Tympanic part
Encyclopedia
The tympanic part of the temporal bone
is a curved plate of bone lying below the squama
, in front of the mastoid process
, and surrounding the external acoustic meatus.
It originates as a separate bone (tympanic bone), which in some mammals stays separate through life.
In evolution it is derived from the angular bone of the reptilian lower jaw.
Medially, it presents a narrow furrow, the tympanic sulcus, for the attachment of the tympanic membrane.
Its antero-inferior surface is quadrilateral and slightly concave; it constitutes the posterior boundary of the mandibular fossa
, and is in contact with the retromandibular part of the parotid gland
.
Its upper border fuses laterally with the back of the postglenoid process, while medially it bounds the 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. The central portion of the tympanic part is thin, and in a considerable percentage of skulls is perforated by a hole, the foramen of Huschke.
The external acoustic meatus 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, in the recent state, by the tympanic membrane; 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.
Temporal bone
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis...
is a curved plate of bone lying below the squama
Squama
Squama refers to a structure shaped like the scale of a fish. More specifically, it can refer to:* Squama frontalis* Squama occipitalis* Squama temporalis, the squamous portion of the temporal bone* Squamous cell...
, in front of the mastoid process
Mastoid process
The mastoid process is a conical prominence projecting from the undersurface of the mastoid portion of the temporal bone. It is located just behind the external acoustic meatus, and lateral to the styloid process...
, and surrounding the external acoustic meatus.
It originates as a separate bone (tympanic bone), which in some mammals stays separate through life.
In evolution it is derived from the angular bone 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 external acoustic meatus.Medially, it presents a narrow furrow, the tympanic sulcus, for the attachment of the tympanic membrane.
Its antero-inferior surface is quadrilateral and slightly concave; it constitutes the posterior boundary of the mandibular fossa
Mandibular fossa
The mandibular fossa is the depression in the temporal bone that articulates with the mandibular condyle. In the temporal bone, the mandibular fossa is bounded, in front, by the articular tubercle; behind, by the tympanic part of the bone, which separates it from the external acoustic meatus; it is...
, and is in contact with the retromandibular part of the parotid gland
Parotid gland
The paired parotid glands are the largest of the salivary glands. They are each found wrapped around the mandibular ramus, and secrete saliva through Stensen's ducts into the oral cavity, to facilitate mastication and swallowing and to begin the digestion of starches.-Location:The parotid glands...
.
Borders
Its lateral border is free and rough, and gives attachment to the cartilaginous part of the external acoustic meatus. 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
Petrotympanic fissure
The petrotympanic fissure is a fissure in the temporal bone that runs from the temporomandibular joint to the tympanic cavity....
. The medial part of the lower border is thin and sharp; its lateral part splits to enclose the root of the styloid process
Styloid process
In anatomy, a styloid process , usually serving as points of attachment for muscles, refers to the slender, pointed process of :* temporal bone of the skull - Temporal styloid process...
, and is therefore named the vaginal process. The central portion of the tympanic part is thin, and in a considerable percentage of skulls is perforated by a hole, the foramen of Huschke.
The external acoustic meatus 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, in the recent state, by the tympanic membrane; the upper limit of its outer orifice is formed by the posterior root of the zygomatic process
Zygomatic process
Zygomatic process is a protrusion from the rest of the skull, like the bumper of a car. Most of it belongs to the zygomatic bone, and could therefore be called the zygomatic process of the zygomatic bone...
, immediately below which there is sometimes seen a small spine, the suprameatal spine, situated at the upper and posterior part of the orifice.