 ities sloping a little downwards and backwards. Tlie joint motion is 

 only moderately free. Ko well-marked suture defines its exact locality, 

 as in Harporhynchus and others. The bones that go to form the supe- 

 rior mandible, both above and below, are mutually confluent at all their 

 usual points of contact and articulations, with complete obliteration of 

 their original borders. The nearly perpendicular nasals on either side 

 form the anterior boundary of a triangular opening, of which the lachry- 

 mals and maxillaries form, respectively, the posterior boundary and base. 

 These triangles are not complete, insomuch as the lachrymals do not 

 meet the infraorbital bars at the inferior and inner angles. They lead 

 into the rhiual vacuity on either side. It must be borne well in mind 

 by the reader that in describing the upper mandible in the skulls of all 

 birds, it invariably presupposes the removal of its horny integumental 

 sheath that it wears during life, and gives to this portion of the cra- 

 nium a vastly different shape. Either tomial edge is curved and quite 

 sharp ; their anterior mergence, or point of the beak, is decidedly rounded, 

 and fully a millimetre in width. 



