*The Cranial Nerves.*—From the under front surface of the brain, twelve pairs of nerves emerge and pass to the head, neck, and upper portions of the trunk. These, the cranial nerves, have names suggestive of their function or distribution and, in addition, are given numbers which indicate the order in which they leave the brain (Fig. 136). Unlike the spinal nerves, the cranial nerves present great variety among themselves, scarcely any two of them being alike in function or in their connection with different parts of the body. Several of them have to do with the special senses, and are for this reason very important. They connect the brain with the different parts of the head, neck, and trunk, as follows: 1. The first pair (_olfactory_ nerves; nerves of smell; afferent) connect with the mucous membrane of the nostrils (Fig. 136). 2. The second pair (_optic_ nerves; nerves of sight; afferent) connect with the retina of the eyes. 3. The third, fourth, and sixth pairs (_motores oculi;_ control muscles of the eyes; efferent) connect with the internal and external muscles of the eyeballs (Fig. 136). [Fig. 136] Fig. 136—*Diagram suggesting the distribution and functions of the cranial nerves* (Colton). See also Fig. 132. 4. The fifth pair (_trigeminal_ nerves; nerves of feeling to the face, of taste to the front of the tongue, and of control of muscles of mastication; afferent and efferent) connect with the skin of the face, the mucous membrane of the mouth, the teeth, and the muscles of mastication. 5. The seventh pair (_facial_ nerves; control muscles that give the facial expressions; efferent) connect with the muscles just beneath the skin of the face. 6. The eighth pair (_auditory_ nerves; nerves of hearing; afferent) connect with the internal ear. 7. The ninth pair (_glossopharyngeal_ nerves; nerves of taste to back of tongue and of muscular control of pharynx; afferent and efferent) connect with the back surface of the tongue and with the muscles of the pharynx. 8. The tenth pair (_vagus_, or pneumogastric, nerves; nerves of feeling and of muscular control; afferent and efferent) connect with the heart, larynx, lungs, and stomach. They have the widest distribution of any of the cranial nerves. 9. The eleventh pair (_spinal accessory_ nerves; control muscles of neck; efferent) connect with the muscles of the neck. 10. The twelfth pair (_hypoglossal_ nerves; control muscles of the tongue; efferent) connect with the muscles of the tongue.