Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 120 VERTEBRATA. cord. The lower Vertebrates with cold bloocl have a relatively small brain, the mass of which is still considerably smaller than that of the spinal cord. In the warm-blooded Vertebrates, on the other hand, this proportion is reversed, and the more markedly, the higher the organisation and grade of life of the animal in question. The spinal nerves arise in pairs from the spinal cord : each nerve has two roots—a dorsal sensory root and a ventral motor root. They correspond
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 120 VERTEBRATA. cord. The lower Vertebrates with cold bloocl have a relatively small brain, the mass of which is still considerably smaller than that of the spinal cord. In the warm-blooded Vertebrates, on the other hand, this proportion is reversed, and the more markedly, the higher the organisation and grade of life of the animal in question. The spinal nerves arise in pairs from the spinal cord : each nerve has two roots—a dorsal sensory root and a ventral motor root. They correspond in number with the vertebne, between which they pass out, so that the spinal cord repeats in a general manner the seg- mentation of the vertebral column. In the brain the arrangement of the nerves presents several com- plications which are further increased by the origin of two sensory nerves —the olfactory and optic. In spite of the differences in form
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