. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 744 Biology of the Vertebrates. 10. Spinal Accessory Nerve (XI) The spinal accessory nerve, found only in amniotes, is composed entirely of visceral efferent fibers. Part of these fibers, arising from the posterior portion of the medulla and running to join the vagus, are probably represented in lower vertebrates by posterior root- lets of the vagus. The others, arising by a series of rootlets from the anterior cervical region of the spinal cord, are thoug
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 744 Biology of the Vertebrates. 10. Spinal Accessory Nerve (XI) The spinal accessory nerve, found only in amniotes, is composed entirely of visceral efferent fibers. Part of these fibers, arising from the posterior portion of the medulla and running to join the vagus, are probably represented in lower vertebrates by posterior root- lets of the vagus. The others, arising by a series of rootlets from the anterior cervical region of the spinal cord, are thought to correspond to spino-occipital nerves of lower forms. These fibers of spinal origin innervate the trapezius and sternocleidomastoid muscles. The fibers which join with the vagus are distrib- uted with it to the striated muscles of the pharynx and larynx and to the autonomic nervous system. 11. Hypoglossal Nerve (XII) The hypoglossal nerve is made up of somatic motor fibers which innervate the muscles of the tongue. Although it is found only in amniotes, it probably corresponds to some of the spino-occipi- tal nerves of fishes. The functions of the cranial nerves are cartooned in Figure 658. C D Fig. 658. The functions of the cranial nerves. A, smelling and seeing (I, II). b, smelling and seeing (I, II); conver- gence and accommodation (III); de- pression of eyeballs (III, IV); mastica- tion (V); salivation and tasting (VII, IX); swallowing (X, XII); tongue movements (VII). c, a moment of vigilance, with outward rolling of the eye (VI); facial and ear movements (VII); listening (VIII). d, digesting (X). The only omission is the spinal accessory (XI), supplying certain neck muscles which may have been used various times in this sequence. (As summarized by Dr. Stanley Cobb, in Stiles, The Nervous System and its Conservation. W. B. Saunders Co.) XI. THE AUTONOMIC NERVOUS SYSTEM Much of the routine work of the body, particularly of the circulatory and respiratory apparatus, of
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