560 



THE NEKVOUS SYSTEM 



Cuneate nucleus 

 Tractus spinalis of 

 fifth nerve 

 Nucleus tractus 

 spinalis n. trigemini 

 Fasciculus .spino- 

 cerebellaris 



tract 



Detached anterior 

 column of gray matter 



Decussation of 

 pyramids 



Anterior basis-bundle 



FIG. 492. SECTION THROUGH THE INFERIOR PART OF THE 

 MEDULLA OBLONGATA OF THE ORANG. 



nucleus appears in the form of a relatively slender mass of gray matter in th 

 interior of the funiculus gracilis. 



The cuneate nucleus is a direct offshoot from that part of the base of th 



posterior column of gray matter which is preserved as a portion of the centra 



gray mass. In transverse section it is seen to invade the funiculus cuneatus upoi 



its deep aspect, and it gradually grows backwards into its substance. It present 



Graciie nucleus a very different appearance froi 



cuneate nucleus ^^ j the gracile nucleus, becaus 



throughout its whole length th 

 gray nucleus and the fibres d 

 the strand are separated froii 

 each other by a sharp line <j 

 demarcation. A little higher M\ 

 a second and much smaller ma : 

 of gray matter appears in tli 



iculus cuneatus, superficial 

 the main nucleus. This is terim 

 the accessory or the lateral cunea 

 nucleus (Fig. 491). 



As a series of sections 

 studied from below upwards, 

 will be noticed that the numb 

 of fibres in the gracile ai 

 cuneate funiculi rapidly decreases, until, at the level of the clava and cunea 

 tubercles, it is seen that these eminences are composed almost entirely of t 

 gray nuclei, covered by a thin layer of the few remaining fibres of the two fascic 

 involved. It would appear that no fibres belonging to the funiculus gracilis a 

 funiculus cuneatus get beyond these nuclei. They all end in fine termii 

 ramifications around the cells of the nuclei. In the case of the funiculus cuneat 

 the bundles of fibres, as they pass from the surface into the subjacent gray nucle 

 are very distinctly seen in transverse sections through the bulb. 



When the medulla oblongata opens up into the fourth ventricle the grao 

 and cuneate nuclei are pushed laterally by the expanding ventricular floor, a 

 the gracile nucleus soon comes to an end ; but the cuneate nucleus extei i 

 upwards for a short 



distance farther,and cili " '^^^^"^^^m^^^^i^^^' Graciie nucleus 



terminates only 

 when the restiform 

 body begins to take 

 definite shape on its 

 lateral aspect. 



Decussat io 

 Lemniscorum. 

 Immediately above 

 the level of the de- 

 cussation of the 

 pyramids another 

 decussation of fibres 

 takes place in the 

 substance of the 

 medulla oblongata 

 in the median plane, 

 and upon the dorsal 

 aspect of the pyra- 

 mids. This is the decussation of the lemniscus medialis, or the sensory decussa n 

 so-called in contradistinction to the term " motor decussation," which is somet * 

 applied to the decussation of the pyramids. The fibres which take part in u 

 decussation are called internal arcuate fibres, and they are derived from the eel < 

 the gracile and cuneate nuclei. From the deep aspects of these nuclei these f 



Inferior end 

 of olive 



Cuneate 

 nucleus 



Nucleus tra 

 spinalis ner 

 trigemini 



Decussatioi; 



lemniscus 



medialis 



Medial 

 accessory 

 olivary nuc 

 Fila of 

 hypoglo? 

 nerve 



Pyramid 



FIG. 493. TRANSVERSE SECTION THROUGH THE CLOSED PART OF A Fan 

 MEDULLA, IMMEDIATELY ABOVE THE DECUSSATION OF THE PYRAMIDS. 

 Treated by Weigert-Pal method. 



