Temporal Bones

What is the Temporal Bone

The temporal bone, one of the eight cranial bones, is a paired bone that constitutes a significant portion of the base and lateral wall of the skull. These bones safeguard the temporal lobe of the brain, hence their name.

Where is the Temporal Bone Located

The temporal bones are positioned on the lateral aspects of the cranial floor.

Key Points

Functions

• Provide support to the structure of the skull.
• Safeguard the temporal lobe of the brain.
• Facilitate the opening and closing of the mouth, in conjunction with the mandible.
• Encompass the ear canal and shield auditory nerves and internal ear structures that contribute to the control of hearing and balance.

Temporal Bone Anatomy

The temporal bone can be categorized into three primary parts: squamous, petromastoid, and tympanic.

1. Squamous Part

Also known as the squama temporalis, it is the largest section of the temporal bone, situated anterosuperiorly. This flat and plate-like segment forms the lateral part of the middle cranial fossa. Its outer surface is smooth and slightly convex and constitutes a part of the temporal fossa. Conversely, its inner surface is concave, bearing impressions of the temporal lobe, specifically the folds (sulci and gyri). The inner surface also features a groove through which the middle meningeal vessels pass.

The lower part of the squamous section bears an anterior bony projection referred to as the zygomatic process. Initially, the process projects laterally, then changes direction and moves anteriorly to articulate with the temporal process of the zygomatic bone, forming the zygomatic arch. At the root of the zygomatic process is a small tubercle known as the articular tubercle or articular process. This tubercle forms the anterior boundary of the mandibular fossa, a socket-like structure through which the bone articulates with the mandible, forming the temporomandibular joint. This segment of the bone also articulates with the sphenoid and parietal bone, anteriorly and laterally, respectively.

2. Petromastoid Part

It comprises two components: the mastoid and petrous.

i. Mastoid Part

This is the posterior portion of the temporal bone. Its outer surface is roughened by muscular attachments. This part features an inferior conical bony projection called the mastoid process, which is palpable just behind the ear. On the medial surface of the mastoid process, there is a depression known as the mastoid notch, and a deep groove called the sigmoid sulcus. The sigmoid sinus is situated in this sigmoid sulcus. This part also contains mastoid air cells, hollowed-out areas within the temporal bone. These cells serve as an air reservoir, safeguard the delicate structures of the ear, and equalize the air pressure within the middle ear.

ii. Petrous Part

This is a pyramid-shaped section of the bone that projects medially and anteriorly from the squamous part. It forms a bony mass between the sphenoid and occipital bones within the cranial cavity. This part divides the middle and posterior cranial fossae. Its internal surface is grooved by the inferior temporal gyrus and trigeminal ganglion. The petrous part articulates laterally with the squamous part of the temporal bone, while the posterior area is continuous with the inner surface of the mastoid part.

3. Tympanic Part

Situated inferiorly to the squamous and anteriorly to the petromastoid part, this is a curved plate-like section located just below the zygomatic process. It fuses with the petrous part internally and the squamous and mastoid parts posteriorly. The concave posterior surface forms the anterior wall, floor, and part of the posterior wall of the external auditory canal. The external opening of the auditory canal is visible here. A narrow bony projection, referred to as the styloid process, extends downwards and anteriorly from the inferior surface of the tympanic part. It is usually straight, but can sometimes be curved, usually on the anterior surface. A foramen, named stylomastoid foramen, lies between the styloid process and the mastoid process.

Articulations

As mentioned, the temporal bone articulates with seven skull bones: the sphenoid, parietal, occipital, zygomatic, mandible, frontal, and maxilla. Among these, it only articulates with the mandible via a synovial joint known as the temporomandibular joint (TMJ). It becomes fused with the remaining bones via respective sutures.

Muscle Attachments

Muscles that attach to the temporal bone include:

1. Temporalis muscle
2. Sternocleidomastoid
3. Splenius capitis
4. Longissimus capitis  
5. Digastrics
6. Stylopharyngeus
7. Styloglossus
8. Stylohyoid muscles

Ossification and Development

The temporal bone ossifies from eight centers: one for the squamous part, four for the petrous and mastoid parts, one for the tympanic part, and two for the styloid process.

References

1. Temporal bone – Kenhub.com
2. The Temporal Bone – Teachmeanatomy.info
3. Temporal bone – Radiopaedia.org
4. Temporal Bone Anatomy – Getbodysmart.com
5. Temporal bone – Anatomy.app