Customarily, the cranial nerves are described as comprising twelve pairs and each is referred to by number.

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.

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 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 glosso-palatine nerve (sensory root or pars intermedia of facial, nerve of Wrisberg) contains both sensory and motor fibers.

The Sympathetic Ganglia of the Head and Their Associations with the Cranial Nerves

The sympathetic system of the head, like that of the remainder of the body described below, is arranged in the form of a continuous gangHated plexus subdivided into sub-plexuses.

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 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.

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