228 THE CEREBRUM. 



the accessory fillet and the inner portion of the middle three- 

 fifths of the basis pedunculi. Upper Extremity Fibers (Figs. 70 

 and 105). The fibers of the pyramidal tract that end in the 

 cervical part of the spinal cord, and through it innervate the 

 muscles of the upper extremity, take their origin from that part 

 of the anterior central gyrus adjacent to the foot of the middle 

 frontal gyrus: their origin lies between meridians which intersect 

 the central sulcus at the genu inferius and the genu superius, re- 

 spectively. These fibers run through the pars occipitalis of the 

 internal capsule just behind the genu, and through the basis 

 pedunculi immediately lateral to the head and neck fibers. Those 

 fibers which innervate the muscles of the thumb, fingers and hand, 

 rise lowest down in the arm area of the cortex and occupy the 

 posterior part of the arm bundle in the internal capsule and the 

 lateral part of it in the peduncle. The fibers which control the 

 shoulder muscles rise in the upper part of the cortical area and 

 form the anterior and medial part of the arm bundle in the cap- 

 sula interna and basis pedunculi, respectively; while the wrist, 

 forearm, elbow and arm are innervated by means of fibers which 

 are intermediate in both origin and course. Trunk Fibers. 

 The trunk fibers of the pyramidal tract rise in that projection of 

 the anterior central gyrus which is situated just above the genu 

 superius of the central sulcus. In the internal capsule, the trunk 

 fibers run just behind those to the ringers and just lateral to them 

 in the basis pedunculi. Lower Extremity Fibers (Figs. 70 and 105). 

 A large number of the pyramidal fibers terminate in the lumbar 

 enlargement of the spinal cord and carry impulses to the nerves 

 of the lower extremity. They originate in the upper fourth of 

 the anterior central gyrus and in the paracentral lobule. The hip 

 fibers rise farthest downward and the toe fibers farthest upward, 

 immediately in front of the sulcus centralis. The fibers have 

 the same relative position in the internal capsule; in the base of 



Description to Fig. 72. 



a, a. Motor cells of cerebral cortex, b, b. End-tufts of sensory fibers in cortex, c. Nu- 

 cleus of funiculus cuneatus, showing end-tufts of fibers from the cord. d. Nucleus of funic- 

 ulus gracilis, containing end-tufts of fibers from cord. e. Section of medulla at fillet de- 

 cussation. f. Section of medulla at pyramidal decussation. g, g. Motorial end-plates. 

 b. Section of cervical cord, showing terminations of fibers of anterior and lateral pyramidal 

 tract, i, i. Spinal ganglia, j, k. Short sensory fibers. 1. Long sensory fibers, m, m, m. Sen- 

 sory end-organs, n. Section of lumbar cord. 



