Cu. I.] OF THE DODO. ; 77 
the lower sharp edge of the internal wall of the tympanic cavity, arching from the paroccipital angle to 
the posterior border of the basilar pyramidal protuberance, which projects vertically downwards; a rough 
prominent ridge, notched in the centre, ascends, inclining inwards and backwards along its internal edge, 
and with its fellow forms the anterior boundary of the occipital facet, indicating nearly the division between 
the sphenoid and occipital bones. The supra-occipital plate presents, in the centre, a triangular, broad and 
depressed cerebellar elevation ; the truncated apex is on a level with the infra-occipital ridge, a line above 
which it is perforated mesially by a short canal, half a line in diameter, opening internally immediately 
within the upper margin of the foramen magnum: a slight crest traverses the median line, becoming more 
apparent as the convexity subsides towards the base, the angles of which extend to the most concave part 
of the supra-occipital ridge ; below it enters the furrow leading to the orifice just mentioned. The large 
oblong surface, external to the central protuberance on each side, is divided into two subequal portions, by 
a convexity directed downwards and inwards from the origin of the superior occipital ridge to that of the 
inferior, it corresponds to the semicircular canals within; on the left side it is widest and most promi- 
nent superiorly, and subsides towards the lateral venous groove ; the floor of the inner segment is slightly 
elevated towards the supra-occipital ridge, but on the right side it is raised into a triangular convexity, 
more prominent than the canalicular elevation, to which it is parallel, separated only by a slight digital 
impression. The lateral venous groove passes obliquely inwards and upwards, above the infra-occipital 
ridge, and terminates at the margin of the cerebellar protuberance, in a short oval canal perforating the 
cranium, two lines and a half above the foramen magnum ; and opening upwards, internally, at the margin 
of the cerebellar fossa; it transmits the lateral venous sinus. The groove contracts in the centre of its 
course, and is there covered by a narrow osseous bridge on the left side; a small canal lodging a muscular 
vein opens downwards into the internal segment. Externally, it curves round the origin of the infra- 
occipital ridge ; a narrow tract, one line in breadth, separating its termination from the groove for the bulb 
of the jugular vem, which the lateral sinus joins. 
The area of the strongly pitted muscular impression, on each side, is elliptical ; its inner angle is pro- 
longed inwards across the base of the cerebellar protuberance; the outer occupies the upper part of the 
paroccipital process, the lower portion of which is smooth. In its centre it extends from the venous groove 
to the supra-occipital ridge, and the surface is increased by the elevations already described. The cerebellar 
eminence is smooth and polished. From the notch between the paroecipital process and mastoid, inwards 
for half an inch, the digastric and occipital impressions are separated only by a smooth convex edge ; more 
internally, a prolongation of the parietal tract intervenes, the apex extending to the canalicular elevation : 
where the supra-occipital ridge originates. 
This ridge is broad and rough externally ; it ascends on each side, becoming narrow and rounded, 
following the undulation of the surface to the angle of the cerebellar elevation; from thence it descends to 
near the mesial line, over which it arches: it presents a slight notch at the upper and inner angle of the 
canalicular convexity, from which a groove leads outwards and downwards to a canal perforating that 
eminence, and traversing the cranial diploé to open on the lateral facet below the superior pneumatic fora- 
men ; it transmits a vein from the integuments of the cranium. The supra-occipital ridge is defined by the 
subsidence of the posterior surface, not by its elevation above the parietal tract. 
The convex margin of the paroccipital process increases 1 breadth inferiorly, and is rough and flat- 
tened, giving origin to the Biventer maxilla muscle; a strong lgament passing from its lower angle, 
forwards and inwards to the apex of the basilar facet of the ramus of the lower jaw, is still present. 
The infra-occipital ridge is broad, rough, and prominent externally, the lateral venous groove bending 
round its origin; the roughness subsides internally, as it passes mto the cerebellar eminence. The foramen 
