. Comparative anatomy. Anatomy, Comparative. THE NERVOUS SYSTEM 517 only by dorsal and ventral nerve roots, but also by external dorso-lateral and ventro-Iateral grooves or sulci, which extend lengthwise of the cord. The medullary sheaths of the fibers which compose the funiculi develop at different times in ontogenesis as the fibers come into functional activity. By the study of the time of myelination of fibers and their degeneration after they are cut, it has been learned that fibers of similar origin and function occur in bundles or tracts. Each funiculus consists of a number of such tract
. Comparative anatomy. Anatomy, Comparative. THE NERVOUS SYSTEM 517 only by dorsal and ventral nerve roots, but also by external dorso-lateral and ventro-Iateral grooves or sulci, which extend lengthwise of the cord. The medullary sheaths of the fibers which compose the funiculi develop at different times in ontogenesis as the fibers come into functional activity. By the study of the time of myelination of fibers and their degeneration after they are cut, it has been learned that fibers of similar origin and function occur in bundles or tracts. Each funiculus consists of a number of such tracts, together with groups of tracts or fasciculi. A tract or a fasciculus may contain either ascending sensory fibers or PARIETAL LOBE-^>; INTERNAL CAPSULE CEREBRAL PEDUNCLE TEMPORAL LOBE CORTICAL MOTOR AREA CAUDATE NUCLEUS LENTICULAR NUCLEUS VENTRAL CEREBRO-SPINAL TRACT. LATERAL CEREBRO-SPINAL TRACT. 't-VENTRAL ROOT OF SPINAL NERVE SPINAL CORD Fig. 431.—Diagram of the descending (pyramidal) conduction paths. (Redrawn after Morris.) descending motor fibers. A fasciculus may contain both kinds. Fibers may have their origin or termination at any level and relatively few extend the entire length of the cord. (Fig. 430) Among the more important ascending fiber tracts are: The fasciculi gracilis and cuneatus, which consist chiefly of sensory fibers from the dorsal roots. Most of these sensory neurites connect with neurones in the spinal cord, chiefly with association neurones of the Golgi type II. Those which reach the brain have synaptic relations with secondary neurones in the wall of the medulla oblongata. The fasciculus spinocerebellaris dorsalis, formed by neurites of ganglion cells in the nucleus dorsalis or Clark's column of the cord. These fibers reach the cerebellum by way of the restiform Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may
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