Tympanic part of the temporal bone
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The tympanic part of the
temporal bone The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temple (anatomy), temples, and house the structur ...

temporal bone
is a curved plate of bone lying below the squamous part of the temporal bone, in front of the
mastoid process The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has Foramen, openings for blood vessels. From its bo ...

mastoid process
, and surrounding the external part of the
ear canal The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the pinna (anatomy), pinna to the eardrum and is about in length and in di ...
. It originates as a separate bone (tympanic bone), which in some
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...

mammal
s stays separate through life. Evolutionarily, a portion of it is derived from the
angular bone The angular is a large bone A bone is a rigid organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Ele ...
of the reptilian lower jaw.


Surfaces

Its postero-superior surface is concave, and forms the anterior wall, the floor, and part of the posterior wall of the bony
ear canal The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the pinna (anatomy), pinna to the eardrum and is about in length and in di ...
. Medially, it presents a narrow furrow, the ''tympanic sulcus'', for the attachment of the
tympanic membrane In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped biological membrane, membrane that separates the external ear from the middle ear. Its function is to transm ...

tympanic membrane
. Its antero-inferior surface is quadrilateral and slightly concave; it constitutes the posterior boundary of the
mandibular fossa The mandibular fossa, also known as the glenoid fossa in some dental literature, is the depression in the temporal bone that articulates with the mandible. Structure In the temporal bone, the mandibular fossa is bounded anteriorly by the ...

mandibular fossa
, and is in contact with the retromandibular part of the
parotid gland The parotid gland is a major salivary gland in many animals. In humans, the two parotid glands are present on either side of the human mouth, mouth and in front of both ears. They are the largest of the salivary glands. Each parotid is wrapped ar ...
.


Borders

Its lateral border is free and rough, and gives attachment to the cartilaginous part of the ear canal. Internally, the tympanic part is fused with the petrous portion, and appears in the retreating angle between it and the squama, where it lies below and lateral to the orifice of the auditory tube. Posteriorly, it blends with the squama and mastoid part, and forms the anterior boundary of the tympanomastoid fissure. Its upper border fuses laterally with the back of the postglenoid process, while medially it bounds the
petrotympanic fissure The petrotympanic fissure (also known as the squamotympanic fissure or the glaserian fissure) is a fissure in the temporal bone that runs from the temporomandibular joint to the tympanic cavity. The mandibular fossa is bounded, in front, by the a ...

petrotympanic fissure
. The medial part of the lower border is thin and sharp; its lateral part splits to enclose the root of the styloid process, and is therefore named the ''vaginal process''.


Ear canal

The central portion of the tympanic part is thin, as it gives rise to the bony inner two-thirds of the
ear canal The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the pinna (anatomy), pinna to the eardrum and is about in length and in di ...
, and in 5 - 20% of skulls the lower surface is perforated by a hole, the ''foramen of Huschke'' that opens onto the
temporomandibular joint In anatomy, the temporomandibular joints (TMJ) are the two joints connecting the jawbone to the skull. It is a bilateral Synovial joint, synovial articulation between the temporal bone of the skull above and the Human mandible, mandible below; ...

temporomandibular joint
due to incomplete fusion of the anterior and posterior prominences during development. The bony portion of the ear canal is nearly 2 cm long and is directed inward and slightly forward: at the same time it forms a slight curve, so that the floor of the canal is convex upward. In sagittal section it presents an oval or elliptical shape with the long axis directed downward and slightly backward. Its anterior wall and floor and the lower part of its posterior wall are formed by the tympanic part; the roof and upper part of the posterior wall by the squama. Its inner end is closed, by the tympanic membrane which originates from the tympanic sulcus; the upper limit of its outer orifice is formed by the posterior root of the zygomatic process, immediately below which there is sometimes seen a small spine, the ''suprameatal spine'', situated at the upper and posterior part of the orifice. The auditory bulla (pl. bullae) is a hollow bony structure on the ventral, posterior portion of the skull that encloses parts of the
middle
middle
and
inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in ...

inner ear
. In most species, it is formed by the tympanic part of the temporal bone.


Other animals

In all extant and extinct
primate Primates are a diverse order (biology), order of mammals. They are divided into the Strepsirrhini, strepsirrhines, which include the lemurs, galagos, and lorisids, and the Haplorhini, haplorhines, which include the Tarsiiformes, tarsiers and ...

primate
s, including humans, the auditory bulla is formed by the petrosal bone (the petrous part of the temporal bone). This is a diagnostic trait that can be used to distinguish primates, including anthropoids,
tarsier Tarsiers ( ) are Haplorhini, haplorhine primates of the family (biology), family Tarsiidae, which is itself the lone extant family within the infraorder Tarsiiformes. Although the group was once more widespread, all of its species living today ar ...

tarsier
s,
lemur Lemurs ( ) (from Latin ''lemures'' – ghosts or spirits) are Strepsirrhini, wet-nosed primates of the Superfamily (biology), superfamily Lemuroidea (), divided into 8 Family (biology), families and consisting of 15 genera and around 100 exist ...

lemur
s, and
loris Loris is the common name for the strepsirrhine mammals of the subfamily Lorinae (sometimes spelled Lorisinae) in the family Lorisidae. ''Loris'' is one genus in this subfamily and includes the slender lorises, ''Nycticebus'' is the genus contain ...

loris
es, from all other mammals.


Additional images

File:Gray189.png, Left infratemporal fossa. File:Gray907.png, External and
middle ear The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear). The mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in ...

middle ear
, opened from the front. Right side. File:Bulles auditives sur crâne de renard roux.JPG, Auditory bullae on a
red fox The red fox (''Vulpes vulpes'') is the largest of the true foxes and one of the most widely distributed members of the Order (biology), order Carnivora, being present across the entire Northern Hemisphere including most of North America, Europe ...

red fox
skull (').


References


External links

* - "Osteology of the Skull: Lateral Surface of Skull" {{Authority control Bones of the head and neck