STRUCTURE 01' THE MKhl'LLA 



799 



the grey commissure gives rise to two thick dorsal outgrowths on each side of the 

 mid-line. These dor.-al projections of grey substance comprise the nuclei of termina- 

 tion (relays) of the chief ascending or sensory cerobro-spinal fasciculi of the .spinal 

 i-oi-il. The nucleus funiculi gracilis (nucleus of < lull's column) arises a, little before 

 the nucleus funiculi cuneati (nucleus of Burdach's column). The former extends 

 slightly downwards from its point of origin, so thai its inferior extremity is included 

 in sections through the deciissation of the pyramids (fig. 592). It produces a slight 

 bulbous enlargement (the darn) of the end of the funiculus gracilis, while the nucleus 

 funiculi cuneaii correspond.- to the cunxttc tubercle of the external contour of the 

 medulla (figs. 5S'J and 591). From the colls of these nuclei arise the lenmiseus the 

 cephalad continuation of the cerebro-spinal pat h way which conveys the general bodily 

 sensat ions to the cerebrum. In passing out of the nuclei the fibres of the lemniscus 



FIG. 594. DIAGRAM OF THE DECUSSATION OF THE LEMNISCI. 



Sfflk-- I' Y HAM ID 



/.A'.V.V/.VfV.V IFIl.l.KT) 

 . INFERIOR OLIVARY NUCLEUS 



rorm.KAm trill) 

 .. XL'rLKfS At, II TKAL'TI'S ."// 



\.U.1S TKIliKMIXl 

 KBSTIFOR1I BIIHY 



<!/ - - NUCLEUS VESTIKULARIS 

 (VIII) 



DECUSSA TION OF LEMNWI 



__KUCLKDS AKIt TKM'rr.l SI-IXALIS 



TKII:KHIKI 

 INTERNAL AIHTATK FlttRES 



.vrr/,/;r> FUNirri.i 



NUCLEUS FUNICULI QRACIL1S 



FABCICl I US ' -r. \EATUS (Goll) 



GRACILIS (Burdach) 



course in a ventro-medial direction. Curving around the region of the central canal, 

 t hey contribute largely to the internal arcuate fibres, then, sweeping across the mid- 

 line, they convert it into the raphe, and immediately after crossing (decussating) they 

 turn cephalad and collect to form the bundle known as the lemniscus. 



In tlie medulla, the lemnisci are two thin bands of fibres spread vertically on each 

 side of the raphe, with their lower or ventral edges thicker than their dorsal edges. 

 In their course towards the cerebrum they increase in bulk, owing chiefly to fibres 

 being added to them from the nuclei of termination of the afferent roots of the cranial 

 nerves. In passing through the region of the pons. the lemnisci gradually become 

 spread horizontally, and beyond the pons their then more outer portions are further 

 displaced and come to course in the lateral borders of the isthmus rhombencephali 

 and mesencephalon, while the inner portions remain nearer the mid-line. This 

 lateral spreading of each lemniscus produces the lateral lemniscus and the medial 



