Posterior Belly of the Diagastric Muscle

  • The posterior belly, longer than the anterior belly, arises from the mastoid notch which is on the inferior surface of the skull, medial to the mastoid process of the temporal bone. It lies posterior to the parotid gland and the facial nerve. The mastoid notch is a deep groove between the mastoid process and the styloid process. The mastoid notch is also referred to as the digastric groove or the digastric fossa.
  • The posterior belly is supplied by the digastric branch of facial nerve.
  • The digastric muscle stretches between the mastoid process of the cranium to the mandible at the chin, and part-way between, it becomes a tendon which passes through a tendinous pulley attached to the hyoid bone. It originates from the second pharyngeal arch
  • “The resident’s friend”: Few qualms are as useful as the posterior belly of the digastric muscle.

It helps us to recognize…

  • Nerves: its cranial border is related to the facial nerve (VII PC), its caudal border to the spinal nerve or accessory (XI PC). 
  • Vessels: on its ventral face rests the facial vein (posterior) or the retromandibular vein, on its dorsal face the facial artery.

They constitute, together with the omohyoid muscle (also morphologically digastric), the “protectors” of the internal jugular vein. Both muscles stand in the way of the surgeon’s scalpel to the junction of the vascular axis of the neck (the posterior belly does so at level IIa, the intermediate tendon of the omohyoid at the boundary between III-IV).

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