STRUCTURE OF MEDULLA OBLONGATA 501 



of intermingled grey and white matter. The upward prolongation of the 

 separated head of the posterior grey column forms the nucleus of the spina* 

 tract of the trigeminal nerve, which lies partly in the dorsal and partly in the 

 lateral area. Medial to it lie the upward prolongations of the nucleus 

 gracilis and the nucleus cuneatus, and at a higher level the nuclei of the 

 vestibular portion of the acoustic nerve. Medial to the nucleus gracilis, 

 on the margin of the grey matter of the floor of the fourth ventricle, is the 

 fasciculus solitarius, a strand of nerve fibres and nerve cells ; the fibres 

 being fibres of the glosso-pharyngeal and the vagus nerves passing to the 

 cells of the strand which forms one of their nuclei. 



The white fibres of the posterior area are longitudinal and oblique. The 

 most important longitudinal fibres are (i) the fibres of the spinal root 

 of the trigeminal nerve which descend, close to the surface, and superficial 



Anterior medullary velum 



,. . . Grey matter on floor 



Ventricle iv. v of ventr i c le iv. 



Mesencephahc root of ^sr^^^rsfe^^^a^ Brachium 



trigeminal nerve ^T^g^ ~~ t&L^*'' conjunctivum 



Medial longitudinal V^Sgl ' ^ s ^^\ 



bundle "jHp?l ^P*^*-' Lateral lemniscus 

 Formatio reticularis - 



Nucleus of 'M conjunctivum 



lateral lemniscus ^ Mi Medial lemniscus 



Pyramidal bundles (cerebro-spinal 

 fasciculi) 



FIG. 203. Transverse section through the upper part of the Pons 

 - of the Orang. 



to the nucleus, which is formed by the upward prolongation of the head of 

 the posterior column of grey matter ; and (2) the fibres of the fasciculus 

 solitarius (see above). The oblique fibres consist of fibres of the restiform 

 body, fibres passing from the nucleus gracilis and nucleus cuneatus, and of 

 fibres passing to the olivary nucleus of the opposite side. 



Internal Structure of the Pons. When transverse sections are made 

 through the pons, it is seen to consist of two well-defined parts, viz., a 

 ventral and a dorsal. Broadly speaking, the ventral part, pars basalts, 

 corresponds to the pyramidal parts of the medulla oblongata, and the basal 

 parts of the pedunculi cerebri ; whilst the dorsal part corresponds to the 

 formatio reticularis of the medulla oblongata and the tegmental parts of the 

 pedunculi cerebri. 



The basilar part of the pons is 'the larger of the two subdivisions. It 

 is composed of a large number of transverse bundles of fibres, through 

 the midst of which coarse longitudinal bundles of fibres proceed down- 



