744 COURSE OF THE TRACTS FOR VOLUNTARY MOVEMENTS. 



The fibers that pass from the thalamus and the quadrigeminate bodies through 

 the tegmentum of the cerebral peduncle (6, 6, 7) represent, according to Meynert, 

 reflex paths. Accordingly, the cerebral masses mentioned would be the centers 

 for certain extensive coordinated reflexes. This is indicated by the fact that after 

 destruction of the paths for the conduction of voluntary impulses in animals the 

 technical perfection of the movements, in so far as these are induced by reflex 

 activity, remains intact. The fibers named pass in the spinal cord at first down- 

 ward upon the same side (m) , but they probably cross below in the spinal cord 

 itself. 



Finally there passes out of the entire gray matter of the central cavity a 

 group of fibers that constitute the projection-system of the third order. These are 

 the peripheral nerves, sensory and motor. They exhibit in their totality an in- 

 crease of fibers as compared with the number of fibers in the projection-system 

 of the second order. 



The cerebellum represents a separate central organ of special character con- 

 taining gray matter in part as a cortical layer and in part as central accumulations. 

 It is connected with the cerebrum (i) through the superior cerebellar peduncles, 

 formed of fibers from the system of the corona radiata, passing then into the 

 tegmentum, and reaching the cerebellum after total decussation; and (2) through 

 the middle cerebellar peduncles to the pons and from the pons through the cerebral 

 peduncles to the hemispheres. The cerebellum is connected also with the spinal 

 cord, namely (i) with the posterior column (cuneate and gracile columns) and (2) 

 with the anterior column (restiform body). The two hemispheres are connected 

 by the transverse commissural fibers of the pons. 



The distribution of the cerebral vessels is deserving of consideration from the 

 practical standpoint. The artery of the fossa of Sylvius supplies the motor areas 

 of the cortex in animals in man the paracentral lobule is supplied by the anterior 

 cerebral artery. The region of the third frontal convolution, which is of such 

 importance for the function of speech, is supplied by a special branch of 

 the Sylvian artery. Those portions of the frontal lobe, injury of which, according 

 to Ferrier, causes derangement of intelligence, are supplied by the anterior cerebral 

 artery. The middle cerebral artery supplies the internal capsule, with the excep- 

 tion of its most posterior portion, which, together with the uncinate gyrus, is 

 supplied by the anterior choroid artery. Those portions of the cortex, lesions of 

 which, according to Ferrier, give rise to hemianesthesia, are supplied by the pos- 

 terior cerebral artery. Isolated anemia of this area is believed to have some 

 connection with melancholic states in human beings. 



Course of the Tracts for Voluntary Movements: Psychomotor or 

 Corticomuscular Paths (Fig. 255). From the motor regions of the cere- 

 bral cortex, from which impulses are sent for voluntary movements in 

 the distribution of the cerebral and spinal motor nerves, the fibers that 

 constitute the pyramidal tracts (Fig. 255, a, 6, c) pass through the 

 anterior two-thirds of the posterior limb of the internal capsule (Fig. 255, 

 G.i; Figs. 263, 264), and then through the crusta of the cerebral peduncle 

 ( Fi g- 2 54, middle portion of the lower free circumference of the crusta), 

 through the pons on the same side (P) into the pyramid (Py) of 

 the medulla oblongata. At this point the majority of the fibers cross 

 through the pyramidal decussation to the opposite side and pass down- 

 ward in the lateral column (lateral pyramidal tract, a) to the level of the 

 spinal cord (Fig. 25 5), from which the anterior root for the transmission 

 of the voluntary impulse in question makes its exit. Before entering the 

 anterior root the fibers enter into communication with the ganglion-cells 

 of the anterior horn (surrounding them by delicate arborizations). 

 From each ganglion-cell there passes as a neurite a motor filament into 

 the nerve-fiber of the anterior root. The largest number of decussated 

 fibers in the pyramids pass to the motor nerves of the extremities. A 

 smaller number of fibers (Fig. 255, b), however, do not decussate in 

 the pyramid, but pass on the same side in the anterior column 

 of the spinal cord (anterior pyramidal tract, b, z) and remain 



