78 OSTEOLOGY [Parr II. 
magnum has an ovate form, subangular above ; it is six lines and a half high, and nearly five lnes broad, 
inferiorly; the vestibular elevation in the interior of the cranium, projects on each side into the area of the 
foramen beneath the centre, rendering it fiddle-shaped, but to a greater extent on the left than on the night 
side; it is four lines in width where thus constricted. Its margin is separated from the infra-occipital 
ridge all round by a groove, which widens below from the inclination forwards of the plane of the foramen ; 
its breadth is one line and one-third above mesially, and three lines and a half below. This recess lodges 
the great posterior cerebellar sinus, which discharges itself by a large branch perforating the posterior 
occipito-atlantal ligament, to form the bulb of the internal jugular vein. 
The occipital condyle is subpedunculated ; its axis is directed downwards and backwards, so that its 
posterior surface, above, is nearly in the same vertical plane as the margin of the foramen magnum ; 
the articular surface is separated by a groove from the peduncle laterally, but is continued on it inferiorly, 
indicating a considerable amount of downward flexion of the head on the neck ; its form is subhemispherical, 
flattened, and notched above by the prolongation of the fossa for the medulla oblongata ; its posterior surface 
is marked by a faint median vertical groove; its height is three lines, and its breadth four lines. 
The lateral basilar fossa presents posteriorly the shallow oval concavity for the bulb of the jugular vein ; 
it is most distinct on the right side; its imner angle is separated from the groove surrounding the foramen 
magnum by a convex ridge, it is directed outwards and forwards to the foramen lacerum posterius, grooving 
its inner edge; and is four lines and a half long, and two and a half broad. The outer boundary of the 
deep elliptic fossa, four lines and a half long and two broad, common to the posterior lacerated and carotic 
foramina, is formed by the inner wall of the tympanic cavity, the lower sharp edge of which, concave infe- 
riorly, extends as already indicated from the paroccipital angle to the pyramidal protuberance ; its inner 
margin is more deeply concave than the external, thin and notched behind, thick and rounded in front. 
The fossa is divided by a roughened transverse convexity, forming the floor of the vestibule leading to the 
foramen ovale and f. rotundum; the foramen caroticum, transmitting the internal carotid and its accom- 
panying sinus, leads forwards and inwards from the anterior angle ; while, from the posterior, passes upwards, 
curving forwards round the vestibule just mentioned, a canal, which transmits an artery and accompanying 
vein, with the glosso-pharyngeal and sympathetic nerves; its inferior orifice corresponds in part to the fora- 
men lacerum posterius of mammals; its outer wall is perforated, a line above its margin, by a rounded 
aperture leading to a broad groove on the base of the paroccipital process anteriorly ; it transmits the 
venous sinus of the membrana tympani to the internal jugular vein. The condyloid foramen for the 
passage of the hypoglossal nerve, perforates the base of the peduncle of the occipital condyle, one line and 
one-third external to the foramen magnum; one line and a half from it, towards the carotic canal, is the 
large aperture, transmitting the pneumogastric and spinal accessory nerves. Two minute apertures sepa- 
rated by an osseous line, and probably giving exit to small venules, perforate the lower part of the inter- 
space between the condyloid and pneumogastric foramina on the left side; on the right side they are a line 
and a half apart. 
The lateral fossa is bounded in front, by the posterior convex surface of the triangular basilar pyramid, 
whose elongated inner edge extends inwards, sloping backwards to the groove, uniting the inner and ante- 
rior angles of the fossa of each side beneath the occipital condyle. The apex and narrow outer surface are 
rough : a scabrous tubercle is developed at the foot of the inner edge, separated from its fellow by a smooth 
mesial notch. The breadth of the supra-occipital plate, between the mastoid notches, is two inches eight lines 
anda half; from the median line obliquely to the mastoid notch, it measures one inch eight lines and a half ; 
its height, mesially, is nine lines and a half; and its thickness towards the occipital ridge is five lines and a 
half above, and one line and a half below. The distance between the inferior angles of the paroccipital 
