Intermediate morphologies between normal and anomalous morphologies of the superior belly of the omohyoid muscle (Om) were macroscopically and stereomicroscopically observed in 34 cadavers (24 males and 10 females aged between 51 and 97 years; average age 71.0 years) for anatomical practice, which had been preserved in the Department of Morphological Biology, Ohu University School of Dentistry. The intermediate morphologies were classified into four types on the basis of the developmental degree of the muscle fibers and the number and origin of the belly as follows: type 1, the anterior margin of the belly was unclear owing to poor myofiber development; type 2, the superior belly was composed of a posterior large belly and an anterior small belly; type 3, composed of three to five bellies, with the bellies arranged in a roof tile-like morphology; and type 4, the belly was composed of two bellies arranged anterior-posteriorly parallel to each other (the anterior belly was found to be the inferior belly that had developed and reached the superior belly area). For the intermediate morphologies of the Om superior belly observed in the present study, although type 4 was due to the development of an inferior belly, the other three types were considered to be caused by the poor development of the myofibers in the formation process and by the division of the superior belly into two muscles, or secondary lamellar division of the belly with growth.
Muscle bundles of the transverse and vertical muscles of the tongue become flat when they enter the longitudinal muscle layers of the tongue, where they form a tunnel-like structure that surrounds the longitudinal muscle of the tongue. However, the three-dimensional architecture of longitudinal muscle fibers of the tongue has not been clarified. In the present study, we evaluated the function of the intrinsic muscles of the tongue by studying the three-dimensional architecture of the longitudinal muscle. Muscle bundles of the longitudinal muscle of the anterior part of a rabbit's tongue were exposed by the chemical-maceration and modified chemical-maceration methods and examined by scanning electron microscopy. In the longitudinal muscle of the tongue, muscle bundles running in the anteroposterior direction were arranged at regular intervals. These muscle bundles bifurcated or ramified at a sharp angle at each level from the superficial layer to the deep layer and joined or fused with adjacent muscle bundles. In addition, these ramified muscle bundles ran obliquely into shallower or deeper layers of the muscle, as well as in the same plane. Consequently, the longitudinal muscle of the tongue as a whole had a three-dimensional mesh-like structure. The transverse and vertical muscles of the tongue entered this mesh-like structure of muscle bundles of the longitudinal muscle as flat muscle bundles. The transverse and vertical muscles showed no ramification in the center of the tongue, where there is no longitudinal muscle. These results suggest that the three intrinsic muscles of the tongue are interlaced with one another and are bound tightly in the longitudinal muscle. This structure may enable the dorsum of the tongue to harden for pressing food during mastication and shifting the food posteriorly for swallowing.
A case of a combined anomaly of persistent hypoglossal and proatlantal intersegmental arteries, proved on arteriogram obtained by the insertion of a needle into the common trunk of both arteries, is presented. In addition, a case of anomalous occipital artery arising from the internal carotid artery associated with an intracranial aneurysm and arteriovenous malformation is presented. Based upon analysis of the persistent proatlantal intersegmental artery and the anomalous occipital artery, we conclude that both arteries have an identical embryological origin.
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