Location and Borders
The anatomical space of the temporal region is bounded by the following structures:
- Superior and posterior borders: Squamous margin of the temporal bone.
- Inferior border: Infratemporal crest of the greater wing of the sphenoid bone (crista infratemporalis).
- Anterior border: Zygomatic and frontal bones.
- Superficial border: Temporal fascia (fascia temporalis) and zygomatic arch.
- Deep border: Squamous part of the temporal bone (pars squamosa ossis temporalis).
Three fascial/adipose layers are distinguished in the temporal region: the subcutaneous fat layer, the middle layer between the aponeurosis and the muscle, and the deep layer located directly between the temporalis muscle and the bone.
Structure and Biomechanics
The temporalis muscle originates from the periosteum of the temporal fossa (planum temporale) and the deep surface of the temporal aponeurosis.
- Fiber orientation: The muscle fascicles converge inferiorly and anteriorly, transitioning into a robust tendon.
- Insertion: It inserts into the coronoid process (processus coronoideus) as well as the anterior border of the mandibular ramus. A notable surgical consideration is that the tendon is so strongly fixed that during certain procedures, the coronoid process must be osteotomized rather than dissecting the tendon.
- Function: Elevates the mandible, while its posterior fibers retract it (retrusion).
Blood Supply and Innervation
The muscle is supplied by a rich vascular network and is innervated by motor branches of the trigeminal nerve:
- Blood supply: Provided by the anterior and posterior deep temporal arteries (aa. temporales profundae anterior et posterior), which ascend into the temporal fossa between the cranium and the muscle, along with the middle temporal artery (a. temporalis media).
- Innervation: Motor innervation is supplied by the mandibular division of the trigeminal nerve (V3).
Clinical Significance and Topography
The temporalis muscle is closely related to adjacent fascial spaces and pathological processes:
- Spread of infection: The fascial space of the temporal region communicates with the infratemporal fossa, pterygopalatine fossa, buccal fat pad (corpus adiposum buccae), and the deep compartment of the parotido-masseteric region.
- Trauma: A forceful blow directed superiorly onto the chin with clenched teeth can cause the powerful temporalis muscle to shear off the thin coronoid process of the mandible. In zygomatic arch fractures, masticatory dysfunction is often secondary to injury of the temporalis and masseter muscles.