530 



TEXT-BOOK OF PHYSIOLOGY. 



three distinct tracts: e.g., the pyramidal tract, the fronto-cerebellar tract, 

 and the occipito-temporo-cerebellar tract (Fig. 245). 



The pyramidal or motor tract descends from the cortex of the cerebrum 

 mainly from the gyms anterior to the central fissure, passes through the 

 posterior one-third of the anterior segment and the anterior two-thirds of the 

 posterior segment of the internal capsule, the middle two-fifths of the crusta, 

 behind the transverse fibers of the pons, to become the anterior pyramid of 

 the medulla, beyond which it divides into the direct and crossed pyramidal 

 tracts of the cord. In its course some of the fibers and their collaterals 

 arborize around efferent cells from the anterior extremity of the aqueduct of 

 Sylvius to the termination of the spinal cord. 



FIG. 245. SCHEMA OF THE PROJECTION FIBERS OF THE CEREBRUM AND OF THE PEDUNCLES OF 

 THE CEREBELLUM; LATERAL VIEW OF THE INTERNAL CAPSULE. A, Tract from the frontal gyri 

 to the pons nuclei, and so to the cerebellum (frontal cerebro-cortico-pontal tract) ; B, the motor 

 (pyramidal) tract; C, the sensory (body sense) tract; D, the visual tract; E, the auditory tract; F, 

 the fibers of the superior peduncle of the cerebellum; G, fibers of the middle peduncle uniting with 

 A in the pons; H, fibers of the inferior peduncle of the cerebellum; /, fibers between the auditory 

 nucleus and the inferior quadrigeminal body; K, motor (pyramidal) decussation in the bulb; Vt, 

 fourth ventricle. The numerals refer to the cranial nerves. (Modified from Starr.) 



The fronto-cerebellar tract descends from the cortex of the frontal gyri 

 of the anterior lobe, passes through the anterior portion of the anterior 

 segment of the internal capsule, the inner fifth of the crusta to the poris, 

 where its fibers terminate or arborize around the nucleus pontis of the same 

 and opposite sides. 



The occipito-temporo-cerebellar tract descends from the occipital and 

 temporal lobes, passes to the inner side of the lenticular nucleus, and con- 

 tinues downward on the outer side of the crusta, occupying about one-fifth of 

 its bulk, to the pons, where its fibers also arborize around the nucleus pontis 

 of the same and opposite sides. By means of fibers in the middle peduncle 

 eseht descending fibers are brought into relation with the cerebellum. 



