The material consists of 6 human embryos which are 4.5, 10, 16, 20, 22 and 27mm long.
According to Streeter our 4.5mm long embryo is at the horizon XIV developmental stage, 10mm long at XVII, 16 and 20mm long are at XVIII. The other 2 embryos have each more advanced characteristics in the structures of the chondrocranium.
In 4.5mm long embryo the tubo-tympanic recess which is the outward prolongation of the cavity of the primitive pharynx consists of first and second pharyngeal pouches so that this wide opening is limited by the first arch cranially, by the third caudally.
Dorsal to the opening comes the internal carotic artery which runs cranio-caudal. The form of the cavity of this tubo-tympanic recess is not simple, as there are 2 dorsolateral prolongations of the first and second pouches and these prolongations continue ventromedially so that there exist 2 sulci between first, second and third arch The epithel of these sulci contact with that of the outer first and second groove respectively at first which condition is not visible in elder embryos in which always there is mesenchymal tissue between epithels of inner sulci and outer grooves.
Moreover there is a swelling protruding ventro cranially in this cavity so that the opening to the pharynx is limited cranial and ventral to this swelling.
To this swelling T. Mitamura gave the name Promontorium-Anlage in his in 1954 published paper about this tubotympanic cavity.
Above mentioned condition is invariable in elder 10, 16 and 20mm embryos, among which in 20mm long there appears a narrowing process at the caudal margin of the opening of the tubotympanic recess cavity (pl. 3). In this 20mm long embryo at first there appears the tubal part which is almost inconceivable in the younger specimens. The same narrowing process is also in 22mm long embryo visible, by which the tubotympanic recess cavity is yet wide open to the pharynx. Both sides openings of this embryo are symmetrical and long elliptic, at left 850μ long and 130μ wide, at right 900 and 130μ respectively. The narrowing tubal part at the caudal margin is a little more swelling than that of 20mm long, but only insignificant, so that the openings are very wide. In the next 27mm long embryo the openings become very narrow so that their diameters amount 300 μ craniocaudal, 101 μ dorsoventral at right, 300 and 93 μ respectively at left. There is no doubt about the existence of the tubal part in this embryo. According to Hammar his 20.5mm embryo has not yet, but his 24.0mm definitely tubal part. According to Frazer indicates his 18mm long embryo not, 22 and 26mm long slight narrowing and his 35mm long one definitely tubal part. As in our specimens is the definite tubal part not yet in 22, but in 27mm long to be seen, so it seems to appear the tubal part in these developmental stages, in which the chondrocranium becomes stout so that the outlines of the cartilageous tissue become sharp which in the young specimens there remain many condensed mesenchymal parts; manubrium mallei for example.

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