The vagus or pneumogastric nerves are the longest of the cranial nerves, and they are remarkable for their almost vertical course, their asymmetry, and their extensive distribution, for, in addition to supplying the lung and stomach, as the name ' pneumo-gastric ' indicates, each nerve gives branches to the external ear, the pharynx, the larynx, the trachea, the oesophagus, the heart, and the abdominal viscera. They are commonly referred to as the tenth pair of cranial nerves.
The oculo-motor or third cranial nerve is a purely motor nerve. Each supplies seven muscles connected with the eye, two of which, the sphincter of the iris and cihary muscle, are within the ocular bulb.
The olfactory nerve-fibers are the central processes of the bipolar olfactory nerve cell-bodies situated in the olfactory region of the nasal mucous membrane. In man, the olfactory region comprises the epithelium upon the superior third of the nasal septum and that upon practically the whole of the superior nasal concha.
The fibers of the optic nerve are the central processes of the ganglion cells of the retina. Within the ocular bulb they converge to the optic papilla, where they are accumulated into a rounded bundle, the optic nerve.
The vestibular nerve is purely sensory. With the peripheral processes of its cells of origin terminating in the neuro-epithelium of the semicircular canals and the vestibule, and their central processes conveying impulses which are distributed to the gray substance of the cerebellum and spinal cord, the nerve comprises a most important part of the apparatus for the equilibration of the body.
The hypoglossal nerves are exclusively motor; they supply the genio-hyoidei and the extrinsic and intrinsic muscles of the tongue except the glosso-palatini. They are usually designated as the twelfth pair of cranial nerves.
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