. A treatise on anatomy, physiology, and hygiene : designed for colleges, academies, and families. t*nerve. 7, The third pair of nerves. 8, The pons varol,,. 9, Thefourthj«rfnerves 10 The lower portion of the medulla oblongata. It, U, The spinal cord.~ Spta. nerves. 13, 13, The brachia. plexus. 14, 14, The lumbar and , 758. How many pairs of nerves issue from the spinal cord ? Explain128. Fig. 129. ^^ 342 ANATOMY, PHYSIOLOGY, AND HYGIENE. roots ; an anterior, or motor root, and a posterior, or sensitiveroot. Each nerve, when minutely examined, is found to con-sist of an aggregate
. A treatise on anatomy, physiology, and hygiene : designed for colleges, academies, and families. t*nerve. 7, The third pair of nerves. 8, The pons varol,,. 9, Thefourthj«rfnerves 10 The lower portion of the medulla oblongata. It, U, The spinal cord.~ Spta. nerves. 13, 13, The brachia. plexus. 14, 14, The lumbar and , 758. How many pairs of nerves issue from the spinal cord ? Explain128. Fig. 129. ^^ 342 ANATOMY, PHYSIOLOGY, AND HYGIENE. roots ; an anterior, or motor root, and a posterior, or sensitiveroot. Each nerve, when minutely examined, is found to con-sist of an aggregate of very delicate filaments, enclosed in acommon cellular envelope. 759. The anterior roots arise from a narrow white lineupon the anterior columns of the spinal cord. The posteriorroots arise from a narrow gray band formed by the internalgray substance of the cord. They are larger, and the fila-ments of origin more numerous than those of the anteriorroots. A ganglion is found upon each of the posterior rootsin the openings between the bones of the spinal column throughwhich the nerve Fig. 130. A section of the spinal cord, surrounded by its sheath. B, A spinalnerve, formed by the union of the motor root (C) and the sensitive root (D.) At D,the ganglion upon this root is seen. 760. After the formation of the ganglion, the two rootsunite, and constitute a spinal nerve, which passes through theopening between the vertebras on the sides of the spinalcolumn. The nerves divide and subdivide, until their minutefilaments ramify on the tissues of the different organs. 7-59. Give the origin of the anterior roots. Of the posterior roots. In•what respect do the posterior roots differ from the anterior ? 760. Whendo the two roots unite, and where do they pass ? ANATOMY OF THE NERVOUS SYSTEM. 343 761. The spinal nerves are divided into — Cervical, 8 pairs, Dorsal, 12 Lumbar, 5 Sacral, rf 6 762. The four lower cervical and upper dorsal pass intoeach other, and then separate to
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