Temporal Bones

Unlike the parietal bones the paired temporal bones do not touch each other, and they not only form part of the calvarium but also form part of the base of the skull. This important bone houses the auditory and equilibrium organs. It also forms the superior articulation area for the temporomandibular joint. This area is the mandibular fossae although older literature may use the term glenoid fossa. The temporomandibular joints are the only synovial joints in the skull and will be discussed in more detail later. The temporal bone also contains the mastoid air cells located within the mastoid process which is the point of insertion of the large sternocleidomastoid muscle. Let us look at the temporal bone in more depth.

Figure 5.

Figure 5.

Parts – There are five parts that can be found in the temporal bone. The flat bone portion of the temporal bone is termed the squamous part of the bone. The horizontal portion of the bone that is part of the skull base is the petrous portion. The petrous portion houses the inner ear and acts to separate the middle and posterior cranial fossae. These two parts combine to form most of the middle cranial fossa.

From a lateral view or inferior view of the skull we can also see the large mastoid part of the bone which is mainly made up of the mastoid process mentioned earlier. This hollow area drains into the middle ear unlike other sinuses in the skull which drain into the nasal cavity.

Just anterior to the mastoid part of the bone is the large opening of the external acoustic meatus (canal) which along with the styloid process are the main landmarks of the tympanic part of the bone.

Anteriorly the temporal bone has a process that is important to dental professionals known as the zygomatic process as it articulates with the zygomatic bone to form the zygomatic arch. It is on this process that the articular surface for the mandible is found.

Openings – The largest opening is the external acoustic meatus (canal) which is the tunnel that acts to funnel air vibrations to the tympanic membrane to start the sensing of auditory stimuli. There is also a passageway for nerves found between the mastoid and styloid processes known logically as the stylomastoid foramen. Seen only on the internal surface there is also a passage for the 7 ^th and 8^th cranial nerves known as the internal acoustic meatusinternal acoustic meatus (canal). This is found in the petrous portion of the bone and is where the two nerves leave the cranium.

Figure 6.

Figure 6.

Figure 7.

Figure 7.

In addition to the nerve exits, the internal carotid arteries pass through the petrous portion of the temporal bone through the carotid canal. The internal jugular vein draining blood from the brain passes through an opening between the temporal and occipital bones known as the jugular foramen.

Muscle attachments – As mentioned earlier the sternocleidomastoid muscle attaches to the mastoid process and the temporalis muscle has a broad insertion that includes portions of the temporal bone. In addition, the styloid process is an attachment point for both the stylopharyngeus muscle and the stylomandibular ligament attaches to that process also. The stylomandibular ligament is important to limiting the movement of the temporomandibular joint (TMJ).