The human temporalis muscle: superficial, deep, and zygomatic parts comprise one structural unit

The structure of the temporalis muscle was examined in detail from cadaveric specimens (32 specimens from 16 subjects: 5 males, average age 80.6 years; 11 females, average age 88.6 years) and Computerized Tomography (CT) and T1-weighted Magnetic Resonance (MR) images from normal clinical patients (10 females: average age 45.0 years). Three parts of the muscle were clearly delineated in all cadaveric specimens: (1) the classically recognized superficial part, (2) a zygomatic part, and (3) a complex deep part. In one female specimen, the superficial temporalis demonstrated extensive insertions into the zygomatic process and temporomandibular joint. The zygomatic temporalis originates from the zygomatic arch to insert into the superficial part of the temporalis as it inserts into the lateral surface of the coronoid process. In all specimens, the deep temporalis contained muscle bundles that originated from various crests along the anterior surface of the temporal fossa and inserted into the internal aspect of the coronoid process and retromolar triangle, interdigitating with the buccinator, mylohyoid, and superior constrictor muscles. The confluence of muscle fibers into the buccinator muscle was confirmed in all CT/MRI images. The deep and zygomatic parts described were regarded as accessory muscle bellies previously, but are demonstrably part of the temporalis muscle as a whole.