PONS VAROLII. 63 



nucleus diminishes. It is much broken up by longitudinal fibres (ascending 

 auditory fibres of Eoller). The connection of this nucleus with the auditory nerve 

 is very doubtful. It undergoes no alteration when the auditory nerve is severed in 

 the new-born animal, whereas section of the spinal cord in the upper cervical region 

 of the new-born rabbit is followed by degeneration and atrophy of this nucleus 

 (Monakow). It becomes atrophied after removal of the cerebellar hemisphere of 

 the same side in the new-born animal (see also p. 55). 



The ventral nucleus of the auditory nerve (see p. 55) which is represented 

 in the upper part of the medulla oblongata by a collection of nerve-cells lying in the 

 angle between the restiform body and the two portions of the root of the auditory 

 nerve (fig. 47, n. Vlll.ac} and by cells interpolated amongst the fibres of the cochlear 

 root (p. 55), is placed in the region of the pons between the restiform body and the 

 flocculus, and the cochlear root here issues directly from it (fig. 49). Its cells, which 

 are small and rounded but multipolar, are enclosed like those of a ganglion, each in 

 a nucleated capsule. 



The nucleus of the sixth nerve (common nucleus of the sixth and seventh 

 of some authors) consists of a group (column) of large multipolar cells lying on 

 either side of the median sulcus (fig. 50, n.VI). It corresponds to the part of the 

 fasciculus teres which lies immediately above the medullary striee on the floor of 

 the fourth ventricle. It has a close relation to the root of the facial, which runs 

 along its mesial side (Vila), curves round it eventually, and appears to receive 

 some fibres from it, but it is doubtful if this is really the case (Growers). The fibres 

 of the nerve run in bundles obliquely ventralwards and downwards (caudalwards) to 

 emerge at the lower border of the pons. Between this nucleus and the median 

 groove, along the middle of the fourth ventricle, is an oval bundle of nerve fibres 

 (fig. 50), which runs longitudinally upwards for about 5 mm., and occupies 

 nearly the same position with regard to the nucleus of the sixth nerve that the 

 longitudinal fibres which cover the hypoglossal nucleus occupy with regard to the 

 origin of that nerve. The bundle in question is the ascending part of the root 

 of the seventh nerve (p. 61), and when followed upwards in sections its fibres are 

 seen to turn sharply outwards and ventralwards, and to become the issuing root of 

 the facial. From the nucleus of the abducens, nerve-fibres pass to join the pos- 

 terior longitudinal bundle, and in this they run upwards to the mid-brain, where as 

 Duval and Laborde have shown they join the issuing oculomotor roots of the oppo- 

 site side. This crossed connection between the third and sixth nerves explains 

 those cases of lesion of the pons in which paralysis of the external rectus muscle 

 of one side is accompanied by that of the internal rectus of the opposite eye. 



Course of nerve-fibres from the spinal cord upward through the medulla 

 oblongata and pons. Assuming for convenience of description the existence of 

 three white columns of the spinal cord on each side, the various parts of these are 

 continued upwards as follows : 



The posterior column is continued in the medulla oblongata as the white sub- 

 stance of the funiculus gracilis and funiculus cuneatus. The longitudinal fibres 

 appear to end by terminal arborisations in the grey matter which forms the nuclei ; 

 and numerous deep arched fibres enter or emerge from the same collections of grey 

 matter, passing through the raphe from the other side of the medulla, where they 

 are continuous with the longitudinal fibres dorsal to the pyramids which form the 

 main tract of the fillet (Edinger) (interolivary layer of Flechsig). The solitary bundle 

 and the " ascending " root of the fifth morphologically represent, as their mode of 

 development from ingrowing nerve fibres shows, parts of the postero-lateral column 

 of the cord. 



Some fibres also pass from these nuclei, especially from the outer or large-celled 

 cuneate nucleus directly into the restiform body of the same side. 



