MEDULLA OBLONGATA 



425 



an H. The fibers from the hemispheres, which descend to the motor 

 cells of the cord, run mostly in the lateral funiculi, as previously stated. 

 They descend from the brain, however, in the ventral funiculi, in which 

 they form the pyramids in the upper part of the medulla (Fig. 437). 

 In the lower part of the medulla they decussate, crossing to the lateral 

 funiculus of the opposite side, as shown in Fig. 436; they appear to cut 

 off the ventral columns (horns) from the remainder of the gray H. 

 Then they descend in the spinal cord as the lateral cerebro-spinal tract 

 (also called crossed pyramidal). A few fibers, however, descend in the 

 ventral funiculi of the cord without having crossed in the medulla. Such 

 fibers of the ventral cerebro-spinal tract (direct pyramidal) cross to the op- 



t.s.n.t.-/- 



f.c.l 



FIG. 436. SECTION AT THE LEVEL OF THE 

 FIRST CERVICAL NERVE. (After Dejerine.) 



The right half of the section shows the effect 

 of Weigert's stain, the myelinated portions 

 being dark; the left half shows the gray 

 substance stippled; the white is blank, f. 

 c., Fasciculus cu neat us; f. c. 1., fasciculus 

 cerebro-spinalislateralis; f . c. v., fasciculus 

 cerebro-spinalis ventralis; f. g., fasciculus 

 gracilis; d. c., dorsal column; d. p., decus- 

 sation of the pyramids; d. r., dorsal root of 

 first cervical nerve; v. c., ventral column. 



FIG. 437. SECTION OF THE MEDULLA. (After 

 Dejerine.) 



d. c., Dorsal column; d. L, decussation of the 

 lemnisci; f. c., fasciculus cuneatus; n. ace., 

 nucleus of the accessory nerve; n. c., cuneate 

 nucleus; n. g., gracile nucleus; py. f pyramid; 

 t. s. n. t., spinal tract of the trigeminal 

 nerve; v. c., ventral column. 



posite side in the cord before terminating in contact with the motor cells 

 of the ventral columns. 



The fibers in the cerebro-spinal tracts are the neuraxons of the py- 

 ramidal cells in the outer layers of the hemispheres, which will be described 

 in a following section. They descend through the internal capsule (which 

 in a layer of white substance lateral to the thalami), thence through the 

 cerebral peduncles, pons, medulla oblongata and spinal cord, without in- 

 terruption. This motor path from the hemispheres to the voluntary 

 muscles includes, therefore, only two neurones or nerve cells, one from the 

 cortex to the motor cells of the ventral column of the cord, and the other 

 from the ventral column to the end plate on the muscle fiber. Other 

 motor fibers from the hemispheres to the cord terminate in the red nucleus 

 deep within the substance of the mid-brain; cells of the red nucleus send 

 neuraxons to the opposite side, and these descend in the lateral funiculi 

 of the cord as the rubro-spinal tract. They terminate in relation with 



