The bony carotid canal is a tube-like bone with a rough surface in contrast to smooth surfaces of the other parts of the temporal bone petrosal portion (petrosa): it takes an impression of the additional, out-sourcing product. No study had been conducted to evaluate a contribution of the adjacent sphenoid and pharyngotympanic tube (PTT) to the carotid canal. We examined sagittal and horizontal histological sections of hemi-heads from 37 human fetuses at 10 to 37 weeks. At 10 to 18 weeks, the future carotid canal was identified as a wide loose space between the cartilaginous cochlea and the ossified or cartilaginous sphenoid elements (ala temporalis and pterygoid). A linear mesenchymal condensation extending between the cochlear wall and ala temporalis suggested the future antero-inferior margin of the carotid canal. This delineation was more clearly identified in later stages. After 25 weeks, 1) the growing pterygoid pushed the PTT upward and, in turn, the PTT pushed the internal carotid artery (ICA) upward toward the petrosa: 2) a membranous ossification occurs in the dense mesenchymal tissue, the latter of which took an appearance of an anterior process of the petrosa; 3) the bony process of the petrosa involved the ICA inside or posteriorly. The bony carotid canal was made with membranous ossification in the dense mesenchymal tissue between the petrosa and sphenoid. The mother tissue was detached from the sphenoid by the PTT. The ossification of the septum between the ICA and tympanic cavity seemed to continue after birth.

The bony carotid canal is a tube-like bone with a rough surface in contrast to smooth surfaces of the other parts of the temporal bone petrosal portion (petrosa): it takes an impression of the additional, out-sourcing product. No study had been conducted to evaluate a contribution of the adjacent sphenoid and pharyngotympanic tube (PTT) to the carotid canal. We examined sagittal and horizontal histological sections of hemi-heads from 37 human fetuses at 10 to 37 weeks. At 10 to 18 weeks, the future carotid canal was identified as a wide loose space between the cartilaginous cochlea and the ossified or cartilaginous sphenoid elements (ala temporalis and pterygoid). A linear mesenchymal condensation extending between the cochlear wall and ala temporalis suggested the future antero-inferior margin of the carotid canal. This delineation was more clearly identified in later stages. After 25 weeks, 1) the growing pterygoid pushed the PTT upward and, in turn, the PTT pushed the internal carotid artery (ICA) upward toward the petrosa: 2) a membranous ossification occurs in the dense mesenchymal tissue, the latter of which took an appearance of an anterior process of the petrosa; 3) the bony process of the petrosa involved the ICA inside or posteriorly. The bony carotid canal was made with membranous ossification in the dense mesenchymal tissue between the petrosa and sphenoid. The mother tissue was detached from the sphenoid by the PTT. The ossification of the septum between the ICA and tympanic cavity seemed to continue after birth.

Striated muscle fiber crossings at almost right angle are known to exist in the face, soft palate, pharyngeal wall and tongue. We aimed to identify a specific interface tissue at the crossing. We observed histological sections from 22 halfheads of 12 near-term fetuses at 26–40 weeks (crown-rump length, 215–334 mm). For comparison, we also observed tongue frontal sections from 5 elderly cadavers (75–85 years old). At the angle of mouth as well as in the soft palate and pharyngeal wall, a solitary striated muscle fiber (e.g., levator) consistently crossed a fiber bundle of the antagonist muscle (e.g., depressor), but a solitary-to-solitary fiber interdigitation was unlikely with the antagonist muscle. Near the external nasal orifice as well as in the tongue intrinsic muscle layer, at every section, there was a crossing with an endomysium-to-endomysium contact:the nasalis and platysma muscles and; the vertical and transverse (or inferior longitudinal) tongue muscles. Therein, the functional vectors crossed at almost right angle. Also in adult tongue, the vertical and transverse muscle fibers sometimes (0–2 sites per section) crossed with an endomysium-to-endomysium contact. At the muscle crossing with an endomysium contact, the endomysium and basement membrane seemed to receive a friction stress between two muscles. Although some crossings might disappear due to high muscle activity after birth, not a few of them were likely to maintain. To minimize the mechanical stress, a minute nervous control of the timing, duration and strength of muscle contraction seemed to be necessary.

Striated muscle fiber crossings at almost right angle are known to exist in the face, soft palate, pharyngeal wall and tongue. We aimed to identify a specific interface tissue at the crossing. We observed histological sections from 22 halfheads of 12 near-term fetuses at 26–40 weeks (crown-rump length, 215–334 mm). For comparison, we also observed tongue frontal sections from 5 elderly cadavers (75–85 years old). At the angle of mouth as well as in the soft palate and pharyngeal wall, a solitary striated muscle fiber (e.g., levator) consistently crossed a fiber bundle of the antagonist muscle (e.g., depressor), but a solitary-to-solitary fiber interdigitation was unlikely with the antagonist muscle. Near the external nasal orifice as well as in the tongue intrinsic muscle layer, at every section, there was a crossing with an endomysium-to-endomysium contact:the nasalis and platysma muscles and; the vertical and transverse (or inferior longitudinal) tongue muscles. Therein, the functional vectors crossed at almost right angle. Also in adult tongue, the vertical and transverse muscle fibers sometimes (0–2 sites per section) crossed with an endomysium-to-endomysium contact. At the muscle crossing with an endomysium contact, the endomysium and basement membrane seemed to receive a friction stress between two muscles. Although some crossings might disappear due to high muscle activity after birth, not a few of them were likely to maintain. To minimize the mechanical stress, a minute nervous control of the timing, duration and strength of muscle contraction seemed to be necessary.

