The auricle, or pinna, is the visibly external portion of the ear, whose trumpet shape enables it to collect air vibrations. It consists of a thin plate of elastic cartilage with a tightly adherent covering of skin. The external auditory canal (EAC) is an S-shaped skin-lined tube that extends from the auricle to the tympanic membrane. The outer one-third of the EAC is composed of an incomplete cartilaginous tube; its thick skin contains hair follicles and apocrine and sebaceous glands. The inner two-thirds of the canal is composed of bone covered by a thin layer of tightly adherent skin, which is easily torn by minimal trauma.
The blood supply to the external ear is derived from the posterior auricular, superficial temporal, and deep auricular arteries. Venous drainage of the external ear is into the superficial temporal and posterior auricular veins and then into the external jugular vein. The posterior auricular vein frequently connects to the sigmoid sinus, providing a route for extension of infection into the intracranial cavity.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.