NUCLEUS OF THE OLIVARY BODY. 55 



floor of the ventricle it lies lateral or dorso-lateral to the hypoglossal nucleus. These 

 cells form the upper or bulbar part of the nucleus of the spinal accessory. 1 

 Above the level where the roots of this nerve cease to come off a mass of grey matter 

 with numerous cells is seen lying lateral to the hypoglossal nucleus in a situation 

 near the floor of the ventricle corresponding to the prominence of the ala cinerea 

 (trigonum vagi) which appears on the surface, and it extends upwards as far as the 

 fovea inferior. In connection with it there arise successively bundles of fibres of the 

 roots of the vagus and glosso-pharyngeal nerves (lUth and 9th cranial nerves) : 

 those of the vagus beginning at the commencement of the ventricle, and arising 

 along the length of the ala cinerea ; and those of the glosso-pharyngeal coming for 

 the most part from the upper part of the ala cinerea, and from beneath the inferior 

 fovea. The grey matter in question forms then the principal nucleus of the 

 pneumogastric and glosso-pharyngeal nerves. 



It has been inferred from the clinical and pathological evidence met with in cases of 

 bulbar paralysis that the motor fibres to the palate and vocal cords, which leave the medulla 

 oblongata by the spinal accessory roots, have their real origin in the hypoglossal nucleus. On 

 the other hand \jh.e pars intermedia of the seventh nerce is said to arise from the upper end of 

 the glossopharyngeal nucleus (Duval.) 



Close to this nucleus, but placed somewhat more deeply in the grey matter, is a 

 round longitudinal bundle of white fibres termed ihefuniculus solitarius (figs. 44, s., 

 46, /.). This bundle, which is surrounded by gelatinous grey matter with many 

 small nerve-cells, occupies the same relation to the ninth and tenth nerves that the 

 so-called ascending root of the fifth occupies to the trigeminal. Its fibres appear to 

 lose themselves amongst the cells of the enclosing grey matter, and this and the 

 bundle gradually disappear when traced towards the spinal cord : traced upwards 

 they pass out with the bundles of nerve-roots which go to form the vagus and glosso- 

 pharyngeal, especially the latter. Both this bundle and those forming the ascending 

 root of the fifth have their niyelin sheath developed at an early period. As His has 

 shown, they grow into the medulla oblongata from the ganglia of the vagus and 

 glosso-pharyngeal, in the same way as the posterior roots grow into the medulla 

 spinalis from the spinal ganglia. 



Lying in the reticular formation and ventral to the principal mass of grey matter 

 which here occupies the floor of the fourth ventricle, is a small detached pear-shaped 

 mass of grey matter containing nerve-cells, which is connected by a kind of stalk 

 with the rest of the grey matter. This nucleus, which was formerly termed the 

 nucleus ambiguus, gives origin to fibres which pass along the stalk obliquely towards 

 the floor of the fourth ventricle and then turn outwards and forwards to issue with 

 the root-bundles of the 'tenth nerve from the side of the bulb. It is therefore an 

 accessory vagal nucleus and, in its relation to the grey matter and in the size 

 and character of its cells it is a counterpart of the nucleus of the seventh nerve, 

 which appears in sections somewhat higher up (in the pons). A prolongation of this 

 nucleus gives origin higher up to fibres of the glossopharyngeal. 



The issuing bundles of the auditory nerve pass partly dorso-lateral and partly 

 ventro-mesial to the restiform body. The dorsal division contains a large number of 

 nerve-cells (ganglion radicis cochlearis), which probably give origin to many of 

 its fibres. Ventral to the restiform body and between the two roots is another mass of 

 ganglion-cells, which has been termed the accessory auditory nucleus (Schwalbe) 

 (fig. 47, n. VHI.ac}. From these cells fibres are seen both in the upper part of the bulb 

 and in the pons passing transversely towards the opposite side ; they belong to the 



1 The bulbar or accessory part of the nerve : the spinal part of the nerve takes origin in the ventro- 

 lateral group of cells of the anterior horn of the spinal cord (cervical region). 



