. Comparative zoology, structural and systematic : for use in schools and colleges. Zoology; Anatomy, Comparative; Physiology, Comparative. THE NERVOUS SYSTEM. 169 two cords with a ventral chain of ganglia—one pair, ap- parently a single one, for each segment. In the lower Arthropods, such as Crustacea, Centipedes, and Larval In- sects, the arrangement is substan- tially the same. In higher Insects and Crustacea, many of the gan- glia are fused together in the head and thorax, indicating a concen- tration of organs for sensation and locomotion. In Vertebrates, the nervous system is more highly
. Comparative zoology, structural and systematic : for use in schools and colleges. Zoology; Anatomy, Comparative; Physiology, Comparative. THE NERVOUS SYSTEM. 169 two cords with a ventral chain of ganglia—one pair, ap- parently a single one, for each segment. In the lower Arthropods, such as Crustacea, Centipedes, and Larval In- sects, the arrangement is substan- tially the same. In higher Insects and Crustacea, many of the gan- glia are fused together in the head and thorax, indicating a concen- tration of organs for sensation and locomotion. In Vertebrates, the nervous system is more highly developed, more complex, and more concen- trated than in the lower forms. In fact, there are some parts, as the brain, to which wTe find nothing homologous in the Invertebrates; and while the actions of the lat- ter are mainly, if not wholly, au- tomatic, those of backboned ani- mals are voluntary. Its position, moreover, is peculiar, the great mass of the nervous matter being accumulated on the dorsal side, and enclosed by the neural arches of the skeleton. The brain and spinal cord lie in the cavity of the skull and spinal column, wrapped in three membranes. Both consist of gray and white nervous matter; but in the brain the gray is on the out- side, and the white within ; while the white of the spinal cord is external, and the gray in- ternal. Both are double, a deep fissure running from the. Fig. 137.—Human Brain and Spinal Cord, one fifth natural size: a, great longitudinal fissure; b, an- terior lobe ; c, middle lobe; d, medulla oblongata; e, cerebel- lum ; /, first spinal nerve; g, brachial plexus of nerves supply- ing the arms; h, dorsal nerves; i, lumbar nerves; k, sacral plexus of nerves for the limbs ; I, cauda equina: the figures indicate the twelve pairs of cranial nerves, of which 1 is olfactory, 2 optic, and 8 Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1883
