OCR Text |
Show 1871.] MR. COLLETT ON THE SKULL OF STRIX TENGMALMI. 741 tinues without any incision of its margin down to the ' os occipitale.' From this cause there exists, in the two species last named, to a greater degree than in the others, a wall, open in front and closed behind, projecting to the sides. When the skulls are seen in front the ' cristae' appear in these two species very distinctly, while in the rest they are almost completely hidden behind the 'processus orbi-talis posterior.' I have not had an opportunity of examining the other species of the northern fauna not named here (Strix funerea, S. liturata, S. lapponica and S.psilodadyla) ; but I have seen several non-European species. The wall just mentioned is peculiarly adapted to throw back the vibrations of sound and carry them on to the ' membrana tympani' in all the species which I have examined. I am therefore inclined to attribute to the nearly allied Strix otus and S. brachyotus a highly developed power of hearing. In a still greater degree, however, is this the case in S. tengmalmi, where this bone, and by consequence several of those adjoining it, has a very peculiar formation. In Strix tengmalmi the ' crista' which the ' os squamosum ' pushes forth in front of the ear-opening projects more considerably than in the other species ; and as the outer edge of the ' crista' widens about the middle into a long tongue-shaped process, the whole ' os squamosum ' surrounds a larger and deeper ear-cavity than in any of the other species with which I am acquainted. But at the same time a very remarkable asymmetry appears in this * crista.' On the right side (see figs. 2, 3, & 6, p. 740) it projects far upward and behind the upper edge of the ' os alisphenoideum;' and on the left side (see figs. 2, 4, & 6, p. 740), on the contrary, it leans immediately on the foremost edge of that bone and somewhat beneath its upper part. On both sides it normally joins in its lower part the ' os occipitale laterale' extending on the right considerably more (its height being here 20 mm.) than on the left, where its height is only 15 m m . On the right side, where this ' crista' has its largest extent and at the same time is drawn furthest back, it apparently projects at the top behind the point where the projecting end of the ' os parietale' meets the upper edge of the ' os squamosum.' Between where the 'crista' begins and the foremost edge of the remaining part of the ' os squamosum ' (that point at which the last-mentioned bone touches the hinder edge of the ' os alisphenoideum') there is a proportionately considerable distance, amounting in four of the skulls examined by me to 7*25 m m . On the left side, on the contrary, the ' crista' projects at the top immediately at the point which the ' os squamosum ' forms with the ' parietale,' ' frontale,' and the hinder edge of the ' alisphenoideum.' Here the ' crista' leans upon the upper (but not the uppermost) end of the ' processus orbitalis posterior.' Though this ' crista ' at its upper end joins the ' os squamosum' very differently on either side, its lower part is apparently symmetrical and proceeds normally on both sides to the lateral parts of the perfectly symmetrical 'occipitale.' In most of the Northern Strigidce the outer edge of the ' crista' has a distinct incision, bending downwards to the ** os occipitale' |