The heart is the pump that distributes oxygenated blood throughout the body and is enclosed in a sac known as the pericardium. The pericardial sac is made of the fibrous and serous pericardium. The heart has four chambers, which are divided by septums to prevent exchange of blood between adjacent chambers. The chambers of the heart are the right atrium, right ventricle, left artium, and left ventricle. The right atrium receives blood from the superior and inferior vena cavae. Blood then passes from the right atrium to the reight ventrical via the tricuspid valve. The right ventricle pumps blood into the pulmonary arteries for transport tot he lungs to receive oxygen. Following gas exchange, the pulmonary veins return the blood to the left atrium of the heart. The blood them passes through the bicuspid (mitral) valve before entering the left ventricle. The left ventricle pumps the blood into the aorta to be carried through arteries to the tissues of the body.

The middle mediastinum is the area bordered by the left and right pleural cavities. The major structures found within the middle division are the heart, the pericardium, the main bronchus, phrenic nerves, arch of the azygos vein, and the vessels coming out of the heart such as the aorta, pulmonary arteries, and veins. The arch of the aorta and the trachea are found in the superior mediastinum. The esophagus is found in the superior and posterior mediastinum.

The musculocutaneous nerve arises from the lateral cord of the brachial plexus. It innervates the biceps brachii, the coracobrachialis, and the brachialis muscle. All of these are muscles of the anterior arm. 

The crista terminalis is a specialized region in the upper part of the right atrium. It houses the sinoatrial (SA) node, which is responsible for initiating the electrical impulses that cause the heart to contract.

The tricuspid valve separates the right atrium and the right ventricle. The bicuspid, or mitral, valve is located between the left atrium and left ventricle. The pulmonary valve is a semilunar valve that prevents backflow of blood from the pulmonary veins into the right ventricle.

The pericardium lines the outside of the heart and serves as a protective covering sac that holds the heart in place within the mediastinum. The parietal pericardium layer is the superficial layer of the serous pericardium, while the visceral pericardium covers and adheres to the heart directly. The heart wall itself is composed of three layers. The outermost layer is the epicardium, which functions to lubricate the heart. The thick middle layer is the myocardium and is a specialized form of cardiac muscle responsible for continuously pumping out blood. Finally, the innermost layer of the heart is the endocardium, which serves a protective role in covering inner heart valves.

The common bile duct stems from the joining of the common hepatic duct and the cystic duct. The common hepatic duct comes from the left and right hepatic ducts and lobes of the liver. The cystic duct comes from the gall bladder. These two ducts become the common bile duct which drains into the duodenum.

The correct pathway of sound is from the outer portion of the ear, the pinna, to the auditory canal (the hole of the ear), to the eardrum, ossicles, and finally to the cochlea where the process of hearing actually beings. The structures prior to the cochlea are all involved in transmitting or "catching" sound and not interpretation. The cochlea is part of the inner ear. Note that the brain is where auditory processing actually occurs. 

Sebaceous glands are found within the dermis and produce sebum, an oily secretion that moisturizes skin and hair. The epidermis is the outermost layer of the skin and does not contain any glands, rather it consists of stratified epithelium and lacks a blood supply. The hypodermis is composed of adipose tissue, fibroblasts, and contains many blood vessels and nerves. There is no such thing as the extradermis.

The body is divided into the three cavities: cranial (commonly referred to as the skill, which contains the central nervous system), the thoracic (also known as the thorax, which contains all structures below the neck and above the diaphragm), and the abdominopelvic (sometimes may be divided into abdominal and pelvic, which contains the organs below the diaphragm, but above the lower limbs). Typically, cervical region refers to the neck or the "neck" of the cervix in females. The lumbar region refers to the five vertebrae lower back.