Striated muscle fiber crossings at almost right angle are known to exist in the face, soft palate, pharyngeal wall and tongue. We aimed to identify a specific interface tissue at the crossing. We observed histological sections from 22 halfheads of 12 near-term fetuses at 26–40 weeks (crown-rump length, 215–334 mm). For comparison, we also observed tongue frontal sections from 5 elderly cadavers (75–85 years old). At the angle of mouth as well as in the soft palate and pharyngeal wall, a solitary striated muscle fiber (e.g., levator) consistently crossed a fiber bundle of the antagonist muscle (e.g., depressor), but a solitary-to-solitary fiber interdigitation was unlikely with the antagonist muscle. Near the external nasal orifice as well as in the tongue intrinsic muscle layer, at every section, there was a crossing with an endomysium-to-endomysium contact:the nasalis and platysma muscles and; the vertical and transverse (or inferior longitudinal) tongue muscles. Therein, the functional vectors crossed at almost right angle. Also in adult tongue, the vertical and transverse muscle fibers sometimes (0–2 sites per section) crossed with an endomysium-to-endomysium contact. At the muscle crossing with an endomysium contact, the endomysium and basement membrane seemed to receive a friction stress between two muscles. Although some crossings might disappear due to high muscle activity after birth, not a few of them were likely to maintain. To minimize the mechanical stress, a minute nervous control of the timing, duration and strength of muscle contraction seemed to be necessary.

Striated muscle fiber crossings at almost right angle are known to exist in the face, soft palate, pharyngeal wall and tongue. We aimed to identify a specific interface tissue at the crossing. We observed histological sections from 22 halfheads of 12 near-term fetuses at 26–40 weeks (crown-rump length, 215–334 mm). For comparison, we also observed tongue frontal sections from 5 elderly cadavers (75–85 years old). At the angle of mouth as well as in the soft palate and pharyngeal wall, a solitary striated muscle fiber (e.g., levator) consistently crossed a fiber bundle of the antagonist muscle (e.g., depressor), but a solitary-to-solitary fiber interdigitation was unlikely with the antagonist muscle. Near the external nasal orifice as well as in the tongue intrinsic muscle layer, at every section, there was a crossing with an endomysium-to-endomysium contact:the nasalis and platysma muscles and; the vertical and transverse (or inferior longitudinal) tongue muscles. Therein, the functional vectors crossed at almost right angle. Also in adult tongue, the vertical and transverse muscle fibers sometimes (0–2 sites per section) crossed with an endomysium-to-endomysium contact. At the muscle crossing with an endomysium contact, the endomysium and basement membrane seemed to receive a friction stress between two muscles. Although some crossings might disappear due to high muscle activity after birth, not a few of them were likely to maintain. To minimize the mechanical stress, a minute nervous control of the timing, duration and strength of muscle contraction seemed to be necessary.

Striated muscle fiber crossings at almost right angle are known to exist in the face, soft palate, pharyngeal wall and tongue. We aimed to identify a specific interface tissue at the crossing. We observed histological sections from 22 halfheads of 12 near-term fetuses at 26–40 weeks (crown-rump length, 215–334 mm). For comparison, we also observed tongue frontal sections from 5 elderly cadavers (75–85 years old). At the angle of mouth as well as in the soft palate and pharyngeal wall, a solitary striated muscle fiber (e.g., levator) consistently crossed a fiber bundle of the antagonist muscle (e.g., depressor), but a solitary-to-solitary fiber interdigitation was unlikely with the antagonist muscle. Near the external nasal orifice as well as in the tongue intrinsic muscle layer, at every section, there was a crossing with an endomysium-to-endomysium contact:the nasalis and platysma muscles and; the vertical and transverse (or inferior longitudinal) tongue muscles. Therein, the functional vectors crossed at almost right angle. Also in adult tongue, the vertical and transverse muscle fibers sometimes (0–2 sites per section) crossed with an endomysium-to-endomysium contact. At the muscle crossing with an endomysium contact, the endomysium and basement membrane seemed to receive a friction stress between two muscles. Although some crossings might disappear due to high muscle activity after birth, not a few of them were likely to maintain. To minimize the mechanical stress, a minute nervous control of the timing, duration and strength of muscle contraction seemed to be necessary.