INTEKNAL STEUCTUKE OF MEDULLA OBLONGATA AND PONS. 555 



In the specific case we are considering the vestibular nucleus and the cerebellum 

 eceive their chief supply of afferent fibres from the incoming vestibular nerve : hence 

 here is no reason for migration. Similarly the nucleus gracilis and nucleus cuneatus 

 eceive the fibres which come up through the funiculus posterior and remain where 

 ,hey are. But the nuclei pontis, the olivary nucleus, and the arcuate nuclei are 

 fed " with impulses passing downwards (and some perhaps upwards) in the basal 

 amina, close to the median plane, and they "migrate" towards the direction from 

 vhich their afferent paths are approaching ; the nuclei pontis towards the peduncles 

 if the cerebrum bringing cerebro-pontine fibres from the cerebral cortex, and the 

 ilivary nucleus to the neighbourhood of certain descending tegmental tracts and 

 ,scending spinal sensory tracts that seem to supply the attractive force, which leads 

 hem to forsake the rhombic lip of the alar lamina and migrate into the basal lamina. 



The majority of the cells destined to form the nuclei pontis wander obliquely 

 ipwards and forwards between the facial and acoustic nerves to reach the basal 



Restifonn body 



Vago-glossopharyngeal 

 roots 

 | Nucleus of the 



tractus solitarius 

 | Trenia 



Fasciculus teetospinalis 



Vagus nucleus 



Tractus solitarius 



Descending root of vestibular nerve 



Vago-glossopharyngeal roots 



sciculus spinocerebellaris 

 posterior 



Fasciculus longitudinalis 

 medialis 



Nucleus tractus spinalis 

 nervi trigemini [nerve 



Tractus spinalis of trigeminal 

 Nucleus ambiguus 

 Fasciculus rubrospinalis 

 Olivo-cerebellar fibres 



.sciculus spinothalamicus 

 Dorsal accessory olivary nucleus 

 Fasciculus spinocerebellaris anterior 

 :ternal arcuate fibres 

 niscus medialis 



ial accessory olivary nucleus 



;ulus tegmento-dlivaris 

 Inferior olivary nucleus 



Pyramid 



mate nucleus < 



1 External arcuate fibres 



;[Q. 486. TRANSVERSE SECTION THROUGH THE MIDDLE OF THE OLIVARY REGION OF THE HUMAN MEDULLA 



OBLONGATA. 



L, 



The floor of the fourth ventricle is seen, and it will be noticed that the restiform body, on each side, has 

 now taken definite shape. Some of the descending tracts in red ; ascending tracts in blue. 



ina of the metencephalon. But strewn along this pathway from the edge of 

 ie fossa rhomboidea to the front of the pons are scattered nerve-cells which have, 

 ) to speak, fallen by the way, and remain to indicate in the adult brain the path 

 ken by the majority of their sister cells. This remnant forms the corpus ponto- 

 ilbare: the pontine fibres that spring from its cells and are making their way 

 pwards to fall in line (Fig. 499, p. 566) with the other transverse fibres of the pons 

 Tin the fasciculus obliquus [pontis], and the cerebro-pontine fibres that pass below 

 e pons in order to reach this outlying part (corpus ponto-bulbare) of the nuclei 

 >ntis constitute the fasciculus circumolivaris pyramidis (Fig. 517, p. 583). 

 But not all of the elements of the nuclei pontis that migrate pass into the 

 >encephalon; a certain proportion of them invariably pass into the myelen- 

 'phalon. These collect upon the anterior surface of the pyramids to form small 

 regular patches of gray matter which have received the name nuclei arcuati. 

 ferent fibres (probably cerebro-pontine) come from the pyramids ; and their 

 'ent fibres (which proceed to the cerebellum) form some of the fibrae arcuatae 



which are visible upon the surface of the medulla oblongata (Fig. 486). 

 Dlivary Nuclei. The most conspicuous of the isolated clumps of gray matter 



