70 LABORATORY OUTLINE OF NEUROLOGY 



layer of white matter separating these nuclei. From the dorsal 

 border of this layer the fibers of the mesencephalic root can be 

 followed in the series of sections forward and dorsalward to take 

 their positions along the lateral wall of the aqueduct of Sylvius; 

 here they extend through the entire length of the midbrain. 

 These fibers are the innermost myelinated fibers in this region 

 and they are of very large size, though few in number. Most 

 of them are descending fibers arising from the cells of the 

 mesencephalic V nucleus, which can be seen in favorable prepa- 

 rations as a row of large flask-shaped nerve-cells accompanying 

 the tract. Others ascend from cell bodies lying in the semi- 

 lunar ganglion. This root of the V nerve has often been re- 

 garded as motor and is so described in many works; but its 

 sensory character is now well established, though the functions 

 of its ascending and descending fibers are not understood. In 

 the guinea-pig the descending fibers enter the muscular branches 

 for the masseter, pterygoid and temporal muscles (Allen) 

 and probably serve the muscle sense. 



See Allen ('19), Herrick ('18), Chap. IX; Johnston ('05); 

 Morris ('14), Fig. 654, p. 828; Otto May and Victor Horsley, 

 ('10). 



76. The dorsal funiculi of the cord. In the gross specimens 

 both of the human and the sheep's brain identify the fasciculus 

 gracilis and the clava, into which its fibers run to end among the 

 cells of the underlying nucleus of the fasciculus gracilis. Iden- 

 tify also the fasciculus cuneatus and the tuber culum cuneatum, 

 within which lies the nucleus of the fasciculus cuneatus. 



Now examine the microscopic sections of the human brain in 

 the region of transition between spinal cord and medulla oblon- 

 gata and locate all of the structures mentioned in the preceding 

 paragraph. See lists of references under required drawings, 

 Section 62 (1), (2), and (3). Follow the fibers of the fasciculus 

 gracilis and fasciculus cuneatus downward through the four 

 levels of the spinal cord and enter them in your sketches of 

 these levels. Then, beginning at the upper end of the cord, 

 follow these fasciculi upward into their nuclei under the clava 

 and tuber culum cuneatum respectively, where their fibers end. 

 The axons arising from the cells of these nuclei form the 

 medial lemniscus (fillet). 



