116° OSTEOLOGY. 
in a narrow curved fissure overhung by a sharp scale of bone. In this is lodged the 
ductus endolymphaticus. The ridge above it corresponds to the upper half of the 
posterior semicircular canal. 
Connexions.—The temporal bone articulates with the malar, sphenoid, parietal, and occipital 
bones, and by a movable jomt with the inferior maxilla. Occasionally the temporal articulates 
with the frontal, as happens normally in the 
anthropoid apes; although the region of the 
pterion is characterised by an X-lke form in 
the lower races of man there is no evidence 
that the occurrence of a fronto-squamosal suture 
is more frequent in the lower than the higher 
races, its occurrence being due to the manner of 
fusion of the so-called epipteric ossicles with the 
surrounding bones. 
Architecture.—The temporal bone is re- 
markable for the hardness and density of its 
petrous part, wherein is lodged the osseous 
labyrinth which contains the delicate organs 
associated with the senses of hearing and equi- 
libration. The middle ear or tympanum is a 
cavity which contains the small auditory 
ossicles and is separated from the 
Internal external auditory meatus by the 
auditory membrana tympani. In front it 
meatus i = 
ympani 
oe attic 
Cavity of tympanum 
—Tegmen t 
Superior semicircular canal 
External semicireular canal 
\Leading into aqueeductus Fallopii 
p _ meatus communicates with the pharynx 
Osseous Eustachian _— : : Sool 
canal } by the Eustachian tube ; behind, it 
Vestibule opens into the mastoid antrum and 
“ pee eiue ins Eeleps mastoid air-cells by the aditus ad 
fenestra ovalis cut across 2 Y pA Rot tan s 
Mh) Honesto rotuidalent across antrum. Super iorly, it is se parated 
Superior opening of the eanal for the tym- from the middle cranial fossa by a 
panic branch of glosso-pharyngeal thin plate of bone called the 
Fic. 88.—VeERTICAL TRANSVERSE SECTION THROUGH LEFT tegmen tympani. Inferiorly, 1ts 
TemporRAL Bonk (Anterior Half of Section). floor is formed in part by the roof 
of the jugular fossa and the carotid 
canal. Internally, it is related to the structures which form the inner ear, notably the cochlea 
and vestibule, in front of which it is separated by a thin plate of bone from the carotid canal. 
Curving over the cavity of the tympanum is the aqueductus Fallopii, 
the thin walls of which are occasionally deficient. These details will be 
further dealt with in the section devoted to the Organs of Sense. 
Variations. — The occurrence of a deficiency in the floor of the 
external auditory meatus is not uncommon in the adult. It is met with 
commonly in the child till about the age of five, and is due to incomplete 
ossification of the tympanic plate. The line of the petro-squamosal 
suture is occasionally grooved for the lodgment of a sinus (petro- 
squamosal) ; sometimes the posterior end of this is continuous with a 
canal which pierces the superior border of the bone and opens into the 
lateral sinus. Anteriorly the 
groove may pass into a canal 
which pierces the root of the 
External semicircular canal 
Superior semicircular 
zygoma and appears externally AERP SN 
above the external extremity of ‘ AL gat 
: Opening leading 
the Glaserian fissure. These are into mastoid 
the remains of channels through Vestibule into antrum. 
4 a =) F ; Aqneeductus 
which the blood passed in the __ openings of Pallopii 
semicircular canals aoe 
foetal condition (see ante). Syming- eee Canalis stapedii 
ton has described a case in which auditory AGG 
the squamous part was distinct 
and separate from the rest of the — ponestra ovalis 
temporal bone in an adult ; whilst cut across 
Hyrtl has observed the division of Fenestra rotunda 
the temporal squama into two by gees 
a transverse suture. 
Tympanum 
External 
auditory meatus 
Ossification.—The petro- 
mastoid portion of the bone is Fic. 89.—VerticaL TRANSVERSE SECTION THROUGH LEFT 
developed by the deposition TEMPORAL BONE (Posterior Half of Section). 
of earthy matter in the cartil- 
laginous ear capsule and the perichondrium lining the labyrinth. The squamous and 
tympanic parts are ossified in membrane. 
Ossification commences in the ear capsule in the fifth month, and proceeds so rapidly 
