Sir, traditionally the masseter muscle was considered to be bilayered, consisting of superficial and deep layers.1 Recently, Mezey et al. at the University of Basel discovered a third deeper layer of the masseter muscle (Musculus masseter pars coronidea) in a cadaveric study.2 They noted that this layer originates on the zygomatic process of the temporal bone, running anteromedially attaching at the base and the posterior margin of the coronoid process of the mandible. It is supplied by the masseteric nerve and artery supporting the common origin of these layers. Although the exact independent function of this muscle is unknown, it is likely that it helps in retracting the mandible due to its oblique angulation as opposed to other layers which elevate the mandible.

A 65-year-old patient presented with progressively worsening pain of the left face and jaw-locking for prolonged periods of the day. Examination revealed palpable swelling over the right TMJ and parotid region. Multiple cross-sectional imaging revealed a calcified mass lesion posterior to the right mandibular condyle suspicious of synovial osteochondromatosis (Fig. 1). A preauricular approach with temporal extension was planned and executed to access this tumour. The deeper layer of masseter was noted during dissection and a pictorial description is presented here (Fig. 2).

Fig. 1
figure 1

Right condylar synovial osteochondromatosis

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Fig. 2
figure 2

Deep layer of masseter muscle (white arrows)

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