Retromandibular vein Ref: BDC Anatomy 4/e vol. III p157; Gray's Anatomy 40/e p441The Retromandibular vein lies superficial to the posterior belly of digastric.Structures lying deep to the posterior belly of digastric are:a.Transverse process of atlasb.Muscles- hyoglossus, superior oblique and the rectus capitis lateralisc. Aeries- internal carotid, external carotid, lingual, facial and occipital aeriesd.Vein- internal jugular veine. Nerves- vagus, accessory and hypoglossal cranial nerves.The digastric muscle (named digastric as it has two bellies) lies below the body of the mandible, and extends, in a curved form, from the mastoid process to the symphysis menti. C-,11.fvn-*/The digastric muscle consists of two fleshy bellies united by an intermediate rounded tendon. The two bellies of the digastric muscle have different embryological origins, supplied by different cranial nerves.Posterior belly- The posterior belly arises from the mastoid notch on the medial surface of the mastoid process of the temporal bone, and passes downwards and forwards.- The posterior belly is supplied by the digastric branch of facial nerve.Anterior belly- The anterior belly arises from the digastric fossa, on the base of mandible, close to the symphysis, and passes downward and backward.- The anterior body is supplied by the mylohyoid nerve, a branch of the inferior alveolar nerve, itself a branch of the mandibular division of the trigeminal nerve.Intermediate tendon- The two bellies end in an intermediate tendon which perforates the Stylohyoid muscle, and run in a fibrous loop attached to the body and the greater cornu of the hyoid boneAction- When the digastric muscle contracts, it acts to elevate the hyoid bone.- If the hyoid is being held in place (by the infrahyoid muscles), it will tend to depress the mandible (open the mouth).