Gross examination of the chimpanzee skull revealed that: there are three ethmoidal sinuses; the sphenoid sinus is immense and is divided into a superior and inferior part; the huge maxillary sinus contains a distinct bony canal for the nasolacrimal duct; the anterior and middle ethmoidal sinuses drain into the superior meatus; the frontal sinus drains via the middle ethmoid; the posterior ethmoid and sphenoid sinuses open into the sphenoethmoidal recess and also communicate with each other; the maxillary sinus opens into the middle meatus through a large ostium; the nasolacrimal duct drains into the inferior meatus; the mastoid process is small but contains a central cavity which communicates with the middle ear; the broad and smooth planum tympanum serves as the floor of the external auditory canal, the latter forming an angle of 30° with the horizontal; the tympanic membrane makes an angle of 30° with the floor of the canal and is deeply recessed antero-inferiorly; except for the extreme slope of the tympanic membrane and the malleus, the middle ear is similar to man; the inner ear is likewise similar; the carotid artery and the large carotid plexus lie in a definite osseous tube surrounded by pneumatized bone but attached to the periotic capsule; the chimpanzee is subject to otitis media.