ANATOMY. 
auditory procefs, reckoned among the external procefi'es, 
that femicircular ridge, which, running between the root 
of the maftoid and zygomatic procedes, forms the under 
part of the external meatus audiiorius. 
The finuofities or depreffions on the external furface of 
each temporal bone are thefe: A long folia at the inner 
and back part of the root of the mammary procefs, where 
the pofterior head of the digaftric mufcle has its origin. 
Immediately before the root of the zygomatic procefs, a 
conliderable hollow is left for lodging the crotaphite muf¬ 
cle. Between the zygomatic, auditory, and vaginal, pre¬ 
cedes, a large cavity is formed; thro’ the middle of which, 
from top to bottom, a fidure is obfervable, into which part 
of the ligament that fecures the articulation of the lower 
jaw with this bone is fixed. The fore-part of the cavity 
being lined with tire fame cartilage which covers the tu¬ 
bercle before it, receives the condyle of the jaw; and in 
the back-part a fmall fhare of the parotid gland, and a 
cellular fatty fubftance, are lodged. At the inlide of the 
root of the ftyloid apophyle, there is a thimble-like cavi¬ 
ty, where the beginning of the internal jugular vein, or 
end of the lateral (inns, is lodged. Round the external 
meatus auditorius, feveral finuofities are formed for re¬ 
ceiving the cartilages and ligaments of the ear, and for 
their firm adhefion. 
The holes that commonly appear on the outfide of each 
of theie bones, and are proper to each of them, are five. 
The firfi, fituated between the zygomatic andmaftoid pre¬ 
cedes, is the orifice of a large funnel-like canal, which 
leads to the organ of hearing; and is therefore called mea¬ 
tus auditorius e.xternus. The fecond gives pad’age to the 
portio dura of the feventh pair of nerves; and from its 
fituation between the muftoid and ftyloid procefi'es, is call¬ 
ed foramen Jlylo-maJloideum. Some way before, and to the 
infide of the ftyloid procefs, is the third hole: the canal 
from which runs firft upwards, then forwards, and receives 
into it the internal carotid artery, and the beginning of the 
intercoftal nerve; where this canal is about to make the 
turn forwards, one, or fometimes two, very fmall holes go 
oft' towards the cavity of the ear, called tympanum. Thro’ 
thefe Valfalva affirms the proper arteries of that cavity are 
fent. On the anterior edge of this bone, near the former, 
a fourth hole is obfervable, being the orifice of a canal 
which runs outwards and backwards, in a horizontal di¬ 
rection, till it terminates in the tympanum. The whole 
canal is named iter a palato ad aurem, or Evjlachian tube. 
On the external fide of the bony part of this canal, and on 
the top of the chink, in the cavity that receives the con¬ 
dyle of the lower jaw, is the courfe of the little nerve, 
called chorda tympani, and commonly laid to be reflected 
from the lingual branch of the fifth pair, till it enters the 
tympanum, to run acrofs this cavity. The fifth hole is 
very uncertain, appearing fometimes behind the maftoid 
procefs; fometimes it is common to the temporal and oc¬ 
cipital bones; and in feveral fkulls there is no fuch hole. 
The internal furface of the ofik temporum is unequal; 
the upper circular edge of the fquamous part having nu¬ 
merous fmall ridges and furrows for its conjunction with 
the parietal bones ; and the reft of ft is irregularly mark¬ 
ed with the convolutions of the middle part of the brain, 
and with furrows made by the branches of the arteries of 
the dura mater. From the under part of this internal 
furface, a larger tranfverfe hard craggy protuberance runs 
horizontally inwards and forwards, with a ftiarp edge 
above, and two flat fides, one facing obliquely forwards 
and outwards, and the other as much backwards and in¬ 
wards. To the ridge between thefe two fides, the large 
Lateral procefs of the dura mater is fixed. 
The internal proper foramina of each of thefe bones are, 
firft, the internal meatus auditorius in the pofterior plain 
fide of the petrous procefs. This hole foon divides into 
twoq one of which is the beginning of the fcqueduCt of 
Fallopius; the other ends in feveral very fmall canals that 
allow a paflage to the branches of the portio mollis of the 
feventh pair of nerves, into tire veftibule and cochlea. 
