the basisphenoid; a process from that border being applied to the external surface
of the parietal. In youth, the petrous bone enters into the formation of the inner
wall of the cranium, and has thus the greater portion of the lower border of the
parietal applied to it. There is a small flattened process from the border of the
parietal resting on the petrous over the internal auditory foramen, always present
in young skulls. This process plays an important part in the economy of this region
of the skull, as it expands with increasing years, and materially contributes to the
after exclusion of the petrous from forming any portion of the inner wall of the
skull; but in this it is much assisted by the growth of, the false petrous process of
the basisphenoid, by the outward growth of the basi-occipital and by the inward
and anterior strengthening of the basicranial margins of the exoccipital. In adult
life, this portion of the parietal is closely applied to the postauditory process of
the basisphenoid, and anterior to that the border of the bone is bent downwards and
articulated to the posterior division of the wings of the basisphenoid; forming the
inner and upper wall of that portion of the great ear-chamber, which is prolonged
forwards above the pterygoid process of the squamosal. By its inward growth it
also contributes to the division of this fissure in the cranial walls into two parts:
one the foramen lacerum anterius, defined anteriorly by the posterior division of the
wings of the basisphenoid, externally by the basisphenoid, posteriorly by the false
petrous portion of the basisphenoid by the shelving petrous processes of the parietal,
and superiorly by the thickened, lower border of the parietal; the other the foramen
lacerum posterius, behind the two last-mentioned processes which define its
anterior border, its inner margin being formed by a deep concavity lying between the
Grlasserian process of the basisphenoid and the strong, outward projection of the
basi-occipital which constitutes the anterior border of the precondyloid foramen of
the occipital. The posterior wall is formed exclusively by the extremity of the
downwardly, outwardly and forwardly projecting strong ridge of the exoccipital,
along which the lateral sinus is placed and which also defines the posterior wall of
the precondyloid foramen. Its upper wall is formed entirely by the thick, lower
border of the parietal. The inner wall of the bone is deeply concave, marked by
depressions for the cerebral convolutions and meningeal vessels, and by numerous
nutrient foramina.
.'Frontal (PI. XXXIX, figs. 1 and 2 f mid PI. XL, fig. 1).—This bone
consists of a central, vertical or cerebro-nasai plate, the anterior surface of which,
with the exception of a narrow strip down the middle of its anterior aspect and
which forms the upper part of the hinder wall of the nares, is covered on either
side by the ascending plates of the maxillaries and partially by the upper extremities
of the premaxillaries. Projecting outwards, forwards and downwards like a
pair of wings from the external borders of the vertical plate are the tempero-orbital
plates, to the inner surface of which the ascending plates of the maxillaries are
also applied. The orbit is placed on the under surface of the free extremity of the
plate and has behind it the pit for the reception of the zygoma. The posterior
surface of this plate constitutes the anterior wall of the temporal fossa. Projecting
backwards, outwards and slightly inwards from the base of the former there is
another smaller plate, the temporal, which forms the internal surface of the temporal
fossa.
The cerebro-nasal plate when viewed from the cerebral surface is almost quadrangular,
and in young skulls the two original halves of the bone can be detected
(PI. XL, fig. 1). In that period of its history it is almost vertical, the most anterior
portion of the cerebral lobes being lodged in two deep concavities in the upper
two-thirds, separated from each other by a moderately developed, internal, vertical
crest; but in aged skulls, the internal surface of the frontal has an upward and
backward direction and the concavities for the cerebral lobes are perforated by
numerous foramina. In two skulls, I noted a deep pit in the upper part of the left
cerebral fossa close to the well-developed, vertical crest, and opposite to it on the
other side of the crest a smaller pit. These pits are probably due to the presence
on the surface of the brain of cystic parasites, which, pressing against the skull, produce
absorption of its walls (?) In one brain the surface bore numerous cysts, which
in some cases had corresponding depressions in the skull. In a nearly adult female
skull of which I have made a vertical section through the posterior extremities of
the frontals, a large well-defined sinus occurs on the left side; while the corresponding
position of the opposite side is filled up with finely cancellated tissue;
in young skulls, however, there are no traces of these sinuses.
The anterior surface of the vertical plate presents a prominent nodose-like ridge,
bearing on the sides of its upper end the minute nasals. I t is continuous with the
nasal septum, but has a strong twist to the left, which confers on the right side of
the plate a longer surface than on the left. The sides of this aspect of the plate
are defined by the orbitotemporal wings, and below by the orbitosphenoid which is
invested by the alar processes of the vomer. At the junction of the orbitosphenoid
and parietals, in young skulls, there is an elongated fissure or imperfection of ossification
internal to where the sphenoidal fissure opens on the anterior surface of the
united bones. The orbitotemporal plates differ in form, the right having a straight
anterior margin, while the left is outwardly curved in the upper first-half of its
extent owing to the sinistral distortion of the skull. They are deeply concave from
above downwards and forwards; and their lower extremities, which are thin triangular
plates directed downwards, forwards and slightly inwards, are traversed by the
optic canals; a small portion of their posterior margin constituting a part of the
upper boundary of the pterygomaxillary fissure. The inner surface of these parts
of the orbitotemporal plates presents a rather broad but shallow furrow, which terminates
in the' orbit and along which the nerves and blood vessels pass; and below it
are two small grooves, along which branches of the second or median branch of the
trigeminal pass into the maxillary to appear on the front aspect of that bone. At
the inner end of the first-mentioned fissure and on the inner wall of the canal-like
continuation of the sphenoidal fissure, there is a minute orifice, the opening of the
orbitosphenoid portion of the optic canal. So far the two inner branches of the
fifth nerve lie in that canal, and at this point two nerves from the most external