Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: D: Digastricus (Posterior belly)

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Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: D

Digastricus (Posterior belly)

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

A close relationship exists between the posterior belly of digastricus and the stylohyoid. Both are also innervated by the facial nerve. One or the other may fail to separate from the common mass of mesenchyme, from which they are derived.

A bundle of muscle fibers sometimes pass from the tip of the styloid process to the angle of the mandible, forming what may be termed stylomandibularis. The posterior belly of digastricus may originate from any part of the mastoid groove or even from the outer portion of the superior nuchal line. Occasionally, it fuses with the stylohyoid. In certain cases, if the anterior belly does not differentiate from the stylohyoid, the posterior belly inserts onto the angle of the mandible instead of the hyoid bone. Fasiculi may also pass from either belly (posterior or anterior) to neighboring structures.

Digastricus is usually divided by a tendinous inscription. A case of a "digastric muscle" with no connection has been reported. The anterior belly arose from the digastric fossa and inserted on the side of the tendinous hyoid body and the posterior belly arose from the mastoid incisura and inserted on the styloid process.

A trigastric muscle, with the third head arising from the inferomedial aspect of the mandible and inserting on the intertendon has been reported. Another form of trigastric involved the splitting of stylohyoideus, permitting passage of the external carotid with its facial and occipital branches. The more superficial portion of the muscle accompanied the posterior belly of the digastric inserted into the intertendon of the digastric muscle.

Syn.: See Digastricus (anterior belly).

References

See m. digastricus (anterior belly).

See Corsy, Curnow, Dratsch, Focacci,and Gruber references.

Jordan, J. (1963) On the deep stylohyoid muscle in man. Folia Morphol. (Warsaw) 22:7-10.

Macalister, A. (1871) The varieties of the styloid muscles. J. Anat. Physiol. 5:28-31.

Perrin, J.B. (1871) A peculiar additional digastric muscle. J. Anat. Physiol. 5:251-256.

Thiel, W. (1954-55) Eine seltene Varietät des Venter mastoideus m. biventeris und ihre phylogenetische Deutung. Anat. Anz. 101:16-23.

Weber, A. (1918) Signification du muscle stylohyoidien profound. Soc. Biol., Comptes Rendus Hebdomadaires des Séances et Mémories. 81:816-817.

West, S.H. (1874) A peculiar digastric muscle - a variety of occipito-hyoid. J. Anat. Physiol. 8:150-151.

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