The mastoid part of the temporal bone is its posterior component. The inferior projection of the mastoid part is called the mastoid process.
The mastoid part is normally pneumatized by the mastoid air cells and is perforated by the mastoid foramen. The roof of the mastoid antrum, which separates the mastoid from the cranial cavity, is called the tegmen mastoideum, and is a posterior extension of the tegmen tympani.
The mastoid part has an outer rough surface that provides attachment to occipitalis and auricularis posterior muscles. The lateral aspect of the mastoid process is sometimes called the mastoid cortex. It continues inferiorly as the mastoid process, which is a conical bony projection that provides attachment for a number of muscles:
Lateral attachments (from superior to inferior)
- auricularis posterior (anterior) occipital belly of occipitofrontalis (posterior)
- splenius capitis
- longissimus capitis muscles
- the posterior belly of the digastric muscle
On the medial aspect of the mastoid process is a deep groove, called the digastric fossa, where the digastric muscles attach. Medial to this is the occipital groove, which is traversed by the occipital artery. The sigmoid sulcus, which lodges the sigmoid sinus, lies in the internal surface of the mastoid part of the temporal bone.
Mastoid part of temporal bone articulates with the following bones:
- the superior border articulates with the mastoid angle of the parietal bone
- the posterior border articulates with the inferior border of the occipital bone
- anteriorly it is fused with the descending process of the squamous temporal bone inferior to the supramastoid crest