Midsagittal perspective of endonasal anatomy and the ventricular system. The lateral wall of the nasal cavity is not flat, and consists of scroll-like projections of bone called conchae or turbinates. The superior and middle turbinates are features of the ethmoid bone while the inferior turbinates are separate facial bones that articulate with the maxillae. Inferior to the turbinates are meatuses (superior, middle, inferior) for drainage of the paranasal sinuses and nasolacrimal duct. Posterior ethmoidal air cells drain into the superior meatus. The frontal, anterior and middle ethmoidal air cells, and maxillary sinuses drain into the middle meatus, and the nasolacrimal duct drains tears into the inferior meatus. Posterior to the superior tubinate is the sphenoethmoidal recess where the sphenoid sinus drains. The pituitary gland is located within the hypophyseal fossa in the superior aspect of the body of the sphenoid. Also in this view, the ventricular system of the brain can be seen. The right lateral ventricle (as well as the left lateral ventricle) communicates with the midline third ventricle via the foramen of Monro. The massa intermedia is a variably present flattened band of tissue that connects the right and left thalami across the midline of the third ventricle. The third ventricle opens to the cerebral aqueduct within the midbrain, which continues to the fourth ventricle located posterior to the pons and medulla. (Image courtesy of AL Rhoton, Jr.)