114 OSTEOLOGY. 
jugular foramen, internal to which it has a sharp curved border, often grooved, 
reaching to the apex. This groove, which is completed by articulation with the 
outer side of the basioc cipital, lodges the inferior petrosal venous sinus. 
The superior border is a twi isted edge which is continuous with the upper margin 
of the groove for the lateral sinus posteriorly, and anteriorly and internally reaches 
the apex of the bone. Running along it there is usually a well-marked groove for 
the superior petrosal venous sinus, and near its inner extremity it is slightly notched 
for the passage of the trigeminal nerve. Along the entire length of this border the 
tentorium cerebelli is attached. 
On the inferior surface of the petrous part, which is bounded in front by the 
anterior border internally and the tympanic plate externally, and behind by the 
posterior border, the follow- 
ing structures are to be 
noted. Springing from and 
Canal for chorda tympani : es : 
j pie ee nei ensheathed by the vaginal 
/ /Carotid canal process is the slender and 
f pointed styloid process (pro- 
fh Weise cessus styloideus), the length 
’ if of which varies much. Pro- 
jecting downwards and 
shehtly forwards and in- 
war ds, it affords attachments 
to the stylo-glossus, stylo- 
Ul aeave/for hyoid, and stylo-pharyngeus 
petrosal sinus ~~ muscles as well as the stylo- 
Aqueduct of cochlea hyoid and stylo-mandibular 
Canal:for Jacpuspus ligaments. Just behind it, 
Jugular fossa and between it and the mas- 
~Canal for Arnold’s —— toid_s process, 1s the  stylo - 
i att mastoid foramen (foramen 
ee culanianrince stylomastoideum), which hes 
at the anterior end of the 
digastric groove, and trans- 
mits the facial nerve and the 
stylo-mastoid artery. Im- 
mediately within the styloid 
process thereisadeep,smooth, 
excavated hollow, the jugular 
fossa (fossa Jugularis), which 
is converted into a foramen 
(jugular) by articulation with the occipital bone. Behind and external to the fossa 
there is a small quadrilateral surface, which is united to the extremity of the jugular 
process of the exoccipital by a synchondrosis. Inside the fossa, on its outer 
aspect, or placed on its external border, is the opening of a small canal 
(canaliculus mastoideus), which passes outwards to open into the canalis 
facialis, and transmits the auricular branch of the vagus (Arnold’s nerve), which 
ultimately escapes through the auricular fissure (see ante). In front of the 
jugular fossa and separated from it by a sharp crest, and just internal to the 
tympanic plate, is the circular opening of the inferior orifice of the carotid canal 
(canalis caroticus). Directed at first upwards, this canal bends at a right angle and 
turns forwards and inwards, lying parallel to the anterior border; reaching the fore 
part of the apex of the bone,it opens in front by an oblique ragged orifice. Through 
the canal the internal carotid artery, accompanied by a plexus of sympathetic 
nerves, passes into the cranium. On the ridge of bone separating the jugular fossa 
from the carotid canal is the opening of a small canal (canaliculus tympanicus), 
through which the tympanic branch of the glosso-pharyngeal (nerve of Jacobson) 
passes to reach the tympanum. Within the orifice of the carotid canal another 
small opening or openings (canaliculi earotici tympanici) may be noticed which 
afford passage to the tympanic branches of the internal carotid artery and carotid 
Temporal surface 
| Zygomatic surface 
x y 
aay ti 
Uy 
/ 
Tubercle 
Eminentia 
articularis 
Glenoid fossa 
Glaserian fissure 
Tympanic plate 
Ext. auditory meatus \ 
Styloid process — | 
Vaginal process 
Auricular fissure 
Stylo-mastoid 
foramen \ 
Mastoid process { 
Digastric groove 
Groove for 
occipital artery 
Fic. 87.—RicHTt TEMPORAL BONE AS SEEN FROM BELOW. 
