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Show 1889.] MR. W. K. PARKER ON STEATORNIS CARIPENSIS. 171 There is no zygomatic snag to the squamosal, which at its anterior corner clamps a very short " sphenotic process " of the alisphenoid. The bone in front of the squamosal and sphenotic, formed above by the frontal, and below by the alisphenoid, makes a perfect back-wall to the orbit, and floor to the tilted cranial cavity ; this is a closed, not a fenestrate skull. The low, smooth, wide occipital plane (Plate XVIII. fig. 1) is emarginate above, and slants backwards, so as to form an obtuse angle with the base. The foramen magnum (f.m.) is pyriform, with the narrow end above ; the condyle (oc.c.) is reniform and transverse, 2 millim. by 1*3 millim. in size. Where the basitemporals (Plate X V I I . fig. 3, b.t.) are fused with the upper outgrowths of the basisphenoid, to form the openings of the " anterior tympanic recesses," there they are 18 millim. across ; behind they are 13 millim. wide, and their average width is 3 millim.,-very narrow as compared with the great, massive, triangular plate formed by these two bones in Geese and Fowls. In front they form a projecting lip, and a narrow tongue of bone grows from the middle of this neat lip under the common Eustachian vestibule (Eu.) ; the openings into the right and left tubes are 3 millim. apart. The opening of the tympanic cavity (ty.c.) is partly protected in front by a pair of distinct tympanic bones (ty., ty'.), the size of these is very small. The entrance to the tympanic cavity is very large, but it is greatly overshadowed by the quadratum in front, and obliquely half-closed by the " tympanic wing " of the exoccipital (Leo.) behind. That wing, which runs obliquely forwards, inwards, and downwards, has an /-shaped front edge, concave above, and rounded below; its back face, the outer edge of the occipital plane, is plano-convex. This wing is 10 millim. in extent, and the right and left wings are only 13 millim. apart along their inner edge. The whole breadth across the occipital plane, over the top of the tympanic wings, is 31 millim. Laterally these wing-like outgrowths enclose the hinder basi-cranial territory, which is margined with passages for the internal carotid arteries (i.e.), the vagus and glosso-pharyngeal nerves (X.), the hypoglossal nerves (XII.), and some small veins ; all these passages are normal in Steatornis. The back of the quadrate is concave above, and then bulges backwards ; thus the tympanic entrance is, at first, 3 millim., and then only 2 millim. wide. Inside that narrow, oblique, high doorway there is the most confusing multiplicity of passages leading into the outer and inner chambers of the auditory labyrinth. The middle ear or tympanic cavity is as complex as in the Crocodile, but after a different fashion ; whilst the inner ear or membranous labyrinth is enclosed in cavities, tubular and ventricose, very similar to those of the higher modern reptiles. Behind and between the crura of the otic process of the quadrate there is the opening into the " upper tympanic recess," and in front of that double condyle the Eustachian openings; and behind and more inwards there is a common vestibular opening leading to the fenestra ovalis and/, rotunda. All these tympanic openings lie in the mouth of a trumpet-shaped cavity, formed by the wings of the basisphenoid above, and the |