Cu. I.] OF THE DODO. 89 
upper end; it is sharp in the centre. The septum is translucent centrally, and its thinness gives increased 
space for the lodgement of the olfactory apparatus. 
The relatively small cerebral cavity has its axis placed more horizontally, than in other Pigeons; so 
that the brain is, as it were, rotated on its transverse axis, and this rotation gives rise, or is related, to the 
verticality of the occipital facet. 
The apex of the cerebral case is so depressed as to be nearly equidistant between the upper and 
under surfaces of the cranium, and to correspond externally to a point a little behind the centre of the 
groove on the interorbital septum. The frontals attain a median thickness of one inch and two or three 
lines, above the truncated apex, formed by a broad septum separating the olfactory foramina ; which open 
directly into the bases of their respective fossee. This septum is not homologous with the erista galli of 
the ethmoid, but is a prolongation upwards of the thick interorbital septum, or body of the olfactory vertebra, 
to coalesce with the frontals mesially, and thus to divide the anterior orifice of the cerebral tube into two 
foramina for the transmission of the olfactory peduncles, and so far to close it: the non-existence of any 
vertebral segment anterior to the frontal, permits the olfactory capsules to converge towards the median 
line and to be separated only by a thin septum, the prolongation of the anterior centrum; they are thus 
most exposed to the mspiratory currents of air loaded with odorous particles; the optic and auditory 
capsules, on the contrary, are situated between two adjacent vertebre and project laterally. The thick- 
ness of the interorbital septum, beneath the olfactory foramina, is one inch two lines, and diminishes one 
half at the optic outlets. The length of the cerebral cavity, measured from the upper or lower margin 
of the foramen magnum to the olfactory septum, is one inch nine lines and a half; its breadth between the 
foramina for the transmission of the ophthalmic branch of the fifth is one inch; the extreme width of the 
cerebral fossze is perhaps one inch nine lines, and its greatest height from the floor of the optic groove, 
probably about ten lnes. 
The basilar fossa for the lodgement of the medulla oblongata is slightly concave transversely, and rises 
towards the posterior clinoid plate, which projects with a subconvex border over the pit containing the 
orifices of the carotic canals, at the posterior part of the shallow and broad sella turcica; this plate is 
traversed at its base by the canal for the abducens nerve. The extreme length of the basilar fossa, from 
its posterior angle on the upper surface of the occipital condyle to the clinoid process, is one inch and a 
third of a line ; its transverse diameter is equal to that of the lower segment of the foramen magnum : it 
presents, posteriorly and laterally, the condyloid foramen ; and in front of it, the large infundibular pneumo- 
gastric orifice overhung by the vestibular prommence, which projects into the area of the foramen magnum 
at the centre of its lateral margin; a narrow convex ridge separates this aperture from the meatus auditorius 
internus, which has a subacute anterior edge running backwards on the vestibular convexity, between it and 
the petrosal fossa. The cerebellar fossa is relatively narrow, its length from the upper margin of the 
foramen magnum to its apex, dividing the cerebral fossa posteriorly, is oue inch; its surface is considerably 
depressed beneath the level of the cerebral fosse ; it neither presents the longitudinal venous groove, nor 
transverse furrows corresponding to the lamine of the cerebellum ; along its margin posteriorly is seen the 
lateral venous groove terminating in the lateral occipital foramen ; its lower angle, immediately above the 
foramen magnum, is perforated by the mesial occipital aperture. The fossa for the optic lobe is relatively 
very shallow internally, and its edges undefined ; at its apex, beneath the lateral venous groove, there is a 
tumid pneumatic projection about the size of a large pea, overhanging the petrosal excavation. The thin 
floor of the optic fossa is pierced by the foramen giving passage to the ophthalmic branch of the fifth pair ; 
internal to which it is grooved by the fourth nerve, which perforates the thin plate forming the posterior 
