558 



THE NEEVOUS SYSTEM. 



According to Sherrington, an anterior cerebro-spinal tract in the spinal medulla of th 

 anthropoid apes stands in connexion with the arm-centre in the cerebral cortex. If this i 

 the case in man it must have other connexions as well, seeing that it is carried down th 

 spinal medulla for a considerable distance beyond the level of the spinal segments whicl 

 give motor fibres to the upper limb. In the lower apes an anterior cerebro-spinal trac 



Funiculus gracilis Gracile nucleus d eS n0t , ^ 6m tO ^ 



the whole pyrami 

 crosses over to the oj 

 posite side of the spim 

 medulla in the shap 

 of the lateral cerebn 

 spinal tract. 



Funiculus cuneatus 



Cuneate nucleus 



Tractus spinalis of 

 trigeminal nerve 



Nucleus tractus 

 -spinalis nervi 

 trigemini 



Central gray matter 



Central canal 



Lateral cerebro- 

 'spinal tract 



Detached head of anterior 

 column of gray matter 



As we have note< 

 the decussating pyr; 

 midal bundles pa; 

 through the anterii 

 column of gray ma 

 ter, and cut it in 

 two portions (Fig 

 489 and "490). TI 

 basal part remains 

 position on the a 

 terior and later 

 aspect of the cent] 

 canal, and forms ps 

 of the thick layer 

 gray matter whi 

 surrounds it. T 



detached head of the anterior column is set free ; and from the large multipo" 

 cells which lie in its midst some of the fibres of the anterior root of the fi 

 cervical nerve, and also some of .the root fibres of the accessory nerve, take origin 

 As we proceed into the medulla oblongata another effect of the decussati 

 of the pyramids is seen in the submergence from the surface of the strand 

 fibres which, in the anterior funiculus of the spinal medulla, lies to the lateral s -. 

 of the anterior cerebro-spinal tract, and which receives the name of the fascicu i 

 anterior proprius. While the decussation is going on the fasciculus propriusi 

 thrust aside, and in the medulla oblongata, it takes up its position as a flatter 1 

 band -like strand on 



Funiculus gracilis 



^i^y9iMb^.^'' 'SOU f&^WlSiSSS^ 

 Gracile nucleus 



Fasciculus anterior proprius Decussation of pyramids 



Pyramid Pyramid 



FIG. 489. SECTION THROUGH THE INFERIOR END OP THE MEDULLA OBLONGATA 

 OF A CHIMPANZEE. 



Cuneate 

 nucleus 



Gray matter 

 around canal 



the lateral side of the 

 pyramid (Fig. 489). 

 When the decussation 

 is completed, this 

 strand is seen to lie 

 close to the median 

 plane on the dorsal 



aspect Of the pyramid, Central canal 



where it is separated 

 from its fellow of the r ^ 



. , , . , Decussation of. 

 Opposite Side by the pyramids 



median raph'e alone 

 (Fig. 491). In the 

 upper part of the 

 medulla oblongata it 

 approaches still nearer 



Funiculus 

 cuneatus 



Tractus spi 

 of fifth ner 

 Nucleus 

 tractus spi 

 alls nervi 

 trigemini 



Fasciculus 



spino- 



cerebellari 



Detached 1 i 

 of auterioi 

 column 



Fasciculus 

 anterior propr 



Fissura medians anterior 



FIG. 490. TRANSVERSE SECTION THROUGH THE INFERIOR END OF T 

 MEDULLA OBLONGATA OF A FULL-TIME FCETUS, 



to the dorsal Surface Treated by the Weigert-Pal method. The gray matter is bleached white, ' 

 and appears to form the medullated tracts of fibres are black. 



the greater part of a 



strand, which is termed the medial longitudinal bundle (Figs. 



The detached head of the anterior column of gray matter of the spinal med 



