Anatomy of the Middle Mediastinum

• pericardium
• fibrous pericardium - outer surface; protects against sudden overfilling; attached to diaphragm, so affected by breathing
• serous pericardium - mesothelial layer; allows for smooth sliding
• parietal layer - inner lining of the fibrous layer
• visceral layer (epicardium) - outer lining of heart
• pericardial cavity - space between visceral and parietal layers

• transverse pericardial sinus - lies posterior to aorta and pulmonary trunk
• oblique pericardial sinus - posterior to heart, U shaped recess formed by pulmonary veins and inferior vena cava

• ligamentum arteriosum - connects aortic arch and pulmonary trunk; remnant of ductus arteriosus
• left vagus nerve - passes over lateral aspect of aorta; runs medial to phrenic
• recurrent laryngeal nerve - branch of the vagus; runs under ligamentum arteriosum then superiorly

• ascending aorta
• pulmonary trunk
• inferior vena cava
• superior vena cave
• pulmonary veins - left and right, superior and inferior

• coronary (atrioventricular) groove (sulcus) - runs obliquely around heart; separates atria and ventricles
• anterior ventricular groove - separates ventricles on anterior side
• posterior ventricular groove - separated ventricles on posterior side

• left coronary artery - originates from ascending aorta
• orifice of left coronary artery - origin of LCA
• anterior interventricular branch - travels anterior interventricular sulcus to apex
• circumflex branch - follows coronary sulcus to posterior aspect of LV

• right coronary artery - follows coronary sulcus to right aspect of heart
• anterior right atrial branch - arises close to origin of RCA; runs under right auricle along anteromedial wall of atrium
• marginal branch - runs on anterior aspect of RV
• posterior interventricular branch - runs down posterior interventricular sulcus

• coronary sinus - posterior along coronary sulcus; empties into RA; most veins in heart are tributaries
• great cardiac vein - main branch of coronary sinus; runs anteroirly and then down with LAD
• middle cardiac vein - branches near opening into right atrium, runs on posterior interventricular sulcus

• aortic valve - three cusps: left, right, posterior (non-cornonary)
• nodule - fibrous thickening at middle of free margin
• pulmonary valve - three cusps: left, right, anterior

• right atrium - smooth posterior wall; rough anterior wall; fed by vena cavae and coronary sinus
• pectinate muscles - on anterior atrial wall
• crista terminalis - vertical ridge separates anterior and posterior walls along line of vena cavae
• valve of coronary sinus
• atrioventricular (tricuspid) orifice - surrounded by fibrous ring (anulus)
• fossa ovalis - depression on interatrial wall; site of closed foramen ovale
• right ventricle
• tricuspid valve - anterior, posterior, septal leaflets
• chordae tendineae - connect leaflets and papillary muscles
• anterior: largest; connects to anterior and posterior leaflets
• posterior: connects posterior and septal leaflets
• septal: small and numerous; connect septal and anterior cusps
• trabeculae carneae - muscular ridges
• septomarginal trabecula (moderator band) - stretches from interventricular septum to base of anterior papillary muscle
• orifice of pulmonary trunk
• conus arteriosis (infundibulum) - cone shaped portion of the orifice; funnel to pulmonary trunk

• left atrium - fed by four pulmonary veins; smooth except for small pectinate muscles in auricle
• left atrioventricular (mitral) orifice
• foramen ovale - usually seen as a curved ridge

• left ventricle - higher pressure bulges interventricular wall out into RV
• mitral valve - two leaflets: anterior, posterior; two papillary muscles: anterior, posterior
• trabeculae carneae
• muscular part of the interventricular septum
• membranous part of the interventricular septum - fingernail size; just inferior to attached margins of right and non coronary cusps of aortic valve; last septum to close in development