OCR Text |
Show 1903.] OSTEOLOGY OF THE CUCULIFORMES. 261 Cuculi, is triangular ; but it differs from the Cuculine plate in that it is somewhat swollen, a feature which is especially well-marked in Schizorhis. The two sides of the triangle are produced backwards over the paroccipital notch to join the lateral occipital wing of the tympanic cavity: thus they come to project beyond the base of the triangle, though they are less conspicuous than in some of the Cuculi. There is a barely perceptible precondylar fossa. The Lateral Aspect of the Cranium. The tympanic cavity is oval or oblong in form and of moderate size. It isi bounded in front by the quadrate, behind by the lateral occipital tympanic wing, below by the basitemporal plate, and above by the squamosal prominence and by the head of the quadrate. Within the mouth of this cavity lie several smaller apertures. The largest of these is that of the recessus tympanicus anterior. Immediately below this is the mouth of the Eustachian tube. The foramen ovale and foramen rotundum, three foramina of the sinus petrosus, and the mouth of the posterior tympanic recess open into the cavity by a common aperture-the fenestra! recess- which is very small, and lies mesiad of the articular surface for the otic head of the quadrate. The mouth of the posterior tympanic recess is completely concealed, and can only be made out by cutting away its outer wall and passing a bristle through from its cavity into the common aperture of the foramina in question. In some birds, e. g. Falco, the posterior tympanic recess communicates with the tympanic cavity by two apertures-one caudad of the foramina ovale and rotundum, and lying within the fenestra through which these are approached; and the other external to this fenestra, separated therefrom by a bony column, and lying immediately beneath the articular surface for the otic head of the quadrate. This external aperture is wanting in the Cuculiformes. Immediately above the head of the quadrate, and between the otic and squamosal heads, will be found the aperture of the superior tympanic recess, which is reduced in this group to extremely small dimensions. The foramen of the 7th (facial nerve) opens also into the tympanic cavity between the otic articular surface for the quadrate and the rim of the anterior tympanic recess. The squamosal and otic articular surfaces for the quadrate form a dumbbell-shaped area immediately in front of the aperture of the superior tympanic cavity. The actual articular surfaces are formed by the expanded ends of the dumbbell only. Where the pneumatic area is very large, as in the Striges and Falconiformes for example, it breaks through the connecting portion of these two articular surfaces so that they become quite isolated. The Squamosal Prominence.-The size of this prominence depends largely upon the development of the temporal fossa. When this is deep the prominence is large; but when shallow the prominence is quite inconspicuous. Its anterior angle is produced |