OF THE NERVUS OCTAVUS: 97 



p. The portio internet in the embryo of the rabbit and its 

 atrophy after root-section in the young born animal. 



Till now the Marchi-method has shown degenerated fibres in the 

 intermediary and dorsal octavus-sy stems crossing the nucleus of 

 DEITERS and in the descending root. 



Now in the oblongata of the elder foetus of the rabbit (Plate 



XII fig. 17, A, B and C) are found likerwise medullated fibres, 

 in the intermediary system (Plate XII, fig. 17 A, h = s. 

 interm) , in the dorsal system (Plate XII (fig. 1 7 A , B and C , 

 fasc. dors. N. VIII) and in the descending root (Plate XII fig. 17 

 A r. desc. N. VIII) , whereas in the area of DEITERS itself only 

 a few medullated fibres, mostly passing through it, are seen. 



In this way the portio interim appears to have medullated fibres 

 in all systems, wherein Marchi-method demonstrates degenerate 

 fibres after root-section. 



And as in this still unborn e young rabbit , the area ovalis , of 

 the C. R. , according to the medullated dorsal ascending spino- 

 cerebellar tract , is partly myelinisated , its portio interna is clearly 

 divided into four quadrants, among which the medio-dorsal and 

 the triangular latero-ventral area's are not yet provided with medul- 

 lated fibres. 



Still more evident than in the rabbit (Plate XII fig. 1 7 A) this 

 division is in the young born cat (fig. 5 on Plate I). There again 

 the very powerful internieclial system , the very important system 

 of transverse dorsal fibres, and also the descending root-fibres are 

 medullated, the dorso-medial quadrant and the nucleus of DEITERS 

 have only a few, the latero-ventral area between area ovalis and 

 the V th spinal root is without myelinisation. 



Sagittal sections, through the medulla of the rabbit demonstrate 

 the same facts. Between the area ovalis and the V th spinal root , 

 a long stretched area is found (Plate XIII fig. 18 D), crossed 

 proximally by the medullated intermedial system (Plate XIII fig. 

 18 D in h (HELD)). Medullated are also the medial (Plate XIII fig. 

 18 D) and the descending roots (Plate XIII fig. 18 E and E in 

 rad. desc. N. VIII), whereas the medio-dorsal quadrant (Plate 



XIII fig. 18 E and E) dorsally from it is not. 



The transverse dorsal fibres, also medullated (Plate VI 19 C) 

 are best demonstrated on horizontal sections, where their whole 

 course towards the fasciculus longitudinalis posterior may be seen. 



Now if the frontal (Plate XII fig. 17 A) or horizontal (Plate 

 VI fig. 19 C) sections through the medulla of the rabbit-foetus, 



Verhand. der Ron. Akad. v. Wetensch. (Tweede Sectie.) Dl. XIV. 7 



