1889.] MR. "W. K. PARKER ON STEATORNIS CARIPENSIS. 1/1 



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. 

 fiw. 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 TS millim. in size. Where the basitem- 

 porals (Plate XVII. 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 miUim. 

 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 {t.eo.) 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 milhm. 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 milhm. wide. 



Inside that narrow, oblique, high doorway there is the most con- 

 fusing multiphcity 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. 



KW. these tympanic openings he in the mouth of a trumpet-shaped 

 cavity, formed by the wings of the basisphenoid above, and the 



