~~ 
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 
JSenestrate 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 basitem- 
porals (Plate XVII. fig. 3, 6.¢.) 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 (Zu.) ; 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., ¢y’.), the size of these is very small. The entrance to the 
tympanic cavity is very large, but it is greatly overshadowed by the 
uadratum in front, and obliquely half-closed by the “ tympanic 
wing” of the exoccipital (¢.eo.) behind. That wing, which runs 
obliquely forwards, inwards, and downwards, has an f-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.c.), 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 con- 
fusing 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 f. rotunda. 
All these tympanic openings lie in the mouth of a trumpet-shaped 
cavity, formed by the wings of the basisphenoid above, and the 
