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Purpose In the Union for International Cancer Control classification, extrinsic muscle involvement in oropharyngeal cancers is systematically defined as a T4a tumor, although the term extrinsic may incorrectly imply that these muscles are outside the tongue. Our aim was to describe the topography of extrinsic tongue muscles and show that their involvement in oropharyngeal cancers does not always correspond to T4a staging. Methods This cadaveric study was based on dissections of the tongues of ten healthy subjects. Dissections were carried out using sections, and careful macroscopic examination with a 3.5-diopter magnifying glass allowed the identification of muscles from their origin to their termination. Imagery and histology were excluded to stay as close as possible to the clinical evaluation. Results The sample comprised seven men and three women, with a mean age 82 years. In all the ten cases, the extrinsic muscles were located at the periphery of the tongue. The genioglossus was the only deep extrinsic muscle, extending to the periphery and under the mucous membrane of the tongue. As a result, a T1 tumor can invade the mucous membrane and affect the extrinsic muscles without transforming into a T4a tumor. Conclusion As extrinsic tongue muscles are peripheral and submucosal, the use of the term “deep” is erroneous, as is the systematic usage of extrinsic muscles to define T4a oropharyngeal cancers. This study attempts to explain this error, which is recurrent in the different editions of the Union for International Cancer Control and American Joint Committee on Cancer.

The effects of physical characteristics of foods on the coordination of extrinsic tongue muscle activities during natural mastication were evaluated. Electromyograms of tongue-retractor (styloglossus, SG) and tongue-protractor (genioglossus, GG) muscles as well as the jaw-movement trajectories were recorded during raw rice and chow pellet chewing in the freely moving rabbit. Each masticatory cycle included a jaw closing (Cl) phase consisting of a fast-closing (FC) and a slow-closing (SC) phase, and a jaw opening (Op) phase. The duration of the Cl and SC phases was found to be much larger while the duration of the FC phase was much smaller during rice chewing than pellet chewing. The jaw movements during rice chewing had smaller amplitudes of the gape and lateral excursion of the jaw as compared with those during pellet chewing. The SG muscle had a double-peaked burst activity in each masticatory cycle with one peak during the Op phase (the SG1 burst) and the other during the Cl phase (the SG2 burst). They were significantly larger during pellet chewing as compared with rice chewing, but the duration of the SG2 burst was significantly longer during rice chewing than pellet chewing. The offset of the SG2 burst was delayed during rice chewing as compared with that during pellet chewing. There was little difference in the activity pattern of the GG burst between the foods. Our present results suggest that the SG muscle activity could be modified by the sensory feedback possibly to adapt to environmental demands during chewing.

An attempt has been made to clarify the exteroceptive control mechanism of extrinsic tongue muscles in cats. For this purpose, excitatory and inhibitory receptive fields of extrinsic tongue muscle motor units on the tongue surface have been investigated in urethanechloralose anesthetized or decerebrate cats.1. Styloglossal motor units responded with spike discharges to gentle stroking of the anterior part of the tongue dorsum. The receptive field of this reflex response has been classified into 5 types; ipsilateral filiform type (iF type), ipsilateral nonfiliform type (iNF type), bilateral nonfilifbrm ype (bNF type), ipsilateral filifbrm plus ipsilateral nonfliform type (iF+iNF type) and ipsilateral filifbrm plus bilateral nonfiliform type (iF+bNF type). The majority of styloglossal motor units were of the bNF type in urethane-chloralose anesthetized cats. On the other hand, motor units of the iF type dominated in decerebrate cats.2. Hyoglossal motor units were divided into two groups; ventral and dorsal. Ventral hyoglossal motor units responded with spike discharges to gentle stroking of the ipsilateral posterior part of the tongue dorsum, while dorsal hyoglossal motor units to that of the ipsilateral filiform area of the anterior tongue dorsum.3. Only a minority of genioglossal motor units responded with spike discharges to tactile stimulation of the filiform area of the anterior tongue. In most responsive genioglossal motor units, the excitatory receptive fieldwas located in the ipsi-or bilateral filiform area of the anterior tongue. In a few cats, however, the excitatory receptive field was in the ipsilateral Dosterior part of the tongue dorsum.4. Some styloglossal and hyoglossal motor units responded with spike discharges to tactile stimulation of the ventral surface of the tongue, but none of the genioglossal motor units responded to it.5. Some genioglossal and ventral hyoglossal motor units exhibited nonrespiratory spontaneous discharges, but no styloglossal and dorsal hyo-glossal motor units showed them. However, the majority of styloglossal motor units responded with spike discharges to jaw opening.6. Inhibition of spike discharges was demonstrated with styloglossal and genioglossal motor units. The inhibitory receptive field of styloglossal motor unit was located on the ipsilateral posterior part of the tongue dorsum. In most genioglossal motor units, the inhibitory receptive field was on the ipsi-, contra- or bilateral posterior part of the tongue dorsum.