Vo*.. I. No. 34. 
537 
Through it alfo an artery is fer.t, to be diftributed to the 
organ of hearing. The fecond hole, which is on the ante¬ 
rior plain fide of the craggy procefs, gives paflage to a re¬ 
flected branch of the fecond branch of the fifth pair of 
nerves, which joins the portio dura of the auditory nerve, 
while it is in the aqueduct, fmall branches of blood-vef- 
fels accompanying the nerves, or palling through fmaller 
lroles near it. The paflage of the cutaneous vein into the 
lateral finus, or of a branch of the occipital artery, is 
feen about the middle of the large folia for that finus ; and 
the orifice of the canal of the carotid artery is evident at 
the under part of the point of the petrous procefs. The 
upper round part of the fquamous bones is thin, but equal; 
while the low petrous part is thick and ftrong, but irregu¬ 
lar and unequal, having the diftinCtion of tables and di- 
ploe confounded, with feveral cavities, procelfes, and 
bones, within its fubftance, which are parts of the organ 
of hearing. 
The temporal bones are joined above to the parietal 
bones by the fquamous futures and their pofterior addita- 
menta. Before, to the fphenoid bone, by the future of 
that name; to the cheek bones, by the zygomatic futures; 
and to the occipital bone, by the lambdoid future and its 
additaments. 
Os occipitis, fo called from its fituation, is convex on 
the outfide, and concave internally. Its figure is an irre¬ 
gular fquare, or rather rhomboid; the lower angle of which 
is ftretched forward in the form of a wedge, and thence 
is called the cuneiform procefs. The external furface is 
convex, except at the cuneiform apophyle, where it is flat¬ 
ted. At the bafe of this triangular procefs, on each fide 
of the great hole, the large oblong protuberances, named 
the condyles, appear, to lerve for the articulation of this 
bone with the firft vertebra of the neck. Though the 
motion of the head is performed on the cond) les, yet the 
centre of gravity of that globe does not fall between them, 
but is a good way farther forward; from which mechan- 
ifm it is evident, that the nrufcles which pull the head 
back mtift be in a conttant ftate of contrattion ; which is 
ftronger than the natural contraction of the proper flex¬ 
ors, elfe the head would always fall forwards, as it does 
when a man is alleep, or labours under a pally, as well as 
in infants, where the weight of the head far exceeds the 
proportional ftrength of thefe mufcles. This feeming 
diladvantageous fituation of the condyles is, however, of 
Angular ufe, by allowing fufficient fpace for the cavities of 
the mouth and fauces, and for lodging a fufficient number 
of mufcles, which commonly ferve for other ufes; but 
may at pleafure be directed to adl on the head, and thea 
they have an advantageous lever to aft with, fo as to be 
able to fuftain a conliderable weight, or other force ap„ 
plied to pull the head back. 
Somewhat more externally than the condyles, there is 
a fmall rifing and femilunated hollow in each fide, which 
make part of the holes common to the occipital and petrous 
bones. Immediately behind this, on each fide, afeabrous 
ridge is extended from the middle of the condyle towards 
the root of the maftoid procefs. Into this ridge the muf- 
culus lateralis, commonly aferibed to Fallopius, is infert- 
ed. About the middle of the external convex furface, a 
large arch runs acrofs the bone ; from the upper lateral 
parts of which the occipital mufcles have their rife; to 
its middle the trapezii are attached ; and half-way between 
this and the great hole, a letter arch is extended. In the 
hollows between the middle of thefe arches the complexi 
are inferted; and, in the depreffions more external and 
farther forward than thefe, the fplenii are inferted. 
On the inner furface of the os occipitis we fee two ridges ; 
one Handing perpendicularly, the other running horizon¬ 
tally acrofs the firft. The upper part of the perpendicular 
limb, to which the falx is fixed, is hollowed in the mid¬ 
dle, or often on one fide, for the reception of the fuperior 
longitudinal finus ; and the lower part of it has the fmall 
or third procefs of the dura mater fattened to it, and is 
fometimes hollowed by the occipital finus., .Each fide of. 
X , the 
