Pronator teres accessorius: A new variant in flexor antebrachial musculature.

Muscles of flexor compartment of forearm have a common origin from medial epicondyle of humerus. Additional bellies of flexor muscles are commonly reported but presence of supernumerary muscles is an infrequent phenomenon. The present study describes an unusual muscle mass in flexor compartment of forearm simulating pronator teres. During routine dissection the upper limb of a 50 years old male cadaver, a supernumerary muscle was found on left side of the upper limb in the flexor compartment. The origin of the muscle was 2cm wide and aponeurotic in nature and attached to an oblique line extending from the inferior surface of the medial epicondyle and the medial surface of the trochlea. It was inserted on an oblique line 2.5cm wide on the radius in area between supinator superiorly and flexor digitorum profundus inferiorly. Existence of accessory muscles, which connect flexor muscles, could be explained embryologically by incomplete cleavage of flexor mass during development. The flexor muscles of the forearm develop from the flexor mass which subsequently divides into two layers: superficial and deep. The deep layer gives rise to flexor digitorum superficialis, flexor digitorum profundus and flexor pollicis longus. These supernumerary muscles are extremely rare entities and probably represent deranged embryological development or the process of atavism in which the anomalous part persist for a longer time in the tree of evolution.

Bilateral clavicular attachment of omohyoid muscle.

Omohyoid muscle present in cervical region is of particular importance to anatomists as it defines anteriorly the carotid triangle and divides the posterior cervical triangle. It has superior and inferior bellies and an intermediate common tendon. Like sternohyoid, sternothyroid and thyrohyoid muscles, omohyoid is also an infrahyoid muscle, but it differs from them in its course. The infrahyoid muscles are formed from a muscle primordium occurring in the anterior cervical area. Anderson (Anderson, 1881) theorized that the superior belly of the omohyoid muscle is a true infrahyoid muscle, whereas the inferior belly most likely shares a common embryology with the subclavius muscle. In the present study, during routine dissection in the neck region of an adult male cadaver of 50 years age, an anomalous origin of inferior belly of omohyoid with absence of intermediate tendon was observed bilaterally. It was arising from clavicle on both sides. Both the muscle bellies were measured from the lateral end of fascial sling. The inferior belly of omohyoid extending from the lateral margin of sling to clavicular surface was measured 3.3cm in length on left side and 3.6cm on right side. The omohyoid is important in neck dissections because it is considered as an ideal landmark for level III and IV lymph node metastases. Knowledge of variations of this muscle is very important for surgeries in neck region because of its close relation to the internal jugular vein and brachial plexus. Its crucial relationship to vascular structures in the neck makes it an important landmark during neck surgeries.