Human Anatomy, Part 1 - K. A. Dyubenko, A. K. Kolomiytsev, Yu. B. Chaykovsky 2002

Special Part
Axial skeleton, sceleton axiale — Bones of the neurocranium
Temporal bone

The temporal bone, os temporale, is a paired bone (Fig. 41) of complex shape and Structure. It contributes to The formation of the cranial base and completes the lateral walls of the cranial vault. The temporal bone houses the Organs of Hearing and Balance, while its canals transmit vital nerves and Blood Vessels. On its external surface lies the external acoustic opening, porus acusticus externus, surrounded by the three PARTS OF THE temporal bone: the squamous part, pars squamosa; the petrous part, pars petrosa; and the tympanic part, pars tympanica.

Class="center">

Fig. 41. Temporal bone, os temporale:

A - external surface; B - internal surface

Fig. 41. Temporal bone, os temporale (Continued): C - inferior surface

The squamous and tympanic parts develop in Connective Tissue, whereas the petrous part develops within Cartilage.

The squamous part, pars squamosa, is shaped like a thin plate oriented in the sagittal plane. The squamous suture unites its free margin with the inferior border of the Parietal bone and the greater wing of the Sphenoid bone. The lower part of the squama adjoins the petrous and tympanic parts, being separated from the former by the petrosquamous fissure, fissura petrosquamosa, and from the latter by the tympanosquamous fissure, fissura tympanosquamosa. The posterior region of the squama features the groove for the middle temporal artery, sul. a. temporalis mediae. The inferoposterior region exhibits the temporal line. Superior and slightly anterior to the squama arises the zygomatic process, processus zygomaticus, which originates from a broad ROOT and then tapers. It articulates with The process of the Zygomatic bone to form the zygomatic arch, arcus zygomaticus. On the Inferior surface of its root lies the mandibular fossa, fossa mandibularis. Anteriorly, the articular fossa is bounded by the articular tubercle, tuberculum articulare, and posteriorly by the retroarticular tubercle, tuberculum retroarticulare. On the internal cerebral surface of the squama, digital impressions, cerebral eminences, and grooves for the middle meningeal artery, a. meningea media, are visible; damage to the squama may result in aneurysms of this artery, a factor that must be considered in clinical (neurosurgical) practice.

The petrous part, pars petrosa, is shaped like a three-sided pyramid, with its apex directed anteromedially and its base posterolaterally. The petrous part presents three surfaces: anterior, facies anterior partis petrosae, posterior, facies posterior partis petrosae, and inferior, facies inferior partis petrosae, as well as superior, posterior, and anterior angles.

The anterior surface of the pyramid faces the cranial cavity. Nearly at the middle of the anterior surface lies the arcuate eminence, eminentia arcuata, which corresponds to the anterior semicircular canal of the labyrinth.

The roof of the tympanic cavity adjoins this eminence. On the anterior surface of the pyramid, near its apex, is the trigeminal impression, impressio trigeminalis, for the Trigeminal nerve ganglion. Lateral to it lies the hiatus for the greater petrosal nerve, hiatus canalis n. petrosi majoris, from which the groove for the greater petrosal nerve, sul. n. petrosi majoris, runs medially. Slightly anterior and lateral to this is the upper hiatus for the lesser petrosal nerve, hiatus canalis n. petrosi minoris, from which the groove for the lesser petrosal nerve, sul. n. petrosi minoris, originates. These apertures transmit the corresponding nerves.

On the posterior surface of the petrous part, approximately in the middle, is the internal acoustic opening, porus acusticus internus, which leads into the internal acoustic meatus, meatus acusticus internus. Near the superior margin of the petrous part, in the area between the internal acoustic opening and the external aperture of the vestibular aqueduct, lies the subarcuate fossa, fossa subarcuata. Near the inferior margin is the external aperture of the cochlear canaliculus, apertura externa aqueductus cochleae. Superior and lateral to this aperture lies the external aperture of the vestibular aqueduct, apertura externa aqueductus vestibuli, through which passes the endolymphatic duct, ductus endolymphaticus.

