599 Int. J. Morphol., 24(4):599-600, 2006. The Subclavius Posticus Muscle: its Phylogenetic Retention and Clinical Relevance Músculo Subclavio Posticus: Presencia Filogenética y Relevancia Clínica Prakash Shetty; Mangala M. Pai; Latha V. Prabhu; Rajanigandha Vadgaonkar; Soubhagya R. Nayak & R. Shivanandan SHETTY, P.; PAI, M. M.; PRABHU, L. V.; VADGAONKAR, R.; NAYAK, S. R. & SHIVANANDAN, R. The subclavius posticus muscle: its phylogenetic retention and clinical relevance. Int. J. Morphol., 24(4):599-600, 2006. SUMMARY: During routine dissection practice a supernumerary muscle was found on the right side infraclavicular region of a male cadaver. This muscle was arising from the superior surface of the first rib and its coastal cartilage and inserted to a thick ligament that extended from the medial end of the suprascapular notch to the capsule of the acromioclavicular joint. This accessory muscle slip was innervated by a branch from the nerve to subclavius. According to its location and innervation the aberrant muscle was considered to be the subclavius posticus. The anatomic relationships of the muscle make it clinically significant. KEY WORD: Subclavius posticus muscle; Muscular variation; Hypobranchial musculature; Accessory phrenic nerve. INTRODUCTION The subclavius posticus (chondroscapularis) is an aberrant muscle described by Rossenmuller in 1800 (Akita et al., 2000). This excess intermediary muscle between the subclavius and inferior belly of omohyoid appears to be more closely related to the subclavius, based on the innervation of this muscle (Akita et al., 1996). Conventionally, the proximal attachment is to the first rib and distally to the transverse scapular ligament or/and to the superior margin of the scapula. The muscle described in this case morphologically is suggestive of subclavius posticus however presents a variable anatomy. CASE REPORT An aberrant muscle, subclavius posticus, was revealed in the left infraclavicular region of an adult male cadaver during routine dissection studies. This muscle lying inferior to the subclavius originated from the superior surface of the sternal end of first rib and its coastal cartilage. The muscle belly coursed dorsolaterally beneath the clavicle crossing the axillo- subclavian vessels and the cords of brachial plexus. It then inserted into a considerably thick additional ligament that extended from the medial margin of the suprascapular notch, immediately medial to the attachment of inferior belly of omohyoid and laterally blended with the capsule of the acromioclavicular joint. The suprascapular artery coursed above the ligament whereas the nerve passed below, however both the artery and nerve ran superior to the suprascapular (transverse scapular) ligament. The accessory muscle measuring 16.6 cm in length received innervation from nerve to subclavius. The presence of accessory phrenic nerve was also noted. Case Report Department of Anatomy, Center for Basic Sciences, Kasturba Medical College, Bejai, Mangalore- 575004, Karnataka, India. Fig. 1 This photograph shows the left infraclavicular region. The subclavius muscle along with the subclavius posticus is visualized. Note the course of the axillary artery (AA) and the cords of brachial plexus (BP) beneath the above mentioned muscle slip.