50 
one on either side of the longitudinal midline of the floor, which mark the 
origin of the abducent or sixth nerve from the ventral region of the medulla. 
From each of these openings a long, straight passage leads forward with 
a downward inclination into the pituitary cavity debouching immediately 
below the hinder rim of the pituitary fossa, and in close proximity* to the 
foramen for the third and fourth nerves. The two passages are parallel 
to each other and pierce the basisphenoid in its median elevation behind 
the pituitary fossa. From the position of the anterior end of these passages 
it is presumed that the sixth nerve, a purely motor nerve supplying the 
external rectus muscle of the eye, found exit also from the large aperture 
apportioned to nerves III and IV. 
The foramen for the seventh or facial nerve, behind the foramen 
ovale, and separated externally from it by a surface of bone measuring 
about 11 mm. across, is small and inconspicuous. A narrow but well- 
defined channel leads downward and forward from it toward the deep 
groove, beneath the flange of the basisphenoid, which terminates below 
at the lower entrance of the internal carotid artery. This foramen pierces 
the prootic as in the alligator. 
Behind the exit of the seventh nerve, and distant from it externally 
about 16 mm., is a rather large opening, the fenestra ovalis + the fenestra 
rotunda, which internally communicates directly inward with the brain 
cavity by a small oval aperture, the internal auditory meatus, through 
which the eighth or auditory nerve left the brain and reached the auditory 
organ by means of its various branches. Rising upward in the thickness 
of the bone from the passage between the outer opening and the internal 
meatus is a large space which apparently marks the position of the laby- 
rinth. The semicircular canals are not preserved in the specimen (para- 
type) nor has it been possible to detect any representation of other parts 
of the auditory organ. The side wall of the brain-case is thickened inwardly 
at this position of the labyrinth causing a marked convexity of the surface 
of the bone in the brain-cavity over a considerable area above the internal 
auditory meatus. At about the middle of this convex area, at about 
10 mm. above the meatus is a small opening, between 2 and 3 mm. wide, 
connecting the large space within the bone with the brain-cavity. 
Four foramina of rather small but nearl}^ equal size occupy a definite 
sunken area bounded below by the lateral convexity of the occipital 
condyle, and in front and above by a prominent ridge which latter runs 
upward from the basi-occipital behind the fenestra ovalis and continues 
almost horizontally backward to the paroccipital process of the exoccipital. 
This sunken area is most depressed in front where it ends as an excavation 
beneath the ridge. Of the four foramina two are close together in front, 
one above the other, and are overhung by the ridge and partly concealed 
by it in a lateral view of the skull. Anteriorly the ridge is sharp-edged 
behind and about 12 mm. broad. The third foramen is at a short distance 
behind the front pair, and the fourth follows the third at a somewhat 
increased interval. The lower anterior opening and the two posterior 
ones are in an almost straight line horizontally. The upper of the two 
front apertures, slightly larger than the lower one, is the foramen lacerum 
posterius transmitting the glossopharyngeal (IX), the pneumogastric (X), 
and the spinal accessory nerves. The direction of the passage outward 
through the bone for these nerves is obliquely backward. The inner end 
