. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. The Dominating Factor 687 /Dorsal Sulcus (Fissure) Dorsal Median Septum *~"^8$J5 Dorsal Horn—w| Lateral Column P?i«^feg Nucleus Dorsalis"" (Clarkes Column). Dorsal Funiculus -Dorsal Commissure Ventral Horn '---Lateral Funiculus ' Central Canal " Ventral Commissure c2&- 'Ventral Funiculus Ventral Fissure Fig. 616. Cross section through the fourth thoracic segment of the human spinal cord. (From Kappers, Huber and Crosby, The Compara-
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. The Dominating Factor 687 /Dorsal Sulcus (Fissure) Dorsal Median Septum *~"^8$J5 Dorsal Horn—w| Lateral Column P?i«^feg Nucleus Dorsalis"" (Clarkes Column). Dorsal Funiculus -Dorsal Commissure Ventral Horn '---Lateral Funiculus ' Central Canal " Ventral Commissure c2&- 'Ventral Funiculus Ventral Fissure Fig. 616. Cross section through the fourth thoracic segment of the human spinal cord. (From Kappers, Huber and Crosby, The Compara- tive Anatomy of the Nervous System of Vertebrates, including Man, copyright 1936, by permission of The Macmillan Company, publishers.) the several branches of the spinal nerves to the surface of the body or to the internal organs. Their neurites complete the dorsal roots and extend into the cord where many of them grow forward to the brain by way of the dorsal part of the white matter. These myelinated neurites also have a neurolemmal sheath up to the point where they enter the cord. Thus the alar plate, the dorsal part of the lateral wall of the cord, is given over to cells and fibers of afferent, or sensory, neurons, concerned with bringing in impressions from without, while the ventral part, or basal plate, be- comes headquarters for efferent, or motor, neurons, that convey messages outward to various effector mechanisms. As the sensory fibers enter the cord those from the outer surface of the body, somatic sensory component, are more medial than those from the internal organs, visceral sen- sory component (Fig. 617). In like man- ner the cell bodies of the somatic motor component, which supplies the voluntary muscles, are in the more medial ventral horn while those of the visceral motor component, running chiefly to the autonomic nervous system, are in the lateral column, the more lateral part of the gray matter of the basal plate. Thus the gray matter includes. Please
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