Serpents lack an external ear, a tympanic membrane, a tympanic cavity, and a Eusta- chain tube. These negative but very significant characteristics are seen phylogenetically, especially in connection with the reduction of the eye (Le., Nopsca, 1923; N.B., today Pachyophis is grouped together with the Simoliophidae, furthermore Mahendra, 1938; Walls, 1940, 1942; Bellairs and Underwood, 1951). Other authors mention these cha- racteristics in connection with characteristics of ingestion (Berman and Regal, 1967). They claim that the formation of a tender tympanic membrane and a tympanic cavity is incompatible with the mobility of the quadratum and its adjacent musculature. The energy of sound can be transmitted either by the bones of the skull or the otic capsule or by the intercalare (medially adjacent to the quadratum) with the stapes and the. base of the columella (for the intercalare or rather the extracolumella see De Beer, 1926 and 1937; McDowell, 1967).
The vibrations of the apparatus added to the vesti- buloquadratum type (Sertakowa, 1950) initiate a movement of the perilymph in the sinus pericapsularis (sinus juxtastapedialis), in the cisterna perilymphatica and in the scala tympani with the helicotrema. This stimulates the sense organs of the papilla basilaris located on the membrana basilaris in the pars limbi of the ductus cochlearis filled with endolymph.