On the inferior surface of the petrous part (see Fig. 41C) lies the oval jugular fossa, fossa jugularis, at the floor of which runs a small groove leading to the opening of the mastoid canaliculus. The posterior margin of the jugular fossa is bounded by the jugular notch, incisura jugularis. Anterior to the jugular fossa is the external opening of the carotid canal, apertura externa canalis carotici, which leads into the carotid canal, canalis caroticus, opening at the apex of the petrous part via the internal opening of the carotid canal, apertura interna canalis carotici. Near the external opening on the posterior wall of the carotid canal are the openings of the caroticotympanic canaliculi, canaliculi caroticotympanici, which open into the tympanic cavity and transmit blood Vessels and nerves. Between the jugular fossa and the external opening of the carotid canal lies the petrosal fossula, fossula petrosa, deep within which is the inferior opening of the tympanic canaliculus, apertura inferior canaliculi tympanici (BNA). Lateral to the jugular fossa is the inferiorly directed styloid process, processus styloideus, which serves as the attachment site for the "styloid apparatus" (mm. styloglossus, stylohyoideus, stylopharyngeus) and the stylohyoid and stylomandibular ligaments (ligg. stylohyoideum et stylomandibulare). Posterior to the root of the process lies the stylomastoid foramen, foramen stylomastoideum. Anterior and lateral to the styloid process is the bony PROJECTION OF THE tympanic part—the vaginal process of the styloid process, Vagina processus styloidei.

The superior border of the petrous part separates its anterior surface from the posterior surface. Along this border runs the superior petrosal sulcus, sul. sinus petrosi superioris. The posterior border of the petrous part separates the posterior surface from the inferior surface. Along this border runs the inferior petrosal sulcus, sul. sinus petrosi inferioris. The anterior border of the petrous part separates its anterior surface from the inferior surface. On this border, lateral to the internal opening of the carotid canal, is the opening of the musculotubular canal, canalis musculotubarius, which connects the tympanic cavity with the nasal part of the Pharynx.

Inferiorly, the Base of the petrous part extends into the mastoid process, processus mastoideus, the external surface of which is rough due to Muscle attachment. A cross-section of the mastoid process reveals mastoid Cells, cellulae mastoideae, lined with mucous membrane. The largest Cell, termed the mastoid antrum, antrum mastoideum, communicates with the Middle ear cavity. In cases of middle ear inflammation (otitis), infection may spread into these cells and lead to purulent inflammation (mastoiditis), the Treatment of which requires surgical intervention.

Lateral to the mastoid process run two grooves: the medial one for the occipital artery, sul. a. occipitalis, and slightly lateral to it, the mastoid notch, incisura mastoidea, to which the digastric muscle attaches. The mastoid process is separated from the tympanic part by the tympanomastoid fissure, fissura tympanomastoidea, which transmits the auricular branch of the Vagus nerve.

In the region between the Occipital bone and the mastoid process lies the mastoid foramen, foramen mastoideum—the widest and most constant of all emissary foramina. Most commonly, the mastoid foramen is situated within the occipitomastoid suture (C. Libersa, 1934). On the external surface of the mastoid process, the mastoid triangle (MacEwen's triangle) is conventionally delineated, serving as the landmark for trepanation (antrotomy) in inflammatory conditions of the middle ear (cells and antrum). On the internal surface of the mastoid process runs the groove for the sigmoid sinus, sul. sinus sigmoidei. Alongside the S-shaped configuration, hooked, sickle-shaped, straight, and arched forms also occur (H. D. Bourdei, 1951, 1955). In the middle region of the sigmoid sinus groove opens the mastoid foramen, foramen mastoideum, which transmits the mastoid emissary vein connecting the sigmoid sinus with the suboccipital venous plexus.

The tympanic part, pars tympanica, surrounds the external acoustic meatus, meatus acusticus externus. It bounds the external acoustic opening, porus acusticus externus, and the tympanic cavity, cavitas tympanica, inferiorly and posteriorly, while its free margin fuses with the squama and the mastoid process. It is separated from the squama by the tympanosquamous fissure, fissura tympanosquamosa, into which a process of the roof of the tympanic cavity projects. This process divides the fissure into two parts: the petrosquamous fissure, fissura petrosquamosa, and the petrotympanic fissure, fissura petrotympanica (Glaserian fissure), through which the chorda tympani, a branch of the intermediate nerve, exits the tympanic cavity. Above the external acoustic opening lies the suprameatal spine, spina suprameatica. The cartilaginous part of the acoustic meatus is attached to the free, rough margin of the tympanic part that bounds the external acoustic opening.

Ossification. The temporal bone of an infant consists of three parts. The first ossification centers appear in the squama during the 8th week of intrauterine development, and in the tympanic part by the 3rd month. By the 5th month, five ossification centers develop within the cartilaginous model of the petrous part. In the newborn, the parts of the temporal bone are separated by connective tissue-filled fissures that fuse During the first year of life.