34 Anatomy of the Nervous System 



continue upward through the midbrain to end finally in the 

 diencephalon. It is not possible to observe the course of 

 these fibres in the sections from normal material. 



The dorsal funiculi of the cord are interrupted at the 

 lower end of the medulla oblongata. As one approaches 

 this region, passing up the spinal cord, the dorsal gray columns 

 are seen to spread apart somewhat, and a little below the decus- 

 sation of the pyramids, a small mass of gray matter appears 

 projecting dorsally from the central gray among the fibres of 

 the fasciculus cuneatus. This is the beginning of the nucleus 

 cuneatus. A little farther up than the lower end of the 

 pyramidal decussation, a broad median eminence also appears 

 on the dorsal surface of the central gray matter, the nucleus 

 gracilis. Still farther forward, another small part of the 

 nucleus gracilis is seen on each side among the fibres of its 

 fasciculus, and this becomes continuous with the projection 

 from the central gray matter. The latter, moreover, divides 

 into a small median nucleus and two lateral portions, con- 

 necting as just described with the groups of cells within the 

 white matter (PI. VI.). The cuneate and gracile nuclei 

 increase rapidly in size, and as the fibres of the fasciculi end 

 within them, the latter are correspondingly reduced and 

 finally disappear. The cells of these funicular nuclei give 

 rise to secondary fibres which take a course ventrally and 

 medially in small groups, appearing in sections as internal 

 arcuate fibres. They cross the middle line, forming the 

 decussation of the lemniscus, and take up a position close to 

 the raphe (PI. VII.). Here they form an ascending tract 

 which is known as the medial lemniscus {lemniscus medialis, 

 medial fillet), and which can be followed right through the 

 medulla oblongata in about the same position, though the 

 shape of its cross-section changes somewhat. It is a little 

 less conspicuous in the rat than in man. The details of form 

 of the gracile and cuneate nuclei in man also differ consider- 

 ably from those of the rat described above. 



