338 PROFESSOR OWEN ON THE GENUS DINORNIS. 
of Pl. LIII. and fig. 1 of Pl. LIV. of the present Memoir with Pl. XXIII. of the Memoir 
(Part v.) above cited. 
The mutilation of the two crania is nearly the same in kind and degree ; but with the 
present specimen there is a tympanic bone and the mandible. 
The base of the occipital tubercle (Pls. LILI. & LIV. fig. 1,1) is 4 lines across, 23 lines 
vertically ; the foramen magnum (PI. LIII. fig. 3, m) is 7 lines vertically and 6 lines across. 
The superoccipital, or confluent upper parts of the exoccipitals, slightly overarches the 
foramen ; the middle of the transverse occipital ridge (ib. 3) is 8 lines above the foramen, 
and extends outward with a slight descent to the paroccipital (ib. 4), having a total 
transverse extent of 3 inches 3 lines. The broad and low superoccipital surface, so 
defined superiorly, is divided by a thick, low, median vertical ridge. It shows no 
cerebellar protuberance, but four rough and shallow muscular depressions, defined by a 
protuberant part of the middle of each half of the transverse occipital ridge. A venous 
canal extends from each protuberance to a foramen (ib. w) near the middle of the outer 
depression. The basioccipital (PI. LIII. fig. 3, 1;) descends 5 lines below the tubercle, 
this vertical part showing a pair of depressions (ib. & Pl. LIV. fig. 1,7); it swells out 
below on each side into a pair of large smooth tuberosities (ib. 1’) with extremely thin 
walls, covering the pneumatic cellular structure of the bone. 
The basisphenoid (Pl. LIV. fig. 1,5) probably contributes the anterior part of these 
tuberosities (ib. m), between which it is concave. The Eustachian canals (ib. fig. 1, e, e), 
with sharp margins, groove the sides of the basisphenoid, converging as they extend 
forward, and losing definition as they approach the middle of the fore part of 5. The 
beginning of the posterior ridge forms the outer boundary of the fossa for the sym- 
pathetic and entocarotid foramina (ib. s,c). The alisphenoid is indicated by the 
foramen for the third and second divisions of the trigeminal nerve, and by the fossa of 
the optic lobe on its inner surface. The loss of the outer plate of the connate basi- and 
pre-sphenoids exposes the pneumatic diploé and the wall (ib. d) of the ‘sella’ or bony 
cup for the hypophysial appendage of the mesencephalon, which marks the boundary 
of the second and third cranial vertebre. 
The mastoid (8) is large, thick, and obtuse, excavated below by a single oblong, 
oblique articular cavity (Pl. LIV. fig. 1, uv) for the undivided similarly shaped convex 
head of the tympanic (ib. fig. 2, e) ; the articular cavity is directed from behind forward 
and outward. There is no epiphysis upon the border of the tympanic cavity, which is 
large, and shows several pneumatic foramina besides the stapedial fossa leading to the 
fenestra ovalis. 
The temporal fossa (Pls. LILI. & LIV. fig. 1, 7), which excavates the contiguous parts 
of the alisphenoid, mastoid, parietal, and postfrontal, is narrow and deep, subsiding 
gradually upon the upper surface of the cranium (PI. LIII. fig. 1, 7), which is smooth, 
broad, and slightly convex, for an extent of nearly 2 inches, between the fosse. The 
whole cranium is remarkably broad and depressed (ib. fig. 3): its greatest vertical 
