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Sensory or Corticipetal Projection Fibers

olfactory, neurones, stria, nucleus, anterior, medial and fasciculus

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SENSORY OR CORTICIPETAL PROJECTION FIBERS The sensory or corticipetal projection fibers of the tegmentum comprise the medial, superior and lateral fillets; the spino thalamic tract; the brachium conjunctivum of the cerebellum; a part of the medial longitudinal bundle; and certain other ascending fibers of the formatio reticularis. Excepting a small number of fibers, all these bundles terminate in the basal ganglia; but the paths of conduction are continued through the internal capsule. The medial fillet carries impressions of the tactile and the muscular senses; the spino-thalamic tract con ducts tactile, pain and temperature impulses; while all varieties of common sensory impulses may be carried by the brachium conjunctivum cerebelli, its chief function appears to be the con duction of coordinating impulses to the red nucleus and thala mus. Chiefly through these three tracts, common sensory impressions arrive in the lateral nucleus of the thalamus. In the capsula interna the corticipetal projection fibers constitute the cortical fillet and the optic, acustic and gustatory radiations. The former end in the somesthetic area of the cerebral cortex, the latter in the visual, auditory and gustatory cortex.

The olfactory projection fibers are contained neither in the tegmentum nor in the internal capsule. They proceed from the nasal mucous membrane to the olfactory bulb, through the olfactory tract and its striae, directly to the cerebral cortex. The afferent olfactory neurones are of three orders, first, second and third. The first order neurones are the olfactory nerve neurones, which reach from the nasal mucous membrane to the stratum glomerulosum of the bulb. The second order are the mitral and brush neurones whose dendrites receive the first order neurones and whose axones form the olfactory tract; they terminate in the cortex of the tract, in the olfactory tri angle, the anterior perforated substance and the septum pellu cidum, where the bodies of the third order neurones are lo cated. The third order neurones form the olfactory strive: The lateral stria rises in the olfactory triangle and ends in the uncus hippocampi.

The intermediate stria is made up of four bundles—the olfacto-hippocampal of the fornix rises in the olfactory triangle, anterior perforated substance and septum pellucidum and ter minates in the hippocampal formation; the olfacto-amygdalate bundle rises in the anterior perforated substance and septum pellucidum and, partially decussating through the anterior commissure, runs through the stria terminalis to the nucleus amygdalx. As it ascends some of its fibers end in the anterior nucleus of the thalamus. The olfacto-habenular fasciculus and the olfacto-mesencephalic fasciculus form a part of the intermediate stria; they are described below with the reflex olfactory neurones.

The medial stria, the stria Lancisii, originates in the olfactory triangle and runs, perhaps with several relays, through the subcallosal and supracallosal gyri, the fasciola cinerea and gyrus subsplenialis, and the dentate fascia to the hippocampal formation (Retzius, \ginger, Elliot Smith, etc.).

Efferent Reflex Olfactory these neurones are associative, they belong to efferent chains that reach to motor nuclei and form intermediate links of reflex arcs; hence, they may be considered in this place.

hippocampo-mammillary fasciculus rises in the hippocampus, hippocampal gyrus, dentate fascia and gyrus cinguli (fibrin perforantes) and terminates in the medial nucleus of the mammillary body, chiefly on the same side but partly on the opposite side. The hippocampo-habenular fasciculus has the same origin. It runs through the crus and body of the fornix with the former bundle to the columna fornicis; there it turns backward and proceeds through the stria medullaris thalami and commissura habenularum to the opposite nucleus haben ulx—a few fibers end on the same side.

The olfacto-habenular fasciculus originates in the anterior perforated substance and septum pellucidum; ascending to the stria medullaris thalami it runs through that and the com missura habenularum to the opposite nucleus habenulm. Some of its fibers terminate in the tectum, especially in superior colliculi.

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