THE TEMPORAL BONES. 115 
sympathetic plexus. In front of the jugular fossa, and internal to the orifice of the 
carotid canal, there is a V-shaped depression (fossula fenestrae cochleze), on the floor 
of which and close to the posterior border is the orifice of the aqueduct of the 
cochlea (apertura externa aquieductus cochlez). In the fossa is lodged the petrous 
ganglion of the glosso-pharyngeal nerve, and the aqueduct transmits a tubular pro- 
longation of the dura mater, which forms a channel of communication between the 
perilymph of the cochlea and the subarachnoid space. A small vein also passes 
through it. In front of and internal to the orifice of the carotid canal the 
under surface of the apex of the bone corresponds to a rough quadrilateral surface 
which forms the floor of the carotid canal, and also serves for the attachment of the 
cartilaginous part of the Eustachian tube as well as the origin of the levator 
palati muscle ; elsewhere it has attached to it the dense fibrous tissue which fills up 
the cleft (petro-basilar fissure) between it and the basilar process of the occipital bone. 
The superior or anterior surface bears the impress of the convolutions of the 
under surface of the temporal lobe of the cerebrum, which rests upon it; in 
addition, however, a distinct but shallow depression (impressio trigemini) near the 
apex, corresponding to the roof of the carotid canal, can be seen; in this is lodged 
the Gasserian ganglion on the sensory root of the V. cranial nerve. External to the 
middle of the upper surface, and close to its posterior border, is the elevation 
(eminentia arcuata), more or less pronounced, which marks the position of the 
superior semicircular canal here lodged within the bone. A little in front of this, and 
in line with the angle formed by the anterior border and the squamous part, is the 
slit-like opening of the hiatus Fallopii (hiatus canalis facialis), within the projecting 
lip of which two small orifices can usually be seen. These are the openings of the 
aqueductus Fallopii (canalis facialis); if a bristle be passed through the inner of the 
two-openings it will be observed to pass into the bottom of the imternal auditory 
meatus, if into the outer, it will pass through the aqueduct of Fallopius, and, provided 
the channel be clear, will appear on the under surface of the bone at the stylo- 
mastoid foramen. Leading forwards and inwards from the hiatus towards the 
anterior border is a groove; in this lies the great superficial petrosal nerve which 
passes out of the hiatus. A small branch of the middle meningeal artery also 
enters the bone here. A little external to the hiatus is another small opening 
(apertura superior canalis tympanici), often difficult to see; from this a groove runs 
forwards which channels the upper surface of the roof of the canal for the tensor 
tympani muscle. Through this foramen and along this groove passes the lesser 
superficial petrosal nerve. Behind this, and in front of the arcuate eminence, the 
bone is usually thin (as may be seen by holding it up to the light falling through 
the external auditory meatus), roofing in the cavity of the tympanum and forming 
the tegmen tympani. Externally the line of fusion of the petrous with the squamous 
part is often indicated by a faint and irregular petro-squamous fissure. 
The most conspicuous object on the posterior surface of the petrous part of the 
bone is the internal auditory meatus (meatus acusticus internus), which has an 
oblique oval aperture and leads outwards and slightly downwards into the substance of 
the bone, giving passage to the auditory and facial nerves, together with the pars inter- 
media. The canal appears to end blindly; but if it be large, or still better, if part 
of it be cut away, its fundus will be seen to be crossed by a horizontal ridge, the 
falciform crest, which divides it into two fosse, the floors of which (laminz cribrose) 
are pierced by numerous small foramina for the branches of the auditory nerve and 
the vessels passing to the membranous labyrinth, whilst in the fore and upper part 
of the higher fossa the orifice of the Fallopian aqueduct (canalis facialis), through 
which the facial nerve passes, is seen leading in the direction of the hiatus Fallopii 
(see ante). External to the internal auditory meatus and above it, close to the 
superior border, an irregular depression, often faintly marked, with one or two small 
foramina opening into it, is to be noticed. This is the floccular fossa (fossa subarcuata), 
best seen in young bones, where it forms a distinct recess, which is bounded above 
by the bulging caused by the superior semicircular canal, within the concavity of 
which it is placed; it lodges a process of the dura mater. Below and external to 
this, separated from it by a smooth, elevated curved ridge, is the opening of the 
aqueduct of the vestibule (apertura externa aqueductus vestibuli), often concealed 
8a 
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